Carboxylated Polystyrene Nanoparticles Research Articles

Nanostickers for cells: a model study using cell–nanoparticle hybrid aggregates

We present direct evidence that nanoparticles (NPs) can stick together cells that are inherently non-adhesive. Using cadherin-depleted S180 murine cells lines, which exhibit very low cell-cell adhesion, we show that NPs can assemble dispersed single cells into large cohesive aggregates. The dynamics of aggregation, which is controlled by diffusion and collision, can be described as a second-order kinetic law characterized by a rate of collision that depends on the size, concentration, and surface chemistry of the NPs. We model the cell-cell adhesion induced by the "nanostickers" using a three-state dynamical model, where the NPs are free, adsorbed on the cell membrane or internalized by the cells. We define a "sticking efficiency parameter" to compare NPs and look for the most efficient type of NP. We find that 20 nm carboxylated polystyrene NPs are more efficient nanostickers than 20 nm silica NPs which were reported to induce fast wound healing and to glue soft tissues. Nanostickers, by increasing the cohesion of tissues and tumors, may have important applications for tissue engineering and cancer treatment.

Nano-sized polystyrene affects feeding, behavior and physiology of brine shrimp Artemia franciscana larvae

Nano-sized polymers as polystyrene (PS) constitute one of the main challenges for marine ecosystems, since they can distribute along the whole water column affecting planktonic species and consequently disrupting the energy flow of marine ecosystems. Nowadays very little knowledge is available on the impact of nano-sized plastics on marine organisms. Therefore, the present study aims to evaluate the effects of 40nm anionic carboxylated (PS-COOH) and 50nm cationic amino (PS-NH2) polystyrene nanoparticles (PS NPs) on brine shrimp Artemia franciscana larvae. No signs of mortality were observed at 48h of exposure for both PS NPs at naplius stage but several sub-lethal effects were evident. PS-COOH (5–100μg/ml) resulted massively sequestered inside the gut lumen of larvae (48h) probably limiting food intake. Some of them were lately excreted as fecal pellets but not a full release was observed. Likewise, PS-NH2 (5–100µg/ml) accumulated in larvae (48h) but also adsorbed at the surface of sensorial antennules and appendages probably hampering larvae motility. In addition, larvae exposed to PS-NH2 undergo multiple molting events during 48h of exposure compared to controls. The activation of a defense mechanism based on a physiological process able to release toxic cationic NPs (PS-NH2) from the body can be hypothesized. The general observed accumulation of PS NPs within the gut during the 48h of exposure indicates a continuous bioavailability of nano-sized PS for planktonic species as well as a potential transfer along the trophic web. Therefore, nano-sized PS might be able to impair food uptake (feeding), behavior (motility) and physiology (multiple molting) of brine shrimp larvae with consequences not only at organism and population level but on the overall ecosystem based on the key role of zooplankton on marine food webs.

Nanoparticle-Induced Membrane Pore Formation Studied with Lipid Bilayer Arrays

Nanoparticles are present environmentally as byproducts of industrial processes and in a wide range of consumer goods. Although toxicity studies of nanoparticles and other nanomaterials have only begun relatively recently, a diverse range of nanoparticles has already been shown to be toxic. Nanoparticle cytotoxicity assays provide little information about the mechanisms of nanoparticle toxicity, which are potentially complex and are not likely the same for diverse nanoparticle species. For this reason, artificial lipid bilayer platforms have begun to be used as model systems for controlled studies allowing variation of experimental parameters not possible with cellular studies, such as membrane and solution composition. Unfortunately, in some cases the low throughput characteristic of lipid bilayer experimentation can limit the experimental scope. We have recently described a lipid bilayer array platform with simultaneous bilayer formation and measurement over a 32-element array with ∼80% yield and no operator input following fluid addition.[1] The platform is modular and allows rapid cycling of the apparatus for repeated measurement. We have used this platform to measure the interactions of aminated and carboxylated polystyrene nanoparticles and a range metal oxide nanoparticle species with lipid bilayers in a wide variety of experimental conditions, including nanoparticle concentration, bilayer composition, bilayer charge, presence of serum protein, solution ionic strength, and pH. The array format permitted several thousand bilayers to be measured in total with sufficient redundancy to give statistical significance to measured results. Detailed analysis of the electrical measurements shows pore formation that is dependent on electric field, ionic strength, and nanoparticle species.1. “Lipid bilayer arrays cyclically formed and measured,” Bin Lu, Gayane Kocharyan and Jacob J. Schmidt, Biotechnology Journal 9, 446-451 (2014)

Nanoparticles modify dendritic cell homeostasis and induce non-specific effects on immunity to malaria.

