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

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]}$${}^{[1]}$^([1]){ }^{[1]} In addition to flexibility, biosensors in wearable electronics also need high sensitivity and selectivity, because the analytes in body fluids such as ascorbic acid (AA), dopamine (DA), and uric acid (UA) are usually combined together in very low concentrations ( $\times {10}^{-6}$$\times {10}^{-6}$xx10^(-6)\times 10^{-6} or $\times {10}^{-9}\mathrm{m}$$\times {10}^{-9}\mathrm{m}$xx10^(-9)m\times 10^{-9} \mathrm{~m} level). ${}^{[2]}$${}^{[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（ $\times {10}^{-6}$$\times {10}^{-6}$xx10^(-6)\times 10^{-6} 或 $\times {10}^{-9}\mathrm{m}$$\times {10}^{-9}\mathrm{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]}$${}^{[4]}$^([4]){ }^{[4]} Therefore, the detection capability of the OECT does not depend on specific instruments or spectrometers, and the miniaturization of the OECT will not result in the loss of sensitivity. Additionally, the transistor configuration of the OECT helps to magnify the signals from analytes with low concentrations, thus effectively improving the limits of detection (LOD). Moreover, OECTs are easily constructed on flexible substrates, since the electroactive semiconductors in OECTs are organic species, which also provides advantages to OECT-based biosensors, including high biocompatibility and a low operating voltage. ${}^{[1c,3a,5]}$${}^{[1c,3a,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]}$${}^{[4]}$^([4]){ }^{[4]} 因此，OECT 的检测能力不依赖于特定的仪器或光谱仪，而且 OECT 的微型化不会导致灵敏度下降。此外，OECT 的晶体管配置有助于放大低浓度分析物的信号，从而有效提高检测限（LOD）。此外，由于 OECT 中的电活性半导体是有机物，因此很容易在柔性基底上构建 OECT，这也为基于 OECT 的生物传感器提供了优势，包括高生物相容性和低工作电压。 ${}^{[1c,3a,5]}$${}^{[1c,3a,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. ${}^{[6a,7a,8]}$${}^{[6a,7a,8]}$^([6a,7a,8]){ }^{[6 a, 7 a, 8]} The negative impacts of these precious metals on the OECTs are not merely the increased costs. More importantly, the precious metal gate electrodes may lose their electrocatalytic abilities due to poisoning by sulfur, chlorine, phosphorus, and other substances, which inevitably harms the stability and reproducibility of the OECT sensors. ${}^{[9]}$${}^{[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。 ${}^{[6a,7a,8]}$${}^{[6a,7a,8]}$^([6a,7a,8]){ }^{[6 a, 7 a, 8]} 这些贵金属对 OECT 的负面影响不仅仅是成本增加。更重要的是，贵金属栅极电极可能会因硫磺、氯、磷等物质的毒害而失去电催化能力，从而不可避免地损害 OECT 传感器的稳定性和可重复性。 ${}^{[9]}$${}^{[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 $(\mathrm{N})$$(\mathrm{N})$(N)(\mathrm{N}), oxygen (O), and sulfur (S). ${}^{[12]}$${}^{[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.
$(\mathrm{N})$$(\mathrm{N})$(N)(\mathrm{N}) 、氧 (O) 和硫 (S) 等杂原子。 ${}^{[12]}$${}^{[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}^{\circ }\mathrm{C}$${750}^{\circ }\mathrm{C}$750^(@)C750^{\circ} \mathrm{C}, and the amounts and species of N and O atoms on their surfaces can be easily tuned by changing the atmosphere (oxidative, inert, or reductive) during the carbonization process. In a three-electrode electrochemical sensing system, the NOCC electrode obtained under reductive conditions exhibits higher sensitivity toward AA than DA, while the NOCC electrode from the oxidative atmosphere has a better selectivity for the detection of DA. More importantly, the different sensing capabilities of the NOCC electrodes are acquired by the OECTs when the NOCC electrodes are used as the gate electrodes, thus enabling the fabrication of OECT sensors with excellent sensitivity and selectivity toward AA and DA. As verified by the experimental results and theoretical calculations, the surface engineering of carbonaceous gate electrodes by modifying the heteroatoms on their surfaces provides an efficient strategy for the design and construction of high-performance OECT biosensors.
