In this study, the antibacterial activity and mechanism of action of chlorogenic acid against bacteria were assessed. The data from minimum inhibitory concentration (MIC) values showed that chlorogenic acid effectively inhibited the growth of all tested bacterial pathogens, and the MIC values were ranging from 20 to 80 μg/mL. An investigation into action mode of chlorogenic acid against the pathogen indicated that chlorogenic acid significantly increased the outer and plasma membrane permeability, resulting in the loss of the barrier function, even inducing slight leakage of nucleotide. The leakage of cytoplasmic contents was also observed by electron micrographs. These results supported our hypothesis that chlorogenic acid bound to the outer membrane, disrupted the membrane, exhausted the intracellular potential, and released cytoplasm macromolecules, which led to cell death.

We presented a new aptasensor for mycotoxins, which was based on multiplexed fluorescence resonance energy transfer (FRET) between multicolor upconversion fluorescent nanoparticles (UCNPs) as donors and graphene oxide (GO) as the entire and effective acceptor. BaY(0.78)F(5):Yb(0.2), Er(0.02) and BaY(0.78)F(5):Yb(0.7), Tm(0.02) upconversion nanoparticles were synthesized and functionalized, respectively, with immobilized ochratoxin A (OTA)-aptamers and fumonisin B(1) (FB(1))-aptamers. On the basis of the strong π-π stacking effect between the nucleobases of the aptamers and the sp(2) atoms of GO, the aptamer modified-UCNPs can be brought in close proximity to the GO surface. The strong upconversion fluorescence both of BaY(0.78)F(5):Yb(0.2), Er(0.02) and BaY(0.78)F(5):Yb(0.2), Tm(0.02) can be completely quenched by the GO, because of a good overlap between the fluorescence emission of multicolor UCNPs and the absorption spectrum of GO. In contrast, in the presence of OTA and FB(1), the aptamers preferred to bind to their corresponding mycotoxins, which led to changes in the formation of aptamers, and therefore, aptamer modified-UCNPs were far away from the GO surface. Our study results showed that the fluorescence intensity of BaYF(5):Yb Er and BaYF(5):Yb Tm were related to the concentration of OTA and FB(1). We therefore developed a sensitive and simple platform for the simultaneous detection of OTA and FB(1) with multicolor UCNPs and GO as the FRET pair. The aptasensor provided a linear range from 0.05 to 100 ng·mL(-1) for OTA and 0.1 to 500 ng·mL(-1) for FB(1); the detection limit of OTA was 0.02 ng·mL(-1) and FB(1) was 0.1 ng·mL(-1). As a practical application, the aptasensor was used to monitor OTA and FB(1) level in naturally contaminated maize samples with the results consistent with that of a classic ELISA method. More importantly, the novel multiplexed FRET was established for the first time based on multiplexed energy donors to the entire energy acceptor; this work was expected to open up a new field of FRET system applications for various targets.

A novel polymer/room-temperature ionic liquid (RTIL) composite material based on chitosan (Chi) and 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIM.BF(4)) was explored. The composite system can be readily used as an immobilization matrix to entrap proteins and enzymes. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. A pair of well-defined quasireversible redox peaks of hemoglobin were obtained at the Chi-BMIM.BF(4)-Hb composite-film-modified glassy carbon (GC) electrode by direct electron transfer between the protein and the GC electrode. Dramatically enhanced biocatalytic activity was exemplified at the Chi-BMIM.BF(4)-Hb/GC electrode by the reduction of oxygen and trichloroacetic acid. Thermogravimetric analysis (TGA) suggests that the Chi-BMIM.BF(4)-Hb composite has higher thermal stability than Chi-Hb itself. The Chi-BMIM.BF(4)-Hb film was also characterized by UV-visible spectra, indicating excellent stability in solution and good biocompatibility for protein. The unique composite material based on polymer and ionic liquid can find wide potential applications in direct electrochemistry, biosensors, and biocatalysis.

