Facile synthesis of water-soluble and size-homogeneous cadmium selenide nanoparticles and their application as a long-wavelength fluorescent probe for detection of Hg(II) in aqueous solution

Hydrophilic graphene quantum dots as turn-off fluorescent nanoprobes for toxic heavy metal ions detection in aqueous media

Efforts are being made to develop fast, cost-effective and sensitive sensor to detect water contamination by toxic heavy metal ions. The oxygenated functional groups decorated graphene quantum dots (GQDs) effectively enhances the aqueous solubility and considered as a more desirable and simple sensing material with high sensitivity. Here, photoluminescence (PL) property of GQDs has been employed to devise an optical nanosensor for the detection of toxic heavy metal ions in aqueous media. Hydrothermal method was employed to synthesize highly fluorescent and water soluble GQDs. The fluorescence intensity reduces with the increase in toxic heavy metal ions concentration. The observed PL was analyzed by the Stern-Volmer equation to study the fluorescent quenching mechanism of the system. Nonlinear behavior of Stern-Volmer plot suggests that the reduction in the fluorescent intensity is due to the combination of dynamic and static processes. The fluorescence quenching results showed that, the as synthesized GQDs are an efficient fluorescent probe for heavy metal ions viz. Hg²⁺, Cd²⁺ and Pb²⁺ with the detection limit of 1.171 μM, 2.455 μM and 2.011 μM respectively. This study shows the viability of GQDs as promising material for sensing the heavy metal ions in aqueous solution.

A New Fluorescence Sensor for Cerium (III) Ion Using Glycine Dithiocarbamate Capped Manganese Doped ZnS Quantum Dots

A new fluorescence sensor for Ce(3+)ions is reported in this paper. This sensor is based on the fluorescence quenching of glycine dithiocarbamate (GDTC)-functionalized manganese doped ZnS quantum dots (QDs) in the presence of Ce(3+)ions. The synthesis of ultra-small GDTC-Mn:ZnS quantum dots (QDs) is based on the co-precipitation of nanoparticles in aqueous Solution. The nanoparticles are characterized with fluorescence spectroscopy, UV-vis absorption spectra, high-resolution transmission electron microscopy, X-ray power diffraction (XRD), and infrared spectroscopy. In the test carried out, it was found that the interaction between Ce(3+)ions and GDTC capped Mn:ZnS QDs quenches the original fluorescence of QDs according to the Stern-Volmer equation and the results show the existence of collisional quenching process. A linear relationship was observed between the extent of quenching and the concentration of Ce(3+)in the range of 2.0 × 10(-6) to 3.2 × 10(-5) mol.L(-1), with a detection limit of 2.29 × 10(-7) mol.L(-1). The relative standard deviation of 1.61% was obtained for five replicate measurements. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra. The interference of other cations was negligible on the quantitative determination of Ce(3+). This method proved to be simple, sensitive, low cost, and also reliable for practical applications.

Colorimetric detection of trace Hg²+ with near-infrared absorbing squaraine functionalized by dibenzo-18-crown-6 and its mechanism

In this contribution, an improved near-infrared absorbing colorimetric detection of Hg(2+) ion with high selectivity and sensitivity had been developed by using bis-dibenzo-18-crown-6-based squaraine (BCSQ) as sensor in aqueous media. The proposed method was applied to analyze trace Hg(2+) in synthetic Hg(2+) samples and natural Hg(2+) samples. Under the optimum conditions, the detection had a linear range of 7.5-150 × 10(-8) mol L(-1) with a correlation coefficient (R) of 0.9983 combining a limit detection (3σ, n=20) of 5.6 × 10(-9) mol L(-1). The relative standard deviation (RSD) was lower than 2.4% (n=5). The proposed method possesses the advantages of simplicity, rapidity, high selectivity and sensitivity. The action mechanism between BCSQ and Hg(2+) was discussed in details.

A sensitive localized surface plasmon resonance sensor for determining mercury(II) ion using noble metal nanoparticles as probe

The noble metal nanoparticles (NPs), including gold nanorods (AuNRs), gold nanospheres (AuNSs) and silver nanoplates (AgNPTs), were synthesized and Tween 20 stabilized NPs (Tween 20-NPs) were used as the probes for determining Hg(2+). Hg(2+) was determined based on the strong affinity between Au (Ag) and Hg. Hg(2+) was reduced to Hg in the presence of sodium borohydride. Hg interacts with the NPs and the diameter of the NPs decreases with the increase of Hg(2+) concentration, which causes the shift in absorption peak of Tween 20-NPs. The peak shifts are linearly related to Hg(2+) concentrations. Compared with AuNSs and AgNPTs, when the AuNRs was used, the sensitivity for determining Hg(2+) was higher. The developed method shows a good selectivity for Hg(2+) and can be applied to the determination of Hg(2+) in water samples.

Citrate-capped Mn-modified CdSe/CdS quantum dots as luminescent probes for levodopa detection in aqueous solution

A novel kind of citrate capped Mn-modified CdSe/CdS quantum dots (QDs) was developed. The Mn-modified CdSe/CdS QDs had a narrow, symmetric emission and strong fluorescence with quantum yield over 41%. The interaction between the QDs and levodopa was investigated. The results showed that levodopa selectively quenched the fluorescence intensity of the QDs. Based on the fluorescence quenching of the synthesized QDs by levodopa, a simple, rapid and specific quantitative method for levodopa was proposed. The factors affecting the fluorescence detection for levodopa were studied. Under the optimum conditions, the quenched intensity of the fluorescence versus levodopa concentration from 1 to 100 μM gave a linear response with an excellent correlation coefficient of 0.9996, and the limit of detection (3σ/K) was 2 × 10(-7)M. The contents of levodopa in pharmaceutical tablets were determined by the proposed method and the results agreed with the claimed values.

Probing metabolic stability of CdSe nanoparticles: alkaline extraction of free cadmium from liver and kidney samples of rats exposed to CdSe nanoparticles

Cadmium selenide nanoparticles (CdSe NPs) exhibit novel optoelectronic properties for potential biomedical applications. However, their metabolic stability is not fully understood because of the difficulties in measurement of free Cd from biological tissues of exposed individuals. In this study, alkaline dissolution with tetramethylammonium hydroxide (TMAH) is demonstrated for selective determination of free Cd and intact NPs from liver and kidney samples of animals that were exposed to thiol-capped CdSe NPs. Aqueous suspensions of CdSe NPs (3.2 nm) were used to optimize the conditions for extracting free Cd without affecting NPs. Nanoparticles were found to aggregate when heated in TMAH without releasing any significant Cd to solution. Performance of the method in discriminating free Cd and intact NPs were verified by Dogfish Liver (DOLT-4) certified reference material. The samples from the animals were digested in 4 mL TMAH at 70°C to extract free Cd followed by analysis of aqueous phase by ICP-MS. Both liver and kidney contained significant levels of free Cd. Total Cd was higher in the liver, while kidney accumulated mostly free Cd such that up to 47.9% of total Cd in the kidney was free Cd when NPs were exposed to UV-light before injection.