Molecular recognition by gold, silver and copper nanoparticles

The intrinsic physical properties of the noble metal nanoparticles,which are highly sensitive to the nature of their local molecular environment,make such systems ideal for the detection of molecular recognition events.The current review describes the state of the art concerning molecular recognition of Noble metal nanoparticles.In the first part the preparation of such nanoparticles is discussed along with methods of capping and stabilization.A brief discussion of the three common methods of functionalization:Electrostatic adsorption;Chemisorption;Affinity-based coordination is given.In the second section a discussion of the optical and electrical properties of nanoparticles is given to aid the reader in understanding the use of such properties in molecular recognition.In the main section the various types of capping agents for molecular recognition;nucleic acid coatings,protein coatings and molecules from the family of supramolecular chemistry are described along with their numerous applications.Emphasis for the nucleic acids is on complementary oligonucleotide and aptamer recognition.For the proteins the recognition properties of antibodies form the core of the section.With respect to the supramolecular systems the cyclodextrins,calix[n]arenes,dendrimers,crown ethers and the cucurbitales are treated in depth.Finally a short section deals with the possible toxicity of the nanoparticles,a concern in public health.

Characterization and Antitumor Activity of Chitosan/Poly （Vinyl Alcohol） Blend Doped with Gold and Silver Nanoparticles in Treatment of Prostatic Cancer Model

The application of nanotechnology in various fields of science has earned a great concern over the past decades. The natural products and surface-modified polymers and metallic nanoparticles （NPs） have evolved as promising nanomaterials for targeted prostate cancer treatment. In the present study, Chitosan/poly （vinyl alcohol） （Cs/PVA） blend was synthesized by gamma radiation which could behave a nanoreactor for silver （Ag） and gold （Au） nanoparticle with promising anticancer applications. （Cs/PVA/Ag） and （Cs/PVA/Au） nanocomposites were confirmed by SEM （scanning electron microscope） and TEM （transmission electron microscope） analysis. The swelling properties have been investigated as a function of time and pH. The anti-cancer activity of the prepared nanocomposites was demonstrated in prostatic cancer cell line. It has a significant effect against prostatic cancer. However, metal nanoparticles have shown a good experimental success in the field of nanomedicine especially in cancer treatment, which has always been an area of high concern. The collaboration of biomedical research in the identification and characterization of biomedical strategies using the interesting metal nanocomposite will impact the future nanomedicine greatly.

Synthesis of silver and gold nanoparticles from leaf of Litchi chinensis and its biological activities

Objective: To synthesize and isolate silver and gold nanoparticles from Litchi chinensis leaf methanolic extract, and to evaluate its comparative biological activities including muscles relaxant, analgesic, anti-inflammatory and antidiarrheal. Methods: The gold and silver nanoparticles were synthesized by dissolving methanolic extract in gold chloride and silver nitrate solution separately which were confirmed by colour change and UV-Vis spectroscopy, and pellets were collected through centrifugation. Biological activities of the extract were conducted on BALB/c mice through various standard methods and the data were subjected to One-way ANOVA. Results: The colorless gold chloride solution changed to purple soon after the addition of plant extract, demonstrating that the reaction took place and gold ions were reduced to gold nanoparticles, while colorless silver nitrate solution changed to light and dark brown that was indicative of silver nanoparticles. The muscles relaxant activity showed that silver nanoparticles were more effective than gold nanoparticles and methanolic extract in traction test. The analgesic activity showed that silver and gold nanoparticles showed highest percentage decrease in acetic acid induced writhing at the doses of 50, 100 and 150 mg/kg b.w. The highest anti-inflammatory activity was produced by gold nanoparticles followed by silver nanoparticles, while low activity was observed in methanolic leaf extract. Only the crude methanolic extract showed significant antidiarrheal activity as compared to the standard drug atropine sulphate, while antidiarrheal activities of gold and silver nanoparticles were non-significant. Conclusions: The present work concludes that isolated silver and gold nanoparticles from leaf methanolic extract shows strong muscles relaxant, analgesic and anti-inflammatory activities while crude methanolic extract possesses good antidiarrheal activity.

