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The authors report on the development of copper nanocluster stabilized with tannic acid (TA CuNC) as a fluorescent nanoprobe for the turn on detection of a catecholamine neurotransmitter, dopamine. The nanocluster is obtained through a microwave assisted synthesis and exhibit distinct blue emission peak at 450 nm during excitation at 370 nm. The luminescence in the present system is effectively quenched by Fe(III) ions. The quenching happens through an electron transfer mechanism, which operate between the nanocluster and Fe(III) ions. The quenching is linear proportional to the concentration of Fe(III) between 0.25 and 1 μM and the detection limit is as low as 1.28 nM. Addition of dopamine into the quenched system causes the removal Fe(III) ions from the cluster surface and thereby leads to the retrieval of luminescence. The quenched system exhibited high sensitivity and selectivity for dopamine with a limit of detection 45 nM. The adaptability of the nanocluster as a turn on fluorescent probe is tested in real samples for the detection of dopamine and the recovery of fluorescence is in the range of 95%. [ABSTRACT FROM AUTHOR]

Dopamine being a neurotransmitter and chemical messenger plays a vivacious role in a number of significant medical conditions like Parkinson's disease, Attention Deficit Hyperactivity Disorder, Schizophrenia, and drug addiction. As turn-on sensors have a superior level of selectivity than fluorescence quenching based sensors, we developed a fluorescence retrieval strategy for dopamine sensing. Here, highly fluorescent amino phenyl boronic acid ( APBA)-conjugated gold nanocluster ( Au-BSA-APBA probe) has been synthesised from bovine serum albumin-protected gold nanocluster ( Au-BSA NCs). Boronic acid forms boronate ester with disaccharides such as lactose due to its affinity to polyols. Hence fluorescence of Au-BSA-APBA probe is quenched when it binds with lactose molecules through boronate ester formation. The fluorescence of Au-BSA-APBA-lactose system can be retrieved (turn-on) with dopamine by the competitive displacement of lactose from the probe surface which suggests the higher affinity of boronic acid to the catechol group of dopamine. Furthermore, real samples spiked with dopamine including human serum and urine were analysed using this turn-on sensor and showed excellent recovery percentage. The developed fluorescent sensor offered high selectivity for dopamine over other catecholamines and aminoacids with detection limit as low as 0.7 μM. [ABSTRACT FROM AUTHOR]