Influence of different cleaning processes on the surface chemistry of gold nanoparticles

Novel TiO2-Supported Gold Nanoflowers for Efficient Photocatalytic NOx Abatement

In this study, we pioneered the synthesis of nanoflower-shaped TiO2-supported Au photocatalysts and investigated their properties. Au nanoflowers (Au NFs) were prepared by a Na-citrate and hydroquinone-based preparation method, followed by wet impregnation of the derived Au NFs on the surface of TiO2 nanorods (TNR). A uniform and homogeneous distribution of Au NFs was observed in the TNR + NF(0.7) sample (lower Na-citrate concentration), while their distribution was heterogeneous in the TNR + NF(1.4) sample (higher Na-citrate concentration). The UV-Vis DR spectra revealed the size- and shape-dependent optical properties of the Au NFs, with the LSPR effect observed in the visible region. The solid-state EPR spectra showed the presence of Ti3+, oxygen vacancies and electron interactions with organic compounds on the catalyst surface. In the case of the TNR + NF(0.7) sample, high photocatalytic activity was observed in the H2-assisted reduction of NO2 to N2 at room temperature under visible-light illumination. In contrast, the TNR + NF(1.4) catalyst as well as the heat-treated samples showed no ability to reduce NO2 under visible light, indicating the presence of deformed Au NFs limiting the LSPR effect. These results emphasized the importance of the choice of synthesis method, as this could strongly influence the photocatalytic activity of the Au NFs.

Conjugation to gold nanoparticles of methionine gamma-lyase, a cancer-starving enzyme. Physicochemical characterization of the nanocomplex for prospective nanomedicine applications

The pyridoxal 5'-dependent enzyme methionine γ-lyase (MGL) catalyzes the degradation of methionine. This activity has been profitable to develop an antitumor agent exploiting the strict dependence of most malignant cells on the availability of methionine. Indeed, methionine depletion blocks tumor proliferation and leads to an increased susceptibility to anticancer drugs. Here, we explore the conjugation of MGL to gold nanoparticles capped with citrate (AuNPs) as a novel strategy to deliver MGL to cancer cells. Measurements of Transmission Electron Microscopy, Dynamic Light Scattering, Asymmetrical Flow Field-Flow Fractionation, X-ray Photoelectron Spectroscopy, and Circular Dichroism allowed to achieve an extensive biophysical and biochemical characterization of the MGL-AuNP complex including particle size, size distribution, MGL loading yield, enzymatic activity, and impact of gold surface on protein structure. Noticeably, we found that activity retention was improved over time for the enzyme adsorbed to AuNPs with respect to the enzyme free in solution. The acquired body of knowledge on the nanocomplex properties and this encouraging stabilizing effect upon conjugation are the necessary basis for further studies aimed at the evaluation of the therapeutic potential of MGL-AuNP complex in a biological milieu.

High-Throughput Nanoparticle Characterization via Glow Discharge Optical Emission Spectroscopy Elemental Mapping

Nanoparticle (NP) characterization is critical in many fields due to the use of NPs in numerous applications. Traditional NP characterization techniques, however, are limited by low sample throughput, and few can measure the size and elemental composition. Furthermore, sample throughput limitations are compounded in elemental mapping (EM) techniques for obtaining NP spatial distribution. Glow discharge optical emission spectroscopy (GDOES) EM can provide large area maps directly and cost-effectively from solid samples within tens of seconds. Here, GDOES EM is demonstrated for the first time for NP characterization in terms of mass, elemental composition, and size/structure dimensions. The effects of GD pulsed power, pressure, and sample substrate were studied, and optimized conditions resulted in limits of detection at single pg levels. While this is not at the level of single nanoparticle sensitivity, size differentiation of Ag and Au nanoparticles was successfully demonstrated between 5 and 100 nm, while the internal dimensions of complex core-shell NPs were also identified through the optical emission changes as a function of time.

Analytical separation techniques: toward achieving atomic precision in nanomaterials science

The size- and shape-dependence of the properties are the most characteristic features of nanoscale matter. In many types of nanomaterials, there is a size regime wherein every atom counts. In order to fully realize the idea of 'maneuvering things atom by atom' envisioned by Richard Feynman, synthesis and separation of nanoscale matter with atomic precision are essential. It is therefore not surprising that analytical separation techniques have contributed tremendously toward understanding the size- as well as shape-dependent properties of nanomaterials. Fascinating properties of nanomaterials would not have been explored without the use of these techniques. Here we discuss the pivotal role of analytical separation techniques in the progress of nanomaterials science. We begin with a brief overview of some of the key analytical separation techniques that are of tremendous importance in nanomaterials research. Then we describe how each of these techniques has contributed to the advancements in nanomaterials science taking some of the nanosystems as examples. We discuss the limitations and challenges of these techniques and future perspectives.

