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 (IAg–captopril/IAg