Development of a carbon paste electrode modified with a nanocomposite of mercaptopyrimidine-functionalized HMS silica and gold nanoparticles for total atropine and scopolamine determination in plant-based food supplements

A chemical sensor was developed for the quantification of the total concentration of two naturally occurring toxic anticholinergic compounds, atropine (At) and scopolamine (Sc), which may be present in plant-based food supplements. The sensor is based on a carbon paste electrode modified with mesostructured silica functionalized with mercaptopyrimidine and coated with electrogenerated gold nanoparticles (AuNPs@MPY-HMS-CPE). Sensor preparation and operational parameters were optimized, including deposition time, potential, and HAuCl₄ concentration (400 s, − 0.4 V, 6 mM), as well as stirring time and measurement buffer (60 s stirring in phosphate buffer, pH 8.0). A peak potential of approximately +0.9 V was selected for signal acquisition. The current intensity at this potential was inversely proportional to the total tropane alkaloids concentration, independent of their relative proportions, confirming that the detection mechanism involves inhibition of MPY group oxidation by At and Sc. The sensor exhibited a linear calibration range from 10 to 100 nM ( R = 0.9997), a detection limit of 5.6 nM (sum of At and Sc), and acceptable reproducibility (RSD ≈ 3%). Selectivity was assessed in the presence of structurally similar compounds and major components of plant-based supplements. The sensor demonstrated rapid response and miniaturization potential, enabling in situ analysis without sample pretreatment. Application to real samples revealed concentrations of 16 nM for both alkaloids in one supplement, with recovery rates between 96% and 104% in spiked samples. These results highlight the sensor's suitability for reliable, selective, and sensitive detection of tropane alkaloids in complex matrices.