Biotechnological synthesis of Pd/Ag and Pd/Au nanoparticles for enhanced Suzuki–Miyaura cross-coupling activity

Bimetallic nanoparticle catalysts have attracted considerable attention due to their unique chemical and physical properties. The ability of metal-reducing bacteria to produce highly catalytically active monometallic nanoparticles is well known; however, the properties and catalytic activity of bimetallic nanoparticles synthesized with these organisms is not well understood. Here, we report the one-pot biosynthesis of Pd/Ag (bio-Pd/Ag) and Pd/Au (bio-Pd/Au) nanoparticles using the metal-reducing bacterium, Shewanella oneidensis, under mild conditions. Energy dispersive X-ray analyses performed using scanning transmission electron microscopy (STEM) revealed the presence of both metals (Pd/Ag or Pd/Au) in the biosynthesized nanoparticles. X-ray absorption near-edge spectroscopy (XANES) suggested a significant contribution from Pd(0) and Pd(II) in both bio-Pd/Ag and bio-Pd/Au, with Ag and Au existing predominately as their metallic forms. Extended X-ray absorption fine-structure spectroscopy (EXAFS) supported the presence of multiple Pd species in bio-Pd/Ag and bio-Pd/Au, as inferred from Pd–Pd, Pd–O and Pd–S shells. Both bio-Pd/Ag and bio-Pd/Au demonstrated greatly enhanced catalytic activity towards Suzuki–Miyaura cross-coupling compared to a monometallic Pd catalyst, with bio-Pd/Ag significantly outperforming the others. The catalysts were very versatile, tolerating a wide range of substituents. This work demonstrates a green synthesis method for novel bimetallic nanoparticles that display significantly enhanced catalytic activity compared to their monometallic counterparts.     

Potential of Chilopsis linearis for gold phytomining: using XAS to determine gold reduction and nanoparticle formation within plant tissues

This study reports on the capability of the desert plant Chilopsis linearis (Cav.) Sweet (desert willow) to uptake gold (Au) from gold-enriched media at different plant-growth stages. Plants were exposed to 20, 40, 80, 160, and 320 mg Au L(-1) in agar-based growing media for 13, 18, 23, and 35 d. The Au content and oxidation state of Au in the plants were determined using an inductively coupled plasma/optical emission spectrometer (ICP/OES) and X-ray absorption spectroscopy (XAS), respectively. Gold concentrations ranging from 20 to 80 mg Au L(-1) did not significantly affect Chilopsis linearis plant growth. The concentration of gold in the plants increased as the age of the plant increased. The Au concentrations in leaves for the 20, 40, 80, and 160 mg Au L(-1) treatments were 32, 60, 62, and 179 mg Au kg(-1) dry weight mass, respectively, demonstrating the gold uptake capability of desert willow. The XAS data indicated that desert willow produced gold nanoparticles within plant tissues. Plants exposed to 160 mg Au L(-1) formed nanoparticles that averaged approximately 8, 35, and 18 A in root, stem, and leaves, respectively. It was observed that the average size of the Au nanoparticles formed by the plants is related to the total Au concentration in tissues and their location in the plant     

Dopamine-Induced Growth of Au and Ag Nanoparticles on ITO Substrate and Their Application in PCPDTBT-Based Polymer Solar Cell

The direct attachment and growth of gold or silver nanoparticles (NPs) on indium tin oxide (ITO) surfaces was demonstrated using a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method by chemical reduction of the precursor metal salts with dopamine aqueous solution. Ag NPs on ITO substrate were approximately spherical with an average particle size of about 57 nm, but had a wide particle size distribution. Compared with Ag NPs, under the same 10 SILAR cycles, Au NPs have higher density packing and smaller average particle size of about 36 nm. XRD characterization and surface chemistry analysis confirmed the formation of Ag and Au NPs on ITO substrate with small amounts of dopamine-quinone adsorbed on the surface of them. Although Au NPs showed characteristic plasmon absorption, this did not result in performance enhancement in solar cell with the structure of ITO/ZnO/PCPDTBT:[6,6]-phenyl C₇₁/MoO₃/Ag because of the energy level mismatch between ZnO and dopamine molecules adsorbed on the surface of metal NPs.     