在这里，我们展示了如何制作 N/O 掺杂碳布 (NOCC) 作为具有不同灵敏度和选择性的柔性 OECT 传感器的栅电极。NOCC 电极是通过在 ${750}^{\circ }\mathrm{C}$${750}^{\circ }\mathrm{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。

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. ${}^{[13a,15]}$${}^{[13a,15]}$^([13 a,15]){ }^{[13 a, 15]} Therefore, the ability to detect AA and DA in body fluids using wearable biosensors would be valuable for the real-time monitoring and diagnosis of the related syndromes. Among the common body fluids, urine is more suitable than blood and sweat for the wearable sensing systems, because it can be easily collected in sufficient amounts by the diapers, without the need for intrusive inspection. ${}^{[16]}$${}^{[16]}$^([16]){ }^{[16]} The concentrations of AA and DA in human urine should be in the ranges of $(0.114-0.170)\times {10}^{-3}$$(0.114-0.170)\times {10}^{-3}$(0.114-0.170)xx10^(-3)(0.114-0.170) \times 10^{-3} and $(0.661-2.645)\times {10}^{-6}\mathrm{M},{}^{[17]}$$(0.661-2.645)\times {10}^{-6}\mathrm{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]}$${}^{[14]}$^([14]){ }^{[14]} 血液或尿液中 AA 和 DA 的异常水平通常与代谢或神经系统的潜在疾病有关。 ${}^{[13a,15]}$${}^{[13a,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]}$${}^{[16]}$^([16]){ }^{[16]} 人体尿液中的 AA 和 DA 浓度应分别在 $(0.114-0.170)\times {10}^{-3}$$(0.114-0.170)\times {10}^{-3}$(0.114-0.170)xx10^(-3)(0.114-0.170) \times 10^{-3} 和 $(0.661-2.645)\times {10}^{-6}\mathrm{M},{}^{[17]}$$(0.661-2.645)\times {10}^{-6}\mathrm{M},{}^{[17]}$(0.661-2.645)xx10^(-6)M,^([17])(0.661-2.645) \times 10^{-6} \mathrm{M},{ }^{[17]} 范围内，因此需要高灵敏度的传感器进行检测。检测 AA 和 DA 所面临的挑战不仅在于它们在尿液中的低浓度和共存性。AA的还原性强，氧化还原电位低，可能会引起多巴胺邻醌（DA的氧化态）的还原，特别是当AA的量远高于DA时，会干扰DA的电化学检测。 ${}^{[18]}$${}^{[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}^{\circ }\mathrm{C}$${750}^{\circ }\mathrm{C}$750^(@)C750^{\circ} \mathrm{C} caused the carbonization of the PANI, which generated a N - and O -codoped carbon layer on the CC, resulting in NOCC electrodes with good flexibility (Figure S1, Supporting Information). During the carbonization of the PANI, the amount and type of N and O atoms on the surface of the NOCC electrodes was manipulated by adjusting the atmosphere. In this work, three kinds of gases, including oxygen/argon $({\mathrm{O}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}$$\left({\mathrm{O}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}\right.$(O_(2)5v//v%:}\left(\mathrm{O}_{2} 5 \mathrm{v} / \mathrm{v} \%\right., Ar $95\mathrm{v}/\mathrm{v}\mathrm{\%}$$95\mathrm{v}/\mathrm{v}\mathrm{\%}$95v//v%95 \mathrm{v} / \mathrm{v} \% ), pure argon ( $100\mathrm{v}/\mathrm{v}\mathrm{\%}$$100\mathrm{v}/\mathrm{v}\mathrm{\%}$100v//v%100 \mathrm{v} / \mathrm{v} \% ), and hydrogen/argon $({\mathrm{H}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}$$\left({\mathrm{H}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}\right.$(H_(2)5v//v%:}\left(\mathrm{H}_{2} 5 \mathrm{v} / \mathrm{v} \%\right., Ar $95\mathrm{v}/\mathrm{v}\mathrm{\%}$$95\mathrm{v}/\mathrm{v}\mathrm{\%}$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 ( ${\mathrm{O}}_2/\mathrm{Ar})$$\left.{\mathrm{O}}_2/\mathrm{Ar}\right)${:O_(2)//Ar)\left.\mathrm{O}_{2} / \mathrm{Ar}\right), NOCC-I $(\mathrm{Ar})$$(\mathrm{Ar})$(Ar)(\mathrm{Ar}) and NOCC-R $\left({\mathrm{H}}_2/\mathrm{Ar}\right)$$\left({\mathrm{H}}_2/\mathrm{Ar}\right)$(H_(2)//Ar)\left(\mathrm{H}_{2} / \mathrm{Ar}\right).
