One-Pot Green Synthesis of Amino Acid-Capped Gold Nanoparticles for Selective Sensing of Cyanide and Heavy Metals

In this study, 20 amino acids were utilized both as reducing and capping agents in a one-pot green synthesis of gold nanoparticles (GNPs) to be used in sensor applications for water, environment, and food monitoring. Tyrosine, tryptophan, valine, serine, phenylalanine, arginine, glutamic acid, and cysteine proved to be more suitable under the tested conditions, compared to the other amino acids, considering their colloidal stability. Amino acid-capped GNPs (AAGNPs) were then characterized in terms of absorbance spectrum, size, zeta potential, polydispersity index, geometry, and atomic content. After characterization, synthesized AAGNPs were utilized in sensory applications for Cyanide (CN^-) and heavy metal (Al³⁺, Cu²⁺, and Fe³⁺) detection. The synthesized AAGNPs exhibited promising CN^- detection capability that is comparable to conventionally synthesized GNPs via the Turkevich method. Besides, ArgGNPs, GluGNPs, and CysGNPs exhibited distinct sensing behaviors, reflecting differences in surface chemistry and interaction mechanisms. Sensing platforms that utilized PheGNPs, TrpGNPs, and TyrGNPs showed detection limits in the range of 0.3-0.7 μM. Amino acid capping of GNPs imparted differential recognition capability toward various heavy metal ions, where detection limits were calculated for various AAGNPs as 0.27 mM for Cu²⁺ with CysGNPs, 0.25 mM for Al³⁺ with GluGNPs, and 0.44 mM for Fe³⁺ with SerGNPs. This phenomenon shows that synthesizing and capping GNPs with various amino acids not only alters the size and geometry, but also the capability of AAGNPs as parts of recognition elements of sensor systems. This study highlights the potential of amino acid-mediated green synthesis as an environmentally friendly and versatile approach for developing functional nanomaterials with tunable sensing capabilities for pollutant detection.