Elucidating the effect of TiO2 nanoparticles on mung bean rhizobia via in vitro assay: Influence on growth, morphology, and plant growth promoting traits

Titanium dioxide nanoparticles (TiO2 NPs) are among the most commonly used nanomaterials and are most likely to end up in soil. Therefore, it is pertinent to study the interaction of TiO2 NPs with soil microorganisms. The present in vitro broth study evaluates the impacts of low-dose treatments (0, 1.0, 5.0, 10.0, 20.0, and 40.0 mg L-1 ) of TiO2 NPs on cell viability, morphology, and plant growth promoting (PGP) traits of rhizobia isolated from mung bean root nodule. Two types of TiO2 NPs, that is, mixture of anatase and rutile, and anatase alone were used in the study. These TiO2 NPs were supplemented in broth along with a multifunctional isolate (Bradyrhizobium sp.) and two reference cultures. The exposure of TiO2 (anatase+rutile) NPs at low concentrations (less than 20.0 mg L-1 ) enhanced the cell growth, and total soluble protein content, besides improving the phosphate solubilization, Indole-3-acetic acid (IAA) production, siderophore, and gibberellic acid production. The TiO2 (anatase) NPs enhanced exopolysaccharide (EPS) production by the test rhizobial cultures. The radical scavenging assay was performed to reveal the mode of action of the nano-TiO2 particles. The study revealed higher reactive oxygen species (ROS) generation by the TiO2 (anatase) NPs as compared with TiO2 (anatase+rutile) NPs. Exposure to TiO2 NPs also altered the morphology of rhizobial cells. The findings suggest that TiO2 NPs could act as promoters of PGP traits of PGP bacteria when applied at appropriate lower doses.

Transport of Nanoparticles into Plants and Their Detection Methods

Nanoparticle transport into plants is an evolving field of research with diverse applications in agriculture and biotechnology. This article provides an overview of the challenges and prospects associated with the transport of nanoparticles in plants, focusing on delivery methods and the detection of nanoparticles within plant tissues. Passive and assisted delivery methods, including the use of roots and leaves as introduction sites, are discussed, along with their respective advantages and limitations. The barriers encountered in nanoparticle delivery to plants are highlighted, emphasizing the need for innovative approaches (e.g., the stem as a new recognition site) to optimize transport efficiency. In recent years, research efforts have intensified, leading to an evendeeper understanding of the intricate mechanisms governing the interaction of nanomaterials with plant tissues and cells. Investigations into the uptake pathways and translocation mechanisms within plants have revealed nuanced responses to different types of nanoparticles. Additionally, this article delves into the importance of detection methods for studying nanoparticle localization and quantification within plant tissues. Various techniques are presented as valuable tools for comprehensively understanding nanoparticle-plant interactions. The reliance on multiple detection methods for data validation is emphasized to enhance the reliability of the research findings. The future outlooks of this field are explored, including the potential use of alternative introduction sites, such as stems, and the continued development of nanoparticle formulations that improve adhesion and penetration. By addressing these challenges and fostering multidisciplinary research, the field of nanoparticle transport in plants is poised to make significant contributions to sustainable agriculture and environmental management.

Next-Generation Nanopore Sensors Based on Conductive Pulse Sensing for Enhanced Detection of Nanoparticles

Nanopore sensing has been successfully used to characterize biological molecules with single-molecule resolution based on the resistive pulse sensing approach. However, its use in nanoparticle characterization has been constrained by the need to tailor the nanopore aperture size to the size of the analyte, precluding the analysis of heterogeneous samples. Additionally, nanopore sensors often require the use of high salt concentrations to improve the signal-to-noise ratio, which further limits their ability to study a wide range of nanoparticles that are unstable at high ionic strength. Here, a new paradigm in nanopore research that takes advantage of a polymer electrolyte system to comprise a conductive pulse sensing approach is presented. A finite element model is developed to explain the conductive pulse signals observed and compare these results with experiments. This system enables the analytical characterization of heterogeneous nanoparticle mixtures at low ionic strength . Furthermore, the wide applicability of the method is demonstrated by characterizing metallic nanospheres of varied sizes, plasmonic nanostars with various degrees of branching, and protein-based spherical nucleic acids with different oligonucleotide loadings. This system will complement the toolbox of nanomaterials characterization techniques to enable real-time optimization workflow for engineering a wide range of nanomaterials.

