A highly sensitive photoelectrochemical sensor for the detection of theophylline based on the photoelectrocatalytic activity of a nanocomposite of polydopamine nanospheres and gold nanoparticles

Abstract

A label-free photoelectrochemical (PEC) sensor for detecting theophylline (TP) was exploited based on electrodes modified with a nanocomposite of polydopamine nanospheres (PDSs) and gold nanoparticles (AuNPs). PDS particles were prepared by oxidative autopolymerization, and their reducibility was utilized in one step to reduce the gold nanoparticles in situ. The AuNPs-PDS/ZnS PEC sensor was constructed by electrochemical deposition and drop coating. The detection medium employed was TP in 0.1 M phosphate buffered saline (PBS, pH 7.00). The proposed PEC sensor demonstrated exceptional photoelectric catalytic capability with respect to TP oxidation. Under light irradiation, electron–hole pairs were generated in ZnS. Electrons from TP oxidation trapped holes and produced an anodic photocurrent. The modification process of electrodes and TP oxidation recognition performance were studied by the I–T method. A linear relationship was observed between the oxidation photocurrent of TP and its concentration over a range of 0.5 to 50 μg mL⁻¹. The detection limit was established at 0.13 μg mL⁻¹ (S/N = 3). This sensor exhibited optimal selectivity, prolonged stability, and commendable reproducibility when determining TP. It was successfully applied to measure TP content in various matrices, including tea, biological samples, and blood samples, with acceptable recovery rates ranging from 95.3% to 107.7%.