High sensitivity cysteine detection using novel fluorescent Ag nanoclusters

Abstract

Fluorescent Ag nanoclusters (AgNCs) stabilized by carboxymethyl dextran (CMD) were prepared by the photochemical reduction of a mixture of CMD and [Ag(NH₃)₂]⁺ under ultraviolet C (UVC) light irradiation. Further study showed that the as-prepared AgNCs had the maximum fluorescence emission peak near the located surface plasmon resonance (LSPR) wavelength of AgNCs. Thus, these AgNCs are defined as LSPR-AgNCs. The maximum excitation wavelength of AgNCs is 250 nm and the maximum emission wavelength is 425 nm. In solution, the fluorescence of AgNCs could be quenched in the presence of cysteine. Based on this phenomenon, AgNCs were developed as a fluorescent probe for the detection of cysteine. The fluorescence intensity quenching value (ΔI) has a linear relationship with the concentration of cysteine, which follows a linear equation of ΔI = 4.25 × 10⁹c + 36.84 with the correlation coefficient of r = 0.9967 in the linear range of 5.0 × 10⁻¹⁰ to 1.0 × 10⁻⁷ mol L⁻¹. The detection limit (3σ/k) was 3.2 × 10⁻¹⁰ mol L⁻¹. It has been applied to the cysteine concentration detection with the accepted results in the synthesized samples and compound amino acids injection sample.