Extracellular biosynthesis of functionalized silver nanoparticles by strains of Cladosporium cladosporioides fungus

In the present investigation, we report the extracellular biosynthesis of silver nanoparticles (AgNP) employing the fungus Cladosporium cladosporioides. The extracellular solution of C. cladosporioides was used for the reduction of AgNO(3) solution to AgNP. The present study includes time dependent formation of AgNP employing UV-vis spectrophotometer, size and morphology by employing TEM (transmission electron microscopy), structure from powder X-ray diffraction (XRD) technique and understanding of protein-AgNP interaction from Fourier transform infrared (FT-IR) spectroscopy. The AgNP were 10-100nm in dimensions as measured by TEM images.     

Clay-mediated synthesis of silver nanoparticles exhibiting low-temperature melting

Nanohybrids of silver nanoparticles (AgNPs) supported on mica clay were synthesized by in situ reduction of silver nitrate in an aqueous solution. The required mica platelets of high aspect ratio were previously prepared by the exfoliation of mica clay stacks in a multilayered structure through an ionic exchange reaction with poly(oxypropylene)-amine-salt. The exfoliated nanoscale mica platelets (Mica) are polydispersed such that each platelet is 300-1000 nm in width and 1 nm in thickness. These platelets possess ionic charges in the form of ≡SiO(-)Na(+) at 120 mequiv/100 g and are suitable for supporting AgNPs in the process of in situ reduction of silver nitrate. Transmission electronic microscopy revealed the formation of AgNPs with a narrow size distribution of ca. 8 nm in diameter on the rim of individual Mica platelets. However, the pristine layered Mica structure without exfoliation failed to produce a fine AgNP distribution but instead generated particles larger than 30 nm and some precipitates. Characterization by differential scanning calorimetry and field emission scanning electron microscopy revealed that the fine AgNPs on Mica platelets exhibited a low melting temperature of 110 °C. The AgNP/Mica nanohybrid not containing an organic dispersant is considered to be a "naked" silver particle.     

Biosynthesis of silver nanoparticles using Onosma sericeum Willd. and evaluation of their catalytic properties and antibacterial and cytotoxic activity

In this study, silver nanoparticle (AgNP) synthesis was carried out using Onosma sericeum Willd. aqueous extract for the first time, with a simple, economical, and green method without the need for any other organic solvent or external reducing or stabilizing agent. A variety of AgNPs, all of different particle sizes, were synthesized by controlling the silver ion concentration, extract volume, temperature, and pH. It was determined that the optimum conditions for AgNP synthesis were 1 mM AgNO3, pH 8, 25 °C, 20 g/200 mL extract, silver nitrate, and extract ratio 5:1 (v/v). The AgNPs were defined using UV-Vis spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The particle size distribution and zeta potential measurements of the AgNPs were measured using the dynamic light scattering (DLS) technique. It was determined that the AgNPs with a particle size of less than 10 nm showed a higher catalytic effect in the reduction of 2-nitrobenzenamine. It was also found that these nanoparticles had a cytotoxic effect on the MCF-7 breast cancer cell line depending on dosage and time. The resulting IC50 values were between 76.63 µg/mL and 169.77 µg/mL. Furthermore, the biosynthesized AgNPs showed effective antibacterial activity against the Acinetobacter baumannii bacteria. The results of the study showed that synthesized AgNPs can have a promising role in biomedical and nanobiotechnology applications.     

Measuring silver nanoparticle dissolution in complex biological and environmental matrices using UV-visible absorbance