Spray Flame Synthesis and Multiscale Characterization of Carbon Black-Silica Hetero-Aggregates

The increasing demand for lithium-ion batteries requires constant improvements in the areas of production and recycling to reduce their environmental impact. In this context, this work presents a method for structuring carbon black aggregates by adding colloidal silica via a spray flame with the goal of opening up more choices for polymeric binders. The main focus of this research lies in the multiscale characterization of the aggregate properties via small-angle X-ray scattering, analytical disc centrifugation and electron microscopy. The results show successful formation of sinter-bridges between silica and carbon black leading to an increase in hydrodynamic aggregate diameter from 201 nm to up to 357 nm, with no significant changes in primary particle properties. However, segregation and coalescence of silica particles was identified for higher mass ratios of silica to carbon black, resulting in a reduction in the homogeneity of the hetero-aggregates. This effect was particularly evident for silica particles with larger diameters of 60 nm. Consequently, optimal conditions for hetero-aggregation were identified at mass ratios below 1 and particle sizes around 10 nm, at which homogenous distributions of silica within the carbon black structure were achieved. The results emphasise the general applicability of hetero-aggregation via spray flames with possible applications as battery materials.

Solid Lipid Nanoparticles vs. Nanostructured Lipid Carriers: A Comparative Review

Solid-lipid nanoparticles and nanostructured lipid carriers are delivery systems for the delivery of drugs and other bioactives used in diagnosis, therapy, and treatment procedures. These nanocarriers may enhance the solubility and permeability of drugs, increase their bioavailability, and extend the residence time in the body, combining low toxicity with a targeted delivery. Nanostructured lipid carriers are the second generation of lipid nanoparticles differing from solid lipid nanoparticles in their composition matrix. The use of a liquid lipid together with a solid lipid in nanostructured lipid carrier allows it to load a higher amount of drug, enhance drug release properties, and increase its stability. Therefore, a direct comparison between solid lipid nanoparticles and nanostructured lipid carriers is needed. This review aims to describe solid lipid nanoparticles and nanostructured lipid carriers as drug delivery systems, comparing both, while systematically elucidating their production methodologies, physicochemical characterization, and in vitro and in vivo performance. In addition, the toxicity concerns of these systems are focused on.

Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering

In this work, we take on an in-depth characterization of the complex particle structures made by spray flame synthesis. Because of the resulting hierarchical aggregates, very few measurement techniques are available to analyze their primary particle and fractal properties. Therefore, we use small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) to investigate the influence of the precursor concentration on the fractal structures of zirconia nanoparticles. The combination of information gained from these measurement results leads to a detailed description of the particle system, including the polydispersity and size distribution of the primary particles. Based on our findings, unstable process conditions could be identified at low precursor concentrations resulting in the broadest size distribution of primary particles with rough surfaces. Higher precursor concentrations lead to reproducible primary particle sizes almost independent of the initial precursor concentration. Regarding the fractal properties, the typical shape of aggregates for aerosols is present for the investigated range of precursor concentrations. In conclusion, the consistent results for SAXS and TEM show a conclusive characterization of a complex particle system, allowing for the identification of the underlying particle formation mechanism.

Hyaluronic Acid-Dexamethasone Nanoparticles for Local Adjunct Therapy of Lung Inflammation

The delivery of a dexamethasone formulation directly into the lung appears as an appropriate strategy to strengthen the systemic administration, reducing the dosage in the treatment of lung severe inflammations. For this purpose, a hyaluronic acid-dexamethasone formulation was developed, affording an inhalable reconstituted nanosuspension suitable to be aerosolized. The physico-chemical and biopharmaceutical properties of the formulation were tested: size, stability, loading of the spray-dried dry powder, reconstitution capability upon redispersion in aqueous media. Detailed structural insights on nanoparticles after reconstitution were obtained by light and X-ray scattering techniques. (1) The size of the nanoparticles, around 200 nm, is in the proper range for a possible engulfment by macrophages. (2) Their structure is of the core-shell type, hosting dexamethasone nanocrystals inside and carrying hyaluronic acid chains on the surface. This specific structure allows for nanosuspension stability and provides nanoparticles with muco-inert properties. (3) The nanosuspension can be efficiently aerosolized, allowing for a high drug fraction potentially reaching the deep lung. Thus, this formulation represents a promising tool for the lung administration via nebulization directly in the pipe of ventilators, to be used as such or as adjunct therapy for severe lung inflammation.

