Thiol-Capped Gold Nanoparticle Biosensors for Rapid and Sensitive Visual Colorimetric Detection of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis>

In the last few years, gold nanoparticle biosensors have been developed for rapid, precise, easy and inexpensive with high specificity and sensitivity detection of human, plant and animal pathogens. Klebsiella pneumoniae serotype K2 is one of the common gram-negative pathogens with high prevalence. Therefore, it is essential to provide the effective and exclusive method to detect the bacteria. Klebsiella pneumoniae serotype K2 strain ATCC9997 genomic DNA was applied to establish the detection protocol either with thiol-capped oligonucleotide probes and gold nanoparticles or polymerase chain reaction based on K2A gene sequence. In the presence of the genomic DNA and oligonucleotide probes, a change in the color of gold nanoparticles and maximum changes in wavelength at 550-650 nm was achieved. In addition, the result showed specificity of 15?×?10⁵ CFU/mL and 9 pg/μL by gold nanoparticles probes. The lower limit of detection obtained by PCR method was 1 pg/μL. Moreover, results demonstrated a great specificity of the designed primers and probes for colorimetric detection assay and PCR. Colorimetric detection using gold nanoparticle probe with advantages such as the lower time required for detection and no need for expensive detection instrumentation compared to the biochemical and molecular methods could be introduced for rapid, accurate detection of the bacteria.     

碳纳米管表面金纳米颗粒的形成与结构转变

利用分子动力学模拟研究了室温下金纳米颗粒在碳纳米管表面的结构和作用能.研究结果表明,金纳米颗粒随着尺寸的增大会发生不同于孤立状态下的结构转变.当原子数小于130时,颗粒属于无序结构;当原子数大于140时,呈现面心立方晶体结构.小金纳米颗粒和碳纳米管结合紧密,相互作用能正比于面对碳纳米管的颗粒表面面积. 关键词： 金纳米颗粒 碳纳米管 分子动力学模拟     

Trace determination of thiram using SERS-active hollow sea-urchin gold nanoparticles

Surface-enhanced Raman scattering (SERS) is greatly structure-dependent on the absorbed nanoparticles. Nanostructures with different novel morphologies show different Raman enhancement factor orders of magnitude. Herein, a unique nanostructure with fruitful SERS-active sites, composed of hollow interiors and thorns which named as hollow sea-urchin gold nanoparticles (HSU-GNPs), was synthesized by using a one-pot galvanic replacement method. And the corresponding morphologies and optical properties were characterized by TEM images and absorption spectra. Importantly, the synthetic parameters of HSU-GNPs were optimized to obtain a superior SERS performance by analyzing the formation mechanism and the SERS spectra of R6G-labeled HSU-GNPs which obtained at different concentrations of AgNO₃. Furthermore, the SERS-based application of HSU-GNPs was performed on the dose-response detection of thiram. The experimental result shows this detection strategy is available for thiram with decent sensitivity and reproducibility, which suggests that it is an excellent candidate for the detection of pesticides.

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Graphical abstract This study reports a low-cost and easy-operated pesticide residues detection method based on hollow sea-urchin gold nanoparticles using SERS.

     

Preparation of Aromatic Polycarbonate Nanoparticles using Supercritical Carbon Dioxide

A novel synthetic process for producing aromatic polycarbonate (PC) nanoparticles using supercritical CO₂ was developed. The objective of the present research work was to synthesize high molecular weight PC nanoparticles using transesterification between bisphenol-A (BPA) and diphenyl carbonate (DPC) in supercritical CO₂ which is an excellent plasticizing agent and a good solvent for phenol, a by-product of the reaction. Poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) tri-block copolymer with CO₂-phobic anchor and CO₂-philic tail group was used as a stabilizer for the preparation of stable dispersions of BPA–DPC mixture in a CO₂ continuous phase. As the reaction was proceeding, phenol formed from the reaction was dissolved and diffused into supercritical CO₂ phase. The PC nanoparticles were isolated by simple venting of the supercritical CO₂ from the reactor. Spherical morphology of PC particles was confirmed by scanning electron microscopy. Particle size and morphology of PC particles were modified upon variation of the process conditions. The resulting PC particles with a nano-size of 30–140nm have a high molecular weight (M _w) of 3.1×10⁵ (g/mol).     

