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Manipulating the Sensitivity and Selectivity of OECT-Based Biosensors via the Surface Engineering of Carbon Cloth Gate Electrodes
通过碳布栅电极表面工程操纵基于 OECT 的生物传感器的灵敏度和选择性

Xin Xi, Dongqing Wu,* Wei Ji, Shinan Zhang, Wei Tang, Yuezeng Su, Xiaojun Guo,* and Ruili Liu*
Xin Xi、Dongqing Wu、* Wei Ji、Shininan Zhang、Wei Tang、Yuezeng Su、Xiaojun Guo*和Ruili Liu*

Abstract 摘要

Organic electrochemical transistors (OECTs) provide the opportunity to fabricate flexible biosensors with high sensitivity. However, there are currently very few methods to improve the selectivity of OECT sensors. In this work, nitrogen/oxygen-codoped carbon cloths (NOCCs) are prepared by the carbonization of polyaniline-wrapped carbon cloths at 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} under different atmospheres. The resulting NOCC electrodes exhibit different electrochemical sensing behaviors toward ascorbic acid (AA) and dopamine (DA), enabling the fabrication of OECT sensors with high sensitivity and selectivity that are comparable to the state-of-the-art OECT sensors for AA and DA. The structural characterization and theoretical calculation reveal that the electrochemical sensing behaviors of the NOCC electrodes are closely related to their surface compositions, providing an unprecedented strategy for the design of flexible OECT sensors with high sensitivity and selectivity.
有机电化学晶体管（OECT）为制造具有高灵敏度的柔性生物传感器提供了机会。然而，目前提高有机电化学晶体管传感器选择性的方法还很少。在这项工作中，通过在 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} 不同气氛下对包裹聚苯胺的碳布进行碳化，制备了氮/氧掺杂碳布（NOCC）。所制备的 NOCC 电极对抗坏血酸（AA）和多巴胺（DA）表现出不同的电化学传感行为，从而能够制备出具有高灵敏度和高选择性的 OECT 传感器，其灵敏度和选择性可与最先进的 AA 和 DA OECT 传感器相媲美。结构表征和理论计算揭示了 NOCC 电极的电化学传感行为与其表面成分密切相关，为设计具有高灵敏度和高选择性的柔性 OECT 传感器提供了前所未有的策略。

1. Introduction 1.导言

With the rapid development of wearable electronics, flexible biosensors have received intensive attention since they can provide the opportunity to monitor the real-time biological and medical information of the wearer. [ 1 ] [ 1 ] ^([1]){ }^{[1]} In addition to flexibility, biosensors in wearable electronics also need high sensitivity and selectivity, because the analytes in body fluids such as ascorbic acid (AA), dopamine (DA), and uric acid (UA) are usually combined together in very low concentrations ( × 10 − 6 × 10 − 6 xx10^(-6)\times 10^{-6} or × 10 − 9 m × 10 − 9 m xx10^(-9)m\times 10^{-9} \mathrm{~m} level). [ 2 ] [ 2 ] ^([2]){ }^{[2]} In this respect, organic electrochemical transistors (OECTs) offer an appealing solution for the construction of highly sensitive flexible biosensors. [ 3 ] [ 3 ] ^([3]){ }^{[3]} The sensing behavior of the OECT sensor is determined by the reduction/oxidation
随着可穿戴电子设备的快速发展，柔性生物传感器受到了广泛关注，因为它们可以提供监测穿戴者实时生物和医疗信息的机会。 [ 1 ] [ 1 ] ^([1]){ }^{[1]} 除了灵活性，可穿戴电子设备中的生物传感器还需要高灵敏度和高选择性，因为体液中的分析物，如抗坏血酸 (AA)、多巴胺 (DA) 和尿酸 (UA) 通常以极低的浓度（ × 10 − 6 × 10 − 6 xx10^(-6)\times 10^{-6} 或 × 10 − 9 m × 10 − 9 m xx10^(-9)m\times 10^{-9} \mathrm{~m} 水平）结合在一起。 [ 2 ] [ 2 ] ^([2]){ }^{[2]} 在这方面，有机电化学晶体管（OECT）为构建高灵敏度的柔性生物传感器提供了一种极具吸引力的解决方案。 [ 3 ] [ 3 ] ^([3]){ }^{[3]} 有机电化学晶体管传感器的传感行为是由还原/氧化决定的。
The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm. 201905361.
本文作者的 ORCID 识别码可在 https://doi.org/10.1002/adfm 下找到。201905361.
DOI: 10.1002/adfm. 201905361
DOI: 10.1002/adfm.201905361
(redox) reactions of the analytes on the gate electrode. [ 4 ] [ 4 ] ^([4]){ }^{[4]} Therefore, the detection capability of the OECT does not depend on specific instruments or spectrometers, and the miniaturization of the OECT will not result in the loss of sensitivity. Additionally, the transistor configuration of the OECT helps to magnify the signals from analytes with low concentrations, thus effectively improving the limits of detection (LOD). Moreover, OECTs are easily constructed on flexible substrates, since the electroactive semiconductors in OECTs are organic species, which also provides advantages to OECT-based biosensors, including high biocompatibility and a low operating voltage. [ 1 c , 3 a , 5 ] [ 1 c , 3 a , 5 ] ^([1c,3a,5]){ }^{[1 c, 3 a, 5]}
(分析物在栅电极上的氧化还原反应。 [ 4 ] [ 4 ] ^([4]){ }^{[4]} 因此，OECT 的检测能力不依赖于特定的仪器或光谱仪，而且 OECT 的微型化不会导致灵敏度下降。此外，OECT 的晶体管配置有助于放大低浓度分析物的信号，从而有效提高检测限（LOD）。此外，由于 OECT 中的电活性半导体是有机物，因此很容易在柔性基底上构建 OECT，这也为基于 OECT 的生物传感器提供了优势，包括高生物相容性和低工作电压。 [ 1 c , 3 a , 5 ] [ 1 c , 3 a , 5 ] ^([1c,3a,5]){ }^{[1 c, 3 a, 5]}
Due to the enhanced sensitivity, the selectivity of OECTs toward analytes with similar redox potentials is crucial for their practical applications. [ 6 ] [ 6 ] ^([6]){ }^{[6]} To improve the selectivity of OECT-based biosensors, one common strategy is to deposit electronegative polymers such as chitosan and perfluorinated sulfonic acid on their gate electrodes, [ 7 ] [ 7 ] ^([7]){ }^{[7]} which can effectively prevent the electron-rich analytes from having access to the surface of the electrodes. However, the polymers used for the electrode modification may cause interface resistance between the polymers and gate electrodes, which will then reduce the sensitivity of the OECT. Therefore, the fabrication of gate electrodes for flexible OECTs with both high sensitivity and high selectivity remains a challenge.
由于灵敏度提高，OECTs 对具有相似氧化还原电位的分析物的选择性对其实际应用至关重要。 [ 6 ] [ 6 ] ^([6]){ }^{[6]} 为了提高基于 OECT 的生物传感器的选择性，一种常见的策略是在栅电极上沉积壳聚糖和全氟磺酸等电负性聚合物， [ 7 ] [ 7 ] ^([7]){ }^{[7]} 这可以有效阻止富电子分析物进入电极表面。但是，用于电极修饰的聚合物可能会导致聚合物与栅电极之间产生界面电阻，从而降低 OECT 的灵敏度。因此，如何为柔性 OECT 制备既具有高灵敏度又具有高选择性的栅电极仍然是一项挑战。
As demonstrated in previous work, the gate electrodes of OECT sensors consist mainly of gold or platinum. [ 6 a , 7 a , 8 ] [ 6 a , 7 a , 8 ] ^([6a,7a,8]){ }^{[6 a, 7 a, 8]} The negative impacts of these precious metals on the OECTs are not merely the increased costs. More importantly, the precious metal gate electrodes may lose their electrocatalytic abilities due to poisoning by sulfur, chlorine, phosphorus, and other substances, which inevitably harms the stability and reproducibility of the OECT sensors. [ 9 ] [ 9 ] ^([9]){ }^{[9]} Recently, carbonaceous gate electrodes were utilized in OECT sensors, which exhibited excellent sensing performances similar to those utilizing precious metal gate electrodes. [ 10 ] [ 10 ] ^([10]){ }^{[10]} Compared with precious metals, carbon materials have obvious advantages, including natural abundance, low fabrication cost, chemical stability and mechanical flexibility. [ 11 ] [ 11 ] ^([11]){ }^{[11]} Even more intriguing, the electrocatalytic activity, conductivity and electrolyte affinity of carbon materials can all be judiciously adjusted by the replacement of carbon atoms on
正如以前的工作所证明的那样，OECT 传感器的栅电极主要由金或铂组成。 [ 6 a , 7 a , 8 ] [ 6 a , 7 a , 8 ] ^([6a,7a,8]){ }^{[6 a, 7 a, 8]} 这些贵金属对 OECT 的负面影响不仅仅是成本增加。更重要的是，贵金属栅极电极可能会因硫磺、氯、磷等物质的毒害而失去电催化能力，从而不可避免地损害 OECT 传感器的稳定性和可重复性。 [ 9 ] [ 9 ] ^([9]){ }^{[9]} 最近，人们在 OECT 传感器中使用了碳质栅电极，它表现出了与使用贵金属栅电极类似的优异传感性能。 [ 10 ] [ 10 ] ^([10]){ }^{[10]} 与贵金属相比，碳材料具有明显的优势，包括天然丰富、制造成本低、化学稳定性和机械灵活性。 [ 11 ] [ 11 ] ^([11]){ }^{[11]} 更有趣的是，碳材料的电催化活性、电导率和电解质亲和性都可以通过替换栅极上的碳原子来进行调整。
Figure 1. The schematic illustration of the flexible NOCC electrode fabrication process. a) The adsorption of aniline monomers (ANIs) on the surface of the carbon cloth. b) The heterogeneous nucleation and polymerization of burr-like PANI. c) The carbonization of the PANI-CC composites under the different atmospheres.
图 1：柔性 NOCC 电极制造工艺示意图。a) 苯胺单体（ANIs）在碳布表面的吸附；b) 毛刺状 PANI 的异质成核和聚合；c) PANI-CC 复合材料在不同气氛下的碳化。
their surfaces with heteroatoms such as nitrogen ( N ) ( N ) (N)(\mathrm{N}), oxygen (O), and sulfur (S). [ 12 ] [ 12 ] ^([12]){ }^{[12]} Therefore, the surface engineering of carbon materials with heteroatoms provides alternative methodologies for the design of unconventional carbonaceous gate electrodes for OECTs with high sensitivity and selectivity.
( N ) ( N ) (N)(\mathrm{N}) 、氧 (O) 和硫 (S) 等杂原子。 [ 12 ] [ 12 ] ^([12]){ }^{[12]} 因此，带有杂原子的碳材料表面工程为设计具有高灵敏度和选择性的 OECT 非传统碳质栅电极提供了替代方法。
Here, we demonstrate the fabrication of N/O-codoped carbon cloths (NOCCs) as the gate electrodes in flexible OECT sensors with different sensitivities and selectivities. The NOCC electrodes are prepared by the carbonization of polyanilinewrapped carbon cloths at 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C}, and the amounts and species of N and O atoms on their surfaces can be easily tuned by changing the atmosphere (oxidative, inert, or reductive) during the carbonization process. In a three-electrode electrochemical sensing system, the NOCC electrode obtained under reductive conditions exhibits higher sensitivity toward AA than DA, while the NOCC electrode from the oxidative atmosphere has a better selectivity for the detection of DA. More importantly, the different sensing capabilities of the NOCC electrodes are acquired by the OECTs when the NOCC electrodes are used as the gate electrodes, thus enabling the fabrication of OECT sensors with excellent sensitivity and selectivity toward AA and DA. As verified by the experimental results and theoretical calculations, the surface engineering of carbonaceous gate electrodes by modifying the heteroatoms on their surfaces provides an efficient strategy for the design and construction of high-performance OECT biosensors.
在这里，我们展示了如何制作 N/O 掺杂碳布 (NOCC) 作为具有不同灵敏度和选择性的柔性 OECT 传感器的栅电极。NOCC 电极是通过在 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} 下碳化聚苯胺包裹的碳布制备的，在碳化过程中通过改变气氛（氧化性、惰性或还原性）可以很容易地调整其表面上 N 原子和 O 原子的数量和种类。在三电极电化学传感系统中，还原条件下获得的 NOCC 电极对 AA 的灵敏度高于 DA，而氧化气氛下的 NOCC 电极对 DA 的检测具有更好的选择性。更重要的是，当把 NOCC 电极用作栅电极时，OECTs 就能获得 NOCC 电极的不同传感能力，从而制造出对 AA 和 DA 具有出色灵敏度和选择性的 OECT 传感器。实验结果和理论计算证实，通过改变碳质栅电极表面的杂原子对其进行表面工程处理，为设计和构建高性能的 OECT 生物传感器提供了一种有效的策略。