Facile Biogenic Synthesis and Characterization of Seven Metal-Based Nanoparticles Conjugated with Phytochemical Bioactives Using Fragaria ananassa Leaf Extract

In this investigation, for the first time, we used Fragaria ananassa (strawberry) leaf extract as a source of natural reducing, capping or stabilizing agents to develop an eco-friendly, cost-effective and safe process for the biosynthesis of metal-based nanoparticles including silver, copper, iron, zinc and magnesium oxide. Calcinated and non-calcinated zinc oxide nanoparticles also synthesized during a method different from our previous study. To confirm the successful formation of nanoparticles, different characterization techniques applied. UV-Vis spectroscopy, X-ray Diffraction (XRD) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS), Photon Cross-Correlation Spectroscopy (PCCS) and Fourier Transformed Infrared Spectroscopy (FT-IR) were used to study the unique structure and properties of biosynthesized nanoparticles. The results show the successful formation of metal-based particles in the range of nanometer, confirmed by different characterization techniques. Finally, the presented approach has been demonstrated to be effective in the biosynthesis of metal and metal oxide nanoparticles.

Green Silver and Gold Nanoparticles: Biological Synthesis Approaches and Potentials for Biomedical Applications

The nanomaterial industry generates gigantic quantities of metal-based nanomaterials for various technological and biomedical applications; however, concomitantly, it places a massive burden on the environment by utilizing toxic chemicals for the production process and leaving hazardous waste materials behind. Moreover, the employed, often unpleasant chemicals can affect the biocompatibility of the generated particles and severely restrict their application possibilities. On these grounds, green synthetic approaches have emerged, offering eco-friendly, sustainable, nature-derived alternative production methods, thus attenuating the ecological footprint of the nanomaterial industry. In the last decade, a plethora of biological materials has been tested to probe their suitability for nanomaterial synthesis. Although most of these approaches were successful, a large body of evidence indicates that the green material or entity used for the production would substantially define the physical and chemical properties and as a consequence, the biological activities of the obtained nanomaterials. The present review provides a comprehensive collection of the most recent green methodologies, surveys the major nanoparticle characterization techniques and screens the effects triggered by the obtained nanomaterials in various living systems to give an impression on the biomedical potential of green synthesized silver and gold nanoparticles.

Tackling Complex Analytical Tasks: An ISO/TS-Based Validation Approach for Hydrodynamic Chromatography Single Particle Inductively Coupled Plasma Mass Spectrometry

Nano-carrier systems such as liposomes have promising biomedical applications. Nevertheless, characterization of these complex samples is a challenging analytical task. In this study a coupled hydrodynamic chromatography-single particle-inductively coupled plasma mass spectrometry (HDC-spICP-MS) approach was validated based on the technical specification (TS) 19590:2017 of the international organization for standardization (ISO). The TS has been adapted to the hyphenated setup. The quality criteria (QC), e.g., linearity of the calibration, transport efficiency, were investigated. Furthermore, a cross calibration of the particle size was performed with values from dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to an additional Y-piece, an online-calibration routine was implemented. This approach allows the calibration of the ICP-MS during the dead time of the chromatography run, to reduce the required time and enhance the robustness of the results. The optimized method was tested with different gold nanoparticle (Au-NP) mixtures to investigate the characterization properties of HDC separations for samples with increasing complexity. Additionally, the technique was successfully applied to simultaneously determine both the hydrodynamic radius and the Au-NP content in liposomes. With the established hyphenated setup, it was possible to distinguish between different subpopulations with various NP loads and different hydrodynamic diameters inside the liposome carriers.

Green-Synthesized FeSO4 Nanoparticles Exhibit Antibacterial and Cytotoxic Activity by DNA Degradation

OBJECTIVE

The current study reports a green, rapid and one-pot synthesis of FeSO4 nanoparticles using Hibiscus rosasinensis floral extract as a reducing and capping agent. 0.5M of FeSO4 was stirred with the floral extract of H. rosasinensis for around 20 minutes at 37ºC and pH 7.

METHODS

The development of pink color was considered as the endpoint of reduction and the nanoparticles were characterized by UV-Vis spectrum, EDAX, DLS, FTIR, FESEM, and XRD. UV-Vis spectral analysis indicated a peak at 530 nm and EDAX measurement revealed the presence of Fe, S, O and C elements in the nanoparticle sample. The FTIR analysis showed amines, alcohol and alkene groups that act as capping agents for the produced nanoparticles. FESEM and XRD determination presented FeSO4 nanoparticles of 40-60 nm in size. The synthesized nanoparticles were found to have antibacterial activity against 6 pathogenic bacteria with MIC and MBC of 40 mg/mL.

RESULTS

To determine the toxicity at the eukaryotic level, brine shrimp toxicity assay was conducted and 100% mortality was found at concentrations >0.06 mg/mL. Gel shift assay suggested the mechanism of toxicity of FeSO4 NPs by binding and degradation of DNA molecules.

