Electrogenerated Chemiluminescence of Luminol on a Gold-Nanorod-Modified Gold Electrode

Electrogenerated chemiluminescence (ECL) of luminol on a gold-nanorod-modified gold electrode was studied, and five ECL peaks were obtained under conventional cyclic voltammetry in both neutral and alkaline solutions. Among them, four ECL peaks (ECL-1-4) were also observed on a gold-nanosphere-modified gold electrode, but the intensities of these ECL peaks were enhanced about 2-10-fold on a gold-nanorod-modified gold electrode in neutral solution. One new strong ECL peak (ECL-5) was obtained at -0.28 V (vs SCE) on a gold-nanorod-modified gold electrode in both neutral and alkaline solutions and enhanced with an increase in pH. In strong alkaline solutions, ECL-1 and ECL-2 on a gold-nanosphere-modified electrode were much stronger than those on a gold-nanorod-modified gold electrode, while ECL-3-5 appeared to only happen on a gold-nanorod-modified gold electrode. The emitter of all the ECL peaks was identified as 3-aminophthalate. The ECL peaks were found to depend on the scan direction, the electrolytes, the pH, and the presence of O(2) and N(2). The reaction pathways for ECL-4 have been further elucidated, and the mechanism of the new ECL peak (ECL-5) has been proposed. The results indicate that a gold-nanorod-modified gold electrode has a catalytic effect on luminol ECL different from that of a gold-nanosphere-modified gold electrode, revealing that the shape of the metal nanoparticles has an important effect on the luminol ECL behavior. The strong ECL of luminol in neutral solution obtained on a gold-nanorod-modified electrode may be used for the sensitive detection of biologically important compounds in physiological conditions.

Plasmon Coupling in Nanorod Assemblies: Optical Absorption, Discrete Dipole Approximation Simulation, and Exciton-Coupling Model

The shape anisotropy of nanorods gives rise to two distinct orientational modes by which nanorods can be assembled, i.e., end-to-end and side-by-side, analogous to the well-known H and J aggregation in organic chromophores. Optical absorption spectra of gold nanorods have earlier been observed to show a red-shift of the longitudinal plasmon band for the end-to-end linkage of nanorods, resulting from the plasmon coupling between neighboring nanoparticles, similar to the assembly of gold nanospheres. We observe, however, that side-by-side linkage of nanorods in solution shows a blue-shift of the longitudinal plasmon band and a red-shift of the transverse plasmon band. Optical spectra calculated using the discrete dipole approximation method were used to simulate plasmon coupling in assembled nanorod dimers. The longitudinal plasmon band is found to shift to lower energies for end-to-end assembly, but a shift to higher energies is found for the side-by-side orientation, in agreement with the optical absorption experiments. The strength of plasmon coupling was seen to increase with decreasing internanorod distance and an increase in the number of interacting nanorods. For both side-by-side and end-to-end assemblies, the strength of the longitudinal plasmon coupling increases with increasing nanorod aspect ratio as a result of the increasing dipole moment of the longitudinal plasmon. For both the side-by-side and end-to-end orientation, the simulation of a dimer of nanorods having dissimilar aspect ratios showed a longitudinal plasmon resonance with both a blue-shifted and a red-shifted component, as a result of symmetry breaking. A similar result is observed for a pair of similar aspect ratio nanorods assembled in a nonparallel orientation. The internanorod plasmon coupling scheme concluded from the experimental results and simulations is found to be qualitatively consistent with the molecular exciton coupling theory, which has been used to describe the optical spectra of H and J aggregates of organic molecules. The coupled nanorod plasmons are also suggested to be electromagnetic analogues of molecular orbitals. Investigation of the plasmon coupling in assembled nanorods is important for the characterization of optical excitations and plasmon propagation in these nanostructures. The surface plasmon resonance shift resulting from nanorod assembly also offers a promising alternative for analyte-sensing assays.

Nanocompatible Chemistry toward Fabrication of Target-Specific Gold Nanoparticles

Nanocompatible chemistry which utilizes a novel nontoxic phosphino amino acid as a reducing agent has resulted in the development of therapeutically useful gold nanoparticles under biologically benign media. Stabilization of gold nanoparticles by the edible gum arabic matrix has provided an effective pathway toward in vivo stable target-specific gold nanoparticles.

[Photocatalytic degradation of formaldehyde and VOCs in air on the porous nickel mesh coated with nanometer TiO2]

Three different metal ions doped TiO2 photocatalysts, which were prepared by the sol-gel method, were immobilized to porous nickel mesh by coating. The photocatalytic degradation activity of the supported photocatalyst on formaldehyde and volatile organic compounds (VOCs) was investigated. The results show that the nanometer TiO2 has an anatase structure. The photocatalytic degradation rate of formaldehyde and VOCs of 1.5% La3+ doped TiO2 coated on porous nickel mesh at 90 min are: 94% and 87%, higher than undoped TiO2: 83% and 72%, Fe3+ doped TiO2: 62% and 62%, Ag+ doped TiO2: 86% [Chinese character: see text] 81%. The orders of photocatalytic degradation rate on formaldehyde and VOCs with different content of La3+ doped TiO2 are as follows: 1.5% > 1% > 2% > undoped, 1.5% is the optimum La3+ doped content. Decreasing circular wind speed and using 254 nm or 365 nm ultraviolet wavelength will not influence the photocatalytic degradation rate of formaldehyde and VOCs.

