Cite this: Chem. Sci., 2021, 12, 14432 引用此文：Chem.科学，2021，12，14432
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Received 28th July 2021 2021 年 7 月 28 日收到
Accepted 9th October 2021 2021 年 10 月 9 日接受
DOI: 10.1039/d1sc04138j DOI：10.1039/d1sc04138j rsc.li/chemical-science
Plasticizer and catalyst co-functionalized PEDOT:PSS enables stretchable electrochemical sensing of living cells †\dagger 增塑剂和催化剂共官能化 PEDOT:PSS 可实现活细胞的可拉伸电化学传感 †\dagger
Recently, stretchable electrochemical sensors have stood out as a powerful tool for the detection of soft cells and tissues, since they could perfectly comply with the deformation of living organisms and synchronously monitor mechanically evoked biomolecule release. However, existing strategies for the fabrication of stretchable electrochemical sensors still face with huge challenges due to scarce electrode materials, demanding processing techniques and great complexity in further functionalization. Herein, we report a novel and facile strategy for one-step preparation of stretchable electrochemical biosensors by doping ionic liquid and catalyst into a conductive polymer (poly(3,4ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS). Bis(trifluoromethane) sulfonimide lithium salt as a small-molecule plasticizer can significantly improve the stretchability and conductivity of the PEDOT:PSS film, and cobalt phthalocyanine as an electrocatalyst endows the film with excellent electrochemical sensing performance. Moreover, the functionalized PEDOT:PSS retained good cell biocompatibility with two extra dopants. These satisfactory properties allowed the real-time monitoring of stretch-induced transient hydrogen peroxide release from cells. This work presents a versatile strategy to fabricate conductive polymer-based stretchable electrodes with easy processing and excellent performance, which benefits the in-depth exploration of sophisticated life activities by electrochemical sensing. 最近，可拉伸电化学传感器已成为检测软细胞和组织的有力工具，因为它们可以完美地适应生物体的变形，并同步监测机械诱发的生物分子释放。然而，由于电极材料稀缺、加工技术要求高以及进一步功能化的复杂性，现有的可拉伸电化学传感器制造策略仍面临巨大挑战。在此，我们报告了一种新颖而简便的策略，即在导电聚合物（聚（3,4-亚乙二氧基噻吩）：聚（苯乙烯磺酸），PEDOT：PSS）中掺杂离子液体和催化剂，从而一步制备可拉伸的电化学生物传感器。双（三氟甲烷）磺酰亚胺锂盐作为小分子增塑剂可显著改善 PEDOT:PSS 薄膜的拉伸性和导电性，而酞菁钴作为电催化剂则赋予了薄膜优异的电化学传感性能。此外，添加了两种掺杂剂的功能化 PEDOT:PSS 还具有良好的细胞生物相容性。这些令人满意的特性允许对拉伸诱导的细胞瞬时过氧化氢释放进行实时监测。这项工作提出了一种制造基于导电聚合物的可拉伸电极的多功能策略，它易于加工且性能卓越，有利于通过电化学传感深入探索复杂的生命活动。
Introduction 导言
Cells in the body are constantly exposed to mechanical forces and could perceive and transduce them into biochemical signals. ^(1-6){ }^{1-6} Currently, cell mechanotransduction has gained tremendous attention due to the crucial role of mechanical forces in cell function, and the accurate characterization of the ensuing biochemical signals during the mechanotransduction process is vitally important for understanding cellular mechanical signalling. ^(2-5){ }^{2-5} Since cell mechanotransduction involves rapid mechanochemical conversion (within a second), ^(3){ }^{3} soft stretchable electrochemical sensors with a fast response and high sensitivity have emerged as a powerful technique to induce the mechanical deformation of cells and simultaneously monitor the transient biochemical response in real time. ^(7-11){ }^{7-11} Recently, stretchable electrochemical sensors have made significant progress in exploring dynamic mechanotransduction, and mechanically evoked molecules (e.g. 人体内的细胞不断受到机械力的作用，它们可以感知机械力并将其转化为生化信号。 ^(1-6){ }^{1-6} 目前，由于机械力在细胞功能中的关键作用，细胞机械传导受到了极大的关注，而准确描述机械传导过程中随之产生的生化信号对于理解细胞机械信号至关重要。 ^(2-5){ }^{2-5} 由于细胞的机械传导涉及快速的机械化学转换（一秒钟内）， ^(3){ }^{3} 具有快速响应和高灵敏度的软拉伸电化学传感器已成为诱导细胞机械变形并同时实时监测瞬时生化响应的强大技术。 ^(7-11){ }^{7-11} 近来，可拉伸电化学传感器在探索动态机械传导方面取得了重大进展，机械诱发的分子（如钙离子、镁离子、钾离子、镁离子等）也在研究中得到了应用。
