Ultrafast electron relaxation dynamics in coupled metal nanoparticles in aggregates

We report the effect of aggregation in gold nanoparticles on their ultrafast electron-phonon relaxation dynamics measured by femtosecond transient absorption pump-probe spectroscopy. UV-visible extinction and transient absorption of the solution-stable aggregates of gold nanoparticles show a broad absorption in the 550-700-nm region in addition to the isolated gold nanoparticle plasmon resonance. This broad red-shifted absorption can be attributed to contributions from gold nanoparticle aggregates with different sizes and/or different fractal structures. The electron-phonon relaxation, reflected as a fast decay component of the transient bleach, is found to depend on the probe wavelength, suggesting that each wavelength interrogates one particular subset of the aggregates. As the probe wavelength is changed from 520 to 635 nm across the broad aggregate absorption, the rate of electron-phonon relaxation increases. The observed trend in the hot electron lifetimes can be explained on the basis of an increased overlap of the electron oscillation frequency with the phonon spectrum and enhanced interfacial electron scattering, with increasing extent of aggregation. The experimental results strongly suggest the presence of intercolloid electronic coupling within the nanoparticle aggregates, besides the well-known dipolar plasmon coupling.     

Enhanced two-photon emission in coupled metal nanoparticles induced by conjugated polymers

Interactions between noble metal (Ag and Au) nanoparticles and conjugated polymers as well as their one- and two-photon emission have been investigated. Ag and Au nanoparticles exhibited extraordinary quenching effects on the fluorescence of cationic poly(fluorinephenylene). The quenching efficiency by 37-nm Ag nanoparticles is ～19 times more efficient than that by 13-nm Au nanoparticles, and 9-10 orders of magnitude more efficient than typical small molecule dye-quencher pairs. On the other hand, the cationic conjugated polymers induce the aggregate formation and plasmonic coupling of the metal nanoparticles, as evidenced by transmission electron microscopy images and appearance of a new longitudinal plasmon band in the near-infrared region. The two-photon emissions of Ag and Au nanoparticles were found to be significantly enhanced upon addition of conjugated polymers, by a factor of 51-times and 9-times compared to the isolated nanoparticles for Ag and Au, respectively. These studies could be further extended to the applications of two-photon imaging and sensing of the analytes that can induce formation of metal nanoparticle aggregates, which have many advantages over the conventional one-photon counterparts.     

酶提取-单颗粒电感耦合等离子质谱法分析樱桃番茄纳米银颗粒及其吸收规律研究

为探究复合保鲜涂膜中AgNPs的迁移情况,采用酶提取的前处理方式,结合单颗粒电感耦合等离子体质谱（SP-ICP-MS）,考察了前处理方式、驻留时间、校准方式以及Ag+浓度等条件对AgNPs准确测定的影响。结果表明：0.1 g樱桃番茄样品在柠檬酸盐体系下使用0.2 g的R-10离析酶可达到消解最适酶剂量;当驻留时间小于100 μs时,测定结果有较好的积分条件以及较高的信背比;采用AgNP尺寸方式进行校准比单独用Ag+标准溶液校准方式的颗粒尺寸测定结果更加准确。采用该方法测定樱桃番茄中加标AgNPs颗粒回收率达到88.9%,粒径实测值为47.8±0.3 nm,粒径检出限为13 nm,颗粒浓度检出限为 7.5×104 particles/L。通过将樱桃番茄暴露于AgNPs涂膜中来探究AgNPs迁移行为,复合保鲜涂膜后的樱桃番茄通过三次洗涤后能够在表面去除大部分AgNPs,但仍有少量AgNPs穿过果表皮浸入果肉组织。该方法灵敏度高,操作简单,能够为揭示AgNPs在农产品及农业生产中的风险提供可靠、准确的表征方法。     

The determination of an inhomogeneous linewidth for a strongly coupled adsorbate system

We present a set of experiments that provide a complete mapping of coherent and incoherent vibrational relaxation times for a molecule on a metal surface, CO/Ir{111}. Included is the first detection of a midinfrared photon echo from a metallic surface, some 15 years after the analogous measurement on a semiconductor surface, which sets a precedent for the ability to manipulate and rephase polarization on a subpicosecond time scale on surfaces. For the C-O stretch in a strongly dipole-coupled CO layer we obtain a total linewidth of 5.6 cm-1, composed of a homogeneous width of 2.7 cm-1 and an inhomogeneous contribution of 3.0 cm-1. Pure dephasing is negligible at liquid nitrogen temperatures, making CO/Ir{111} an attractive model system for quantum computing.     

