Detection of melamine in infant milk powder by micro-Raman spectroscopy using biosynthesized zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO-NPs) were green synthesized using Carica papaya peel extract as a reducing agent and used to develop a novel Micro Raman Spectroscopy method to detect melamine in infant milk powder. Citrate was coated on the biosynthesized ZnO-Np, as a melamine-binding agent. SEM, AFM, TEM, FTIR, MRS, and XRD were used to confirm the morphology, size, and nature of ZnO-Np, citrate-coated ZnO-Np (ZnO-W/C), and ZnO-W/C conjugated with melamine. The zeta potential was − 43.5 mV, and the ZnO-W/C particle size ranged from 50 to 100 nm. Using MRS with a laser wavelength of 785 nm for a Raman shift ranging from 400 to 1200 cm⁻¹, ZnO-W/C was utilized to detect melamine. ZnO-W/C conjugated with melamine showed a Raman shift at 677 cm⁻¹. A linear regression model based on the Raman shift at different melamine concentrations was developed to quantify melamine in the spiked milk powder. With spiked infant milk powder, the lowest melamine detection level was 0.125 ppm. This is a sensitive and effective way to detect melamine in infant milk powder. This work suggests that ZnO-NPs, synthesized using fruit industry waste as a starting material, can serve as a diagnostic tool to ensure food safety.