Synthesis and Characterization of Bimetallic Gold-Silver Core-Shell Nanoparticles: A Green Approach

Bimetallic gold-silver core-shell nanoparticles were prepared by chemical reduction in aqueous solution, following a method that was friendly to the environment, allowing us to use this for medicinal purposes. Gold nanoparticles were synthesized, and silver cations were then reduced on the nanoparticles. Using the optical properties of metallic nanoparticles, surface plasmon resonance was determined by UV-Vis spectroscopy, and the values obtained for gold and silver were approximately 520 nm and 400 nm in wavelength, respectively. The absorption peaks of the surface plasmon band show a clear red-shift due to size effect in the case of the silver surface, and a plasmon coupling effect, in the case of gold. To obtain a better understanding of the coating conditions, high resolution transmission electron microscopy was used. The average hydrodynamic size and the size distribution of the synthesized nanoparticles were obtained by dynamic light scattering. The development of this process, which is benign for the environment, opens the possibility for many applications in the areas of renewable energy, medicine and biology.

Development of Biotechnology for Microbial Synthesis of Gold and Silver Nanoparticles

Several bacterial strains of Actinomycetes belonging to Streptomyces and Arthrobacter genera for the first time were used to study the biotechnology of synthesis of gold and silver nanoparticles. The experimental conditions of gold and silver nanoparticles production by the cells of studied strains in aqueous chloroauric acid （HAuCIq） and in silver nitrate （AgNO3） solutions, respectively, were determined. Concentration and time-dependences of nanoparticle formation were investigated. The complex of optical and analytical methods was used for testing the gold and silver nanoparticles in the bacterial biomass. The TEM （Transmission Electron Microscopy） and XRD （X-ray Diffraction） data in all cases demonstrated the presence of crystals with fcc （face centered cubic） structure. The results obtained show that the Actinomycetes are capable of producing gold and silver nanoparticles of spherical shape extracellularly when exposed to suitable compounds. The particle size distribution shows that the sizes of nanoparticles are in the range of 5 nm to 80 nm. The biomass obtained may be used for industrial as well as medical and pharmaceutical purposes.

Influence of Gadolinium with Small Content on Recrystallization Behaviour in Silver-Gold Alloys

The influence of small addition of RE element Gd on recrystallization behaviour in isomorphous Ag-Au alloys was studied by differential scanning calorimetry, optical microscopy, transmission electron microscopy and hardness measurement. It is shown that in alloys with 0.2% Gd, disperse second-phase particles are formed, which results in obvious increase in the recrystallization temperature and grain refining. The recrystallization temperature of AgAuGd0.2 alloys also increases with cold working. Small addition of Gd raises the apparent activation energy of recrystallization for Ag-Au alloys.

Antibacterial Action and Physicochemical Properties of Stabilized Silver and Gold Nanostructures on the Surface of Disperse Silica

This work is devoted to the synthesis and stabilization of nanosized Ag/SiO2 and Au/SiO2 disperse materials and investigation their morphology, optical and antimicrobial properties. First, Ag and Au nanoparticles (NPs) were produced in colloids via chemical (Ag) or photochemical (Au) reduction of appropriate ions. To prevent the oxidation of Ag NPs in colloid solution, external binary stabilizing agents PVP and SDS were used. Then, Ag and Au NPs (0.01-0.05% wt) were adsorbed from their colloid solutions on high disperse silica surface (Ssp=260m2/g) and samples prepared were dried. Materials obtained were studied by UV-vis, XRD, and TEM methods. Ag and Au NPs adsorbed on silica demonstrated a fair crystallinity in XRD. The surface plasmon resonance (SPR) band positions inherent to Ag and Au NPs on silica surface as well as the intensities of optical spectra were stable during 7 month and more. Obtained Ag NPs in colloids and Ag/SiO2 composites demonstrated excellent antimicrobial activity against a series of the microorganisms (Escherichia coli, Staphylococcus aurous, and Candida albicans). Au/SiO2 samples did not reveal any bactericide properties relative to the test microorganisms grown. The mechanisms of Ag(Au) NPs interaction with silica surface were analyzed.

Low Temperature Formation of Silver and Silver-Copper Alloy Nano-Particles Using Plasma Enhanced Hydrogenation and Their Optical Properties

In this paper, a novel method of producing nanoparticles at low temperatures using hydrogen bombardment of thin films, deposited on glass substrates, is introduced. Silver nanoparticles were obtained by this method in our Plasma Enhanced Chemical Vapor Deposition system. Optical and morphological characteristics of these nanoparticles were extensively studied for various conditions of plasma treatment, such as plasma power density, temperature, duration of hydrogen bombardment, thickness of the initial thin metallic film etc. In addition, Ag-Cu alloy nanoparticles on glass substrates were also achieved. The process of nanoparticle formation in this method shows that several kinds of metals and semiconductors nanoparticles can be obtained using this approach. Scanning Electron Microscopy, Atomic Force Microscopy and Transmission Electron Microscopy were used to analyze the nanostructures.

