Surface plasmon resonance-based colorimetric sensing of amoxicillin in pharmaceuticals using Psidium guajava leaf extract-mediated silver nanoparticles

This study presents a quantification method for the antibiotic Amoxicillin (AMX) using silver nanoparticles synthesized from guava leaf extract (AgNPs-GuLE) as an analytical reagent, extending their previously reported properties beyond antibacterial activity and dye removal. Key influential parameters were selected for investigation during the development of the analytical procedure. Under optimized conditions (pH 4–4.5, the volume ratio of AgNPs to analyte 1:1, and the buffer concentration of 160 mM), the accuracy of the method was determined with a recovery rate of 108.8% (± 6.3%), repeatability relative standard deviation (RSD r ) of 2.8%, and intermediate precision relative standard deviation (RSD I ) of 6.5%. The calibration curve exhibited linearity in the range of 2–10 mg/L. The limits of detection (LOD) and quantification (LOQ) were 2.5 mg/L and 2.7 mg/L, respectively. Analysis of commercial samples yielded results within the acceptable range of 90–110% (as specified by the Vietnamese Pharmacopoeia). The AMX analytical procedure, based on the aggregation of AgNPs-GuLE, as demonstrated by Dynamic Light Scattering (DLS) analysis and Scanning Transmission Electron Microscopy (STEM) imaging, enables detection and quantification of AMX in pharmaceutical dosage forms (capsules, tablets, and powders). The current validation was restricted to pharmaceutical samples. The extension to food or environmental matrices would require additional validation and is identified as a future research direction. These findings demonstrate that AgNPs-GuLE can serve as a promising reagent in green analytical chemistry.