Emission based sensing of N-acetyl cysteine via silver equipped anthraquinone derivatives

In this work we investigated emission-based response of silver complexes of two newly synthesized anthraquinone derivatives for N-acetylcysteine (NAC) and thioglycolic acid. The interaction of the probes, DHA-dibenzonitrile and DHA-dibutanenitrile with silver nanoparticles resulted in metal chelation and following quenching of the fluorescence. To determine whether the emission intensity of the complexes was re-stored again, thiol compounds; NAC and thioglycolic acid were used. The released dyes re-emitted light, allowing the system to exhibit an intensity-based turn-on type sensor behavior for the NAC and thioglycolic acid, respectively. The re-stored fluorescence was monitored as a strong emission based analytical signal at 560 nm. The complex stoichiometries were investigated using several approaches, including Job's plot, density functional theory (DFT) and FT-IR measurements. The findings relying on HOMO-LUMO and energy gap calculations highlight that Ag coordination and following acetylcysteine adduction significantly re-shape both local nucleophilic and electrophilic regions, modulating the global electronic structure and reactivity of anthraquinone derivatives. N-acetylcysteine exhibited an exceptional spectral response at pH 9.0 in a buffered solution exhibiting 13.6 and 14.4-fold enhancement in the emission intensity, respectively. The reported linear responses for a concentration range of; 1.0 × 10^-5 M -1.0 × 10^-2 M, can easily be adopted to determination of the NAC levels in drugs, in vitro studies or in serum samples. Limit of detection (LOD) and limit of quantification (LOQ) values of the DHA-dibutanenitrile derivative for the NAC molecule were found to be 1.28 × 10^-6 and 1.21 × 10^-5 mol × L^-1, respectively. Similarly, the DHA-dibenzonitrile exhibited 1.11 × 10^-6 and 1.28 × 10^-5 mol × L^-1 of LOD and LOQ values, respectively.