Modification-free boron-doped diamond as a sensing material for direct and reliable detection of the antiretroviral drug nevirapine

In this work, non-modified boron-doped diamond (BDD) was employed first time ever as the sensing material for the in-depth voltammetric study of the antiretroviral drug nevirapine (NVP) used to treat HIV infections. Two types of electrode surface pre-treatments, anodic oxidation and alumina-polishing, yielded BDD of different surface chemistry, denoted as O-BDD and p-BDD, respectively. Induced alterations in BDD surface composition reflected in distinct voltammetric responses of NVP, also dependant on the pH of the medium. The electrochemical oxidation of NVP on both electrodes, whose mechanism is proposed herein, has an irreversible character and is controlled by diffusion. The analytical figures of merit were assessed in a pH 2.0 buffer on O-BDD, and in supporting electrolytes of pH 5.0 and 13.0 on p-BDD using differential pulse voltammetry. Overall, NVP provided signals of excellent intra- and inter-day repeatability (RSD ≤ 5.0%) which remained unaffected even in the presence of common interfering compounds (e.g., glucose, ascorbic acid, uric acid, and dopamine). Even though the O-BDD electrode outperformed the p-BDD electrode in terms of sensitivity and the lowest detection limit achieved (0.04 μM), both O-BDD and p-BDD provided highly favourable analytical parameters fulfilling the requirements for clinical application for NVP sensing and monitoring in biofluids. This was also proved by electroanalysis of NVP in synthetic serum samples where recovery values between 96.3 and 103.0% were successfully achieved. Finally, unique properties of BDD allowed to develop a direct, modification-free, and reliable protocol for NVP detection, which paves the way for the full sensor development.