Biosynthesised silver nanoparticles as an efficient colorimetric sensor towards detection of melamine

With the recent development in the field of nanotechnology, there have been significant improvements in synthesis protocols. Greener methods for synthesis are more favoured as compared to the conventional modes as the latter  possesses huge number of disadvantages. In this context, our work reports biosynthesis of plasmonic silver nanoparticles (AgNPs), where freshly prepared Malus Pumila (Apple) peel extract was utilised both as a functionalising and a reducing agent. Upon addition of the extract to the precursor solution, it's colour changes to yellow; indicating formation of AgNPs, validated by a strong absorbance peak at around 420 nm corresponding to Localised Surface Plasmon resonance (LSPR) peak of AgNPs. To normalize the synthesis procedure, pH, reaction time, temperature of synthesis and the concentration of the green extract were altered. X-Ray Diffraction (XRD) data revealed formation of (FCC) crystalline structure nanoparticles, with an approximate crystalline size of 10 nm. Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM) images affirmed that the synthesised nanoparticles were roughly spherical in morphology with size ranging between 10 to and 50 nm. FTIR analysis revealed the presence of “bio-polyphenols”, which is responsible for reducing and functionalising the nanoparticles. These nanoparticles were further used as a colorimetric sensor to detect toxic milk adulterant melamine. This resulted in aggregation as indicated by colour change. The colorimetric results obtained was validated by UV–Vis study of the samples—where the absorbance at 423 nm decreased linearly with increase in concentration of melamine up to a limit of 0.5 ppm.