From Bench to Bedside: Realizing On-Chip Electrophoretic Immunoassays for Protein Biomarkers Using a Standard 9V Battery

While significant recent attention has been paid to point-of-care (POC) screening diagnostics, innovation in confirmatory diagnostics has lagged. Critically important to infectious disease diagnosis (HIV, hepatitis C), confirmation of a positive screening result requires robust quantitation of biomarkers. Analytical grade performance – not simply the ‘yes/no’ screening readout (lateral flow, ‘dip stick’ assays) – is a hallmark of confirmatory tests. To this end, powerful bench-top electrophoretic immunoassays routinely provide robust, quantitative results that directly inform patient treatment. Nevertheless, a major technological gap exists.  Electrophoresis drives species to differentially electromigrate through a sieving matrix, thus yielding protein specific identifying information – but thousands of volts are needed to drive separations over centimeters of separation length. Consequently, the resources (power, time, material, labor) demanded by electrophoresis severely limit POC applicability. To move electrophoretic immunoassays from the bench to the POC, we report the first, to our knowledge, confirmatory grade electrophoretic assay designed for use with a standard 9V battery.  Key to our design strategy is an immunoassay that requires only a single, ultra-short (300 um) separation channel with 2 terminal fluid reservoirs to inject a moving boundary (front of material).  In contrast, conventional approaches define a ‘plug’ (not a front) of material in the separation channel and, thus, require 2 intersecting channels (mm-to-cm in length) and 4 fluid ports. Consequently, owing to the millimeters of separation distance demanded by on-chip electrophoretic assays, applied potentials of ~ 10³ V are routine. The striking reduction in power realized here stems from rational device, separation matrix, and assay design.  A standard battery technology is now feasible in lieu of bulky, expensive high voltage supplies. We will further detail the minimum power requirements, as well as sources of dispersion. By surmounting power and time shortcomings, we make electrophoretic immunoassays feasible at the POC for the first time.  This versatile diagnostic format paves the way for analytical quality in near-patient, emergency, and global health settings including compatibility with cellular phone technologies.