CONCLUSION

From the results, the authors demonstrate the ease of green synthesis of FeSO4 nanoparticles and its bioactivity that may have potential applications as drugs and drug delivery systems against various diseases.

Nanoparticle Characterization: What to Measure?

What to measure? is a key question in nanoscience, and it is not straightforward to address as different physicochemical properties define a nanoparticle sample. Most prominent among these properties are size, shape, surface charge, and porosity. Today researchers have an unprecedented variety of measurement techniques at their disposal to assign precise numerical values to those parameters. However, methods based on different physical principles probe different aspects, not only of the particles themselves, but also of their preparation history and their environment at the time of measurement. Understanding these connections can be of great value for interpreting characterization results and ultimately controlling the nanoparticle structure-function relationship. Here, the current techniques that enable the precise measurement of these fundamental nanoparticle properties are presented and their practical advantages and disadvantages are discussed. Some recommendations of how the physicochemical parameters of nanoparticles should be investigated and how to fully characterize these properties in different environments according to the intended nanoparticle use are proposed. The intention is to improve comparability of nanoparticle properties and performance to ensure the successful transfer of scientific knowledge to industrial real-world applications.

A Microfluidic Split-Flow Technology for Product Characterization in Continuous Low-Volume Nanoparticle Synthesis

A key aspect of microfluidic processes is their ability to perform chemical reactions in small volumes under continuous flow. However, a continuous process requires stable reagent flow over a prolonged period. This can be challenging in microfluidic systems, as bubbles or particles easily block or alter the flow. Online analysis of the product stream can alleviate this problem by providing a feedback signal. When this signal exceeds a pre-defined range, the process can be re-adjusted or interrupted to prevent contamination. Here we demonstrate the feasibility of this concept by implementing a microfluidic detector downstream of a segmented-flow system for the synthesis of lipid nanoparticles. To match the flow rate through the detector to the measurement bandwidth independent of the synthesis requirements, a small stream is sidelined from the original product stream and routed through a measuring channel with 2 × 2 µm cross-section. The small size of the measuring channel prevents the entry of air plugs, which are inherent to our segmented flow synthesis device. Nanoparticles passing through the small channel were detected and characterized by quantitative fluorescence measurements. With this setup, we were able to count single nanoparticles. This way, we were able to detect changes in the particle synthesis affecting the size, concentration, or velocity of the particles in suspension. We envision that the flow-splitting scheme demonstrated here can be transferred to detection methods other than fluorescence for continuous monitoring and feedback control of microfluidic nanoparticle synthesis.

High-Performance Chromatographic Characterization of Surface Chemical Heterogeneities of Fluorescent Organic-Inorganic Hybrid Core-Shell Silica Nanoparticles

In contrast to small-molar-mass compounds, detailed structural investigations of inorganic core-organic ligand shell hybrid nanoparticles remain challenging. The assessment of batch-reaction-induced heterogeneities of surface chemical properties and their correlation with particle size has been a particularly long-standing issue. Applying a combination of high-performance liquid chromatography (HPLC) and gel permeation chromatography (GPC) to ultra-small (<10 nm diameter) poly(ethylene glycol)-coated (PEGylated) fluorescent core-shell silica nanoparticles, we elucidate here previously unknown surface heterogeneities resulting from varying dye conjugation to nanoparticle silica cores and surfaces. Heterogeneities are predominantly governed by dye charge, as corroborated by molecular dynamics simulations. We demonstrate that this insight enables the development of synthesis protocols to achieve PEGylated and targeting ligand-functionalized PEGylated silica nanoparticles with dramatically improved surface chemical homogeneity, as evidenced by single-peak HPLC chromatograms. Because surface chemical properties are key to all nanoparticle interactions, we expect these methods and fundamental insights to become relevant to a number of systems for applications, including bioimaging and nanomedicine.

Efficient Copper Removal from an Aqueous Anvironment using a Novel and Hybrid Nanoadsorbent Based on Derived-Polyethyleneimine Linked to Silica Magnetic Nanocomposites

Due to the extreme rise of sludge pollution with heavy metals (e.g. copper), the options for its disposal or treatment are decreasing. On the contrary, properly heavy metal-cleaned sludge can be used as an alternative sustainable energy and agriculture source. The aim of this study was to develop a novel nanoadsorbent, based on irreversibly linked amino-rich polymer onto previously silica-coated magnetic nanoparticles (MNPs) that can be applied efficiently for metal removal. MNPs were coated uniformly by 3 nm thick silica layer (core-shell structure), and were additionally modified with systematic covalent attachment of derived branched polyethyleneimine (bPEI). The formed structure of synthesized MNPs composite was confirmed with several analytical techniques. Importantly, nanoadsorbents exhibit high density of chelating amino groups and large magnetic force for easier separation. The importance of introduced bPEI, effect of pH, initial heavy metal concentration onto copper uptake efficiency and, further, nanoadsorbent regeneration, were studied and explained in detail. The adsorption isotherm was well fitted with Langmuir model, and the maximum adsorption capacity was shown to be 143 mg·g¹ for Cu2+. The reusability and superior properties of silica-coated MNPs functionalized with derived-bPEI for copper adsorption underlie its potential for the removal application from heavy metals contaminated sludge.