hydrogen peroxide (H_(2)O_(2))\left(\mathrm{H}_{2} \mathrm{O}_{2}\right), nitric oxide (NO) and serotonin) release from stretched endothelial cells and inflated intestine were successfully monitored. ^(9,12-15){ }^{9,12-15} This notable advance is of great benefit to study the mechanism of force-activated signalling in mechanotransduction. (H_(2)O_(2))\left(\mathrm{H}_{2} \mathrm{O}_{2}\right) 过氧化氢、一氧化氮（NO）和血清素）的释放。 ^(9,12-15){ }^{9,12-15} 这一显著进步对研究机械传导中力激活信号的机制大有裨益。
As for the fabrication of stretchable electrodes, most of the reported sensors were based on well-designed zero- or onedimensional nanomaterials. Zero-dimensional nanomaterials with high density, such as agglomerated Au nanoparticles, ^(16){ }^{16} could fill stretch-evoked interspaces between the particles to retain continuous electronic pathways. One-dimensional nanomaterials, such as Au nanowires, ^(17)Au{ }^{17} \mathrm{Au} nanotubes ^(7,18){ }^{7,18} or carbon nanotubes (CNTs), ^(9,19,20){ }^{9,19,20} could accommodate the applied strain by sliding and rotating against each other. However, the available materials that could be employed to construct stretchable electrodes are still very lacking, and the fabrication of stretchable electrodes usually involves demanding and timeconsuming processes to in situ synthesize these engineered nanomaterials. ^(716,17){ }^{716,17} Moreover, to monitor the very weak biochemical signals in the primary mechanotransduction, stretchable electrodes usually need further functionalization to improve their performance, such as sensitivity, selectivity or stretchability. 9,13,15,199,13,15,19 Therefore, stretchable electrochemical sensors face with great challenges due to the limitation of both 至于可拉伸电极的制造，大多数报道的传感器都是基于精心设计的零维或一维纳米材料。高密度的零维纳米材料，如团聚金纳米粒子， ^(16){ }^{16} 可以填充粒子之间的拉伸间隙，从而保留连续的电子通路。一维纳米材料，如金纳米线、 ^(17)Au{ }^{17} \mathrm{Au} 纳米管 ^(7,18){ }^{7,18} 或碳纳米管（CNT） ^(9,19,20){ }^{9,19,20} ，可以通过相互滑动和旋转来适应所施加的应变。然而，目前可用来构建可拉伸电极的材料仍然非常缺乏，而且制造可拉伸电极通常需要在原位合成这些工程纳米材料，工艺要求高，耗时长。 ^(716,17){ }^{716,17} 此外，为了监测初级机械传导中非常微弱的生化信号，可拉伸电极通常需要进一步功能化以提高其性能，如灵敏度、选择性或可拉伸性。 9,13,15,199,13,15,19 因此，可拉伸电化学传感器面临着巨大的挑战，因为它们受到以下两方面的限制
electrode materials and processing techniques, and facile and versatile fabrication strategies are urgently needed to advance their applications. 电极材料和加工技术，以及简便、多功能的制造策略，这些都是推动其应用的迫切需要。
