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This work demonstrates a facile electropolymerization of a dl-methionine (dl-met) conducting polymeric film on a gold nanoparticle (AuNPs)-modified glassy carbon electrode (GCE). The resulting sensor was successfully applied for the sensitive detection of paroxetine·HCl (PRX), a selective serotonin (5-HT) reuptake inhibitor (SSRIs), in its pharmaceutical formulations. The sensor was characterized morphologically using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) and electrochemical techniques such as differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The proposed sensor, poly (dl-met)/AuNPs-GCE, exhibited a linear response range from 5 × 10−11 to 5 × 10−8 M and from 5 × 10−8 to 1 × 10−4 M using DPV with lowest limit of detection (LOD = 1 × 10−11 M) based on (S/N = 3). The poly (dl-met)/AuNPs-GCE sensor was successfully applied for PRX determination in three different pharmaceutical formulations with percent recoveries between 96.29% and 103.40% ± SD (±0.02 and ±0.58, respectively).

Vardenafil (VRL) is one of the highly potent PDE-5 inhibitor pharmaceutical compounds used for treatment of erectile dysfunction. In this work, the sensor was fabricated via electropolymerization of pyrrole (Py) as a functional monomer in presence of VRL on a platinum electrode (PtE) modified with electrodeposited platinum nanoparticles (PtNPs) followed by electrochemical overoxidation to yield overoxidized polypyrrole (OPPy). During the sensor’s fabrication, seven factors need to be optimized including, pyrrole concentration (PyConc.) (mM), VRL concentration (VRLconc.) (mM), no of polymerization cycles (no. of cycles), incubation time (t.rebind) (min), pH of the incubation (pH), accumulation time (t.acc) (s) and accumulation potential (Pot.acc) (V). That is why fractional factorial design was first applied for screening the most significant factors followed by central composite design (CCD) optimization in order to have a correlative overview of the different interactions between these variables at the same time, unlike the traditional approach involving changing one factor at a time. Stepwise construction of the sensor was characterized electrochemically using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and topographically using Scanning electron microscopy (SEM). The sensor showed linearity over the range of concentrations (1 × 10-12 M – 5 × 10-8 M) using differential pulse voltammetry (DPV) and EIS with a significantly low limit of detections 2 × 10-13 M and 0.9 × 10-13 M (S/N = 3), respectively under optimum conditions. The fabricated (OPPy/PtNPs/PtE) sensor was successfully applied to determine VRL in two pharmaceutical formulations, spiked urine and serum samples with percent recoveries between (98.9 % and 102.2 %) ± SD (±0.02 and ± 0.48).