这为 PANI-CC 复合材料提供了氧原子。在 ${750}^{\circ }\mathrm{C}$${750}^{\circ }\mathrm{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 $({\mathrm{O}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}$$\left({\mathrm{O}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}\right.$(O_(2)5v//v%:}\left(\mathrm{O}_{2} 5 \mathrm{v} / \mathrm{v} \%\right. , Ar $95\mathrm{v}/\mathrm{v}\mathrm{\%}$$95\mathrm{v}/\mathrm{v}\mathrm{\%}$95v//v%95 \mathrm{v} / \mathrm{v} \% )、纯氩气 ( $100\mathrm{v}/\mathrm{v}\mathrm{\%}$$100\mathrm{v}/\mathrm{v}\mathrm{\%}$100v//v%100 \mathrm{v} / \mathrm{v} \% )和氢气/氩气 $({\mathrm{H}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}$$\left({\mathrm{H}}_{2}5\mathrm{v}/\mathrm{v}\mathrm{\%}\right.$(H_(2)5v//v%:}\left(\mathrm{H}_{2} 5 \mathrm{v} / \mathrm{v} \%\right. , Ar $95\mathrm{v}/\mathrm{v}\mathrm{\%}$$95\mathrm{v}/\mathrm{v}\mathrm{\%}$95v//v%95 \mathrm{v} / \mathrm{v} \% )，研究了氧化性、惰性和还原性气氛对 NOCC 电极表面成分和电化学行为的影响。相应地，得到的样品被称为 NOCC-O（ ${\mathrm{O}}_2/\mathrm{Ar})$$\left.{\mathrm{O}}_2/\mathrm{Ar}\right)${:O_(2)//Ar)\left.\mathrm{O}_{2} / \mathrm{Ar}\right) 、NOCC-I $(\mathrm{Ar})$$(\mathrm{Ar})$(Ar)(\mathrm{Ar}) 和 NOCC-R $\left({\mathrm{H}}_2/\mathrm{Ar}\right)$$\left({\mathrm{H}}_2/\mathrm{Ar}\right)$(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\pm 1\mu \mathrm{m}$$9\pm 1\mu \mathrm{m}$9+-1mum9 \pm 1 \mu \mathrm{~m}. Except for some groove-like structures, the carbon fibers had relatively smooth surfaces. In contrast, the carbon fibers in the PANI-CC composite were homogeneously coated with a layer of burr-like PANI fibers (Figure S2d-f, Supporting
首先利用场发射扫描电子显微镜（FE-SEM）和透射电子显微镜（TEM）对NOCC电极的形态和微观结构进行了表征。如图 S2a-c（佐证资料）所示，原始 CC 具有典型的编织结构，由垂直交错的碳纤维组成，直径为 $9\pm 1\mu \mathrm{m}$$9\pm 1\mu \mathrm{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 ${\mathrm{H}}_2/\mathrm{Ar}$${\mathrm{H}}_2/\mathrm{Ar}$H_(2)//Ar\mathrm{H}_{2} / \mathrm{Ar}, while the surface roughness of NOCC-I, obtained under Ar, was between those of NOCC-O and NOCC-R (Figure 2a-c). The TEM images of the carbon fibers from the NOCC electrodes further illustrated the different effects of the carbonization atmospheres. As shown in Figure 2d-f and Figure S4 (Supporting Information), the edges of the carbon fibers from the three samples showed different contrast of the light and dark areas, which was used to estimate the thickness of the carbon derived from the pyrolysis of PANI. Accordingly, the thickness of the PANI-derived carbon in