Eco-Friendly N, S Co-Doped Graphene Quantum Dots for Sensing 3-Nitro-L-Tyrosine via Dark State Formation: Evidence From Photoluminescence and Single-Particle Spectroscopy

Abstract

3-Nitro-L-tyrosine (3NT) is a key biomarker of oxidative stress associated with neurodegenerative and cardiovascular diseases. Here, we report a selective optical sensing strategy based on photoluminescence (PL) quenching of nitrogen and sulfur co-doped graphene quantum dots (NS-GQDs) synthesized from garlic, a natural and sustainable precursor. PL quenching by 3NT is driven by static interactions, as revealed by single-particle near-field IR spectroscopy. Time-dependent density functional theory indicates that complexation with 3NT induces a significant reduction in the oscillator strength of key excited states in the NS-GQDs, suppressing radiative transitions and suggesting the formation of a non-emissive “dark states”. This interaction creates an unambiguous optical fingerprint for 3NT, enabling highly selective molecular recognition. Our findings establish a mechanistic blueprint for the rational design of biocompatible carbon-based nanomaterials for next-generation sensing platforms.