Selection of cryoprotectants for freezing and freeze-drying of gold nanoparticles towards further uses in various applications

Recently, cryopreservation of AuNPs without aggregation has been attempted to improve their long-term stability. This study investigated criteria to select cryoprotectants for AuNPs using a variety of materials, including sugar (sucrose), surfactant (Tween 20), polymers (polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP)), and biopolymer (pectin). For cryoprotective performance, UV-vis spectroscopy reveals the potential of all cryoprotectants for preventing citrate-capped AuNPs (cit-AuNPs) from irreversible aggregation under freezing. While sucrose, PVP, and pectin were more suitable than Tween 20 and PVA as cryoprotectants for lyophilization of AuNPs with the maintained redispersability. For storage and further use, Luria-Bertani agar plate, dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicate impacts of the cryoprotectant coexisted with AuNPs after resuspension and imply that washing of the restored AuNPs is encouraged. Otherwise, running the restored AuNPs through applications, such as functionalization, protein conjugation, and surface-enhanced Raman scattering (SERS), without washing the cryoprotectant could lead to inaccurate results. This study also serves as a guideline for a comprehensive practice flow of AuNP handling, encompassing the synthesis step, cryopreservation, and use after resuspension.

Bimetallic gold-platinum nanoparticles as a drug delivery system coated with a new drug to target glioblastoma

A drug delivery nanosystem of noble bimetallic nanoparticles (NPs) which consists of Au NPs capped with Pt NPs (Au@Pt NPs) is constructed and functionalised with a quinazoline based small molecule (Au@Pt@Q NPs), acting as a theranostic agent against glioblastoma. Two different hydrothermal synthetic procedures for bimetallic Au@Pt NPs are presented and the resulting nanostructures are fully characterised by means of spectroscopic and microscopic methods. The imaging and targeting capacity of the new drug delivery system is assessed through fluorescent optical microscopy and cytotoxicity evaluations. The constructed Au@Pt NPs consist a monodispersed colloidal solution of 25 nm with photoluminescent, fluorescent and X-Ray absorption properties that confirm their diagnostic potential. Haemolysis testing demonstrated that Au@Pt NPs are biocompatible and fluorescent microscopy confirmed their entering the cells. Cytological evaluation of the NPs through MTT assay showed that they do not inhibit the proliferation of control cell line HEK293, whereas they are toxic in U87MG, U251 and D54 glioblastoma cell lines; rendering them selective targeting agents for treating glioblastoma.

Human blood biocompatibility and immunogenicity of scFvD2B PEGylated gold nanoparticles

Single chain variable D2B antibody fragments (scFvD2Bs) exhibit high affinity binding to prostate specific membrane antigens overexpressed in metastatic prostate cancer (PC). Conjugation of scFvD2B to gold nanoparticles (AuNPs) would enhance its stability and plasma half-life circulation to shuttle theranostic agents in PC. In this study, we synthesized PEGylated scFvD2B-AuNPs (AuNPs-scFvD2B-PEG) and tested their integrity, biocompatibility, and immunogenicity in freshly withdrawn human blood. Prior to blood incubation, Zeta potential measurements, UV-Vis spectroscopy, and dynamic light scattering (DLS) were used to assess the physicochemical properties of our nano-complexes in the presence or absence of PEGylation. A surface plasmon resonance band shift of 2 and 4 nm confirmed the successful coating for AuNPs-scFvD2B and AuNPs-scFvD2B-PEG, respectively. Likewise, DLS revealed a size increase of ∼3 nm for AuNPs-scFvD2B and ∼19 nm for AuNPs-scFvD2B-PEG. Zeta potential increased from -34 to -19 mV for AuNPs-scFvD2B and reached -3 mV upon PEGylation. Similar assessment measures were applied post-incubation in human blood with additional immunogenicity tests, such as hemolysis assay, neutrophil function test, and pyridine formazan extraction. Interestingly, grafting PEG chains on AuNPs-scFvD2B precluded the binding of blood plasma proteins and reduced neutrophil activation level compared with naked AuNPs-citrate counterparts. Most likely, a hydrated negative PEG cloud shielded the NPs rendering blood compatiblility with less than 10% hemolysis. In conclusion, the biocompatible AuNPs-scFvD2B-PEG presents promising characteristics for PC targeted therapy, with minimal protein adsorption affinity, low immunorecognition, and reduced hemolytic activity.

