Search

One-step chemical reduction approach is developed to synthesize nearly monodispersed Ag–Au alloy nanoparticles stabilized by CTAB molecules. By controlling the molar ratios of Ag(I) and Au(III), the surface plasmon resonance (SPR) band of alloy nanoparticles observe between 410 and 530 nm, which are the absorption maxima of silver and gold nanoparticles, respectively. The transmission electron microscope (TEM) shows that the obtained alloy nanoparticles are spherical in shape having size from 12 to 17 nm which provides high catalytic activity towards hydrogenation reactions. The catalytic efficiency of Ag NPs are less compared to pure Au NPs, whereas their activity can be modulated in between these two by appropriately controlling their molar ratio in the resultant Ag–Au alloy NPs. Moreover, with regards to high stability and recyclability, Ag–Au alloy NPs shows ~ 100% conversion efficiency up to five consecutive reaction cycles while monometallic nanoparticle are incapable. Thus, it is possible to modulate and enhance the catalytic activity of Ag NPs by making an alloy with Au NPs of desired composition.

Huma Rizwan,1 Jagdeep Mohanta,2 Satyabrata Si,1,2 Arttatrana Pal3 1School of Biotechnology, KIIT University, Bhubaneswar, India; 2School of Applied Sciences, KIIT University, Bhubaneswar, India; 3Department of Zoology, School of Life Sciences, Mahatma Gandhi Central University, Bihar, India Abstract: Hyperglycemia is a risk factor for cardiovascular mortality and morbidity, and directly responsible for exacerbating macrophage activation and atherosclerosis. We showed that gold nanoparticles (AuNPs) reduce the high glucose (HG)-induced atherosclerosis-related complications in macrophages via oxidative-nitrosative stress-regulated inflammation and apoptosis. The effects of AuNPs on oxidative-nitrosative stress markers such as cellular antioxidants were attenuated by HG exposure, leading to reduction in the accumulation of reactive oxygen/nitrogen species in cellular compartments. Further, these abnormalities of antioxidants level and reactive oxygen/nitrogen species accumulations initiate cellular stress, resulting in the activation of nuclear factor κB (NF-κB) via ERK1/2mitogen-activated protein kinase (MAPK)/Akt/tuberin- mammalian target of rapamycin (mTOR) pathways. The activated NF-κB stimulates inflammatory mediators, which subsequently subdue biomolecules damage, leading to aggravation of the inflammatory infiltration and immune responses. Treatment of AuNPs inhibits the intracellular redox-sensitive signaling pathways, inflammation, and apoptosis in macrophages. Together, our results indicate that AuNPs may modulate HG-induced oxidative-nitrosative stress. These effects may be sealed tight due to the fact that AuNPs treatment reduces the activation of NF-κB by ERK1/2MAPK/Akt/tuberin-mTOR pathways-mediated inflammatory genes expression and cellular stress responses, which may be beneficial for minimizing the atherosclerosis. Keywords: gold nanoparticles, oxidative-nitrosative stress, apoptosis, macrophages, atherosclerosis&nbsp

The present work describes the catalytic activity of gold nanoparticles towards the reduction of 4-nitrophenol and their modulation through surface tailoring using various organic ligands. One step protocol is used to prepare CTAB capped gold nanoparticles of size 15 ± 2 nm and the catalysis reaction using these particles simultaneously follow both zero-order and first-order reaction kinetics. The zero-order rate constant, k0=0.418 mol lit−1 min−1 and first-order rate constant, k1=0.938 min−1 is achieved just by using 8 nM of gold catalyst. On the other hand citrate capped gold nanoparticles of similar sizes (13 ± 3 nm) follow only the first-order kinetics with k1=0.243 min−1, which is about four times less compared to CTAB capped gold nanoparticles. Moreover, the reaction kinetics is changed to zero-order rate with k0=0.345 mol lit−1 min−1 simply by replacing citrate with CTAB on the gold nanoparticles surface. On the other hand, replacing the citrate with PVP on the nanoparticles surface, the reaction rate still follows the first-order kinetics, but with two-fold increase in the rate constant with k1=0.587 min−1. Further, silica coating of the CTAB capped gold nanoparticles and their use as catalyst for 4-nitrphenol reduction exclusively follows the zero-order kinetics with k0=0.305 mol lit−1 min−1 and are better recyclable upto five cycles without affecting their conversion efficiency.