[Nanoelectrochemistry of cytochrome P450s: direct electron transfer and electrocatalysis]

The present study demonstrates the direct electron transfer between cytochrome P450 2B4 (CYP2B4), P450 1A2 (CYP1A2), sterol 14alpha-demethylase (CYP51MT) and screen printed graphite electrodes, modified with gold nanoparticles and didodecyldimethylammonium bromide (DDAB). Electrodetection of heme proteins is possible when 2-200 pmol P450/electrode were adsorbed on the surface of nanostructured electrochemical interfaces. Electron transfer, direct electrochemical reduction and interaction with P450 substrates (oxygen, benzphetamine, lanosterol) and inhibitor ketoconazole were analyzed using cyclic voltammetry (CV), square wave (SWV) or differential pulse (DPV) voltammetry, amperometry.

Unidirectional movement of an actin filament taking advantage of temperature gradients

An actin filament with heat acceptors attached to its Cys374 residue in each actin monomer could move unidirectionally even under heat pulsation alone, while in the total absence of both ATP and myosin. The prime driver for the movement was temperature gradients operating between locally heated portions on an actin filament and its cooler surroundings. In this report, we investigated how the mitigation of the temperature gradients induces a unidirectional movement of an actin filament. We then observed the transversal fluctuations of the filament in response to heat pulsation and their transition into longitudinally unidirectional movement. The transition was significantly accelerated when Cys374 and Lys336 were simultaneously excited within an actin monomer. These results suggest that the mitigation of the temperature gradients within each actin monomer first went through the energy transformation to transversal fluctuations of the filament, and then followed by the transformation further down to longitudinal movements of the filament. The faster mitigation of temperature gradients within actin monomer helps build up the transition from the transversal to longitudinal movements of the filament by coordinating the interaction between the neighboring monomers.

Understanding mercapto ligand exchange on the surface of FePt nanoparticles

Tailoring the surface of nanoparticles is essential for biological applications of magnetic nanoparticles. FePt nanoparticles are interesting candidates owing to their high magnetic moment. Established procedures to make FePt nanoparticles use oleic acid and oleylamine as the surfactants, which make them dispersed in nonpolar solvents such as hexane. As a model study to demonstrate the modification of the surface chemistry, stable aqueous dispersions of FePt nanoparticles were synthesized after ligand exchange with mercaptoalkanoic acids. This report focuses on understanding the surface chemistry of FePt upon ligand exchange with mercapto compounds by conducting X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies. It was found that the mercapto end displaces oleylamine on the Pt atoms and the carboxylic acid end displaces the oleic acid on the Fe atoms, thus exposing carboxylate and thiolate groups on the surface that provide the necessary electrostatic repulsion to form stable aqueous dispersions of FePt nanoparticles.

Au nanoparticles encapsulated in Ru carbonyl carboxylate shells

A two-step surface functionalization approach has been used to encase Au nanoparticles in monolayer organometallic Ru-complex shells by the reaction of an intermediate surface-bound mercaptopropanoic acid capping species with Ru dodecacarbonyl (Ru3(CO)12) clusters. Vibrational (infrared and Raman) spectroscopy shows that insertion of carboxylate groups into the Ru clusters results in their fragmentation and the formation of a shell of Ru dicarbonyl carboxylate oligomers that remain attached to the Au nanoparticles through the original Au-alkanethiolate bonds. The structural integrity of the metallic nanoparticulate Au cores has been verified by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. The organometallic Ru-complex shell may be decomposed thermally to eliminate the mercaptopropanoate and carbonyl groups and leave a mixed phase of Au and RuO2.

PVP-coated iron nanocrystals: Anhydrous synthesis, characterization, and electrocatalysis for two species

We report the synthesis of Fe nanocrystals (approximately 9 nm) in an anhydrous media, formamide, using poly(N-vinyl-2-pyrrolidone) (PVP) as a protecting agent. The morphology, structure, and composition of the PVP-coated Fe nanocrystals are studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and FT-Raman spectroscopy. The surface properties of the PVP-coated Fe nanocrystals are studied by electrochemistry and micro-surface-enhanced Raman scattering (mSERS) using pyridine as a probing molecule. The PVP-coated Fe nanocrystals, when immobilized on an electrode substrate, display very good electrocatalytic activities in the selective reduction of H2O2 in the presence of oxygen and in the oxidation of NO.

Formation of Silver Nanoparticles in Deoxyribonucleic Acid−Poly(o-methoxyaniline) Hybrid: A Novel Nano-biocomposite

A novel nano-biocomposite of silver and poly(o-methoxy aniline) (POMA)/DNA hybrid has been prepared by adding DNA solution to an aqueous solution of POMA (emeraldine base, EB) and AgNO(3) mixture. The mixture was aged for 10 days and was freeze-dried to form the hybrid nanocomposite (weight fraction of DNA = 0.75). FESEM pictures show a fibrillar network morphology of the biomolecular hybrid with silver nanoparticles on its surface. The TEM picture also corroborates silver nanoparticle formation in the biomolecular hybrid, and the denser population of nanoparticles in the TEM micrograph as compared to that in the SEM micrograph indicates that the nanoparticles are present inside the fibrils in greater proportion. The dc conductivity value of the hybrid indicates that POMA (EB) is doped by silver ion and the doped POMA form complexes with DNA through electrostatic interaction of the radical cation of POMA (emeraldine salt form, ES) and the DNA anion. During the doping process and Ag nanoparticle formation, a fluctuation of the pi band to polaron band transition peak occurs together with a complementary fluctuation of the polaron band to pi* band transition peak. After 53 h of aging, the former shows a slow but continuous red shift with aging time. This has been attributed to the slow uncoiling of POMA on the DNA surface. The conformation and crystal structure of DNA remain intact during the nano-biocomposite formation. The dc conductivity value of the nano-biocomposite is almost the same as that of the pure POMA-DNA hybrid at the same composition, but the I-V characteristic curve of the nano-biocomposite is somewhat different showing an insulating region on low applied voltage. At higher applied voltage, it shows a semiconducting property characterizing the large band gap semiconducting behavior of the nano-biocomposite.

