Amino acid-stabilized luminescent gold clusters for sensing pterin and its analogues

Pteridines are important low molecular weight biomarkers used in the diagnostics of inflammation, oxidative stress, phenylketonuria, cancer, etc. In this experimental study, we present a simple and selective approach to determine pteridines (pterin, leucopterin and folic acid) and nucleobase guanine concentration using luminescent gold clusters stabilized by aromatic amino acids. We synthesized several new gold clusters (AA-Au NCs) stabilized by various aromatic amino acids - 3,4-dihydroxy-L-phenylalanine (DOPA), L-tryptophan (Trp), L-tyrosine (Tyr) and L-phenylalanine (Phe), emitting in the violet-green spectral range. Their luminescence appeared to be sensitive to the presence of pterin, leucopterin, folic acid and guanine depending on the stabilizing matrix. Thus, a facile and cost-effective approach for the detection of pteridines is proposed. AA-Au NC-based sensors work according to "turn-off" and "turn-on" mechanisms. The possible physical origins of their luminescence quenching and enhancement are discussed.