酶消解-单颗粒电感耦合等离子质谱法测定农产品中纳米铂颗粒

铂纳米颗粒在汽车行业中被广泛用作汽车尾气催化剂。随着铂纳米颗粒在工业生产中的广泛应用,它在环境中广泛分布并可能从植物累积进入食物链中。因此,建立一种在农产品中的定量分析方法是至关重要的。以酶消解的前处理方法结合单颗粒-电感耦合等离子体质谱法(Single particle ICP-MS,SP-ICP-MS)测定农产品中纳米铂颗粒(PtNPs)粒径分布及颗粒数量浓度。通过优化前处理提取条件,当Macerozyme R-10酶为10 mg、柠檬酸缓冲溶液浓度为5 mmol/L、提取时间36 h时,农产品中PtNPs提取效果较高。PtNPs粒径检出限为20 nm,颗粒浓度检出限为5×10⁵ particle/L,铂颗粒浓度回收率在(81±3)%~(91±4)%,加标后平均粒径(41±3)~(47±2)nm,与50 nm PtNPs标准溶液粒径接近。方法操作简单、检出限低、准确度高,适用于农产品中PtNPs定量分析,为客观评价农产品铂纳米毒性效应提供可靠的分析技术。     

Preparation and dynamics of vibrational hot spots in polyatomics via raman scttering

We exploit a recent time dependent formulation of resonance Raman scattering to examine vibrational hot spot production in molecules which have dissociative excited states. The excited-state dynamics are described by a Raman wavefunction which is used to obtain the resonance Raman (RR) spectrum. The RR spectrum will contain the spectral signature of the subsequent dynamics and decay of the hot spot initial condition.     

Crucial importance of the water-entropy effect in predicting hot spots in protein-protein complexes

"Hot spots" are residues accounting for the majority of the protein-protein binding free energy (BFE) despite that they comprise only a small fraction of the protein-protein interface. A hot spot can be found experimentally by measuring the BFE change upon mutating it to alanine: the mutation gives rise to a significantly large increase in the BFE. Theoretical prediction of hot spots is an enthusiastic subject in biophysics, biochemistry, and bioinformatics. For the development of a reliable prediction method, it is essential to understand the physical origin of hot spots. To this end, we calculate the water-entropy gains upon binding both for a wild-type complex and for its mutant complex using a hybrid method of the angle-dependent integral equation theory applied to a molecular model for water and the morphometric approach. We note that this type of calculation has never been employed in the previously reported methods. The BFE change due to alanine mutation is evaluated only from the change in the water-entropy gain with no parameters fitted to the experimental data. It is shown that the overall performance of predicting hot spots in our method is higher than that in Robetta, a standard free-energy-based method using fitting parameters, when the most widely used criterion for defining an actual hot spot is adopted. This result strongly suggests that the water-entropy effect we calculate is the key factor governing basic physics of hot spots.     

Nucleation of gold nanoparticles on latex particle surfaces

Gold particles were nucleated on functionalized (i.e., sulfonate or imidazole groups) latex particle surfaces. Gold ions were associated with the functional groups present on the surface of the latex particles by metal‐ligand formation and were then reduced to nucleate gold particles on the particle surface. The use of imidazole groups favored the metal‐ligand formation more effectively compared with sulfonic acid groups, so gold nucleation was investigated on the surface of imidazole‐functionalized model latex particles. The desorption of gold atoms or their surface migration first occurred during the reduction process and then gold nanoparticles were nucleated. The utilization of strong reductants, such as NaBH₄ and dimethylamine borane (DMAB) under mildly acidic conditions (i.e., pH 4) led to the deprotonation of imidazole‐rich polymer chains present on the surface of the model latex particles followed by deswelling of hydrophilic polymer surface layers. As a result, well‐dispersed gold nanoparticles were embedded in the hydrophilic polymer surface. On the other hand, the use of weak reductants led to the formation of localized gold aggregates on the surface of the latex particles. The removal of residual styrene monomer is very important because gold ions can be coordinated with the vinyl groups present in styrene monomer and would then be reduced by nucleophilic water addition. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 912–925, 2008     

Reactive capture of gold nanoparticles by strongly physisorbed monolayers on graphite

Anthracene Diels Alder adducts (DAa) bearing two long side chains (H-(CH₂)₂₂O(CH₂)₆OCH₂-) at the 1- and 5-positions form self-assembled monolayers (SAMs) at the phenyloctane - highly oriented pyrolytic graphite (HOPG) interface. The long DAa side chains promote strong physisorption of the monolayer to HOPG and maintain the monolayer morphology upon rinsing or incubation in ethanol and air-drying of the substrate. Incorporating a carboxylic acid group on the DAa core enables capture of 1-4 nm diameter gold nanoparticles (AuNPs) provided (i) the monolayer containing DAa-carboxylic acids is treated with Cu²⁺ ions and (ii) the organic coating on the AuNP contains carboxylic acids (11-mercaptoundecanoic acid, MUA-AuNP). AuNP capture by the monolayer proceeds with formation of Cu²⁺ - carboxylate coordination complexes. The captured AuNP appear as mono- and multi-layered clusters at high coverage on HOPG. The surface density of the captured AuNPs can be adjusted from AuNP multi-layers to isolated AuNPs by varying incubation times, MUA-AuNP concentration, the number density of carboxylic acids in the monolayer, the number of MUA per AuNP, and post-incubation treatments.     

