Highly sensitive and selective fluorescence and smartphone-based sensor for detection of L-dopa using nitrogen sulphur graphene quantum dots

The level of L-dopa in the body has a significant impact on treatment of Parkison's disease. L-Dopa, a precursor to the neurotransmitter dopamine has been unanimously recommended as the gold standard for treating the condition. The present work focuses on creating a flexible platform for the quantitative and targeted detection of L-dopa using nitrogen sulphur co-dopped graphene quantum dots (NSGQD). The NSGQD were prepared by using thiourea and citric acid via calcination process. The synthesised NSGQD emitted bright bluish green light with the addition of L-Dopa to NSGQD in basic condition the fluorescence of NSGQD was quenched. L-dopa is transformed into dopaquinone in an alkaline environment and photoinduced electron transfer causes fluorescence quenching. As a result, the intensity of the NSGQD fluorescence gradually decreased as the L-dopa concentration rose in wide concentration range and low limit of detection (LOD) was established to be 7.8 nM relative to other analytes, quinone derivatives and amino acids the NSGQD showed greater specificity to L-dopa. The sensing mechanism was thoroughly investigated using steady state, time-resolved fluorescence spectroscopy, UV–Vis absorption measurements and fluorescent studies. Additionally, this also proves through smartphones portable device using color detector software. Our research paves the way for the creation of an affordable biosensor that will work well for finding L-dopa in actual samples. Computational studies were carried out using density functional theory for better understanding the interactions of dopa with NSGQD indicating hydrogen bonds are formed between carbonyl group of dopaquinone with functional groups of NSGQD.