Norvancomycin-capped silver nanoparticles: Synthesis and antibacterial activities against E. coli

The synthesis of norvancomycin (NVan)-capped silver nanoparticles (Ag@NVan) and their notable in vitro antibacterial activities against E. coli, a Gram-negative bacterial strain (GNB), are reported here. Mercaptoacetic acid-stabilized spherical silver nanoparticles with a diameter of 16±4 nm are prepared by a simple chemical reaction. The formation process of the silver nanoparticles is investigated by UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). NVan is then grafted to the terminal carboxyl of the mercaptoacetic acid in the presence of N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC). The TEM images of single bacteria treated with Ag@NVan show that plenty of Ag@NVan aggregate in the cell wall of E. coli. A possible antibacterial mechanism is proposed that silver nanoparticles may help destroy the stability of the outer membrane of E. coli, which makes NVan easier to bind to the nether part of the peptidoglycan structure. The antibacterial activities of silver nanoparticles on their own, together with the rigid polyvalent interaction between Ag@NVan and cell wall, enables Ag@NVan to be an effective inhibitor of GNB. This kind of bionanocomposites might be used as novel bactericidal materials and we also provide an effective synthesis method for preparing functional bioconjugated nanoparticles here.     

Rapid and ultrasensitive E. coli O157:H7 quantitation by combination of ligandmagnetic nanoparticles enrichment with fluorescent nanoparticles based two-color flow cytometry

A novel, fast and sensitive determination strategy for E. coli O157:H7 has been developed by combination of ligandmagnetic nanoparticles (LMNPs) enrichment with a fluorescent silica nanoparticles (FSiNPs) based two-color flow cytometry assay (LMNPs@FSiNPs-FCM). E. coli O157:H7 was first captured and enriched through the lectin concanavalin A (Con A) favored strong adhesion of E. coli O157:H7 to the mannose-conjugated magnetic nanoparticles. The enriched E. coli O157:H7 was further specially labeled with goat anti-E. coli O157:H7 antibody modified RuBpy-doped FSiNPs, and then stained with a nucleic acid dye SYBR Green I (SYBR-I). After dual-labeling with FSiNPs and SYBR-I, the enriched E. coli O157:H7 was determined using multiparameter FCM analysis. With this method, the detection sensitivity was greatly improved due to the LMNPs enrichment and the signal amplification of the FSiNPs labelling method. Furthermore, the false positives caused by aggregates of FSiNPs conjugates and nonspecific binding of FSiNPs to background debris could be significantly decreased. This assay allowed the detection of E. coli O157:H7 in PB buffer at levels as low as 7 cells mL(-1). The total assay time including E. coli O157:H7 sample enrichment and detection was less than 4 h. An artificially contaminated bottled mineral water sample with a concentration of 6 cells mL(-1) can be detected by this method. It is believed that the proposed method will find wide applications in biomedical fields demanding higher sensitive bacterial identification.     

Bacteria and bacteriophage inactivation by silver and zinc oxide nanoparticles

Microbial contaminants such as bacteria and viruses are of great concern in water. As nanotechnology continues to grow, understanding the interactions of nanoparticles with bacteria and viruses is important to protect public health and the environment. In this study, the effect of two commonly used nanoparticles, silver nanoparticles (AgNPs, average particle size=21 nm) and zinc oxide nanoparticles (ZnO NPs, average particle size=39 nm), on the growth of bacteria (Eschericia coli) and bacteriophages (MS2) were evaluated using a standard double agar layer (DAL) method and a turbidimetric microtiter assay. A 1-h prior exposure of MS2 to nanoparticles did not inactivate MS2 at the highest nanoparticle concentrations tested (5mg/L total Ag and 20 mg/L ZnO). No bacteriophage inactivation was observed in the presence of AgNPs, Ag(+)/AgNPs (50:50 in mass ratio) or Ag(+) ions, all at the total Ag concentration of 5mg/L. In a binary (bacteria-phages) system where the E. coli host was exposed to MS2 and nanoparticles simultaneously, the dynamic changes of active bacteria and MS2 phages during incubation demonstrated that exposure of AgNPs (5mg/L Ag) and ZnO NPs (20mg/L ZnO) increased the number of phages by 2-6 orders of magnitude. These results suggested that exposure of nanoparticles could greatly facilitate bacterial viruses like MS2 to infect the E. coli host.     

