Liquid Nebulization–Ion Mobility Spectrometry Based Quantification of Nanoparticle–Protein Conjugate Formation

Condensable Vapor Sorption by Low Charge State Protein Ions

Measurement of the gas-phase ion mobility of proteins provides a means to quantitatively assess the relative sizes of charged proteins. However, protein ion mobility measurements are typically singular values. Here, we apply tandem mobility analysis to low charge state protein ions (+1 and +2 ions) introduced into the gas phase by nanodroplet nebulization. We first determine protein ion mobilities in dry air and subsequently examine shifts in mobilities brought about by the clustering of vapor molecules. Tandem mobility analysis yields mobility-vapor concentration curves for each protein ion, expanding the information obtained from mobility analysis. This experimental procedure and analysis is extended to bovine serum albumin, transferrin, immunoglobulin G, and apoferritin with water, 1-butanol, and nonane. All protein ions appear to adsorb vapor molecules, with mobility "diameter" shifts of up to 6-7% at conditions just below vapor saturation. We parametrize results using κ-Köhler theory, where the term κ quantifies the extent of uptake beyond Köhler model expectations. For 1-butanol and nonane, κ decreases with increasing protein ion size, while it increases with increasing protein ion size for water. For the systems probed, the extent of mobility shift for the organic vapors is unaffected by the nebulized solution pH, while shifts with water are sensitive to pH.

Multidimensional Nanoparticle Characterization through Ion Mobility-Mass Spectrometry

Multidimensional techniques that combine fully or partially orthogonal characterization methods in a single setup often provide a more comprehensive description of analytes. When applied to nanoparticles, they have the potential to reveal particle properties not accessible to more conventional 1D techniques. Herein, we apply recently developed 2D characterization techniques to nanoparticles using atmospheric-pressure ion mobility-mass spectrometry (IM-MS), and we demonstrate the analytical capability of this approach using ultraporous mesostructured silica nanoparticles (UMNs). We show that IM-MS yields a 2D particle size-mass distribution function, which in turn can be used to calculate not only important 1D distributions, i.e. particle size distributions, but also nanoparticle structural property distributions not accessible by other methods, including size-dependent particle porosity and the specific pore volume distribution function. IM-MS measurement accuracy was confirmed by measurement of NIST-certified polystyrene latex particle standards. For UMNs, comparison of IM-MS results with TEM and N₂ physisorption yields quantitative agreement in particle size and qualitative agreement in average specific pore volume. IM-MS uniquely shows how within a single UMN population, porosity increases with increasing particle size, consistent with the proposed UMN growth mechanism. In total, we demonstrate the potential of IM-MS as a standard approach for the characterization of structurally complex nanoparticle populations, as it yields size-specific structural distribution functions.

Possibilities of single particle-ICP-MS for determining/characterizing titanium dioxide and silver nanoparticles in human urine

OBJECTIVE

The current use of nanoparticles in personal care and cosmetics, food safety, agriculture, medicine and pharmacy has led to a growing concern on the toxicity of these emerging materials to humans and also to the environment. Nanoparticles assessment (determination and size distribution) is a challenge mainly due to limitations of the current analytical instrumentation, but also because nanoparticles in foodstuff and environmental samples are usually found at low concentrations. The scenario is even more critical when dealing with clinical samples, mainly when trying to assess nanoparticles at basal levels in complex samples such as blood and urine. The aim of this paper is to find data regarding the presence of nanoparticles at basal levels in urine human samples.

METHODS

The use of single particle - inductively couple plasma - mass spectrometry (sp-ICP-MS) has been explored to determine and characterize silver and titanium dioxide nanoparticles in human urine. Urine samples were directly diluted (1:5 to 1:10) with 1%(v/v) glycerol before sp-ICP-MS measurements, and efforts were made for validating the over-all procedure.

RESULTS

The limit of detection and quantification for Ag NPs were 5.72 × 10³ and 1.91 × 10⁴ Ag NPs mL^-1, respectively; whereas, values for TiO₂ NP concentrations were 4.31 × 10³ and 1.44 × 10₄ TiO₂ NPs mL^-1. The limit of detection in size after applying several methods (3σ/5σ criteria) was found to be within the 8-9 nm for Ag NPs, and from 15 to 18 nm for TiO₂ NPs. Within-batch precision for Ag NP concentration was 15% (11% for mean size of nanoparticle distributions). Repeatability for TiO₂ NPs was 25% (TiO₂ NP concentration) and 9% (TiO₂ NP mean size). Good analytical recovery rates were found for spiked experiments with Ag NP standards of 40 and 60 nm (values within the 104-106% range), and also for TiO₂ NPs of 50 and 100 nm (96-98%). Finally, basal levels of Ag NPs and TiO₂ NPs, as well as total Ag and Ti concentrations, in human urine were assessed. Low Ag and Ag NP concentrations were found. Ag NPs exhibited mean sizes of approximately 16-17 nm. Total Ti levels, however, were higher than total Ag concentration, and TiO₂ NP concentrations within the 1.56 × 10⁴-2.80 × 10⁴ NPs mL^-1 range were measured (TiO₂ NP mean sizes were from 76 to 98 nm).

