ascorbic-acid and cadmium-sulfide

We present a Förster resonance energy transfer (FRET)-based fluorescence detection of vitamin C [ascorbic acid (AA)] using cadmium sulphide quantum dots (CdS QDs) and diphenylcarbazide (DPC). Initially, DPC was converted to diphenylcarbadiazone (DPCD) in the presence of CdS QDs to form QD-DPCD. This enabled excited-state energy transfer from the QDs to DPCD, which led to the fluorescence quenching of QDs. The QD-DPCD solution was used as the sensor solution. In the presence of AA, DPCD was converted back to DPC, resulting in the fluorescence recovery of CdS QDs. This fluorescence recovery can be used to detect and quantify AA. Dynamic range and detection limit of this sensing system were found to be 60-300 nM and 2 nM, respectively. We also performed fluorescence lifetime analyses to confirm existence of FRET. Finally, the sensor responded with equal accuracy to actual samples such as orange juice and vitamin C tablets. Graphical abstract Schematic showing the FRET based fluorescence detection of ascorbic acid.

Topics: Ascorbic Acid; Cadmium Compounds; Fluorescence Resonance Energy Transfer; Limit of Detection; Quantum Dots; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Sulfides

The gamma irradiation method has provided a route for synthesis of highly water-soluble, good-quality luminescent CdS/dendrimer nanocomposites with amino- or carboxyl-terminated PAMAM dendrimer. An attempt has been made to probe ascorbic acid with the as-synthesized CdS/dendrimer nanocomposites (DNC). Ascorbic acid (AA) is an important biological antioxidant and marker for different diseases in clinical chemistry as well as in quality control in the food industry. Micromolar concentrations of AA significantly quenched the photoluminescence (PL) of both amino (-NH(2)) and carboxylic (-COOH) functionalized semiconductor nanocomposites. The quenching followed a linear Stern-Volmer equation and time-resolved photoluminescence spectroscopy confirmed its static nature. A strong size dependence of the quenching pattern was observed. The binding constants, and the corresponding thermodynamic parameters DeltaG(theta), DeltaH(theta), DeltaS(theta) at different temperatures were calculated. CdS DNC showed selectivity towards ascorbic acid even in the presence of possible interfering molecules, such as uric acid, tartaric acid and citric acid. Nanocomposites-based assay techniques could override the complications involved in multitudes of assay procedures, providing a simple and fast new strategy for the quantification of Ascorbic acid in the range of 16.6 to 100 microM (R=0.998, n=9). The proposed method was applied to the detection of ascorbic acid in Vitamin C tablets with satisfactory results.

Topics: Ascorbic Acid; Cadmium Compounds; Dendrimers; Fluorescence; Fluorometry; Nanostructures; Particle Size; Photochemistry; Quantum Dots; Semiconductors; Spectrophotometry, Ultraviolet; Sulfides; Surface Properties; Temperature; Thermodynamics