LAUSR

A simple and low-cost continuous flow (CF) electrochemical paper-based analytical device (ePAD) coupled with thermoplastic electrodes (TPE) was developed. The fast, continuous flow combined with flow injection analysis was made possible by adding two inlet reservoirs to the same paper-based hollow channel flowing over detection electrodes, terminating in a fan-shaped pumping reservoir. The upstream inlet reservoir was filled with buffer and provided constant flow through the device. Sample injections were performed by adding 2 L of sample to the downstream sample inlet. Differences in flow resistance resulted in sample plugs displacing buffer as the solution flowed over the working electrodes. The electrodes were fabricated by mixing carbon black and polycaprolactone (50 % w/w). CF-TPE-ePADs were characterized with chronoamperometry using ferrocenylmethyl trimethylammonium as the electrochemical probe. Optimized flow rates and injection volumes gave analysis times roughly an order of magnitude faster than previously reported flow injection analysis ePADs. To demonstrate applicability, the CF-TPE-ePADs were used to quantify caffeic acid in three different tea samples. The proposed method had a linear range from 10 to 500 µmol L-1 and limit of detection and quantification of 2.5 and 8.3 μmol L-1, respectively. Our approach is promising for fabricating simple, inexpensive yet high performance flow injection analysis devices using paper substrates and easy to make electrodes that do not require external mechanical pumping systems or complicated valves.