The successful coating of thin porous silica layers of various thicknesses [(10±1), (12±1), and (14±1) nm] on cetyl trimethylammonium bromide (CTAB) capped gold nanorods was achieved through a modified Stöber procedure. The resulting material was applied as a novel catalyst for the reduction of 4-nitrophenol. The catalytic activities of the gold nanorods increased up to eight times after coating with a layer of porous silica and the reaction followed a zero-order kinetics, having a rate constant as high as 2.92×10(-1) mol L(-1) min(-1). The spectral changes during the reduction reaction of 4-nitrophenol were observed within a very short span of time and a complete conversion to 4-aminophenol occured within 5-6 mins, including the induction period of ≈2 mins. The reusability of the catalyst was studied by running the catalytic reaction during five consecutive cycles with good efficiency without destroying the nanostructure. The methodology can be effectively applied to the development of composite catalysts with highly enhanced catalytic activity.

The massive exploitation of modern technology results in increasing demand of energy of the entire world, which has urged extensive research and development in the areas of energy production from non-conventional resources, their storage and distribution. Electrolyte is one of the components in various electrochemical devices, like solar cells, fuel cells, rechargeable battery etc. Besides the conventional liquid electrolytes, polymer based electrolytes gain particular attention because of their solid nature, flexibility and ease of availability. For the last few decades, use of inorganic nanoparticles as additives is one of the most promising ways to improve the electrochemical performance of polymer electrolytes. The resulting nanocomposite polymer electrolytes can display enhanced conductivity, mechanical stability and improved interfacial stability towards electrode materials. This review highlights the recent research efforts given to the nanocomposites systems containing various layered transition metal hydroxides for making solid polymer electrolytes. Also various approaches adopted to understand the ion conduction mechanism of solid polymer electrolytes has also been discussed.

The present work describes the synthesis of some poly(ethylene oxide)-based nanocomposite polymer electrolyte films using various silica nanostructures as the inorganic filler by simple solution mixing technique, in which the nature of the silica nanostructures play a vital role in modulating their electrochemical performances at room temperature. The silica nanostructures are prepared by ammonical hydrolysis of tetraethyl orthosilicate following the modified St6ber method. The resulting films are characterized by X-ray diffraction and differential scanning calorimeter to study their crystallinity. Room temperature AC impedance spectroscopy is utilized to determine the Li+ ion conductivity of the resulting films. The observed conductivity values of various NCPE films depend on the nature of silica filling as well as on their surface characteristics and also on the varying PEO-Li+ ratio, which is observed to be in the order of 10(-7)-10(-6) S cm(-1).

Peptide−polymer hybrid bioconjugates containing poly(methyl methacrylate) chains attached with oligopeptide molecules were prepared by atom transfer radical polymerization (ATRP) using designed peptide-initiators. These initiators were synthesized from newly designed peptides with 2-bromoisobutyric acid via a standard coupling reaction. ATRP of methyl methacrylate was conducted using Br-terminated peptide as macroinitiator and copper(I) chloride/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as the catalyst system in dimethyl sulfoxide (DMSO) at an elevated temperature (90 °C). The peptide−polymer bioconjugates with controllable molecular weights and low polydispersities (PDI < 1.35) were obtained. We devised a simple solution approach in assembling the peptide−polymer bioconjugate molecules into hybrid micro/nanospheres in different organic solvents as confirmed from transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and dynamic light scattering (DLS) results. The ...

Ligand exchange on [Au25(SCH2CH2Ph)18−] [TOA+] is studied with two chiral ligands R/S-BINAS and NILC/NIDC in THF with induction of metal-based optical activity. Under the applied condition the ligand exchange is only partial, showing that also within a mixed ligand shell significant optical activity can be induced. The ligand exchange resulted in the change of particle size as observed by UV−vis spectroscopy.