NOCC-O was only $30\pm 4\mathrm{nm}$$30\pm 4\mathrm{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\pm 14$$130\pm 14$130+-14130 \pm 14 and $200\pm 28\mathrm{nm}$$200\pm 28\mathrm{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 ${\mathrm{H}}_2/\mathrm{Ar}$${\mathrm{H}}_2/\mathrm{Ar}$H_(2)//Ar\mathrm{H}_{2} / \mathrm{Ar} 下得到的 NOCC-R 少很多突起，而在氩气下得到的 NOCC-I 的表面粗糙度介于 NOCC-O 和 NOCC-R 之间（图 2a-c）。NOCC 电极碳纤维的 TEM 图像进一步说明了碳化气氛的不同影响。如图 2d-f 和图 S4（佐证资料）所示，三个样品的碳纤维边缘显示出不同的明暗区域对比。因此，NOCC-O 中 PANI 衍生碳的厚度仅为 $30\pm 4\mathrm{nm}$$30\pm 4\mathrm{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\pm 14$$130\pm 14$130+-14130 \pm 14 和 $200\pm 28\mathrm{nm}$$200\pm 28\mathrm{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{\mathrm{cm}}^{-1}$$1500{\mathrm{cm}}^{-1}$1500cm^(-1)1500 \mathrm{~cm}^{-1} were assigned to the stretching vibration of C-O groups in ethers or phenols, the stretching vibration of $\mathrm{C}-\mathrm{N}$$\mathrm{C}-\mathrm{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]}$${}^{[20]}$^([20]){ }^{[20]} The XRD patterns of the samples had similar broad diffractions at $\approx {26}^{\circ },{43}^{\circ }$$\approx {26}^{\circ },{43}^{\circ }$~~26^(@),43^(@)\approx 26^{\circ}, 43^{\circ}, and ${54}^{\circ }$${54}^{\circ }$54^(@)54^{\circ}, which were indexed to the (002), (100)/(101), and (102) planes of graphitic carbon in the CC substrate due to its high weight ratio in the NOCC electrodes (Figure S5b, Supporting Information). ${}^{[21]}$${}^{[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{\mathrm{cm}}^{-1}$$1590{\mathrm{cm}}^{-1}$1590cm^(-1)1590 \mathrm{~cm}^{-1} are the characteristic disordered (D) and graphitic (G) bands of carbon materials, ${}^{[22]}$${}^{[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_{\mathrm{D}}/I_{\mathrm{G}}$$I_{\mathrm{D}}/I_{\mathrm{G}}$I_(D)//I_(G)I_{\mathrm{D}} / I_{\mathrm{G}} value $(0.88)$$(0.88)$(0.88)(0.88) for NOCC-O than for NOCC-I (0.79) and NOCC-R (0.75). ${}^{[23]}$${}^{[23]}$^([23]){ }^{[23]} However, the full width at half maximum (FWHM) of the D band of NOCC-O was smaller than those of the other samples, corresponding to a narrow distribution of ${\mathrm{sp}}^2$${\mathrm{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]}$${}^{[23,24]}$^([23,24]){ }^{[23,24]} This phenomenon suggested that the aromatic carbon in NOCC-O had a higher graphitic degree than did those in NOCC-I and NOCC-R, which was in accordance with the TEM images (Figure 2g).
