We present a novel method for the selective detection of cysteine, a sulfur-containing amino acid, which plays a crucial role in many important biological functions such as protein folding. Surface-modified colloidal CdS nanoparticles have been used as a fluorescent probe to selectively detect cysteine in the presence of other amino acids in the micromolar concentration range. Cysteine quenches the emission of CdS in the 0.5-10 µM concentration range, whereas the other amino acids do not affect its emission. Among the other amino acids, histidine is most efficient in quenching the emission of the CdS nanoparticles. The sulfur atom of cysteine plays a crucial role in the quenching process in the 0.5-10 µM concentration range. Cysteine is believed to quench the emission of the CdS nanoparticles by binding to their surface via its negatively charged sulfur atom. This method can potentially be applied for its detection in biological samples.
Nanocomposites of gold nanoparticles and semiconductor ZnO with wurtzite structure, made by solution combustion synthesis (SCS), as a function of the Zn/fuel ratio with polyethylene glycol (PEG) as fuel exhibit the presence of both nanoparticles and clusters. Atomic gold clusters present on the surface of ZnO nanorods which can be identified by XPS and SEM are easily monitored and characterized by positive ion MALDI experiments as mostly odd numbered clusters, Au3 to Au11 in decreasing amounts. Low concentrations of the fuel produce AuClO and nanoparticles (NPs), with no clusters. Au-ZnO nanocomposites at all [Au] exhibit single blue shifted plasmon absorption and corresponding photoluminescence (PL). Increasing particle size prefers surface plasmon resonance (SPR) scattering of metal that could lead to PL enhancement; however, available ZnO surface in the Au-ZnO composite becomes more important than the particle size of the composite with higher [Au]. The catalytic activity of these Au-ZnO nanocomposites tested on 4-nitrophenol clearly revealed the presence of an intermediate with both NPs and clusters playing different roles. An in vitro study of cytotoxicity on MCF-7 cell lines revealed that these gold nanostructures have turned out to be powerful nanoagents for destruction of cancer cells even with small amounts of gold particles/clusters. The nanorods of ZnO, known to be nontoxic to normal cells, play a lesser role in the anticancer activity of these Au-ZnO nanocomposites.
Tuning the photocatalytic property of zinc oxide (ZnO) nanoparticles (NPs) is timely. Dependence of photocatalysis upon size, morphology and effective surface area of the particles used has led to optimization in various synthesis procedures. The current article addresses to dictate a cost-effective, bio-friendly, modified ease-process for this issue. The synthesis of ZnO NPs with differing photophysical properties, sizes and morphologies, in order to tune its photocatalytic activity, have been extensively studied. Polyethylene glycol as the structure directing agent and different synthesis strategies were adopted. Spectroscopic and microscopic characterization techniques were employed to understand the nature of the as-synthesized samples. Photocatalytic property and photostability of the samples were determined based on experiments performed with common xanthene and azo dyes. Based on analysing the results, certain characteristics, such as smaller particle size, less agglomerated structure, higher surface area and superior lifetime of the photogenerated electrons and holes upon light illumination, were essential for ZnO NPs to act as an efficient photocatalyst.
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