Detection of lamivudine using liquid-surface-enhanced Raman spectroscopy†

Antiretroviral medications such as lamivudine (LAM) are central to the treatment of HIV/AIDS. Because of the rise in the substandard production of these pharmaceuticals, new methods of quality control are required. In this study, the use of silver nanoparticles (AgNPs) for the detection and quantification of LAM at low concentrations was explored using a new method known as liquid-surface enhanced Raman spectroscopy (liquid-SERS). AgNPs (20–80% v/v) were prepared by chemical reduction and subsequently characterized by assessing their size, shape, absorbance, and molecular properties. A series of LAM samples (0–80 μg ml⁻¹) were then spiked with AgNPs and evaluated using liquid-SERS. Subsequently, a partial least-square analysis was conducted to determine the linearity (R²), sensitivity, limit of detection (LOD) and quantification (LOQ) of selected peak ratios. The results show an improved sensitivity for the 783 cm⁻¹ band of the drug when coupled with the 945 cm⁻¹ band of the citrate stabilizer, which is likely facilitated by intermolecular forces such hydrogen bonding dipole–dipole forces between the functional groups. Secondly, the R² ranged between 0.96–0.98, while the LOD and LOQ reached 1.12 to 10.49 and 3.39 to 31.77 μg ml⁻¹ respectively. These values were found to be comparative to results reported using common techniques such as UV-vis spectroscopy and high-performance liquid chromatography. As such, it was concluded that further investigation into drug/AgNPs and liquid-SERS could provide new methods of quality control for pharmaceutical products at low concentrations, through a rapid, complementary and cost-effective photonics approach.