The Tunable and Well-Controlled Surface Plasmon Resonances of Au Hollow Nanostructures by a Chemical Route

Au plasmonic hollow spherical nanostructures were synthesized by electrochemical reduction (GRR, the Galvanic Replacement Reaction) using Ag nanoparticles as templates. From UV-visible absorption spectroscopy, it was found that the surface plasmon resonance (SPR) of gold hollow spherical nanostructures first showed red shift and then blue shift. However, further addition of gold precursor (HAuCl₄) resulted into a red shift of SPR peak. The morphological changes from Ag nanoparticles to Au hollow nanostructures were assessed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX)analysis. The Mie Scattering theory based simulations of SPR of Au hollow nanostructures were performed which are in good agreement with the experimental observations. Based on the experimental observations and theoretical calculations, a complete growth mechanism for Au hollow nanostructures is proposed.     

Synthesis of metallic nanoparticles using plant extracts

Biomolecules present in plant extracts can be used to reduce metal ions to nanoparticles in a single-step green synthesis process. This biogenic reduction of metal ion to base metal is quite rapid, readily conducted at room temperature and pressure, and easily scaled up. Synthesis mediated by plant extracts is environmentally benign. The reducing agents involved include the various water soluble plant metabolites (e.g. alkaloids, phenolic compounds, terpenoids) and co-enzymes. Silver (Ag) and gold (Au) nanoparticles have been the particular focus of plant-based syntheses. Extracts of a diverse range of plant species have been successfully used in making nanoparticles. In addition to plant extracts, live plants can be used for the synthesis. Here we review the methods of making nanoparticles using plant extracts. Methods of particle characterization are reviewed and potential applications of the particles in medicine are discussed.     

Phase-Transfer Identification of Core-Shell Structures in Bimetallic Nanoparticles

On the basis of a combination of previously published experimental procedures, ultraviolet–visible spectroscopy, transmission electron microscopy, and energy-dispersive X-ray measurements, a systematic investigation was carried out on the phase-transfer characteristics of different bimetallic nanoparticles (Ag–Au, Ag–Pt, Ag–Ru, Au–Pt, Au–Ru, and Pt–Ru) formed by the seed-mediated growth reactions. The different phase-transfer characteristics of the monometallic nanoparticles of Au, Ag, Pt, and Ru were used to form the basis of differentiation between various possible structures existing in the bimetallic systems (core-shell particles or a physical mixture of nanoparticles). The experimental results indicate clearly the formation of core-shell nanoparticles of Ag–Au, Ag–Pt, Ru–Ag, Pt–Au, Au–Ru, and Pt–Ru when the nanoparticles of the first metal were used as the seeds in the seed-mediated growth reactions. However, when the order of the synthesis was reversed using the nanoparticles of the second metal as the seeds, only a physical mixture of the two metal nanoparticles was obtained instead.Parts of the data on Au–Ru and Ag–Pt systems have been published in Analytica Chimica Acta (2005, 537, 279–284) and Journal of Physical Chemistry B (2005, 109, 5468–5472), respectively.     

Yeast Extract Mannitol medium and its constituents promote synthesis of Au nanoparticles

While evaluating the potential of microorganisms to generate Au nanoparticles, we found that inclusion of HAuCl₄ in Yeast Extract Mannitol (YEM) medium turns it wine red on autoclaving. UV–vis spectra and TEM investigations confirmed that alteration in color of medium was due to formation of Au nanoparticles. Yeast extract and mannitol were key components of YEM medium responsible for formation of Au nanoparticles. In general, nanoparticles formed by YEM medium, yeast extract and mannitol were nearly spherical and in the size range of ～4–20, ～4–12 and ～10–20 nm, respectively. PXRD analysis suggested fcc geometry of Au nanoparticles in all cases. These findings caution autoclaving of metal salts along with microbial culture medium for authentic impact assessment studies of trace/toxic metals. Our findings also furnish ideal protocol for green synthesis of Au nanoparticles using yeast extract or mannitol under sterile aqueous conditions, which may find potential application in medicine, cosmetics and engineering.     

