tellurium and melamine

A facile strategy was developed to prepare mesoporous structured ratiometric fluorescence molecularly imprinted sensor for highly sensitive and selective determination of melamine using CdTe QDs as target sensitive dye and hematoporphyrin as reference dyes. One-pot synthesis method was employed because it could simplify the imprinting process and shorten the experimental period. The as-prepared fluorescence MIPs sensor, which combined ratiometric fluorescence technique with mesoporous silica materials into one system, exhibited excellent selectivity and sensitivity. Under optimum conditions, these mesoporous structured ratiometric fluorescence MIP@QDs sensors showed detection limit as low as 38 nM, which was much lower than those non-mesoporous one. The recycling process was sustainable at least 10 times without obvious efficiency decrease. The feasibility of the developed method in real samples was successfully evaluated through the analysis of melamine in raw milk and milk powder samples with satisfactory recoveries of 92-101%. The developed method proposed in this work proved to be a convenient, rapid, reliable and practical way to prepared high sensitive and selective fluorescence sensors with potentially applicable for trace pollutants analysis in complicated samples.

Topics: Animals; Biosensing Techniques; Cadmium Compounds; Chemistry Techniques, Synthetic; Fluorescent Dyes; Food Contamination; Hematoporphyrins; Milk; Molecular Imprinting; Quantum Dots; Silicon Dioxide; Spectrometry, Fluorescence; Tellurium; Triazines

A novel procedure for the optosensing of clenbuterol and melamine was developed using molecularly imprinted polymer-capped CdTe quantum dots (MIP-CdTe QDs). The MIP-CdTe QDs were synthesized by a radical polymerization process among CdTe QDs, a template, 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS). The sizes of the MIP-CdTe particles were controlled by the speed of polymerization, concentration of the template, concentration of the quantum dots, and the ratio of template, monomer and cross-linker. Excellent selectivity and high sensitivity of MIP-CdTe QDs toward clenbuterol/melamine molecules were observed based on the fluorescence quenching of QDs. Experimental results showed that the optimum molar ratios of template, monomer, and cross-linker were 1:8:20 and 1:4:20 for analyzing clenbuterol and melamine, respectively. Under optimum conditions, these MIP-CdTe QDs showed a limit of detection of 0.4 μM (120 ng/mL) for clenbuterol and 0.6 μM (75 ng/mL) for melamine. The feasibility of the developed method in real samples was successfully evaluated through the analysis of clenbuterol and melamine in milk and liver samples with satisfactory recoveries of 92-97%. The MIP-CdTe QDs could be easily regenerated for subsequent sample analysis with water.

Topics: Adrenergic beta-Agonists; Animals; Biosensing Techniques; Cadmium Compounds; Clenbuterol; Food Contamination; Limit of Detection; Milk; Molecular Imprinting; Propylamines; Quantum Dots; Silanes; Tellurium; Triazines

In this paper, we constructed the fluorescence resonance energy transfer (FRET) system between MPA-capped CdTe quantum dots (QDs) and Rhodamine B (RB) in the environment of cetyltrimethylammonium bromide (CTAB). In this system, CdTe QDs were treated as energy donors, whilst RB was treated as energy acceptor. CTAB was used to make the distance between the particles of CdTe QDs and RB closer to improve the efficiency of FRET system. We optimized some important factors which would affect the efficiency of FRET system. Under the optimized experimental conditions, melamine (MB) could be detected based on the fluorescence intensity changes of RB in the FRET system. We could get a linear relationship between the fluorescence intensity of RB and the concentration of MB in the range of 0.05-4.0 μmol/L and the detection limit was 0.01 μmol/L. The proposed method was applied for the determination of melamine in milk samples with satisfactory results.

Topics: Animals; Cattle; Fluorescence; Fluorescence Resonance Energy Transfer; Food Contamination; Limit of Detection; Milk; Quantum Dots; Rhodamines; Tellurium; Triazines

Water-soluble CdTe quantum dots of different sizes capped with thioglycolic acid (TGA-CdTe QDs) were synthesised via a microwave-assisted method. It was found that melamine could quench the fluorescence emission of TGA-CdTe QDs in aqueous solution. Based on this, a novel method for the determination of melamine has been developed. Under optimum conditions, the fluorescence intensity of TGA-CdTe QDs versus melamine concentrations gave a linear response according to the Stern-Volmer equation. The proposed method has been successfully used to detect melamine in liquid milk with a detection limit of 0.04 mg L⁻¹, and the whole process including sample pre-treatment could be accomplished within 30 min. The obvious merits provided by this method, such as simplicity, rapidity, low cost and high sensitivity would make it promising for on-site screening of melamine adulterant in milk products. The possible mechanism involved in the interaction of melamine with TGA-CdTe QDs is discussed.

Topics: Animals; Cadmium Compounds; Calibration; Feasibility Studies; Fluorescent Dyes; Food Contamination; Food Inspection; Hydrogen-Ion Concentration; Limit of Detection; Milk; Particle Size; Quantum Dots; Solubility; Spectrometry, Fluorescence; Surface Properties; Tellurium; Thioglycolates; Time Factors; Triazines

We here report an efficient and enhanced fluorescence energy transfer system between confined quantum dots (QDs) by entrapping CdTe into the mesoporous silica shell (CdTe@SiO₂) as donors and gold nanoparticles (AuNPs) as acceptors. At pH 6.50, the CdTe@SiO₂-AuNPs assemblies coalesce to form larger clusters due to charge neutralization, leading to the fluorescence quenching of CdTe@SiO₂ as a result of energy transfer. As compared with the energy transfer system between unconfined CdTe and AuNPs, the maximum fluorescence quenching efficiency of the proposed system is improved by about 27.0%, and the quenching constant, K(sv), is increased by about 2.4-fold. The enhanced quenching effect largely turns off the fluorescence of CdTe@SiO₂ and provides an optimal "off-state" for sensitive "turn-on" assay. In the present study, upon addition of melamine, the weak fluorescence system of CdTe@SiO₂-AuNPs is enhanced due to the strong interactions between the amino group of melamine and the gold nanoparticles via covalent bond, leading to the release of AuNPs from the surfaces of CdTe@SiO₂; thus, its fluorescence is restored. A "turn-on" fluorimetric method for the detection of melamine is proposed based on the restored fluorescence of the system. Under the optimal conditions, the fluorescence enhanced efficiency shows a linear function against the melamine concentrations ranging from 7.5 × 10⁻⁹ to 3.5 × 10⁻⁷ M (i.e., 1.0-44 ppb). The analytical sensitivity is improved by about 50%, and the detection limit is decreased by 5.0-fold, as compared with the analytical results using the CdTe-AuNPs system. Moreover, the proposed method was successfully applied to the determination of melamine in real samples with excellent recoveries in the range from 97.4 to 104.1%. Such a fluorescence energy transfer system between confined QDs and AuNPs may pave a new way for designing chemo/biosensing.

Topics: Cadmium Compounds; Fluorescence Resonance Energy Transfer; Food Contamination; Food Inspection; Gold; Metal Nanoparticles; Quantum Dots; Silicon Dioxide; Tellurium; Triazines