Investigation of nano-sized debris released from CoCrMo secondary interfaces in total hip replacements: Digestion of the flakes

The in vivo release of wear debris and corrosion products from the metallic interfaces of total hip replacements is associated with a wide spectrum of adverse body reactions and systemic manifestations. The origin of debris and the electrochemical conditions at the sites of material loss both play a role in determining the physicochemical characteristics of the particles, and thus influence their in vivo reactivity. Debris retrieved from revised CoCrMo tapers and cement-stem interfaces consists of heterogeneous flakes that comprise mechanically mixed metal particles, corrosion products and organic material. Detailed investigation of the size and composition of the metal debris contained within these composites requires the digestion of the flakes to release the small metal particles. Here, we compare alkaline and enzymatic digestion methods that both aim to fragment the flakes and reveal their smallest building blocks. The characterization of debris cleaned with both methods revealed crystalline Cr oxide nanoparticles and clusters. Comparison between the treatments showed that the alkaline method is more efficient in fragmenting the flakes and provided cleaner and generally smaller nanoparticles than exhibited in debris released with the enzymatic treatment. The provision of cleaner nanoparticles from the alkaline method also allows the physicochemical properties of the particles to be more clearly identified. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 424-434, 2019.

Characterization of Mega-Dalton-Sized Nanoparticles by Superconducting Tunnel Junction Cryodetection Mass Spectrometry

The characterization of nanomaterials is critical to understand the size/structure-dependent properties of these particles. In this report, a form of heavy ion mass spectrometry, namely, superconducting tunnel junction (STJ) cryodetection mass spectrometry (MS) is used to characterize quantum dot semiconductor nanocrystals and gold nanoparticles. The nanoparticles studied ranged in mass from 200 kDa to >1.5 MDa and included lead sulfide quantum dots, various cadmium selenide and/or telluride-based core-shell quantum dots coated with different ligands, and gold nanoparticles. Nanoparticles were ionized by both matrix-assisted laser desorption ionization (MALDI) and laser desorption ionization (LDI), shot with an aimed ion gun into a flight tube, mass separated by time-of-flight (TOF), and detected by an energy-sensitive STJ cryodetector. STJ cryodetection MS can be used to analyze intact heterogeneous nanoparticles, allowing determination of average particle mass, dispersity, and ligand loading. Some nanoparticles, however, do undergo fragmentation during the MALDI or LDI-TOF mass analyses. The measurement of the energy deposited into the detector was found to be different for different types of particles. Metastable fragments from these nanoparticles were observed at lower energies. The lower energies deposited for metastable fragments can provide insight into the stability and surface compositions of these materials. Cadmium selenide core-shell quantum dots (655 nm emission) conjugated to biomacromolecules, such as cholera toxin B and human serum transferrin, were also analyzed. When compared to unconjugated particles by mass, it was determined that ∼96 cholera toxin B and ∼14 transferrin proteins were attached to the surface of these nanoparticles.

Measuring the Hydrodynamic Size of Nanoparticles Using Fluctuation Correlation Spectroscopy

Fluctuation correlation spectroscopy (FCS) is a well-established analytical technique traditionally used to monitor molecular diffusion in dilute solutions, the dynamics of chemical reactions, and molecular processes inside living cells. In this review, we present the recent use of FCS for measuring the size of colloidal nanoparticles in solution. We review the theoretical basis and experimental implementation of this technique and its advantages and limitations. In particular, we show examples of the use of FCS to measure the size of gold nanoparticles, monitor the rotational dynamics of gold nanorods, and investigate the formation of protein coronas on nanoparticles.