Capillary electrophoresis of ultrasmall carboxylate functionalized silicon nanoparticles

Capillary electrophoresis is used to separate ultrasmall ( approximately 1 nm) carboxylate functionalized Si nanoparticles (Si-np-COO(-)) prepared via hydrosilylation with an omega-ester 1-alkene. The electropherograms show a monodisperse Si core size with one or two carboxylate groups added to the surface. On-column detection of their laser-induced fluorescence demonstrates that the individual Si-np-COO(-) have narrow emissions (full width at half maximum = 30-40 nm) with a nearly symmetric lineshape. Preparative scale electrophoresis should be a viable route for purification of the Si-np-COO(-) for further study and future applications.

Bacillus subtilis Assisted Assembly of Gold Nanoparticles into Long Conductive Nodous Ribbons

Gold nanopraticles with diameters of about 20 nm were assembled onto the surfaces of Bacillus subtilis by keeping the mixture of the nanoparicles and the bacteria in the dark without disturbance for over a month. During the aging process, the bacteria connected to each other end-to-end to form long wires and gold nanoparticles were coated compactly onto the surfaces of the wires simultaneously. The resulting composite wires were collapsed into ribbons with a width of about 1 microm after drying in air. The ribbons present a novel structure with nodes on their backbones and have lengths of several millimeters. They are conductive and showed Ohmic behavior, which provides potential applications in the fabrication of electronic nanodevices.

Model systems for flavoenzyme activity: recognition and redox modulation of flavin mononucleotide in water using nanoparticles

We have used mixed monolayer protected gold clusters (MMPCs) to provide flavoenzyme model systems with a high affinity and ability to modulate cofactor reduction potential.

Extinction coefficient of gold nanoparticles with different sizes and different capping ligands

Extinction coefficients of gold nanoparticles with core size ranging from approximately 4 to 40 nm were determined by high resolution transmission electron microscopy analysis and UV-vis absorption spectroscopic measurement. Three different types of gold nanoparticles were prepared and studied: citrate-stabilized nanoparticles in five different sizes; oleylamide-protected gold nanoparticles with a core diameter of 8 nm, and a decanethiol-protected nanoparticle with a diameter of around 4 nm. A linear relationship between the logarithms of extinction coefficients and core diameters of gold particles was found independent of the capping ligands on the particle surface and the solvents used to dissolve the nanoparticles. This linear relation may be used as a calibration curve to determine the concentration or average size of an unknown nanoparticle or nanoparticle-biomolecule conjugate sample.

In-situ incorporation of gold nanoparticles of desired sizes into three-dimensional macroporous matrixes

We present here a facile route to the incorporation of gold nanoparticles (GNPs) with desired sizes into three-dimensionally ordered macroporous (3DOM) matrixes. Our route combined the first attachment of small GNPs to the silica colloidal crystal templates as precursors and their subsequent controlled growth by the in-situ chemical reduction method. The desired enlargement of GNPs was acquired via their alternating and repeated exposure to solutions of auric salts and reducing agent NH(3)OH. Such gold-decorated silica templates were also converted into self-sustained polystyrene (PS) macroporous films with GNPs embedded in their wall structures. The growth of gold seeds can be easily followed by their UV-vis absorbance spectra. The route provides an alternative way to incorporate GNPs with predetermined sizes into 3DOM matrixes without destroying their ordered structures. A highlight of our approach is that it obviates the need for the preformation of various-sized GNPs, which is an indispensable step in many other approaches.

DNA Binding to Protein−Gold Nanocrystal Conjugates

The E. coli DNA binding protein lac repressor (LacI) and a derivative with a designed thiol (T334C) were developed as gold nanocrystal conjugates to assess the effects of conjugation on DNA binding function. The designed derivative was engineered with a solvent-accessible thiol to promote oriented conjugation, avoiding obstruction of the DNA-binding domain by the nanocrystal. Analytical ultracentrifugation (AU) and electrophoretic mobility shift assays (EMSA) were used to evaluate the ability of conjugated repressors to bind the natural operator DNA sequence O(1). The results show that LacI does not retain significant DNA binding function when conjugated to gold nanocrystals, presumably because the basic DNA-binding domain is the site for nonspecific conjugation. T334C, with the potential for both directed and nonspecific conjugation, shows enhanced interaction with O(1) when conjugated. Interestingly, the order of component addition is a key factor in producing functional lac repressor conjugates.

Quenching and Blinking of Fluorescence of a Single Dye Molecule Bound to Gold Nanoparticles

A fluorescein derivative (SAMSA) bound to gold nanoparticles of different diameters is investigated by time-resolved fluorescence at the single molecule level in a wide dynamic range, from nanosecond to second time scale. The significant decrease of both SAMSA excited state lifetime and fluorescence quantum yield observed upon binding to gold nanoparticles can be essentially traced back to an increase of the nonradiative deactivation rate, probably due to energy transfer, that depends on the nanoparticle size. A slow single molecule fluorescence blinking, in the ms time scale, has a marked dependence on the excitation intensity both under single and under two photon excitation. The blinking dynamics is limited by a low probability nonlinear excitation to a high energy state from which a transition to a dark state occurs. The results point out a strong coupling between the vibro-electronic configuration of the dye and the plasmonic features of the metal nanoparticles that provide dye radiationless deactivation channels on a wide dynamic range.

Biomedical applications of plasmon resonant metal nanoparticles

The strong optical absorption and scattering of noble metal nanoparticles is due to an effect called localized surface plasmon resonance, which enables the development of novel biomedical applications. The resonant extinction, which can be tuned to the near-infrared, allows the nanoparticles to act as molecular contrast agents in a spectral region where tissue is relatively transparent. The localized heating due to resonant absorption, also tunable into the near-infared, enables new thermal ablation therapies and drug delivery mechanisms. The sensitivity of these resonances to their environment leads to simple affinity sensors for the detection of low-level molecular analytes. Coupled with their general lack of toxicity, these applications suggest that noble metal nanoparticles are a highly promising class of nanomaterials for new biomedical applications.