2. Results and Discussion
2.结果与讨论

In this work, AA and DA were selected as the target analytes to evaluate the effects of surface engineering on the sensing behavior of the carbonaceous gate electrodes in OECTs. Commonly known as vitamin C, AA is a very important biological molecule in many metabolic reactions, including collagen and neurotransmitter biosynthesis, growth and repair of tissue, and
本研究选择 AA 和 DA 作为目标分析物，以评估表面工程对 OECTs 中碳栅电极传感行为的影响。AA 通常被称为维生素 C，是许多新陈代谢反应中非常重要的生物分子，包括胶原蛋白和神经递质的生物合成、组织的生长和修复，以及
free radical scavenging. [ 13 ] [ 13 ] ^([13]){ }^{[13]} DA is one of the most important neurotransmitters in the human nervous system and plays a vital role in many brain activities and functions. [ 14 ] [ 14 ] ^([14]){ }^{[14]} Abnormal levels of AA and DA in blood or urine are usually associated with potential diseases in the metabolic or neural systems. [ 13 a , 15 ] [ 13 a , 15 ] ^([13 a,15]){ }^{[13 a, 15]} Therefore, the ability to detect AA and DA in body fluids using wearable biosensors would be valuable for the real-time monitoring and diagnosis of the related syndromes. Among the common body fluids, urine is more suitable than blood and sweat for the wearable sensing systems, because it can be easily collected in sufficient amounts by the diapers, without the need for intrusive inspection. [ 16 ] [ 16 ] ^([16]){ }^{[16]} The concentrations of AA and DA in human urine should be in the ranges of ( 0.114 − 0.170 ) × 10 − 3 ( 0.114 − 0.170 ) × 10 − 3 (0.114-0.170)xx10^(-3)(0.114-0.170) \times 10^{-3} and ( 0.661 − 2.645 ) × 10 − 6 M , [ 17 ] ( 0.661 − 2.645 ) × 10 − 6 M , [ 17 ] (0.661-2.645)xx10^(-6)M,^([17])(0.661-2.645) \times 10^{-6} \mathrm{M},{ }^{[17]} respectively, thus requiring highly sensitive sensors for detection. The challenges in the detection of AA and DA are not only their low concentrations and coexistence in urine. The strong reducibility of AA with low redox potential may cause the re-reduction of dopamine o-quinone (the oxidation state of DA), especially when the amount of AA is much higher than that of DA, which will interfere with the electrochemical detection of DA. [ 18 ] [ 18 ] ^([18]){ }^{[18]} Therefore, preventing the access of AA to the electrode surface is crucial for the detection capability of OECT-based DA sensors.
清除自由基。 [ 13 ] [ 13 ] ^([13]){ }^{[13]} DA是人体神经系统中最重要的神经递质之一，在许多大脑活动和功能中发挥着重要作用。 [ 14 ] [ 14 ] ^([14]){ }^{[14]} 血液或尿液中 AA 和 DA 的异常水平通常与代谢或神经系统的潜在疾病有关。 [ 13 a , 15 ] [ 13 a , 15 ] ^([13 a,15]){ }^{[13 a, 15]} 因此，利用可穿戴生物传感器检测体液中的 AA 和 DA，对于实时监测和诊断相关综合征非常有价值。在常见的体液中，尿液比血液和汗液更适合用于可穿戴传感系统，因为尿液很容易被尿布收集到足够的量，而无需进行侵入性检查。 [ 16 ] [ 16 ] ^([16]){ }^{[16]} 人体尿液中的 AA 和 DA 浓度应分别在 ( 0.114 − 0.170 ) × 10 − 3 ( 0.114 − 0.170 ) × 10 − 3 (0.114-0.170)xx10^(-3)(0.114-0.170) \times 10^{-3} 和 ( 0.661 − 2.645 ) × 10 − 6 M , [ 17 ] ( 0.661 − 2.645 ) × 10 − 6 M , [ 17 ] (0.661-2.645)xx10^(-6)M,^([17])(0.661-2.645) \times 10^{-6} \mathrm{M},{ }^{[17]} 范围内，因此需要高灵敏度的传感器进行检测。检测 AA 和 DA 所面临的挑战不仅在于它们在尿液中的低浓度和共存性。AA的还原性强，氧化还原电位低，可能会引起多巴胺邻醌（DA的氧化态）的还原，特别是当AA的量远高于DA时，会干扰DA的电化学检测。 [ 18 ] [ 18 ] ^([18]){ }^{[18]} 因此，防止 AA 进入电极表面对基于 OECT 的 DA 传感器的检测能力至关重要。
To obtain flexible OECT sensors with different selectivities toward AA and DA, a surface engineering process for the NOCC electrodes was developed in this work. As illustrated in Figure 1, a piece of carbon cloth (CC) was first immersed in an acidic solution of aniline. With the successive addition of ammonium peroxydisulfate (APS) as the oxidant, the mixture was treated with an ice-water bath for 24 h to allow the slow oxidative polymerization of the aniline. In this step, the in situ formation of polyaniline (PANI) led to the uniform deposition of PANI fibers on the surface of the CC, which was evidenced by the color variation of the CC from light gray to dark green (Figure S1, Supporting Information). The consecutive hydrolysis of the PANI introduced oxygenic carbonyl and phenolic sites, [ 19 ] [ 19 ] ^([19]){ }^{[19]}
为了获得对 AA 和 DA 具有不同选择性的柔性 OECT 传感器，本研究开发了一种 NOCC 电极表面工程工艺。如图 1 所示，首先将一块碳布（CC）浸入苯胺的酸性溶液中。在连续加入过氧化二硫酸铵（APS）作为氧化剂后，混合物在冰水浴中处理 24 小时，使苯胺缓慢氧化聚合。在这一步骤中，聚苯胺（PANI）的原位形成导致 PANI 纤维均匀地沉积在 CC 表面，CC 的颜色从浅灰到深绿的变化证明了这一点（图 S1，佐证资料）。PANI 的连续水解引入了含氧羰基和酚类位点， [ 19 ] [ 19 ] ^([19]){ }^{[19]}
Figure 2. Morphology and structure characterization of the NOCC electrodes. FE-SEM images of the carbon fibers from a) NOCC-O, b) NOCC-I, and c) NOCC-R. TEM and high-resolution TEM images of the carbon fibers from d,g) NOCC-O, e,h) NOCC-I, and f,i) NOCC-R.
图 2.NOCC 电极的形态和结构特征。a) NOCC-O、b) NOCC-I 和 c) NOCC-R 的碳纤维的 FE-SEM 图像。d,g) NOCC-O、e,h) NOCC-I 和 f,i) NOCC-R 的碳纤维的 TEM 和高分辨率 TEM 图像。
which provided oxygen atoms to the PANI-CC composites. The following thermal treatment of the as-prepared PANI-CC at 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} caused the carbonization of the PANI, which generated a N - and O -codoped carbon layer on the CC, resulting in NOCC electrodes with good flexibility (Figure S1, Supporting Information). During the carbonization of the PANI, the amount and type of N and O atoms on the surface of the NOCC electrodes was manipulated by adjusting the atmosphere. In this work, three kinds of gases, including oxygen/argon ( O 2 5 v / v % O 2 5 v / v % (O_(2)5v//v%:}\left(\mathrm{O}_{2} 5 \mathrm{v} / \mathrm{v} \%\right., Ar 95 v / v % 95 v / v % 95v//v%95 \mathrm{v} / \mathrm{v} \% ), pure argon ( 100 v / v % 100 v / v % 100v//v%100 \mathrm{v} / \mathrm{v} \% ), and hydrogen/argon ( H 2 5 v / v % H 2 5 v / v % (H_(2)5v//v%:}\left(\mathrm{H}_{2} 5 \mathrm{v} / \mathrm{v} \%\right., Ar 95 v / v % 95 v / v % 95v//v%95 \mathrm{v} / \mathrm{v} \% ), were utilized to examine the influence of oxidative, inert, and reductive atmospheres on the surface compositions and electrochemical behaviors of the NOCC electrodes. Correspondingly, the resulting samples were denoted as NOCC-O ( O 2 / Ar ) O 2 / Ar {:O_(2)//Ar)\left.\mathrm{O}_{2} / \mathrm{Ar}\right), NOCC-I ( Ar ) ( Ar ) (Ar)(\mathrm{Ar}) and NOCC-R ( H 2 / Ar ) H 2 / Ar (H_(2)//Ar)\left(\mathrm{H}_{2} / \mathrm{Ar}\right).
这为 PANI-CC 复合材料提供了氧原子。在 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} 下对制备好的 PANI-CC 进行热处理会导致 PANI 碳化，从而在 CC 上生成掺杂 N 原子和 O 原子的碳层，形成具有良好柔韧性的 NOCC 电极（图 S1，佐证资料）。在 PANI 碳化过程中，NOCC 电极表面 N 原子和 O 原子的数量和类型可通过调节气氛来控制。本研究利用三种气体，包括氧气/氩气 ( O 2 5 v / v % O 2 5 v / v % (O_(2)5v//v%:}\left(\mathrm{O}_{2} 5 \mathrm{v} / \mathrm{v} \%\right. , Ar 95 v / v % 95 v / v % 95v//v%95 \mathrm{v} / \mathrm{v} \% )、纯氩气 ( 100 v / v % 100 v / v % 100v//v%100 \mathrm{v} / \mathrm{v} \% )和氢气/氩气 ( H 2 5 v / v % H 2 5 v / v % (H_(2)5v//v%:}\left(\mathrm{H}_{2} 5 \mathrm{v} / \mathrm{v} \%\right. , Ar 95 v / v % 95 v / v % 95v//v%95 \mathrm{v} / \mathrm{v} \% )，研究了氧化性、惰性和还原性气氛对 NOCC 电极表面成分和电化学行为的影响。相应地，得到的样品被称为 NOCC-O（ O 2 / Ar ) O 2 / Ar {:O_(2)//Ar)\left.\mathrm{O}_{2} / \mathrm{Ar}\right) 、NOCC-I ( Ar ) ( Ar ) (Ar)(\mathrm{Ar}) 和 NOCC-R ( H 2 / Ar ) H 2 / Ar (H_(2)//Ar)\left(\mathrm{H}_{2} / \mathrm{Ar}\right) 。
The morphology and microstructure of the NOCC electrodes were first characterized by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). As shown in Figure S2a-c (Supporting Information), the pristine CC had a typical woven fabric structure, consisting of perpendicularly interlaced carbon fibers with diameters of 9 ± 1 μ m 9 ± 1 μ m 9+-1mum9 \pm 1 \mu \mathrm{~m}. Except for some groove-like structures, the carbon fibers had relatively smooth surfaces. In contrast, the carbon fibers in the PANI-CC composite were homogeneously coated with a layer of burr-like PANI fibers (Figure S2d-f, Supporting
首先利用场发射扫描电子显微镜（FE-SEM）和透射电子显微镜（TEM）对NOCC电极的形态和微观结构进行了表征。如图 S2a-c（佐证资料）所示，原始 CC 具有典型的编织结构，由垂直交错的碳纤维组成，直径为 9 ± 1 μ m 9 ± 1 μ m 9+-1mum9 \pm 1 \mu \mathrm{~m} 。除了一些槽状结构外，碳纤维的表面相对光滑。与此相反，PANI-CC 复合材料中的碳纤维均匀地包覆着一层毛刺状的 PANI 纤维（图 S2d-f，佐证材料
Information), which were formed during the oxidative polymerization at low temperature. The SEM characterization further indicated that the NOCC electrodes had smoother surfaces than did the PANI-CC (Figure 2 and Figure S3, Supporting Information), which was attributable to the deformation and decomposition of the PANI fibers during the carbonization process. Moreover, the atmosphere during the thermal treatment showed profound influence on the surface morphology of the three NOCC electrodes. NOCC-O, obtained under the oxidative atmosphere, had many fewer protuberances than did NOCC-R, obtained under H 2 / Ar H 2 / Ar H_(2)//Ar\mathrm{H}_{2} / \mathrm{Ar}, while the surface roughness of NOCC-I, obtained under Ar, was between those of NOCC-O and NOCC-R (Figure 2a-c). The TEM images of the carbon fibers from the NOCC electrodes further illustrated the different effects of the carbonization atmospheres. As shown in Figure 2d-f and Figure S4 (Supporting Information), the edges of the carbon fibers from the three samples showed different contrast of the light and dark areas, which was used to estimate the thickness of the carbon derived from the pyrolysis of PANI. Accordingly, the thickness of the PANI-derived carbon in NOCC-O was only 30 ± 4 nm 30 ± 4 nm 30+-4nm30 \pm 4 \mathrm{~nm}, while the carbon layers from the PANI in NOCC-I and NOCC-R had much higher thicknesses of 130 ± 14 130 ± 14 130+-14130 \pm 14 and 200 ± 28 nm 200 ± 28 nm 200+-28nm200 \pm 28 \mathrm{~nm}, respectively. Moreover, the high resolution TEM images of NOCC-O indicated that the skeleton of the PANI-derived carbon had pseudographitic crystalline layers
信息），它们是在低温氧化聚合过程中形成的。扫描电镜表征进一步表明，NOCC 电极的表面比 PANI-CC 电极更光滑（图 2 和图 S3，佐证资料），这归因于碳化过程中 PANI 纤维的变形和分解。此外，热处理过程中的气氛也对三种 NOCC 电极的表面形态产生了深远的影响。在氧化气氛下得到的 NOCC-O 比在 H 2 / Ar H 2 / Ar H_(2)//Ar\mathrm{H}_{2} / \mathrm{Ar} 下得到的 NOCC-R 少很多突起，而在氩气下得到的 NOCC-I 的表面粗糙度介于 NOCC-O 和 NOCC-R 之间（图 2a-c）。NOCC 电极碳纤维的 TEM 图像进一步说明了碳化气氛的不同影响。如图 2d-f 和图 S4（佐证资料）所示，三个样品的碳纤维边缘显示出不同的明暗区域对比。因此，NOCC-O 中 PANI 衍生碳的厚度仅为 30 ± 4 nm 30 ± 4 nm 30+-4nm30 \pm 4 \mathrm{~nm} ，而 NOCC-I 和 NOCC-R 中 PANI 衍生碳层的厚度要高得多，分别为 130 ± 14 130 ± 14 130+-14130 \pm 14 和 200 ± 28 nm 200 ± 28 nm 200+-28nm200 \pm 28 \mathrm{~nm} 。此外，NOCC-O 的高分辨率 TEM 图像表明，PANI 衍生碳的骨架具有假形晶层
(Figure 2 g ), which was different from the amorphous carbon layers with disordered micropores in NOCC-I and NOCC-R (Figure 2h,i).
(图 2 g），这与 NOCC-I 和 NOCC-R 中具有无序微孔的无定形碳层不同（图 2h，i）。
The microstructures and chemical compositions of the samples were further compared using their Fourier transform infrared (FTIR), Raman, and X-ray diffraction (XRD) spectra. In the FTIR spectra of the NOCC electrodes (Figure S5a, Supporting Information), the absorption bands near 1150, 1300, and 1500 cm − 1 1500 cm − 1 1500cm^(-1)1500 \mathrm{~cm}^{-1} were assigned to the stretching vibration of C-O groups in ethers or phenols, the stretching vibration of C − N C − N C-N\mathrm{C}-\mathrm{N} groups, and the ring vibration of pyridinic N or pyrrolic N groups, respectively, confirming the doping of N and O atoms in the carbon framework. [ 20 ] [ 20 ] ^([20]){ }^{[20]} The XRD patterns of the samples had similar broad diffractions at ≈ 26 ∘ , 43 ∘ ≈ 26 ∘ , 43 ∘ ~~26^(@),43^(@)\approx 26^{\circ}, 43^{\circ}, and 54 ∘ 54 ∘ 54^(@)54^{\circ}, which were indexed to the (002), (100)/(101), and (102) planes of graphitic carbon in the CC substrate due to its high weight ratio in the NOCC electrodes (Figure S5b, Supporting Information). [ 21 ] [ 21 ] ^([21]){ }^{[21]} In contrast, the Raman spectra of the NOCCs provided more information about the structure of the N and O codoped carbon layer. As shown in Figure S5c (Supporting Information), the peaks near 1350 and 1590 cm − 1 1590 cm − 1 1590cm^(-1)1590 \mathrm{~cm}^{-1} are the characteristic disordered (D) and graphitic (G) bands of carbon materials, [ 22 ] [ 22 ] ^([22]){ }^{[22]} confirming the carbonization of PANI. More importantly, the D band of NOCC-O had much higher intensity than those of NOCC-I and NOCC-R, which was attributable to the decrease in aromaticity of the carbon framework under the oxidative atmosphere, which resulted in a much higher I D / I G I D / I G I_(D)//I_(G)I_{\mathrm{D}} / I_{\mathrm{G}} value ( 0.88 ) ( 0.88 ) (0.88)(0.88) for NOCC-O than for NOCC-I (0.79) and NOCC-R (0.75). [ 23 ] [ 23 ] ^([23]){ }^{[23]} However, the full width at half maximum (FWHM) of the D band of NOCC-O was smaller than those of the other samples, corresponding to a narrow distribution of sp 2 sp 2 sp^(2)\mathrm{sp}^{2} bonded clusters with different ring sizes, because the amorphous carbon domains were more easily etched under the oxidative atmosphere. [ 23 , 24 ] [ 23 , 24 ] ^([23,24]){ }^{[23,24]} This phenomenon suggested that the aromatic carbon in NOCC-O had a higher graphitic degree than did those in NOCC-I and NOCC-R, which was in accordance with the TEM images (Figure 2g).