Bioreduction of precious and heavy metals by Candida species under oxidative stress conditions

The aim of the present work was to evaluate whether Candida species can reduce both precious and toxic pure metals from the respective molecular ions. From these results, the nanoparticles formed were studied using scanning electron microscopy with energy-dispersive spectroscopy, Raman spectroscopy, X-ray fluorescence spectroscopy and synchrotron radiation. Our results showed that the metal ions were reduced to their corresponding metallic nanoconglomerate or nanoparticles by Candida species. This is the first report on how yeasts of this genus are capable of achieving homeostasis (resilience) in the presence of metal ions of both precious and toxic metals by reducing them to a metallic state.     

Formation of nanometal particles in the dialdehyde starch matrix

Environmentally friendly method of the preparation of dialdehyde starch (DAS) based composites containing nanosilver (DAS/Ag) and nanogold (DAS/Au) as reducing and protecting agents was developed. UV–vis spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed formation of about 10 nm ball shaped Ag and Au nanoparticles situated within the polysaccharide template. Thermal properties of the composites were characterized involving differential scanning calorimetry (DSC), whereas molecular weights of polysaccharide chains of the matrix were estimated with the size exclusion chromatography coupled with multiangle laser light scattering and refractometric detectors (HPSEC-MALLS-RI).     

Investigating the Effect of Ag and Au Nanostructures with Spherical and Rod Shapes on the Emission Wavelength of OLED

Noble metals, especially Ag and Au nanostructures, have unique and adjustable optical attributes in terms of surface plasmon resonance. In this research, the effect of Ag and Au nanoparticles with spherical and rod shapes on the light extraction efficiency and the FWHM of OLED structures was investigated using the finite difference time domain (FDTD) method. The simulation results displayed that by changing the shape and size of Ag and Au nanostructures, the emission wavelength can be adjusted, and the FWHM can be reduced. The presence of Ag and Au nanoparticles in the OLEDs showed a blue and red shift of the emission wavelength, respectively. Also, the Ag and Au nanorods caused a significant reduction in the FWHM and a shift to the longer wavelengths in the structures. The structures containing Ag nanorods showed the narrowest FWHM and longer emission wavelength than the other structures.

     

Microbially supported synthesis of catalytically active bimetallic Pd-Au nanoparticles

Bimetallic nanoparticles are considered the next generation of nanocatalysts with increased stability and catalytic activity. Bio-supported synthesis of monometallic nanoparticles has been proposed as an environmentally friendly alternative to the conventional chemical and physical protocols. In this study we synthesize bimetallic bio-supported Pd-Au nanoparticles for the first time using microorganisms as support material. The synthesis involved two steps: (1) Formation of monometallic bio-supported Pd(0) and Au(0) nanoparticles on the surface of Cupriavidus necator cells, and (2) formation of bimetallic bio-supported nanoparticles by reduction of either Au(III) or Pd(II) on to the nanoparticles prepared in step one. Bio-supported monometallic Pd(0) or Au(0) nanoparticles were formed on the surface of C. necator by reduction of Pd(II) or Au(III) with formate. Addition of Au(III) or Pd(II) to the bio-supported particles resulted in increased particle size. UV-Vis spectrophotometry and HR-TEM analyses indicated that the previously monometallic nanoparticles had become fully or partially covered by Au(0) or Pd(0), respectively. Furthermore, Energy Dispersive Spectrometry (EDS) and Fast Fourier Transformation (FFT) analyses confirmed that the nanoparticles indeed were bimetallic. The bimetallic nanoparticles did not have a core-shell structure, but were superior to monometallic particles at reducing p-nitrophenol to p-aminophenol. Hence, formation of microbially supported nanoparticles may be a cheap and environmentally friendly approach for production of bimetallic nanocatalysts.     