Surface-Enhanced Raman Scattering Studies of Human Transcriptional Coactivator p300

We report for the first time the surface-enhanced Raman scattering (SERS) studies on p300, a large multidomain transcriptional coactivator protein. Vibration spectral analysis has been performed in an attempt to understand the structure of the p300 in the absence of its crystal structure. Strong Raman bands associated with amides I-III have been observed in the protein spectra. This has been confirmed by performing SERS on deuterated p300. We also observe Raman bands associated with the alpha-helix, tryptophan, phenylalanine, tyrosine, and histidine. These bands will provide an ideal tool to study the drug-protein interactions in therapeutics using SERS. We have successfully demonstrated the chloride ion effect on the SERS of p300. The Raman intensity increases in the SERS spectra upon addition of chloride ion along with appearance of new modes. We have developed a new method, namely, the "sandwich technique", which could be used to perform SERS experiments on proteins in dry conditions.

Ni/NiO Core/Shell Nanoparticles for Selective Binding and Magnetic Separation of Histidine-Tagged Proteins

Ni/NiO core/shell nanoparticles having high affinity with polyhistidine were synthesized by decomposition of a Ni surfactant complex followed by air oxidation. Ni/NiO nanoparticles showed selective and efficient binding to histidine-tagged proteins and easy separation by using a magnet. These provided a more convenient way to efficient purification of histidine-tagged proteins compared with the conventional Ni-NTA complex-bound resins and microbeads.

Localized surface plasmon resonance biosensors

In this review, the most recent progress in the development of noble metal nano-optical sensors based on localized surface plasmon resonance (LSPR) spectroscopy is summarized. The sensing principle relies on the LSPR spectral shifts caused by the surrounding dielectric environmental change in a binding event. Nanosphere lithography, an inexpensive and simple nanofabrication technique, has been used to fabricate the nanoparticles as the LSPR sensing platforms. As an example of the biosensing applications, the LSPR detection for a biomarker of Alzheimer’s disease, amyloid-derived diffusable ligands, in human brain extract and cerebrospinal fluid samples is highlighted. Furthermore, the LSPR sensing method can be modified easily and used in a variety of applications. More specifically, a LSPR chip capable of multiplex sensing, a combined electrochemical and LSPR protocol and a fabrication method of solution-phase nanotriangles are presented here.

Silver Colloid Nanoparticles: Synthesis, Characterization, and Their Antibacterial Activity

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.

Extraction of nanosize copper pollutants with an ionic liquid

Speciation and possible reaction paths of nanosize copper pollutants extracted with a RTIL (room-temperature ionic liquid ([C4mim][PF6], 1-butyl-3-methylimidazolium hexafluorophosphate)) have been studied in the present work. Experimentally, in a very short contact time (2 min), 80-95% of nanosize CuO as well as other forms of copper (such as nanosize Cu, Cu2+, or Cu(II)(ads) (in the channels of MCM-41)) in the samples could be extracted into the RTIL. The main copper species extracted in the RTIL as observed by XANES (X-ray absorption near edge structure) were Cu(II). Existence of Cu-N bondings with coordination numbers (CNs) of 3-4 for copper extracted in the RTIL was found by EXAFS (extended X-ray absorption fine structural) spectroscopy. Interestingly, chelation of Cu(II) with 1-methylimidazole (MIm) in the RTIL during extraction was also observed by 1H NMR (nuclear magnetic resonance). At least two possible reaction paths for the rapid extraction of nanosize copper pollutants with the RTIL might occur: (1) an enhanced dissolution of nanosize CuO (to form Cu2+) and (2) formation of [Cu(MIm)4(H2O)2]2+ that acted as a carrier of copper into the RTIL matrix.

Mapping patterned potential energy landscapes with diffusing colloidal probes

We report a new method for mapping patterned surfaces based on monitoring the interactions of freely diffusing colloidal probes with pattern features to generate measured potential energy landscapes. Evanescent wave scattering and video microscopy are used to track 3D center positions of nominal 2 microm silica colloids as they diffuse over 5-20-nm-thick patterned gold films. An analysis of ensemble-averaged particle height histograms on different pattern features using Boltzmann's equation produces local electrostatic and van der Waals potentials in good agreement with independent measurements and predictions. Absolute separation is obtained from theoretical fits to measured potential-energy profiles and direct measurement by depositing silica colloids onto gold surfaces via electrophoretic deposition. As colloidal probe and pattern feature dimensions become comparable, potential energy profiles suffer some distortion due to the increased probability of probes sampling pattern feature edges. An analysis of interfacial colloidal probe diffusion in conjunction with potential energy measurements demonstrates a consistent interpretation of dissipative and conservative forces in these measurements. Future extensions of this work should produce similar approaches for interrogating physical, chemical, and biomolecular heterogeneous/patterned surfaces and structures with diffusing colloidal probes.

Asymmetric functionalization of gold nanoparticles with oligonucleotides

Gold nanoparticles (AuNPs) were anisotropically functionalized with two different oligonucleotide sequences using magnetic microparticles as geometric restriction templates for site-selective enzymatic extension of particle-bound oligonucleotides. The divalent linking capability of the resulting AuNPs allowed for the design and programmable assembly of discrete nanoparticle heterostructures.

Estimation of Dielectric Function of Biotin-Capped Gold Nanoparticles via Signal Enhancement on Surface Plasmon Resonance

Biotin-capped gold nanoparticles assembled on flat gold with volume fraction f are studied by surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM) in order to estimate the dielectric function of the gold nanoparticles based on the Maxwell-Garnett (MG) theory. The complex dielectric function (epsilon',epsilon'') of the spherical nanoparticles at three representative wavelengths in the vis-near-IR region, i.e., lambda = 543, 632.8, and 1152 nm, is estimated for a surface homogeneously covered with nanoparticles in order to discuss the wavelength dependence of the dielectric function. The SPR response of a surface covered with particles in 2D aggregates is also analyzed. The experimental SPR curve of the particle aggregates deviates from the theoretical predictions, suggesting dipole interactions between particles.

