Microfluidic-based ion-selective thermoplastic electrode array for point-of-care detection of potassium and sodium ions.

A microfluidic paper-based thermoplastic electrode (TPE) array has been developed for point-of-care detection of Na+ and K+ ions using a custom-made portable potentiometer. TPEs were fabricated using polystyrene as the binder and two different types of graphite to compare the electrode performance. The newly designed TPE array embedded in a polymethyl methacrylate chip consists of two working electrodes modified with carbon black nanomaterial and an ion-selective membrane, and an all-solid-state reference electrode modified with Ag/AgCl ink and poly(butyl methacrylate-co-methyl methacrylate) membrane via drop-casting. Ion-selective membrane compositions and conditioning steps were optimized. Under optimized conditions, ion-selective TPEs demonstrated fast response time (4 s) and good stability. The TPE array demonstrated a Nernstian behavior for K+ with a sensitivity of 59.2 ± 0.2 mV decade-1 and near-Nernstian response for Na+ with a sensitivity of 54.0 ± 1.1 mV decade-1 in the range 10-1 - 10-4 M and 1 -  10-3 M, respectively. The detection limits were 1 × 10-5 M and 1 × 10-4 M for K+ and Na+, respectively. In addition, a K+ and Na+ selective microfluidic paper-based analytical device (µPAD) was applied to artificial serum analysis and found in good agreement with average recoveries of 101.3% and 99.7%, respectively, suggesting that the developed ISE array is suitable for detection of sodium and potassium in complex matrix.