Synthesis of Silver and Gold Nanoparticles Using Cashew Nut Shell Liquid and Its Antibacterial Activity Against Fish Pathogens

This study reveals a green process for the production of multi-morphological silver (Ag NPs) and gold (Au NPs) nanoparticles, synthesized using an agro-industrial residue cashew nut shell liquid. Aqueous solutions of Ag⁺ ions for silver and chloroaurate ions for gold were treated with cashew nut shell extract for the formation of Ag and Au NPs. The nano metallic dispersions were characterized by measuring the surface plasmon absorbance at 440 and 546 nm for Ag and Au NPs. Transmission electron microscopy showed the formation of nanoparticles in the range of 5–20 nm for silver and gold with assorted morphologies such as round, triangular, spherical and irregular. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analyses of the freeze-dried powder confirmed the formation of metallic Ag and Au NPs in crystalline form. Further analysis by Fourier transform infrared spectroscopy provided evidence for the presence of various biomolecules, which might be responsible for the reduction of silver and gold ions. The obtained Ag and Au NPs had significant antibacterial activity, minimum inhibitory concentration and minimum bactericidal concentration on bacteria associated with fish diseases.     

Simultaneous Photoluminescence and SERS Observation of Nanodiamond at Laser Deposition on Noble Metals

The metal-modified luminescence and surface-enhanced Raman scattering (SERS) occurring near nanostructured surfaces of noble metals recently have been observed for different kinds of nanocrystals associated with the metal nanostructures. In the present work, the photoluminescence and Raman scattering of diamond nanocrystals of sizes 100 and 300 nm patterned on Ag and Au thin nanostructured films via laser accelerated deposition using a femtosecond laser are discussed. The laser accelerated deposition forms ordered periodical nanodiamond–metal nanostructures and allows adjusting the interaction between nanodiamond and metal by varying the laser acceleration parameters as well as by using different metals (Ag and Au), and varying the structure of the metal film. Correspondingly, the spectroscopic properties of the system determined by interaction between nanoparticles and metal are tuned. The enhancement of nanodiamond photoluminescence together with SERS of graphite fraction and disordered carbon of nanodiamonds are observed for nanodiamond–Ag structures at 488- and 532-nm excitations, while for the nanodiamond–Au structure some characteristic SERS effects are observed at 785-nm excitation. The mechanisms of enhancement are discussed considering the nanodiamond–metal interaction and laser acceleration effect on nanodiamond.     

Synthesis of thermally stable carboxymethyl cellulose/metal biodegradable nanocomposites for potential biological applications

A green approach is described that generates bulk quantities of nanocomposites containing transition metals such as Cu, Ag, In, and Fe at room temperature using a biodegradable polymer, carboxymethyl cellulose (CMC), by reacting respective metal salts with the sodium salt of CMC in aqueous media. These nanocomposites exhibit broader decomposition temperatures when compared with control CMC, and Ag-based CMC nanocomposites exhibit a luminescent property at longer wavelengths. The noble metals such as Au, Pt, and Pd do not react at room temperature with aqueous solutions of CMC, but do so rapidly under microwave irradiation (MW) conditions at 100 degrees C. This environmentally benign approach, which provides facile entry to the production of multiple shaped noble nanostructures without using any toxic reducing agent such as sodium borohydride (NaBH4), hydroxylamine hydrochloride, and so forth, and/or a capping/surfactant agent, and which uses a benign biodegradable polymer CMC, could find widespread technological and medicinal applications. The ensuing nanocomposites derived at room temperature and MW conditions were characterized using scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, UV-visible spectroscopy, X-ray mapping, energy-dispersive analysis, and thermogravimetric analysis.     