Tuning the hydrophilicity of gold nanoparticles templated in star block copolymers

We report on a simple procedure to tune the hydrophilicity of hybrid gold nanoparticles. The nanoparticles have been prepared in the core of a poly(ethylene glycol)-block-poly(epsilon-caprolactone) (PEG-b-PCL) five-arm star block copolymer. A hydrophilic corona was then added to these hybrid gold nanoparticles by direct chemisorption of trithiocarbonate-containing poly(acrylic acid) chains. These polymers were synthesized by RAFT polymerization with a trithiocarbonate as the chain-transfer agent. The efficiency of the grafting was evidenced by TEM, AFM, and DLS and by the successful transfer of these nanoparticles from organic solvent to water.

Surface-enhanced Raman spectroscopy of dodecanethiol-bound silver nanoparticles at the liquid/liquid interface

Adsorption and domain formation of dodecanethiol (DT)-bound silver nanoparticles (SNPs) at the cyclohexane/water interface were studied by means of total internal reflection (TIR) light scattering microscopy and TIR surface-enhanced Raman scattering (SERS). By the TIR light scattering microscopy, the extent of the interfacial adsorption and domain formation of SNP was observed, which was produced by the reaction between citrate-reduced SNPs in the aqueous phase and DT in the cyclohexane phase. The Raman spectra of DT on SNP showed that the relative intensity ratios of gauche to trans conformers in the nu(C-S) band region decreased with the increase of the initial concentration of DT, suggesting the change from the liquidlike structure to the solidlike structure of the DT. The residue of the negative charges on the SNPs at the interface was detected by the resonance SERS (SERRS) peaks of the adsorbed cationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine (TMPyP). The efficiency of the interfacial SNPs domains as a SERS substrate for TMPyP strongly depended on the adsorption state of the DT.

Silver and gold glyconanoparticles for colorimetric bioassays

The color changes associated with the aggregation of metal nanoparticles has led to the development of colorimetric-based assays for a variety of target species. We have examined both silver- and gold-based nanoparticles in order to establish whether either metal exhibits optimal characteristics for bioassay development. These silver and gold nanoparticles have been stabilized with a self-assembled monolayer of a mannose derivative (2-mercaptoethyl alpha-d-mannopyranoside) with the aim of inducing aggregation by exploiting the well-known interaction between mannose and the lectin Concanavalin A (Con A). Both metal glyconanoparticles were determined to be ca. 16 nm in diameter (using TEM measurements). Aggregation was observed on addition of Con A to both silver and gold nanoparticles resulting in a shift in the surface plasmon absorption band and a consequent color change of the solution, which was monitored using UV-visible spectrophotometry. Mannose-stabilized silver nanoparticles at a concentration of 3 nM provide an assay for Con A with the largest linear range (between 0.08 and 0.26 microM). Additionally, the kinetic rate of aggregation of the silver-nanoparticle-based bioassay was significantly greater than that of the gold-nanoparticle system. However, in terms of sensitivity, the mannose-stabilized gold-nanoparticle-based assay was optimum with a limit of detection of 0.04 microM Con A, as compared with a value of 0.1 microM obtained for the mannose-stabilized silver nanoparticles. Additionally, a lactose derivative (11-mercapto-3,6,9-trioxaundecyl beta-D-lactoside) was used to stabilize gold nanoparticles to induce aggregation upon addition of the galactose specific lectin Ricinus communis agglutinin (RCA(120)). To examine the specificity of the bioassay, lactose-stabilized gold nanoparticles were mixed with a solution of mannose-stabilized silver nanoparticles to give an aggregation assay capable of detecting two different lectins. When either Con A or RCA(120) was added to the mixed glyconanoparticles, selective recognition of the respective natural ligand was shown by aggregation of a single metal nanoparticle. Centrifugation and removal of the aggregated species enabled further bioassay measurements using the second glyconanoparticle system.

In Situ Surface-Enhanced IR Absorption Spectroscopy on CO Adducts of Iron Protoporphyrin IX Self-Assembled on a Au Electrode

The surface coordination chemistry of carbon monoxide with the reduced form (Fe(II)PP) of iron(III) protoporphyrin IX (Fe(III)PP) monolayer self-assembled on a Au electrode in 0.1 M HClO4 was studied for the first time by using in situ ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Both mono- and biscarbonyl adducts [simplified as Fe(II)(CO)PP and Fe(II)(CO)2PP, respectively] were detected, depending on the history of potential control. Initially, the Fe(II)(CO)PP predominates, and the intermediate transition potential for the conversion of Fe(II)(CO)PP to Fe(III)PP and CO was spectrally determined to be ca. 0.09 V (vs SCE). The ratio of Fe(II)(CO)2PP and Fe(II)(CO)PP increases after a potential excursion to a sufficiently positive value. Fe(II)(CO)2PP is much more stable against its electro-oxidation to Fe(III)PP than its counterpart Fe(II)(CO)PP with increasing potential. The observed change of coordination properties may be ascribed to an irreversible structural reorganization of the FePP adlayer caused by the potential excursion.

