Amino Acid-Functionalized AuNPs and AgNPs as Probes for the Selective Detection of Heavy Metals in the Environment

The literature collected from various search engines and high-quality scientific databases reveals that amino acid (AA)-functionalized nanoparticles have emerged as a promising field for selective detection and remediation of heavy metals (HMs). Among the various nanoparticles (NPs), gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) have drawn considerable attention, attributed to their unique optical, catalytic, and surface plasmon resonance properties. Functionalization with amino acids significantly enhances nanoparticle stability, biocompatibility, and metal-binding affinity through diverse functional groups. AA-functionalized AuNPs, including glycine, cystine, leucine, methionine, tyrosine, aspartic acid, histidine, and lysine-capped systems, exhibit tunable selectivity toward heavy metal ions. Bifunctionalization strategies further enhance sensitivity by inducing nanoparticle aggregation or signal amplification. Beyond single amino acids, polypeptides and protein-functionalized AuNPs offer enhanced molecular recognition and multivalent binding, expanding their applicability in complex matrices. Similarly, amino acid-functionalized AgNPs, such as those capped with similar amino acids stated above, exhibit strong interactions with heavy metals, AA bifunctionalization, and bimetallic nanoparticles (BNPs), particularly amino acid-functionalized Au–Ag systems, which combine the advantages of both metals, leading to improved sensitivity, selectivity, and signal strength. Although these advances have been made, a major gap remains in the systematic comparison of different amino acids, peptides, and bimetallic systems under real-world conditions. This gap can be addressed by standardized testing methods, clearer structure–function relationships and combined experimentation to guide the rational design of more efficient AA-functionalized nanoparticles.