Water-soluble and stable CdTe quantum dots were synthesized in aqueous solution with thioglycolic acid as the stabilizer. A spectrofluorometric method for the determination of iron (II) has been developed based on quenching of the fluorescence of CdTe quantum dots by iron (II) in aqueous solutions. It can perform an accurate and simple determination of iron (II) concentration in water samples. Under optimum conditions, the quenched fluorescence intensity increased linearly with the concentration of iron (II) ranging from 5.0 Â 10 À8 to 4.0 Â 10 À6 mol=L with a correlation coefficient R ¼ 0.9969. The limit of detection for iron (II) was found to be 1.2 Â 10 À8 mol=L. As an application, the proposed method was successfully applied to the analysis of iron (II) in water samples, and the results were satisfactory.
A sensitive and selective colorimetric biosensor for determination of gentamicin, amikacin and tobramycin was proposed with the unmodi¯ed gold nanoparticles (GNPs) as the sensing element. Gentamicin, amikacin and tobramycin can rapidly induce the aggregation of gold nanoparticles and is accompanied by a color change from red to blue. The concentration of gentamicin, amikacin and tobramycin can be determined by using UV-Vis spectrometer. The experimental parameters were optimized with regard to pH, incubation time and the concentration of the GNPs. Under optimal experimental conditions, the linear range of the colorimetric sensor for gentamicin/amikacin/tobramycin were 2.67À33.93 ng mL À1 , 13.33À66.67 ng mL À1 and 20À180 ng mL À1 , respectively. The corresponding limit of detection (3) was 0.354 ng mL À1 , 0.999 ng mL À1 and 0.579 ng mL À1 , respectively. This assay was simple and used to detect aminoglycoside antibiotics in milk and medicine products.
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