Unraveling the Fluorescence Quenching of Colloidal Graphene Quantum Dots for Selective Metal Ion Detection

A sustainable microplasma synthesis of GQDs as fluorescent sensors for Cu2+ detection is reported. The GQDs are synthesized from starch at ambient conditions using microplasma–liquid synthesis. The prepared GQDs exhibit selective detection of Cu2+ with high quenching ratio and low limit of detection (LoD) of 0.5 μM. Detailed density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations show that fluorescence quenching occurs due to the forbidden emission process of the excited electrons. This work presents a sustainable and scalable method to synthesize GQDs and provides insight into the charge transfer process for fluorescent-based metal ion detection.