A series of newly designed ascorbic acid based room temperature ionic liquids were successfully used to prepare quasi-spherical and anisotropic gold nanostructures in an aqueous medium at ambient temperature. The synthesis of these room temperature ionic liquids involves, first, the preparation of a 1-alkyl (such as methyl, ethyl, butyl, hexyl, octyl, and decyl) derivative of 3-methylimidazolium hydroxide followed by the neutralization of the derivatised product with ascorbic acid. These ionic liquids show significantly better thermal stability and their glass transition temperature (Tg) decreases with increasing alkyl chain length. The ascorbate counter anion of these ionic liquids acts as a reducing agent for HAuCl4 to produce metallic gold and the alkylated imidazolium counter cation acts as a capping/shape-directing agent. It has been found that the nature of the ionic liquids and the mole ratio of ionic liquid to HAuCl4 has a significant effect on the morphology of the formed gold nanostructures. If an equimolar mixture of ionic liquid and HAuCl4 is used, predominantly anisotropic gold nanostructures are formed and by varying the alkyl chain length attached to imidazolium cation of the ionic liquids, various particle morphologies can formed, such as quasispherical, raspberry-like, flakes or dendritic. A probable formation mechanism for such anisotropic gold nanostructures has been proposed, which is based on the results of some control experiments.

We have developed an efficient and versatile method for the synthesis of polyhedral oligomeric silsesquioxanes (POSS)-polymethacrylate hybrids, such as POSS-poly(methyl methacrylate) (POSS-PMMA), POSS-poly(ethyl methacrylate) (POSS-PEMA), and POSS-poly(benzyl methacrylate) (POSS-PBzMA) of controllable molecular weights and low polydispersities by thiol-mediated radical polymerization at elevated temperature (100 °C). By tuning the reactant concentrations and degree of polymerization of the grafted polymethacrylate chains, POSS content in these hybrid materials could be varied. MALDI-TOF-MS analysis of the hybrid molecule shows that the nanoscale POSS moiety is connected to the end of polymethacrylate chain through the sulfur atom bridge. These hybrid materials were further characterized using various techniques such as FTIR, XRD, NMR, TGA, and DSC. In all synthesized hybrids, the incorporation of POSS moiety at the end of polymethacrylate chain resulted in the decrease of glass transition temperature (Tg) compared to that of neat polymethacrylates of comparable molecular weights. Surprisingly, POSS-PMMA hybrids only with relatively high POSS content (∼ 10 and 16 wt %) showed physical aging behavior as reveled by DSC study.

Synthetic oligopeptides with a tryptophan residue at the C-terminus have been used for the synthesis of gold and silver nanoparticles at pH 11. The tryptophan residue in the peptides is responsible for the reduction of metal ions to the respective metals, possibly through electron transfer. A mechanistic pathway has been proposed to explain the reductive properties of the tryptophan moiety of the peptide based on some spectroscopic techniques, such as UV-visible and fluorescence spectroscopy. This study reveals that some of the peptide molecules are converted to its corresponding ditryptophan, kynurenine form and some cross-linked products, all of which are highly fluorescent species. The resultant peptide-functionalized metal nanoparticles have also been characterized by UV-visible spectroscopy, transmission electron microscopy, and Fourier transform IR spectroscopy and thermogravimatric analysis.

is an allotrope of carbon which is the basic structural unit of other allotropic forms of carbon, viz., graphite, carbon nanotubes and fullerenes. Structurally, it is a �耀at monolayer of carbon atoms with honeycomb lattice, which can be wrapped up into 0D fullerenes, rolled into 1D nanotubes or stacked into 3D graphite. �怀e 2010 Nobel Prize in Physics was jointly awarded to Andre Geim and Konstantin Novoselov for their revolutionary work on graphene, which implies its potential impact in future nanotechnology. Graphene is known to be a zero bandgap semiconductor material, therefore the Fermi level can be altered to form n-doped or p-doped material through simple physicochemical processes. Owing to its interesting properties, graphene is being used in various applications including supercapacitors, transistors, electrode materials, display screens, chemical sensors, membranes, etc. �怀e present review highlights the various synthetic strategies, fundamental properties and their potential techno- logical application.

