Role of a cationic surfactant in mediating interaction of flavonoids with 3-mercaptopropanoic acid capped CdTe quantum dots (3MPA-CdTe QDs)

Photocatalytic removal of imidacloprid pesticide from wastewater using CdS QDs passivated by CQDs containing thiol groups

Over the past decade, CdS QDs have become versatile semiconductors. Surface modification of CdS QDs has become an interesting case study, as it can eliminate surface defects and improve their photochemical properties. In this study, we report a new strategy of using carbon quantum dots containing a large number of thiol groups (CQDs-SH) as a passivating agent for the stabilization of CdS quantum dots (QDs). Various characterization techniques have clearly revealed that the CdS QDs have been successfully passivated by CQDs-SH. The photocatalytic performance of CQDs-SH/CdS QDs was investigated for the degradation of the insecticide imidacloprid from an aqueous solution. Parameters affecting the photodegradation process, including the light source, photocatalyst amount, initial concentration of the pollutant, radiation time, pH, oxidizing agent, and temperature, were investigated. Furthermore, the HPLC technique was applied to quantitatively analyze imidacloprid and its degradation products. The results of the HPLC analysis revealed that under simulated visible light at pH 9, imidacloprid scarcely existed after 90 min of irradiation (90.13% degradation). The LC-MS method was also used to detect the degradation products and investigate the mechanism of photodegradation of the pesticide. The results showed that the CQDs-SH/CdS QDs composite was a promising photocatalyst for the degradation of imidacloprid in wastewater.

A simple strategy to enhance the sensitivity of fluorescent sensor-based CdS quantum dots by using a surfactant for Hg2+ detection

A simple strategy to enhance the detection sensitivity of fluorescent sensor-based CdS quantum dots (CdS QDs) for the detection of mercury ions (Hg²⁺) was demonstrated. L-Cysteine-capped CdS QDs (L-Cyst-CdS QDs) were synthesized and utilized as a probe for selective detection of Hg²⁺. The fluorescence intensity of the L-Cyst-CdS QDs was quenched in the presence of Hg²⁺. However, the detection sensitivity was unsatisfactory. Upon the addition of sodium dodecyl sulfate (SDS), the fluorescence intensity of L-Cyst-CdS QDs can be effectively enhanced. On the other hand, the fluorescence intensity of the L-Cyst-CdS QDs in the presence of SDS (SDS@L-Cyst-CdS QDs) was able to be dramatically decreased with the addition of Hg²⁺. Furthermore, the proposed sensor displayed excellent selectivity towards Hg²⁺ compared to other cations. Under optimized conditions, the proposed sensor could be applied to detect trace amounts of Hg²⁺ with a limit of detection of approximately 36 nM. The applicability of this sensor was demonstrated by the determination of Hg²⁺ in real water samples, and the results agreed with those obtained from cold vapor atomic absorption spectrometry (CVAAS).

Glutathione Modified Fluorescent CdS QDs Synthesized Using Environmentally Benign Pathway for Detection of Mercury Ions in Aqueous Phase

An adept, rapid and novel water-soluble glutathione functionalized CdS quantum dots (GSH@CdS QDs) were fabricated using green pathway for sensing of heavy metal contamination prevalent in industrial wastewater. GSH@CdS QDs were facilely synthesized in an aqueous phase reaction and were effectively characterized using FT-IR, XRD, FESEM, HRTEM and EDX techniques. The distinct fluorescence characteristics of GSH@CdS QDs were explored and the QDs showed selective sensitivity towards mercury ions with a low limit of detection of 0.54 nM under optimal conditions. The detailed interaction between GSH@CdS QDs and Hg²⁺ and the probable fluorescence quenching mechanism were established in this study. In comparison to already reported fluorescent probes, GSH@CdS QDs showed high sensitivity, biocompatibility, long fluorescence stability and convenient removal of mercury ions. Graphical Abstract Facile green route for the fabrication of glutathione capped CdS quantum dots for fluorescence-based detection of toxic Hg²⁺ ions.

A fluorescent microsensor for the selective detection of bifenthrin

Based on the fluorescence quenching phenomenon, a smart fluorescent microsensor was synthesized. The bifenthrin (BI) microsensor inherited the high selectivity of molecular imprinted polymers (MIPs) and the excellent fluorescence properties of aqueous CdTe quantum dots (QDs). Aqueous CdTe QDs are functionalized by octadecyl-4-vinylbenzyl-dimethyl-ammonium chloride (OVDAC). A type of functional monomer, 4-vinylphenylboronic acid (VPBA), was used and its boronic acid groups could covalently combine with a cis-diol compound for direct imprinting polymerization. The OVDAC-functionalized aqueous CdTe QDs were used as solid supports and auxiliary monomers. Under optimal conditions, experimentation showed that BI had a linear detection range of 10 to 300 μmol L⁻¹ with a correlation coefficient of 0.9968 and a high imprinting factor (IF) of 4.53. In addition, the prepared MIP-OVDAC/CdTe QDs were successfully used to detect BI in water samples. Therefore, this work provided a highly selective and sensitive fluorescence probe for the detection of BI. In addition, the fluorescence probe could be used to detect other targets by changing the functional monomers.

Based on the fluorescence quenching phenomenon, a smart fluorescent microsensor was synthesized.

Physical and Chemical Stability of Formulations Loaded with Taxifolin Tetra-octanoate

Chemically stable ester derivatives of taxifolin have become a focus of interest for their role in the satisfactory effects on human health. Accordingly, the aim of this study was to evaluate the physical and chemical stability of different formulations containing 0.02% taxifolin tetra-octanoate, which was proved to possess higher inhibitory effect on tyrosinase activity compared with taxifolin in a cell-free system. In the studies of physical stability, a Brookfield viscometer was used to determine rheological behavior of formulations containing taxifolin tetra-octanoate, and a portable pH meter was used to determine pH change. Moreover, chemical stability was determined by HPLC with UV detection. Formulations were evaluated for 12 weeks stored at 25 and 40°C. Results showed that storage time had no significant influence on viscosity of the formulations containing taxifolin tetra-octanoate, and pH value was relatively stable, which was within the limits of normal skin pH range. In the chemical stability studies, taxifolin tetra-octanoate in the essence formulation was most unstable at 40°C with about 81% degradation in 12 weeks of storage, however, the percentage of remaining taxifolin tetra-octanoate in cream formulation stored for 12 weeks at 25°C was the highest, about 93%. The results in this study may contribute to the development of more stable formulations containing taxifolin tetra-octanoate.