Acetate stabilization of metal nanoparticles and its role in the preparation of metal nanoparticles in ethylene glycol

Acetate-stabilized ruthenium nanoparticles were prepared by the NaBH4 reduction of the metal precursor salt at room temperature. Nanoparticles with a mean diameter of 2.20 nm and a standard deviation of 1.03 nm could be obtained under experimental conditions. The Ru nanoparticles so obtained could be easily extracted to a toluene solution of alkylamine, giving rise to alkylamine-stabilized Ru nanoparticles with a mean diameter of 2.96 nm and a standard deviation of 0.92 nm. The new found role of acetate stabilization was used to formulate a mechanism for the formation of metal (Pt, Ru) nanoparticles in ethylene glycol. In this mechanism metal nanoparticles are stabilized in ethylene glycol by adsorbed acetate ions, which are produced as a product of the OH- catalyzed reaction between the metal precursor salt and ethylene glycol.     

Investigation of polymer-protected noble metal nanoparticles by transmission electron microscopy: control of particle morphology and shape

 Noble metal nanoparticles were prepared by the in situ reduction of the respective metal salt precursors in the presence of various protective polymers. Transmission electron microscopy (TEM) has been used to determine the particle shapes and morphologies. These are strongly influenced by the reduction methods and conditions chosen, but the choice of the protective polymer is equally important for controlling the particle morphologies and for the stabilization of the colloids. A whole spectrum of nanoparticle morphologies and shapes was obtained, ranging from nanoagglomerates which are nevertheless well-defined and well-stabilized to nanosized single crystals with triangular shape. Received: 2 February 1998 Accepted: 29 May 1998     

The surface functionalisation of gold nanoparticles with metal complexes

The use of nanoparticles is now expanding well beyond the field of pure materials science. In particular, the modification of the surface functionality is playing a key role in catalysis, sensor applications and immobilisation of biomolecules. The use of coordinated metals on the outer surface of gold nanoparticles is the focus of this short article.     

Photopolymerization of metal nanoparticles on multiwall carbon nanotubes

A facile method for the functionalization of multiwall carbon nanotubes (MWCNT) by photopolymerization of 5-mercapto-2,2'-bithiophene modified metal (Au or Ag) nanoparticles on the surface of the MWCNT is developed.     

Electrodeposition of noble metal nanoparticles on carbon nanotubes

Noble metal nanoparticles can be electrodeposited on carbon nanotubes under potential control. The nanotube sidewalls serve both as the electrodeposition template and as the wire electrically connecting the deposited nanoparticles.     

Entrapment of metal nanoparticles in polymer stomatocytes

Polymersomes assembled from amphiphilic block copolymers containing a glassy hydrophobic segment can be further re-engineered to perform a controlled shape transformation from a thermodynamically stable spherical morphology to a kinetically trapped stomatocyte structure. The stable bowl-shape stomatocyte morphology is ideal for the specific physical entrapment of nanoparticles for potential use in heterogeneous catalysis and drug delivery. Herein we report two approaches to obtain a selective and controlled entrapment of platinum nanoparticles (PtNP) of different sizes and shapes inside the stomatocyte structure. In the first approach, the stomach of the stomatocytes is used to template the growth of the PtNP by controlling and confining the nucleation points inside the cavity. In the second method, preformed nanoparticles are engulfed during the stomatocyte formation process. Synergistically, the reverse effect is observed, that is, differently shaped nanoparticles were shown to exhibit a templating effect on the stomach formation of the stomatocytes.     

Light source spectrum strongly influences the in vitro estimation of sun protection factor

Irradiation from an artificial solar simulator that matches the relative cumulative erythema effectiveness (RCEE) of sunlight is used for in vivo sun protection factor (SPF) testing, whereas irradiation that matches the spectrum of natural sunlight (NS) is generally used for in vitro SPF testing. This study was designed to clarify whether this difference is important. Eight sunscreens spread on artificial substrates and several optical filters as sunscreen mimics were used. Their in vitro SPF values were evaluated using RCEE-compliant and NS spectrum-matching light sources in calculation. The calculated in vitro SPF values obtained using NS light (SPF [NS]) were lower than those obtained using RCEE light (SPF [RCEE]). The in vitro SPF (RCEE) values showed a better correlation and better agreement with in vivo SPF values, as compared with the in vitro SPF (NS) values. A marked difference between in vitro SPF values obtained with the two light sources in calculation was found for sunscreens showing low transmittance in the ultraviolet B region. To obtain in vitro SPF values that correspond well to in vivo SPF values measured with currently accepted methodology, it is important to use an RCEE-compliant light source.