Magnetization and Mossbauer studies have been performed on the polymer coated magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in the temperature dependence of magnetization (TM) is found to be inconsistent with the particle size (DTEM). The effective magnetic anisotropy (Kan) is found to increase with the decrease of DTEM, which is attributed to the increase of surface anisotropy. The absence of coercivity and remanence of magnetization noticed well above TM indicates the superparamagnetic behaviour, which has also been observed in the temperature dependent Mossbauer results. The temperature dependence of hyperfine field is found to follow similar dependence of saturation magnetization for bulk magnetite.

The assembly/disassembly process of carboxylated peptide-functionalized gold nanoparticles (peptide-GNPs) was studied within the pH interval of 2.5 to 10. The assembly process was not well controlled at pH 2.5, leading to the formation of 3D structures of GNPs, whereas at pH 4 we observed controlled assembly with the formation of only a network of 1D chains. In the pH range of 2.5 to 4, the assembly proceeded with the formation of a combination of two extremes (i.e., having both 1D and 2D nanostructures). The assembly process was reversed on changing the pH of the medium to 10. The assembly/disassembly process was monitored using UV-vis spectroscopy and finally confirmed by TEM analysis. This assembly resulted from the intermolecular H-bonding between two carboxylic acid groups of peptides bound to the two adjacent GNPs and were confirmed by FTIR spectroscopy.

Synthetic oligopeptides containing redox-active tyrosine residues have been employed to prepare gold and silver nanoparticles. In this reduction process an electron from the tyrosinate ion of the peptide is transferred to the metal ion at basic pH through the formation of a tyrosyl radical, which is eventually converted to its dityrosine form during the reaction. This reaction mechanism was confirmed from UV-visible, fluorescence, and EPR spectroscopy and was found to be pH-dependent. Transmission electron microscopy measurement shows that the average size and the monodispersity of gold nanoparticles increase as the number of tyrosine residues in the peptide increases. The kinetic study, based on spectrophotometric measurements of the surface plasmon resonance optical property, shows that the rate of formation of gold nanoparticles was much faster at higher pH than at lower pH and was also dependent on the number of tyrosine residues present in the peptide. The dityrosine form of the peptide was found to retain reducing properties like those of tyrosine in basic medium.

A novel gold nanoparticle-tripeptide (GNP-tripeptide) conjugate was prepared by peptide in-situ redox technique at ambient temperatureusing a newly designed tripeptide. This new tripeptide was nso designed that it has a C-terminus tyrosine residue, which reduced Au+3 to Au, and the terminally located free amino group was bound to the gold nanoparticle (GNP) surface resulting in highly stable Au colloids. The average diameter of the tripeptide-stabilized GNP is 8.7 +/- 2.3 nm. Tripeptide bound gold nanoparticles formed three-dimensional assemblies in the presence of an excess of similar or disimilar tripeptides. The aggregation of GNPs results in a red shift in the surface plasmon resonance from lambda max = 527 to 556 nm. The effect of the solvent, concentration, and nature of the tripeptides on the assembly process were investigated by TEM and UV-visible spectroscopy.

Magnetite nanoparticles of nearly uniform size have been prepared by precipitating ferrous ions in the presence of two different polyelectrolytes, viz., poly(acrylic acid) and the sodium salt of carboxymethyl cellulose at high pH (∼13). The size of the magnetite nanoparticles can be controlled easily by varying the concentration of the polyelectrolyte in the medium. Transmission electron microscopy study indicates that the average particle size varies from 5 to 15 nm, depending on the concentration and the nature of the polyelectrolyte. X-ray diffraction study shows the presence of only magnetite phase. FTIR spectroscopy and thermogravimetric analysis confirmed the presence of polyelectrolyte on the magnetite surface. The magnetization and Mossbauer studies were performed on two samples with mean diameters 7.0 and 14.7 nm. Magnetization measurements suggest that both of these particles are of single magnetic domain. The measurements also estimate the superparamagnetic blocking temperature, TB = 145 K for ...