Doping and alloying in atomically precise gold nanoparticles

The recent success in the synthesis and total structure determination of atomically precise gold nanoparticles has provided exciting opportunities for fundamental studies as well as the development of new applications. These unique nanoparticles are of molecular purity and possess well defined formulas （i.e., specific numbers of metal atoms and ligands）, resembling organic compounds. Crystallization of such molecularly pure nanoparticles into macroscopic single crystals allows for the determination of total structures of nanoparticles （i.e., the arrangement of metal core atoms and surface ligands） by X-ray crystallography. In this perspective article, we summarize recent efforts in doping and alloying gold nanoparticles with other metals, including Pd, Pt, Ag and Cu. With atomically precise gold nanoparticles, a specific number of foreign atoms （e.g., Pd, Pt） can be incorporated into the gold core, whereas a range of Ag and Cu substitutions is observed but, interestingly, the total number of metal atoms in the homogold nanoparticle is preserved. The heteroatom substitution of gold nanoparticles allows one to probe the optical, structural, and electronic properties truly at the single-atom level, and thus provides a wealth of information for understanding the intriguing properties of this new class of nanomaterials.

Shaped gold and silver nanoparticles

Advance in the synthesis of shaped nanoparticles made of gold and silver is reviewed in this article. This review starts with a new angle by analyzing the relationship between the geometrical symmetry of a nanoparticle shape and its internal crystalline structures. According to the relationship, the nanoparticles with well-defined shapes are classified into three categories： nanoparticles with single crystallinity, nanoparticles with angular twins, and nanoparticles with parallel twins. Discussion and analysis on the classical methods for the synthesis of shaped nanoparticles in each category are also included and personal perspectives on the future research directions in the synthesis of shaped metal nanoparticles are briefly sum marized. This review is expected to provide a guideline in designing the strategy for the synthesis of shaped nanoparticles and analyzing the corresponding growth mechanism.

Comparative study of the effects of gold and silver nanoparticles on the metabolism of human dermal fibroblasts

The purpose of this article was to explore the effects of gold nanoparticles(GNPs)and silver nano-particles(SNPs)with different cytotoxicities on human dermal fibroblasts(HDFs)at the metabolic level.First,~20 nm of GNPs and SNPs were prepared,and their effects on the proliferation of HDFs were evaluated.Then,a metabolomics technique was used to analyse the effects of GNPs and SNPs on the expression profiles of metabolites in HDFs after 4,8 and 24h of treatment.Furthermore,the key metabolites and key metabolic pathways involved in the interaction of GNPs and SNPs with HDFs were identified through expression pattern analysis and metabolic pathway analysis of differentially expressed metabolites and were finally verified by experiments.The results of the cytotoxicity experiments showed that there was no cytotoxicity after the treatment of GNPs for 72 h,while the cytotoxicity of the SNPs reached grade 1 after 72 h.By using metabolomics analysis,29,30 and 27 metabolites were shown to be differentially expressed in HDFs after GNP treatment,while SNPs induced the differential expression of 13,33 and 22 metabolites after 4,8 and 24h of treatment,respectively.Six and four candidate key metabolites in the GNP and SNP groups were identified by expression pattern analysis and metabolic pathway analysis,respec-tively.The key metabolic pathways in the GNP and SNP groups were identified as the glutathione metabolic pathway(the key metabolite of which was glutathione)and the citrate cycle pathway(the key metabolite of which was malic acid).Based on the experiments used to verify the key metabolites and key metabolic pathways,it was found that the increase in glutathione after GNP treatment might trigger an oxidative stress protection mechanism and thus avoid cytotoxicity.After exposure to SNPs,the citric acid content was increased,mainly through the citrate cycle path-way,thereby inhibiting the synthesis of malic acid to affect the formation of ATP and finally leading to cytotoxicity.