By virtue of high conductivity and good electrochemical performance, the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) commonly dispersed in poly(styrene sulfonate) (PSS) aqueous solution has been extensively used as an electrode material. ^(21-24){ }^{21-24} However a low fracture strain ( ∼5%\sim 5 \% ) hinders the direct application of PEDOT:PSS film in stretchable electrodes. Many recent efforts have been devoted to increasing the stretchability by blending PEDOT:PSS with various additives, including elastomeric polymers and smallmolecule plasticizers. ^(25-27){ }^{25-27} Generally, polymeric blends lead to worse conductivity due to the addition of insulating polymers. ^(28,29){ }^{28,29} Although small-molecule plasticizers (e.g. Zonyl ^(30){ }^{30} and Triton X-100 ^(31){ }^{31} ) could enhance both the elastic modulus and conductivity, the leaching of these toxic additives posed a threat to biological systems. Very recently, the doping of ionic liquids into PEDOT:PSS has achieved the coexistence of high stretchability and conductivity as well as satisfactory biocompatibility. ^(32,33){ }^{32,33} However, no impressive progress in stretchable electrodes based on PEDOT:PSS for electrochemical biosensing has been witnessed so far. 导电聚合物聚（3,4-亚乙二氧基噻吩）（PEDOT）通常分散在聚（苯乙烯磺酸盐）（PSS）水溶液中，具有高导电性和良好的电化学性能，因此被广泛用作电极材料。 ^(21-24){ }^{21-24} 然而，低断裂应变（ ∼5%\sim 5 \% ）阻碍了 PEDOT:PSS 薄膜在可拉伸电极中的直接应用。最近，许多人致力于通过将 PEDOT:PSS 与各种添加剂（包括弹性聚合物和小分子增塑剂）混合来提高拉伸性。 ^(25-27){ }^{25-27} 一般来说，聚合物混合物会因加入绝缘聚合物而导致导电性变差。 ^(28,29){ }^{28,29} 虽然小分子增塑剂（如 Zonyl ^(30){ }^{30} 和 Triton X-100 ^(31){ }^{31} ）可以提高弹性模量和导电性，但这些有毒添加剂的浸出对生物系统构成威胁。最近，通过在 PEDOT:PSS 中掺入离子液体，实现了高拉伸性和导电性的共存以及令人满意的生物相容性。 ^(32,33){ }^{32,33} 然而，基于 PEDOT:PSS 的可拉伸电极在电化学生物传感方面迄今尚未取得令人瞩目的进展。
Herein, we report a facile method to fabricate a PEDOTbased stretchable electrochemical biosensor for the first time. The functionalized polymer was obtained by straightforwardly incorporating bis(trifluoromethane) sulfonimide lithium salt (LiTFSI) and cobalt phthalocyanine (CoPc) into PEDOT:PSS solution via simply mixing and stirring, forming the complex PEDOT:PSS-LiTFSI-CoPc (PPLC) (Scheme 1A). LiTFSI significantly improved the stretchability and conductivity of the PEDOT:PSS film, and CoPc endowed the film with excellent electrocatalytic property toward the oxidation of H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} (a signaling molecule in diverse biological processes ^(34,35){ }^{34,35} ). As a proof-of-concept, the stretchable PPLC/PDMS sensor was used 在此，我们首次报告了一种制造基于 PEDOT 的可拉伸电化学生物传感器的简便方法。通过简单的混合和搅拌，将双三氟甲烷磺酰亚胺锂盐（LiTFSI）和酞菁钴（CoPc）直接加入 PEDOT:PSS 溶液中，形成复合物 PEDOT:PSS-LiTFSI-CoPc (PPLC)（方案 1A），从而获得功能化聚合物。LiTFSI 明显改善了 PEDOT:PSS 薄膜的拉伸性和导电性，而 CoPc 则赋予了薄膜对 H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} （多种生物过程中的信号分子 ^(34,35){ }^{34,35} ）氧化的优异电催化性能。作为概念验证，使用了可拉伸的 PPLC/PDMS 传感器
to in situ load strains and simultaneously monitor mechanically induced H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} release from human bronchial epithelial cells (Scheme 1B). 同时监测机械诱导的人类支气管上皮细胞 H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} 释放（方案 1B）。
Results and discussion 结果和讨论
Fabrication and characterization of PPLC polymer PPLC 聚合物的制造和表征
The functionalized PPLC polymer was obtained by simple blending of the plasticizer LiTFSI and catalyst CoPc with the solution of PEDOT:PSS. To investigate the microstructures of different polymer systems, PEDOT:PSS (PP), PEDOT:PSS-LiTFSI (PPL) and PPLC films were characterized by using an atomic force microscope (AFM). As a conductive polymer, PP dispersions are typically described as gel-like particles, which are composed of PEDOT-rich cores stabilized by PSS-rich shells in aqueous solvent ^(36,37){ }^{36,37} (Scheme 1A, left), and thus a large number of aggregated small grains appeared in the pristine PP film (Fig. 1A). Meanwhile, after being doped with the plasticizer LiTFSI, the polymer film processed distinct nanofibrous structures with good continuity (Fig. 1B). The morphological change is attributed to that LiTFSI can easily interact with both negatively charged PSS and positively charged PEDOT, and the weakened coulombic interaction between PSS and PEDOT chains allows PEDOT to decouple from the highly coiled PSS and grow into large-scale conducting domains, forming a continuous nanofiber network ^(33){ }^{33} (Scheme 1A, right). Interestingly, the subsequent incorporation of catalyst CoPc molecules had little impact on the fibrous morphology (Fig. 1C), which will be beneficial for retaining the stable conductivity of the stretchable sensor. 功能化 PPLC 聚合物是通过将增塑剂 LiTFSI 和催化剂 CoPc 与 PEDOT:PSS 溶液简单混合而得到的。为了研究不同聚合物体系的微观结构，我们使用原子力显微镜（AFM）对 PEDOT:PSS（PP）、PEDOT:PSS-LiTFSI（PPL）和 PPLC 薄膜进行了表征。作为一种导电聚合物，PP分散体通常被描述为凝胶状颗粒，由富含PEDOT的核和富含PSS的壳组成，并稳定在水性溶剂 ^(36,37){ }^{36,37} 中（方案1A，左图），因此原始PP薄膜中出现了大量聚集的小颗粒（图1A）。同时，在掺入增塑剂 LiTFSI 后，聚合物薄膜形成了明显的纳米纤维结构，并具有良好的连续性（图 1B）。这种形态变化的原因是 LiTFSI 易于与带负电荷的 PSS 和带正电荷的 PEDOT 发生相互作用，PSS 和 PEDOT 链之间的库仑相互作用减弱，从而使 PEDOT 从高度卷曲的 PSS 中脱钩并生长为大尺度的导电畴，形成连续的纳米纤维网 ^(33){ }^{33} （方案 1A，右图）。有趣的是，随后加入的催化剂 CoPc 分子对纤维形态的影响很小（图 1C），这将有利于保持可拉伸传感器的稳定导电性。
Subsequently, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were performed to further characterize the composition of the PPLC/ PDMS film respectively. Compared with that of original PP, the FTIR spectrum of PPLC displayed characteristic absorption 随后，傅立叶变换红外光谱（FTIR）和 X 射线光电子能谱（XPS）分别用于进一步表征 PPLC/ PDMS 薄膜的成分。与原始 PP 相比，PPLC 的傅立叶变换红外光谱显示出特征吸收
Scheme 1 (A) Schematic diagram representing the microstructures of traditional PEDOT:PSS (PP, left) and stretchable PEDOT:PSS (PPLC, right) functionalized with LiTFSI and CoPc. (B) Fabrication of a stretchable PPLC/PDMS film for monitoring cell mechanotransduction. (i) Spin-coating PPLC on PDMS. (ii) Cell seeding and culture. (iii) Electrochemical detection of H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} release from stretched cells. 方案 1 (A) 传统 PEDOT:PSS（PP，左）和用 LiTFSI 和 CoPc 功能化的可拉伸 PEDOT:PSS（PPLC，右）的微结构示意图。(B) 制作用于监测细胞机械传导的可拉伸 PPLC/PDMS 薄膜。(i) 在 PDMS 上旋涂 PPLC。(ii) 细胞播种和培养。(iii) 拉伸细胞释放 H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} 的电化学检测。
Furthermore, UV-visible spectra were recorded to investigate the existing form of the catalyst CoPc in the PPLC film (Fig. 1F). Compared with that of PSS-LiTFSI-CoPc, the spectrum of PPLC showed that the existence of PEDOT made the peak corresponding to the B band of CoPc at 322 nm shift to 335 nm , and the peaks at 619 nm and 694 nm corresponding to the Q bands of CoPc shift to 635 nm and 724 nm , respectively. ^(43){ }^{43} These red shifts in the spectrum revealed that CoPc molecules were assembled on the PEDOT chains via pi-pi\pi-\pi interaction. 此外，还记录了紫外可见光谱，以研究催化剂 CoPc 在 PPLC 薄膜中的存在形式（图 1F）。与 PSS-LiTFSI-CoPc 的光谱相比，PPLC 的光谱显示，由于 PEDOT 的存在，CoPc 在 322 nm 处的 B 带峰移至 335 nm 处，CoPc 在 619 nm 和 694 nm 处的 Q 带峰分别移至 635 nm 和 724 nm 处。 ^(43){ }^{43} 光谱中的这些红色偏移表明 CoPc 分子是通过 pi-pi\pi-\pi 相互作用组装在 PEDOT 链上的。
Mechanical properties of the PPLC/PDMS electrode PPLC/PDMS 电极的机械性能
