Electrochemical Dopamine Biosensor Based on Plant-Derived Peroxidase Immobilized on Titanate Nanowires

Dysregulation of dopamine (DA) levels is strongly associated with a range of neurodegenerative and psychiatric disorders, including Parkinson's disease. Limitations inherent to conventional analytical techniques have prompted the development of alternative methods, particularly electrochemical biosensors, which provide rapid response and real-time analysis. Among enzyme-based biosensors, peroxidases are notable for their catalytic efficiency and versatility. In this study, gherkin (Cucumis anguria L.) extract was immobilized onto titanate nanowires (TNWs) to fabricate four electrochemical biosensors for DA detection. Calibration curves generated by square-wave voltammetry demonstrated a linear range of 5-65.4 μmol L^-1 for all biosensors. The most effective biosensor (TNW-C) exhibited the equation I _pa = 0.573_DA + 2.44 (R ² = 0.999), with a limit of detection of 0.400 μmol L^-1, a limit of quantification of 1.21 μmol L^-1, and a sensitivity of 8.19 μA μmol L^-1 cm^-2. Application of TNW-C to a commercial sample resulted in a DA concentration of 4.99 ± 0.40 mg mL^-1, corresponding to a relative error of -0.2% compared to the labeled value of 5 mg mL^-1. Evaluation of urea as a potential interferent revealed only a slight current decrease (-0.9%). Additional assays with uric acid showed well-resolved oxidation peaks, with the DA current for TNW-C being 3.68 times higher than that of uric acid. The response also agreed with UV-vis analysis and the labeled pharmaceutical value, supporting real-sample applicability. These results demonstrate that peroxidase-rich gherkin extract is an effective and potentially cost-effective biocatalyst for DA biosensing, serving as a promising alternative to commercial horseradish peroxidase in nanobiocomposite sensing platforms.