Optical Properties of Au−Ag Nanoboxes Studied by Single Nanoparticle Spectroscopy

The optical properties of two Au-Ag nanobox samples with average edge lengths of 44 and 58 nm and wall thicknesses of 6 and 8 nm, respectively, have been studied by single particle spectroscopy. The measurements gave an average line width of Gamma = 306 +/- 7 meV with a standard deviation of sigma = 30 meV for the 44-nm boxes, and Gamma = 350 +/- 9 meV with sigma = 35 meV for the 58-nm boxes. These line widths are much broader than those of gold nanorods with comparable resonance energies. The increased broadening is attributed to a combination of surface scattering of electrons, as well as increased radiation damping for the nanoboxes. Discrete dipole approximation calculations have been performed with and without surface scattering of electrons to compare with the experimental spectra. The calculations confirm that both electron-surface scattering and radiation damping are important effects in this system.

Fivefold Symmetry in Superlattices of Monolayer-Protected Gold Nanoparticles

Three-dimensional (3D) superlattices of gold nanoparticles were prepared at an air/solution interface. The surface of the gold nanoparticles used is protected by N-acetylglutathione (NAG). Morphological studies revealed that the superlattices formed fivefold symmetric structures such as pentagonal rod, decahedron, and icosahedron, which were probably developed by multiple twinning. Moreover, high-resolution surface images of the superlattices in fivefold symmetry showed excellent ordered arrangements of nanoparticles with both close-packed and non-close-packed structures.

Thermosensitive pluronic micelles stabilized by shell cross-linking with gold nanoparticles

Gold nanoparticles were employed to prepare shell cross-linked Pluronic micelles that exhibit a reversibly thermosensitive swelling/shrinking behavior. Two terminal hydroxyl groups of Pluronic F127 were thiol-functionalized to form self-assembling Pluronic micelles in aqueous solution with exposed -SH groups in an outer shell layer. The thiol groups present in the outer shell were cross-linked by gold nanoparticles synthesized through NaBH4 reduction of gold precursor anions. The resultant shell cross-linked gold-Pluronic micelles exhibited a temperature-dependent volume transition: their hydrodynamic diameter was changed from 157.1 +/- 15.6 nm at 15 degrees C to 53.4 +/- 5.5 nm at 37 degrees C as determined by dynamic light scattering. The critical micelle temperature measured by a pyrene solubilization technique suggested that the reversible swelling/shrinking behavior of the micelles was caused by hydrophobic interactions of cross-linked or grafted Pluronic copolymer chains in the micelle structure with increasing temperature. Transmission electron microscopy directly revealed that the shell cross-linked micelles were indeed produced by gold nanoparticles covalently clustered on the surface. These novel self-assembled organic/inorganic hybrid micelles would hold great potential for diagnostic and therapeutic applications.

Study of electrolyte induced aggregation of gold nanoparticles capped by amino acids

This work reports the electrolyte induced aggregation of gold nanoparticles directly conjugated to amino acid by chemical reduction in aqueous solution. The study was focused on three different classes of amino acids depending on the nature of alpha substituent, viz. l-cysteine, l-leucine, and l-asparagine. The band broadening and the red shift of surface plasmon band with increase in flocculation parameter showed the aggregation of gold nanoparticles with increase in electrolyte concentration and decrease in pH as monitored by UV-visible spectrophotometer. The (1)H NMR spectrum demonstrates that the sulfide bond of cysteine and alpha amino group of leucine and asparagine interact with nanoparticles surface. Furthermore, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) were performed to characterize and to support the fate of stabilization of the gold nanoparticles by amino acid.

Manipulating the generation of Ca-alginate microspheres using microfluidic channels as a carrier of gold nanoparticles

In this paper the manipulation of Ca-alginate microspheres, using a microfluidic chip, for the encapsulation of gold nanoparticles is presented. Our strategy is based on hydrodynamic-focusing on the forming of a series of self-assembling sphere structures, the so-called water-in-oil (w/o) emulsions, in the cross-junction microchannel. These fine emulsions, consisting of aqueous Na-alginates, are then dripped into a solution of 20% calcium salt to accomplish Ca-alginate microspheres in an efficient manner. Experimental data show that microspheres with diameters ranging from 50 microm to 2000 microm with a variation less than 5% were precisely generated. The size and gap of the droplets are tunable by adjusting the relative sheath/sample flow rate ratio. Furthermore, we applied them to encapsulated gold nanoparticles, and this one shot operation performs the 'Lab on a Chip'.

DNA-Induced Size-Selective Separation of Mixtures of Gold Nanoparticles

We present a novel method for size-selectively separating mixtures of nanoparticles in aqueous media utilizing the inherent chemical recognition properties of DNA and the cooperative binding properties of DNA-functionalized gold nanoparticles. We have determined that the melting temperatures (T(m)s) of aggregates formed from nanoparticles interconnected by duplex DNA are dependent upon particle size. This effect is proposed to derive from larger contact areas between the larger particles and therefore increased cooperativity, leading to higher T(m)s. The separation protocol involves taking two aliquots of a mixture of particles that vary in size and functionalizing them with complementary DNA. These aliquots are mixed at a temperature above the T(m) for aggregates formed from the smaller particles but below the T(m) for aggregates formed from the larger particles. Therefore, the aggregates that form consist almost exclusively of the larger particles and can be easily separated by sedimentation and centrifugation from the smaller dispersed particles. This unusual size-dependent behavior and separation protocol are demonstrated for three binary mixtures of particles and one ternary mixture.

RNA-mediated synthesis of palladium nanoparticles on Au surfaces

RNA catalysts for the shape-controlled synthesis of Pd particles from the precursor complex trisdibenzylideneacetone dipalladium ([Pd2(DBA)3] were recently discovered in our laboratory (J. Am. Chem. Soc. 2005, 127, 17814-17818). In the work described here, RNA codes for hexagonal Pd platelets and Pd cubes were covalently immobilized on gold surfaces and evaluated for their activity toward particle synthesis. When coupled to gold via oligoethylene glycol linkers, both RNA sequences were able to catalyze the formation of Pd particles with the same shape control previously observed in solution. For low surface coverages, the average distance between RNA molecules on the surface was estimated at ca. 300 nm, yet large (e.g., dimensions of hundreds of nanometers) Pd hexagons and cubes still formed. This surprising result suggests that a single RNA molecule may be sufficient for nucleating and controlling the shapes of these particles. Finally, the use of surface-bound RNA as a tool for directing the orthogonal synthesis of materials on surfaces was demonstrated. Patterning the RNA code for Pd hexagons next to the code for Pd cubes, followed by incubation in a solution containing [Pd2(DBA)3], resulted in the spontaneous formation of spatially distinct spots of hexagonal and cubic particles.