Distinguishing the toxic effects of nanoparticles (NPs) themselves from the well-studied toxic effects of their ions is a critical but challenging measurement for nanotoxicity studies and regulation. This measurement is especially difficult for silver NPs (AgNPs) because in many relevant biological and environmental solutions, dissolved silver forms AgCl NPs or microparticles. Simulations predict that solid AgCl particles form at silver concentrations greater than 0.18 and 0.58 μg/mL in cell culture media and moderately hard reconstituted water (MHRW), respectively. The AgCl NPs are usually not easily separable from AgNPs. Therefore, common existing total silver techniques applied to measure AgNP dissolution, such as inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption, cannot accurately measure the amount of silver remaining in AgNP form, as they cannot distinguish Ag oxidation states. In this work, we introduce a simple localized surface plasmon resonance (LSPR) UV–visible absorbance measurement as a technique to measure the amount of silver remaining in AgNP form for AgNPs with constant agglomeration states. Unlike other existing methods, this absorbance method can be used to measure the amount of silver remaining in AgNP form even in biological and environmental solutions containing chloride because AgCl NPs do not have an associated LSPR absorbance. In addition, no separation step is required to measure the dissolution of the AgNPs. After using ICP-MS to show that the area under the absorbance curve is an accurate measure of silver in AgNP state for unagglomerating AgNPs in non-chloride-containing media, the absorbance is used to measure dissolution rates of AgNPs with different polymer coatings in biological and environmental solutions. We find that the dissolution rate decreases at high AgNP concentrations, 5 kDa polyethylene glycol thiol coatings increase the dissolution rate, and the rate is much higher in cell culture media than in MHRW.     

Spin Selectivity in Electron Transfer in Photosystem I

Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons’ spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high‐spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high‐spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.     

The stabilization of nanodisperse silver in a sulfo cation exchanger

Silver-ion exchanger (electron ion exchanger, EI) composites with equivalent silver and hydrogen counterion contents were prepared by chemical deposition. Microscopic and X-ray data showed that silver nanoparticles and their ensembles isolated from each other and stabilized by a polymeric matrix were formed. Contact of Ag⁰-EI in the H⁺ form with solutions of silver salts caused the occurrence of two processes, ion exchange and metal recrystallization. These processes were interrelated because they involved one common particle, the silver counterion. Recrystallization proceeded by the electron-ion mechanism, but, because of matrix isolation of silver particles, electron transfer occurred inside separate structural elements (ensembles of particles) rather than over the whole composite volume. The transfer of silver ions largely occurred over ionogenic matrix centers, which substantially decreased their mobility. The low electronic conductivity of the composite and limited mobility of counterions were charge stabilization factors, which hindered recrystallization and, along with matrix stabilization, contributed to the retention of nanosized silver particles.     

One‐Step Synthesis of Silver Nanoparticle‐Decorated Hydroxyapatite Nanowires for the Construction of Highly Flexible Free‐Standing Paper with High Antibacterial Activity

A highly flexible and free‐standing paper with high antibacterial activity made from silver nanoparticle (AgNP)‐decorated ultralong hydroxyapatite nanowires (HAPNWs) is reported. The HAPNWs@AgNPs nanocomposites were obtained from a facile one‐step solvothermal process and utilized for the construction of highly flexible and free‐standing inorganic paper through a simple vacuum‐filtration procedure. The structure and properties of the HAPNWs@AgNPs paper were characterized in detail. Scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs show that AgNPs are highly dispersed and stabilized in the nanocomposite and exhibit a narrow particle size distribution. The effects of the concentration of silver nitrate, solvothermal temperature and time on the product were systematically investigated. This method is simple, convenient and reproducible. The as‐prepared HAPNWs@AgNPs paper shows long‐time sustained silver‐ion release, high antibacterial activity against both Gram‐negative and Gram‐positive bacteria, and good biocompatibility. Overall, this work provides a novel pathway for the preparation of a new type of highly flexible, free‐standing and antibacterial inorganic paper made from silver nanoparticle‐decorated hydroxyapatite nanowires for various applications, as a promising functional biomaterial.     

无机纳米晶-生物界面作用的分子机制

无机纳米晶材料以其独特的光、电、磁、力学性质,成为疾病诊断与治疗功能的关键材料.本文总结了无机纳米晶的表面化学活性、离子释放性、晶相结构、晶格缺陷、表面吸附和表面修饰等与尺寸相关的理化性质与生物效应之间的关系.综述了无机纳米晶与蛋白质、磷脂生物膜间的界面相互作用,探讨了纳米晶-生物界面作用的分子机理.这有助于理解无机纳米晶的生物行为和毒理性质,指导设计安全、高效的纳米晶生物医学材料.     

