Quantum dots (QDs) are usually used as fluorescent probe, and they are difficult to use in colorimetric detection. However, in this report carboxyl-functionalized CdS (COF-CdS) QDs were synthesized in aqueous solution for colorimetric detection following a classic method. On the basis of inducing the aggregation of COF-CdS QDs, a simple naked eye colorimetric method with high sensitivity and selectivity was developed for the sensing of Co(2+) ions in aqueous solutions. The Co(2+) ions induced COF-CdS QDs results in a marked enhancement of the UV-vis absorption spectra at 360 nm, and the process was accompanied by a visible color change from colorless to yellowish brown within 5 min, which proves a sensitive detection of Co(2+) ions. The sensing of Co(2+) ions can therefore be easily achieved by a UV-vis spectrophotometer or even by the naked eye. Under the optimized circumstances, this method yields excellent sensitivity (LOD = 0.23 μg mL(-1)) and selectivity toward Co(2+) ions. The calibration plot of (A - A(0)) at 360 nm against concentration of Co(2+) ions was linear over the range from 0.5 to 14 μg mL(-1) with a correlation coefficient of 0.9996. The accuracy and reliability of the method were further ascertained by recovery studies via standard addition method with percent recoveries in the range of 99.63-102.46%. The plausible mechanism for the color change reaction has also been discussed. Our attempt may provide a cost-effective, rapid, and simple solution for the inspection of Co(2+) ions in the presence of a complex matrix from environmental aqueous samples.

No abstract

This study reports the interaction and energy transfer between fluorescent carbon quantum dots (CQDs) and D-Penicillamine capped gold nanoparticles (DPA-AuNPs). The CQDs was synthesized by a simple chemical oxidation method at room temperature. The prepared CQDs shows a strong fluorescence at λ em  = 430 nm when excited at λ ex  = 320 nm. The interaction of CQDs with DPA-AuNPs was characterized by fluorescence spectroscopy, Transmission Electron Microscopy (TEM) study and Dynamic Light Scattering (DLS) techniques. The fluorescence study shows the continuous quenching in the fluorescence intensity of CQDs in presence of increasing concentrations of DPA-AuNPs. The change in fluorescence spectra of CQDs in presence of increasing concentration of DPA-AuNPs and quenching are suggestive of a rapid adsorption of CQDs on the surface of DPA-AuNPs. The K sv , K, K q and n values were calculated and results indicated that the dynamic type of quenching takes place. The distance between donor and acceptor (r) is 6.07 nm which supports the energy transfer by Fluorescence Resonance Energy Transfer (FRET) phenomenon. The plausible mechanism for FRET is also discussed.

We here for the first time demonstrate an analytical approach for the highly selective and sensitive detection of amoxicillin (Amox) in aqueous medium based on the fluorescence quenching of quantum dots (QDs). The change in fluorescence intensity of mercaptopropionic acid-capped cadmium sulphide (MPA-CdS) QDs is attributed to the increasing concentration of Amox. The results show that the fluorescence quenching of QDs by Amox takes place through both static and dynamic types of quenching mechanism. The fluorescence quenching of QDs with increase in concentration of Amox shows the linear range between 5 μg ml and 30 μg ml and the limit of detection (LOD) is 5.19 μg ml . There is no interference of excipients, which are commonly present in pharmaceutical formulation and urine samples. For the practical application approach, the developed method has been successfully applied for the determination of Amox in pharmaceutical formulations and urine samples with acceptable results.

A cadmium sulfide quantum dot based dual fluorescent "On-Off-On" probe was designed and applied for monitoring of mercuric ions and N-acetylcysteine in aqueous solution.