Many current vaccines to a specific pathogen influence responses to other pathogens in a process called heterologous immunity. We propose that their particulate nature contributes to non-specific effects. Herein, we demonstrate polystyrene nanoparticles modulate dendritic cell (DC) homeostasis, thereby promoting a persistent enhanced state of immune readiness to a subsequent infectious challenge. Particles (approximately 40 nm and 500 nm carboxylated polystyrene nanoparticles; PSNPs) alone or conjugated to a model antigen were injected in mice, and DCs in draining lymph nodes (dLNs) and bone-marrow (BM) quantified by flow cytometry. BM cells were tested for capacity to generate DCs upon culture with granulocyte and macrophage colony stimulating factor. Mice were challenged with Plasmodium yoelli. Blood parasitaemias were monitored by GIEMSA. Sera was analyzed for antibodies by ELISA. Intradermal administration of 40 nm PSNPs induced anti-inflammatory cytokines, chemokines and growth factors, increased numbers and proportions of DCs in the dLN, and increased the capacity of BM to generate DCs. Consistent with these unexpected changes, 40 nm PSNPs pre-injected mice had enhanced ability to generate immunity to a subsequent malarial infection. Intradermal administration of 40 nm PSNPs modifies DC homeostasis, which may at least in part explain the observed beneficial heterologous effects of current particulate vaccines. Further nanotechnological developments may exploit such strategies to promote beneficial non-specific effects.

Nanoparticle ζ-potential measurements using tunable resistive pulse sensing with variable pressure

Modern resistive pulse sensing techniques can be used to measure nanoparticle electrophoretic mobility, and hence ζ-potential. In contrast to conventional light scattering methods, resistive pulse sensing produces particle-by-particle data. We have used tunable resistive pulse sensing (TRPS) to compare methods for measuring the ζ-potential of carboxylated polystyrene nanoparticles. The five particle sets studied had nominal surface charge density (σ) between 0 and −0.67Cm−2, and diameters in the range 160–230nm. Data were collected with pressure in the range ±500Pa applied across a tunable pore. In each experiment, pressure was varied either continuously or in discrete steps. Calculations of the ζ-potential were obtained by analysing both the rate and the full-width half maximum duration of resistive pulses. Data obtained from duration analyses were more reproducible than rate methods, yielding typical variations smaller than ±5mV. When σ was greater (less negative) than −0.32Cm−2, all of the analysis methods studied yielded a monotonic relationship between ζ-potential and σ. Complicated pulse data were observed near the pressure at which the net particle flux is zero, and these observations have been explored by examining competition between electrokinetic and pressure-driven transport. The typical difference between ζ-potentials obtained using TRPS and phase analysis light scattering was 15% (<5mV), with an experimental error of ∼10% attributable to both techniques.

Paracrine signalling of inflammatory cytokines from an in vitro blood brain barrier model upon exposure to polymeric nanoparticles

Nanoparticle properties, such as small size relative to large highly modifiable surface area, offer great promise for neuro-therapeutics and nanodiagnostics. A fundamental understanding and control of how nanoparticles interact with the blood-brain barrier (BBB) could enable major developments in nanomedical treatment of previously intractable neurological disorders, and help ensure that nanoparticles not intended to reach the brain do not cause adverse effects. Nanosafety is of utmost importance to this field. However, a distinct lack of knowledge exists regarding nanoparticle accumulation within the BBB and the biological effects this may induce on neighbouring cells of the Central Nervous System (CNS), particularly in the long-term. This study focussed on the exposure of an in vitro BBB model to model carboxylated polystyrene nanoparticles (PS COOH NPs), as these nanoparticles are well characterised for in vitro experimentation and have been reported as non-toxic in many biological settings. TEM imaging showed accumulation but not degradation of 100 nm PS COOH NPs within the lysosomes of the in vitro BBB over time. Cytokine secretion analysis from the in vitro BBB post 24 h 100 nm PS COOH NP exposure showed a low level of pro-inflammatory RANTES protein secretion compared to control. In contrast, 24 h exposure of the in vitro BBB endothelium to 100 nm PS COOH NPs in the presence of underlying astrocytes caused a significant increase in pro-survival signalling. In conclusion, the tantalising possibilities of nanomedicine must be balanced by cautious studies into the possible long-term toxicity caused by accumulation of known 'toxic' and 'non-toxic' nanoparticles, as general toxicity assays may be disguising significant signalling regulation during long-term accumulation.

