Point-of-care testing (POCT) generally refers to the implementation of laboratory tests near the patient with the goal to minimize turnaround time, reduce medical cost, and improve medical outcome. The aim of this research is to develop, validate, and optimize a preliminary POCT system for body fluid diagnostics using our existing analytical platform, Rotating Sample System (RSS). The RSS is a convective platform for different optical and electrochemical analyses in microliter-sized samples.
In this work we have developed a reagent-free electrochemical micro pH-stat for in vitro enzyme assays where a titrant of acid or base is produced by water electrolysis on the RSS platform. As water electrolysis induces no volume change and the current that generates the reagent can be precisely measured even at low levels, very small samples in the 1-20 μL volume range become accessible for pH-stating: a reduction of more than an order of magnitude in specimen size relative to the most conventional methods. More importantly, analysis using untreated biological sample is feasible as turbidity would not influence pH-stat measurement. The RSS micro pH-stat effectively operates as a galvanostat with an output range of ±0.1-100 μA and can withstand sample impedance up to 100 kΩ. The cathodic current efficiency is virtually 100% in both buffer and serum samples. Results of cholinesterase activities in both buffer and serum using the proposed reagent-free pH-stat have been validated with standard optical techniques (r2 ≥ 0.97). This novel technique hence has great potential to become a miniaturized analyzer for point-of-care diagnostics.