A versatile strategy to fabricate hydrogel-silver nanocomposites and investigation of their antimicrobial activity

In this study, hydrogel-silver nanocomposites have been synthesized by a unique methodology, which involves formation of silver nanoparticles within swollen poly (acrylamide-co-acrylic acid) hydrogels. The formation of silver nanoparticles was confirmed by transmission electron microscopy (TEM) and surface plasmon resonance (SPR) which was obtained at 406 nm. The TEM of hydrogel-silver nanocomposites showed almost uniform distribution of nanoparticles throughout the gel networks. Most of the particles, as revealed from the particle-size distribution curve, were 24-30 nm in size. The X-ray diffraction pattern also confirmed the face centered cubic (fcc) structure of silver nanoparticles. The nanocomposites demonstrated excellent antibacterial effects on Escherichia coli (E. coli). The antibacterial activity depended on size of the nanocomposites, amount of silver nanoparticles, and amount of monomer acid present within the hydrogel-silver nanocomposites. It was also found that immersion of plain hydrogel in 20 mg/30 ml AgNO(3) solution yielded nanocomparticle-hydrogel composites with optimum bactericidal activity.     

Au纳米标记物增强电化学免疫分析大肠杆菌的研究

通过在Au纳米颗粒表面修饰辣根过氧化酶(HRP)标记的大肠杆菌抗体制备了一种新型的Au纳米标记物, 并将该纳米标记物应用于增强电化学免疫分析大肠杆菌. 经过酶联免疫反应后, Au纳米标记物、免疫磁性颗粒(IMB)和大肠杆菌形成了IMB/抗体-大肠杆菌-Au纳米标记物的三明治式免疫复合物. 以3,3,5,5-四甲基联苯二胺(TMB)溶液作为底物, 采用电化学与流动注射检测(FIA)相结合的技术测定HRP的活性. 检测到的电流大小与免疫复合物上HRP的量成正比, 从而与大肠杆菌的浓度成正比. Au纳米颗粒增加了HRP的负载量, 增强了电化学信号, 大大提高了大肠杆菌的检测灵敏度. 实验结果表明, 大肠杆菌浓度在 1.0×102～5.0×104 cfu•mL－1范围内与电流大小成线性相关, 最低检测限达50 cfu•mL－1, 若对大肠杆菌样品溶液进行预浓缩, 将得到更宽的检测范围和更低的检测限. 本方法总的分析时间比其他方法短, 在1 h内就能完成对大肠杆菌样品的快速检测.     

Convective assembly of bacteria for surface-enhanced Raman scattering

A sample preparation method based on convective assembly for "whole-microorganism" identification using surface-enhanced Raman scattering (SERS) is developed. With this technique, a uniform sample can easily be prepared with silver nanoparticles. During the deposition process, bacteria and nanoparticles are assembled to form a unique well-ordered structure with great reproducibility. The SERS spectra acquired from the samples prepared with this technique have better quality and improved reproducibility for SERS spectra obtained from the same sample and limited variation due to the consistent sample preparation. E. coli, a Gram-negative bacilli, and Staphylococcus cohnii, a Gram-positive coccus, are studied as model bacteria.     

Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria

The antimicrobial activity of silver nanoparticles against E. coli was investigated as a model for Gram-negative bacteria. Bacteriological tests were performed in Luria-Bertani (LB) medium on solid agar plates and in liquid systems supplemented with different concentrations of nanosized silver particles. These particles were shown to be an effective bactericide. Scanning and transmission electron microscopy (SEM and TEM) were used to study the biocidal action of this nanoscale material. The results confirmed that the treated E. coli cells were damaged, showing formation of "pits" in the cell wall of the bacteria, while the silver nanoparticles were found to accumulate in the bacterial membrane. A membrane with such a morphology exhibits a significant increase in permeability, resulting in death of the cell. These nontoxic nanomaterials, which can be prepared in a simple and cost-effective manner, may be suitable for the formulation of new types of bactericidal materials.     

Track membrane with immobilized colloid silver particles

A method for modification of track membranes by immobilization of polymer complexes of colloid silver nanoparticles on the surface of microfiltration membranes was developed. The antimicrobial properties of track membranes modified with silver nanoparticles were tested on E. coli, Ps. aeruginosa, St. aureus, and B. cereus.     

Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation

A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO(2)) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO(2) nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2 min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80 nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV-visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO(2) nanoparticles, respectively. The prepared Ag@SiO(2) nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on St?ber method, which need 4-24 h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO(2) nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO(2) nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).     

Eco-friendly synthesis and antibacterial activity of silver nanoparticles reduced by nano-wood materials

Hydrothermal treatment of nano-structured wood, prepared by precision grinding, with cationic silver was found to give silver nanoparticles (Ag NPs) of 2–40-nm size range embedded in the wood tissue. The size and distribution of Ag NPs depended strongly on the starting silver ion concentration and reaction temperature. Higher temperature tended to give larger size and wider distribution. The obtained Ag NPs were characterized using various methods, including high-resolution transmission electron microscopy, UV–visible spectroscopy, and X-ray diffraction. The antibacterial effect of the product against Escherichia coli was evaluated by static and dynamic culture experiments, revealing that the Ag NPs-loaded nano-wood materials have great promise as antimicrobial agents against E. coli.     

