Green emissive nitrogen-doped graphene quantum dots for fluorescence off-on probing methimazole via palladium (II) mediated assay

A palladium ion (Pd2+)-mediated nitrogen-doped graphene quantum dots (N-GQDs/Pd2+) was developed as a fluorescent "off-on" probe for methimazole (MZ). Fluorescent N-GQDs interact with Pd2+ through coordination interactions, leading to weak photoluminescence (PL) owing to the quenching ability of Pd2+. Upon introducing MZ, the stronger binding between N-GQDs and Pd2+ destroys the N-GQDs/Pd2+ complex and restores the PL of N-GQDs. The probe exhibits a linear PL response to MZ concentrations from 3.0 to 50.0 mu M with a detection limit down to 4.5 nM. In addition, the probe has been used to detect MZ in real samples including natural water sources and human urine.