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 pi-pi 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 Ag2S. Under the optimal conditions, the activated fluorescence intensity at 477 nm is linearly proportional to dopamine in the range of 0.33-65 x 10(-9) m with a detection limit of 0.1 x 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.