Carboxylate-modified Polystyrene Nanoparticles Research Articles

Removal of nanoplastics from aqueous solution by aggregation using reusable magnetic biochar modified with cetyltrimethylammonium bromide

Nanoplastics (NPs) pollution has become an emerging threat to the aquatic environment and its organisms. The removal of NPs from contaminated water is a global challenge. In this study, an efficient and reusable composite was prepared from cetyltrimethylammonium bromide (CTAB) modified magnetic biochar. The performances of CTAB modified magnetic biochar (CMB) to remove polystyrene (PS) and carboxylate-modified polystyrene (CPS) nanoparticles from water were systematically evaluated. The results showed that the PS and CPS removal performance of magnetic biochar was improved by CTAB modification. These increases were assigned to the increase in the surface hydrophobicity of CMB. Due to the strong electrostatic repulsion between the nanoparticles, PS and CPS maintained high stability in alkaline conditions, resulting in a significant decrease in removal efficiency. The removal efficiency was decreased to 67.4% for PS and to 40.7% for CPS at pH 11. The inhibition effects of NaCl on the PS and CPS removal efficiencies were decreased gradually with the increase of NaCl concentration. Among the anions studied, H2PO4− had the biggest impact on the removal performance of CMB. Besides, CMB could be used to remove PS and CPS in real surface water, and the removal efficiencies of PS and CPS were 95.3% and 97.8%, respectively. Particularly, the removal efficiencies of PS and CPS were 90.2% for PS and 94.8% for CPS when CMB was recycled five times. According to the characterization results of XRD, TGA, SEM, FTIR and XPS, PS and CPS nanoparticles were removed by CMB from water mainly through aggregation instead of adsorption. The efficient removal of PS and CPS by CMB via aggregation process offers new insight into the removal of NPs from aquatic environment.

Probing Amino Acid Interaction with a Polystyrene Nanoparticle Surface Using Saturation-Transfer Difference (STD)-NMR.

The interaction between individual amino acids and the surface of carboxylate-modified polystyrene nanoparticles in solution was studied using Saturation-Transfer Difference (STD)-Nuclear Magnetic Resonance (NMR). Individual amino acids were screened for nanoparticle binding using an STD-NMR experiment at a fixed saturation time, and STD buildup curves were measured for those amino acids that exhibited significant STD difference signals in the initial screening. The strongest STD effects were measured for protons of aromatic side chains, with relatively weaker effects observed for protons in long-chain aliphatic and positively charged side chains. This indicates that there are several modes of binding to these polystyrene nanoparticles: electrostatic attraction between the negatively charged surface of the carboxylate-modified polystyrene nanoparticle and positively charged amino acids, hydrophobic effects between long aliphatic side chains and the nanoparticle surface, and π-π interactions between aromatic amino acids and aromatic groups in styrene. This information can be used in future studies to predict and understand interactions between nanoparticle surfaces and specific amino acid residues in small peptides and proteins.

Separation of polystyrene nanoparticles in polydimethylsiloxane microfluidic devices with a combined titania and sodium dodecyl sulfate inner coating

It is known for hydrophobic small molecules and proteins to be strongly adsorbed on the surface of polydimethylsiloxane (PDMS) based microdevices. However, no systematic studies have addressed issues related to the sorption of nanoparticles (NPs) on PDMS surfaces. The authors have used carboxylate-modified polystyrene nanoparticles (PS NPs), with sizes of <100 nm and prepared in different curing agent ratios, to study their sorption by native PDMS of different brands. It is found that both dynamic coating with sodium dodecyl sulfate and sol-gel modification can relieve the sorption issues, but only the co-treatment with both species gives satisfactory results in terms of suppressing bulk absorption. This combined coating strategy was further testified by an on-chip separation of a mixture of PS NPs (of 20 nm, 50 nm and 500 nm average diameter) based on a linear node array with enhanced mixing and diffusion-biased recovery of smaller nanoparticles. Instead of changing device design, optimal parameters for nano-separation can be achieved by changing the flow rate between a pair of syringe pumps. A more than 10-fold enrichment of 20 nm NPs was obtained when analyzing a mixture of nanoparticles. Since PDMS is still the preferred choice as a microfluidic substrate, this combined coating strategy is perceived to be highly beneficial in on-chip nano-separation and nanosynthesis using PDMS based microdevices.