Corrosion behaviours of the dental magnetic keeper complexes made by different alloys and methods

The keeper and cast dowel-coping, as a primary component for a magnetic attachment, is easily subjected to corrosion in a wet environment, such as the oral cavity, which contains electrolyte-rich saliva, complex microflora and chewing behaviour and so on. The objective of this in vitro study was to examine the corrosion resistance of a dowel and coping-keeper complex fabricated by finish keeper and three alloys （cobalt-chromium, CoCr; silver-palladium-gold, PdAu; gold-platinum, AuPt） using a laser- welding process and a casting technique. The surface morphology characteristics and microstructures of the samples were examined by means of metallographic microscope and scanning electron microscope （SEM）. Energy-dispersive spectroscopy （EDS） with SEM provided elements analysis information for the test samples after 10% oxalic acid solution etching test. Tafel polarization curve recordings demonstrated parameter values indicating corrosion of the samples when subjected to electrochemical testing. This study has suggested that massive oxides are attached to the surface of the CoCr-keeper complex but not to the AuPt-keeper complex. Only the keeper area of cast CoCr-keeper complex displayed obvious intergranular corrosion and changes in the Fe and Co elements, Both cast and laser-welded AuPt-keeper complexes had the highest free corrosion potential, followed by the PdAu-keeper complex. We concluded that although the corrosion resistance of the CoCr-keeper complex was worst, the keeper surface passive film was actually preserved to its maximum extent. The laser-welded CoCr- and PdAu-keeper complexes possessed superior corrosion resistance as compared with their cast specimens, but no significant difference was found between the cast and laser-welded AuPt-keeper complexes. The Fe-poor and Cr-rich band, appearing on the edge of the keeper when casting, has been proven to be a corrosion-prone area.

Au-Ag合金纳米粒子的绿色制备及其催化还原性能研究

以AgNO_(3)和HAuCl_(4)为前驱体,以羧甲基壳聚糖(CMC)同时为还原剂和稳定剂制备了金银合金纳米粒子(Au-Ag ANPs),研究了反应温度、时间、NaOH和CMC浓度的影响。通过紫外-可见吸收光谱(UV-Vis)、透射电子显微镜(TEM)、傅里叶变换红外光谱(FT-IR)和X-射线衍射(XRD)对Au-Ag ANPs进行了表征。考察了Ag_(0.5)Au_(0.5)投加量、4-NP/NaBH_(4)摩尔比、反应温度和不同条件下制备的Au-Ag ANPs对水溶液中4-硝基苯酚(4-NP)的催化还原性能的影响。结果表明:通过控制Au-Ag ANPs制备时AgNO_(3)和HAuCl_(4)的体积比(V AgNO_(3)/V HAuCl_(4))即可灵活调整Au-Ag ANPs中Au、Ag元素的含量。相同V AgNO_(3)/V HAuCl_(4)时,NaOH和CMC浓度也会影响Au-Ag ANPs中Au、Ag元素的含量。Au-Ag ANPs的平均粒径在(4.5±1.2)nm(Ag_(0.8)Au_(0.2))至(6.5±1.3)nm(Ag_(0.2)Au_(0.8))之间,均小于AuNPs[(16.8±3.7)nm]和AgNPs[(11.7±1.4)nm]的平均粒径。不同Au、Ag元素含量的Au-Ag ANPs对4-NP的催化还原活性均大于AuNPs和AgNPs。在30℃,催化剂投加量60μL,4-NP/NaBH_(4)=1/500时,催化反应30min,Au_(0.6) Ag_(0.4)对4-NP的转化率为91.1%,反应速率常数为0.1289min^(-1)。

金银合金纳米星/聚氯乙烯柔性表面增强拉曼基底的制备及其对毒死蜱的检测

该文制备了一种金银合金纳米星/聚氯乙烯柔性表面增强拉曼光谱(surface-enhanced Raman scattering,SERS)基底,该基底具有透明度高、灵活性强和SERS增强性能显著的优点,可以快速实现对果蔬表面毒死蜱残留的定性和定量检测。在复合基底制备中,首先优化聚氯乙烯(polyvinyl chloride,PVC)添加量获得柔性良好的PVC基底,并优化氯金酸/硝酸银体积比制备了形貌鲜明且SERS增强效应显著的各向异性金银合金纳米星(gold-silver alloy nanostars,Au@Ag NSs),其次以拉曼信号分子4-巯基苯甲酸为对象,通过拉曼光谱仪测定其在复合基底上的SERS强度,确定了Au@Ag NSs溶液的最优浓缩倍数,进一步验证了基底的良好SERS效应、重现性和稳定性,最后成功应用于苹果表皮毒死蜱残留的检测。

Enhanced catalytic activity of monodispersed AgPd alloy nanoparticles assembled on mesoporous graphitic carbon nitride for the hydrolytic dehydrogenation of ammonia borane under sunlight

