Detection of Dopamine in Human Fluids Using N-Doped Carbon Dots

Herein, we fabricated nanoparticles of doped carbon dots with nitrogen (N-CDs) with an ecofriendly and easy approach, yielding spherical nanoparticles (mean size: 19 nm). N-CDs were further characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and fluorescence spectroscopy. In addition, we developed a fluorometric method for determination of dopamine (DA) in human fluids at nanomolar concentrations (rapid and highly sensitive). The quenching effect over the emission of the doped CDs at 438 nm was the basis of the quantification of DA. A linear trend between 0 and 652 nM was the range of application with a detection limit at 4 nM, acceptable accuracy (>80%), and precision (relative standard deviation < 10%), showing a highest selectivity with related analytes. The obtained sensing method was applied for DA determination in human fluids (urine and serum samples) with acceptable accuracy. In order to understand the interaction of DA with the nanoparticles of N-CDs, we applied density functional theory. The bonding between the -NH3+ moiety of DA and the corresponding N-CD surface ligand consists of the formation of hydrogen bonds. It is demonstrated that the selected geometrical models explain the spectroscopic experiments performed on such nanoparticles.