A Novel Turn-On Fluorescence Probe for Selective Picomolar Detection of Uric Acid Using Green Carbon Dots (G-NCDs) from Waste Brachyura Shells

In the current study, a Novel synthesis of fluorescent Green carbon dots (G-NCDs) is reported from waste Brachyura shells using a simple, green technique. G-NCDs function as a TURN-ON fluorescent probe for the selective detection Uric Acid (UA) in presence of Dopamine (DA). The synthesized carbon dots are sand colored under visible light and exhibit pale green fluorescence under UV radiation. The G-NCDs are characterized using UV-vis, FTIR, XPS, SEM-EDAX, HR-TEM, X-ray diffraction, and PL spectroscopic technique. The SEM-EDAX data of G-NCDs shows a layered, fibrous morphology and confirms the presence of only Carbon, Nitrogen, and Oxygen in the matrix. FTIR and XPS response confirms the presence of functional groups like & horbar;C equivalent to N, & horbar;C equivalent to C & horbar;, CH, & boxH;C & horbar;H, O & horbar;H on the surface of G-NCDs. XRD data confirms G-NCDs to be crystalline with a particle size of 4.51 nm. The quantum yield found to be 99.8%. PL response confirms a TURN OFF fluorescence with increased addition of DA. Fluorescence resonance energy transfer (FRET), a form of dynamic quenching is responsible for the DA quenching, confirmed through linear Stern- Volmer plot. With increase in addition of UA in presence of DA fluorescence TURNs ON with a minimum selective detection limit of UA as 0.23 x 10-12 M. Selective detection of UA in presence of DA is due to the following reasons i) decrease in bandgap of G-NCDs in presence of UA ii) electrostatic attraction between negatively charged carboxyl group of G-NCDs and positively charge secondary amine group of UA molecule ii) UA molecules near to the surface of G-NCDs switches off the formation of polydopamine iv) formation of surface defects due to the formation of hydrogen bonds between the ketone/hydroxyl group in the UA molecule and the amino group on the surface of G-NCD resulting in fluorescence. The first time the lowest detection limit of 0.23 x 10-12 M of UA is been reported in presence of DA using G-NCDs. In future, G-NCDs will be used for the detection of UA in biological fluids.