Optimal single particle tracking experiments in live cells requires small and photostable probes, which do not modify the behavior of the molecule of interest. Current fluorescence-based microscopy of single molecules and nanoparticles is often limited by bleaching and blinking or by the probe size. As an alternative, we present in this chapter the synthesis of a small and highly specific gold nanoprobe whose detection is based on its absorption properties. We first present a protocol to synthesize 5-nm-diameter gold nanoparticles and functionalize them with a nanobody, a single-domain antibody from camelid, targeting the widespread green fluorescent protein (GFP)-tagged proteins with a high affinity. Then we describe how to detect and track these individual gold nanoparticles in live cell using photothermal imaging microscopy. The combination of a probe with small size, perfect photostability, high specificity, and versatility through the vast existing library of GFP-proteins, with a highly sensitive detection technique enables long-term tracking of proteins with minimal hindrance in confined and crowded environments such as intracellular space.

Optimal single particle tracking experiments in live cells requires small and photostable probes, which do not modify the behavior of the molecule of interest. Current fluorescence-based microscopy of single molecules and nanoparticles is often limited by bleaching and blinking or by the probe size. As an alternative, we present in this chapter the synthesis of a small and highly specific gold nanoprobe whose detection is based on its absorption properties. We first present a protocol to synthesize 5-nm-diameter gold nanoparticles and functionalize them with a nanobody, a single-domain antibody from camelid, targeting the widespread green fluorescent protein (GFP)-tagged proteins with a high affinity. Then we describe how to detect and track these individual gold nanoparticles in live cell using photothermal imaging microscopy. The combination of a probe with small size, perfect photostability, high specificity, and versatility through the vast existing library of GFP-proteins, with a highly sensitive detection technique enables long-term tracking of proteins with minimal hindrance in confined and crowded environments such as intracellular space.

The amplitude of optical forces on flowing dielectric microparticles can be actuated by coating them partially with metallic nanospheres and exposing them to laser light within the surface plasmon resonance. Here, optical forces on both pure silica particles and silica-gold raspberries are characterized within an optical chromatography setup by measuring the Stokes drag versus laser beam power. Results are compared to Mie theory predictions for both core dielectric particles and core-shell ones where the shell is described by a continuous dielectricmetal composite of dielectric constant determined from the Maxwell Garnett approach. The nice observed quantitative agreement demonstrates that radiation pressure forces are directly related to the metal concentration present at the microparticle surface and that nano-metallic objects increase the magnitude of optical forces compared to pure dielectric particles of the same overall size, even at very low metal concentration. Behaving as “micro-sized nanoparticles", the benefit of microparticles coated with metallic nanospheres is thus twofold: (i) to enhance optofluidic manipulation and transport at the microscale and (ii) to increase sensing capabilities at the nanoscale, compared to separated pure dielectric particles and single metallic nanosystems.

International audience; We report experimentally and theoretically on the significant exaltation of optical forces on microparticles when they are partially coated by metallic nanodots and shined with laser light within the surface plasmon resonance. Optical forces on both pure silica particles and silica-gold raspberries are characterized using an optical chromatography setup to measure the variations of the Stokes drag versus laser beam power. Results are compared to the Mie theory prediction for both pure dielectric particles and core-shell ones with a shell described as a continuous dielectric-metal composite of dielectric constant determined from the Maxwell-Garnett approach. The observed quantitative agreement demonstrates that radiation pressure forces are directly related to the metal concentration on the microparticle surface and that metallic nanodots increase the magnitude of optical forces compared to pure dielectric particles of the same overall size, even at very low metal concentration. Behaving as "micro-sized nanoparticles", the benefit of microparticles coated with metallic nanodots is thus twofold: it significantly enhances optofluidic manipulation and motion at the microscale, and brings nanometric optical, chemical or biological capabilities to the microscale.

SiO2 nanotubes (NTs) and helical nanosprings (NSs) with outer and inner diameters of 35±4 and 10±4 nm respectively were synthesized through inorganic transcription using organic amphiphilic self-assemblies as templates. Three-point bending tests were performed using an atomic force microscope (AFM), for the determination of the mechanical properties of the SiO2 NTs and nanosprings. The resonance frequency was also determined using finite element method (FEM) calculations.