利用傅立叶变换红外光谱（FTIR）、拉曼光谱和 X 射线衍射（XRD）光谱进一步比较了样品的微观结构和化学成分。在 NOCC 电极的傅立叶变换红外光谱中（图 S5a，佐证资料），1150、1300 和 1500 cm − 1 1500 cm − 1 1500cm^(-1)1500 \mathrm{~cm}^{-1} 附近的吸收带分别归属于醚或酚中 C-O 基团的伸缩振动、 C − N C − N C-N\mathrm{C}-\mathrm{N} 基团的伸缩振动以及吡啶 N 或吡咯 N 基团的环振动，证实了碳框架中 N 原子和 O 原子的掺杂。 [ 20 ] [ 20 ] ^([20]){ }^{[20]} 样品的 XRD 图样在 ≈ 26 ∘ , 43 ∘ ≈ 26 ∘ , 43 ∘ ~~26^(@),43^(@)\approx 26^{\circ}, 43^{\circ} 和 54 ∘ 54 ∘ 54^(@)54^{\circ} 处有类似的宽衍射，由于 NOCC 电极中石墨碳的重量比很高，这些衍射与 CC 基底中石墨碳的 (002)、(100)/(101) 和 (102) 平面有关（图 S5b，佐证信息）。 [ 21 ] [ 21 ] ^([21]){ }^{[21]} 相反，NOCC 的拉曼光谱提供了更多有关 N 和 O 共掺碳层结构的信息。如图 S5c（佐证资料）所示，1350 和 1590 cm − 1 1590 cm − 1 1590cm^(-1)1590 \mathrm{~cm}^{-1} 附近的峰是碳材料特有的无序带 (D) 和石墨带 (G)， [ 22 ] [ 22 ] ^([22]){ }^{[22]} 证实了 PANI 的碳化。更重要的是，NOCC-O 的 D 带强度远高于 NOCC-I 和 NOCC-R，这是因为在氧化气氛下碳框架的芳香度降低，导致 NOCC-O 的 I D / I G I D / I G I_(D)//I_(G)I_{\mathrm{D}} / I_{\mathrm{G}} 值 ( 0.88 ) ( 0.88 ) (0.88)(0.88) 远高于 NOCC-I (0.79) 和 NOCC-R (0.75)。 [ 23 ] [ 23 ] ^([23]){ }^{[23]} 然而，NOCC-O的D波段的半最大全宽（FWHM）小于其他样品，对应于不同环尺寸的 sp 2 sp 2 sp^(2)\mathrm{sp}^{2} 键合簇的狭窄分布，这是因为无定形碳域在氧化气氛下更容易被蚀刻。 [ 23 , 24 ] [ 23 , 24 ] ^([23,24]){ }^{[23,24]} 这一现象表明，NOCC-O 中的芳香碳比 NOCC-I 和 NOCC-R 中的芳香碳具有更高的石墨化程度，这与 TEM 图像相符（图 2g）。
The performances of the obtained NOCC electrodes as sensors for AA and DA were first evaluated in a three-electrode electrochemical sensing system (Figure 3a). As a common analyte coexisting with AA and DA in body fluids, UA was added as the interference. [ 25 ] [ 25 ] ^([25]){ }^{[25]} The differential pulse voltammetry (DPV) and cyclic voltammetry (CV) profiles of the NOCCs were first recorded in phosphate buffer saline (PBS, 0.1 m , pH = 7.4 0.1 m , pH = 7.4 0.1m,pH=7.40.1 \mathrm{~m}, \mathrm{pH}=7.4 ) containing AA ( 300 × 10 − 6 m ) 300 × 10 − 6 m (300 xx10^(-6)(m))\left(300 \times 10^{-6} \mathrm{~m}\right), DA ( 10 × 10 − 6 m ) 10 × 10 − 6 m (10 xx10^(-6)(m))\left(10 \times 10^{-6} \mathrm{~m}\right), and UA ( 10 × 10 − 6 m ) [ 12 b ] 10 × 10 − 6 m [ 12 b ] (10 xx10^(-6)(m))^([12b])\left(10 \times 10^{-6} \mathrm{~m}\right){ }^{[12 \mathrm{~b}]} As indicated in Figure 3b, the well-defined peaks from the oxidation of AA ( ≈ − 66 mV ≈ − 66 mV ~~-66mV\approx-66 \mathrm{mV} ), DA ( ≈ 117 mV ) ( ≈ 117 mV ) (~~117mV)(\approx 117 \mathrm{mV}) and UA ( ≈ 234 mV ≈ 234 mV ~~234mV\approx 234 \mathrm{mV} ) were observed in the DPV curves of the three electrodes. [ 12 b , 26 ] [ 12 b , 26 ] ^([12 b,26]){ }^{[12 b, 26]} According to the current intensities of the peaks (Figure 3c), NOCC-O and NOCC-I showed much greater responses to DA than to AA and UA, while NOCC-R showed distinct detection behavior by delivering a higher oxidation current to AA than to DA and UA. The different sensing behaviors of the NOCC electrodes were also confirmed by their CV curves (Figure S6a, Supporting Information). Considering the significant differences in the responses of the NOCC electrodes toward the analytes, NOCC-R had obvious advantages in the detection of AA, while NOCC-O was more suitable for the electrochemical sensing of DA. In contrast to NOCC-O, NOCC-I had very similar DPV responses toward DA and UA, making
首先在一个三电极电化学传感系统中评估了所获得的 NOCC 电极作为 AA 和 DA 传感器的性能（图 3a）。作为与 AA 和 DA 共存于体液中的常见分析物，UA 被添加为干扰物。首先在含有 AA ( 300 × 10 − 6 m ) 300 × 10 − 6 m (300 xx10^(-6)(m))\left(300 \times 10^{-6} \mathrm{~m}\right) 、DA ( 10 × 10 − 6 m ) 10 × 10 − 6 m (10 xx10^(-6)(m))\left(10 \times 10^{-6} \mathrm{~m}\right) 和 UA ( 10 × 10 − 6 m ) [ 12 b ] 10 × 10 − 6 m [ 12 b ] (10 xx10^(-6)(m))^([12b])\left(10 \times 10^{-6} \mathrm{~m}\right){ }^{[12 \mathrm{~b}]} 的磷酸盐缓冲盐水（PBS， 0.1 m , pH = 7.4 0.1 m , pH = 7.4 0.1m,pH=7.40.1 \mathrm{~m}, \mathrm{pH}=7.4 ）中记录 NOCC 的差分脉冲伏安法（DPV）和循环伏安法（CV）曲线、和 UA ( 10 × 10 − 6 m ) [ 12 b ] 10 × 10 − 6 m [ 12 b ] (10 xx10^(-6)(m))^([12b])\left(10 \times 10^{-6} \mathrm{~m}\right){ }^{[12 \mathrm{~b}]} 如图 3b 所示，在三个电极的 DPV 曲线中观察到 AA（ ≈ − 66 mV ≈ − 66 mV ~~-66mV\approx-66 \mathrm{mV} ）、DA（ ( ≈ 117 mV ) ( ≈ 117 mV ) (~~117mV)(\approx 117 \mathrm{mV}) ）和 UA（ ≈ 234 mV ≈ 234 mV ~~234mV\approx 234 \mathrm{mV} ）氧化产生的明确峰值。 [ 12 b , 26 ] [ 12 b , 26 ] ^([12 b,26]){ }^{[12 b, 26]} 根据峰值的电流强度（图 3c），NOCC-O 和 NOCC-I 对 DA 的响应远大于对 AA 和 UA 的响应，而 NOCC-R 则表现出不同的检测行为，对 AA 的氧化电流高于对 DA 和 UA 的氧化电流。NOCC 电极的 CV 曲线也证实了它们的不同检测行为（图 S6a，佐证资料）。考虑到 NOCC 电极对分析物反应的显著差异，NOCC-R 在检测 AA 方面具有明显优势，而 NOCC-O 则更适合 DA 的电化学传感。与 NOCC-O 相比，NOCC-I 对 DA 和 UA 的 DPV 反应非常相似，这使得
it a less appealing electrode for the detection of DA due to its low selectivity.
由于其选择性较低，该电极在检测 DA 方面的吸引力较小。
The DPV responses of NOCC-R with the gradual addition of AA, summarized in Figure 3d, indicated that the peak current intensities ( I p ) I p (I_(p))\left(I_{\mathrm{p}}\right) of NOCC-R increased linearly as the concentrations of AA varied from 10 × 10 − 6 10 × 10 − 6 10 xx10^(-6)10 \times 10^{-6} to 1300 × 10 − 6 m 1300 × 10 − 6 m 1300 xx10^(-6)m1300 \times 10^{-6} \mathrm{~m}. The corresponding calibration equation of the response currents versus the concentrations of AA was expressed as I p = 1.145 C + 245.441 I p = 1.145 C + 245.441 I_(p)=1.145 C+245.441I_{\mathrm{p}}=1.145 C+245.441, with a high sensitivity of 1.145 μ A μ M − 1 cm − 2 1.145 μ A μ M − 1 cm − 2 1.145 muAmuM^(-1)cm^(-2)1.145 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} and a correlation coefficient of 0.9905 (Figure 3d inset). Accordingly, NOCC-R had a very low LOD of 3.41 × 10 − 6 m 3.41 × 10 − 6 m 3.41 xx10^(-6)m3.41 \times 10^{-6} \mathrm{~m} for the detection of AA at a signal-to-noise (S/N) ratio of 3 . The DPV profiles and the calibration curve shown in Figure 3 g and the inset suggest that NOCC-O possessed an excellent detection capability toward DA with a wide linear detection range of ( 0.3 − 55 ) × 10 − 6 M ( R 2 = 0.9973 ) ( 0.3 − 55 ) × 10 − 6 M R 2 = 0.9973 (0.3-55)xx10^(-6)M(R^(2)=0.9973)(0.3-55) \times 10^{-6} \mathrm{M}\left(R^{2}=0.9973\right), a high sensitivity of 19.194 μ A μ M − 1 cm − 2 19.194 μ A μ M − 1 cm − 2 19.194 muAmuM^(-1)cm^(-2)19.194 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} and a low LOD of 0.18 × 10 − 6 m 0.18 × 10 − 6 m 0.18 xx10^(-6)m0.18 \times 10^{-6} \mathrm{~m} ( S / N = 3 ) ( S / N = 3 ) (S//N=3)(\mathrm{S} / \mathrm{N}=3). The amperometric current-time ( i − t i − t i-ti-t ) measurements of the NOCC electrodes further confirmed the different detection capabilities of NOCC-R and NOCC-O (Figure S6b,c, Supporting Information). [ 27 ] [ 27 ] ^([27]){ }^{[27]} As shown in Figure 3e and the inset, NOCC-R delivered an instant and significant response current with the addition of AA that was proportional to the accumulated concentrations of AA from 0.3 × 10 − 6 0.3 × 10 − 6 0.3 xx10^(-6)0.3 \times 10^{-6} to 1400 × 10 − 6 m 1400 × 10 − 6 m 1400 xx10^(-6)m1400 \times 10^{-6} \mathrm{~m} with a correlation coefficient of 0.9984 . According to the corresponding regression equation (Figure 3f), the sensitivity and LOD of NOCC-R toward AA were 0.141 μ A μ M − 1 cm − 2 0.141 μ A μ M − 1 cm − 2 0.141 muAmuM^(-1)cm^(-2)0.141 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} and 0.26 × 10 − 6 m ( S / N = 3 ) 0.26 × 10 − 6 m ( S / N = 3 ) 0.26 xx10^(-6)m(S//N=3)0.26 \times 10^{-6} \mathrm{~m}(\mathrm{~S} / \mathrm{N}=3), which were similar to the results from the DPV measurement (Table S1, Supporting Information). Similarly, the i − t i − t i-ti-t curves of NOCC-O at a potential of +0.2 V (Figure 3 h and inset) verified its excellent DA sensing behavior, with a sensitivity of 0.326 μ A μ M − 1 cm − 2 ( R 2 = 0.9968 ) 0.326 μ A μ M − 1 cm − 2 R 2 = 0.9968 0.326 muAmuM^(-1)cm^(-2)(R^(2)=0.9968)0.326 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2}\left(R^{2}=0.9968\right) and a LOD of 0.17 × 10 − 6 m ( S / N = 3 ) 0.17 × 10 − 6 m ( S / N = 3 ) 0.17 xx10^(-6)m(S//N=3)0.17 \times 10^{-6} \mathrm{~m}(\mathrm{~S} / \mathrm{N}=3), which was comparable to the recently reported three-electrode-based electrochemical DA sensors (Table S2, Supporting Information).
图 3d 总结了逐渐添加 AA 时 NOCC-R 的 DPV 响应，结果表明随着 AA 浓度从 10 × 10 − 6 10 × 10 − 6 10 xx10^(-6)10 \times 10^{-6} 到 1300 × 10 − 6 m 1300 × 10 − 6 m 1300 xx10^(-6)m1300 \times 10^{-6} \mathrm{~m} 的变化，NOCC-R 的峰值电流强度 ( I p ) I p (I_(p))\left(I_{\mathrm{p}}\right) 呈线性增加。响应电流与 AA 浓度的对应校准方程为 I p = 1.145 C + 245.441 I p = 1.145 C + 245.441 I_(p)=1.145 C+245.441I_{\mathrm{p}}=1.145 C+245.441 ，灵敏度为 1.145 μ A μ M − 1 cm − 2 1.145 μ A μ M − 1 cm − 2 1.145 muAmuM^(-1)cm^(-2)1.145 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} ，相关系数为 0.9905（图 3d 插图）。因此，在信噪比（S/N）为 3 时，NOCC-R 检测 AA 的 LOD 很低，为 3.41 × 10 − 6 m 3.41 × 10 − 6 m 3.41 xx10^(-6)m3.41 \times 10^{-6} \mathrm{~m} 。图 3 g 和插图所示的 DPV 曲线和校准曲线表明，NOCC-O 对 DA 具有出色的检测能力，线性检测范围 ( 0.3 − 55 ) × 10 − 6 M ( R 2 = 0.9973 ) ( 0.3 − 55 ) × 10 − 6 M R 2 = 0.9973 (0.3-55)xx10^(-6)M(R^(2)=0.9973)(0.3-55) \times 10^{-6} \mathrm{M}\left(R^{2}=0.9973\right) 宽，灵敏度 19.194 μ A μ M − 1 cm − 2 19.194 μ A μ M − 1 cm − 2 19.194 muAmuM^(-1)cm^(-2)19.194 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} 高，LOD 0.18 × 10 − 6 m 0.18 × 10 − 6 m 0.18 xx10^(-6)m0.18 \times 10^{-6} \mathrm{~m} ( S / N = 3 ) ( S / N = 3 ) (S//N=3)(\mathrm{S} / \mathrm{N}=3) 低。NOCC 电极的安培电流-时间（ i − t i − t i-ti-t ）测量进一步证实了 NOCC-R 和 NOCC-O 的不同检测能力（图 S6b、c，佐证资料）。 [ 27 ] [ 27 ] ^([27]){ }^{[27]} 如图 3e 和插图所示，NOCC-R 在添加 AA 后会立即产生显著的响应电流，该电流与从 0.3 × 10 − 6 0.3 × 10 − 6 0.3 xx10^(-6)0.3 \times 10^{-6} 到 1400 × 10 − 6 m 1400 × 10 − 6 m 1400 xx10^(-6)m1400 \times 10^{-6} \mathrm{~m} 的 AA 累积浓度成正比，相关系数为 0.9984。根据相应的回归方程（图 3f），NOCC-R 对 AA 的灵敏度和 LOD 分别为 0.141 μ A μ M − 1 cm − 2 0.141 μ A μ M − 1 cm − 2 0.141 muAmuM^(-1)cm^(-2)0.141 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} 和 0.26 × 10 − 6 m ( S / N = 3 ) 0.26 × 10 − 6 m ( S / N = 3 ) 0.26 xx10^(-6)m(S//N=3)0.26 \times 10^{-6} \mathrm{~m}(\mathrm{~S} / \mathrm{N}=3) ，与 DPV 测量的结果相似（表 S1，佐证信息）。同样，NOCC-O 在电位为 +0.2 V（图 3 h 和插图）验证了其出色的 DA 感测性能，灵敏度为 0.326 μ A μ M − 1 cm − 2 ( R 2 = 0.9968 ) 0.326 μ A μ M − 1 cm − 2 R 2 = 0.9968 0.326 muAmuM^(-1)cm^(-2)(R^(2)=0.9968)0.326 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2}\left(R^{2}=0.9968\right) ，LOD 为 0.17 × 10 − 6 m ( S / N = 3 ) 0.17 × 10 − 6 m ( S / N = 3 ) 0.17 xx10^(-6)m(S//N=3)0.17 \times 10^{-6} \mathrm{~m}(\mathrm{~S} / \mathrm{N}=3) ，与最近报道的基于三电极的电化学 DA 传感器相当（表 S2，佐证信息）。