We address the composition-controlled synthesis of monodispersed AgPd alloy nanoparticles （NPs）, their assembly for the first time on mesoporous graphitic carbon nitride （mpg-C3N4）, and the unprecedented catalysis of mpg-CgN4@AgPd in the hydrolytic dehydrogenation of ammonia borane （AB） at room temperature. Monodispersed AgPd alloy NPs were synthesized using a high-temperature organic-phase surfactant-assisted protocol comprising the co-reduction of silver（I） acetate and palladium（II） acetylacetonate in the presence of oleylamine, oleic acid, and 1-0ctadecene. This protocol allowed the synthesis of four different compositions of AgPd alloy NPs. The AgPd alloy NPs were then assembled on mpg-C3N4, reduced graphene oxide, and Ketjenblack using a liquid-phase self-assembly method. Among the three supports tested, the mpg-CBN4@AgPd catalysts provided the best activity because of the Mott-Schottky effect, which was driven by the favorable work function difference between mpg-CBN4 and the metal NPs. Moreover, the activity of the mpg-CBN4@AgPd catalyst was further enhanced by an acetic acid treatment （AAt）, and a record initial turnover frequency of 94.1 mOl（hydrogen）＇mOl（catalyst）-l-min-1 was obtained. Furthermore, the mpg-CBN4@Ag42Pdss-AAt catalyst also showed moderate durability for the hydrolysis of AB. This study also includes a wealth of kinetic data for the mpg-CBN4@AgPd-catalyzed hydrolysis of AB.

酪蛋白-金银合金纳米簇的制备及其对金霉素的荧光检测

以酪蛋白为保护剂和还原剂,采用优化的一锅加热合成方法,成功制备一种新型金银合金纳米簇(Au-AgNCs@casein)。产物在325 nm最佳激发波长下有双荧光发射峰,通过红外光谱、透射电子显微镜等方法对其进行结构表征。在常见离子或氨基酸存在下,金霉素(CTC)可明显增强比率型探针Au-AgNCs@casein的荧光,其结构类似物却无明显影响。因此,本研究中制备的纳米簇可快速、灵敏、选择性检测CTC。

多色比色法在生物传感平台的研究进展

比色法是生物传感中较为常用的一种检测手段,因其具有较高的灵敏度和特异性而受到广泛关注。其中,基于多色探针的多色比色法已成为近年来的研究热点,灵敏度较单色比色法显著提高、且具有更高的分辨率和肉眼辨识度,通过观察颜色变化可进行可视化半定量检测,又可通过计算颜色比率或基于智能手机图像处理软件进行快速定量检测。基于有机小分子荧光显色、纳米材料显色及酶促反应显色3种不同的显色机理,综述了多色荧光小分子探针、多色纳米材料比色探针及多色酶促反应比色探针的检测机理以及它们在实际样本检测中的应用,并进一步探讨了其面临的挑战及未来发展机遇。

金银复合纳米粒子的合成及其光散射特性

根据Ag+和AuCl-4还原能力的不同,采用分步进料,柠檬酸钠一步还原的方法制备不同摩尔比的AuAg复合纳米粒子。通过紫外可见光吸收光谱、透射电镜等手段对所得复合纳米粒子进行了表征。结果表明,AuAg复合纳米粒子的形状近乎球形,结构密实,单分散性好。金银摩尔比1∶1组成的复合纳米粒子的粒径为48.7nm,最大吸收波长为459nm。采用同步光散射和发射光谱对金、银及复合纳米粒子光散射特性进行了研究。实验显示,随着复合纳米粒子中银摩尔分数的减小,主散射峰逐步红移,其峰值与Ag摩尔分数呈线性关系,λmax=619.5-153.4XAg,相关系数r=-0.9927,散射光强度与Ag摩尔分数也呈线性关系,线性方程为Is=272.1+625.7XAg,相关系数r=0.9957;采用不同的激发波长均能获得多个倍频峰和分频峰,激发波长越短,分频峰的强度越大,说明AuAg复合纳米粒子具有非线性光学特性。复合纳米粒子散射波长、散射强度对组成的这种依赖特性,对于设计特定要求的光学探针具有重要的意义。

超声辐射法制备与表征DDP修饰锡纳米微粒

DDP-coated Sn nanoparticles were prepared by ultrasonic irradiation method. The nanoparticles were found to be well dispersed and coated with the surfactant DDP. The tetragonal phase of the as-prepared nanoparticles was characterized by selected area electron diffraction (SAED) and X-ray diffraction (XRD). In addition, the powder was found to have an excellent antiwear property by tribological test.