Biomolecularly capped uniformly sized nanocrystalline materials: glutathione-capped ZnS nanocrystals

Abstract

Micro-organisms such as bacteria and yeasts form CdS to detoxify toxic cadmium ions. Frequently, CdS particles formed in yeasts and bacteria were found to be associated with specific biomolecules. It was later determined that these biomolecules were present at the surface of CdS. This coating caused a restriction in the growth of CdS particles and resulted in the formation of nanometre-sized semiconductors (NCs) that exhibited typical quantum confinement properties. Glutathione and related phytochelatin peptides were shown to be the biomolecules that capped CdS nanocrystallites synthesized by yeasts Candida glabrata and Schizosaccharomyces pombe. Although early studies showed the existence of specific biochemical pathways for the synthesis of biomolecularly capped CdS NCs, these NCs could be formed in vitro under appropriate conditions. We have recently shown that cysteine and cysteine-containing peptides such as glutathione and phytochelatins can be used in vitro to dictate the formation of discrete sizes of CdS and ZnS nanocrystals. We have evolved protocols for the synthesis of ZnS or CdS nanocrystals within a narrow size distribution range. These procedures involve three steps: (1) formation of metallo-complexes of cysteine or cysteine-containing peptides, (2) introduction of stoichiometric amounts of inorganic sulfide into the metallo-complexes to initiate the formation of nanocrystallites and finally (3) size-selective precipitation of NCs with ethanol in the presence of Na+. The resulting NCs were characterized by optical spectroscopy, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction and electron diffraction. HRTEM showed that the diameter of the ZnS-glutathione nanocrystals was 3.45±0.5 nm. X-ray diffraction and electron diffraction analyses indicated ZnS-glutathione to be hexagonal. Photocatalytic studies suggest that glutathione-capped ZnS nanocrystals prepared by our procedure are highly efficient in degrading a test model compound.

Synthesis and Cell‐Imaging Applications of Glutathione‐Capped CdTe Quantum Dots

“…[12] Glutathione has also been directly used as a capping agent for ZnS [13] and CdS QDs, [14] however, their fluorescence spectra were dominated by a broad trap emission band. Baumle et al examined glutathione-capped CdSe QDs, which have a single fluorescence color at 533 nm and a moderate QY of 16 %.…”

Efficient Photocatalytic Degradation of Environmental Pollutants with Mass-Produced ZnS Nanocrystals

“…Gram quantities of ZnS NCs were produced by a colloidal synthesis route as detailed previously (14,15). Glutathione (GSH) or cysteine capping agents were employed for synthesis of highly concentrated ZnS NC solutions (13,15).…”

“…Size fractionation reduces size heterogeneity of the sample (13)(14)(15)21). The fractions were analyzed for zinc, sulfide, and capping material concentrations to account for the composition of the photocatalyst.…”

“…Based on the biological synthesis of CdS nanocrystallites by yeasts in which peptide-metal complexes form matrices for incorporation of sulfide (12), our group has developed a method for inexpensive, high-throughput synthesis of ZnS NCs (13)(14)(15). To demonstrate the potential applicability of these NCs in environmental remediation, we have investigated the photocatalytic degradation of two model pollutants, p-nitrophenol (pNP) and Acid Orange 7 (AO7), using ZnS nanocrystals produced on a gram-scale synthesis.…”

EXAFS study of confined nanocrystalline oxides

“…Nanocrystalline SnO 2 can be easily prepared by sol-gel routs as 3 nm crystals; however, grain growth is evident after heating to 400 °C [11,12], affecting both the sensitivity and long-term stability of the sensor. A range of methods, attempting to restrict the grain growth of nanocrystalline materials has been investigated, including surface treatment [13,14], growing the crystals in porous silica [15,16], or hydrothermal treatment of sol solutions [17]. The use of a second phase to restrict grain growth is widely used in the preparation of ceramics [18] and is referred to as Zener Pinning, [19,20].…”