L-Cysteine (Cys) is a non-essential sulfur-containing amino acid, crucial for protein synthesis, detoxification, and several metabolic functions. Cys is widely used in the agricultural, food, cosmetic, and pharmaceutical industries. So, a suitable sensitive and selective sensing approach is of great interest, and a low-cost sensor would be necessary. This article presents silver nanoparticles (EuAgNPs) synthesized by a green synthesis method using Eugenia uniflora L. extracts and photoreduction. The nanoparticles were characterized by UV/VIS, transmission electron microscopy, high-performance liquid chromatography (HPLC), FTIR, and Zeta potential. With the addition of Cys in the EuAgNPs solution, the terminal thiol part of L-cysteine binds on the surface of nanoparticles through AgÀ S bond. The EuAgNPs and CysAgNPs coexist until flavonoids bound the amino group of Cys, enhancing the red color of solutions. The EuAgNPs provided selectivity to detect Cys among other amino acids, and its detection limit was found to be 3.8 nM. The sensor has the advantages of low-cost synthesis, fast response, high selectivity, and sensitivity.

ALA is a natural metabolite in all living cells and possesses low toxicity. ALANPs exhibit high antimicrobial activity, promote plant growth and have the potential to show photodynamic herbicidal properties under solar illumination.

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