Electrochemiluminescence on bipolar electrodes for visual bioanalysis

Rapid and sensitive detection of tumor biomarkers plays a critical role in the early diagnosis of cancer and better understanding of disease progression. We report here a novel wireless electrochemiluminescence (ECL) strategy for visualizing prostate-specific antigen (PSA) on the basis of electrical switch control of ECL generation on bipolar electrodes (BPEs). The visual device comprises a two-channel microfluidic chip with two indium tin oxide (ITO) bands with a gap of 200 μm. The gap between the two ITO bands in one channel could be regarded as an electrical switch, the conductivity of which controls ECL generation on the ITO bands in the other channel, which are used as bipolar electrodes (BPEs). The electronic conductivity of the electrical switch could be tuned by PSA guided silver particles deposition via an immunosandwich assembly and a silver enhancement strategy. At the "on" state of the electrical switch, PSA induced deposition of silver particles forms an electronic circuit between the adjacent BPEs and makes them behave like a continuous H-shaped BPE, which results in only one ECL signal. Meanwhile, the external voltage for driving the oxidation reactions of Ru(bpy)32+ and TPA is significantly reduced compared with the "off" state. This important characterization of the electrical switch could eliminate the background signal and enable a sensitive measurement of PSA by observing the ECL lightspots on BPEs, providing a simple and sensitive visual means of detecting cancer biomarkers. Besides, this two-channel design avoids the chemical interference between sensing and reporting reactions. Combining the advantages of BPE and the high visual sensitivity of the electrical switch, it could be easily expected to achieve sensitive screening of other biomarkers.