利用傅立叶变换红外光谱（FTIR）、拉曼光谱和 X 射线衍射（XRD）光谱进一步比较了样品的微观结构和化学成分。在 NOCC 电极的傅立叶变换红外光谱中（图 S5a，佐证资料），1150、1300 和 $1500{\mathrm{cm}}^{-1}$$1500{\mathrm{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、 $\mathrm{C}-\mathrm{N}$$\mathrm{C}-\mathrm{N}$C-N\mathrm{C}-\mathrm{N} 基团的伸缩振动以及吡啶 N 或吡咯 N 基团的环振动，证实了碳框架中 N 原子和 O 原子的掺杂。 ${}^{[20]}$${}^{[20]}$^([20]){ }^{[20]} 样品的 XRD 图样在 $\approx {26}^{\circ },{43}^{\circ }$$\approx {26}^{\circ },{43}^{\circ }$~~26^(@),43^(@)\approx 26^{\circ}, 43^{\circ} 和 ${54}^{\circ }$${54}^{\circ }$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]}$${}^{[21]}$^([21]){ }^{[21]} 相反，NOCC 的拉曼光谱提供了更多有关 N 和 O 共掺碳层结构的信息。如图 S5c（佐证资料）所示，1350 和 $1590{\mathrm{cm}}^{-1}$$1590{\mathrm{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]}$${}^{[22]}$^([22]){ }^{[22]} 证实了 PANI 的碳化。更重要的是，NOCC-O 的 D 带强度远高于 NOCC-I 和 NOCC-R，这是因为在氧化气氛下碳框架的芳香度降低，导致 NOCC-O 的 $I_{\mathrm{D}}/I_{\mathrm{G}}$$I_{\mathrm{D}}/I_{\mathrm{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 ${\mathrm{sp}}^2$${\mathrm{sp}}^2$sp^(2)\mathrm{sp}^{2} 键合簇的狭窄分布，这是因为无定形碳域在氧化气氛下更容易被蚀刻。 ${}^{[23,24]}$${}^{[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]}$${}^{[25]}$^([25]){ }^{[25]} The differential pulse voltammetry (DPV) and cyclic voltammetry (CV) profiles of the NOCCs were first recorded in phosphate buffer saline (PBS, $0.1\mathrm{m},\mathrm{pH}=7.4$$0.1\mathrm{m},\mathrm{pH}=7.4$0.1m,pH=7.40.1 \mathrm{~m}, \mathrm{pH}=7.4 ) containing AA $(300\times {10}^{-6}\mathrm{m})$$\left(300\times {10}^{-6}\mathrm{m}\right)$(300 xx10^(-6)(m))\left(300 \times 10^{-6} \mathrm{~m}\right), DA $(10\times {10}^{-6}\mathrm{m})$$\left(10\times {10}^{-6}\mathrm{m}\right)$(10 xx10^(-6)(m))\left(10 \times 10^{-6} \mathrm{~m}\right), and UA $(10\times {10}^{-6}\mathrm{m}){}^{[12\mathrm{b}]}$$\left(10\times {10}^{-6}\mathrm{m}\right){}^{[12\mathrm{b}]}$(10 xx10^(-6)(m))^([12b])\left(10 \times 10^{-6} \mathrm{~m}\right){ }^{[12 \mathrm{~b}]} As indicated in Figure 3b, the well-defined peaks from the oxidation of AA ( $\approx -66\mathrm{mV}$$\approx -66\mathrm{mV}$~~-66mV\approx-66 \mathrm{mV} ), DA $(\approx 117\mathrm{mV})$$(\approx 117\mathrm{mV})$(~~117mV)(\approx 117 \mathrm{mV}) and UA ( $\approx 234\mathrm{mV}$$\approx 234\mathrm{mV}$~~234mV\approx 234 \mathrm{mV} ) were observed in the DPV curves of the three electrodes. ${}^{[12b,26]}$${}^{[12b,26]}$^([12 b,26]){ }^{[12 b, 26]} According to the current intensities of the peaks (Figure 3c), NOCC-O and NOCC-I showed much greater responses to DA than to AA and UA, while NOCC-R showed distinct detection behavior by delivering a higher oxidation current to AA than to DA and UA. The different sensing behaviors of the NOCC electrodes were also confirmed by their CV curves (Figure S6a, Supporting Information). Considering the significant differences in the responses of the NOCC electrodes toward the analytes, NOCC-R had obvious advantages in the detection of AA, while NOCC-O was more suitable for the electrochemical sensing of DA. In contrast to NOCC-O, NOCC-I had very similar DPV responses toward DA and UA, making
