All-Additive Solution Processed Silver/Silver Chloride Reference Electrode for Handheld Ion-Sensitive Field-Effect Transistor Sensing System

Silver/silver chloride (Ag/AgCl) reference electrodes (REs) for ion-sensitive field-effect transistors (ISEFTs) are fabricated using all-additive solution processes based on dispensing of Ag paste on large-size plastic substrate, which has the advantages of vacuum-free low-cost manufacturing with great material saving and capability of constructing miniaturized electrochemical systems. After deposition of a polyvinyl butyral protective layer on top, the fabricated Ag/AgCl REs can maintain stable electrochemical potential in KCl solution with a negligible drift rate of 0.37 mV/h and remain stable under different light conditions and in different electrolyte solutions over a wide range of concentration from 10
⁻⁷
to 10
⁻¹
 mol/L. ISFET measurements for hydrogen ions using the fabricated RE combing with an indium tin oxide working electrode show a high sensitivity of 58.47 mV/pH with excellent linearity in a wide range from
${\text{pH}}= {\text{2}}$
to
${\text{pH}}= {\text{12}}$
. Finally, the feasibility of the reliable Ag/AgCl RE is demonstrated by constructing a handheld ISFET pH measurement system with a calibration program to effectively compensate the variations among different samples and directly convert the measured signals to pH values.