Because of the different detection behaviors of NOCC-R and NOCC-O, they can be used as the gate electrodes for the sensing of AA and DA, respectively, in flexible OECTs (Figure 4a and Figure S7, Supporting Information). Note that OECT sensors with the typical transistor structure have a working mechanism that is different than that of three-electrode electrochemical sensors. As illustrated in Figure 4 b , the redox reactions of the analytes (DA or AA) at the gate/electrolyte interface caused changes in the effective gate voltage ( V G V G V_(G)V_{G} eff ), thus reducing the channel current ( I DS I DS I_(DS)I_{\mathrm{DS}} ) between the source ( S ) and drain (D) electrodes. [ 3 b , 6 a ] [ 3 b , 6 a ] ^([3b,6a]){ }^{[3 \mathrm{~b}, 6 \mathrm{a}]} Correspondingly, the concentrations of the analytes were determined by monitoring the variation of I DS I DS I_(DS)I_{\mathrm{DS}} in the OECT sensors (Supporting Information). [ 6 b ] [ 6 b ] ^([6b]){ }^{[6 b]} As displayed in Figure S8 (Supporting Information), the transfer characteristic curves ( I DS I DS I_(DS)I_{\mathrm{DS}} vs V GS V GS V_(GS)V_{\mathrm{GS}} ) of the OECT sensors with NOCC-R and NOCC-O as gate electrodes clearly shifted to lower gate voltages with the addition of AA, DA, and UA, verifying their sensing capabilities toward these analytes. [ 6 a , 28 ] [ 6 a , 28 ] ^([6a,28]){ }^{[6 \mathrm{a}, 28]} When V GS V GS V_(GS)V_{\mathrm{GS}} was changed from -0.5 to 1.5 V , the offset voltages in the transfer curves of the OECT sensors were ≈ − 150 , 0 ≈ − 150 , 0 ~~-150,0\approx-150,0, and 110 mV for AA , DA AA , DA AA,DA\mathrm{AA}, \mathrm{DA}, and UA, respectively, which were in agreement with the values obtained from the three-electrode electrochemical sensing systems. To examine the effect of V GS V GS V_(GS)V_{\mathrm{GS}} on the sensing behavior of the OECTs, the normalized current responses (NCRs) of the
由于 NOCC-R 和 NOCC-O 具有不同的检测行为，因此它们可分别用作柔性 OECT 中传感 AA 和 DA 的栅极（图 4a 和图 S7，佐证资料）。请注意，具有典型晶体管结构的 OECT 传感器的工作机制与三电极电化学传感器不同。如图 4 b 所示，分析物（DA 或 AA）在栅极/电解质界面上的氧化还原反应会导致有效栅极电压（ V G V G V_(G)V_{G} eff）发生变化，从而降低源极（S）和漏极（D）之间的沟道电流（ I DS I DS I_(DS)I_{\mathrm{DS}} ）。 [ 3 b , 6 a ] [ 3 b , 6 a ] ^([3b,6a]){ }^{[3 \mathrm{~b}, 6 \mathrm{a}]} 相应地，分析物的浓度是通过监测 OECT 传感器中 I DS I DS I_(DS)I_{\mathrm{DS}} 的变化确定的（证明资料）。 [ 6 b ] [ 6 b ] ^([6b]){ }^{[6 b]} 如图 S8（佐证资料）所示，以 NOCC-R 和 NOCC-O 为栅电极的 OECT 传感器的转移特性曲线（ I DS I DS I_(DS)I_{\mathrm{DS}} vs V GS V GS V_(GS)V_{\mathrm{GS}} ）在添加 AA、DA 和 UA 后明显转向较低的栅极电压，验证了它们对这些分析物的传感能力。 [ 6 a , 28 ] [ 6 a , 28 ] ^([6a,28]){ }^{[6 \mathrm{a}, 28]} 当 V GS V GS V_(GS)V_{\mathrm{GS}} 从-0.5 V变为1.5 V时，OECT传感器转移曲线上的偏移电压分别为 ≈ − 150 , 0 ≈ − 150 , 0 ~~-150,0\approx-150,0 ， AA , DA AA , DA AA,DA\mathrm{AA}, \mathrm{DA} 和UA分别为110 mV，这与三电极电化学传感系统得到的数值一致。为了研究 V GS V GS V_(GS)V_{\mathrm{GS}} 对 OECT 传感器传感行为的影响，对 V GS V GS V_(GS)V_{\mathrm{GS}} 和 UA 的归一化电流响应（NCR）进行了分析。
Figure 3. The structure and sensing performances of the three-electrode electrochemical sensing system with the NOCCs as the working electrodes. a) Schematic illustration of the three-electrode electrochemical sensing system. b) DPV curves of the NOCC electrodes. c) The comparison of the current densities of the NOCC electrodes toward AA, DA, and UA. d) DPV curves for NOCC-R in PBS solution containing DA ( 5 × 10 − 6 m ) 5 × 10 − 6 m {:5xx10^(-6)(m))\left.5 \times 10^{-6} \mathrm{~m}\right), UA ( 10 × 10 − 6 m ) 10 × 10 − 6 m {: 10 xx10^(-6)(m))\left.10 \times 10^{-6} \mathrm{~m}\right) and different concentrations of AA from 10 × 10 − 6 10 × 10 − 6 10 xx10^(-6)10 \times 10^{-6} to 1300 × 10 − 6 m 1300 × 10 − 6 m 1300 xx10^(-6)m1300 \times 10^{-6} \mathrm{~m}; inset: the corresponding calibration curve. e) Typical amperometric i − t i − t i-ti-t curve of NOCC-R at an applied potential of 0 V versus SCE. f) The linear calibration curve for i − t i − t i-ti-t currents of NOCC-R versus the concentrations of AA. g) DPV curves of NOCC-O in PBS solution containing AA ( 300 × 10 − 6 M ) 300 × 10 − 6 M (300 xx10^(-6)M)\left(300 \times 10^{-6} \mathrm{M}\right), UA ( 20 × 10 − 6 M ) 20 × 10 − 6 M (20 xx10^(-6)M)\left(20 \times 10^{-6} \mathrm{M}\right), and different concentrations of DA from 0.3 × 10 − 6 0.3 × 10 − 6 0.3 xx10^(-6)0.3 \times 10^{-6} to 55 × 10 − 6 M 55 × 10 − 6 M 55 xx10^(-6)M55 \times 10^{-6} \mathrm{M}; inset: the corresponding calibration curve. h) Typical amperometric i − t i − t i-ti-t curve of NOCC-O at an applied potential of +0.2 V versus SCE. i) The linear calibration curve for i − t i − t i-ti-t currents of NOCC-O versus the concentrations of DA.
图 3.以 NOCC 为工作电极的三电极电化学传感系统的结构和传感性能 a) 三电极电化学传感系统示意图。c) NOCC 电极对 AA、DA 和 UA 的电流密度比较。 d) NOCC-R 在含有 DA（ 5 × 10 − 6 m ) 5 × 10 − 6 m {:5xx10^(-6)(m))\left.5 \times 10^{-6} \mathrm{~m}\right) 、UA（ 10 × 10 − 6 m ) 10 × 10 − 6 m {: 10 xx10^(-6)(m))\left.10 \times 10^{-6} \mathrm{~m}\right) 和不同浓度 AA（从 10 × 10 − 6 10 × 10 − 6 10 xx10^(-6)10 \times 10^{-6} 到 1300 × 10 − 6 m 1300 × 10 − 6 m 1300 xx10^(-6)m1300 \times 10^{-6} \mathrm{~m} ）的 PBS 溶液中的 DPV 曲线；插图：相应的校准曲线。e) NOCC-R 在施加 0 V 电位时的典型安培 i − t i − t i-ti-t 曲线与 SCE 的关系。 f) NOCC-R 的 i − t i − t i-ti-t 电流与 AA 浓度的线性校准曲线。 g) NOCC-O 在含有 AA ( 300 × 10 − 6 M ) 300 × 10 − 6 M (300 xx10^(-6)M)\left(300 \times 10^{-6} \mathrm{M}\right) 、UA ( 20 × 10 − 6 M ) 20 × 10 − 6 M (20 xx10^(-6)M)\left(20 \times 10^{-6} \mathrm{M}\right) 和不同浓度 DA（从 0.3 × 10 − 6 0.3 × 10 − 6 0.3 xx10^(-6)0.3 \times 10^{-6} 到 55 × 10 − 6 M 55 × 10 − 6 M 55 xx10^(-6)M55 \times 10^{-6} \mathrm{M} ）的 PBS 溶液中的 DPV 曲线；插图：相应的校准曲线。h) NOCC-O 在 +0.2 V 外加电位下的典型安培 i − t i − t i-ti-t 曲线与 SCE 的关系。 i) NOCC-O 的 i − t i − t i-ti-t 电流与 DA 浓度的线性校准曲线。
NOCC-R-based OECT with the addition of AA, DA, and UA at different V GS V GS V_(GS)V_{\mathrm{GS}} are summarized in Figure S9 (Supporting Information). The results indicated that the improved values of V GS V GS V_(GS)V_{\mathrm{GS}} significantly increased the response currents of the OECT sensors toward AA ( V G S >≈ 0 V V G S >≈ 0 V V_(GS)>≈0VV_{G S}>\approx 0 \mathrm{~V} ), DA ( V G S >≈ 0.1 V V G S >≈ 0.1 V V_(GS)>≈0.1VV_{G S}>\approx 0.1 \mathrm{~V} ), and UA ( V G S >≈ 0.2 V ) V G S >≈ 0.2 V (V_(GS)>≈0.2(V))\left(V_{G S}>\approx 0.2 \mathrm{~V}\right), which was attributable to the enhanced oxidation reactions of the analytes on the surface of the gate electrode. [ 28 ] [ 28 ] ^([28]){ }^{[28]} However, the increased responses of the OECT sensor to all three compounds inevitably decreased its selectivity toward AA. In contrast, the OECT sensor with negative V GS V GS V_(GS)V_{\mathrm{GS}} had very weak response currents, indicative of the much depressed electrochemical oxidation capacity of the gate electrode. Therefore, a proper V GS V GS V_(GS)V_{\mathrm{GS}} was necessary for the accurate detection of the target analytes with the OECT sensors.
图 S9（佐证资料）总结了在不同 V GS V GS V_(GS)V_{\mathrm{GS}} 条件下添加 AA、DA 和 UA 的基于 NOCC-R 的 OECT。结果表明， V GS V GS V_(GS)V_{\mathrm{GS}} 值的提高显著增加了 OECT 传感器对 AA（ V G S >≈ 0 V V G S >≈ 0 V V_(GS)>≈0VV_{G S}>\approx 0 \mathrm{~V} ）、DA（ V G S >≈ 0.1 V V G S >≈ 0.1 V V_(GS)>≈0.1VV_{G S}>\approx 0.1 \mathrm{~V} ）和 UA（ ( V G S >≈ 0.2 V ) V G S >≈ 0.2 V (V_(GS)>≈0.2(V))\left(V_{G S}>\approx 0.2 \mathrm{~V}\right) ）的响应电流，这归因于分析物在栅电极表面的氧化反应增强。 [ 28 ] [ 28 ] ^([28]){ }^{[28]} 然而，OECT 传感器对这三种化合物的反应增强，不可避免地降低了其对 AA 的选择性。相比之下，负 V GS V GS V_(GS)V_{\mathrm{GS}} 的 OECT 传感器的响应电流非常弱，表明栅电极的电化学氧化能力大大降低。因此，适当的 V GS V GS V_(GS)V_{\mathrm{GS}} 对于用 OECT 传感器准确检测目标分析物是必不可少的。
The real-time channel currents ( I DS I DS I_(DS)I_{\mathrm{DS}} ) of the NOCC-R-based OECT sensor with the successive injection of AA to the PBS solution were subsequently recorded at a gate potential of 0 V . As shown in Figure 4c, the NOCC-R-based OECT delivered rapid and significant current responses when the concentration of AA was higher than 10 × 10 − 9 m 10 × 10 − 9 m 10 xx10^(-9)m10 \times 10^{-9} \mathrm{~m}, which was much lower than the LODs of NOCC-R in the three-electrode system and the recently reported AA sensors (Table S3, Supporting Information). In contrast, the channel currents of the NOCC-Rbased OECT sensor barely changed until the concentrations of DA and UA were higher than 1 × 10 − 6 M 1 × 10 − 6 M 1xx10^(-6)M1 \times 10^{-6} \mathrm{M} (Figure S10a,b, Supporting Information). Using the changes of the response currents with the addition of AA, the calculated variation of the effective gate voltage ( Δ V G eff Δ V G eff  DeltaV_(G)^("eff ")\Delta V_{\mathrm{G}}{ }^{\text {eff }} ) was fitted to the logarithmic AA
随后在栅极电位为 0 V 时记录了基于 NOCC-R 的 OECT 传感器在向 PBS 溶液中连续注入 AA 时的实时通道电流（ I DS I DS I_(DS)I_{\mathrm{DS}} ）。如图 4c 所示，当 AA 浓度高于 10 × 10 − 9 m 10 × 10 − 9 m 10 xx10^(-9)m10 \times 10^{-9} \mathrm{~m} 时，基于 NOCC-R 的 OECT 会产生快速而显著的电流响应，这远低于 NOCC-R 在三电极系统和最近报道的 AA 传感器中的 LOD（表 S3，佐证资料）。相比之下，基于 NOCC-R 的 OECT 传感器的通道电流几乎没有变化，直到 DA 和 UA 的浓度高于 1 × 10 − 6 M 1 × 10 − 6 M 1xx10^(-6)M1 \times 10^{-6} \mathrm{M} （图 S10a、b，佐证资料）。利用响应电流随添加 AA 而发生的变化，计算出的有效栅极电压变化（ Δ V G eff Δ V G eff  DeltaV_(G)^("eff ")\Delta V_{\mathrm{G}}{ }^{\text {eff }} ）与对数 AA
Figure 4. The structure, working mechanism, and sensing performance of the organic electrochemical transistors (OECT) with NOCC-R or NOCC-O as the gate electrodes. a) Schematic illustration of the flexible OECTs. b) The potential drops between the gate and channel of the OECT before (blue solid line) and after (red dash line) the addition of analytes (DA or AA) to the PBS solution ( 0.1 m , pH = 7.4 0.1 m , pH = 7.4 0.1m,pH=7.40.1 \mathrm{~m}, \mathrm{pH}=7.4 ). c) Channel current responses and d) the corresponding effective gate voltage changes of the NOCC-R-based OECT toward the addition of AA with different concentrations at a gate potential of 0 V . e) Channel current responses and f) the corresponding effective gate voltage changes of the NOCC-O-based OECT with the addition of DA at different concentrations at a gate potential of 0.15 V . g) Transfer characteristics of the flexible OECT with NOCC-R as the gate electrode in PBS solution with different bending status. Inset: photographs of the flexible OECT bent to both sides with the bending angle of 90 ∘ 90 ∘ 90^(@)90^{\circ}. h) Transfer characteristics of the flexible OECT in PBS solution after bending to both sides with a bending angle of 90 ∘ 90 ∘ 90^(@)90^{\circ}, for 0 , 100 , 300 0 , 100 , 300 0,100,3000,100,300, and 500 repetitions.
图 4.以 NOCC-R 或 NOCC-O 为栅电极的有机电化学晶体管 (OECT) 的结构、工作机制和传感性能。c) 基于 NOCC-R 的 OECT 在栅极电位为 0 V 时对添加不同浓度 AA 的通道电流响应和 d) 相应的有效栅极电压变化。 e) 基于 NOCC-O 的 OECT 在栅极电位为 0.15 V 时对添加不同浓度 DA 的通道电流响应和 f) 相应的有效栅极电压变化。 g) 以 NOCC-R 为栅极的柔性 OECT 在不同弯曲状态的 PBS 溶液中的转移特性。插图：以 90 ∘ 90 ∘ 90^(@)90^{\circ} 的弯曲角度向两侧弯曲的柔性 OECT 的照片。 h) 以 90 ∘ 90 ∘ 90^(@)90^{\circ} 的弯曲角度向两侧弯曲后的柔性 OECT 在 PBS 溶液中的转移特性，为 0 , 100 , 300 0 , 100 , 300 0,100,3000,100,300 和 500 次重复。
