Recent Advancements in Bipolar Electrochemical Methods of Analysis

Abstract

The goal of this review is to provide an overview of the advancements made in the field of bipolar electrochemistry over the past 2 years, with an emphasis on analysis. Bipolar electrodes (BPEs) are versatile, and in electroanalysis, they have been used extensively to screen electrocatalysts(1−4) and to sense biomarkers.(5−10) Their ability to modulate local electric fields lends them to the manipulation of cells and to the enrichment and separation of analytes.(11−17) Finally, by virtue of the polar and often graded profile of the interfacial potential across BPEs, they provide a platform for synthesis of Janus particles, useful as sensors and as microswimmers(18−22) and other materials with compositional gradients.(23,24) BPEs are particularly well-suited to analytical challenges that demand multiplexing or amenability to point-of-need (PON) application because even large arrays of BPEs can be controlled with simple equipment yet yield quantitative information about a system. In this review, we discuss recent progress in reactions that transduce current to a visible signal, sensing mechanisms, bipolar electrochemical cell design, integration of bipolar electrochemistry with spectroscopic techniques, BPEs at the nanoscale, and the application of BPEs to electrokinetics and materials preparation. Throughout the discussion, we identify promising trends, innovative directions, and remaining challenges in the field. Disciplines Disciplines Analytical Chemistry Comments Comments

Filtering and continuously separating microplastics from water using electric field gradients formed electrochemically in the absence of buffer

“…In this report, we present detailed experimental results and nite element simulations aimed at understanding electrokinetics within microchannels that contain a bipolar electrode (BPE) and unbuffered electrolyte solution. This study is in contrast to earlier, related results from our group 1,2 and others [3][4][5] that relied on buffered solutions to modulate the local electric eld in microchannels. Our new ndings reveal that faradaic water hydrolysis at a BPE modulates both the ionic conductivity and the ionic current passing through an unbuffered solution.…”

“…When a sufficiently high voltage is applied across the length of the microuidic channel, water electrolysis occurs at the ends of the BPE. 5,29,30 For example, water reduction occurs at the BPE cathode to form OH À (eqn (1)). If Tris buffer is present in solution, then OH À reacts with TrisH + to yield neutral Tris (eqn (2)).…”

Control of Interfacial Potentials and Redox Reactions on Bipolar Electrodes Using Ag/AgCl

“…The current generated by the electrode reaction flows through the working and auxiliary electrodes. In contrast to this traditional setup, bipolar electrochemical systems have been used for electroanalysis since the beginning of the 21st century [4][5][6][7][8][9], particularly to solve problems related to integrating the many working electrodes required for multiplexing [10][11][12]. The application field of this technique is steadily expanding, with recent reports on its use for the detection of H 2 O 2 [13][14][15], glucose [15], uric acid [15], ATP and tobramycin [16], aflatoxin B1 [17], microRNA [18][19], αfetoprotein [20], carcinoembryonic antigen [20][21], prostate-specific antigen [22], alkaline phosphatase [23], and MCF-7 cells [14], as well as for the measurement of Cas9 activity [24].…”

Redox Cycling at an Array of Interdigitated Bipolar Electrodes for Enhanced Sensitivity in Biosensing**

“…BPEs have found application in many areas including electrochemical imaging, 1 electrokinetic separations, 2-5 materials synthesis, 6,7 electrocatalyst screening, 8 micromotors, 9,10 singlecell analysis, [11][12][13] visual voltammetry, 14,15 point-of-care sensing 16 and biosensing. 17 Recent advancements in bipolar electrochemical methods of analysis are discussed in a recent review by Rahn et al 18 A BPE comprises a conductor immersed in an electrolyte solution. When a potential is applied to the electrolyte by an external pair of driving electrodes, the interfacial potential difference that develops between the solution and the BPE drives faradaic reactions at its opposing ends (Scheme 1).…”

“…BPEs have found application in many areas including electrochemical imaging, [1] electrokinetic separations, [2–5] materials synthesis, [6,7] electrocatalyst screening, [8] micromotors, [9,10] single‐cell analysis, [11–13] visual voltammetry, [14,15] point‐of‐care sensing [16] and biosensing [17] . Advancements in bipolar electrochemical methods of analysis are discussed in a recent review by Rahn et al [18] . A BPE comprises a conductor immersed in an electrolyte solution.…”