Haifeng Bao

Mechanism of antimicrobial activity of CdTe quantum dots.

The antimicrobial activity and mechanism of CdTe quantum dots (QDs) against Escherichia coli were investigated in this report. Colony-forming capability assay and atomic force microscopy (AFM) images show that the QDs can effectively kill the bacteria in a concentration-dependent manner. Results of photoluminescence spectrophotometry, confocal microscopy, and antioxidative response tests indicate that the QDs bind with bacteria and impair the functions of a cells antioxidative system, including down-regulations of antioxidative genes and decreases of antioxidative enzymes activities. The oxidative damage of protein and lipid is also observed with thiobarbituric reacting substances and protein carbonyl assays, respectively. On the basis of these results, it is proposed that the mechanism of the antimicrobial activity of CdTe QDs involves QDs-bacteria association and a reactive oxygen species-mediated pathway. Thus, CdTe QDs could have the potential to be formulated as a novel antimicrobial material with excellent optical properties.

Extracellular microbial synthesis of biocompatible CdTe quantum dots.

An efficient bacterial synthesis method to harvest cadmium telluride (CdTe) quantum dots (QDs) with tunable fluorescence emission using Escherichia coli is demonstrated. Ultraviolet-visible, photoluminescence, X-ray diffraction and transmission electron microscopy analysis confirmed the superior size-tunable optical properties, with fluorescence emission from 488 to 551 nm, and the good crystallinity of the as synthesized QDs. A surface protein capping layer was confirmed by hydrodynamic size, zeta potential and Fourier transform infrared spectroscopy measurements, which could maintain the viability (92.9%) of cells in an environment with a QD concentration as high as 2 microM. After functionalization with folic acid the QDs were used to image cultured cervical cancer cells in vitro. Investigations of bacterial growth and morphology and the biosynthesis of CdTe QDs in Luria-Bertani medium containing E. coli-secreted proteins showed that extracellular synthesis directly relied on the E. coli-secreted proteins, and a mechanism for protein-assisted biosynthesis of QDs is proposed. This work provides an economical approach to fabricate highly fluorescent biocompatible CdTe QDs via an environmentally friendly production process. The biosynthesized QDs may have great potential in broad bio-imaging and bio-labeling applications.

Electrical transport and photovoltaic effects of core–shell CuO/C60 nanowire heterostructure

An organic/inorganic hybrid heterostructure consisting of p-type CuO nanowire core and n-type C(60) shell was fabricated and its electrical transport properties were studied for the first time. It was found that the devices with contacts on shell-shell show an ohmic behavior but the devices with contacts on core-shell forms a single p-n junction and display a rectifying behavior. Logarithmic current-voltage curves at various temperatures show that the tunneling transport plays a critical role in the electrical transport. Photovoltaic effects were observed in the core-shell contacted CuO/C(60) junctions under illumination. This work demonstrates that an inorganic/organic coaxial nanowire can provide potential in nanoelectronic devices and could further stack high density hybrid nanowires array as a renewable power source.

Stationary current generated from photocycle of a hybrid bacteriorhodopsin/quantum dot bionanosystem

Bacteriorhodopsin (bR) is a promising biomaterial for broad potential applications in optical and optoelectronic devices. Upon the original photochemical cycle of bR, for the first time we construct a hybrid bR/quantum dot (QD) bionanosystem and a stationary current is generated from the modified photocycle. We propose a model to explain that QDs could act as nanoscaled light sources embedded in bR to assist its generation of a stationary photocurrent, which is completely different from the reported transient spikes from the bR’s photocycle. It opens the horizon for optical devices other than those reported up to date.

Interaction mechanisms of CdTe quantum dots with proteins possessing different isoelectric points

Interactions of surface-immobilized and solution-dispersed quantum dots (QDs) with proteins possessing different isoelectric points, particularly the molecular binding capability and agglomeration of proteins with QDs are examined, indicating an electrostatic attraction nature. A mechanism involving protein surface charge distribution and protein molecular size is elucidated.

Shape-controlled assembly of luminescent dumbbell-like CdTe?cystine nanocomposites

A shape perfect luminescent dumbbell with size up to several microns was prepared by incorporating CdTe quantum dots (QDs) into locally created L-cystine matrices, and the photoluminescence of the shaped dumbbells can be easily tailored by reaction time. The growth mechanism was thoroughly investigated. This work not only gives a potential application in optical devices, but also gives a deep insight on the assembly mechanism of nanomaterials into micron-size objects.