Slurry Nebulization in Plasmas for Analysis of Inorganic Materials

Abstract

This review summarizes and discusses the preparation of slurries for analysis of inorganic materials by inductively coupled plasma optical emission spectrometry (ICP‐OES) and inductively coupled plasma mass spectrometry (ICP‐MS). Details about the grinding step for slurry preparation, the stabilization of slurries, and the calibration strategies are critically discussed. Typical applications described in the literature and the state‐of‐the‐art including advantages and limitations of slurry analysis are presented.     

Microstructured Arrays with Pre-synthesized Capture Probes for DNA Detection Based on Metal Nanoparticles and Silver Enhancement

DNA microarrays exhibiting highly defined squared spot geometry and increased homogeneity in capture DNA distribution were prepared by a combination of microfabrication and DNA spotting. The microfabricated substrates were tested using metal nanoparticles as markers. The optical absorption signal is improved by a silver enhancement step. Experiments demonstrated the specificity and the concentration-dependency of the signal.     

Shape Matters: A Gold Nanoparticle Enabled Shape Memory Polymer Triggered by Laser Irradiation

With incorporation of gold nanoparticles, i.e., nanorods (AuNR) and nanospheres (AuNS), into a polyurethane‐based shape‐memory polymer (SMP) EG‐72D matrix, SMP nanocomposite films capable of being remotely triggered by low‐power laser are fabricated and characterized using UV‐vis‐NIR spectroscopy, X‐ray scattering, and dynamic mechanical analysis (DMA). It is demonstrated that, with incorporation of very low concentration of gold nanorods (≈0.1 wt%), the mechanically programmed EG‐72D/AuNR nanocomposite presents rapid response to low power laser irradiation (785 nm, ≈10 mW). Comparative studies on the laser irradiation response of EG‐72D/AuNS and EG‐72D/AuNR nanocomposite films suggest that AuNRs have significantly higher photothermal conversion efficiency than AuNS and on‐resonance laser irradiation, matching the wavelength of the incident laser with the longitudinal plasmon resonance of AuNR, is necessary to induce the fast response of gold nanoparticle enabled SMP nanocomposites.     

Formation of multifunctional Fe_3O_4/Au composite nanoparticles for dual-mode MR/CT imaging applications

Recent advances with iron oxide/gold(Fe3O4/Au) composite nanoparticles(CNPs) in dual-modality magnetic resonance(MR) and computed tomography(CT) imaging applications are reviewed. The synthesis and assembly of "dumbbelllike" and "core/shell" Fe3O4/Au CNPs is introduced. Potential applications of some developed Fe3O4/Au CNPs as contrast agents for dual-mode MR/CT imaging applications are described in detail.     

Dielectrophoretically Modulated Optical Spectroscopy of Colloidal Nanoparticle Solutions in Microfluidic Channels

Optical spectroscopic techniques (e.g., extinction, scattering, and fluorescence spectroscopies) are important for the analysis of colloidal solutions of nanoparticles (NPs). They are routinely applied to plasmonic and quantum-dot NP samples assuming that these contain a single population of particles with modest size and shape dispersity. However, these spectroscopic techniques become less effective when the sample is a mixture of particles with different sizes, shapes, or composition. Here, an original microfluidic method is proposed for the optical spectroscopic analysis of colloidal NP solutions that combines periodic trapping of NPs by dielectrophoresis (DEP) with in situ optical extinction spectroscopy. The periodic trapping leads to modulation of the continuously monitored optical spectrum depending on the DEP properties of the NPs. DEP-modulated spectroscopy is demonstrated using colloidal gold NPs as small as 40 nm diameter. It is found that the DEP modulation is significantly enhanced when employing suitable microfluidic flow over a multielectrode array. Finally, it is shown that the method can identify and characterize the NP species simultaneously present in a mixture of 40 and 80 nm gold NPs, opening the way toward optical spectroscopic analysis of higher complexity NP mixtures through the combination of the DEP-modulated spectroscopy with chemometric methods.     