Preparation and characterization of activated carbon fibers supported with silver metal for antibacterial behavior

In this work, the effect of immersion in silver nitrate solution on activated carbon fibers (ACFs) was investigated in relation to adsorption behavior and antibacterial activity of ACFs supported with silver (ACF/Ag). The pore and surface properties were studied in terms of BET volumetric measurement with nitrogen adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The antibacterial activities of ACF/Ag were studied in broth dilution tests against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) from a point of view of water purification. As an experimental result, the silver content of ACF/Ag increased with increasing concentration of silver nitrate. It was found that the micropore structure slightly decreased as the silver nitrate concentration increased. Otherwise, it was revealed that the ACF/Ag possessed a strong antibacterial activity and an inhibitory effect for the growing of E. coli and S. aureus, respectively. Silver content on ACF/Ag decreased rapidly because of rough morphology of silver particles in water erosion.     

Electrochemical analysis of chloramphenicol using boron-doped diamond electrode applied to a flow-injection system.

The electrochemical properties of chloramphenicol at a boron-doped diamond thin-film (BDD) electrode were studied using cyclic voltammetry. The highest current response of chloramphenicol was obtained with phosphate buffer, pH 6 (0.1 M) in 1% ethanol. The relationship between the concentration of chloramphenicol and the current response was linear over the range of 0.1-10 mM (R2=0.9990). The amount of chloramphenicol was analyzed by flow-injection analysis. A thin-layer flow cell equipped with a BDD electrode was used as an amperometric detector, and experiments were carried out at -0.7 V (vs. Ag/AgCl). The linear relationship between the current response and the concentration of chloramphenicol in the range of 0.1-50 microM (R2=0.9948) and the limit of detection of 0.03 microM (S/N=3) were obtained. This method has been successfully applied to the determination of chloramphenicol in sterile eye drops and milk sample by the standard addition method. The average recoveries of chloramphenicol in eye drops were 98.0%, and the average recoveries of chloramphenicol from spiked milk were 93.9-103%.     

基于二氧化硅荧光纳米颗粒与核酸染料SYBRGreenⅠ的双色显微成像技术用于E.coliO157:H7的检测

将免疫荧光纳米标记技术与激光共聚焦显微成像方法相结合,发展了一种基于二氧化硅荧光纳米颗粒和核酸染料SYBR Green Ⅰ的双色显微成像技术用于大肠杆菌O157:H7的检测.采用联吡啶钌(RuBpy)二氧化硅荧光纳米颗粒对羊抗大肠杆菌O157:H7抗体进行修饰,基于抗体-抗原相互作用实现了其对目标大肠杆菌O157:H7...     

Catalytic and antibacterial evaluation of silver nanoparticles synthesized by a green approach

In this work, silver nanoparticles were synthesized using Salvia microphylla Kunth leaves extract as reducing agent and stabilizing agent. The effect of reaction time and plant extract amount on the biosynthesized nanoparticles were studied. The UV–Vis spectrum indicated that silver nanoparticles show a characteristic surface plasmon resonance at 427 nm. X-ray diffraction experiments show that the silver nanoparticles have a face-centered cubic crystal structure. The density of nanoparticles increases with increasing extract concentration and reaction time. TEM and SEM observations showed well-dispersed quasi-spherical nanoparticles sized in the range of 15–45 nm. The FT-IR analysis suggested the involvement of phenolic compounds in the reduction and stabilization of silver nanoparticles. Synthesized silver nanoparticles showed good antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Finally, the catalytic properties of silver nanoparticles were demonstrated through the degradation of congo red and methyl orange.     

纳米银对表面吸附荧光素的荧光增强和荧光猝灭效应及KCl的荧光猝灭释放效应

制备了两种不同粒径的纳米银溶胶，研究了在水溶液条件下其对表面吸附荧光素(FL)的荧光性能的影响及KCl电解质对该体系荧光性能的影响。FL溶液中加入纳米银，FL分子吸收峰位发生红移。随着纳米银浓度的增加，FL分子荧光先出现增强，而后又逐渐猝灭。粒径较大的纳米银产生最大荧光增强比率所需浓度较低。在纳米银猝灭FL分子荧光的溶液中加入KCl电解质，随着KCl浓度的增加，荧光逐渐增强，出现了荧光猝灭释放效应。研究结果表明，纳米银对表面吸附FL的荧光作用与FL分子附近局域电磁场增强和分子到金属表面无辐射跃迁能量转移过程决定并与纳米银的浓度、尺寸及电解质等密切相关。     

超细Ag颗粒对葡萄糖氧化酶生物传感器响应灵敏度的增强效应

生物传感器在临床医学、环境和食品工业等方面都有重要的用途［１］,且由于其具有体积小、精度高、灵敏度好和便于现场测定等优点,已成为当前研究的热点课题之一．其中研究得较多的是氧化酶电流型生物传感器,特别是介体型,由于其响应快,灵敏而倍受重视．现已报道的可...     