Plasma protein adsorption and biological identity of systemically administered nanoparticles

Although a variety of nanoparticles (NPs) have been used for drug delivery applications, their surfaces are immediately covered by plasma protein corona upon systemic administration. As a result, the adsorbed proteins create a unique biological identity of the NPs that lead to unpredictable performance. The protein corona on NPs could also impede active targeting, induce off-target effects, trigger particle clearance and even provoke toxicity. This article reviews the fundamentals of NP–plasma protein interaction, the consequences of the interactions, and provides insights into the correlations of protein corona with biodistribution and cellular delivery. We hope that this review will trigger additional questions and possible solutions that lead to more favorable developments in NP-based targeted delivery systems.

Protein Corona-Induced Modification of Silver Nanoparticle Aggregation in Simulated Gastric Fluid

Due to their widespread incorporation into a range of biomedical and consumer products, the ingestion of silver nanoparticles (AgNPs) is of considerable concern to human health. However, the extent to which AgNPs will be modified within the gastric compartment of the gastrointestinal tract is still poorly understood. Studies have yet to fully evaluate the extent of physicochemical changes to AgNPs in the presence of biological macromolecules, such as pepsin, the most abundant protein in the stomach, or the influence of AgNPs on protein structure and activity. Herein, AgNPs of two different sizes and surface coatings (20 and 110 nm, citrate or polyvinylpyrrolidone) were added to simulated gastric fluid (SGF) with or without porcine pepsin at three pHs (2.0, 3.5, and 5.0), representing a range of values between preprandial (fasted) and postprandial (fed) conditions. Rapid increases in diameter were observed for all AgNPs, with a greater increase in diameter in the presence of pepsin, indicating that pepsin facilitated AgNPs aggregation. AgNPs interaction with pepsin only minimally reduced the protein's proteolytic functioning capability, with the greatest inhibitory effect caused by smaller (20 nm) particles of both coatings. No changes in pepsin secondary structural elements were observed for the different AgNPs, even at high particle concentrations. This research highlights the size-dependent kinetics of nanoparticle aggregation or dissolution from interaction with biological elements such as proteins in the gastrointestinal tract. Further, these results demonstrate that, in addition to mass, knowing the chemical form and aggregation state of nanoparticles is critical when evaluating toxicological effects from nanoparticle exposure in the body.

Ion-Mobility-Based Quantification of Surface-Coating-Dependent Binding of Serum Albumin to Superparamagnetic Iron Oxide Nanoparticles

Protein binding and protein-induced nanoparticle aggregation are known to occur for a variety of nanomaterials, with the extent of binding and aggregation highly dependent on nanoparticle surface properties. However, often lacking are techniques that enable quantification of the extent of protein binding and aggregation, particularly for nanoparticles with polydisperse size distributions. In this study, we adapt ion mobility spectrometry (IMS) to examine the binding of bovine serum albumin to commercially available anionic-surfactant-coated superparamagnetic iron oxide nanoparticles (SPIONs), which are initially ∼21 nm in mean mobility diameter and have a polydisperse size distribution function (geometric standard deviation near 1.4). IMS, carried out with a hydrosol-to-aerosol converting nebulizer, a differential mobility analyzer, and a condensation particle counter, enables measurements of SPION size distribution functions for varying BSA/SPION number concentration ratios. IMS measurements suggest that initially (at BSA concentrations below 50 nM) BSA binds reversibly to SPION surfaces with a binding site density in the 0.05-0.08 nm(-2) range. However, at higher BSA concentrations, BSA induces SPION-SPION aggregation, evidenced by larger shifts in SPION size distribution functions (mean diameters beyond 40 nm for BSA concentrations near 100 nM) and geometric standard deviations (near 1.3) consistent with self-preserving aggregation theories. The onset of BSA aggregation is correlated with a modest but statistically significant decrease in the specific absorption rate (SAR) of SPIONs placed within an alternating magnetic field. The coating of SPIONs with mesoporous silica (MS-SPIONs) as well as PEGylation (MS-SPIONs-PEG) is found to completely mitigate BSA binding and BSA-induced aggregation; IMS-inferred size distribution functions are insensitive to BSA concentration for MS-SPIONs and MS-SPIONs-PEG. The SARs of MS-SPIONs are additionally insensitive to BSA concentration, confirming the SAR decrease is linked to BSA-induced aggregation.