L-cysteine capped ZnS:Mn quantum dots for room-temperature detection of dopamine with high sensitivity and selectivity.
Dopamine (DA) is one of the most important catecholamine neurotransmitters of the human central nervous system, and is involved in many behavioral responses and brain functions. Below normal DA levels in biological fluids can lead to different neurodegenerative conditions. For excess DA levels, a failure in energy metabolism is indicated. In this study, a facile room-temperature phosphorescence sensor is developed to detect DA based on l-cysteine capped Mn doped ZnS quantum dots (l-cys ZnS:Mn QDs). The QDs display a prominent orange emission band peaking at ~598nm, which is strongly quenched upon addition of DA in alkaline medium. The sensor exhibits a linear working range of ~0.15-3.00μM, and a limit of detection of ~7.80nM. These results are explained in terms of a pH-dependent electron transfer process, in which the oxidized dopamine quinone functions as an efficient electron acceptor. The QDs-based sensor shows a high selectivity to DA over common interfering biomolecules (including some amino acids, ascorbic acid, chloride and glucose). The sensor has been successfully applied for the detection of DA in urine samples, yielding recoveries as high as 93%. Our findings indicate that our developed sensor exhibits high sensitivity and reproducibility to determine DA even in biological fluids where DA is at low levels, e.g., in the central nervous system, which is the usual clinical profile of a neurodegenerative disorder associated to the Parkinson's disease.