[Study on the synchronous interactions between different thiol-capped CdTe quantum dots and BSA].

The modifier of quantum dots plays an important role in synthesis and nature of quantum dots, however the effect on the interaction between quantum dots and protein is not very clear until up to now. In the present paper, the interactions of CdTe quantum dots with bovine serum album (BSA) were studied by spectroscopy methods including ultraviolet-visible absorption spectrometry (UV-Vis), fluorescence spectrometry (FL) and infrared spectrometry (IR). The CdTe quantum dots were modified by three different thiol-complex including thioglycolic acid, L-cysteine and glutathione, i. e. thioglycolic acid capped CdTe quantum dots (CdTe(T)), L-cysteine capped CdTe quantum dots (CdTe(L)) and glutathione capped CdTe quantum dots (CdTe(G)) respectively. The quenching constant K(sv) and corresponding thermodynamic parameters, such as enthalpy change (deltaH(theta)), entropy change (deltaS(theta)), Gibbs free energy change (deltaG(theta)), were calculated according to Stern-Volmer equations. The results showed that CdTe(T), CdTe(L) and CdTe(G) all have a strong ability of quenching the fluorescence of bovine serum albumin, and the interactions of the three types of thiol-capped CdTe quantum dots with BSA were static quenching process. The quenching constant of K(sv)(TGA) is similar to K(sv)(GSH), which is much less than K(sv)(L-Cys). The binding forces of CdTe(T) and CdTe(L) with the BSA were the main contributions from hydrophobic force according to the thermodynamic parameters (deltaH(theta) > 0, deltaS(theta) > 0 and deltaG(theta) < 0), while the binding forces of CdTe(G) with BSA were composed of both hydrogen bonding force and hydrophobic force according to the thermodynamic parameters(deltaH(theta) < 0, deltaS(theta) > 0 and deltaG(theta) < 0). It was found that different functional group and molecular volume size of thiol surface modified reagent played an important role in the interactions between CdTe QDs and BSA.

Study on the interaction between CdSe quantum dots and hemoglobin.

The interaction between CdSe quantum dots (QDs) and hemoglobin (Hb) was investigated by ultraviolet and visible (UV-vis) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and fluorescence (FL) spectroscopy. The intensity of UV-vis absorption spectrum of a mixture of CdSe QDs and Hb was obviously changed at the wavelength of 406nm at pH 7.0, indicating that CdSe QDs could bind with Hb. The influences of some factors on the interactions between CdSe QDs and Hb were studied in detail. The binding molar ratio of CdSe QDs and Hb was 12:1 by a mole-ratio method. The mechanism of the interaction between CdSe QDs and Hb was also discussed.

The interaction between some diamines and CdSe quantum dots.

The interaction of some diamines (ethylenediamine (EDA), 1,6-hexanediamine (HDA), o-phenylenediamine (OPD)) with CdSe quantum dots (QDs) is reported. With increasing concentration of EDA from 0 to 2.0 x 10(-6) mol l(-1), slight fluorescence enhancement is observed. However, the CdSe QDs fluorescence quenching is seen at relatively higher concentration of EDA. There is a red-shift of 0-7 nm in fluorescence emission spectra of CdSe QDs when the concentration of EDA is changed from 2.0 x 10(-6) to 8.0 x 10(-6) mol l(-1). The resonance light scattering (RLS) spectra of CdSe QDs have little change when the concentration of EDA is less than 5.0 x 10(-6) mol l(-1). It indicates there are little large particles formed in the solution. However, a significant increase of the RLS is observed in the 300-500 nm wavelength range after adding higher concentration than 5.0 x 10(-6) mol l(-1) EDA, which could be attributed to the large particles formed. The interaction between HDA and CdSe QDs is similar to that of EDA. However, with the OPD, it is found that the interaction is much different from those of EDA, HDA, and that the quenching, even at low concentration, is effective for CdSe QDs emission. The quenching phenomenon could be explained by a surface bound complexation equilibrium model.

Preparation and characterization of overcoated II-VI quantum dots.

A convenient route for the synthesis of high-quality overcoated II-VI quantum dots (QDs) is reported in this paper. Simple salts, such as Cd(Ac)2 and Zn(Ac)2 were used to replace organometallics, whose disadvantage is obvious. Size-tunable core/shell structured QDs (CdSe/ZnS, CdSe/CdS, etc.) were synthesized. They were of narrow size distribution and had good monodispersivity and photoluminescence (PL) properties. The spectrum was symmetrical and sharp-pointed (with the full width at half-maximum (fwhm) of about 20-30 nm). The quantum yield (QY) was improved to 60-80% from 20-30% for bare QDs and remained stable at least for 6 months. The primary overcoated QDs were modified with biomacromolecules by a direct mechanical rubbing strategy, which is very simple and fast. The results obtained by UV-vis, PL, atomic force microscopy (AFM), and fluorescence microscopy imaging showed that the modified QDs were of good fluorescent and monodisperse characteristics. They are likely to be used further for biological labels.

Functionalized CdSe quantum dots as selective silver ion chemodosimeter.

CdSe quantum dots (QDs) have been prepared and modified with mercaptoacetic acid. They are water-soluble and biocompatible. To improve their fluorescence intensity and stability in water solution, bovine serum albumin (BSA) was absorbed onto their surface. Based on the quench of fluorescence signals of the functionalized CdSe QDs in the 543 nm wavelength and enhancement of them in the 570-700 nm wavelength range by Ag(I) ions at pH 5.0, a simple, rapid and specific method for Ag(I) determination was proposed. In comparison with single organic fluorophores, these nanoparticles are brighter, more stable against photobleaching, and do not suffer from blinking. Under the optimum conditions, the response is linearly proportional to the concentration of Ag(I) between 4.0 x 10(-7) and 1.5 x 10(-5) mol L(-1), and the limit of detection is 7.0 x 10(-8) mol L(-1). The mechanism of reaction is also discussed.