Single molecule tracking in live cells is the ultimate tool to study subcellular protein dynamics, but it is often limited by the probe size and photostability. Because of these issues, long-term tracking of proteins in confined and crowded environments, such as intracellular spaces, remains challenging. We have developed a novel optical probe consisting of 5 nm gold nanoparticles functionalized with a small fragment of camelid antibodies that recognize widely used green fluorescent proteins (GFPs) with a very high affinity, which we call GFP-nanobodies. These small gold nanoparticles can be detected and tracked using photothermal imaging for arbitrarily long periods of time. Surface and intracellular GFP-proteins were effectively labeled even in very crowded environments such as adhesion sites and cytoskeletal structures both in vitro and in live cell cultures. These nanobody-coated gold nanoparticles are probes with unparalleled capabilities; small size, perfect photostability, high specificity, and versatility afforded by combination with the vast existing library of GFP-tagged proteins.

International audience; Amorphous SiO2 nanotubes (NTs) with outer and inner diameters of 35 ± 4 nm and 10 ± 4 nm, respectively, were synthesized through inorganic transcription using organic amphiphilic self-assemblies as templates. By performing three-point bending tests on suspended SiO2 NTs using an atomic force microscope, their elastic modulus was determined to be 73.3 ± 6.7 GPa which is comparable to that of bulk SiO2 as well as amorphous SiO2 nanowires obtained using chemical vapor deposition. These measurements were validated using finite element method calculations and show the crucial role played by the clamping conditions to determine the actual Young's modulus.

The current study represents the design and synthesis of polyethylene oxide (PEO)-based solid polymer electrolytes by solvent casting approach using surface tailored porous silica as nanofillers. The surface tailoring of porous silica nanostructure is achieved through silanization chemistry using 3-glycidyloxypropyl trimethoxysilane in which silane part get anchored to the silica surface whereas epoxy group get stellated from the silica surface. Surface tailoring of silica with epoxy group increases the room temperature electrochemical performances of the resulting polymer electrolytes. Ammonical hydrolysis of organosilicate precursor is used for both silica preparation and their surface tailoring. The composite solid polymer electrolyte films are prepared by solution mixing of PEO with lithium salt in presence of silica nanofillers and cast into film by solvent drying, which are then characterized by impedance measurement for conductivity study and wide angle x-ray diffraction for change in polymer crystallinity. Room temperature impedance measurement reveals Li+ ion conductivity in the order of 10−4 S cm−1, which is correlated to the decrease in PEO crystallinity. The enhancement of conductivity is further observed to be dependent on the amount of silica as well as on their surface characteristics.

International audience; A one-step, surfactant-assisted, seed-mediated method has been utilized for the growth of short gold nanorods with reasonable yield by modifying an established synthesis protocol. Among the various parameters that influence nanorod growth, the impact of the bromide counterion has been closely scrutinized. During this study it has been shown that, irrespective of its origin, the bromide counterion [cetyltrimethylammonium bromide (CTAB) or NaBr] plays a crucial role in the formation of nanorods in the sense that there is a critical [Br−]/[Au3+] ratio (around 200) to achieve nanorods with a maximum aspect ratio. Beyond this value, bromide can be considered as a poisoning agent unless shorter nanorods are required. The use of AgNO3 helps in symmetry breaking for gold nanorod growth, whereas the bromide counterion controls the growth kinetics by selective adsorption on the facets of the growth direction. Thus, a proper balance between bromide ions and gold cations is also one of the necessary parameters for controlling the size of the gold nanorods; this has been discussed thoroughly. The results have been discussed based on their absorption spectra and finally shape evolution has been confirmed by TEM. Due to their efficient absorption in the near-IR region, these short nanorods were used in photothermal imaging of living COS-7 cells with improved signal-to-background ratios.

An oligopeptide with a free amino group at the N-terminus and a redox active tryptophan residue at the C-terminus was used to synthesize gold nanocrystals of different shapes. The concentration ratio of peptide to HAuCl4 has a significant effect on the shape of the formed nanocrystals and the polyhedral gold nanocrystals are mainly formed at higher such ratio. The effect of medium pH and reaction temperature on the shape of the formed gold nanocrystals has also been investigated. However, an oligopeptide with blocked amino group with tert-butyloxycarbonyl group resulted only spherical gold nanocrystals along with some aggregated structures. A probable mechanism for the formation of polyhedral gold nanocrystals has been described, which indicate the presence of multiple anchoring sites in the peptide molecules is mainly responsible for this type of crystal growth. The formed nanocrystals were well characterized by various experimental techniques like, UV-visible spectroscopy, transmission electron microscopy, and X-ray diffraction.