Effect of doping activated carbon based Ricinodendron Heudelotti shells with AgNPs on the adsorption of indigo carmine and its antibacterial properties

Two adsorbents samples namely ZnCl₂ Activated carbon (ACZ); and a composite from ACZ doped with silver nanoparticles (ACZ/AgNP) made by successful precipitation loading onto ACZ and silver nanoparticles of the Recinodendron heudelotti shells aqueouse extract (RHSNP) were prepared. The ACZ and ACZ/AgNP materials were characterised by scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Fourier Transform Infra-Red (FTIR) spectroscopy, X-ray diffraction (XRD) and particle size by Zeta sizer. The antibacterial activities of ACZ, ACZ/AgNP the RHSNP and the RHS extract was done by the broth microdilution test on Shigella flexneri, Salmonella typhi and Escherichia coli species. Futhermore, the adsorption capacities of the ACZ and the ACZ/AgNP was investigated using the hazardous Indigo Carmine (IC) dye. The SEM results shows spongy rock-like surface on both adsorbents (ACZ and ACZ/AgNP) with the presence of pores, EDX and XRD shows the presence of crystalline zincite on ACZ and Ag on the ACZ/AgNP. The FTIR spectral for both adsorbents preseumes a composite material while the zeta sizer shows that all the materials samples prepared were in the nano-range. The extract and ACZ showed no antimicrobial activities while the antimicrobial properties were proven to be very interesting for the nanoparticles and the ACZ/AgNP but higher for the ACZ/AgNP (7.812 ≤ MIC ≤ 31.25 µg/ml). The adsorption capacities of IC were found to decrease by 33.15% respectively using the maximum concentration at equilibrium. RHS is therefore a good and promising precursor for the preparation of activated carbon and nanoparticles for bacterial containing water purification and for the treatment of bacterial infections.     

Detection and characterization of silver nanoparticles in chicken meat by asymmetric flow field flow fractionation with detection by conventional or single particle ICP-MS

A method of analysis of silver nanoparticles (AgNPs) in chicken meat was developed. The homogenized chicken meat sample, which was spiked with AgNPs, was subjected to enzymolysis by Proteinase K for 40 min at 37 °C. Transmission electron microscopy and inductively coupled plasma mass spectrometry (ICP-MS) in single particle mode were used to characterize the number-based size distribution of AgNPs in the meat digestate. Because similar size distributions were found in the meat digestate and in the aqueous suspension of AgNPs used for spiking the meat, it was shown that no detectable dissolution of the AgNPs took place during the sample preparation stage. The digestate was injected into the asymmetric flow field flow fractionation (AF⁴) -ICP-MS system, which enabled fractionation of nanoparticles from the remaining meat matrix, and resulted in one large peak in the fractograms as well as two smaller peaks eluting close to the void volume. The recovery of silver contained in the large AgNP peak was around 80 %. Size determination of AgNPs in the meat matrix, based on external size calibration of the AF⁴ channel, was hampered by non-ideal (early elution) behavior of the AgNPs. Single particle ICP-MS was applied for determination of the number-based particle size distribution of AgNPs in collected fractions. The presented work describes for the first time the coupling of AF⁴ and ICP-MS for AgNP separation in a food matrix.     

Synthesis of Silver Nanoparticle‐Graphene Composites for Electroanalysis Applications using Chemical and Electrochemical Methods

An electrochemical device was developed for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) using differential pulse voltammetry and glassy carbon (GC) electrodes modified with reduced graphene oxide (rGO) and silver nanoparticle (AgNP) composites, synthesised using both chemical and electrochemical methods. The morphology and electrochemical behaviour of the GC electrodes modified with the rGO/AgNP (chemical method) and rGO‐AgNP (electrochemical method) composites were characterised by scanning electron microscopy and cyclic voltammetry. These techniques demonstrated that, in both methods, the graphene oxide was modified by the AgNPs, and the composite synthesised by the electrochemical method showed a better dispersion of the nanoparticles, resulting in an increase in the surface area compared to the rGO/AgNP composite. The GC/rGO‐AgNP electrode was evaluated and optimised for the simultaneous determination of SMX and TMP, achieving detection limits of 0.6 μmol L⁻¹ for the SMX and 0.4 μmol L⁻¹ for the TMP. The proposed GC/rGO‐AgNP electrochemical device was successfully applied to the simultaneous determination of SMX and TMP in wastewaters samples.     