Centrifugation-induced assembly of dense hotspots based SERS substrate for enhanced Raman scattering and quenched fluorescence

Hanging (aggregation stuck to the centrifugal tube) in the centrifugation process is always regarded as an unwanted condition. In this work, we develop a centrifugation-induced assembly of dense hotspots surface-enhanced Raman scattering (SERS) substrates from the hanging phenomenon. We discovered interesting sintering-resistant behavior (maintain the sharp nanotip features) of star-like Au nanoparticles after centrifugation-induced assembly, which is in stark contrast with the sintering phenomenon of sphere-like nanoparticles. We also found that one side of centrifugal-induced Au assemblies is two-dimensional (2D, root mean square (rms) roughness down to ∼10 nm), while the other is three-dimensional (3D, rms roughness more than 100 nm). The close-packed feature of the Au assemblies makes them candidates as dense hotspots based SERS substrates. Through systematic investigation of SERS performance of centrifugation-induced assemblies with different morphology (star-like and sphere-like, 2D and 3D), it was found that the 3D side of star-like Au nanoparticles assembly exhibits the highest SERS enhancement together with quenched fluorescence. The star-like SERS substrate also displays high detection uniformity (with 10^-7M Rhodamine 6G) and a low detection limit (down to 10^-12M Rhodamine 6G).

Review of ecotoxicological studies of widely used polystyrene nanoparticles

With polystyrene nanoparticles being widely used in various applications, there is a great need for deeper knowledge on the safety, fate and biological effects of these particles on both individual living organisms and the whole ecosystems. Due to this, there is a growing interest in performing ecotoxicological studies using model plastic nanoparticles, and consequently it generates an increasing number of published papers describing the negative impact on wildlife caused by such nanoparticles. Polystyrene is the most studied nanosized plastic, therefore this review focuses on research conducted with manufactured polystyrene nanoparticles. The aim of the present article is to provide a critical methodological outline of the existing ecotoxicological studies on the effects of polystyrene nanoparticles on aquatic organisms. Going through the published articles, we noted that particle characterization especially in the test medium, can be improved. The analysis also highlights the importance of purifying the polystyrene nanoparticles before studying its toxicity. Furthermore, the size characterization of such nanoparticles is underemphasized, and in future studies, authors should consider including more techniques to achieve this goal. Finally, short-term or direct exposure scenarios do not add the most environmentally relevant knowledge in terms of the toxicity caused by polystyrene nanoparticles.

Probing N-Heterocyclic Carbene Surfaces with Laser Desorption Ionization Mass Spectrometry

The proliferation of N-heterocyclic carbene (NHC) self-assembled monolayers (SAMs) on gold surfaces stems from their exceptional stability compared to conventional thiol-SAMs. The prospect of biological applications for NHC-SAMs on gold shows the need for biocompatible techniques (e.g., large biomolecule detection and high throughput) that assesses SAM molecular composition. Herein, we demonstrate that laser desorption ionization mass spectrometry (LDI-MS) is a powerful and facile probe of NHC surface chemistry. LDI-MS of prototypical imidazole-NHC- and benzimidazole-NHC-functionalized AuNPs yields exclusively [NHC₂Au]⁺ ions and not larger gold clusters. Employing benzimidazole-NHC isotopologues, we explore how monolayers pack on a single AuNP and the lability of the NHCs once ligated. Quantitative analysis of the homoleptic and heteroleptic [NHC₂Au]⁺ ions is performed by comparing to a binomial model representative of a randomized monolayer. Lastly, the reduction of nitro-NHC-AuNPs to amine-NHC-AuNPs is tracked via LDI-MS signals, illustrating the ability of LDI-MS to probe postsynthetic modifications of the anchored NHCs, which is critical for current and future applications of NHC surfaces.