γ辐照引发无皂乳液聚合法一步合成Ag-聚4-乙烯基吡啶杂化微凝胶

无机-聚合物纳米复合材料是将聚合物与一种或多种无机纳米粒子复合而成的一种材料,它同时具有无机纳米粒子和聚合物的优良特性,在许多重要技术领域具有广泛的应用前景.近20年来,无机-聚合物纳米复合材料的制备及应用备受关注[1~6].包括杂化微凝胶在内的纳米复合微球是无机-聚合     

Antibacterial properties of novel poly(methyl methacrylate) nanofiber containing silver nanoparticles

Poly(methyl methacrylate) (PMMA) nanofiber containing silver nanoparticles was synthesized by radical-mediated dispersion polymerization and applied to an antibacterial agent. UV-vis spectroscopic analysis indicated that the silver nanoparticles were continually released from the polymer nanofiber in aqueous solution. The antibacterial properties of silver/PMMA nanofiber against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria were evaluated using minimum inhibitory concentration (MIC), the modified Kirby-Bauer method, and a kinetic test. The MIC test demonstrated that the silver/PMMA nanofiber had enhanced antimicrobial efficacy compared to that of silver sulfadiazine and silver nitrate at the same silver concentration.     

Development and validation of single particle ICP-MS for sizing and quantitative determination of nano-silver in chicken meat

The application of nanomaterials is leading to innovative developments in industry, agriculture, consumer products, and food and related sectors. However, due to the special properties of these materials there are concerns about their safety, especially because of our limited knowledge of human health effects and the fact that constantly new nanomaterials and applications thereof are being produced. The development of analytical techniques is a key element to understand the benefits as well as the risks of the application of such materials. In this study, a method is developed and validated for sizing and quantifying nano-silver in chicken meat using single particle inductive coupled plasma mass spectrometry (ICP-MS). Samples are processed using an enzymatic digestion followed by dilution of the digest and instrumental analysis of the diluted digest using single particle ICP-MS. Validation of the method in the concentration of 5–25 mg/kg 60-nm silver nanoparticles showed good performance with respect to trueness (98–99 % for size, 91–101 % for concentration), repeatability (<2 % for size, <11 % for concentration), and reproducibility (<6 % for size, <16 % for concentration). The response of the method is linear, and a detection limit as low as 0.1 mg/kg can be obtained. Additional experiments showed that the method is robust and that digests are stable for 3 weeks at 4 °C. Once diluted for single particle ICP-MS analysis, the stability is limited. Finally, it was shown that nano-silver in chicken meat is not stable. Silver nanoparticles dissolved and were transformed into silver sulfide. While this has implications for the form in which nano-silver will be present in real-life meat samples, the developed method will be able to determine the presence and quantity of nanoparticle silver in such samples.     

SERS-based sandwich immunoassay using antibody coated magnetic nanoparticles for Escherichia coli enumeration

A method combining immunomagnetic separation (IMS) and surface-enhanced Raman scattering (SERS) was developed to enumerate Escherichia coli (E. coli). Gold-coated magnetic spherical nanoparticles were prepared by immobilizing biotin-labeled anti-E. coli antibodies onto avidin-coated magnetic nanoparticles and used in the separation and concentration of the E. coli cells. Raman labels have been constructed using rod shaped gold nanoparticles coated with 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB) and subsequently with a molecular recognizer. Then DTNB-labeled gold nanorods were interacted with gold-coated magnetic spherical nanoparticle-antibody-E. coli complex. The capture efficiency and calibration graphs were obtained and examined in different E. coli concentrations (10(1)-10(7) cfu mL(-1)). The correlation between the concentration of bacteria and SERS signal was found to be linear within the range of 10(1)-10(4) cfu mL(-1) (R(2) = 0.992). The limit of detection (LOD) and limit of quantification (LOQ) values of the developed method were found to be 8 and 24 cfu mL(-1), respectively. The selectivity of the developed immunoassay was examined with Enterobacter aerogenes, Enterobacter dissolvens, and Salmonella enteriditis which did not produce any significant response. The ability of the immunoassay to detect E. coli in real water samples was also investigated and the results were compared with the experimental results from plate-counting methods. There was no significant difference between the methods that were compared (p > 0.05). This method is rapid and sensitive to target organisms with a total analysis time of less than 70 min.