Multiparameter Quantification of Liposomal Nanomedicines at the Single-Particle Level by High-Sensitivity Flow Cytometry

Drug-encapsulated liposomes have been considered the most clinically acceptable drug-delivery systems. However, current methods fall short in the quantitative characterization of individual nanoliposomes because of their small sizes and large heterogeneity. Here, we report a high-throughput method for the absolute quantification of particle size, drug content, fraction of drug encapsulation, and particle concentration of liposomal nanomedicines at the single-particle level. A laboratory-built high-sensitivity flow cytometer was used to simultaneously detect the side-scatter and fluorescence signals generated by individual nanomedicine particles at a speed up to 10 000 nanoparticles/min. To cope with the size dependence of the refractive index of liposomal nanomedicines, different sizes of doxorubicin-loaded liposomes were fabricated and characterized to serve as the calibration standards for the measurement of both particle size and drug content. This method provides a highly practical platform for the characterization of liposomal nanomedicines, and broad applications can be envisioned.

Quantifying the Impact of Nanoparticle Coatings and Nonuniformities on XPS Analysis: Gold/Silver Core-Shell Nanoparticles

Spectral modeling of photoelectrons can serve as a valuable tool when combined with X-ray photoelectron spectroscopy (XPS) analysis. Herein, a new version of the NIST Simulation of Electron Spectra for Surface Analysis (SESSA 2.0) software, capable of directly simulating spherical multilayer NPs, was applied to model citrate stabilized Au/Ag-core/shell nanoparticles (NPs). The NPs were characterized using XPS and scanning transmission electron microscopy (STEM) to determine the composition and morphology of the NPs. The Au/Ag-core/shell NPs were observed to be polydispersed in size, nonspherical, and contain off-centered Au-cores. Using the average NP dimensions determined from STEM analysis, SESSA spectral modeling indicated that washed Au/Ag-core-shell NPs were stabilized with a 0.8 nm layer of sodium citrate and a 0.05 nm (one wash) or 0.025 nm (two wash) layer of adventitious hydrocarbon, but did not fully account for the observed XPS signal from the Au-core. This was addressed by a series of simulations and normalizations to account for contributions of NP nonsphericity and off-centered Au-cores. Both of these nonuniformities reduce the effective Ag-shell thickness, which effect the Au-core photoelectron intensity. The off-centered cores had the greatest impact for the particles in this study. When the contributions from the geometrical nonuniformities are included in the simulations, the SESSA generated elemental compositions that matched the XPS elemental compositions. This work demonstrates how spectral modeling software such as SESSA, when combined with experimental XPS and STEM measurements, advances the ability to quantitatively assess overlayer thicknesses for multilayer core-shell NPs and deal with complex, nonideal geometrical properties.

Biointeractions of ultrasmall glutathione-coated gold nanoparticles: effect of small size variations

Recent in vivo studies have established ultrasmall (<3 nm) gold nanoparticles coated with glutathione (AuGSH) as a promising platform for applications in nanomedicine. However, systematic in vitro investigations to gain a more fundamental understanding of the particles' biointeractions are still lacking. Herein we examined the behavior of ultrasmall AuGSH in vitro, focusing on their ability to resist aggregation and adsorption from serum proteins. Despite having net negative charge, AuGSH particles were colloidally stable in biological media and able to resist binding from serum proteins, in agreement with the favorable bioresponses reported for AuGSH in vivo. However, our results revealed disparate behaviors depending on nanoparticle size: particles between 2 and 3 nm in core diameter were found to readily aggregate in biological media, whereas those strictly under 2 nm were exceptionally stable. Molecular dynamics simulations provided microscopic insight into interparticle interactions leading to aggregation and their sensitivity to the solution composition and particle size. These results have important implications, in that seemingly small variations in size can impact the biointeractions of ultrasmall AuGSH, and potentially of other ultrasmall nanoparticles as well.

Conjugation of Polymer-Coated Gold Nanoparticles with Antibodies-Synthesis and Characterization

The synthesis of polymer-coated gold nanoparticles with high colloidal stability is described, together with appropriate characterization techniques concerning the colloidal properties of the nanoparticles. Antibodies against vascular endothelial growth factor (VEGF) are conjugated to the surface of the nanoparticles. Antibody attachment is probed by different techniques, giving a guideline about the characterization of such conjugates. The effect of the nanoparticles on human adenocarcinoma alveolar basal epithelial cells (A549) and human umbilical vein endothelial cells (HUVECs) is probed in terms of internalization and viability assays.