concentrations of 5 × 10 − 6 M 5 × 10 − 6 M 5xx10^(-6)M5 \times 10^{-6} \mathrm{M} to 1 × 10 − 3 m 1 × 10 − 3 m 1xx10^(-3)m1 \times 10^{-3} \mathrm{~m}, with a high slope value of 240 mV decade − 1 − 1 ^(-1){ }^{-1} (Figure 4d). In contrast, the slope values of the fitting curves for DA and UA were only 100 and 44 mV decade − 1 − 1 ^(-1){ }^{-1} for concentrations ranging from 1 × 10 − 6 1 × 10 − 6 1xx10^(-6)1 \times 10^{-6} to 300 × 10 − 6 m 300 × 10 − 6 m 300 xx10^(-6)m300 \times 10^{-6} \mathrm{~m} (Figure S10c, Supporting Information), clearly indicating that the NOCC-R-based OECT sensor possessed a higher selectivity toward AA than toward DA and UA. On the other hand, the OECT with NOCC-O as the gate electrode had an impressive DA detection capability. According to the amperometric response currents of the OECT, the fitting curve had a high slope value of 151 mV decade − 1 − 1 ^(-1){ }^{-1} for DA concentrations ranging from 1 × 10 − 6 1 × 10 − 6 1xx10^(-6)1 \times 10^{-6} to 300 × 10 − 6 m 300 × 10 − 6 m 300 xx10^(-6)m300 \times 10^{-6} \mathrm{~m} (Figure 4e), which were much higher than the responses to AA and UA (Figure S10d-f, Supporting Information). Moreover, the OECT delivered a response even when the concentration of DA was 1 × 10 − 9 M 1 × 10 − 9 M 1xx10^(-9)M1 \times 10^{-9} \mathrm{M} (inset of Figure 4e), and this high sensitivity was attributable to the transistor configuration of the sensor. [ 28 , 29 ] [ 28 , 29 ] ^([28,29]){ }^{[28,29]} Considering the concentrations of AA and DA in human urine, the detection limit and sensitivity of the OECT sensors in our work is expected to be able to meet the sensing requirements of A A A A AAA A and DA in practical samples. Note that the existence of nonzero gate currents during the sensing process would cause an overpotential ( η ) ( η ) (eta)(\eta) on the gate electrode of the OECT sensors. [ 10 a ] [ 10 a ] ^([10a]){ }^{[10 \mathrm{a}]} To investigate the influence of the overpotential on the NOCCbased OECT sensors, the plots of the initial polarized current density against the potential obtained from a series of potential step measurements were calculated (Figure S11, Supporting Information). The results indicated that the values of η η eta\eta for the NOCC-R- and the NOCC-O-based OECTs were ≈ 5 ≈ 5 ~~5\approx 5 and 2 mV with the addition of AA ( 1 × 10 − 3 m ) AA 1 × 10 − 3 m AA(1xx10^(-3)(m))\mathrm{AA}\left(1 \times 10^{-3} \mathrm{~m}\right) and DA ( 0.3 × 10 − 3 M ) DA 0.3 × 10 − 3 M DA(0.3 xx10^(-3)M)\mathrm{DA}\left(0.3 \times 10^{-3} \mathrm{M}\right), respectively. Compared with the change in the effective gate voltage ( ≈ 200 mV ≈ 200 mV ~~200mV\approx 200 \mathrm{mV} ) of the OECT sensors, the overpotentials of the gate electrodes were too weak, and their influence on the detection results was negligible (Supporting Information).
浓度为 5 × 10 − 6 M 5 × 10 − 6 M 5xx10^(-6)M5 \times 10^{-6} \mathrm{M} 至 1 × 10 − 3 m 1 × 10 − 3 m 1xx10^(-3)m1 \times 10^{-3} \mathrm{~m} 时，斜率值高达 240 mV 十年 − 1 − 1 ^(-1){ }^{-1} （图 4d）。相比之下，在 1 × 10 − 6 1 × 10 − 6 1xx10^(-6)1 \times 10^{-6} 至 300 × 10 − 6 m 300 × 10 − 6 m 300 xx10^(-6)m300 \times 10^{-6} \mathrm{~m} 浓度范围内，DA 和 UA 的拟合曲线斜率值分别只有 100 和 44 mV 十年 − 1 − 1 ^(-1){ }^{-1} （图 S10c，佐证资料），这清楚地表明基于 NOCC-R 的 OECT 传感器对 AA 的选择性高于对 DA 和 UA 的选择性。另一方面，以 NOCC-O 为栅电极的 OECT 对 DA 的检测能力令人印象深刻。根据 OECT 的安培响应电流，当 DA 浓度从 1 × 10 − 6 1 × 10 − 6 1xx10^(-6)1 \times 10^{-6} 到 300 × 10 − 6 m 300 × 10 − 6 m 300 xx10^(-6)m300 \times 10^{-6} \mathrm{~m} 时，拟合曲线的斜率值高达 151 mV 十年 − 1 − 1 ^(-1){ }^{-1} （图 4e），远高于对 AA 和 UA 的响应（图 S10d-f，佐证资料）。此外，即使当 DA 的浓度为 1 × 10 − 9 M 1 × 10 − 9 M 1xx10^(-9)M1 \times 10^{-9} \mathrm{M} 时，OECT 也能产生响应（图 4e 插图），这种高灵敏度归功于传感器的晶体管配置。 [ 28 , 29 ] [ 28 , 29 ] ^([28,29]){ }^{[28,29]} 考虑到人体尿液中 AA 和 DA 的浓度，我们工作中的 OECT 传感器的检测限和灵敏度有望满足实际样品中 A A A A AAA A 和 DA 的检测要求。需要注意的是，在传感过程中，非零栅电流的存在会导致 OECT 传感器的栅电极上出现过电位 ( η ) ( η ) (eta)(\eta) 。 [ 10 a ] [ 10 a ] ^([10a]){ }^{[10 \mathrm{a}]} 为了研究过电位对基于 NOCC 的 OECT 传感器的影响，我们计算了一系列电位阶跃测量得到的初始极化电流密度与电位的关系图（图 S11，佐证资料）。 结果表明，加入 AA ( 1 × 10 − 3 m ) AA 1 × 10 − 3 m AA(1xx10^(-3)(m))\mathrm{AA}\left(1 \times 10^{-3} \mathrm{~m}\right) 和 DA ( 0.3 × 10 − 3 M ) DA 0.3 × 10 − 3 M DA(0.3 xx10^(-3)M)\mathrm{DA}\left(0.3 \times 10^{-3} \mathrm{M}\right) 后，基于 NOCC-R 和 NOCC-O 的 OECT 的 η η eta\eta 值分别为 ≈ 5 ≈ 5 ~~5\approx 5 和 2 mV。与 OECT 传感器有效栅极电压（ ≈ 200 mV ≈ 200 mV ~~200mV\approx 200 \mathrm{mV} ）的变化相比，栅极电极的过电位太弱，对检测结果的影响可以忽略不计（佐证资料）。
The good mechanical stability of the NOCC electrodes (Figure S1, Supporting Information) enabled the OECT sensors to reserve their excellent sensing capability at bending states. As shown by their transfer characteristics (Figure 4g,h), the OECTs showed stable sensing performance after 500 repetitions of the bending test. Moreover, the response of I DS I DS I_(DS)I_{\mathrm{DS}} at the bending state (Figure S12, Supporting Information) confirmed that the NOCC-based OECT sensors retained their high sensitivity toward AA (226 mV decade − 1 − 1 ^(-1){ }^{-1} ) and DA ( 193 mV decade − 1 − 1 ^(-1){ }^{-1} ). The OECTs also showed their practicality and reliability in the present study of the determination of AA and DA in artificial urine. As listed in Table S4 (Supporting Information), the relative standard deviations (RSD) were less than 12.1 % 12.1 % 12.1%12.1 \% for AA and 9.8 % 9.8 % 9.8%9.8 \% for DA, resulting from the good recoveries of AA (88.2-112.3%) and DA (88.0-107.3%), which were comparable to those of the recently reported AA and DA sensors (Tables S1-S3, Supporting Information). [ 6 a , 30 ] [ 6 a , 30 ] ^([6a,30]){ }^{[6 a, 30]} Additionally, the reproducibility of the OECT sensors was determined by the comparison of five individual sensors fabricated using the same procedures. To verify the long-term stability of the NOCC electrode, the NOCC-R and NOCC-O electrodes in the fourth and fifth sensors were not freshly prepared but stored in air at room temperature for more than six months. As shown in Figure S13 (Supporting Information), the resulting RSD values of the NCRs from the OECT sensors with the NOCC-R
NOCC 电极良好的机械稳定性（图 S1，佐证资料）使 OECT 传感器在弯曲状态下仍能保持出色的传感能力。如其传递特性（图 4g、h）所示，OECT 传感器在重复 500 次弯曲测试后显示出稳定的传感性能。此外，弯曲状态下 I DS I DS I_(DS)I_{\mathrm{DS}} 的响应（图 S12，佐证资料）证实，基于 NOCC 的 OECT 传感器保持了对 AA（226 mV 十年 − 1 − 1 ^(-1){ }^{-1} ）和 DA（193 mV 十年 − 1 − 1 ^(-1){ }^{-1} ）的高灵敏度。在目前测定人工尿液中 AA 和 DA 的研究中，OECTs 也显示了其实用性和可靠性。如表 S4（佐证信息）所示，AA 和 DA 的相对标准偏差（RSD）分别小于 12.1 % 12.1 % 12.1%12.1 \% 和 9.8 % 9.8 % 9.8%9.8 \% ，这是因为 AA（88.2-112.3%）和 DA（88.0-107.3%）的回收率较高，与最近报道的 AA 和 DA 传感器的回收率相当（表 S1-S3，佐证信息）。 [ 6 a , 30 ] [ 6 a , 30 ] ^([6a,30]){ }^{[6 a, 30]} 此外，OECT 传感器的可重复性是通过比较使用相同程序制造的五个传感器来确定的。为了验证 NOCC 电极的长期稳定性，第四和第五个传感器中的 NOCC-R 和 NOCC-O 电极不是新制备的，而是在室温空气中存放了 6 个多月。如图 S13（佐证资料）所示，使用 NOCC-R 和 NOCC-O 电极的 OECT 传感器的 NCR 的 RSD 值与 NOCC-R 和 NOCC-O 电极的 NCR 的 RSD 值相差无几。
and NOCC-O electrodes were 10.85 % 10.85 % 10.85%10.85 \% and 6.31 % 6.31 % 6.31%6.31 \%, respectively. The repeatability of the OECT sensors was evaluated with the addition of AA or DA from five independent solutions, and the RSDs of the NOCC-R- and NOCC-O-based OECTs maintained low values of 3.76 % 3.76 % 3.76%3.76 \% and 5.07 % 5.07 % 5.07%5.07 \%, respectively (Figure S13, Supporting Information). Moreover, the fabricated OECT sensors with the NOCC-R and NOCC-O electrodes retained 87.5 % 87.5 % 87.5%87.5 \% and 84.9 % 84.9 % 84.9%84.9 \% of the initial response after storage in air at room temperature for 14 days, indicating the good stability of the NOCCbased OECT sensors.
分别为 10.85 % 10.85 % 10.85%10.85 \% 和 6.31 % 6.31 % 6.31%6.31 \% 。在从五种独立溶液中添加 AA 或 DA 的情况下评估了 OECT 传感器的重复性，基于 NOCC-R 和 NOCC-O 的 OECT 的 RSD 分别保持在 3.76 % 3.76 % 3.76%3.76 \% 和 5.07 % 5.07 % 5.07%5.07 \% 的较低值（图 S13，佐证资料）。此外，用 NOCC-R 和 NOCC-O 电极制造的 OECT 传感器在室温空气中存放 14 天后，仍能保持 87.5 % 87.5 % 87.5%87.5 \% 和 84.9 % 84.9 % 84.9%84.9 \% 的初始响应，这表明基于 NOCC 的 OECT 传感器具有良好的稳定性。
Since the distinguishing feature of the OECT sensors in this work was the gate electrode, their sensing selectivity was expected to be closely related to the detection capability of the NOCC electrodes. To further elucidate the differences in the NOCC electrodes, their electroactive surface areas (ECSAs) were calculated according to the anodic peak currents of their CV curves (Figure S14, Supporting Information) obtained from the three-electrode system at a scan rate of 50 mV s − 1 50 mV s − 1 50mVs^(-1)50 \mathrm{mV} \mathrm{s}^{-1} using [ Fe ( CN ) 6 ] 3 − / 4 − ( 1 × 10 − 3 m ) Fe ( CN ) 6 3 − / 4 − 1 × 10 − 3 m [Fe(CN)_(6)]^(3-//4-)(1xx10^(-3)(m))\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-/ 4-}\left(1 \times 10^{-3} \mathrm{~m}\right) as the redox probe in KCl solution ( 0.1 m ). The NOCC-O had a higher electroactive surface area ( 7.944 cm 2 7.944 cm 2 7.944cm^(2)7.944 \mathrm{~cm}^{2} ) than those of NOCC-I ( 6.961 cm 2 ) 6.961 cm 2 (6.961cm^(2))\left(6.961 \mathrm{~cm}^{2}\right) and NOCC-R ( 6.270 cm 2 ) 6.270 cm 2 (6.270cm^(2))\left(6.270 \mathrm{~cm}^{2}\right), indicating the existence of more active adsorption sites for the analyte molecules in NOCC-O (Table S5, Supporting Information). [ 30 , 31 ] [ 30 , 31 ] ^([30,31]){ }^{[30,31]} The heterogeneous electron transfer (HET) rates were also investigated using the potential separation between the anodic and cathodic peaks ( Δ E p Δ E p DeltaE_(p)\Delta E_{\mathrm{p}} ) in their CV curves (Figure S14, Supporting Information), which provided a preliminary representation of the efficiency of electron transfer ( K 0 ) K 0 (K^(0))\left(K^{0}\right) between the target analyte and electrode surface. NOCC-O exhibited a smaller Δ E p ( ≈ 80 mV ) Δ E p ( ≈ 80 mV ) DeltaE_(p)(~~80mV)\Delta E_{\mathrm{p}}(\approx 80 \mathrm{mV}) than those of the other two electrodes, corresponding to good electron transfer ability with a K 0 K 0 K^(0)K^{0} value ( 8.26 × 10 − 3 cm s − 1 ) 8.26 × 10 − 3 cm s − 1 (8.26 xx10^(-3)(cm)s^(-1))\left(8.26 \times 10^{-3} \mathrm{~cm} \mathrm{~s}^{-1}\right) that was higher than those of NOCC-I ( 6.52 × 10 − 3 cm s − 1 ) 6.52 × 10 − 3 cm s − 1 (6.52 xx10^(-3)(cm)s^(-1))\left(6.52 \times 10^{-3} \mathrm{~cm} \mathrm{~s}^{-1}\right) and NOCC-R ( 3.10 × 10 − 3 cm s − 1 ) 3.10 × 10 − 3 cm s − 1 (3.10 xx10^(-3)(cm)s^(-1))\left(3.10 \times 10^{-3} \mathrm{~cm} \mathrm{~s}^{-1}\right). According to their CV curves at different scan rates (Figure S15, Supporting Information), all the NOCC electrodes exhibited a linear relationship between the redox peak currents ( I pa I pa I_(pa)I_{\mathrm{pa}} and I pc I pc I_(pc)I_{\mathrm{pc}} ) and the square root of the scan rates, revealing that a diffusioncontrolled electron transfer process occurred. [ 12 b ] [ 12 b ] ^([12 b]){ }^{[12 b]} To obtain a more in-depth understanding of the electrochemical kinetics occurring at the interface of electrode/electrolyte, electrochemical impedance spectra (EIS) measurements were also used to investigate the electron transfer resistance ( R ct R ct R_(ct)R_{\mathrm{ct}} ) according to the semicircles in the high-frequency range of the Nyquist curves (Figure S16, Supporting Information). The smaller diameter of NOCC-O demonstrated a lower R ct R ct R_(ct)R_{\mathrm{ct}} value of 26 Ω 26 Ω 26 Omega26 \Omega than those of NOCC-I ( 36 Ω ) ( 36 Ω ) (36 Omega)(36 \Omega) and NOCC-R ( 58 Ω ) ( 58 Ω ) (58 Omega)(58 \Omega), which could be attributed to its large electroactive surface area and high electron transfer rate.
由于本研究中 OECT 传感器的显著特征是栅电极，因此预计其传感选择性与 NOCC 电极的检测能力密切相关。为了进一步阐明 NOCC 电极的差异，我们根据三电极系统在 KCl 溶液（0.1 m）中使用 [ Fe ( CN ) 6 ] 3 − / 4 − ( 1 × 10 − 3 m ) Fe ( CN ) 6 3 − / 4 − 1 × 10 − 3 m [Fe(CN)_(6)]^(3-//4-)(1xx10^(-3)(m))\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-/ 4-}\left(1 \times 10^{-3} \mathrm{~m}\right) 作为氧化还原探针，以 50 mV s − 1 50 mV s − 1 50mVs^(-1)50 \mathrm{mV} \mathrm{s}^{-1} 的扫描速率计算出的 CV 曲线阳极峰电流（图 S14，佐证资料），计算出了它们的电活性表面积（ECSA）。与 NOCC-I ( 6.961 cm 2 ) 6.961 cm 2 (6.961cm^(2))\left(6.961 \mathrm{~cm}^{2}\right) 和 NOCC-R ( 6.270 cm 2 ) 6.270 cm 2 (6.270cm^(2))\left(6.270 \mathrm{~cm}^{2}\right) 相比，NOCC-O 具有更高的电活性表面积（ 7.944 cm 2 7.944 cm 2 7.944cm^(2)7.944 \mathrm{~cm}^{2} ），这表明 NOCC-O 中存在更多的分析分子活性吸附位点（表 S5，佐证信息）。 [ 30 , 31 ] [ 30 , 31 ] ^([30,31]){ }^{[30,31]} 还利用它们的 CV 曲线中阳极峰和阴极峰之间的电位差（ Δ E p Δ E p DeltaE_(p)\Delta E_{\mathrm{p}} ）研究了异质电子转移（HET）率（图 S14，《证明资料》），这初步反映了目标分析物和电极表面之间的电子转移效率 ( K 0 ) K 0 (K^(0))\left(K^{0}\right) 。NOCC-O 的 Δ E p ( ≈ 80 mV ) Δ E p ( ≈ 80 mV ) DeltaE_(p)(~~80mV)\Delta E_{\mathrm{p}}(\approx 80 \mathrm{mV}) 值小于其他两个电极的 K 0 K 0 K^(0)K^{0} 值 ( 8.26 × 10 − 3 cm s − 1 ) 8.26 × 10 − 3 cm s − 1 (8.26 xx10^(-3)(cm)s^(-1))\left(8.26 \times 10^{-3} \mathrm{~cm} \mathrm{~s}^{-1}\right) ，高于 NOCC-I 的 ( 6.52 × 10 − 3 cm s − 1 ) 6.52 × 10 − 3 cm s − 1 (6.52 xx10^(-3)(cm)s^(-1))\left(6.52 \times 10^{-3} \mathrm{~cm} \mathrm{~s}^{-1}\right) 值和 NOCC-R 的 ( 3.10 × 10 − 3 cm s − 1 ) 3.10 × 10 − 3 cm s − 1 (3.10 xx10^(-3)(cm)s^(-1))\left(3.10 \times 10^{-3} \mathrm{~cm} \mathrm{~s}^{-1}\right) 值，表明其具有良好的电子转移能力。根据它们在不同扫描速率下的 CV 曲线（图 S15，佐证资料），所有 NOCC 电极的氧化还原峰电流（ I pa I pa I_(pa)I_{\mathrm{pa}} 和 I pc I pc I_(pc)I_{\mathrm{pc}} ）与扫描速率的平方根之间呈线性关系，这表明发生了扩散控制的电子转移过程。 [ 12 b ] [ 12 b ] ^([12 b]){ }^{[12 b]} 为了更深入地了解电极/电解质界面上发生的电化学动力学，我们还使用电化学阻抗谱（EIS）测量方法，根据奈奎斯特曲线高频范围内的半圆来研究电子转移电阻（ R ct R ct R_(ct)R_{\mathrm{ct}} ）（图 S16，佐证资料）。与 NOCC-I ( 36 Ω ) ( 36 Ω ) (36 Omega)(36 \Omega) 和 NOCC-R ( 58 Ω ) ( 58 Ω ) (58 Omega)(58 \Omega) 相比，直径较小的 NOCC-O 的 R ct R ct R_(ct)R_{\mathrm{ct}} 26 Ω 26 Ω 26 Omega26 \Omega 值较低，这可能归因于其较大的电活性表面积和较高的电子转移率。