A highly sensitive and specific multiplex method for the simultaneous detection of three pathogenic bacteria was fabricated using multicolor upconversion nanoparticles (UCNPs) as luminescence labels coupled with aptamers as the molecular recognition elements. Multicolor UCNPs were synthesized via doping with various rare-earth ions to obtain well-separated emission peaks. The aptamer sequences were selected using the systematic evolution of ligands by exponential enrichment (SELEX) strategy for Staphylococcus aureus, Vibrio parahemolyticus, and Salmonella typhimurium. When applied in this method, aptamers can be used for the specific recognition of the bacteria from complex mixtures, including those found in real food matrixes. Aptamers and multicolor UCNPs were employed to selectively capture and simultaneously quantify the three target bacteria on the basis of the independent peaks. Under optimal conditions, the correlation between the concentration of three bacteria and the luminescence signal was found to be linear from 50-10(6) cfu mL(-1). Improved by the magnetic separation and concentration effect of Fe3O4 magnetic nanoparticles, the limits of detection of the developed method were found to be 25, 10, and 15 cfu mL(-1) for S. aureus, V. parahemolyticus, and S. typhimurium, respectively. The capability of the bioassay in real food samples was also investigated, and the results were consistent with experimental results obtained from plate-counting methods. This proposed method for the detection of various pathogenic bacteria based on multicolor UCNPs has great potential in the application of food safety and multiplex nanosensors.

Porous g-CN nanosheet (PCNS) photocatalyst with a thickness of 2.0 nm, pore volume of 0.61 cm g, and surface area of 190.1 m g was prepared by a simple two-step template-free approach without the addition of extra reagents. Compared with the bulk g-CN (BCN), PCNS possesses a greater number of surface reactive sites, improved efficiency of charge transfer, and accelerated separation of photogenerated electron-hole pairs. Accordingly, the visible-light-driven photocatalytic disinfection performance and organic pollutant degradation activity of PCNS are significantly enhanced. Escherichia coli (E. coli) cells can be killed completely by PCNS within 4 h, whereas only 77.1% of E. coli cells can be killed by BCN. The photodegradation rates of PCNS on methylene blue, Acid Red 27, and bisphenol A are almost 6.4, 4.0, and 1.9 times as fast as that of BCN, respectively. The photocurrent intensity of PCNS is about 3.7 times in comparison with that of BCN. Considering the easy preparation and excellent performance, PCNS could be a promising and competitive visible-light-driven photocatalyst in the field of environment remediation.

CdTe nanocrystals (NCs) capped with thioglycolic acid (TGA) were synthesized via a microwave-assisted method. The chemiluminescence (CL) of CdTe NCs induced by directly chemical oxidation and its size-depended and surfactant-sensitized effect in aqueous solution were then investigated. It was found that oxidants, especially hydrogen peroxide and potassium permanganate, could directly oxidize CdTe NCs to produce strong CL emission in basic conditions. The oxidized CL of CdTe NCs displayed size-dependent effect and its intensity increased along with increasing the sizes of the NCs. Moreover, the CL intensity could, if surfactants CTAB or beta-cyclodextrin were added to the above CL system, be sensitized to some degree. The sensitized CL induced by CTAB and beta-cyclodextrin is mainly contributing to the formation of aggregate nanostructure and the micellar micronanoenvironment, respectively. The possible oxidized CL mechanisms were further examined by means of photoluminescence spectra, CL spectra, and transmission electron microscopy studies. The CL properties of CdTe NCs not only will be helpful to study physical chemistry properties of semiconductor nanocrystals but also are expected to find use in many fields such as luminescence devices, bioanalysis, and multicolor labeling probes.

No abstract

Specially shaped gold nanoparticles have intrigued considerable attention because they usually possess high-sensitivity surface-enhanced Raman scattering (SERS) and thus result in large advantages in trace biodetermination. In this article, starch-capped gold nanoparticles with hexagon and boot shapes were prepared through using a nontoxic and biologically benign aqueous-phase synthetic route. Shape effects of gold nanoparticles on SERS properties were mainly investigated, and found that different-shaped gold nanoparticles possess different SERS properties. Especially, the boot-shaped nanoparticles could induce more 100-fold SERS enhancements in sensitivity as compared with those from gold nanospheres. The extremely strong SERS properties of gold nanoboots have been successfully applied to the detection of avidin. The unique nanoboots with high-sensitivity SERS properties are also expected to find use in many other fields such as biolabel, bioassay, biodiagnosis, and even clinical diagnosis and therapy.