Green synthesis of catalytic gold/bismuth oxyiodide nanocomposites with oxygen vacancies for treatment of bacterial infections.

We have developed a simple and green solution for the synthesis of catalytic gold-doped bismuth oxyiodide (Au/BiOI) nanocomposites at room temperature from an aqueous mixture of gold ions, bismuth ions, and iodide ions. Au nanoparticles (NPs) were formed in situ and doped into BiOI nanosheets. The oxygen vacancies generated in BiOI give rise to its oxidase-like activity, and Au doping facilitated the reaction leading to a 4-fold higher oxidase-like activity of the Au/BiOI nanocomposite. The Au/BiOI nanocomposites showed wide spectrum antimicrobial activity not only against non-multidrug-resistant E. coli, K. pneumoniae, S. enteritidis, S. aureus, and B. subtilis bacteria, but also against multidrug-resistant bacteria, methicillin-resistant S. aureus (MRSA). The gold doping reduced the minimal inhibitory concentration value by ∼2000-fold for the Au/BiOI nanocomposite, in comparison with only BiOI nanoparticles. The bactericidal property of the Au/BiOI nanocomposite arose from the combined effect of the disruption of the bacterial membrane through a strong interaction of the nanocomposite with the bacteria and the generation of reactive oxygen species. Also, the Au/BiOI nanocomposite is highly biocompatible, which has been demonstrated in vitro by analysis of cytotoxicity and hemolysis, and in vivo by evaluating ocular tissue responses. Furthermore, intrastromal administration of Au/BiOI nanocomposites can effectively alleviate S. aureus-induced bacterial keratitis in rabbits, suggesting a significant disinfectant benefit in preclinical studies. The Au/BiOI nanocomposites show great potential for the inactivation of bacterial pathogens in an aqueous environment and treatment of bacterial infection-induced diseases.

Immobilization of aptamer-modified gold nanoparticles on BiOCl nanosheets: Tunable peroxidase-like activity by protein recognition.

A self-assembled nanocomposite is prepared from an aqueous mixture of aptamer-modified gold nanoparticles (Apt-Au NPs), bismuth ions and chloride ions. The Apt-Au NPs are immobilized on bismuth oxychloride (BiOCl) nanosheets in situ to form Apt-Au NPs/BiOCl nanocomposites. The as-prepared nanocomposites exhibit high peroxidase-like activity for the catalytic conversion of Amplex Red (AR) to fluorescent resorufin in the presence of H2O2. The catalytic activity of Apt-Au NPs/BiOCl nanocomposites is at least 90-fold higher than that of Apt-Au NPs or BiOCl nanosheets, revealing synergistic effects on their activity. The catalytic activity of Apt-Au NPs/BiOCl nanocomposites is suppressed by vascular endothelial growth factor-A165 (VEGF-A165) molecules that specifically interact with the aptamer units (Del-5-1 and v7t-1) on the nanocomposite surface. The AR/H2O2-Apt-Au NPs/BiOCl nanocomposites probe shows high selectivity (>1000-fold over other proteins) and sensitivity (detection limit ~0.5nM) for the detection of VEGF-A165. Furthermore, the probe is employed for the detection of VEGF isoforms and for the study of interactions between VEGF and VEGF receptors. The practicality of this simple, rapid, cost-effective probe is validated by the analysis of VEGF-A165 in cell culture media, showing its great potential for the analysis of VEGF in biological samples.

Analyses of functional polymer-modified nanoparticles for protein sensing by surface-assisted laser desorption/ionization mass spectrometry coupled with HgTe nanomatrices.