首先在一个三电极电化学传感系统中评估了所获得的 NOCC 电极作为 AA 和 DA 传感器的性能（图 3a）。作为与 AA 和 DA 共存于体液中的常见分析物，UA 被添加为干扰物。首先在含有 AA $(300\times {10}^{-6}\mathrm{m})$$\left(300\times {10}^{-6}\mathrm{m}\right)$(300 xx10^(-6)(m))\left(300 \times 10^{-6} \mathrm{~m}\right) 、DA $(10\times {10}^{-6}\mathrm{m})$$\left(10\times {10}^{-6}\mathrm{m}\right)$(10 xx10^(-6)(m))\left(10 \times 10^{-6} \mathrm{~m}\right) 和 UA $(10\times {10}^{-6}\mathrm{m}){}^{[12\mathrm{b}]}$$\left(10\times {10}^{-6}\mathrm{m}\right){}^{[12\mathrm{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\mathrm{m},\mathrm{pH}=7.4$$0.1\mathrm{m},\mathrm{pH}=7.4$0.1m,pH=7.40.1 \mathrm{~m}, \mathrm{pH}=7.4 ）中记录 NOCC 的差分脉冲伏安法（DPV）和循环伏安法（CV）曲线、和 UA $(10\times {10}^{-6}\mathrm{m}){}^{[12\mathrm{b}]}$$\left(10\times {10}^{-6}\mathrm{m}\right){}^{[12\mathrm{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（ $\approx -66\mathrm{mV}$$\approx -66\mathrm{mV}$~~-66mV\approx-66 \mathrm{mV} ）、DA（ $(\approx 117\mathrm{mV})$$(\approx 117\mathrm{mV})$(~~117mV)(\approx 117 \mathrm{mV}) ）和 UA（ $\approx 234\mathrm{mV}$$\approx 234\mathrm{mV}$~~234mV\approx 234 \mathrm{mV} ）氧化产生的明确峰值。 ${}^{[12b,26]}$${}^{[12b,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 $\left(I_{\mathrm{p}}\right)$$\left(I_{\mathrm{p}}\right)$(I_(p))\left(I_{\mathrm{p}}\right) of NOCC-R increased linearly as the concentrations of AA varied from $10\times {10}^{-6}$$10\times {10}^{-6}$10 xx10^(-6)10 \times 10^{-6} to $1300\times {10}^{-6}\mathrm{m}$$1300\times {10}^{-6}\mathrm{m}$1300 xx10^(-6)m1300 \times 10^{-6} \mathrm{~m}. The corresponding calibration equation of the response currents versus the concentrations of AA was expressed as $I_{\mathrm{p}}=1.145C+245.441$$I_{\mathrm{p}}=1.145C+245.441$I_(p)=1.145 C+245.441I_{\mathrm{p}}=1.145 C+245.441, with a high sensitivity of $1.145\mu \mathrm{A}\mu {\mathrm{M}}^{-1}{\mathrm{cm}}^{-2}$$1.145\mu \mathrm{A}\mu {\mathrm{M}}^{-1}{\mathrm{cm}}^{-2}$1.145 muAmuM^(-1)cm^(-2)1.145 \mu \mathrm{~A} \mu \mathrm{M}^{-1} \mathrm{~cm}^{-2} and a correlation coefficient of 0.9905 (Figure 3d inset). Accordingly, NOCC-R had a very low LOD of $3.41\times {10}^{-6}\mathrm{m}$$3.41\times {10}^{-6}\mathrm{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)\times {10}^{-6}\mathrm{M}(R^2=0.9973)$$(0.3-55)\times {10}^{-6}\mathrm{M}\left(R^2=0.9973\right)$(0.3-55)xx10^(-6)M(R^(2)=0.9973)(0.3-55) \times 10^{-6} \mathrm{M}\left(R^{2}=0.9973\right), a high sensitivity of $19.194\mu \mathrm{A}\mu {\mathrm{M}}^{-1}{\mathrm{cm}}^{-2}$$19.194\mu \mathrm{A}\mu {\mathrm{M}}^{-1}{\mathrm{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\times {10}^{-6}\mathrm{m}$$0.18\times {10}^{-6}\mathrm{m}$0.18 xx10^(-6)m0.18 \times 10^{-6} \mathrm{~m} $(\mathrm{S}/\mathrm{N}=3)$$(\mathrm{S}/\mathrm{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\times {10}^{-6}$$0.3\times {10}^{-6}$0.3 xx10^(-6)0.3 \times 10^{-6} to $1400\times {10}^{-6}\mathrm{m}$$1400\times {10}^{-6}\mathrm{m}$1400 xx10^(-6)m1400 \times 10^{-6} \mathrm{~m}