To evaluate the mechanical properties of the PPLC-based sensor, a homogeneous mixture of PP, LiTFSI and CoPc was spin-coated on the surface of the PDMS film, which was pretreated with polydopamine to improve the wetting of PPLC solution. Due to the morphology of isolated grains, the fracture strain of the PP film is as low as 5%5 \%, because the grains will separate from each other and lead to a rapid decline in conductivity when strains are applied (Fig. S2A †\dagger ). After introducing LiTFSI and CoPc, the electrostatic interaction between PEDOT and PSS could be greatly weakened, which resulted in the structure of conductive PEDOT-rich domains embedded in the soft PSS matrix, and this will theoretically improve the stable conductivity during stretching (Fig. 2A). Since the ionic liquid is the key to realizing the coexistence of high stretchability and conductivity, the amount of LiTFSI ( 1-3wt%1-3 \mathrm{wt} \% ) in the 为了评估基于 PPLC 的传感器的机械性能，在 PDMS 薄膜表面旋涂了 PP、LiTFSI 和 CoPc 的均匀混合物，并用多巴胺对薄膜进行了预处理，以提高 PPLC 溶液的润湿性。由于孤立晶粒的形态，PP 薄膜的断裂应变低至 5%5 \% ，因为在施加应变时晶粒会相互分离，导致电导率迅速下降（图 S2A †\dagger ）。在引入 LiTFSI 和 CoPc 后，PEDOT 和 PSS 之间的静电作用会大大减弱，从而形成富含导电 PEDOT 的结构域，嵌入到软 PSS 基体中，这将在理论上提高拉伸过程中的稳定导电性（图 2A）。由于离子液体是实现高拉伸性和高导电性共存的关键，因此，LiTFSI（ 1-3wt%1-3 \mathrm{wt} \% ）在拉伸过程中的用量应控制在 0.5%以下。
PPL film was optimized by comparing the cyclic voltammetric (CV) characteristics in K_(3)[Fe(CN)_(6)]\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] (an electrochemical probe) solution (Fig. S3A †\dagger ). The CV curves of PPL films with the additive of 2wt%2 \mathrm{wt} \% and 3wt%3 \mathrm{wt} \% LiTFSI had smaller potential differences than that of the PPL film doped with 1wt%1 \mathrm{wt} \% LiTFSI, and they displayed very similar potential differences and electric capacities. Therefore, we chose 2wt%2 \mathrm{wt} \% as the optimal additive amount in PP solution in principle of less addition of LiTFSI. Though the undeformed PPL/PDMS films spin-coated at a speed of 1000rpm,1500rpm,2000rpm1000 \mathrm{rpm}, 1500 \mathrm{rpm}, 2000 \mathrm{rpm} and 3000 rpm had similar electrochemical performances (Fig. S3B †\dagger ), the PPL/ PDMS film of 1500 rpm had the least cracks after recovering from being stretched to a strain of 50%50 \% and the most stable electrochemical performance (Fig. S4 and S5†). As a result, 2 wt%\mathrm{wt} \% LiTFSI and 1500 rpm speed for 60 s were selected as the optimal conditions for the fabrication of PPL/PDMS and PPLC/ PDMS films, and the thickness of spin-coated PPLC was approximately 400 nm (Fig. S6†\mathrm{S} 6 \dagger ). Besides, we examined the electrical conductivities of PPL and PPLC, and they were 1798.2 +-348.4\pm 348.4 and 1036.2+-120.5Scm^(-1)1036.2 \pm 120.5 \mathrm{~S} \mathrm{~cm}^{-1}, respectively. These results revealed that the doping of the ionic liquid LiTFSI dramatically improved the electrical conductivity of PP whose reported electrical conductivity is about 4Scm^(-1)4 \mathrm{~S} \mathrm{~cm}^{-1}. ^(33){ }^{33} 通过比较 K_(3)[Fe(CN)_(6)]\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] （一种电化学探针）溶液中的循环伏安 (CV) 特性，对 PPL 薄膜进行了优化（图 S3A †\dagger ）。添加了 2wt%2 \mathrm{wt} \% 和 3wt%3 \mathrm{wt} \% LiTFSI 的 PPL 薄膜的 CV 曲线的电位差比掺杂了 1wt%1 \mathrm{wt} \% LiTFSI 的 PPL 薄膜的 CV 曲线的电位差小，而且它们显示的电位差和电容量非常相似。