Nickel selenide-based electrochemical sensors for the determination of Nevirapine drug in wastewater

Abstract

The occurrence of antiretroviral drugs (ARVs) in most water sources in South Africa has been of major concern over the past decade. Though they have been reported to occur in low concentrations (low ng/L and µg/L), their increasing concentration poses health risks to humans, animals, and aquatic organisms. This accelerates the emergence of antiretroviral resistance. The consequences of these adverse effects on human health are therefore very concerning. Nevirapine (NVP) is one of the most extensively used ARVs worldwide for the prevention of mother-to-child transmission and has been often detected in water sources. These drugs enter water systems in various ways, including incorrect disposal of unused or expired drugs, via treated or untreated wastewater from the municipality, discharge from hospital wastewater, effluent from sewage treatment plants and industrial wastewater. Several chromatographic methods have been employed in its detection in water, but their high costs and sophisticated nature limit their use in a variety of applications. Very limited research is available on the electrochemical detection of nevirapine in real wastewater samples, as most studies present its detection in human serum or pharmaceutical formulations. Therefore, this work presents the use of novel electrochemical sensor systems for the detection of nevirapine in real wastewater samples. The electrochemical sensor systems were developed by depositing functionalised nickel selenide quantum dots (NiSe2QD) onto an L-cysteine or Nafion-modified gold electrode. The quantum dots were prepared using a simple and cost-effective aqueous method, capped with banana peel extract (BPE) and 3-mercaptopropionic acid (3-MPA) to improve their stability and prevent agglomeration. Microscopic, spectroscopic, and electrochemical techniques were used to determine the properties of the synthesised quantum dots. Fourier transform infrared spectroscopy (FTIR) confirmed the capping of 3-MPA NiSe2QD, where the SH group absorption band disappeared from the spectra of 3-MPA NiSe2QD and decrease in intensity for the COOH groups. The increase in intensity and the shifting of bands to higher wavenumbers were observed for BPE-NiSe2QD. The size of the quantum dots (˂ 10 nm) was revealed by High-resolution transmission microscopy (HR-TEM) and small-angle X-ray scattering (SAXS). The optical properties of NiSe2QD were studied by ultraviolet-visible spectroscopy (UV-Vis), which produced absorbance bands at 331 nm and 329 nm corresponding to energy bandgap values of 3.91 eV and 2.99 eV for 3-MPA and BPE capped NiSe2QD, respectively. Differential pulse voltammetry (DPV) was used to study the electrochemical responses of 3-MPA-NiSe2QD/L-cyst/Au and Au/BPE-NiSe2QD/Nafion to NVP, with a characteristic oxidation peak at 0.76 V. This was performed in 0.1 M phosphate buffer solution (PBS) at a scan rate of 30 mV/s. The electrochemical sensors exhibited enhanced electroactivity, which was attributed to the catalytic effect of the incorporated quantum dots. This was characterised by the low limit of detection (LOD) values of 0.0035 ng/L and 0.0064 ng/L for 3-MPA-NiSe2QD/L-cyst/Au and Au/BPE-NiSe2QD/Nafion sensors, respectively. However, the 3-MPA-NiSe2QD/L-cyst/Au electrochemical sensor produced the best signal with higher a sensitivity of 6.15 µA/pM compared to 5.52 µA/pM for Au/BPE NiSe2QD/Nafion. The oxidation peak current of NVP had a linear range of 0–1.21 pM with a correlation coefficient of 0.998. The application of both sensors in the determination of nevirapine in real wastewater samples showed good recoveries in the range of 85%-108%, which indicates that the sensors are suitable for real-time sample analysis.