Because all the NOCC electrodes were derived from the same PANI/CC composites, their different electrochemical behaviors should be due to the different amounts and species of the heteroatoms on their surfaces. Thus, X-ray photoelectron spectroscopy (XPS) was utilized to further scrutinize the surface compositions of these samples. As displayed in Figure 5a, the XPS spectra of the NOCC electrodes had three distinct peaks at ≈ 284 , 400 ≈ 284 , 400 ~~284,400\approx 284,400, and 531 eV , which were the characteristic signals from C , N C , N C,N\mathrm{C}, \mathrm{N}, and O atoms, confirming the doping of both N and O atoms on their surface. [ 32 ] [ 32 ] ^([32]){ }^{[32]} The atomic ratios of the three elements in the NOCC electrodes are summarized
由于所有 NOCC 电极都来自相同的 PANI/CC 复合材料，它们的不同电化学行为应该是由于其表面杂原子的数量和种类不同造成的。因此，我们利用 X 射线光电子能谱（XPS）进一步研究了这些样品的表面成分。如图 5a 所示，NOCC 电极的 XPS 光谱在 ≈ 284 , 400 ≈ 284 , 400 ~~284,400\approx 284,400 和 531 eV 处有三个明显的峰，分别是 C , N C , N C,N\mathrm{C}, \mathrm{N} 和 O 原子的特征信号，这证实了它们的表面都掺杂了 N 原子和 O 原子。 [ 32 ] [ 32 ] ^([32]){ }^{[32]} 三种元素在 NOCC 电极中的原子比总结如下
Figure 5. Surface compositions and theoretical simulations of the NOCC electrodes. a) XPS spectra of the PANI-CC and the NOCC electrodes. The interaction and charge transfer characteristics between adsorbed molecules (AA and DA) and N/O-doped graphene. b) The PDOS of the isolated AA molecule and adsorption on NG-5, NG-6, and OG-I. c) The PDOS of the isolated DA molecule and adsorption on NG-5, NG-6, and OG-I. The dotted line represents the Fermi energy, which is assigned a value of zero. Electron density differences of AA absorbed on the d) NG-5, e) NG-6, and f) OG-I. Electron density differences for DA absorbed on the g) NG-5, h) NG-6, and i) OG-I. The red and green areas represent the charge accumulation and charge depletion, respectively. The isosurfaces are 0.0015 electron bohr 3 3 ^(3){ }^{3}. The gray, white, blue, and red balls represent carbon, hydrogen, nitrogen, and oxygen atoms, respectively.
图 5.a) PANI-CC 和 NOCC 电极的 XPS 光谱。b) 分离的 AA 分子的 PDOS 以及在 NG-5、NG-6 和 OG-I 上的吸附。虚线代表费米能，其值为零。吸附在 d) NG-5、e) NG-6 和 f) OG-I 上的 AA 的电子密度差。g) NG-5、h) NG-6 和 i) OG-I 上吸收的 DA 的电子密度差。红色和绿色区域分别代表电荷积累和电荷耗尽。等值面为 0.0015 电子波 3 3 ^(3){ }^{3} 。灰球、白球、蓝球和红球分别代表碳原子、氢原子、氮原子和氧原子。
in Figure S17 (Supporting Information). Among the samples, NOCC-O had the smallest number of N atoms (5.9%) but the highest number of O atoms ( 15.2 % 15.2 % 15.2%15.2 \% ), which was due to the thermal treatment in an oxidative atmosphere. Derived from inert and reductive atmospheres, NOCC-I and NOCC-R had similar contents of N atoms ( 7.7 % 7.7 % 7.7%7.7 \% and 7.9 % 7.9 % 7.9%7.9 \% ), while the content of O atoms in NOCC-R (9.9%) was lower than that of NOCC-I (12.0%). The high-resolution N1s and O1s spectra were further deconvoluted into several subpeaks corresponding to the different types of the atoms (Figure S18, Supporting Information). As summarized in Table S6 (Supporting Information), the N atoms on the surface of the NOCC electrodes included oxidized N ( N − O ) N ( N − O ) N(N-O)\mathrm{N}(\mathrm{N}-\mathrm{O}), graphitic N ( N − Q ) N ( N − Q ) N(N-Q)\mathrm{N}(\mathrm{N}-\mathrm{Q}), pyrrolic N ( N − 5 ) N ( N − 5 ) N(N-5)\mathrm{N}(\mathrm{N}-5), and pyridinic N ( N − 6 ) N ( N − 6 ) N(N-6)\mathrm{N}(\mathrm{N}-6), while the O atoms corresponded to quinone O ( O − I ) O ( O − I ) O(O-I)\mathrm{O}(\mathrm{O}-\mathrm{I}), ether-type O (O-II), and carboxylic O (O-III). The dominating types among the species were N-5, N-6, O-I, and O-II atoms.
见图 S17（佐证资料）。在这些样品中，NOCC-O 的 N 原子数量最少（5.9%），但 O 原子数量最多（ 15.2 % 15.2 % 15.2%15.2 \% ），这是由于在氧化气氛中进行了热处理。从惰性气氛和还原气氛中提取的 NOCC-I 和 NOCC-R 的 N 原子含量（ 7.7 % 7.7 % 7.7%7.7 \% 和 7.9 % 7.9 % 7.9%7.9 \% ）相似，而 NOCC-R 的 O 原子含量（9.9%）低于 NOCC-I（12.0%）。高分辨率的 N1s 和 O1s 光谱被进一步分解成与不同原子类型相对应的几个子峰（图 S18，佐证资料）。如表 S6（佐证资料）所总结的，NOCC 电极表面的 N 原子包括氧化型 N ( N − O ) N ( N − O ) N(N-O)\mathrm{N}(\mathrm{N}-\mathrm{O}) 、石墨型 N ( N − Q ) N ( N − Q ) N(N-Q)\mathrm{N}(\mathrm{N}-\mathrm{Q}) 、吡咯型 N ( N − 5 ) N ( N − 5 ) N(N-5)\mathrm{N}(\mathrm{N}-5) 和吡啶型 N ( N − 6 ) N ( N − 6 ) N(N-6)\mathrm{N}(\mathrm{N}-6) ，而 O 原子则对应于醌型 O ( O − I ) O ( O − I ) O(O-I)\mathrm{O}(\mathrm{O}-\mathrm{I}) 、醚型 O（O-II）和羧基 O（O-III）。各物种的主要原子类型为 N-5、N-6、O-I 和 O-II。
To correlate the effects of the different heteroatoms on the sensing behavior of the NOCC electrodes, the adsorption energy ( E ads E ads E_(ads)E_{\mathrm{ads}} ) of the analyte on the N/O-doped carbon substrates was obtained from a first-principles calculation based on density functional theory (DFT). To ensure the feasibility and effectiveness of the calculation, pristine graphene was assigned as the basic carbon substrate, and N-doped (pyrrolic NG-5
为了将不同杂原子对 NOCC 电极传感行为的影响联系起来，我们根据密度泛函理论（DFT）进行了第一性原理计算，得到了分析物在 N/O 掺杂碳基底上的吸附能（ E ads E ads E_(ads)E_{\mathrm{ads}} ）。为确保计算的可行性和有效性，原始石墨烯被指定为基本碳基底，而掺杂 N（吡咯烷 NG-5
and pyridinic NG-6) and O-doped (quinone OG-I and ethertype OG-II) graphene were chosen as the heteroatom-doped carbon substrates according to the XPS results (Table S6, Supporting Information). According to the calculation results for E ads E ads  E_("ads ")E_{\text {ads }} after geometry optimization (Table S7, Supporting Information), AA could thermodynamically adsorb on the various N/O-doped substrates because all the E ads E ads  E_("ads ")E_{\text {ads }} had negative values in the stable adsorption system. Notably, the E ads E ads  E_("ads ")E_{\text {ads }} values for NG-6 ( − 0.91 eV ) − 0.91 eV ) -0.91eV)-0.91 \mathrm{eV}) and OG-I ( − 0.92 eV ) ( − 0.92 eV ) (-0.92eV)(-0.92 \mathrm{eV}) were higher than that of graphene ( − 0.97 eV ) ( − 0.97 eV ) (-0.97eV)(-0.97 \mathrm{eV}), suggesting that the adsorption of AA on NG-6 or OG-I was less energetically favorable than graphene (Figure S19a, Supporting Information). [ 33 ] [ 33 ] ^([33]){ }^{[33]} In contrast, NG-5 had an E ads E ads  E_("ads ")E_{\text {ads }} of -1.06 eV , lower than that of graphene, which would make it a better substrate for the deposition of AA. Additionally, from the electronic partial density of state (PDOS) of the active group ( -OH ) of AA in different adsorption systems (orange parts in Figure 5b and Figure S20a, Supporting Information), the orbital mixing of AA was far from the Fermi level (dotted line), which therefore had no significant effect on AA. The energy level in the NG-6 system shifted to more negative values, and the OG-I system had weaker PDOS peaks, indicating weaker electronic interactions between AA and these substrates, which was consistent with the analysis of the
根据 XPS 结果（表 S6，佐证资料），我们选择了掺杂 N/O、掺杂 NG-6 和掺杂吡啶 NG-6 以及掺杂 O（醌型 OG-I 和醚型 OG-II）的石墨烯作为杂原子掺杂的碳基底。）根据几何优化后的 E ads E ads  E_("ads ")E_{\text {ads }} 计算结果（表 S7，佐证资料），AA 可以在各种 N/O 掺杂基底上进行热力学吸附，因为在稳定的吸附体系中，所有 E ads E ads  E_("ads ")E_{\text {ads }} 都是负值。值得注意的是，NG-6 ( − 0.91 eV ) − 0.91 eV ) -0.91eV)-0.91 \mathrm{eV}) 和 OG-I ( − 0.92 eV ) ( − 0.92 eV ) (-0.92eV)(-0.92 \mathrm{eV}) 的 E ads E ads  E_("ads ")E_{\text {ads }} 值高于石墨烯 ( − 0.97 eV ) ( − 0.97 eV ) (-0.97eV)(-0.97 \mathrm{eV}) ，这表明 AA 在 NG-6 或 OG-I 上的吸附在能量上不如石墨烯有利（图 S19a，佐证资料）。 [ 33 ] [ 33 ] ^([33]){ }^{[33]} 相反，NG-5 的 E ads E ads  E_("ads ")E_{\text {ads }} 值为 -1.06 eV，低于石墨烯的 E ads E ads  E_("ads ")E_{\text {ads }} 值，这将使其成为 AA 沉积的更好基底。此外，从不同吸附体系中 AA 的活性基团（-OH）的电子部分状态密度（PDOS）（图 5b 和图 S20a 中的橙色部分，佐证资料）来看，AA 的轨道混合远离费米级（虚线），因此对 AA 没有显著影响。NG-6 系统的能级向更负的值移动，而 OG-I 系统的 PDOS 峰较弱，这表明 AA 与这些基质之间的电子相互作用较弱，这与图 5b 和图 S20a 的分析一致。
adsorption energies. The electron density of AA in various systems (Figure 5d-f and Figure S21a-d) suggested that the area of -OH in AA had less charge depletion in the NG-6 and OG-I systems, which therefore had lower catalytic activity toward AA. [ 34 ] [ 34 ] ^([34]){ }^{[34]} Based on the theoretical simulations results, N-6 and O-I were unfavorable for the adsorption of AA on the substrates, while N-5 enhanced the adsorption capability of the carbon substrates. Therefore, the reduced amount of O-I and higher content of N-5 in NOCC-R benefited its AA detection behavior.
吸附能。不同体系中AA的电子密度（图5d-f和图S21a-d）表明，在NG-6和OG-I体系中，AA中的-OH区域电荷耗竭较少，因此对AA的催化活性较低。 [ 34 ] [ 34 ] ^([34]){ }^{[34]} 根据理论模拟结果，N-6 和 O-I 不利于 AA 在基质上的吸附，而 N-5 则增强了碳基质的吸附能力。因此，减少 NOCC-R 中 O-I 的含量和提高 N-5 的含量有利于其 AA 检测行为。
Similarly, the interactions between DA and various substrates were also calculated in this work. The results in Table S7 (Supporting Information) indicate that the adsorption of DA on N-doped graphene had lower E ads E ads  E_("ads ")E_{\text {ads }} values than those of pristine or O-doped graphene, suggesting favorable adsorption and stronger interactions between DA and N -doped graphene (Figure S19b, Supporting Information). From the PDOS of the active group ( -OH ) of DA (Figure 5c), the N -doped graphene produced larger upshifts for DA to energetic levels close to the Fermi level, indicating the strong hybridization between DA and the N-doped substrates. [ 33 b , 35 ] [ 33 b , 35 ] ^([33 b,35]){ }^{[33 b, 35]} For the charge density of DA in different adsorption systems, there was a small amount of charge transfer in both OG-I and pristine graphene, while more charge transfer was apparent on the surface of NG-5 and NG-6 (Figure 5g-i), suggesting stronger electronic interactions in the N -doped systems. Based on the above calculations, the N atoms on the surface of NOCC contributed more to the adsorption of DA than did the O atoms. However, the influence of various N atoms on the DA sensing behavior was very similar. Since the three NOCC electrodes had closed N contents, the best DA detection behavior of NOCC-O was mainly due to the larger electroactive surface areas and higher electron transfer capabilities. Considering the calculation results for AA, the higher selectivity of NOCC-O toward DA should be attributed to its possession of more O-I and N-6 atoms, which were not favorable for the adsorption and oxidation of AA on its surface.
同样，这项工作还计算了 DA 与各种基底之间的相互作用。表 S7（佐证资料）中的结果表明，DA 在 N 掺杂石墨烯上的吸附 E ads E ads  E_("ads ")E_{\text {ads }} 值低于原始石墨烯或 O 掺杂石墨烯，这表明 DA 与 N 掺杂石墨烯之间存在有利的吸附和更强的相互作用（图 S19b，佐证资料）。从DA的活性基团（-OH）的PDOS（图5c）来看，N-掺杂石墨烯产生了更大的上移，使DA的能级接近费米级，这表明DA与N-掺杂基底之间的杂化作用很强。 [ 33 b , 35 ] [ 33 b , 35 ] ^([33 b,35]){ }^{[33 b, 35]} 对于不同吸附体系中DA的电荷密度，OG-I和原始石墨烯中都有少量的电荷转移，而在NG-5和NG-6表面则有更多的电荷转移（图5g-i），这表明N掺杂体系中的电子相互作用更强。根据上述计算，NOCC 表面的 N 原子比 O 原子对 DA 吸附的贡献更大。不过，各种 N 原子对 DA 传感行为的影响非常相似。由于三种 NOCC 电极的 N 原子含量接近，NOCC-O 的 DA 检测性能最好，这主要归功于其较大的电活性表面积和较高的电子传递能力。考虑到 AA 的计算结果，NOCC-O 对 DA 具有更高的选择性应归因于它具有更多的 O-I 原子和 N-6 原子，这些原子不利于 AA 在其表面的吸附和氧化。

