Rapid Analysis in\nContinuous-Flow Electrochemical\nPaper-Based Analytical Devices

Abstract

A simple and low-cost\ncontinuous-flow (CF) electrochemical paper-based\nanalytical device (ePAD) coupled with thermoplastic electrodes (TPEs)\nwas developed. The fast, continuous flow combined with flow injection\nanalysis was made possible by adding two inlet reservoirs to the same\npaper-based hollow channel flowing over detection electrodes, terminating\nin a fan-shaped pumping reservoir. The upstream inlet reservoir was\nfilled with buffer and provided constant flow through the device.\nSample injections were performed by adding 2 μL of the sample\nto the downstream sample inlet. Differences in flow resistance resulted\nin sample plugs displacing buffer as the solution flowed over the\nworking electrodes. The electrodes were fabricated by mixing carbon\nblack and polycaprolactone (50% w/w). CF-TPE-ePADs were characterized\nwith chronoamperometry using ferrocenylmethyl trimethylammonium as\nthe electrochemical probe. Optimized flow rates and injection volumes\ngave analysis times roughly an order of magnitude faster than those\nof previously reported flow injection analysis ePADs. To demonstrate\napplicability, the CF-TPE-ePADs were used to quantify caffeic acid\nin three different tea samples. The proposed method had a linear range\nfrom 10 to 500 μmol L^–1 and limits of detection\nand quantification of 2.5 and 8.3 μmol L^–1, respectively. Our approach is promising for fabricating simple,\ninexpensive, yet high-performance, flow injection analysis devices\nusing paper substrates and easy-to-make electrodes that do not require\nexternal mechanical pumping systems or complicated valves.