Aging the Imprint: Enhanced Performance of a Silver Prussian Blue Analogue–MIP Electrochemical Sensor for Sulfamethoxazole Detection in Milk

Antibiotic residues such as sulfamethoxazole (SMX) in milk pose significant public health risks and contribute to the growing threat of antimicrobial resistance. This work presents a simple, low-cost electrochemical sensor based on a silver Prussian Blue analogue (Ag-PBA) and molecularly imprinted polymer (MIP) for sensitive and selective SMX detection in milk. Silver nanostructures were electrodeposited and modified into Ag-PBA, followed by electropolymerization of a template-monomer solution that had been preincubated for three months to promote stable complex formation onto screen-printed carbon electrodes. This extended incubation strategy, not previously reported for MIP systems, yielded higher sensitivity to SMX than a fresh solution. The Ag-PBA/MIP sensor exhibited a linear detection range from 0.1 to 10 μM, covering the European Union's maximum residue limit of 0.4 μM for SMX in milk. The sensor demonstrated good selectivity against structurally similar sulfonamides and other antibiotic residues found in milk. Milk preparation methods were optimized to enhance SMX oxidation, and analyte loss during sample treatment was assessed by comparing samples spiked with SMX before and after preparation.