Surface enhanced Raman spectroscopic readout on heavy metal ions based on surface self assembly

A new method is reported for detecting heavy metal ions by using the self assembled monolayer (SAM) technique and surface enhanced Raman spectroscopy (SERS). The p‐mercaptobenzoic acid (MBA) served as the SERS readout molecule and the modified tag to attach on the smooth gold substrate as well as the tag of nanoparticles by the SAM method. Two carboxyl groups from MBA molecules which were attached respectively to gold substrate and gold nanoparticles were linked through the heavy metal ions (Cu²⁺, Pb²⁺ and Zn²⁺) as bridge, and thus sandwich structure of ‘MBA modified gold substrate/heavy metal ions/MBA modified gold nanoparticles’ was built for detection. The observation of the oxidation peak of metal nanoparticles from cyclic voltammetry (CV) curve, gold nanoparticles from scanning electron microscopy (SEM) images and SERS signal of MBA from the sandwich structure indicated the existence of heavy metal ions. The difference in the wavenumbers of vibrational modes from MBA in the sandwich structure constructed by different could be used to identify different heavy metal ions. The assembled structure was rinsed by strong chelator of EDTA solution to remove the heavy metal ions from the sandwich structure and thus to obtain a fresh gold substrate modified with MBA for the cyclic detection. Copyright © 2007 John Wiley & Sons, Ltd.     

Core size effects on electrodeposition of gold nanoparticles attached with biferrocene derivatives

Biferrocene-modified gold nanoparticles (Au_n-BFc) comprising 1.7, 2.2 and 2.9 nm in average core diameter, d, were synthesized by a substitution reaction of octyl thiolate-covered nanoparticles with biferrocene-terminated alkanethiol, 1-(9-thiononyl-1-one)-1, 1-biferrocene (BFcS). All sizes of Au_n-BFc undergo two-step oxidation reactions in 0.1 mol dm^-3 Bu₄NClO₄-CH₂Cl₂ and consecutive potential scans including the second oxidation process lead to the formation of an adhesive redox-active gold nanoparticle film on an electrode. The thickness of the Au_n-BFc film is controllable by the number of potential scans. The scanning tunneling microscope images reveal that the Au_n-BFc (d = 2.9 nm) film forms many domains of the assembled Au_n-BFcs, especially the particles are isotropically assembled in line.     

Catalytically active gold clusters and nanoparticles for CO oxidation

Electronic states of gold nanoparticles in mordenite and their transformations under redox treatments have been studied by the methods of FTIR spectroscopy of adsorbed CO and diffuse reflectance UV-visible spectroscopy. Different states of ionic and metallic gold were detected in the zeolite channels and on the external surface of the zeolite - Au⁺ and Au³⁺ ions, charged clusters , and neutral nanoparticles Au_m. Catalytic tests of the samples revealed the existence of two types of active sites of gold in CO oxidation - gold clusters <2 nm (low-temperature activity) and gold nanoparticles (high temperature activity).     

Detection and analysis of cyclotrimethylenetrinitramine (RDX) in environmental samples by surface‐enhanced Raman spectroscopy

Techniques for rapid and sensitive detection of energetics such as cyclotrimethylenetrinitramine (RDX) are needed both for environmental and security screening applications. Here we report the use of surface‐enhanced Raman scattering (SERS) spectroscopy to detect traces of RDX with good sensitivity and reproducibility. Using gold (Au) nanoparticles (∼90–100 nm in diameter) as SERS substrates, RDX was detectable at concentrations as low as 0.15 mg/l in a contaminated groundwater sample. This detection limit is about two orders of magnitude lower than those reported previously using SERS techniques. A surface enhancement factor of ∼6 × 10⁴ was obtained. This research further demonstrates the potential for using SERS as a rapid, in situ field screening tool for energetics detection when coupled with a portable Raman spectrometer. Copyright © 2010 John Wiley & Sons, Ltd.     