南京市14种绿化树种对空气中重金属的累积能力

分析了南京化工厂（污染区）和江苏省林科院（对照区）不同绿化树种叶片重金属元素（Pb、Cd和Cu）的含量,揭示了14种绿化树种对3种重金属污染物的累积能力。结果表明,城市绿化树种对大气重金属污染物具有一定的吸收净化能力,并依重金属和树种的不同具有明显差异;同种植物对不同重金属的累积量也有很大差别,其中对Cu的累积量最高;采样区植物叶片重金属含量明显高于对照区;对Pb累积量高的树种有：杨树、广玉兰、女贞和紫叶李; Cd累积量高的树种为杨树;Cu累积量高的树种为构树;累积3种重金属综合能力最强的树种有杨树、构树、雪松、广玉兰、悬铃木、栾树。     

Rational Selection of Nanorod Plasmons: Material, Size, and Shape Dependence Mechanism for Optical Sensors

The localized surface plasmon resonance dependence on surrounding medium refractive index of Ag, Al, Au, and Cu nanoparticles is examined by electrodynamic approach. The refractive index sensitivity and sensing figure of merit (FOM) dependence of selected metal nanoparticles with similar geometry shows that although, sensing relevant parameters are shape (i.e., aspect ratio), and material dependent below the width 20 nm, but above this size these parameters are material independent under similar geometrical conditions. We have concluded that at optimum size, however, Al shows much higher refractive index sensitivity (RIS) in comparison to Au, Cu, and Ag, but FOM is higher for Ag in comparison to other metals. The observed sensing behavior is expected due to parameters like surface scattering, dynamic depolarization, radiation damping, and interband transitions, which may influence the nanorod plasmons.     

DNA Detection Based on Localized Surface Plasmon Resonance Spectroscopy of Ag@Au Biocomposite Nanoparticles

Noble metal nanoparticles (NPs) have attracted much attention due to their unique physical and chemical properties such as tunable surface plasmonics, high-efficiency electrochemical sensing, and enhanced fluorescence. We produced two biosensor chips consisting of Ag@Au bimetallic nanoparticles (BNPs) on a carbon thin film by simple RF-sputtering and RF-plasma-enhanced chemical vapor co-deposition. We deposited Au NPs with average size of 4 nm (Au₁ NPs) or 11 nm (Au₂ NPs) on a sensor chip consisting of Ag NPs with mean size of 15 nm, and we investigated the effect of shell size (Au NPs) on the chemical activities of the resulting Ag@Au₁ BNPs and Ag@Au₂ BNPs. We estimated the average size and morphology of Ag@Au BNPs by scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. X-ray diffraction (XRD) patterns revealed that Ag NPs and Au NPs had face-centered cubic (FCC) structure. We studied aging of the biosensor chips consisting of Ag@Au BNPs by localized surface plasmon resonance (LSPR) spectroscopy for up to 3 months. UV–visible aging of the prepared samples indicated that Ag@Au₁ BNPs, which corresponded to Ag NPs covered with smaller Au NPs, were more chemically active than Ag@Au₂ BNPs. Furthermore, we evaluated changes in the LSPR absorption peaks of Ag@Au₁ BNPs and bare Ag NPs in the presence of a DNA primer decamer at fM concentrations, to find that Ag@Au₁ BNPs were more sensitive biosensor chips within a short response time as compared to bare Ag NPs.

