Direct synthesis of high-quality water-soluble CdTe:Zn2+ quantum dots.

The synthesis of water-soluble and low-cytotoxicity quantum dots (QDs) in aqueous solution has received much attention recently. A one-step and convenient method has been developed for synthesis of water-soluble glutathione (GSH)-capped and Zn(2+)-doped CdTe QDs via a refluxing route. Because of the addition of Zn ions and the epitaxial growth of a CdS layer, the prepared QDs exhibit superior properties, including strong fluorescence, minimal cytotoxicity, and enhanced biocompatibility. The optical properties of QDs are characterized by UV-vis and fluorescence (FL) spectra. The structure of QDs was verified by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), energy dispersive spectroscopy (EDS), atomic absorption spectrometry (AAS), and Fourier transform infrared spectroscopy (FTIR). Furthermore, the low cytotoxicity of the prepared QDs was proved by the microcalorimetric technique and inductively coupled plasma-atomic emission spectrometry (ICP-AES).

Toxicity evaluation of CdTe quantum dots with different size on Escherichia coli.

Quantum dots (QDs) have a great potential for applications in nanomedicine. However, a few studies showed that they also exhibited toxicity. We used Escherichia coli (E. coli) as the model to study the effect of CdTe QDs on the cell growth by microcalorimetric technique, optical density (OD(600)) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra. Three size aqueous-compatible CdTe QDs with maximum emission of 543 nm (green-emitting QDs, GQDs), 579 nm (yellow-emitting QDs, YQDs) and 647 nm (red-emitting QDs, RQDs) were tested. The growth rate constants (k) and half-inhibiting concentration (IC(50)) were calculated from the microcalorimetric data. The results indicated that CdTe QDs exhibited a dose-dependent inhibitory effect on cell growth. The order of toxicity is GQDs>YQDs>RQDs. The smaller the particle size of QDs is, the more toxicity it is. ATR-FTIR spectra indicated that the outer membrane of the cell was changed or damaged by the QDs, which may induce QDs and harmful by-products to enter into the cells. These could be one of the reasons that CdTe QDs have cytotoxic effects on E. coli.

Study of the bioeffects of CdTe quantum dots on Escherichia coli cells.

Quantum dots (QDs) hold great potential for applications in nanomedicine, however, only a few studies investigate their toxic- and bio-effects. Using Escherichia coli (E. coli) cells as model, we found that CdTe QDs exhibited a dose-dependent inhibitory effect on cell growth by microcalorimetric technique and optical density (OD(600)). The growth rate constants (k) were determined, which showed that they were related to the concentration of QDs. The mechanism of cytotoxicity of QDs was also studied through the attenuated total reflection-fourier transform infrared (ATR-FTIR) spectra, fluorescence (FL) polarization, and scanning electron microscopy (SEM). It was clear that the cell out membrane was changed or damaged by the addition of QDs. Taken together, the results indicated that CdTe QDs have cytotoxic effects on E. coli cells, and this effects might attribute to the damaged structure of the cell out membrane, thus QDs and by-products (free radicals, reactive oxygen species (ROS), and free Cd(2+)) which might enter the cells.

Bovine serum albumin-directed synthesis of biocompatible CdSe quantum dots and bacteria labeling.

A simple method was developed for preparing CdSe quantum dots (QDs) using a common protein (bovine serum albumin (BSA)) to sequester QD precursors (Cd(2+)) in situ. Fluorescence (FL) and absorption spectra showed that the chelating time between BSA and Cd(2+), the molar ratio of BSA/Cd(2+), temperature, and pH are the crucial factors for the quality of QDs. The average QD particle size was estimated to be about 5 nm, determined by high-resolution transmission electron microscopy. With FL spectra, Fourier transform infrared spectra, and thermogravimetric analysis, an interesting mechanism was discussed for the formation of the BSA-CdSe QDs. The results indicate that there might be conjugated bonds between CdSe QDs and -OH, -NH, and -SH groups in BSA. In addition, fluorescence imaging suggests that the QDs we designed can successfully label Escherichia coli cells, which gives us a great opportunity to develop biocompatible tools to label bacteria cells.

Conjugation and fluorescence quenching between bovine serum albumin and L-cysteine capped CdSe/CdS quantum dots.

Water-soluble, biological-compatible, and excellent fluorescent CdSe/CdS quantum dots (QDs) with L-cysteine as capping agent were synthesized in aqueous medium. Fluorescence (FL) spectra, absorption spectra, and transmission electron microscopy (TEM) were employed to investigate the quality of the products. The interactions between QDs and bovine serum albumin (BSA) were studied by absorption and FL titration experiments. With addition of QDs, the FL intensity of BSA was significantly quenched which can be explained by static mechanism in nature. When BSA was added to the solution of QDs, FL intensity of QDs was faintly quenched. Fluorescent imaging suggests that QDs can be designed as a probe to label the Escherchia coli (E. coli) cells. These results indicate CdSe/CdS/L-cysteine QDs can be used as a probe for labeling biological molecule and bacteria cells.

The damage of outer membrane of Escherichia coli in the presence of TiO2 combined with UV light.

The biological consequences of exposure to TiO2, UV light, and their combined effect were studied on the Escherichia coli (E. coli) cells. The damage of outer membrane was observed for the cells after treatment of TiO2 or UV light. TiO2 alone can break down lipopolysacchride (LPS), the outermost layer of the E. coli cells, but was not able to destroy peptidoglycan underneath. The same phenomenon was observed for E. coli under 500 W UV light treatment alone. However, the outer membrane of E. coli could be removed completely in the presence of both TiO2 and UV light, and the cells became elliptical or round without a mechanically strong network. From the analysis of the concentrations for Ca2+ and Mg2+, a large amount of Ca2+ and Mg2+ were detected in the solution of the treated cells by photo-catalysis, and this was attributed to the damage of LPS dispatches. After TiO2 or UV light treatment, a significant decrease in membrane fluidity of E. coli was found from an increase in fluorescence polarization by a fluorescence probe. The permeability of the treated cells increased to some degree that can be confirmed by quantum dots labeling technique.