Hemoglobin/colloidal silver nanoparticles immobilized in titania sol-gel film on glassy carbon electrode: direct electrochemistry and electrocatalysis

By vapor deposition method, both hemoglobin (Hb) and colloidal silver nanoparticles (CSNs) were entrapped in a titania sol-gel matrix on the surface of a glassy carbon electrode (GCE). CSNs could greatly enhance the electron transfer reactivity of Hb and its catalytic ability toward nitrite. Direct fast electron transfer between Hb and the GCE was achieved, and a pair of well-defined, quasi-reversible redox peaks was observed. The anodic and cathodic peak potentials are located at -0.298 V and -0.364 V (vs. Ag/AgCl), respectively. The dependence of the formal potential on solution pH indicated that the direct electron transfer reaction of Hb was a one-electron transfer coupled with a one-proton transfer reaction process. Meanwhile, the catalytic ability of Hb toward the reduction of NO2- was also studied. Accordingly, a NO2- biosensor was prepared, with a linear range from 0.2 mM to 6.0 mM and a detection limit of 34.0 microM. The apparent Michaelis-Menten constant was calculated to be 7.48 mM. Moreover, the biosensor had good long-term stability.     

Facile electrocatalytic redox of hemoglobin by flower-like gold nanoparticles on boron-doped diamond surface

The flower-like gold nanoparticles together with spherical and convex polyhedron gold nanoparticles were fabricated on boron-doped diamond (BDD) surface by one-step and simple electrochemical method through easily controlling the applied potential and the concentration of HAuCl(4). The recorded X-ray diffraction (XRD) patterns confirmed that these three shapes of gold nanoparticles were dominated by different crystal facets. The cyclic voltammetric results indicated that the morphology of gold nanoparticles plays big role in their electrochemical behaviors. The direct electrochemistry of hemoglobin (Hb) was realized on all the three different shapes of nanogold-attached BDD surface without the aid of any electron mediator. In pH 4.5 acetate buffer solutions (ABS), Hb showed a pair of well defined and quasi-reversible redox peaks. However, the results obtained demonstrated that the redox peak potential, the average surface concentration of electroactive heme, and the electron transfer rates of Hb are greatly dependent upon the surface morphology of gold nanoparticles. The electron transfer rate constant of hemoglobin over flower-like nanogold/BDD electrode was more than two times higher than that over spherical and convex polyhedron nanogold. The observed differences may be ascribed to the difference in gold particle characteristics including surface roughness, exposed surface area, and crystal structure.     

Dynamics of the interaction forces at the silver/solution interface during amine adsorption

The forces of interaction between a silver-coated particle and a flat silver surface in an aqueous medium were measured in the presence of a series of organic amines of varying concentrations. Atomic force microscopy (AFM) was used to quantify the replacement rate of adsorbed citrate molecules on the silver surfaces by a variety of amines, under conditions where the time scale of the amine adsorption was significantly slower than the time scale of the AFM measurements. The decay length of the electrostatic double-layer interaction between the silver surfaces was found to be time independent; thus, the change in surface change density (determined from the interaction forces) was used to quantify the replacement rate of adsorbed citrate by amine. In the absence of amine, the interaction force between the silver surfaces exhibited evidence of a multilayer structure of adsorbed citrate molecules on each silver surface. Upon addition of the amine, a decrease in the interaction force was always observed, where the dynamics of the force were dependent on both concentration and the molecular structure of the amine. These results are discussed with respect to formation of colloidal particles in synthesis routes where particle aggregation has a significant impact on the control of particle morphology and size.     

电子显微镜技术表征聚乙二醇包覆的银纳米线的显微结构特征

以缓慢的水热合成法制备聚乙二醇(PEG)包覆的银纳米线,并用电子显微镜对其微观形貌和结构进行了表征。PEG是一种对银表面呈弱亲和性的水溶性聚合物,它在银纳米线合成中既作为Ag+的还原剂,又作为银线的包覆剂。扫描电镜和透射电镜表征显示,这种银纳米线的直径为80～300 nm,长度大于100μm;并且其中一部分银纳米线首尾相接形成了闭合纳米线圈,是首例以化学法制取的金属闭合纳米线圈。闭合环状纳米线的形成进一步支持了金属纳米线的融合生长机制。透射电镜和选区电子衍射以及银纳米线横截面切片的透射电镜表征显示,这种PEG包覆的银纳米线具有轴对称的五重挛晶结构。银纳米线经过长时间的水热孵化而保持其五重挛晶结构,这一点与某些文献报道的情况有所不同,说明银纳米线结构及其演化具有一定的复杂性。     