In this study, we employed HgTe nanostructure-based matrices (nanomartrices; NMs) for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) for the analyses of polyethylene glycol (PEG) derivatives as well as thiol-PEG-modified gold nanoparticles (PEG-Au NPs). Relative to common organic matrices, the use of HgTe NMs as the matrix for SALDI-MS resulted in more highly efficient analyses of PEG derivatives, in terms of sensitivity and reproducibility. The symmetric MS profiles of PEG (Mw: ca. 8000 Da) obtained through HgTe NMs/SALDI-MS analysis revealed the absence of polymer degradation during this process. Under optimal conditions, the HgTe NMs/SALDI-MS system enabled the detection of PEG sample as low as 100 pg and with molecular weights of up to approximately 42,000 Da. We also used this approach for the analyses of PEG-Au NPs in which various functional groups (carboxymethyl, amine, biotin) were present at the PEG termini, revealing that the combination of SALDI-MS and HgTe NMs have great potential for use in the characterization of modified polymer-ligands on nanomaterials. We also demonstrated the PEG-Au NPs can be coupled with HgTe NMs/SALDI-MS for characterization of biorecognition events. After avidin, the target protein, had been selectively captured by the biotin-PEG-Au NPs, we found that the desorption/ionization efficiency of biotin-PEG from the Au NP surface was suppressed; accordingly, this novel SALDI-MS approach allows rapid detection of avidin with high specificity and sensitivity. Au NP surfaces functionalized with other functional-PEG ligands might also allow amplification of signals from other biological interactions.

Detection of adenosine triphosphate through polymerization-induced aggregation of actin-conjugated gold/silver nanorods.

We have developed a simple and selective nanosensor for the optical detection of adenosine triphosphate (ATP) using globular actin-conjugated gold/silver nanorods (G-actin-Au/Ag NRs). By simply mixing G-actin and Au/Ag NRs (length ~56 nm and diameter ~12 nm), G-actin-Au/Ag NRs were prepared which were stable in physiological solutions (25 mM Tris-HCl, 150 mM NaCl, 5.0 mM KCl, 3.0 mM MgCl2 and 1.0 mM CaCl2; pH 7.4). Introduction of ATP into the G-actin-Au/Ag NR solutions in the presence of excess G-actin induced the formation of filamentous actin-conjugated Au/Ag NR aggregates through ATP-induced polymerization of G-actin. When compared to G-actin-modified spherical Au nanoparticles having a size of 13 nm or 56 nm, G-actin-Au/Ag NRs provided better sensitivity for ATP, mainly because the longitudinal surface plasmon absorbance of the Au/Ag NR has a more sensitive response to aggregation. This G-actin-Au/Ag NR probe provided high sensitivity (limit of detection 25 nM) for ATP with remarkable selectivity (>10-fold) over other adenine nucleotides (adenosine, adenosine monophosphate and adenosine diphosphate) and nucleoside triphosphates (guanosine triphosphate, cytidine triphosphate and uridine triphosphate). It also allowed the determination of ATP concentrations in plasma samples without conducting tedious sample pretreatments; the only necessary step was simple dilution. Our experimental results are in good agreement with those obtained from a commercial luciferin-luciferase bioluminescence assay. Our simple, sensitive and selective approach appears to have a practical potential for the clinical diagnosis of diseases (e.g. cystic fibrosis) associated with changes in ATP concentrations.

Highly efficient control of thrombin activity by multivalent nanoparticles.

We have demonstrated that the incorporation of sulfated galactose acid (sulf-Gal) into thrombin-binding-aptamer (TBA)-conjugated gold nanoparticles (TBA-AuNPs) enables highly effective inhibition of thrombin activity toward fibrinogen. AuNP bioconjugates (TBA(15)/TBA(29)/sulf-Gal-AuNPs) were prepared from 13 nm AuNPs, 15-mer thrombin-binding aptamer (TBA(15)), 29-mer thrombin-binding aptamer (TBA(29)), and sulf-Gal. The numbers of TBA and sulf-Gal molecules per AuNP proved to have a strong impact on inhibitory potency. The best results were observed for 15-TBA(15)/TBA(29)/sulf-Gal-AuNPs (with 15 TBA(15) and 15 TBA(29) molecules per AuNP), which, because of their particularly flexible conformation and multivalency, exhibited ultrahigh binding affinity toward thrombin (K(d)=3.4×10(-12) M) and thus extremely high anticoagulant (inhibitory) potency. Compared to the case without inhibitors (the "normal" value), their measured thrombin clotting time (TCT) was 91 times longer, whereas for TBA(15) alone it was only 7.2 times longer. Their anticoagulant activity was suppressed by TBA-complementary-sequence (cTBA)-modified AuNPs (cTBA(15)/cTBA(29)-AuNPs) at a rate that was 20 times faster than that of free cTBA(15)/cTBA(29). Thus, easily prepared, low-cost, multivalent AuNPs show great potential for biomedical control of blood clotting.