3. Conclusion 3.结论

To obtain flexible OECT sensors with both high sensitivity and high selectivity, N and O atom codoped NOCC gate electrodes were fabricated in this work via efficient carbonization of PANIwrapped carbon cloths. The surface engineering of the NOCC electrodes with the modification of the carbonization atmospheres allowed the adjustment of the amounts and types of N and O atoms on the surface of the electrodes, which was then used to tune the sensing behavior of the NOCC-based OECTs. Thus, flexible OECT sensors with excellent detection capabilities toward AA and DA were obtained by the selection of different NOCCs as the gate electrodes. More importantly, this work demonstrated that the heteroatoms on the surface of carbonaceous electrodes can effectively improve their sensitivity and selectivity, thus paving the way for the construction of highperformance OECT sensors.
为了获得兼具高灵敏度和高选择性的柔性 OECT 传感器，本研究通过对包裹 PANI 的碳布进行高效碳化，制造出了 N 原子和 O 原子共掺的 NOCC 栅电极。通过改变碳化气氛对 NOCC 电极进行表面工程处理，可以调整电极表面的 N 原子和 O 原子的数量和类型，从而调整基于 NOCC 的 OECT 的传感性能。因此，通过选择不同的 NOCC 作为栅电极，获得了对 AA 和 DA 具有出色检测能力的柔性 OECT 传感器。更重要的是，这项工作证明了碳质电极表面的杂原子能有效提高其灵敏度和选择性，从而为构建高性能的 OECT 传感器铺平了道路。

