Boronic acid-modified fluorescent sensor using coffee biowaste-based carbon dots for the detection of dopamine

Dopamine (DA) is an indispensable form of neurochemical, which normal levels are highly potential for maintaining proper brain functions. Their abnormal levels are threatening the neurological behavior in humans with aggressive Alzheimer's, Parkinson's, Huntington's diseases, etc. Hence, in this study, a boronic acid-functionalized fluorescent sensor was developed by adapting the conveniently accessible biomass such as coffee waste for the detection of neurotransmitters like DA. In this context, we synthesized carbon dots (CDs) using coffee waste via a simple hydrothermal treatment (C-CDs). The fluorescent sensor was designed using phenylboronic acid namely 3-aminophenylboronic acid (APBA)-modification to the C-CDs through 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxy-succinimide (EDC/NHS) coupling chemistry (B-CDs). Both C-CDs and B-CDs have shown photoluminescence (PL) emission maxima around 452 and 469 nm under the excitation maxima of 335 and 371 nm, respectively. Further, their optical properties were studied through PL response, which showed the distinct excitation-dependent and independent emission behavior, when shifting the excitation wavelengths from 300–500 nm to 300–390 nm, respectively. The C-CDs and B-CDs have displayed light and strong-blue colored emissions under ultraviolet (UV)-illumination, respectively. The B-CDs have shown fluorescence quenching against DA concentrations ranging from 0 to 30 µM with a lower detection limit of 4.25 nM. The applicability of the proposed sensor was investigated in real samples like the human serum, which exhibited good recovery values of 95.9–101.35 %.