Formation of gold nanoparticles using amine reducing agents

We report on the use of amines as reducing agents in the formation of gold nanoparticles. We can predict whether the amines will function as reducing agents in this reaction based on their redox properties. The kinetics of AuNP formation can be understood in terms of Marcus electron transfer theory, where the slower reactions proceed in the inverted region owing to the difference between the Au reduction potential and the amine oxidation potential. For a certain number of the amine reducing agents, following reduction of HAuCl4, a subsequent reaction of the amine radical cation with other reducing agent molecules in solution can form poly(amine)s. These findings point collectively to the utility of amines as reducing agents in AuNP formation and provide information on the conditions under which these reactions will proceed.

Effect of an oscillating magnetic field on the release properties of magnetic collagen gels

The paper describes the effect of an oscillating magnetic field (OMF) on the morphology and release properties of collagen gels containing magnetic nanoparticles and microparticles and fluorescent drug analogues. Collagen gels were prepared through fibrillogenesis of collagen in the presence of iron oxide magnetic particles averaging 10 nm or 3 mum in diameter and rhodamine-labeled dextran (Dex-R) of molecular weights between 3000-70 000 g/mol. Dextran molecules effectively simulate protein-based drugs, since they have similar molecular weights and dimensions. The paper discusses the effect of an OMF on the release properties of the gels and proposes an empirical model to predict the release rate. It also demonstrates the self-repair capability of collagen gels following the structural damage caused by an OMF.

Simultaneous removal of thiolated membrane proteins resulting in nanostructured lipid layers

Self-organization of membrane-embedded peptides and proteins causes the formation of lipid mesostructures in the membranes. One example is purple membranes (PM), which consist of lipids and bacteriorhodopsin (BR) as the only protein component. The BRs form a hexagonal crystalline lattice. A complementary structure is formed by the lipids. Employing BR and PM as an example, we report a method where major parts of the mesoscopic self-assembled protein structures can be extracted from the lipid bilayer membrane. A complementary lipid nanostructure remains on the substrate. To remove such a large number of thiolated proteins simultaneously by applying a mechanical force, they are first reacted at physiological conditions with gold nanoparticles, and then a thin gold film is sputtered onto them that fuses with the gold nanoparticles forming a uniform layer, which finally can be lifted off. In this step, all of the previously gold-labeled proteins are pulled out of the membrane simultaneously. A stable lipid nanostructure is obtained on the mica substrate. Its stability is due to either binding of the lipids to the substrate through ionic bonds or to enough residual proteins to stabilize the lipid nanostructure against reorganization. This method may be applied easily and efficiently wherever thiolated proteins or peptides are employed as self-assembling and structure-inducing units in lipid membranes.

[Preparation of nanometer TiO2 doped with upconversion luminescence agent and investigation on degradation of ethyl violet using visible light]

A novel upconversion luminescence agent 40CdF2 x 60BaF2 x 1.6Er2O3 was synthesized and the fluorescent spectrum was determined. This upconversion luminescence agent can emit five upconversion fluorescent peaks whose wavelengths are all below 387nm under the excitation of 488 nm visible light. This upconversion luminescence agent was mixed into nanometer TiO2 powder by ultrasonic dispersion and the doped nanometer TiO2 photocatalyst utilizing visible light was prepared. The doped TiO2 powder was charactered by XRD and TEM and its photocatalytic activity was checked through the photocatalytic degradation of ethyl violet dye as a model compound under the visible light irradiation emitted by three basic color lamp. Otherwise, in order to compare the photocatalytic activities the same experiment was carried out for undoped photocatalytic TiO2 powder. The degradation ratio of ethyl violet dye in the presence of doped nanometer TiO2 powder reached 99.68% under visible light irradiation at 12.0 h which was obviously higher than the corresponding degradation ratio in the presence of undoped nanometer TiO2 powder, which indicate that the upconversion luminescence agent prepared as dopant can effectively turn visible lights to ultraviolet lights which are absorbed by nanometer TiO2 particles and produce the electron-cavity pairs.

[Adsorption of p-nitrophenol by nanosized titanium dioxide surface modified with 3,5-dinitrosalicylic acid]

Nanometer size titanium dioxide modified with 3,5-dinitrosalicylic acid (3,5-DA) was prepared using chemical adsorption method. The influences of surface modification on the adsorption of p-nitrophenol (PNP) and the dispersion in solvent such as water, benzene and ethanol were studied. The 3,5-dinitrosalicylic acid is bonded to the surface hydroxyl from TiO2 nanoparticles, results in the formation of a stable, six-ring complex which color is buff. The 3, 5-DA-modified TiO2 nanoparticles have good dispersive capacity in water, benzene and ethanol. Under the optimum conditions such as pH value 3, adsorption time 10 min, the adsorption ratio of PNP by TiO2 is improved from 43% to 99.9% through surface modification. A new method could be used to remove directly 3 approximately 10mg/L PNP, and the residual concentrations is below the integrated wastewater discharge standard (GB 8978-1996).