因此，我们选择 2wt%2 \mathrm{wt} \% 作为聚丙烯溶液中的最佳添加量，原则是减少 LiTFSI 的添加量。虽然以 1000rpm,1500rpm,2000rpm1000 \mathrm{rpm}, 1500 \mathrm{rpm}, 2000 \mathrm{rpm} 和 3000 rpm 的速度旋涂的未变形 PPL/PDMS 薄膜具有相似的电化学性能（图 S3B †\dagger ），但 1500 rpm 的 PPL/PDMS 薄膜在拉伸到 50%50 \% 的应变恢复后裂纹最少，电化学性能最稳定（图 S4 和 S5†）。因此，我们选择 2 wt%\mathrm{wt} \% LiTFSI 和 1500 rpm 转速 60 s 作为制备 PPL/PDMS 和 PPLC/ PDMS 薄膜的最佳条件，旋涂 PPLC 的厚度约为 400 nm（图 S6†\mathrm{S} 6 \dagger ）。此外，我们还检测了 PPL 和 PPLC 的电导率，它们分别为 1798.2 +-348.4\pm 348.4 和 1036.2+-120.5Scm^(-1)1036.2 \pm 120.5 \mathrm{~S} \mathrm{~cm}^{-1} 。这些结果表明，离子液体 LiTFSI 的掺杂大大提高了聚丙烯的电导率，据报道聚丙烯的电导率约为 4Scm^(-1)4 \mathrm{~S} \mathrm{~cm}^{-1} 。 ^(33){ }^{33}
To compare the stretchability of different films, the morphologies of PP, PPL and PPLC films were characterized after they were loaded with a series of tensile strains (10-100%) and then released to the original states. The pristine PP film obviously exhibited many wide vertical cracks (ca. 30 mum30 \mu \mathrm{~m} in width) after suffering from only 10%10 \% strain, and the cracks became sharply larger with the increase of mechanical strains (Fig. S2B †\dagger ). In contrast, the surface of the PPL/PDMS film kept smooth even with a strain of 50%50 \%, and only few hairline cracks appeared when stretched up to 100% (Fig. S7, †\dagger top row). Scanning electron microscope (SEM) results showed that the PPL film maintained high integrality within the 50%50 \% strain, and uniform wrinkles and very few tiny cracks (ca. 500 nm in width) were observed under 100%100 \% strain due to the buckling of the PPL 为了比较不同薄膜的拉伸性，我们对 PP、PPL 和 PPLC 薄膜施加一系列拉伸应变（10%-100%）并恢复原状后的形态进行了表征。原始 PP 薄膜在仅承受 10%10 \% 应变后明显出现许多宽垂直裂纹（宽度约 30 mum30 \mu \mathrm{~m} ），并且随着机械应变的增加，裂纹急剧变大（图 S2B †\dagger ）。相比之下，PPL/PDMS 薄膜的表面即使在应变 50%50 \% 的情况下也能保持光滑，拉伸到 100%时也只出现了很少的毛细裂纹（图 S7， †\dagger 顶行）。扫描电子显微镜（SEM）结果表明，PPL 薄膜在 50%50 \% 应变范围内保持了较高的整体性，在 100%100 \% 应变范围内，由于 PPL 的屈曲，观察到了均匀的皱纹和极少的微小裂纹（宽度约 500 nm）。
Fig. 2 (A) Schematic illustration showing the stretchability principle of the PPLC film. (B) Optical microscope (left) and SEM (right) images of the PPLC/PDMS film recovering from being submitted to various strains. Scale bar: 100 mum100 \mu \mathrm{~m} (black) and 10 mum10 \mu \mathrm{~m} (white). CVs of the PPLC/PDMS film obtained in 10mMK_(3)[Fe(CN)_(6)](C)10 \mathrm{mM} \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right](\mathrm{C}) under different tensile strains and (D) after recovering from being bent at different radii (scan rate: 0.05Vs^(-1)0.05 \mathrm{~V} \mathrm{~s}^{-1} ). Statistical results of the CVs of PPLC/PDMS films obtained in 10mMK_(3)[Fe(CN)_(6)]10 \mathrm{mM} \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] after recovering from being (E) stretched to 50%50 \% and (F) bent at a radius of 3 mm for different cycles. 图 2 (A) PPLC 薄膜的拉伸原理示意图。(B) PPLC/PDMS 薄膜在受到各种应变后的光学显微镜（左）和扫描电子显微镜（右）图像。比例尺： 100 mum100 \mu \mathrm{~m} （黑色）和 10 mum10 \mu \mathrm{~m} （白色）。在 10mMK_(3)[Fe(CN)_(6)](C)10 \mathrm{mM} \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right](\mathrm{C}) 中获得的 PPLC/PDMS 薄膜在不同拉伸应变下的 CV 值，以及 (D) 以不同半径弯曲（扫描速率： 0.05Vs^(-1)0.05 \mathrm{~V} \mathrm{~s}^{-1} ）后恢复的 CV 值。在 10mMK_(3)[Fe(CN)_(6)]10 \mathrm{mM} \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] 中得到的 PPLC/PDMS 薄膜在 (E) 拉伸到 50%50 \% 和 (F) 以 3 mm 为半径弯曲不同周期后的 CV 统计结果。
