Simultaneous Femtomolar Detection of Paracetamol, Diclofenac, and Orphenadrine Using a Carbon Nanotube/Zinc Oxide Nanoparticle-Based Electrochemical Sensor

The development of an efficient, selective, and highly sensitive electrochemical sensor for the simultaneous analysis of multiple drugs is a tough challenge. Herein, we report an applied electrochemical sensing platform comprising both acid- and base-functionalized carbon nanotubes (CNTs) with zinc oxide nanoparticles between the layers (COOH-CNTs/ZnO/NH2-CNTs) for the detection of paracetamol, diclofenac, and orphenadrine (PAR, DIC, and ORP) drugs with ultrahigh sensitivity and selectivity as evidenced by intense and well-resolved voltammetric signals. Prior to electrochemical analysis, the nanocomposite/glassy carbon electrode (GCE) surface was characterized by multiple spectroscopic techniques. The performance of fCNTs/ZnO/fCNTs/GCE was probed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square-wave anodic stripping voltammetry (SWASV). The functionalized porous architecture with a large effective surface area provided a conduit for efficient mass transport and active sites for anchoring adsorbate molecules, thus leading to substantially lower oxidation overpotentials and amplified current signals. The fCNTs/ZnO/fCNTs/GCE exhibited a 6-fold increase in active surface area than bare GCE. Under optimized SWASV conditions, the designed sensor demonstrated simultaneous detection of PAR, DIC, and ORP with an unprecedented femtomolar limit of detection (46.8, 78, and 60 fM, respectively) within a time span of just 1 min. Besides the specificity, stability, and reliability studies of the designed sensing platform in multiple biological and pharmaceutical samples, % recoveries of 96–102% highlight the novelty and figures of merit of the designed electrochemical sensor. Moreover, computational studies were carried out that support the experimental outcome of a favorable charge transfer process between functional groups of the drugs and the sensor surface.