Nanoparticles can cross mouse placenta and induce trophoblast apoptosis

IntroductionThe effects of nanoparticles on pregnancy remain unclear. In this study, we investigate whether nanoparticles of a specific size can cross the placenta and affect trophoblast function. MethodsFluorescently labelled carboxylate-modified polystyrene beads with diameters of 20, 40, 100, 200, and 500 nm were chosen as model particles. In vitro, trophoblast cell line (3A-Sub-E) or primary culture of term trophoblasts was used for nanoparticle uptake analysis using flow cytometry, confocal microscopy, BrdU proliferation assay and analysis of cell apoptosis using Western blot. Intravenous injection of nanoparticles into pregnant mice at embryonic day 17 was used to study whether nanoparticles can cross the placenta. The mouse placentas were collected and quantitatively analyzed using high-performance liquid chromatography for nanoparticle uptake. ResultsFluorescent polystyrene particles with diameters of up to 500 nm were taken up by the placenta and were able to cross the placental barrier. The fluorescent polystyrene particles were observed in various organs of fetuses after 4 h of administration to pregnant mice. The nanoparticle uptake by placental tissue was significantly increased in nanoparticles with a diameter of 40 nm. No linear association was evident between nanoparticle size and uptake. Nanoparticles with diameters of 20 nm (200 μg/ml) and 40 nm (500 μg/ml) could induce trophoblast cell apoptosis with increased cleaved caspase 3 and reduced cell proliferation. DiscussionOur findings suggest that nanoparticles can cross the placenta and be taken up by fetal organs. Certain concentrations of carboxylate-modified polystyrene nanoparticles may be cytotoxic to trophoblasts, which could alter placental function.

Cellular Binding of Charged Nanoparticle-Protein Complexes

Nanoparticles used for biomedical applications are exposed to a complex mixture of extracellular serum proteins that non-specifically adsorb to the nanoparticle surface. The resulting “protein corona” dominates interactions of the nanoparticle with the cellular environment. As nanoparticle binding to the cell surface is the first step in the course of most biomedical applications, we have focused on the role of the initial nanoparticle surface charge in the cellular binding of nanoparticles. Cationic, amine-modified and anionic, carboxylate-modified polystyrene nanoparticles were studied as a model system. Although both cationic and anionic nanoparticles form a protein corona, cellular binding follows opposite trends as determined from fluorescence microscopy experiments. The cellular binding of cationic nanoparticles is enhanced in the presence of serum proteins, while anionic nanoparticle binding is inhibited by the presence of serum proteins. Competition assays performed with flow cytometry enabled us to identify the cellular receptors used by the nanoparticle-protein complexes. We have determined that complexes formed with anionic nanoparticles bind to native protein receptors, while those formed with cationic nanoparticles bind to scavenger receptors. Similar trends were observed for anionic nanoparticles with biomedical applications including quantum dots, Au nanospheres, and low-density lipoprotein. To probe the underlying cause for the charge-dependent differences in cellular binding, we are currently characterizing the structure of the adsorbed proteins using circular dichroism, fluorescence spectroscopy, and isothermal titration calorimetry. Preliminary results suggest that protein structure is lost upon binding to cationic nanoparticles, and protein structure is retained on anionic nanoparticle surfaces. Our results indicate that, in the presence of blood serum proteins, initial nanoparticle surface charge mediates nanoparticle-cell interactions.

Size Dependent Disruption of Tethered Lipid Bilayers by Carboxylate-Modified Polystyrene Nanoparticles

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Nanoparticle Surface Charge Directs the Cellular Binding of Nanoparticle-Protein Complexes

Nanoparticles are commonly utilized in biological systems as imaging probes, drug delivery agents and in vivo sensors. In most biological applications, the nanoparticle is exposed to a complex mixture of extracellular proteins that adsorb non-specifically to the nanoparticle surface. The resulting “protein corona” can dominate the interactions of the nanoparticle with the cellular membrane. We have focused on the role of nanoparticle surface charge in the cellular binding of nanoparticles in the presence of extracellular proteins. Cationic, amine-modified polystyrene nanoparticles and anionic, carboxylate-modified polystyrene nanoparticles were studied as a model system. The cellular binding of cationic and anionic nanoparticles is distinctly different, determined from fluorescence microscopy experiments. For cationic nanoparticles, the cellular binding is increased in the presence of serum proteins. In comparison, anionic nanoparticle binding is inhibited by the presence of serum proteins. Competition assays performed with flow cytometry allowed us to quantify differences in binding and to identify the cellular receptors used by the nanoparticle-protein complexes. We have determined that complexes formed with anionic nanoparticles bind to native protein receptors, while those formed with cationic nanoparticles bind to scavenger receptors. These results indicate that for nanoparticles used in biological applications, the initial surface charge of the nanoparticle mediates cellular binding. Currently, we are extending our studies to nanoparticles used for drug and gene delivery.

