Liyang Luo

Functional gold nanoclusters as antimicrobial agents for antibiotic-resistant bacteria

AIMS Our aim was to demonstrate that lysozyme-directed generation of gold nanoclusters (Au NCs) are potential antimicrobial agents for antibiotic-resistant bacteria and broad labeling agents for pathogenic bacteria. MATERIALS & METHODS Lysozyme is an enzyme that is capable of hydrolyzing the cell walls of bacteria. In this study, we demonstrated the generation of functional Au NCs by using lysozyme as the sequester and the reducing agent for Au precursors at 40 degrees C. In addition, to shorten the reaction time, the reaction was conducted under microwave irradiation within a short period of time for the first time. RESULTS The bioactivity of the lysozyme on the Au NCs was retained. Therefore, the as-prepared lysozyme-Au NCs with desirable fluorescence feature were successfully employed to be broad-band labeling agents for pathogenic bacteria. Furthermore, we also demonstrated that the lysozyme-Au NCs can be used to effectively inhibit the cell growth of notorious antibiotic-resistant bacteria, including pan-drug-resistant Acinetobacter baumannii and vancomycin-resistant Enterococcus faecalis. CONCLUSION The potential of employing the lysozyme-Au NCs for bacterial labeling and as antimicrobial agents is expected.

Visible quantum cutting through downconversion in green-emitting K2GdF5:Tb3+ phosphors

Visible quantum cutting under excitations at 212 and 172nm in a green-emitting phosphor K2GdF5:Tb3+ (11%) via a downconversion mechanism is investigated. The authors measured the vacuum ultraviolet (VUV) excitation and emission spectra and proposed mechanisms to rationalize the quantum-cutting effect. One short-UV or one VUV photon absorbed by Tb3+ is split into multiple visible photons emitted by Tb3+ through cross relaxation and direct energy transfer. Calculations indicate an optimal quantum efficiency as great as 189% for this phosphor.

Investigation of Pr3+ as a sensitizer in quantum-cutting fluoride phosphors

A quantum-cutting (QC) phosphor K2GdF5:Eu3+ shows poor optical absorption and a theoretical quantum efficiency (QE) of 107% in the ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectral ranges. Pr3+ was codoped as a sensitizer in K2GdF5:Eu3+, thus increasing the absorption in the UV and VUV spectral regions; the theoretical QE of K2GdF5:Eu3+,Pr3+ was increased to 138%. The spectra indicate that the possible mechanisms of QC and energy transfer differ from those of phosphors containing the Gd3+–Eu3+ couple. Temporally resolved measurements of fluorescence decay confirm the proposed QC mechanism for the phosphor containing the Gd3+–Eu3+,Pr3+ system.

Novel Steroid-Sensing Model and Characterization of Protein Interactions Based on Fluorescence Anisotropy Decay ‡

Intramolecular binding of a ligand with an alkyl link, (-CH(2))(3), covalently bound to a residue near the active site of the protein forms a novel steroid-sensing model. A genetically engineered big up tri, open(5)-3-ketosteroid isomerase (KSI) was designed to conjugate uniquely with this ligand at its Cys-86 through the formation of a disulfide bond. The steady-state protein-ligand binding, mediated by hydrophobic interactions, was confirmed with fluorescence spectra, and the fluorophore-labeled peptide sequence was identified with tandem mass spectra. A comparison of steady-state fluorescence spectra of various fluorophore-labeled KSI mutants reveals that the emission characteristics vary with environmental factors. An evaluation of the decay of the fluorescence anisotropy of the fluorophore indicates the existence of an intramolecular protein-ligand binding interaction. The measurement of time-resolved fluorescence anisotropy of various protein-ligand complexes yielded values of anisotropy decay representing the degrees of freedom of the fluorophore related to its location, inside or outside the steroid-binding domain. When 19-norandrostenedione (19-NA) was added to this protein-ligand system, competitive binding between the ligand and the steroid was observed; this finding confirms the feasibility of the design of steroid detection with engineered KSI. On integration of this protein-ligand system with a silicon-based nanodevice (a p-type field-effect transistor with an ultrathin body), a noncharged steroid, 19-NA, became detectable at a micromolar level ( Biosens. Bioelectron. 2008 , 23 , 1883 ).