Synthesis and Antimicrobial Activity of Gold/Silver–Tellurium Nanostructures

Gold–tellurium nanostructures (Au–Te NSs), silver–tellurium nanostructures (Ag–Te NSs), and gold/silver–tellurium nanostructures (Au/Ag–Te NSs) have been prepared through galvanic reactions of tellurium nanotubes (Te NTs) with Au³⁺, Ag⁺, and both ions, respectively. Unlike the use of less environmentally friendly hydrazine, fructose as a reducing agent has been used to prepare Te NTs from TeO₂ powders under alkaline conditions. The Au/Ag–Te NSs have highly catlaytic activity to convert nonfluorescent Amplex Red to form fluorescent product, revealing their great strength of generating reactive oxygen species (ROS). Au/Ag–Te NSs relative to the other two NSs exhibit greater antimicrobial activity toward the growth of E. coli, S. enteritidis, and S. aureus; the minimal inhibitory concentration (MIC) values of Au/Ag–Te NSs were much lower (>10-fold) than that of Ag–Te NSs and Au–Te NSs. The antibacterial activity of Au/Ag–Te NSs is mainly due to the release of Ag⁺ ions and Te-related ions and also may be due to the generated ROS which destroys the bacteria membrane. <i>In vitro</i> cytotoxicity and hemolysis analyses have revealed their low toxicity in selected human cell lines and insignificant hemolysis in red blood cells. In addition, inhibition zone measurements using a Au/Ag–Te NSs-loaded konjac jelly film have suggested that it has great potential in practial application such as wound dressing for reducing bacterial wound infection. Having great antibacterial activitiy and excellent biocompatibility, the low-cost Au/Ag–Te NSs hold great potential as effective antimicrobial drugs

Self-Assembled Chiral Gold Supramolecules with Efficient Laser Absorption for Enantiospecific Recognition of Carnitine

Stereospecific recognition of chiral molecules is ubiquitous in chemical and biological systems, thus leading to strong demand for the development of enantiomeric drugs, enantioselective sensors, and asymmetric catalysts. In this study, we demonstrate the ratio of d-Cys and l-Cys playing an important role in determining the optical properties and the structures of self-assembled Cys–Au­(I) supramolecules prepared through a simple reaction of tetrachloroaurate­(III) with chiral cysteine (Cys). The irregularly shaped −[d-Cys–Au­(I)]_<i>n</i>– or – [l-Cys–Au­(I)]_<i>n</i>– supramolecules with a size larger than 500 nm possessing strong absorption in the near-UV region and chiroptical characteristics were only obtained from the reaction of Au­(III) with d-Cys or l-Cys. On the other hand, spindle-shaped −[d/l-Cys–Au­(I)]_<i>n</i>– supramolecules were formed when using Au­(III) with mixtures of d/l-Cys. Our results have suggested that Au­(I)···Au­(I) aurophilic interactions, and stacked hydrogen bonding and zwitterionic interactions between d/l-Cys ligands are important in determining their structures. The NaBH₄-mediated reduction induces the formation of photoluminescent gold nanoclusters (Au NCs) embedded in the chiral −[d-Cys–Au­(I)]_<i>n</i>– or −[l-Cys–Au­(I)]_<i>n</i>– supramolecules with a quantum yield of ca. 10%. The as-formed Au NCs/–[d-Cys–Au­(I)]_<i>n</i>– and Au NCs/–[l-Cys–Au­(I)]_<i>n</i>– are an enantiospecific substrate that can trap l-carnitine and d-carnitine, respectively, and function as a nanomatrix for surface-assisted laser desorption/ionization mass spectrometry (LDI-MS). The high absorption efficiency of laser energy, analyte-binding capacity, and homogeneity of the Au NCs/–[Cys–Au­(I)]_<i>n</i>– allow for quantitation of enantiomeric carnitine down to the micromolar regime with high reproducibility. The superior efficiency of the Au NCs/–[d-Cys–Au­(I)]_<i>n</i>– substrate has been further validated by quantification of l-carnitine in dietary supplements with accuracy and precision. Our study has opened a new avenue for chiral quantitation of various analytes through LDI-MS using metal nanocomposites consisting of NCs and metal–ligand complexes