Clozapine sensing through paper-based microfluidic sensors directly modified via electro-deposition and electro-polymerization†

Microfluidic electrochemical sensors (μCS) can be portable, highly sensitive, and low-cost but are less frequently studied nor applied. Additionally, simultaneous electro-deposition of gold nanoparticles (ED (AuNPs)) and electro-polymerization of L-cysteine (EP (L-cys)) are introduced for the first time for modifying the surface of the working electrode through a paper-based microfluidic sensor. This study depicts that by employing such modification, the electrochemically active surface area (ECSA) and the electron transfer rate are increased together and result in improved sensitivity. The modified μCS is depicted to enable sensitive voltametric determination of, e.g., clozapine (CLZ), an anti-psychotic drug to treat schizophrenia. The proposed sensor was characterized by different techniques, and several key parameters were optimized. Under the optimum conditions and using square-wave voltametry (SWV), a linear dose–response for a concentration range from 0.5 to 10.0 μM of CLZ was achieved. The limit of detection and sensitivity resulted in 70.0 nM and 0.045 mA cm⁻² μM⁻¹, respectively. Besides, this excellent sensitivity combines with high stability, which was tested for six repetitive measurements with a single device resulting in high reproducibility. Additionally, this procedure was validated with measurements of clozapine in human blood plasma, which demonstrated the excellent applicability of the device, rendering it a promising platform for point-of-care diagnostics and environmental monitoring.