     

Carbohydrate-directed synthesis of silver and gold nanoparticles: effect of the structure of carbohydrates and reducing agents on the size and morphology of the composites

A monosaccharide (β-d-glucose) and polysaccharide (soluble starch) were used as structure directing and subsequently stabilizing agents for the synthesis of spherical nanoparticles (NPs) and nanowires of silver and gold. Homogeneous monodispersed Ag(0) nanoparticles (Ag NPs) of 15 nm diameter were obtained when 10⁻⁴ M AgNO₃ precursor salt was reduced in starch (1 wt %)–water gel by 1 wt % β-d-glucose. For a second preparation the effect of reducing agents on the synthesis of Au(0) metallic nanoparticles (Au NPs) of 2 × 10⁻⁴ M concentration prepared in a β-d-glucose (0.03 M)–water dispersion was studied first in detail. Different equivalent amounts of NaBH₄ and a number of pH values were evaluated for the reduction of the Au salt HAuCl₄·3H₂O to obtain Au NPs. The type and the amount of reducing agent, as well as the pH of the solution was shown to affect the size and morphology of the NPs. NaBH₄ (4 equiv) produced the smallest (5.3 nm (σ 0.7)) metallic particles compared to larger particles (10.0 nm (σ 1.4)) when the salt was reduced by 1 equiv of NaBH₄. Addition of excess NaBH₄ caused the NPs to settle out as a precipitate forming a mesh or wire structure rather than monodispersed particles. Low pH (pH 6) resulted in incomplete reduction, while at pH 8 the salt was completely reduced. When the salt was reduced by NaOH at pH 8, the particles were larger (14.2 nm) and less homogeneous (σ 2.8) compared to those from NaBH₄ reduction.     

Directing noble metal ion chemistry within a designed ferritin protein

Human H ferritin (HuHF) assembles from 24 four-helix bundles to form an approximately 500 kDa protein with an 8 nm internal cavity. HuHF provides a useful model for studying the transport of metal ions in solution to buried reaction sites in proteins. In this study, HuHF was redesigned to facilitate noble metal ion (Au(3+), Ag(+)) binding, reduction, and nanoparticle formation within the cavity. Computationally determined amino acid substitutions were targeted at four external and four internal surface sites. A variant with a total of 96 cysteines and histidines removed from the exterior surface and 96 non-native cysteines added to the interior surface retained wild-type stability and structure, as confirmed by X-ray crystallography, and promoted the formation of silver or gold nanoparticles within the protein cavity. Crystallographic studies with HuHF variants provide insight into how ferritins control access of metal ions to interior residues that perform chemistry.     

Uptake and retention of metals by cell walls of Bacillus subtilis.

Isolated walls of Bacillus subtilis Marburg, prepared in a manner which avoided metal contamination other than by the growth medium, were incubated in dilute metal solutions, separated by membrane filtration (0.22 mum), and monitored by atomic absorption to give uptake data for 18 metals. Substantial amounts of Mg2+, Fe3+, Cu2+, Na+, and K+ (amounts which were often visible as Au3+, and Ni2+ (the higher atomic-numbered elements also visible as electron scattering), and small amounts of Hg2+, Sr2+, Pb2+, and Ag+ were taken into the wall. Some (Li+, Ba2+, Co2+, and Al3+) were not absorbed. Most metals which had atomic numbers greater than 11 and which could be detected by electron microscopy appeared to diffusely stain thin sections of the wall. Magnesium, on the other hand, partitioned into the central region, and these sections of walls resisted ruthenium red staining, which was not true for the other metals. Areas of the walls also acted as nucleation sites for the growth of microscopic elemental gold crystals when incubated in solutions of auric chloride. Retention or displacement of the metals was estimated by a "chromatographic" method using the walls cross-linked by the carbodiimide reaction to adipic hydrazide agarose beads (which did not take up metal but reduced the metal binding capacity of the walls by ca. 1%) packed in a column. When a series of 12 metal solutions was passed through the column, it became evident that Mg2+, Ca2+, Fe3+, and Ni2+ were strongly bound to the walls and could be detected by both atomic absorption and by their electron-scattering power in thin sections, qhereas the other metals were fisplaced or replaced. Partial lysozyme digestion of the walls (causing a 28% loss of a [3H]diaminopimelic acid label) greatly diminished the Mg2+ retention but not that of Ca2+, Fe3+, or Ni2+, indicating that there are select sites for various cations.