Dopamine sensing by fluorescent carbon nanoparticles synthesized using artichoke extract

The practical and easy detection of dopamine levels in human fluids, such as urine and saliva, is of great interest due to the correlation of dopamine concentration with several diseases. In this work, the one-step synthesis of water-soluble carbon nanoparticles (CNPs), starting from artichoke extract, containing catechol groups, for the fluorescence sensing of dopamine is reported. Size, morphology, chemical composition and electronic structure of CNPs were elucidated by DLS, AFM, XPS, FT-IR, EDX and TEM analyses. Their optical properties were then explored by UV-vis and fluorescence measurements in water. The dopamine recognition properties of these CNPs were investigated in water through fluorescence measurements and we observed the progressive enhancement of the CNP emission intensity upon the progressive addition of dopamine, with a binding affinity value of log K = 5.76 and a detection limit of 0.81 nM. Selectivity towards dopamine was tested over other interfering analytes commonly present in human saliva. Finally, in order to perform a solid point of care test, CNPs were adsorbed on a solid support and exposed to different concentrations of dopamine, thus observing a pseudo-linear response, using a smartphone as a detector. Therefore, the detection of dopamine in simulated human saliva was performed with excellent results, in terms of selectivity and a detection limit of 100 pM.