A bioinspired approach to fabricate fluorescent nanotubes with strong water adhesion by soft template electropolymerization and post-grafting

HYPOTHESIS

In this original work, we aim to control both the surface wetting and fluorescence properties of extremely ordered and porous conducting polymer nanotubes prepared by soft template electropolymerization and post-grafting. For reaching this aim, various substituents of different hydrophobicity and fluorescence were post-grafted and the post-grafting yields were evaluated by surface analyses. We show that the used polymer is already fluorescent before post-grafting while the post-grafting yield and as a consequence the surface hydrophobicity highly depend on the substituent.

EXPERIMENTS

Here, we have chosen to chemically grafting various fluorinated and aromatic substituents using a post-grafting in order to keep the same surface topography. Flat conducting polymer surfaces with similar properties have been also prepared for determining the surface energy with the Owens-Wendt equation and estimating the post-grafting yield by X-ray Photoemission Spectroscopy (XPS) and Time of Flight Secondary Emission Spectrometry (ToF-SIMS). For example, using fluorinated chains of various length (C₄F₉, C₆F₁₃ and C₈F₁₇), it is demonstrated that the surface hydrophobicity and oleophobicity do not increase with the fluorinated chain length due to the different post-grafting yields and because of the presence of nanoroughness after post-grafting.

FINDINGS

These surfaces have high apparent water contact angle up to 130.5° but also strong water adhesion, comparable to rose petal effect even if there are no nanotubes on petal surface. XPS and ToF-SIMS analyses provided a detailed characterisation of the surface chemistry with a qualitative classification of the grafted surfaces (F6 > F4 > F8). SEM analysis shows that grafting does not alter the surface morphology. Finally, fluorescence analyses show that the polymer surfaces before post-treatment are already nicely fluorescent. Although the main goal of this paper was and is to understand the role of surface chemistry in tailoring the wetting properties of these surfaces rather than provide specific application examples, we believe that the obtained results can help the development of specific nanostructured materials for potential applications in liquid transport, or in stimuli responsive antimicrobial surfaces.

Study on the Mechanism of the Reversible Color Change of Polyacrylic Acid Modified Gold Nanoparticles Responding to pH

In view of various explanations regarding the pH response of the nanocomposite of gold nanoparticles (AuNPs) modified with polyacrylic acid (PAA) molecules in reported literature, in this work, AuNPs with a size of 20 nm saturatedly loaded with PAA molecules (AuNPs-PAAs) were used to investigate the following aspects of this issue. We investigated the effects of pH on the stability of AuNPs-PAAs in the presence of salt, CTAB, poly (sodium styrenesulfonate) (PSS), ethanol, and free PAA, respectively. Common techniques were undertaken to evaluate the stability, including UV-Vis spectroscopy, Zeta potential analysis, and TEM. The results show that AuNPs-PAAs could respond to pH variations, having a reversible aggregation-to-disaggregation, accompanying their Zeta potential change. The proposed corresponding mechanism was that this reversible change was attributes to the net charge variation of AuNPs-PAAs induced by a reversible protonation-to-deprotonation of PAA rather than the conformational change. It was found that salt, CTAB, PSS, and free PAA could strengthen the dispersity of AuNPs-PAAs, even though their absolute Zeta potential values were decreased to small values or dropped to nearly zero. This abnormal phenomenon was explained by solvation. It was also found that AuNPs-PAAs have an opposite pH response in aqueous and ethanol solutions, justifying the solvation effect. All these results revealed the conformational stability of PAAs immobilized on AuNPs. The methods and the findings of this investigation give some new insights to understand the pH-response of AuNPs-PAAs composites and the design of AuNPs-PAAs-based functional sensors.

Measurement of Peptide Coating Thickness and Chemical Composition Using XPS

X-ray photoelectron spectroscopy is a highly surface-sensitive analytical technique, capable of providing quantitative information on the chemical composition of materials within the top ∼10 nm of their surface. For samples consisting of distinct underlayer and overlayer materials, the thickness of the coating can also be determined if it falls within this ∼10 nm information depth, which is often the case for peptide layers. Such measurements are simple to perform for flat samples and can also be performed on nanoparticulate samples provided that either the core radius or total particle radius are known. Here, we describe a straightforward protocol for obtaining such measurements from peptide coatings on both flat surfaces and nanoparticles, including preparation of nanoparticle samples from suspension, data acquisition, and analysis.