Unravelling Malaria Antigen Binding to Antibody‐Gold Nanoparticle Conjugates

Conjugates formed by antibody adsorption to gold nanoparticles (AuNP) have found extensive utilization in immunoassays due to the high surface area and interesting optical and electronic properties of the nanomaterials. Nevertheless, the mechanism of formation of antibody‐AuNP conjugates and their antigen binding characteristics have not been sufficiently explored in terms of specificity and consequent clinical applicability. Dynamic light scattering and related techniques have been successfully employed to detect antigen binding to antibody‐AuNP complexes. Here, a range of different techniques from the bionanotechnology realm have been applied to obtain a detailed picture of a competitive immunoassay for malaria antigen detection, based on fluorescence‐quenching by AuNPs. Both agarose gel electrophoresis and differential centrifugal sedimentation (DCS) analyses provide binding constants in the same order of magnitude, for antibody binding to AuNP and for antigen binding to antibody‐AuNP conjugates. Both techniques are also able to reveal inhibition of antigen binding in the presence of a major blood plasma protein, transferrin (via competitive binding). DCS is further used to show inhibition of the binding of the antigen in the presence of human plasma, a realistic testing condition, of high relevance to the implementation of immunoassays at the clinical level.     

Self‐Assemble Polymeric Nanoparticle with GSH Exhaustion for SPECT Imaging–Guided Enhanced Radioisotope Therapy

Exploiting biocompatible nanomaterials for cancer theranostics has attracted great attention in recent years. Herein, a multifunctional self‐assembled nanoparticle based on a biocompatible polymer that contains 3‐(4‐hydroxyphenyl) propionic acid N‐hydroxysuccinimide ester (HOPA) for radiolabeling and piperlongumine (PL) for exhausting endogenous glutathione (GSH) (HOPA‐C18PMH‐PEG/PL) is successfully synthesized. With radionuclide ¹²⁵I labeling, SPECT imaging shows high tumor uptake of HOPA‐C18PMH‐PEG/PL after intravenous injection. The in vitro and in vivo combined radioisotope therapy (RIT) and chemotherapy using ¹³¹I‐labeled HOPA‐C18PMH‐PEG/PL is then carried out, achieving synergistic antitumor effect. This is because the reactive oxygen species (ROS) level in the tumor sites of mice treated with ¹³¹I‐labeled HOPA‐C18PMH‐PEG/PL is increased after the exhaustion of GSH by PL. Additionally, such a strategy (exhausting GSH and increasing ROS) induces no obvious toxicity to normal tissue. Therefore, as‐made polymeric nanoparticles exhibit multifunctional properties for SPECT imaging–guided combined RIT and chemotherapy in one system. This finding will further promote polymeric nanoparticle–based RIT of cancer and is expected to be used for future clinical transformation.     

Development of a Liver‐Targeting Gold–PEG–Galactose Nanoparticle Platform and a Structure–Function Study

For the specific liver parenchymal cell delivery, a series of short heterobifunctional poly(ethylene glycol) (PEG) derivatives containing dimercapto and galactose (Gal) terminals is synthesized for the preparation of gold conjugates. The Gal density on the surface of all gold conjugates can be well controlled and the prepared gold conjugates are stable in various media, even in the presence of serum. For the liver targeting and reflectance imaging applications, the structure–function relationships of this platform, including the influence of the PEG molecular weight and the Gal ligand coverage of hybrid particles on the cytotoxicity and cellular recognition of tumor cells in vitro and on their liver‐targeting ability in small animals, are studied. Biocompatibility results show that HepG2 cells are more sensitive than HeLa cells to gold conjugates. Cellular uptake studies demonstrate that a lower PEG molecular weight, a higher Gal density, or a higher gold concentration can increase the cellular uptake efficiency of these hybrid particles in HepG2 cells when the other parameters are constant. The results reveal the importance of parameter modulation for the design and control of nanoprobes and the gold conjugates with short PEG chains and a high Gal density are a potential vector for active‐targeting therapy.     

Optical probing and imaging of live cells using SERS labels

During surface‐enhanced Raman scattering (SERS), molecules exhibit a significant increase in their Raman signals when attached, or in very close vicinity, to gold or silver nanostructures. This effect is exploited as the basis of a new class of optical labels. Here we demonstrate robust and sensitive SERS labels as probes for imaging live cells. These hybrid labels consist of gold nanoparticles with Rose Bengal or Crystal Violet attached as reporter molecules. These new labels are stable and nontoxic, do not suffer from photobleaching, and can be excited at any excitation wavelength, even in the near infrared. SERS labels can be detected and imaged through the specific Raman signatures of the reporters. In addition, surface‐enhanced Raman spectroscopy in the local optical fields of the gold nanoparticles also provides sensitive information on the immediate molecular environment of the label in the cell and allows imaging of the native constituents of the cell. This is demonstrated by images based on a characteristic Raman line of the reporter as well as by displaying lipids based on the SERS signal of the C H deformation/bending modes at ∼1470 cm⁻¹. Copyright © 2008 John Wiley & Sons, Ltd.     

