An “Off-On” Fluorescence Sensing Platform Based on Aminated Carbon Quantum Dots and Silver Nanoparticles for Sensitive and Selective Quantifying Dopamine in Serum

Aminated carbon quantum dots (N-CQDs) and p-amino thiophenol capped silver nanoparticles (N-AgNPs) are mixed physically to fabricate an optical nanocomposite of N-CQDs/N-AgNPs. A highly selective and sensitive “off-on” fluorescence sensing strategy for monitoring dopamine in human serum is established based on the nanocomposite. Through an electrostatic interaction between N-CQDs and N-AgNPs, N-CQDs/N-AgNPs nanocomposite is assembled. The initial fluorescence of N-CQDs is effectively “off” by N-AgNPs owing to the inner filter effect. However, with the addition of dopamine, stronger π–π stacking or hydrogen bonding ability of super-adhesive polydopamine produced from dopamine at pH 8 to water-soluble N-CQDs can make N-CQDs to dissociate from N-CQDs/N-AgNPs nanocomposite with fluorescence “on” as a result of the termination of inner filter effect. Meanwhile, the dissociation of N-CQDs/N-AgNPs nanocomposite and the existence of oxygen in the air may trigger the formation of Ag 2 S. Under the optimal conditions, the activated fluorescence intensity at 477 nm is linearly proportional to dopamine in the range of 0.33–65 × 10 −9 m with a detection limit of 0.1 × 10 −9 m and 1.2% RSD. The established sensing platform has successfully detected dopamine in serum with satisfactory results and may be an alternative powerful technique for further clinical diagnosis of dopamine-related diseases.