Effect of Carbon Nanotubes Upon Emissions From Cutting and Sanding Carbon Fiber-Epoxy Composites

Carbon nanotubes (CNTs) are being incorporated into structural composites to enhance material strength. During fabrication or repair activities, machining nanocomposites may release CNTs into the workplace air. An experimental study was conducted to evaluate the emissions generated by cutting and sanding on three types of epoxy-composite panels: Panel A containing graphite fibers, Panel B containing graphite fibers and carbon-based mat, and Panel C containing graphite fibers, carbon-based mat, and multi-walled CNTs. Aerosol sampling was conducted with direct-reading instruments, and filter samples were collected for measuring elemental carbon (EC) and fiber concentrations. Our study results showed that cutting Panel C with a band saw did not generate detectable emissions of fibers inspected by transmission electron microscopy but did increase the particle mass, number, and EC emission concentrations by 20% to 80% compared to Panels A and B. Sanding operation performed on two Panel C resulted in fiber emission rates of 1.9×10⁸ and 2.8×10⁶ fibers per second (f/s), while no free aerosol fibers were detected from sanding Panels A and B containing no CNTs. These free CNT fibers may be a health concern. However, the analysis of particle and EC concentrations from these same samples cannot clearly indicate the presence of CNTs, because extraneous aerosol generation from machining the composite epoxy material increased the mass concentrations of the EC.

Removal of thiol ligands from surface-confined nanoparticles without particle growth or desorption

Size-dependent properties of surface-confined inorganic nanostructures are of interest for applications ranging from sensing to catalysis and energy production. Ligand-stabilized nanoparticles are attractive precursors for producing such nanostructures because the stabilizing ligands may be used to direct assembly of thoroughly characterized nanoparticles on the surface. Upon assembly; however, the ligands block the active surface of the nanoparticle. Methods used to remove these ligands typically result in release of nanoparticles from the surface or cause undesired growth of the nanoparticle core. Here, we demonstrate that mild chemical oxidation (50 ppm of ozone in nitrogen) oxidizes the thiolate headgroups, lowering the ligand's affinity for the gold nanoparticle surface and permitting the removal of the ligands at room temperature by rinsing with water. XPS and TEM measurements, performed using a custom planar analysis platform that permits detailed imaging and chemical analysis, provide insight into the mechanism of ligand removal and show that the particles retain their core size and remain tethered on the surface core during treatment. By varying the ozone exposure time, it is possible to control the amount of ligand removed. Catalytic carbon monoxide oxidation was used as a functional assay to demonstrate ligand removal from the gold surface for nanoparticles assembled on a high surface area support (fumed silica).

Nanophotonic force microscopy: characterizing particle-surface interactions using near-field photonics

Direct measurements of particle-surface interactions are important for characterizing the stability and behavior of colloidal and nanoparticle suspensions. Current techniques are limited in their ability to measure pico-Newton scale interaction forces on submicrometer particles due to signal detection limits and thermal noise. Here we present a new technique for making measurements in this regime, which we refer to as nanophotonic force microscopy. Using a photonic crystal resonator, we generate a strongly localized region of exponentially decaying, near-field light that allows us to confine small particles close to a surface. From the statistical distribution of the light intensity scattered by the particle we are able to map out the potential well of the trap and directly quantify the repulsive force between the nanoparticle and the surface. As shown in this Letter, our technique is not limited by thermal noise, and therefore, we are able to resolve interaction forces smaller than 1 pN on dielectric particles as small as 100 nm in diameter.

Light-scattering detection below the level of single fluorescent molecules for high-resolution characterization of functional nanoparticles

Ultrasensitive detection and characterization of single nanoparticles (<100 nm) is important in nanotechnology and life sciences. Direct measurement of the elastically scattered light from individual nanoparticles represents the simplest and the most direct method for particle detection. However, the sixth-power dependence of scattering intensity on particle size renders very small particles indistinguishable from the background. Adopting strategies for single-molecule fluorescence detection in a sheathed flow, here we report the development of high sensitivity flow cytometry (HSFCM) that achieves real-time light-scattering detection of single silica and gold nanoparticles as small as 24 and 7 nm in diameter, respectively. This unprecedented sensitivity enables high-resolution sizing of single nanoparticles directly based on their scattered intensity. With a resolution comparable to that of TEM and the ease and speed of flow cytometric analysis, HSFCM is particularly suitable for nanoparticle size distribution analysis of polydisperse/heterogeneous/mixed samples. Through concurrent fluorescence detection, simultaneous insights into the size and payload variations of engineered nanoparticles are demonstrated with two forms of clinical nanomedicine. By offering quantitative multiparameter analysis of single nanoparticles in liquid suspensions at a throughput of up to 10 000 particles per minute, HSFCM represents a major advance both in light-scattering detection technology and in nanoparticle characterization.