Carboxylated peptide-functionalized gold nanoparticles (peptide-GNPs) self-assemble into two- and three-dimensional nanostructures in the presence of various heavy metal ions (i.e. Pb(2+), Cd(2+), Cu(2+), and Zn(2+)) in aqueous solution. The assembly process is monitored by following the changes in the surface plasmon resonance (SPR) band of gold nanoparticles in a UV/Vis spectrophotometer, which shows the development of a new SPR band in the higher-wavelength region. The extent of assembly is dependent on the amount of metal ions present in the medium and also the time of assembly. TEM analysis clearly shows formation of two- and three-dimensional nanostructures. The assembly process is completely reversible by addition of alkaline ethylenediaminetetraacetic acid (EDTA) solution. The driving force for the assembly of peptide-GNPs is mainly metal ion/carboxylate coordination. The color and spectral changes due to this assembly can be used for detection of these heavy-metal ions in solution.

An in situ reduction approach to synthesizing gold and silver nanoparticles by using a series of newly designed, redox-active amphiphiles at basic pH is described. These amphiphiles are the conjugates of a fatty acid (e.g., oleic acid, stearic acid, and lauric acid) and a redox-active amino acid (e.g., tryptophan or tyrosine). The amphiphile-coated nanoparticles are then efficiently transferred from water to different nonpolar organic media (such as benzene, toluene, xylene, cyclohexane, and hexane) simply by acid treatment. The phase-transfer process was monitored by UV/visible spectroscopy and transmission electron microscopy, and the results showed that the average particle size and size distribution remain almost unchanged after transferring to the organic media. The anchoring of the amphiphile to the nanoparticle surface was confirmed by FTIR spectroscopy and thermogravimetric analysis. A mechanism is proposed to describe the stability of colloidal Au and Ag nanoparticles formed in situ and their phase transfer to organic solvents. The presence of the amphiphile increases the thermal stability of the colloidal gold nanoparticle conjugates in organic solvents.

Single molecule tracking in live cells is the ultimate tool to study subcellular protein dynamics, but it is often limited by the probe size and photostability. Due to these issues, long-term tracking of proteins in confined and crowded environments, such as adhesion sites, synaptic clefts or intracellular spaces, remains challenging. We present a novel optical probe consisting of 5-nm gold nanoparticles functionalized with a small fragment of camelid antibodies that recognize widely used GFPs with a very high affinity (1). These small gold nanoparticles can be detected and tracked using photothermal imaging for arbitrarily long periods of time (1-2). Surface and intracellular GFP-proteins can effectively be labeled even in very crowded environments such as adhesion sites and cytoskeletal structures both in vitro and in live cell cultures. Comparison with performances obtained by superresolution methods such as PALM and STED are presented for single integrin tracking in and out adhesion sites (3). These nanobody-coated gold nanoparticles are single molecule probes with unparalleled capabilities; small size, perfect photostability, high specificity, and versatility afforded by combination with the vast existing library of GFP-tagged proteins.References:(1) C. Leduc, et al Nano Lett. 13, 4, (2013) 1489.(2) D. Lasne Biophys. J, 91 (2006) 4598.(3) O. Rossier, Nature Cell Biology 14 (2012) 1057.

New hybrid materials have been prepared by grafting synthetic peptides in the interlayer spacing of Cu(II) and Co(II) layered simple hydroxides (LSHs). The interlayer spacing of the hybrids depends on the peptide chain length; the dependence is specific for the copper and cobalt-based hybrids. This suggests a metal- or LSH-specific interaction of the peptides with the respective inorganic layers. When tyrosine is present in the peptide, its fluorescence is quenched after grafting the peptide to the LSH. Studies of the luminescence vs. pH indicate deprotonation of the tyrosine moieties to tyrosinate at high pH, accompanied by the onset of luminescence. The luminescence increases with increasing OH− concentration, suggesting an application of the hybrids as chemical sensors. Moreover, the peptides influence the magnetic properties of the hybrids. The copper-based hybrids behave antiferromagnetically and the cobalt-based hybrids are ferrimagnets.