Influence of Nanoparticle Surface Functionalization on the Thermal Stability of Colloidal Polystyrene Films

The installation of large scale colloidal nanoparticle thin films is of great interest in sensor technology or data storage. Often, such devices are operated at elevated temperatures. In the present study, we investigate the effect of heat treatment on the structure of colloidal thin films of polystyrene (PS) nanoparticles in situ by using the combination of grazing incidence small-angle X-ray scattering (GISAXS) and optical ellipsometry. In addition, the samples are investigated with optical microscopy, atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). To install large scale coatings on silicon wafers, spin-coating of colloidal pure PS nanoparticles and carboxylated PS nanoparticles is used. Our results indicate that thermal annealing in the vicinity of the glass transition temperature T(g) of pure PS leads to a rapid loss in the ordering of the nanoparticles in spin-coated films. For carboxylated particles, this loss of order is shifted to a higher temperature, which can be useful for applications at elevated temperatures. Our model assumes a softening of the boundaries between the individual colloidal spheres, leading to strong changes in the nanostructure morphology. While the nanostructure changes drastically, the macroscopic morphology remains unaffected by annealing near T(g).

Quantitative and Rapid DNA Detection by Laser Transmission Spectroscopy

Laser transmission spectroscopy (LTS) is a quantitative and rapid in vitro technique for measuring the size, shape, and number of nanoparticles in suspension. Here we report on the application of LTS as a novel detection method for species-specific DNA where the presence of one invasive species was differentiated from a closely related invasive sister species. The method employs carboxylated polystyrene nanoparticles functionalized with short DNA fragments that are complimentary to a specific target DNA sequence. In solution, the DNA strands containing targets bind to the tags resulting in a sizable increase in the nanoparticle diameter, which is rapidly and quantitatively measured using LTS. DNA strands that do not contain the target sequence do not bind and produce no size change of the carboxylated beads. The results show that LTS has the potential to become a quantitative and rapid DNA detection method suitable for many real-world applications.

Effects of Transport Inhibitors on the Cellular Uptake of Carboxylated Polystyrene Nanoparticles in Different Cell Lines

Nanotechnology is expected to play a vital role in the rapidly developing field of nanomedicine, creating innovative solutions and therapies for currently untreatable diseases, and providing new tools for various biomedical applications, such as drug delivery and gene therapy. In order to optimize the efficacy of nanoparticle (NP) delivery to cells, it is necessary to understand the mechanisms by which NPs are internalized by cells, as this will likely determine their ultimate sub-cellular fate and localisation. Here we have used pharmacological inhibitors of some of the major endocytic pathways to investigate nanoparticle uptake mechanisms in a range of representative human cell lines, including HeLa (cervical cancer), A549 (lung carcinoma) and 1321N1 (brain astrocytoma). Chlorpromazine and genistein were used to inhibit clathrin and caveolin mediated endocytosis, respectively. Cytochalasin A and nocodazole were used to inhibit, respectively, the polymerisation of actin and microtubule cytoskeleton. Uptake experiments were performed systematically across the different cell lines, using carboxylated polystyrene NPs of 40 nm and 200 nm diameters, as model NPs of sizes comparable to typical endocytic cargoes. The results clearly indicated that, in all cases and cell types, NPs entered cells via active energy dependent processes. NP uptake in HeLa and 1321N1 cells was strongly affected by actin depolymerisation, while A549 cells showed a stronger inhibition of NP uptake (in comparison to the other cell types) after microtubule disruption and treatment with genistein. A strong reduction of NP uptake was observed after chlorpromazine treatment only in the case of 1321N1 cells. These outcomes suggested that the same NP might exploit different uptake mechanisms to enter different cell types.

Au-Coated Polystyrene Nanoparticles with High-Aspect-Ratio Nanocorrugations via Surface-Carboxylation-Shielded Anisotropic Etching for Significant SERS Signal Enhancement