Enhanced Electron Transfer Ability via Coordination in Block Copolymer/Porphyrin/Fullerene Micelle

Inspired by structures of antenna-reaction centers in photosynthesis,the complex micelle was prepared from zinc tetra-phenyl porphyrin (ZnTPP),fullerene derivative (PyC60) and poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-bPCL).The core-shell structure made the hydrophobic donor-acceptor system work in aqueous.In micellar core,coordination interaction occurred between ZnTPP and PyC60 molecules which ensured the enhanced energy migration from the donor to the acceptor.The enhanced interaction between porphyrin and fullerene was confirmed by absorption,steady-state fluorescence and transient fluorescence.The generation of singlet oxygen and superoxide radical was detected by iodide method and reduction of nitro blue tetrazolium,respectively,which confirmed that electron transfer reaction in the complex micellar core occurred.Moreover,the complex micelle exhibited effective electron transfer performance in photodebromination of 2,3-dibromo-3-phenylpropionic acid.The complex micellar structure endowed the donor-acceptor system with improved stability under irradiation.This strategy could be helpful for designing new electron transfer platform and artificial photosynthetic system.     

Immobilization of silver nanoparticles into POEGMA polymer brushes as SERS‐active substrates

Surface‐enhanced Raman scattering (SERS) has attracted a great deal of interest during the past four decades and emerged as an ultrasensitive optical technique for chemical and biomedical analysis. It is widely accepted that the facile fabrication of SERS substrates with high activity and good reproducibility is of crucial importance for their applications. Herein, we report on a fast and robust method for the synthesis and immobilization of silver nanoparticles (AgNPs) into poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes under mild conditions without using any reducing agents. POEGMA brushes of different chain lengths were synthesized directly on silicon wafers by surface‐initiated atom transfer radical polymerization with various reaction time. X‐ray photoelectron spectroscopy and field emission scanning electron microscope measurements indicated that the AgNPs were firmly and homogeneously embedded into POEGMA brushes. The resulting POEGMA–AgNP hybrid films were employed as SERS substrates for the detection of 4‐aminothiophenol, giving rise to an enhancement factor of up to 1.9 × 10⁶. The influence of the POEGMA's chain length on SERS performance was also investigated. Copyright © 2016 John Wiley & Sons, Ltd.     

Direct Electrochemistry of Hemoglobin at Silver Electrode Modified by Lipoic Acid Monolayer

Abstract

The direct electrochemistry of hemoglobin (Hb) was studied by cyclic voltammetry(CV) and flow injection analysis(FIA) on a silver electrode modified by a self-assembled monolayer of lipoic acid(LA). Lipoic acid molecules can strongly adsorb onto the Ag electrode surface through the cleavage of the S-H bond and the formation of the Ag-S bond. The observed adsorption coverage of LA demonstrates that the LA molecules spontaneously form a self-assembled monolayer. Experimental data show that LA can promote the redox process of Hb at the modified electrode surface. This chemically modified electrode (CME) exhibits good stability in the CV and FIA. Linear sweep voltammetric measurement of Hb at the CME reveals a linear relationship between the oxidative peak current and the concentration of Hb in the range of 5.0×10^?7-1.5×10^?5 mol/L. The relative standard derivation (RSD) for six replicate measurements of 5.0×10^?6 mol/L Hb in FIA is 2.8%. The detection limit is 2.0×10^?7 mol/L. The reaction mechanism involves the hydrogen bond/ salt bridge formation between the carboxylate of LA and the protonated lysine residues of Hb that can enhance the electron transfer reaction. It can be used to detect Hb in real examples.     

不同水环境对纳米银颗粒聚集体粒径大小及界面电势的影响

研究了不同水环境对无稳定剂与PVP为稳定剂的纳米银颗粒的物化性能的影响。结果表明:随着电解质浓度的增加,纳米银颗粒的粒径与界面电势逐步增大;二价阳离子比一价阳离子更能有效地使纳米银粒径与界面电势增加;稳定剂PVP,腐植酸及其他天然有机物能够增加纳米银溶胶的稳定性;在天然水体中,纳米银在海水中的粒径颗粒与界面电势比湖水中更大。