Electrochemical determination of captopril using a disposable graphite electrode modified with a molecularly imprinted film, accompanied by a ratiometric read-out†

In this research paper, a novel “signal on–off” ratiometric-based electrochemical platform was developed for the sensitive and selective detection of captopril. Ratiometric responses were achieved by fabricating molecularly imprinted polymers (MIPs) on the surface of a graphite electrode (GE) decorated with nitrogen (N) and sulfur (S) co-doped porous carbon and silver nanoparticles (Ag). The MIP layer was formed via electropolymerization of copper coordinated with pyrrole-3-carboxylic acid (functional monomer). Silver nanoparticles (Ag) were incorporated to enhance conductivity and surface area and to serve as an internal reference output. Upon the addition of captopril, there was a decrease in the anodic oxidation current of Ag⁺ at around 0.067 V, coupled with an increase in the oxidation current at 0.54 V (Ag–captopril complex). Under optimized conditions, the electrochemical responses (I_{Ag–captopril}/I_Ag) increased linearly with increasing captopril concentration in the range of 1–450 nM, with a detection limit (S/N = 3) of 0.3 nM. The ratiometric-based MIP electrochemical platform (Cu-MIP/NS-PC@Ag/GE) was successfully applied to detect captopril in complex matrices such as tablets, serum, and urine samples. This platform holds promise for sensitive and selective detection of captopril in various practical applications.