The effect of the size,shape, and structure of metal nanoparticles on the dependence of their optical properties on the refractive index of a disperse medium

The effect of the size, shape, and structure of gold and silver nanoparticles on the dependence of their extinction and integral scattering spectra on the dielectric environment has been investigated. Calculations were performed using the Mie theory for spheres and nanoshells and the T-matrix method for chaotically oriented bispheres, spheroids, and s cylinders with hemispherical ends. The sensitivity of plasmon resonances to variations in the refractive index of the environment in the range 1.3–1.7 for particles of different equivolume size, as well as to variations in the thickness of the metal layer of nanoshells, was studied. For nanoparticles with an equivolume diameter of 15 nm, the maximal shifts of plasmon resonances due to variation in the refractive index of the environment are observed for bispheres and the shifts decrease in the series nanoshells, s cylinders or spheroids, and spheres. For particles 60 nm in diameter, the largest shifts of plasmon resonances occur for nanoshells and the shifts decrease in the series bispheres, s cylinders or spheroids, and spheres. All other conditions being the same, silver nanoparticles are more sensitive to the resonance tuning due to a change in the dielectric environment.     

Peptide-functionalized iron oxide magnetic nanoparticle for gold mining

Here, we present our work on preparing a novel nanomaterial composed of inorganic binding peptides and magnetic nanoparticles for inorganic mining. Two previously selected and well-characterized gold-binding peptides from cell surface display, AuBP1 and AuBP2, were exploited. This nanomaterial (AuBP-MNP) was designed to fulfill the following two significant functions: the surface conjugated gold-binding peptide will recognize and selectively bind to gold, while the magnetic nano-sized core will respond and migrate according to the applied external magnetic field. This will allow the smart nanomaterial to mine an individual material (gold) from a pool of mixture, without excessive solvent extraction, filtration, and concentration steps. The working efficiency of AuBP-MNP was determined by showing a dramatic reduction of gold nanoparticle colloid concentration, monitored by spectroscopy. The binding kinetics of AuBP-MNP onto the gold surface was determined using surface plasmon resonance (SPR) spectroscopy, which exhibits around 100 times higher binding kinetics than peptides alone. The binding capacity of AuBP-MNP was demonstrated by a bench-top mining test with gold microparticles.

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Graphical abstract

     

Triblock copolymer-mediated synthesis of catalytically active gold nanostructures

The design of nanostructures based on poly(ethylene oxide)-poly(propylene)-poly(ethylene oxide) (PEO-PPO-PEO) and metal nanoparticles is becoming an important research topic due to their multiple functionalities in different fields, including nanomedicine and catalysis. In this work, water-soluble gold nanoparticles have been prepared through a green aqueous synthesis method using Pluronic F127 as both reducing and stabilizing agents. The size dependence (varying from 2 to 70 nm) and stability of gold nanoparticles were systematically studied by varying some parameters of synthesis, which were the polymer concentration, temperature, and exposure to UV-A light, being monitored by UV-Vis spectroscopy and TEM. Also, an elaborated study regarding to the kinetic of formation (nucleation and growth) was presented. Finally, the as-prepared Pluronic-capped gold nanoparticles have shown excellent catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride, in which a higher catalytic performance was exhibited when compared with gold nanoparticles prepared by classical reduction method using sodium citrate.

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Graphical abstract Synthesis of catalytically active gold nanostructures mediated by a pluronic triblock copolymer

     

Synthesis of Aucore–Agshell type bimetallic nanoparticles for single molecule detection in solution by SERS method

This paper reports the evolution of a new class of core–shell type, that is, Au_core–Ag_shell bimetallic nanoparticles by seed mediated technique for surface enhanced Raman scattering (SERS) study. Here it is demonstrated how to control the thickness of Ag-shell with the variation of gold seed (15 nm) to Ag ion concentration which in turn control the particle size in the range from 50 to 100 nm with increase of shell thickness. For 50 nm core–shell particles the thickness of the shell was 17 nm, for 70 nm particles the thickness was 27 nm and for 100 nm the thickness was 42 nm. SERS study was performed on those particles using the analyte crystal violet (CV) to examine the impact of the size and field effects of the bimetallics on SERS spectra. A surprising finding is that a small particle as low as 50 nm have been found to be highly efficient for SERS, even it enables the detection of a selected dye molecule down to single molecular level. The sensitivity of the SERS detection limit has been improved further with an activating reagent like NaCl. The newly modeled bimetallic system establishes a relationship between the local electromagnetic (EM) field effect and chemical effect (CE) on the enhancement of SERS spectra, which provides further insight into the enhancement mechanism of SERS.     