composite (Fig. S7,† bottom row), manifesting that it was the LiTFSI additive that greatly improved the stretchability of the PPL film. As for the PPLC/PDMS film (Fig. 2A), similar to that of the PPL film, optical microscope images displayed that few short cracks appeared until the film was stretched up to 100%100 \%, and SEM images revealed that few perceptible wrinkles started to form when stretched to a strain of 50%50 \% (Fig. 2B and S8†\mathrm{S} 8 \dagger ). Whereas, the appeared cracks did not affect the overall continuity and stability of the PPLC film even under 100%100 \% strain. 复合材料（图 S7† 底行），这表明正是 LiTFSI 添加剂极大地改善了 PPL 薄膜的拉伸性。至于 PPLC/PDMS 薄膜（图 2A），与 PPL 薄膜类似，光学显微镜图像显示，在薄膜拉伸到 100%100 \% 时，很少出现短裂纹，而扫描电镜图像显示，当拉伸到应变 50%50 \% 时，开始形成一些可察觉的皱纹（图 2B 和 S8†\mathrm{S} 8 \dagger ）。而出现的裂纹即使在 100%100 \% 应变下也不会影响 PPLC 薄膜的整体连续性和稳定性。
To study the electrical stability of the PPLC-based stretchable sensor, the relative resistance (Delta R//R_(0))\left(\Delta R / R_{0}\right) of the PPLC/PDMS film was recorded in the stretching-releasing cycle ( 0-50-0%0-50-0 \% ) and bending process, and no significant increase in Delta R//R_(0)\Delta R / R_{0} occurred during the dynamic deformations, as well as stretching ( 50%50 \% strain) and bending (a radius of 1 mm ) for 1000 cycles, respectively (Fig. S9†). The almost invariable resistance revealed the stable conductivity in the PPLC polymer. Then, to investigate the electrochemical stability, CVs of the PPLC/PDMS film in K_(3)[Fe(CN)_(6)]\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] solution were collected after subjected to different mechanical deformations, including stretching to various tensile strains ( 0-50%0-50 \% ), bending with different radii ( 0.5-12.5mm0.5-12.5 \mathrm{~mm} ) and repeated loading. The potentials and peak currents of ferricyanide showed high consistency even when the PPLC/PDMS film was stretched with a strain of up to 90%90 \% (Fig. 2C) or bent with a small radius of 0.5 mm (Fig. 2D). Moreover, the currents of reduction (ip_(1))\left(\mathrm{ip}_{1}\right) and oxidation (ip_(2))\left(\mathrm{ip}_{2}\right) peaks and their potential differences ( DeltaE_(p)\Delta E_{\mathrm{p}} ) of the recorded CVs were further analyzed after being repeatedly stretched to a strain of 50%50 \% and bent to a curvature radius of 3 mm for different cycles (Fig. 2E, F and S10 †\dagger ), and they had little change compared with the original undeformed states. The superior electrochemical stability is probably attributed to the percolation network of nanofibrous PEDOT:PSS, which could accommodate the applied strain by rotating and sliding against each 为了研究基于 PPLC 的可拉伸传感器的电稳定性，在拉伸-释放循环（ 0-50-0%0-50-0 \% ）和弯曲过程中记录了 PPLC/PDMS 薄膜的相对电阻 (Delta R//R_(0))\left(\Delta R / R_{0}\right) ，在动态变形过程中，以及分别拉伸（ 50%50 \% 应变）和弯曲（半径为 1 mm）1000 次循环过程中， Delta R//R_(0)\Delta R / R_{0} 没有显著增加（图 S9†）。几乎不变的电阻表明 PPLC 聚合物具有稳定的导电性。然后，为了研究电化学稳定性，我们采集了 K_(3)[Fe(CN)_(6)]\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] 溶液中的 PPLC/PDMS 薄膜在受到不同机械变形（包括拉伸到各种拉伸应变（ 0-50%0-50 \% ）、不同半径弯曲（ 0.5-12.5mm0.5-12.5 \mathrm{~mm} ）和重复加载）后的 CV 曲线。即使 PPLC/PDMS 薄膜受到高达 90%90 \% 的应变拉伸（图 2C）或以 0.5 mm 的小半径弯曲（图 2D），铁氰化钾的电位和峰值电流也表现出高度的一致性。此外，在反复拉伸到应变 50%50 \% 和弯曲到曲率半径为 3 mm 的不同周期后，进一步分析了记录的 CV 的还原 (ip_(1))\left(\mathrm{ip}_{1}\right) 和氧化 (ip_(2))\left(\mathrm{ip}_{2}\right) 峰的电流及其电位差 ( DeltaE_(p)\Delta E_{\mathrm{p}} ) （图 2E、F 和 S10 †\dagger ），它们与原始未变形状态相比变化不大。优异的电化学稳定性可能归功于纳米纤维状 PEDOT:PSS 的渗滤网络，它可以通过旋转和相互滑动来适应所施加的应变。