Comparative Catalytic Properties of Supported and Encapsulated Gold Nanoparticles in Homocoupling Reactions

This report describes strategies to increase the reactive surfaces of integrated gold nanoparticles (AuNPs) by employing two different types of host materials that do not possess strong electrostatic and/or covalent interactive forces. These composite particles are then utilized as highly reactive and recyclable quasi-homogeneous catalysts in a C-C bond forming reaction. The use of mesoporous TiO₂ and poly(N-isopropylacrylamide), PNIPAM, particles allows for the formation of relatively small and large guest AuNPs and provides the greatly improved stability of the resulting composite particles. As these AuNPs are physically incorporated into the mesoporous TiO₂ (i.e., supported AuNPs) and PNIPAM particles (i.e., encapsulated AuNPs), their surfaces are maximized to serve as highly reactive catalytic sites. Given their increased physicochemical properties (e.g., stability, dispersity, and surface area), these composite particles exhibit notably high catalytic activity, selectivity, and recyclability in the homocoupling of phenylboronic acid in water and EtOH. Although the small supported AuNPs display slightly faster reaction rates than the large encapsulated AuNPs, the apparent activation energies (E_a) of both composite particles are comparable, implying no obvious correlation with the size of guest AuNPs under the reaction conditions. Investigating the overall physical properties of various composite particles and their catalytic functions, including the reactivity, selectivity, and E_a, can lead to the development of highly practical quasi-homogeneous catalysts in green reaction conditions.

General and adaptive synthesis protocol for high-quality organosilane self-assembled monolayers as tunable surface chemistry platforms for biochemical applications

The controlled modification of surface properties represents a pervasive requirement to be fulfilled when developing new technologies. In this paper, we propose an easy-to-implement protocol for the functionalization of glass with self-assembled monolayers (SAMs). The adaptivity of the synthesis route was demonstrated by the controlled anchoring of thiol, amino, glycidyloxy, and methacrylate groups onto the glass surface. The optimization of the synthetic pathway was mirrored by extremely smooth SAMs (approximately 150 pm roughness), layer thickness comparable to the theoretical molecule length, absence of silane islands along the surface, quasi-unitary degree of packing, and tailored wettability and charge. The functionalization kinetics of two model silanes, 3-mercapto- and 3-amino-propyltrimethoxysilane, was determined by cross-comparing x-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry data. Our SAMs with tailored physicochemical attributes will be implemented as supports for the crystallization of pharmaceuticals and biomolecules in upcoming studies. Here, the application to a small molecule drug model, namely aspirin, was discussed as a proof of concept.

Good's buffers have various affinities to gold nanoparticles regulating fluorescent and colorimetric DNA sensing

Citrate-capped gold nanoparticles (AuNPs) are highly important for sensing, drug delivery, and materials design. Many of their reactions take place in various buffers such as phosphate and Good's buffers. The effect of buffer on the surface properties of AuNPs is critical, yet this topic has not been systematically explored. Herein, we used halides such as fluoride, chloride, and bromide as probes to measure the relative adsorption strength of six common buffers. Among them, HEPES had the highest adsorption affinity, while MES, citrate and phosphate were weakly adsorbed with an overall ranking of HEPES > PIPES > MOPS > MES > citrate, phosphate. The adsorption strength was reflected from the inhibited adsorption of DNA and from the displacement of pre-adsorbed DNA. This conclusion is also supported by surface enhanced Raman spectroscopy. Furthermore, some buffer molecules did not get adsorbed instantaneously, and the MOPS buffer took up to 1 h to reach equilibrium. Finally, a classic label-free AuNP-based colorimetric sensor was tested. Its sensitivity increased by 15.7-fold when performed in a MES buffer compared to a HEPES buffer. This study has articulated the importance of buffer for AuNP-based studies and how it can improve sensors and yield more reproducible experimental systems.

Aside from maintaining pH, Good's buffers can be adsorbed on gold nanoparticles with different affinities, affecting the stability and its fluorescent and colorimetric sensing performance.