Peristaltic blood flow with gold nanoparticles as a third grade nanofluid in catheter: Application of cancer therapy

Cancer is dangerous and deadly to most of its patients. Recent studies have shown that gold nanoparticles can cure and overcome it, because these particles have a high atomic number which produce the heat and leads to treatment of malignancy tumors. A motivation of this article is to study the effect of heat transfer with the blood flow (non-Newtonian model) containing gold nanoparticles in a gap between two coaxial tubes, the outer tube has a sinusoidal wave traveling down its wall and the inner tube is rigid. The governing equations of third-grade fluid along with total mass, thermal energy and nanoparticles are simplified by using the assumption of long wavelength. Exact solutions have been evaluated for temperature distribution and nanoparticles concentration, while approximate analytical solutions are found for the velocity distribution using the regular perturbation method with a small third grade parameter. Influence of the physical parameters such as third grade parameter, Brownian motion parameter and thermophoresis parameter on the velocity profile, temperature distribution and nanoparticles concentration are considered. The results pointed to that the gold nanoparticles are effective for drug carrying and drug delivery systems because they control the velocity through the Brownian motion parameter $N_b$ and thermophoresis parameter $N_t$. Gold nanoparticles also increases the temperature distribution, making it able to destroy cancer cells.     

Selective optothermal detection of NO2 and H2O with a frequency-tuned CO waveguide laser

The results are reported of the CO-laser optothermal (OT) detection of impurity gases when their absorption spectra overlap with those of an interfering gas. The influence of the latter was avoided using low gas pressures corresponding to a maximum of the OT sensitivity. Frequency tuned in the 5.2–6.3 m wavelength range, ¹²C¹⁶O and ¹³C¹⁶O waveguide lasers were used. The fine frequency tuning at 490 MHz was achieved for 150 laser transitions of both molecules. The OT sensitivity was estimated by NO₂ detection in the presence of water vapor. The minimal detectable concentration proved to be 60 ppb at P _19–18(14) transition of a ¹²C¹⁶O laser for NO₂ and 75 ppb on P _12–11(13) transition of a ¹³C¹⁶O laser for H₂O.     

Indomethacin nanoparticles directly deposited on the fluidized particulate excipient by pulsed laser deposition

Nanoparticles of indomethacin (IM), a sparingly soluble drug in water, were prepared by pulsed laser deposition with Nd: YAG laser at 1064 nm. Variation of the deposition rate (DR) with various experimental conditions, such as species and pressure of the background gas, and laser fluence, was discussed. We obtained highest DR, 2.7 g/cm²min, under He at 100 Pa with the laser fluence of 25 J/cm². In the deposited solid product, no trace of drug decomposition was observed by HPLC. Deposition of IM nanoparticles was achieved on the fluidized excipient, potato starch particles of 20 m regime. By TEM observation and zeta potential distribution measurement, we confirmed that surface of excipient particles was fully covered by nanoparticles of IM. Thus, the present method enables us a new method of one-step preparation of drug-excipient nanocomposites to eliminate tedious problems associated with nanoparticles handling.     

Probing for new physics and detecting non-linear vacuum QED effects using gravitational wave interferometer antennas

Low energy non-linear QED effects in vacuum have been predicted since 1936 and have been subject of research for many decades. Two main schemes have been proposed for such a ‘first’ detection: measurements of ellipticity acquired by a linearly polarized beam of light passing through a magnetic field and direct light–light scattering. The study of the propagation of light through an external field can also be used to probe for new physics such as the existence of axion-like particles and millicharged particles. Their existence in nature would cause the index of refraction of vacuum to be different from unity in the presence of an external field and dependent of the polarization direction of the propagating light. The major achievement of reaching the project sensitivities in gravitational wave interferometers such as LIGO and VIRGO has opened the possibility of using such instruments for the detection of QED corrections in electrodynamics and for probing new physics at very low energies. We show that it is possible to distinguish between various scenarios of new physics in the hypothetical case of detecting unexpected values. Considering the design sensitivity in the strain of the near future VIRGO+ interferometer leads to a variable dipole magnet configuration such that B ² D≥13000 T² m  for a ‘first’ vacuum non-linear QED detection.     

