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Self-Powered Bipolar Electrochromic Electrode Arrays for Direct Displaying Applications Xiaowei Zhang, Lingling Zhang, Qingfeng Zhai, Wenling Gu, Jing Li, and Erkang Wang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b00054 • Publication Date (Web): 09 Feb 2016 Downloaded from http://pubs.acs.org on February 9, 2016
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Analytical Chemistry
Self-Powered Bipolar Electrochromic Electrode Arrays for Direct Displaying Applications Xiaowei Zhang,‡ a,b Lingling Zhang,‡a,b Qingfeng Zhai, a,b Wenling Gu,a,b Jing Li,a,b* and Erkang Wanga,b* a
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, P. R. China b University of Chinese Academy of Sciences, Beijing, 100049, P. R. China ABSTRACT: Here we report a self-powered bipolar electrochromic electrode (termed SP-BP-EC-E) array for the displaying applications including catalyst screening, catalytic activity measurement and enzyme substrate quantification. By replacing the directional (or active) power source with the isotropic chemical energy to drive the bipolar electrochemical reaction, the driving background signal, bipolar electrode (BPE) background signal, uneven reporting signal and the influence of electrolysis which commonly appear in traditional bipolar systems are effectively eliminated from origin. Thus, the reporting signals from the SP-BP-EC-E arrays can be more direct and reliable to reflect the target nature. Such SP-BP-EC-E platform exhibits sensitive response towards the fast analysis of commercial Pt black catalyst, NiPdAu hollow nanospheres, glucose dehydrogenase and glucose. To our knowledge, this test paper-like SP-BP-EC-E is the simplest platform for high-throughput screening to date, which offers a very convenient approach for non-professional people to access the complicated screening and fast analysis of the electrocatalysts and biocatalyst activity and quantification of enzymatic substrates.
Over the past two decades, special attention has been paid in bipolar electrochemistry, 1-3which offers an easy approach to control large-scale bipolar electrodes (BPEs) through an electric field across the solution for various applications. Manz and co-workers first introduced the Ru(bpy)32+ to the bipolar system as the signal reporter and developed a wireless electrochemiluminescence (ECL) sensors.4 Later, Crooks' group proved that there exists a strict quantitative relationship between the two reactions occuring at both ends of the BPE.5 These two principles open up a new way for various applications covering biosensing,6-14 micro motion control and monitoring,15, 16 analyte separation and enrichment,17 electrochemical synthesis,18 and catalyst screening.19-22 However, the need of an active (or directional) driving electric field has become a critical bottleneck limiting the practical application of the bipolar system: (1) Driving potential (Etot) optimization is quite complicated, although it can be approximatively calculated through the ideal formula in open BPE system: ∆Eelec=Etot(lchannel/lelec).1, 2 Unsuitable driving voltage will cause the low output signal or high background signal (BPE background). (2) In a confined cell, the electric field can hardly be even (influenced by cell shape and volume, location and area of the driving electrode, electrolysis of solution, and the location of the BPE), leading to the uneven signal output from a BPE array.1, 2 (3) The electrolysis at the driving electrode (≥ target reactions) may cause a gradient (concentration or pH) across the cell which will further influence the reaction occuring at BPEs from different site of the array. (4) Reactions occuring at the driving electrode in an open bipolar system will cause an overwhelming background signal (driving back-
ground).4 Besides above problems, the external power supply also enlarges the size and decreases the portability of a bipolar device. Based on these consideration, it becomes a contradiction that we want an active and portable power supply to parallelly drive the BPEs at different site without interference at the same time. Thus, the designing of new driving mode is highly desirable yet a great challenge for the bipolar electrochemistry. Electrocatalysts have received increasing attention owing to their important role in the fuel cell industry.23 Therein, Screening new electrocatalysts with high catalytic activity is of critical importance.24 The most common method employed is to test the electrocatalytic behaviour of a catalyst with an electrochemical workstation, which is an information-rich method offering detailed kinetics parameters. However, the handling and interpretation of the obtained results of such method seems a bit difficult for the non-professional people. Moreover, the throughput of this method has become a critical bottleneck. Based on the bipolar electrochemistry, ECL25, fluorescence 21, and metal electrodissolution19 have been coupled to the catalytic reactions for the fast and easy screening of catalyst, even they can hardly provide as much kinetic information as the traditional methods.22 Inspired by these important works, our group developed a bipolar electrochromic electrode as a renewable platform for the rapid and facile screening of catalysts.26 Nevertheless, all these studies may face the similar challedge of the bipolar system mentioned above. Besides, the displaying of enzymes (critical biocatalysts in many biopro-
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Analytical Chemistry
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cess) based on the bipolar electrochemistry has remained untouched. In this study, we demonstrate for the first time that a nondirectional power source (the chemical energy), can be used to drive the bipolar system and developed a self-powered electrochromic sensing platform for high-throughput screening applications based on the bipolar electrochemistry. As shown in Scheme 1, the self-powered bipolar electrochromic electrode (SP-BP-EC-E) is a BPE with one end decorated with an electrochromic material and the other end covered with a catalyst or enzyme. Once the electrode potentials of the electrochromic reaction and the catalytic reaction match each other (ERed
