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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]

Graphical abstract depicting detection of dopamine based on BSA stabilised copper nanocluster. • Rapid detection of dopamine is achieved by using insitu synthesized blue emitting CuNC. • Dopamine showed fast response towards H2O2 added BSA CuNC with a limit of detection 0.1637 pM. • Dopamine detection is further validated with real sample matrices such as human blood serum samples and urine samples. • Dopamine detection is further validated with real sample matrices such as human serum samples and human urine samples. • A portable paper strip detection method is developed for the onsite detection of dopamine. Rapid and real-time monitoring of catecholamine neurotransmitter dopamine receives immense importance since it plays a crucial role as a local chemical messenger for interneuronal communications in mammalian central and peripheral nervous systems. In the present study, blue emitting copper nanocluster was synthesized in presence (BSA CuNC1) and absence (BSA CuNC2) of hydrogen peroxide and fluorescence response of the two systems towards dopamine was analysed. At an excitation of 355 nm, fast response towards dopamine detection was obtained for BSA CuNC1 system having limit of detection 0.1637 pM. The fast interaction of dopamine with BSA CuNC1 can be attributed to the intrinsic peroxidase like activity of CuNC in presence of H 2 O 2. On the other hand, the response of dopamine towards BSA CuNC2 was very slow with a limit of detection 0.024 nM. Encouraged by the fast response and low limit of detection, the BSA CuNC1 system was effectively applied for dopamine detection in real sample matrices. The recovery percentage for serum sample obtained was in the range 90–98.33% and for urine sample was in the range 89–96.66%. In addition to that, a paper test strips using BSA CuNC1 was developed which exhibited colour change as well as fluorescence quenching, creates a low cost approach for the fast monitoring of dopamine. [ABSTRACT FROM AUTHOR]

The authors describe blue-green emitting nitrogen doped carbon dots (NCDs) synthesized through a microwave assisted polyol method and by using lactose as the carbon source, ammonium chloride as nitrogen source and PEG 200 as the reaction medium. The surfaces of the NCDs is rich in carboxy groups and can be functionalized with aminophenylboronic acid (APBA) to obtain APBA-modified carbon dots which are shown to a viable fluorescent probe for dopamine (DA). Operated best at excitation wavelength of 370 nm, the fluorescence of the probe increases with increasing concentration of DA. The detection limit is as low as 89 pM. The probe has good selectivity for DA over other interfering neurotransmitters, saccharides, amino acids and antioxidants. It was successfully employed for the detection of DA in (spiked) human serum samples and gave good recoveries. [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]