Determining the mechanism of interaction between molecules of porphyrin and fullerene and gold nanoparticles,based on luminescence spectroscopy data

Gold nanoparticles are synthesized via laser ablation of a gold target in a liquid. The constants that characterize the efficiency of porphyrins and fullerenes bonding with gold nanoparticles are determined using a modified Stern–Volmer equation. The results from luminescence quenching measurements are presented. It is found that the efficiency of bonding depends on whether there are functional groups in the molecular fragments. Porphyrin containing para-bromphenyl groups at the meso positions of the porphyrin core has the highest affinity for the surfaces of gold nanoparticles.     

Modifications of nano-titania surface for in vitro evaluations of hemolysis,cytotoxicity, and nonspecific protein binding

In the past decade, a variety of drug carriers based on mesoporous silica nanoparticles has been extensively reported. However, their biocompatibility still remains debatable, which motivated us to explore the porous nanostructures of other metal oxides, for example titanium dioxide (TiO₂), as potential drug delivery vehicles. Herein, we report the in vitro hemolysis, cytotoxicity, and protein binding of TiO₂ nanoparticles, synthesized by a sol–gel method. The surface of the TiO₂ nanoparticles was modified with hydroxyl, amine, or thiol containing moieties to examine the influence of surface functional groups on the toxicity and protein binding aspects of the nanoparticles. Our study revealed the superior hemocompatibility of pristine, as well as functionalized TiO₂ nanoparticles, compared to that of mesoporous silica, the present gold standard. Among the functional groups studied, aminosilane moieties on the TiO₂ surface substantially reduced the degree of hemolysis (down to 5%). Further, cytotoxicity studies by MTT assay suggested that surface functional moieties play a crucial role in determining the biocompatibility of the nanoparticles. The presence of NH₂– functional groups on the TiO₂ nanoparticle surface enhanced the cell viability by almost 28% as compared to its native counterpart (at 100 μg/ml), which was in agreement with the hemolysis assay. Finally, nonspecific protein adsorption on functionalized TiO₂ surfaces was examined using human serum albumin and it was found that negatively charged surface moieties, like –OH and –SH, could mitigate protein adsorption to a significant extent.

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Graphical abstract ?

     

Study of intranuclear collision effects in interactions ofK +/π + mesons with Al and Au nuclei at 250 GeV/c

Multiplicity, inclusive, correlation and collective characteristics of multiparticle production processes inK ⁺ Al,K ⁺ Au, ⁺ Al and ⁺ Au interactions at 250 GeV/c are studied with the European Hybrid Spectrometer, providing high statistics and almost 4 acceptance for final state charged particles. It is shown that the proton energy spectrum practically does not depend on the target atomic weight, but the proton angular distributions reveal a strongA-dependence. In a model independent way, the average number of intranuclear collisions is extracted, and it is shown that their dominant part (60% for Al and 80% for Au) is caused by interactions of the non-leading particles produced in the target fragmentation. The multiplication ratio of the produced particles for the Au nucleus changes fromR40 at the smallest rapidities in the target fragmentation region, down toR=0.37±0.06 at the largest rapidities in the beam fragmentation region. It is found that the average total longitudinal momentum of the charged products of the beam fragmentation depends weakly on the number of leading hadron (cluster) intranuclear collisions which are characterized by a low inelasticity coefficient k=0.17±0.03.Partially supported by grants from CPBP 01.06 and 01.09     

Gold aggregates on silica templates and decorated silica arrays for SERS applications

In this work, we report the fabrication and characterization of size controllable gold nanoparticles (NPs) aggregates for their application in surface enhanced Raman scattering (SERS). Aggregates were prepared using two methodologies: (i) by using silica particles arrays as a template to agglomerate gold NPs between the inter-particle interstices, and (ii) by functionalizing silica particles to be used as support to graft gold nanoparticles and thus to form decorated silica particle arrays. These substrates were used in the detection of Rhodamine 6G producing an enhancement factor (EF) from 10⁴ to 10⁶ that is associated to the increment of hot spot (HS) sites, and the fact that plasmon resonance from aggregates and absorption wavelength of test molecules are closely in resonance with excitation wavelength. The EF was also reduced when the plasmon resonance was red-shifted as a result of the increment of aggregate size. In spite of this, the EF is high enough to make these SERS substrates excellent candidates for sensing applications.