Deliberate Introduction of Particle Anisotropy in Helical Gold Nanoparticle Superstructures

Helical nanoparticle (NP) superstructures are an important class of chiral NP assemblies. The nature of the constituent NPs (size and shape) within these assemblies dictates their optical properties. However, the construction of helical NP superstructures consisting of various anisotropic NPs remains challenging. Here, a set of cetyltrimethylammonium bromide derivatives is employed to transform constituent spherical gold NPs (≈3 nm) within a chiral single‐helical assembly into gold nanoprisms (edge length ? 10 nm). Careful optimization of this strategy may lead to designed chiral NP architectures with tunable optical properties.     

Poly(3‐hexylthiophene)/Gold Nanoparticle Hybrid System with an Enhanced Photoresponse for Light‐Controlled Electronic Devices

Light‐controlled electrical behavior of polymer/nanoparticle hybrid system in ambient condition is demonstrated. By embedding gold nanoparticles (Au NPs) in a poly(3‐hexylthiophene) (P3HT) matrix, the photoresponses of the nanocomposite films are enhanced. The electrical behavior of the P3HT/Au NPs nanocomposite transistors and inverters are tuned over a wide range in depletion mode. UV‐visible absorption spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and steady‐state photoluminescence (PL) spectroscopy are used to analyze the nanocomposite films. The findings provide a better understanding of light‐induced threshold voltage shifts of P3HT‐based field‐effect transistors and inverters and demonstrate their potential applications in electronic signal modulation for solution‐processed integrated circuits.     

Polymer-like Behavior of Inorganic Nanoparticle Chain Aggregates

Studies of the behavior of nanoparticle chain aggregates (NCA) have shown properties similar to those of molecular polymers. Like polymer chains, NCA tend to gather up and become more compact when heated. Under tensile stress, folded chain segments pull out and the NCA elongates. When the tension is relaxed, the chains contract. The stretching of NCA may contribute to the ductility of compacts made from nanoparticles, a subject of current research interest. In a well established technological application, carbon black and pyrogenic silica NCA produce remarkable increases in elastic modulus and tensile strength when added to commercial rubber. This may be due to the mechanical interaction between the polymer chains and NCA. However, basic mechanisms of NCA elasticity differ from those of molecular polymers. The alignment of chain segments when the NCA are subjected to tension probably results from rotation and translation at grain boundaries between neighboring nanocrystals. The elastic properties depend on the van der Waals forces between segments of the chain that fold to minimize surface free energy. Under tension, these segments pull out, but tend to reform when the tension is relaxed. The processes that lead to NCA formation and control the strength of interparticle bonds are briefly reviewed.     

3-巯基丙酸包裹的金纳米粒子自组装膜的制备及其层状周期性结构分析

制备了 3-巯基丙酸包裹的金钠米粒子水溶胶。在胺丙基三甲氧基硅烷覆盖的 Si或Si O2 基底上组装了上述金纳米粒子的单层膜和由 1 ,6-二巯基己烷联接的金纳米粒子多层膜。紫外 -可见吸收光谱和 X-射线衍射实验分析了多层膜的层状周期性结构     

Single‐cell resolution in high‐resolution synchrotron X‐ray CT imaging with gold nanoparticles

Gold nanoparticles are excellent intracellular markers in X‐ray imaging. Having shown previously the suitability of gold nanoparticles to detect small groups of cells with the synchrotron‐based computed tomography (CT) technique both ex vivo and in vivo, it is now demonstrated that even single‐cell resolution can be obtained in the brain at least ex vivo. Working in a small animal model of malignant brain tumour, the image quality obtained with different imaging modalities was compared. To generate the brain tumour, 1 × 10⁵ C6 glioma cells were loaded with gold nanoparticles and implanted in the right cerebral hemisphere of an adult rat. Raw data were acquired with absorption X‐ray CT followed by a local tomography technique based on synchrotron X‐ray absorption yielding single‐cell resolution. The reconstructed synchrotron X‐ray images were compared with images obtained by small animal magnetic resonance imaging. The presence of gold nanoparticles in the tumour tissue was verified in histological sections.     

