FRET-based fluorescent probe for drug assay from amino acid@gold-carbon nanoparticles

Biocompatible and luminescent nanostructures synthesized by capping gold-carbon nanoparticles (HOOC-4-C₆H₄-AuNPs) with amino acids tyrosine, tryptophan, and cysteine were used for the quantitative estimation of ranitidine (RNH), a peptic ulcer and gastroesophageal reflux drug. We applied a fluorescence quenching mechanism to investigate the viability of the energy transfer based on gold-carbon nanosensors. Förster resonance energy transfer (FRET) calculations showed a donor-acceptor distance of 1.69 nm (Tyr@AuNPs), 2.27 nm (Trp@AuNPs), and 2.32 nm (Cys@AuNPs). The constant time-resolved fluorescence lifetime measurements supported the static quenching nature. This method was successfully utilized in the detection and quantification of RNH, with a limit of detection (LOD) of 0.174, 0.56, and 0.332 μM for Tyr@AuNP, Trp@AuNP, and Cys@AuNP bioconjugates, respectively. This approach was also successful in the quantification of RNH in spiked serum samples.