Sequestration of Cetyltrimethylammonium Bromide on Gold Nanorods by Human Serum Albumin Causes Its Conformation Change

Serum albumin could potentially be exploited to form a protein corona on gold nanorods (AuNRs) for drug delivery because of its endogenous functionality as a small molecule carrier. However, the cetyltrimethylammonium bromide (CTAB) surfactant, which is a synthesis byproduct passivating AuNRs to confer colloidal stability, could also cause its conformational change upon interaction with serum albumin during the process of corona formation, thus altering its biological functions. Unfortunately, a clear understanding of how exactly human serum albumin (HSA) would change its conformation as it interacts with AuNR-CTAB is presently lacking. Here, we made use of coarse-grain molecular dynamics (CGMD) simulation to elucidate the interaction between HSA and AuNR-CTAB leading to its widely reported conformational change. We showed that HSA could sequester CTAB from the surface of AuNRs and form HSA-CTAB complexes, which could also interact with other adjacent complexes through "cross-linking" by the clusters of CTAB. Such a HSA-CTAB complex resulted in the observed conformational change of HSA, which we verified empirically with an esterase activity assay and by analyzing the root-mean-square-deviation of the HSA molecules from CGMD. The conformational change of HSA was not observed in AuNRs passivated with other negatively or positively charged surface ligands such as polystyrene sulfonate and polydiallyldimethylammonium chloride. Therefore, our study revealed that the conformational change experienced by HSA may not necessarily be attributed to protein unfolding on the surface of the AuNR due to charge interactions but rather to the instability of the surface ligands on the AuNRs which allows them to be sequestered by HSA to form HSA-CTAB complexes.

Single and multiple detections of foodborne pathogens by gold nanoparticle assays

A late detection of pathogenic microorganisms in food and drinking water has a high potential to cause adverse health impacts in those who have ingested the pathogens. For this reason there is intense interest in developing precise, rapid and sensitive assays that can detect multiple foodborne pathogens. Such assays would be valuable components in the campaign to minimize foodborne illness. Here, we discuss the emerging types of assays based on gold nanoparticles (GNPs) for rapidly diagnosing single or multiple foodborne pathogen infections. Colorimetric and lateral flow assays based on GNPs may be read by the human eye. Refractometric sensors based on a shift in the position of a plasmon resonance absorption peak can be read by the new generation of inexpensive optical spectrometers. Surface-enhanced Raman spectroscopy and the quartz microbalance require slightly more sophisticated equipment but can be very sensitive. A wide range of electrochemical techniques are also under development. Given the range of options provided by GNPs, we confidently expect that some, or all, of these technologies will eventually enter routine use for detecting pathogens in food. This article is categorized under: Diagnostic Tools > Biosensing.

Synergism between Specific Halide Anions and pH Effects during Nanosecond Laser Fragmentation of Ligand-Free Gold Nanoparticles

Gold nanoclusters (AuNCs) with diameters smaller than 3 nm are an emerging field of research because they possess interesting optical properties, such as photoluminescence. However, to date, it is still difficult to distinguish whether these properties originate from the cores of the nanoparticles or from the adsorbates on their surfaces. Hence, there is a high demand for ligand-free, ultra-small particles because they make it possible to study ligand and core effects separately. Pulsed laser fragmentation in liquids (LFL) is a convenient route for the synthesis of ligand-free AuNCs. The influence of physical parameters, such as melting and evaporation, on the LFL process is well understood both theoretically and experimentally. However, the impact of the chemical composition of the medium during LFL, which critically affects the particle formation process, has been less well examined. Therefore, in this work, we elucidate the extent to which the ionic strength, the pH value, and the nature of the halide anion that is present, that is, F^-, Cl^-, Br^-, or I^-, influence the particle size distribution of the LFL product and the mean yield of small particles (<3 nm) of the product. We showed that the yield of small particles can be enhanced by the synergism between pH and specific ion effects, which probably is attributable to the adsorption of specific anions. In addition, our findings indicated that anion-based stabilization depends critically on the type of anion. A direct Hofmeister effect was observed for anions in the neutral pH regime, whereas an indirect Hofmeister series was reported in alkaline solution, which probably was due to the more hydrophilic surfaces of the AuNCs that were formed.

The Chameleon Effect: Characterization Challenges Due to the Variability of Nanoparticles and Their Surfaces

Nanoparticles in a variety of forms are increasing important in fundamental research, technological and medical applications, and environmental or toxicology studies. Physical and chemical drivers that lead to multiple types of particle instabilities complicate both the ability to produce, appropriately characterize, and consistently deliver well-defined particles, frequently leading to inconsistencies, and conflicts in the published literature. This perspective suggests that provenance information, beyond that often recorded or reported, and application of a set of core characterization methods, including a surface sensitive technique, consistently applied at critical times can serve as tools in the effort minimize reproducibility issues.