Switchable Electrode-Enabled High-Density Two-Dimensional Chips: A Simple, Generalizable Approach to Yield...

Compact, microfluidic devices integrating a high density of electrochemical sensors can play a relevant role in biomedical applications by enabling high-throughput analyses. Although broadly used, planar electrode architectures encounter obstacles in devising ultradense devices due to their high number of conductive lines/pads. To address this issue, we present a user-friendly and generalizable concept that lies in switching the contacts of equal-sized planar electrodes, with all of them acting as working (WEs) and quasi-reference electrodes (QREs) across measurements in series. This two-electrode assembly notably decreases the number of lines/pads compared to conventional sensors, enabling the integration of diverse sensors on a compact microfluidic chip. Hundreds of sensors (100-120) with Au electrodes were microfabricated on small-sized glass wafer and coupled with microfluidics through reversible bonding on polydimethylsiloxane. Some QREs (2-6) were electrically connected together to ensure proper functioning of the electrochemical cells. Despite the increase in ohmic drop as QREs furthest from WEs were activated, six shorted QREs could match the performance of a conventional system. Importantly, surface characterization and electrochemical outcomes have evidenced two key properties, i.e., switching electrodes between QRE and WE roles does not impact their interfacial properties and equal-sized electrodes can successfully act as QREs even when presenting modified and passivated surfaces. The device demonstrated reliable working across three proof-of-concept applications, i.e., (i) cancer cell (MDA-MB-231 line) proliferation monitoring, (ii) Mpox virus biomarker detection using an immunosensor, and (iii) electrode fouling-prone determination of phosphate for health purposes. The switchable equal-sized planar electrodes may offer a broadly adaptive solution for easily engineering high-density, fully integrated, and compact multisensor devices toward high-throughput assays from multiple, fast measurements in series using a handheld one-channel potentiostat.