Increasing the hot-spot area with high enhancement ability on SERS-active particles is generally acknowledged as one of the efficient ways to significantly improve the average SERS signal of nanoparticles. A method to create roughness on the surface of nanoparticles was proposed by oxygen plasma etching noncarboxylated polystyrene beads. However, the mechanism of nanocorrugation formation was not clear. Thus, in this paper, we employ argon-based reactive ion etching (RIE) incorporated with carboxylated polystyrene nanoparticles to investigate the roles of nanocorrugations’ morphologies for SERS signal enhancement. The formation mechanism of the nanocorrugations has been investigated thoroughly through a comparison with those formed by oxygen-based RIE processes from their high resolution X-ray photoelectron spectra and surface morphologies with or without hydrazine reduction treatment. Moreover, polystyrene beads with more intrinsic carboxyl groups and etched by argon plasma produce higher nanocorrugations. It is suggested that carbonyl groups with high bond energy become nanomasks on polystyrene bead surfaces and provides high selectivity between carboxyl and polystyrene surfaces under RIE. Raman intensity enhancement on a 20-nm gold coated nanocorrugated polystyrene bead array is summarized by three factors: (1) the effect of plasmonic coupling among neighboring particles, (2) the nanocorrugation-contributed roughness, and (3) the pitch size of nanocorrugations, through the analysis of SEM images, AFM height images, and LSPR signals. Among these factors, the pitch size of nanocorrugations (ranging from ∼6 nm to ∼12 nm on the surface of polystyrene beads) dominates the SERS enhancement. The 870 nm/120s oxygen plasma etched polystyrene beads (OPSBs) with a minimum pitch size of 6 nm provides the highest Raman intensity enhancement (measured by 632.8-nm He–Ne laser), which is 12 times greater than the intensity of nontreated (870 nm/0s) polystyrene beads (while the Au/Ti coating is 20 nm/5 nm).

Experimental study of the separation behavior of nanoparticles in micro- and nanochannels

In this article, we investigate the effects of pH, ionic strength, and channel height on the mobility and diffusivity of charged spherical particles within planar microfluidic channels. Specifically, we report results of a broad experimental study on the transport and separation behavior of 50 and 100 nm spherical carboxylated polystyrene nanoparticles, confined in 20 μm, 1 μm, and 250 nm deep fluidic channels. We find that pH, ionic strength, and channel height have coupled impacts on mobility changes. In particular, we show that, depending on pH, the dependence of particle mobility on channel size can have opposing behavior. In addition, we also show that at the nanoscale, at lower ionic strengths, there is a substantial increase in mobility, due to enhanced electric fields within the nanochannels. These effects are important to understand in order to avoid potential downfalls in terms of separation efficiency as well as design for better tuning of separation performance in micro- and nanochannels. Finally, we propose a method to estimate the effective zeta potential of spherical particles from measured electrophoretic mobility data. This could prove useful in characterizing a heterogeneous collection of particles having a distribution over a range of values of the zeta potential.

Dynamic light scattering investigations of nanoparticle aggregation following a light-induced pH jump

There are many important processes where the stability of nanoparticles can change due to changes in solution environment. These processes are often difficult to study under controlled changes to the solution conditions. Dynamic light scattering was used to measure the initial kinetics of aggregation of carboxylated polystyrene nanoparticles after well-defined pH jumps using aqueous solutions of photoacid generator (PAG). With this approach, the pH of the solution was controlled by exposure to ultraviolet (UV) light without the delays from mixing or stirring. The aggregation kinetics of the nanoparticles was extremely sensitive to the solution pH. The UV exposure dose is inversely correlated with the resulting surface charge of the nanoparticles. Decreasing pH decreases the electrostatic repulsion force between particles and leads to aggregation. The reaction-limited or diffusion-limited aggregation kinetics was sensitive to the pH quench depth, relative to the acid-equilibrium constant (pK(a)) of the surface carboxylic acid groups on the nanoparticles. Since numerous PAGs are commercially available, this approach provides a flexible method to study the aggregation of a variety of solvent-dispersed nanoparticle systems.

An improved in vitro model of human intestinal follicle-associated epithelium to study nanoparticle transport by M cells

An alternative in vitro model of human follicle-associated epithelium (FAE) to study nanoparticle transport mechanisms by M cells was developed and characterized. The previous in vitro model of human FAE has been improved by inverting inserts after Caco-2 cell seeding. Raji and M cells were identified only in inverted co-culture cell monolayers by immunohistochemistry, confocal microscopy, and electron microscopy. The M cell conversion rate evaluated by scanning electron microscopy ranged between 15 and 30% of cells. Transport of 200 nm carboxylated polystyrene nanoparticles was higher and more reproducible in the inverted model. Nanoparticle transport was temperature-dependent, not affected by the presence of EGTA or by potassium depletion, but inhibited by EIPA or nystatin, suggesting that it occurs most likely by macropinocytosis. The inverted model appears more physiologic, functional and reproducible than the normally oriented model.