Sensitive Method for Determination of Protein and Cell Concentrations Based on Competitive Adsorption to Nanoparticles and Time-Resolved Luminescence Resonance Energy Transfer between Labeled Proteins

A sensitive mix-and-measure method for the determination of protein and cell concentrations was developed. It is based on the competitive adsorption between the analyte and donor- and acceptor-labeled proteins to carboxylate-modified polystyrene nanoparticles. A high time-resolved luminescence resonance energy transfer (TR-LRET) signal is detected in the absence of the analyte due to the close proximity of the nanoparticle-adsorbed labeled proteins. The increased concentration of the analyte decreases the adsorption of the labeled proteins, leading to the loss of proximity and thus a decrease in the TR-LRET. The detection limit of the assay was 2.6 ng of proteins, which is higher than that of the most sensitive commercial methods. The method was also applied to cell counting, and 200 eukaryotic cells were measured in a microtiter well under the optimized conditions. The average coefficient of variation for both developed assays was approximately 10%, and the protein-to-protein variability for 11 different proteins was no more than 20%. The developed method requires no labeled particles, making the concept optimally applicable to varying targets as the material of the particle may be selected according to the application.

Polystyrene nanoparticle trafficking across MDCK-II

Polystyrene nanoparticles (PNP) cross rat alveolar epithelial cell monolayers via non-endocytic transcellular pathways. To evaluate epithelial cell type-specificity of PNP trafficking, we studied PNP flux across Madin Darby canine kidney cell II monolayers (MDCK-II). The effects of calcium chelation (EGTA), energy depletion (sodium azide (NaN 3) or decreased temperature), and endocytosis inhibitors methyl-β-cyclodextrin (MBC), monodansylcadaverine and dynasore were determined. Amidine-modified PNP cross MDCK-II 500 times faster than carboxylate-modified PNP. PNP flux did not increase in the presence of EGTA. PNP flux at 4°C and after treatment with NaN 3 decreased 75% and 80%, respectively. MBC exposure did not decrease PNP flux, whereas dansylcadaverine- or dynasore-treated MDCK-II exhibited ∼80% decreases in PNP flux. Confocal laser scanning microscopy revealed intracellular colocalization of PNP with clathrin heavy chain. These data indicate that PNP translocation across MDCK-II (1) occurs via clathrin-mediated endocytosis and (2) is dependent on PNP physicochemical properties. We conclude that uptake/trafficking of nanoparticles (NPs) into/across epithelia depends both on properties of the NPs and on the specific epithelial cell type. From the Clinical Editor This basic science study investigates the membrane translocation of polystyrene nanoparticles (PNP) via an epithelial cell monolayer utilizing canine kidney cells. The authors conclude that translocation occurs via clathrin-mediated endocytosis and is dependent on the physicochemical properties of the particular PNP.

Sensitive Fluorometric Nanoparticle Assays for Cell Counting and Viability

We have developed easy-to-use homogeneous methods utilizing time-resolved fluorescence resonance energy transfer (TR-FRET) and fluorescence quenching for quantification of eukaryotic cells. The methods rely on a competitive adsorption of cells and fluorescently labeled protein onto citrate-stabilized colloidal gold nanoparticles or carboxylate-modified polystyrene nanoparticles doped with an Eu(III) chelate. In the gold nanoparticle sensor, the adsorption of the labeled protein to the gold nanoparticles leads to quenching of the fluorochrome. Eukaryotic cells reduce the adsorption of labeled protein to the gold particles increasing the fluorescence signal. In the Eu(III) nanoparticle sensor, the time-resolved fluorescence resonance energy transfer between the nanoparticles and an acceptor-labeled protein is detected; a decrease in the magnitude of the time-resolved energy transfer signal (sensitized time-resolved fluorescence) is proportional to the cell-nanoparticle interaction and subsequent reduced adsorption of the labeled protein. Less than five cells were detected and quantified with the nanoparticle sensors in the homogeneous microtiter assay format with a coefficient of variation of 6% for the gold and 12% for the Eu(III) nanoparticle sensor. The Eu(III) nanoparticle sensor was also combined with a cell impermeable nucleic acid dye assay to measure cell viability in a single tube test with cell counts below 1000 cells/tube. This sensitive and easy-to-use nanoparticle sensor combined with a viability test for a low concentration of cells could potentially replace existing microscopic methods in biochemical laboratories.