Magnetic micro- and nano-particle-based targeting for drug and gene delivery

The use of magnetic micro- and nano-particles as carriers for in vivo targeting of therapeutic compounds was first proposed over 25 years ago. Since then, a variety of animal studies have demonstrated the efficacy of the technique, however, only a handful of Phase I/II clinical trials have taken place. While the theoretical underpinnings have been lacking, recent advances in mathematical modeling of magnetic targeting, as well as the development of novel magnetic nanoparticle carriers and implantable magnets, show promise in progressing this technology from the laboratory to the clinic.

Dendron-like Growth of Silver Nanoparticles Using a Water-Soluble Oligopeptide

A dendron-like nanostructure of silver was grown in solution using a water-soluble tetrapeptide Tyr-Aib-Tyr-Val (Aib, alpha-amino isobutyric acid), silver nitrate, and methanol. These structures are composed of silver nanoparticles having a bimodal size distribution with the median diameters around 2.0 and 19.5 nm, respectively. The dendron-like growth is ascribed to the effect of the local electric field generated by the dipoles associated with the peptide molecules. The optical absorption spectra have been analyzed by Mie scattering theory, which shows that there is a metal-nonmetal transition in silver particles having diameters less than approximately 2.0 nm.

Dye-labeled silver nanoshell-bright particle

Silica beads with average diameters of 40-600 nm were prepared, and Ru(bpy)3(2+) complexes were incorporated into the beads. These beads were coated by silver layer by layer to generate porous but continuous metal nanoshells. The thicknesses of these metal shells were 5-50 nm. The emission band from the dyes in the silica cores was more narrow and the intensity was enhanced with growth of silver shell thickness due to coupling of the emission light from Ru(bpy)3(2+) in the cores with the metal plasmon from the silver shells. The enhancement of emission intensity was also dependent on the size of the silica core, showing that the enhancement efficiency decreased with an increase in the size of the silica beads. Lifetime measurements support the coupling mechanism between the dye and metal shell. This study can be used to develop novel dye-labeled metal particles with bright and narrow emission bands.

Spontaneous CdTe → Alloy → CdS Transition of Stabilizer-Depleted CdTe Nanoparticles Induced by EDTA

CdTe nanoparticles stabilized by l-cysteine are chemically transformed into CdS nanoparticles of the same diameter via an intermediate CdTeS alloy without any auxiliary source of sulfur. The reaction is induced by ethylenediaminetetraacetic acid dipotassium salt dehydrate (EDTA), which was demonstrated experimentally to act as a catalyst by partially removing thiol stabilizers from the nanoparticle surface. It is hypothesized that addition of EDTA facilitates Te(2-) release, and oxidation of Te(2-) drives the nanoparticle transition process. Unlike many reports on reactions catalyzed by nanocolloids, this is likely to be the first observation of a catalytic reaction in which nanoparticles function as a substrate rather than a catalyst. It opens new pathways for the synthesis of novel nanoscale II-VI and other semiconductors and represents an interesting case of chemical processes in nanocolloids with reactivity increased by depletion of the surface layer of thiol stabilizers. This includes but is not limited to accurate control over the particle composition and crystallization rate. The slow rate of the CdTe --> alloy --> CdS transition is important for minimizing defects in the crystal lattice and results in a substantial increase of the quantum yield of photoluminescence over the course of the transition.

Spontaneous Transformation of CdTe Nanoparticles into Angled Te Nanocrystals: From Particles and Rods to Checkmarks, X-Marks, and Other Unusual Shapes

CdTe nanoparticles spontaneously transform into the branched Te nanocrystals with the unique, highly anisotropic shape of checkmarks after partial removal of the stabilizers of L-cysteine. The Te checkmarks are made in a relatively high yield and uniformity; the length of the arms is ca. 150 nm, whereas the angle between the arms is 74 degrees . Subsequent growth of the particle yields mothlike nanocrystals retaining geometrical anisotropy. Unlike the previous synthesis methods of branched nanocrystals, they are formed via a merger of individual rod-shaped crystallites. High-energy crystal faces on their apexes act as the sticky points causing the particles to join in the ends. This is the first demonstration of spontaneous transformation of binary semiconductor particles into highly anisotropic nanocolloids in an angled conformation. The end reactivity of starting Te rods can be used both for bottom-up fabrication of nanoscale electronics and relatively safe and nontoxic method of synthesis of Te-based optical and other materials.

COHERENT EXCITATION OF VIBRATIONAL MODES IN METALLIC NANOPARTICLES

Excitation of metal nanoparticles with subpicosecond laser pulses causes a rapid increase in the lattice temperature, which can impulsively excite the phonon modes of the particle that correlate with the expansion coordinates. The vibrational periods depend on the size, shape, and elastic constants of the particles. Thus, time-resolved spectroscopy can be used to examine the material properties of nanometer-sized objects. This review provides a brief overview of the steady-state and time-resolved electronic spectroscopy of metal particles, which is important for understanding why vibrational motion appears in transient absorption traces. I also describe how the vibrational modes observed in the experiments are assigned, and what information can be obtained from the measurements. Our work has been mainly concerned with noble metal particles (gold and silver) in aqueous solution. The different shapes that have been examined to date include spheres, rods, and triangles, all with different sizes.

Phase transfer of gold nanoparticles from aqueous to organic solution containing resorcinarene

Citrate-capped gold nanoparticles (NPs) in aqueous solution were transferred directly into the organic solution mesitylene containing C-undecylcalix[4]-resorcinarene (C11-resorcinarene). C11-resorcinarene, which has long hydrophobic tails and phenolic hydroxyl groups, acted as both a phase-transfer and a capping agent. The C11-resorcinarene-capped gold particles could be isolated and dispersed in different organic solvents. Optical absorption spectra corresponding to surface plasmon resonance provided a broad band centered at 534 nm for C11-resorcinarene-capped gold NPs in mesitylene. High-resolution transmission electron micrograph images revealed that the average particle diameter of C11-resorcinarene-capped gold NPs is approximately 12 nm.