Experimental Study of a Nanoparticle Virtual Impactor

A nanoparticle virtual impactor was constructed and its performance under different operating conditions was investigated. Experimental evaluations showed that the nanoparticle virtual impactor has a 50% cutoff size ranging from 15 to 60nm. Further, the cutoff size of 60nm can be achieved at an impactor chamber pressure of 220torr when the nozzle upstream pressure is 760torr. This pressure level is much higher than that of thin-plate orifice nozzle impactors, which require 12torr to achieve the cutoff size of 66nm. Thus, the proposed virtual impactor can be operated with a small vacuum pump, which is more preferable for practical applications.In this study, the effects of design parameters on the impactor performance have also been experimentally investigated. The parameters include the separation distance between the collection probe and the acceleration nozzle, the pressure ratio of the upstream and downstream chambers, the diameter ratio of the collection probe and the nozzle, the flow ratio of the minor and total flows, total mass flow rates and the upstream pressure. The experimental data obtained were then scaled with the Stokes number defined by previous researchers. The performance of the proposed nanoparticle virtual impactors can therefore be estimated when the operating variables are given or measured. An important finding in this parametric study is that the optimal diameter ratio of collection probe to nozzle is around 1.8. It is different from the value of 1.4 recommended in previous studies with virtual impactors for submicron particle applications.     

Interface Colloidal Deposition of Nanoparticle Wire Structures

Inspired by natural dewetting phenomena, such as the coffee‐ring effect, researchers are developing strategies for the controlled assembly of colloidal particles into functional nanoparticle conglomerates. Colloidal assembly techniques are regarded as green methods as they reduce or eliminate the use or generation of hazardous substances involved in other manufacturing modalities. This review discusses several recent developments in interface colloidal deposition for preparing nanoparticle wires and integrated nanoparticle wire arrays. Moreover, this review covers real applications of these structures for electric detection of chemical and biological molecules among other functions.     

Therapeutic Pretargeting with Gold Nanoparticles as Drug Candidates for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a binary approach for cancer treatment in which boron-10 atoms and thermal neutrons need to colocalize to become effective. Recent research in the development of BNCT drug candidates focuses increasingly on nanomaterials, with the advantages of high boron loadings and passive targeting due to the enhanced permeability and retention (EPR) effect. The use of small boron-rich gold nanoparticles (AuNPs) in combination with a pretargeting approach is proposed. Small sized polyethylene glycol–stabilized AuNPs (core size 4.1 ± 1.5 nm), are synthesized and functionalized with thiolated cobalt bis(dicarbollide) and tetrazine. To enable in vivo tracking of the AuNPs by positron emission tomography (PET), the core is doped with [⁶⁴Cu]CuCl₂. For the pretargeting approach, the monoclonal antibody Trastuzumab is functionalized with trans-cyclooctene-N-hydroxysuccinimide ester. After proving in vitro occurrence of the antibody conjugation onto the AuNPs by click reaction and the low toxicity of the AuNPs, the boron delivery system is evaluated in vivo using breast cancer xenograft bearing mice and PET imaging. Tumor uptake due to the EPR effect can be witnessed with ≈5% injected dose (ID) cm⁻³ at 24 h postinjection, but with slower clearance than expected. Therefore, no increased retention can be observed using the pretargeting strategy.     

Self‐Assembly of Functionalized Gold Nanoparticles with Rigid and Flexible Multifunctional Linkers

The interparticle spacing of carboxyl functionalized gold nanoparticles (Au–COOH) was mediated by rigid cross‐linkers, octa(3‐aminopropyl)octasilsesquioxane (POSS–NH₃ ⁺) and poly(amidoamine) dendrimer terminated with hydroxyl groups (PAMAM–OH), and a flexible polymeric linker, poly(hexanyl viologen) (6‐VP). Regular interparticle spacing was achieved by utilizing POSS–NH₃ ⁺ and PAMAM–OH dendrimer as cross‐linkers, whereas size growth of Au–COOH was observed featuring no interparticle spacing by utilizing 6‐VP as the cross‐linker.