4. Experimental Section 4.实验部分

Reagents and Materials: Commercial CCs (model: WOS1009, density: ≈ 12 mg cm − 2 ≈ 12 mg cm − 2 ~~12mgcm^(-2)\approx 12 \mathrm{mg} \mathrm{cm}^{-2}, thickness: ≈ 0.33 mm ≈ 0.33 mm ~~0.33mm\approx 0.33 \mathrm{~mm} ) were manufactured by CeTech
试剂和材料：商用 CC（型号：WOS1009，密度： ≈ 12 mg cm − 2 ≈ 12 mg cm − 2 ~~12mgcm^(-2)\approx 12 \mathrm{mg} \mathrm{cm}^{-2} ，厚度： ≈ 0.33 mm ≈ 0.33 mm ~~0.33mm\approx 0.33 \mathrm{~mm} ）由 CeTech 公司生产。
Co., Ltd. Aniline, hydrochloric acid (HCl, 36.0 -38.0%), ammonium persulfate (APS), sodium dodecyl sulfate (SDS), sodium phosphate monobasic dihydrate ( NaH 2 PO 4 ⋅ 2 H 2 O ) NaH 2 PO 4 ⋅ 2 H 2 O (NaH_(2)PO_(4)*2H_(2)O)\left(\mathrm{NaH}_{2} \mathrm{PO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right), disodium phosphate dibasic dodecahydrate ( Na 2 HPO 4 ⋅ 12 H 2 O ) Na 2 HPO 4 ⋅ 12 H 2 O (Na_(2)HPO_(4)*12H_(2)O)\left(\mathrm{Na}_{2} \mathrm{HPO}_{4} \cdot 12 \mathrm{H}_{2} \mathrm{O}\right), potassium chloride ( KCl ), potassium hexacyanoferrate (II) trihydrate ( K 4 [ Fe ( CN ) 6 ] ⋅ 3 H 2 O ) K 4 Fe ( CN ) 6 ⋅ 3 H 2 O (K_(4)[Fe(CN)_(6)]*3H_(2)O)\left(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \cdot 3 \mathrm{H}_{2} \mathrm{O}\right), and potassium ferricyanide ( K 3 [ Fe ( CN ) 6 ] ) K 3 Fe ( CN ) 6 (K_(3)[Fe(CN)_(6)])\left(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\right) were all purchased from Sinopharm Chemical Reagent Co., Ltd. AA, DA, uric acid (UA), glucose (GC), and poly(3,4ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) were provided by Sigma-Aldrich Co. and stored under refrigerated conditions ( ≈ 4 ∘ C ≈ 4 ∘ C ~~4^(@)C\approx 4^{\circ} \mathrm{C} ). All the reagents were analytical grade and used as received without further treatment. Deionized water was used for the preparation of all the aqueous solutions in this work.
有限公司苯胺、盐酸（HCl，36.0 -38.0%）、过硫酸铵（APS）、十二烷基硫酸钠（SDS）、一水磷酸二氢钠 ( NaH 2 PO 4 ⋅ 2 H 2 O ) NaH 2 PO 4 ⋅ 2 H 2 O (NaH_(2)PO_(4)*2H_(2)O)\left(\mathrm{NaH}_{2} \mathrm{PO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right) 、十二水磷酸氢二钠 ( Na 2 HPO 4 ⋅ 12 H 2 O ) Na 2 HPO 4 ⋅ 12 H 2 O (Na_(2)HPO_(4)*12H_(2)O)\left(\mathrm{Na}_{2} \mathrm{HPO}_{4} \cdot 12 \mathrm{H}_{2} \mathrm{O}\right) 、氯化钾（KCl）、三水合六氰铁酸钾 ( K 4 [ Fe ( CN ) 6 ] ⋅ 3 H 2 O ) K 4 Fe ( CN ) 6 ⋅ 3 H 2 O (K_(4)[Fe(CN)_(6)]*3H_(2)O)\left(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \cdot 3 \mathrm{H}_{2} \mathrm{O}\right) 和铁氰化钾 ( K 3 [ Fe ( CN ) 6 ] ) K 3 Fe ( CN ) 6 (K_(3)[Fe(CN)_(6)])\left(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\right) 均购自国药集团化学试剂有限公司。,Ltd.购买。AA、DA、尿酸（UA）、葡萄糖（GC）和聚（3,4-亚乙二氧基噻吩）:聚（苯乙烯磺酸）（PEDOT:PSS）由 Sigma-Aldrich 公司提供，并冷藏保存（ ≈ 4 ∘ C ≈ 4 ∘ C ~~4^(@)C\approx 4^{\circ} \mathrm{C} ）。所有试剂均为分析级，按原样使用，无需进一步处理。本研究中所有水溶液的制备均使用去离子水。
Preparation of the NOCCs: First, the CC was cleaned by ultrasonication in alcohol, acetone, and distilled water to remove the protective greasy coating. Then, aniline ( 228 μ L 228 μ L 228 muL228 \mu \mathrm{~L} ) was dispersed in diluted HCl ( 1 M , 50 mL ( 1 M , 50 mL (1M,50mL(1 \mathrm{M}, 50 \mathrm{~mL} ) in the presence of SDS ( 7.6 mg ) by ultrasonication for 30 min . Subsequently, a piece of CC ( 1.5 cm × 3 cm ) 1.5 cm × 3 cm ) 1.5cmxx3cm)1.5 \mathrm{~cm} \times 3 \mathrm{~cm}) was immersed in the aniline solution, and the resulting mixture was cooled in an ice bath ( ≈ 0 − 5 ∘ C ) ≈ 0 − 5 ∘ C (~~0-5^(@)C)\left(\approx 0-5{ }^{\circ} \mathrm{C}\right) for another 30 min . Next, APS ( ≈ 380 mg ≈ 380 mg ~~380mg\approx 380 \mathrm{mg} ) dissolved in diluted HCl ( 1 m , 2 mL ) HCl ( 1 m , 2 mL ) HCl(1m,2mL)\mathrm{HCl}(1 \mathrm{~m}, 2 \mathrm{~mL}) was added slowly into the above solution to induce the polymerization of the aniline. The system was maintained at 0 − 5 ∘ C 0 − 5 ∘ C 0-5^(@)C0-5{ }^{\circ} \mathrm{C} for 24 h , and then the CC covered with polyaniline fibers (PANI-CC) was taken out of the solution, cleaned by water several times, and then vacuum dried at 60 ∘ C 60 ∘ C 60^(@)C60^{\circ} \mathrm{C} overnight. Finally, the NOCCs were obtained by the thermal treatment of the PANI-CCs under different atmospheres ( 5 % O 2 / 95 % Ar , 100 % Ar 5 % O 2 / 95 % Ar , 100 % Ar 5%O_(2)//95%Ar,100%Ar5 \% \mathrm{O}_{2} / 95 \% \mathrm{Ar}, 100 \% \mathrm{Ar}, or 5 % H 2 / 95 % Ar 5 % H 2 / 95 % Ar 5%H_(2)//95%Ar5 \% \mathrm{H}_{2} / 95 \% \mathrm{Ar} ) at 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} for 2 h . Accordingly, the resulting samples were denoted as NOCC-O (from oxidative atmosphere: 5 % O 2 / 95 % Ar 5 % O 2 / 95 % Ar 5%O_(2)//95%Ar5 \% \mathrm{O}_{2} / 95 \% \mathrm{Ar} ), NOCC-I (from inert atmosphere: 100 % Ar 100 % Ar 100%Ar100 \% \mathrm{Ar} ), and NOCC-R (from reductive atmosphere: 5 % H 2 / 95 % Ar 5 % H 2 / 95 % Ar 5%H_(2)//95%Ar5 \% \mathrm{H}_{2} / 95 \% \mathrm{Ar} ).
制备 NOCC：首先，在酒精、丙酮和蒸馏水中用超声波清洗 CC，以去除保护性油脂涂层。然后，将苯胺（ 228 μ L 228 μ L 228 muL228 \mu \mathrm{~L} ）分散在稀盐酸（ ( 1 M , 50 mL ( 1 M , 50 mL (1M,50mL(1 \mathrm{M}, 50 \mathrm{~mL} ）中，在有 SDS（7.6 毫克）存在的情况下超声处理 30 分钟。随后，将一块 CC ( 1.5 cm × 3 cm ) 1.5 cm × 3 cm ) 1.5cmxx3cm)1.5 \mathrm{~cm} \times 3 \mathrm{~cm}) 浸入苯胺溶液中，并将所得混合物在冰浴 ( ≈ 0 − 5 ∘ C ) ≈ 0 − 5 ∘ C (~~0-5^(@)C)\left(\approx 0-5{ }^{\circ} \mathrm{C}\right) 中冷却 30 分钟。接着，将溶于稀释的 HCl ( 1 m , 2 mL ) HCl ( 1 m , 2 mL ) HCl(1m,2mL)\mathrm{HCl}(1 \mathrm{~m}, 2 \mathrm{~mL}) 中的 APS ( ≈ 380 mg ≈ 380 mg ~~380mg\approx 380 \mathrm{mg} ) 缓慢加入上述溶液中，以诱导苯胺聚合。该体系在 0 − 5 ∘ C 0 − 5 ∘ C 0-5^(@)C0-5{ }^{\circ} \mathrm{C} 下保持 24 小时，然后从溶液中取出覆盖聚苯胺纤维的 CC（PANI-CC），用水清洗数次，然后在 60 ∘ C 60 ∘ C 60^(@)C60^{\circ} \mathrm{C} 下真空干燥过夜。最后，在不同的气氛（ 5 % O 2 / 95 % Ar , 100 % Ar 5 % O 2 / 95 % Ar , 100 % Ar 5%O_(2)//95%Ar,100%Ar5 \% \mathrm{O}_{2} / 95 \% \mathrm{Ar}, 100 \% \mathrm{Ar} 或 5 % H 2 / 95 % Ar 5 % H 2 / 95 % Ar 5%H_(2)//95%Ar5 \% \mathrm{H}_{2} / 95 \% \mathrm{Ar} ）下于 750 ∘ C 750 ∘ C 750^(@)C750^{\circ} \mathrm{C} 热处理 PANI-CC 2 小时，得到 NOCC。因此，得到的样品分别称为 NOCC-O（氧化气氛： 5 % O 2 / 95 % Ar 5 % O 2 / 95 % Ar 5%O_(2)//95%Ar5 \% \mathrm{O}_{2} / 95 \% \mathrm{Ar} ）、NOCC-I（惰性气氛： 100 % Ar 100 % Ar 100%Ar100 \% \mathrm{Ar} ）和 NOCC-R（还原气氛： 5 % H 2 / 95 % Ar 5 % H 2 / 95 % Ar 5%H_(2)//95%Ar5 \% \mathrm{H}_{2} / 95 \% \mathrm{Ar} ）。
Structural Characterization: FE-SEM images were obtained on an Ultra Plus (Zeiss, Germany) at an electric voltage of 5 KV . TEM measurements were conducted on a JEM-200CX (JEOL, Japan) with an accelerating voltage of 200 kV . The fibrous samples were ground and dispersed in ethanol and then transferred onto a Cu grid for the TEM measurements. The thicknesses of the PANI-derived carbon layers in the samples were estimated from ten different sections in five TEM images of each NOCC electrode. In situ diffuse reflectance Fourier transform infrared (DR-FTIR) spectroscopy was carried out with a Nicolet 6700 (Thermo Fisher Scientific, USA) in the range of 600 − 4000 cm − 1 600 − 4000 cm − 1 600-4000cm^(-1)600-4000 \mathrm{~cm}^{-1} using 32 scans. XRD patterns were recorded on a Rigaku Miniflex (JEOL, Japan) using Cu K α Cu K α CuKalpha\mathrm{Cu} \mathrm{K} \alpha radiation ( 40 kV , 15 mA 40 kV , 15 mA 40kV,15mA40 \mathrm{kV}, 15 \mathrm{~mA} ) at a scan rate of 5 ∘ min − 1 5 ∘ min − 1 5^(@)min^(-1)5^{\circ} \mathrm{min}^{-1} from 10 ∘ 10 ∘ 10^(@)10^{\circ} to 80 ∘ 80 ∘ 80^(@)80^{\circ} (20). Raman spectra were recorded on a Senterra R200-L (Bruker Optics, Germany) with the excitation from the 532 nm line of an Ar-ion laser ( 5 mW ). X-ray photoelectron spectra were collected on an ESCALAB 250Xi instrument (Thermo Fisher Scientific, USA) with a monochromatic Al K α X K α X KalphaX\mathrm{K} \alpha \mathrm{X}-ray source.
结构表征：FE-SEM 图像是在 Ultra Plus（蔡司，德国）上以 5 KV 的电压获得的。在加速电压为 200 kV 的 JEM-200CX （日本 JEOL）上进行了 TEM 测量。将纤维样品研磨并分散在乙醇中，然后转移到铜网格上进行 TEM 测量。样品中 PANI 衍生碳层的厚度是从每个 NOCC 电极的五幅 TEM 图像中的十个不同截面估算出来的。使用 Nicolet 6700（美国赛默飞世尔科技公司）在 600 − 4000 cm − 1 600 − 4000 cm − 1 600-4000cm^(-1)600-4000 \mathrm{~cm}^{-1} 范围内使用 32 次扫描进行了原位漫反射傅立叶变换红外（DR-FTIR）光谱分析。在 Rigaku Miniflex（JEOL，日本）上使用 Cu K α Cu K α CuKalpha\mathrm{Cu} \mathrm{K} \alpha 辐射 ( 40 kV , 15 mA 40 kV , 15 mA 40kV,15mA40 \mathrm{kV}, 15 \mathrm{~mA} ) 记录 XRD 图样，扫描速率为 5 ∘ min − 1 5 ∘ min − 1 5^(@)min^(-1)5^{\circ} \mathrm{min}^{-1} 从 10 ∘ 10 ∘ 10^(@)10^{\circ} 到 80 ∘ 80 ∘ 80^(@)80^{\circ} (20)。拉曼光谱是在 Senterra R200-L （布鲁克光学仪器公司，德国）上用氩离子激光器（5 mW）的 532 nm 线激发下记录的。X 射线光电子能谱是在 ESCALAB 250Xi 仪器（美国 Thermo Fisher Scientific 公司）上用单色 Al K α X K α X KalphaX\mathrm{K} \alpha \mathrm{X} 射线源收集的。

Supporting Information 辅助信息

Supporting Information is available from the Wiley Online Library or from the author.
辅助信息可从 Wiley 在线图书馆或作者处获取。

Acknowledgements 致谢

This work was financially supported by the National Natural Science Foundation of China (61575121, 51772189, 21720102002, 21772120, and 21572132) and Science and Technology Commission of Shanghai Municipality (16)C1400703). The authors also thank the Instrumental Analysis Center of Shanghai Jiao Tong University and Advanced Electronics Materials and Devices (AEMD) of Shanghai Jiao Tong University for the characterization of the materials.
本研究得到了国家自然科学基金（61575121、51772189、21720102002、21772120 和 21572132）和上海市科学技术委员会（16）C1400703 的资助。）作者还感谢上海交通大学仪器分析中心和上海交通大学先进电子材料与器件研究所（AEMD）对材料进行了表征。

Conflict of Interest 利益冲突

The authors declare no conflict of interest.
作者声明没有利益冲突。

Keywords 关键词

ascorbic acid sensors, dopamine sensors, flexible organic electrochemical transistors, nitrogen/oxygen-codoped carbon cloths, surface engineering
抗坏血酸传感器、多巴胺传感器、柔性有机电化学晶体管、氮氧掺杂碳布、表面工程
Received: July 3, 2019 收到：2019 年 7 月 3 日
Revised: October 1, 2019 已修订：2019 年 10 月 1 日
Published online: October 25, 2019
在线发表：2019 年 10 月 25 日
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  1. X. Xi, W. Ji, Dr. W. Tang, Prof. Y. Su, Prof. X. Guo, Prof. R. Liu
    X.Xi, W. Ji, Dr. W. Tang, Prof. Y. Su, Prof. X. Guo, Prof. R. Liu
    Department of Electronic Engineering
    电子工程系
    Shanghai Jiao Tong University
    上海交通大学
    800 Dongchuan Road, Shanghai 200240, P. R. China
    中国上海市东川路 800 号 200240
    E-mail: x.guo@sjtu.edu.cn; ruililiu@sjtu.edu.cn
    电子邮件：x.guo@sjtu.edu.cn; ruililiu@sjtu.edu.cn
    Prof. D. Wu, S. Zhang
    D. Wu, S. Zhang 教授
    School of Chemistry and Chemical Engineering
    化学与化学工程学院
    Shanghai Jiao Tong University
    上海交通大学
    800 Dongchuan Road, Shanghai 200240, P. R. China
    中国上海市东川路 800 号 200240
    E-mail: wudongqing@sjtu.edu.cn
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