One-step facile green synthesis of a highly fluorescent molecule through a way towards carbon dots and detection of dopamine based on in-situ formation of silver nanoparticles

Carbon dots derived from citric acid and amines have been gaining considerable attention due to their high quantum efficiency, but there are researches proven the presence of small fluorescent molecules in those materials. In this work, with proper control of the synthetic conditions, highly fluorescent 5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyridine-7-carboxylic acid (TPCA) as nice needle-like crystals were harvested by a simple one-step hydrothermal method directly based on the reaction of citric acid and cysteamine hydrochloride. The proposed synthesis route does not need extra complicated purification process. The yield of TPCA was 46.9% and the quantum yield was as high as 83.2%. Experimental results confirmed that TPCA possesses all advantages of carbon dots reported previously with similar starting materials. In addition, a novel and effective fluorescent probe, TPCA-Ag+, was designed for sensitive and selective sensing of dopamine (DA) based on in-situ formation of sliver nanoparticles. The calibration curve for DA was linear up to 0.4 μmol/L, and a detection limit of 0.75 nmol/L was attained. The method was successfully applied to the determination of DA in dopamine hydrochloride injection and urine samples and the standard addition recoveries were in a range of 87.2-102.8%.