Weighing nanoparticles in solution at the attogram scale

Physical characterization of nanoparticles is required for a wide range of applications. Nanomechanical resonators can quantify the mass of individual particles with detection limits down to a single atom in vacuum. However, applications are limited because performance is severely degraded in solution. Suspended micro- and nanochannel resonators have opened up the possibility of achieving vacuum-level precision for samples in the aqueous environment and a noise equivalent mass resolution of 27 attograms in 1-kHz bandwidth was previously achieved by Lee et al. [(2010) Nano Lett 10(7):2537-2542]. Here, we report on a series of advancements that have improved the resolution by more than 30-fold, to 0.85 attograms in the same bandwidth, approaching the thermomechanical noise limit and enabling precise quantification of particles down to 10 nm with a throughput of more than 18,000 particles per hour. We demonstrate the potential of this capability by comparing the mass distributions of exosomes produced by different cell types and by characterizing the yield of self-assembled DNA nanoparticle structures.

Dual-cycle dielectrophoretic collection rates for probing the dielectric properties of nanoparticles

A new DEP spectroscopy method and supporting theoretical model is developed to systematically quantify the dielectric properties of nanoparticles using continuously pulsed DEP collection rates. Initial DEP collection rates, that are dependent on the nanoparticle dielectric properties, are an attractive alternative to the crossover frequency method for determining dielectric properties. The new method introduces dual-cycle amplitude modulated and frequency-switched DEP (dual-cycle DEP) where the first collection rate with a fixed frequency acts as a control, and the second collection rate frequency is switched to a chosen value, such that, it can effectively probe the dielectric properties of the nanoparticles. The application of the control means that measurement variation between DEP collection experiments is reduced so that the frequency-switched probe collection is more effective. A mathematical model of the dual-cycle method is developed that simulates the temporal dynamics of the dual-cycle DEP nanoparticle collection system. A new statistical method is also developed that enables systematic bivariate fitting of the multifrequency DEP collection rates to the Clausius-Mossotti function, and is instrumental for determining dielectric properties. A Monte-Carlo simulation validates that collection rates improve estimation of the dielectric properties, compared with the crossover method, by exploiting a larger number of independent samples. Experiments using 200 nm diameter latex nanospheres suspended in 0.2 mS/m KCl buffer yield a nanoparticle conductivity of 26 mS/m that lies within 8% of the expected value. The results show that the dual-frequency method has considerable promise particularly for automated DEP investigations and associated technologies.

A quantitative assessment of nanoparticle-ligand distributions: implications for targeted drug and imaging delivery in dendrimer conjugates

Functional nanoparticles often contain ligands including targeting molecules, fluorophores, and/or active moieties such as drugs. Characterizing the number of these ligands bound to each particle and the distribution of nanoparticle-ligand species is important for understanding the nanomaterial's function. In this study, the amide coupling methods commonly used to conjugate ligands to poly(amidoamine) (PAMAM) dendrimers were examined. A skewed Poisson distribution was observed and quantified using HPLC for two sets of dendrimer-ligand samples prepared using the amine-terminated form of the PAMAM dendrimer and a partially acetylated form of the PAMAM dendrimer that has been used for targeted in vivo drug delivery. The prepared samples had an average number of ligands per dendrimer ranging from 0.4 to 13. Distributions identified by HPLC are in excellent agreement with the mean ligand/dendrimer ratio, measured by (1)H NMR, gel permeation chromatography (GPC), and potentiometric titration. These results provide insight into the heterogeneity of distributions that are obtained for many classes of nanomaterials to which ligands are conjugated and belie the use of simple cartoon models that present the "average" number of ligands bound as a physically meaningful representation for the material.

Formation and properties of magnetic chains for 100 nm nanoparticles used in separations of molecules and cells

Optical observations of 100 nm metallic magnetic nanoparticles are used to study their magnetic field induced self assembly. Chains with lengths of tens of microns are observed to form within minutes at nanoparticle concentrations of 10(10) per mL. Chain rotation and magnetophoresis are readily observed, and SEM reveals that long chains are not simple single particle filaments. Similar chains are detected for several 100 nm commercial bio-separation nanoparticles. We demonstrate the staged magnetic condensation of different types of nanoparticles into composite structures and show that magnetic chains bind to immunomagnetically labeled cells, serving as temporary handles which allow novel magnetic cell manipulations.

Theory for nanoparticle retention time in the helical channel of quadrupole magnetic field-flow fractionation

Quadrupole magnetic field-flow fractionation (QMgFFF) is a separation and characterization technique for magnetic nanoparticles such as those used for cell labeling and for targeted drug therapy. A helical separation channel is used to efficiently exploit the quadrupole magnetic field. The fluid and sample components therefore have angular and longitudinal components to their motion in the thin annular space occupied by the helical channel. The retention ratio is defined as the ratio of the times for non retained and a retained material to pass through the channel. Equations are derived for the respective angular and longitudinal components to retention ratio.