other. The slight increase in ip and DeltaE_(p)\Delta E_{\mathrm{p}} in the case of higher strain (e.g. 90%) or being recovered from stretching for more cycles might be attributed to a combined result of more exposed PEDOT:PSS nanofibers (larger electrode area and ip) and some irreversible interlacement with others (higher electrical resistivity and DeltaE_(p)\Delta E_{\mathrm{p}} ). Overall, these results clearly demonstrated the excellent electrochemical stability of the PPLC-based stretchable electrode against mechanical deformations. 其他。在拉伸应变较大（如 90%）或拉伸循环次数较多的情况下，ip 和 DeltaE_(p)\Delta E_{\mathrm{p}} 略有增加，这可能是 PEDOT:PSS 纳米纤维暴露较多（电极面积和 ip 较大）以及与其他纳米纤维发生不可逆置换（电阻率和 DeltaE_(p)\Delta E_{\mathrm{p}} 较高）的综合结果。总之，这些结果清楚地表明，基于 PPLC 的可拉伸电极具有出色的电化学稳定性，能够抵御机械变形。
Moreover, compared with other electrode materials of stretchable electrochemical sensors, the prominent feature of water-soluble PPLC is the high processability, and many processing techniques could be employed for convenient, controllable and high-throughput electrode fabrication. For example, the pattern and size of the PPLC-based electrode could be easily regulated with the aid of photolithography or an ink-jet printer (Fig. S11†). Convincingly, the superb processibility will make PPLC hold great potential application in various flexible and stretchable sensors. 此外，与其他可拉伸电化学传感器的电极材料相比，水溶性 PPLC 的突出特点是可加工性强，可采用多种加工技术方便、可控、高通量地制造电极。例如，可以借助光刻技术或喷墨打印机轻松调节基于 PPLC 的电极的图案和尺寸（图 S11†）。令人信服的是，PPLC 极佳的可加工性将使其在各种柔性和可拉伸传感器中拥有巨大的应用潜力。
Electrochemical sensing performance of the PPLC/PDMS film PPLC/PDMS 薄膜的电化学传感性能
The electrochemical performance of the PPLC/PDMS film was studied after the confirmation of its mechanical stability. Compared with the PP/PDMS electrode, the electrochemical performance of the PPL/PDMS electrode was greatly improved because of the increased conductivity caused by doping LiTFSI. The CV of the PPLC/PDMS electrode was almost the same as that of the PPL/PDMS film, which indicated that the addition of CoPc had little effect on the electron transfer in the original PPL/PDMS electrode (Fig. 3A). Meanwhile, as an electron mediator, CoPc could endow the electrode with remarkable sensing ability by catalyzing the target molecules involved in cell activities, such as the oxidation of H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} to O_(2)\mathrm{O}_{2} via a redox reaction between Co^(II)Pc\mathrm{Co}^{\mathrm{II}} \mathrm{Pc} and Co^("III ")Pc\mathrm{Co}^{\text {III }} \mathrm{Pc} (Fig. 3B). ^(44){ }^{44} It was observed 在确认了 PPLC/PDMS 薄膜的机械稳定性之后，对其电化学性能进行了研究。与 PP/PDMS 电极相比，PPL/PDMS 电极的电化学性能因掺杂 LiTFSI 后电导率的提高而大大改善。PPLC/PDMS 电极的 CV 值与 PPL/PDMS 薄膜的 CV 值基本相同，这表明 CoPc 的加入对原 PPL/PDMS 电极的电子传递影响很小（图 3A）。同时，作为电子介质，CoPc 可以催化参与细胞活动的目标分子，如通过 Co^(II)Pc\mathrm{Co}^{\mathrm{II}} \mathrm{Pc} 和 Co^("III ")Pc\mathrm{Co}^{\text {III }} \mathrm{Pc} 之间的氧化还原反应将 H_(2)O_(2)\mathrm{H}_{2} \mathrm{O}_{2} 氧化为 O_(2)\mathrm{O}_{2} ，从而赋予电极显著的传感能力（图 3B）。 ^(44){ }^{44} 据观察
