Surface Activity of Poly(ethylene glycol)-Coated Silver Nanoparticles in the Presence of a Lipid Monolayer.

We have investigated the surface activity of poly(ethylene glycol) (PEG)-coated silver nanoparticles (Ag-PEG) in the presence or absence of lipid monolayers comprised of monounsaturated dioleoylphosphocholine and dioleoylphosphoglycerol (DOPC/DOPG; 1:1 mol ratio). Dynamic measurements of surface pressure demonstrated that Ag-PEG were surface-active at the air/water interface. Surface excess concentrations suggested that at high Ag-PEG subphase concentrations, Ag-PEG assembled as densely packed monolayers in the presence and absence of a lipid monolayer. The presence of a lipid monolayer led to only a slight decrease in the excess surface concentration of Ag-PEG. Surface pressure-area isotherms showed that in the absence of lipids Ag-PEG increased the surface pressure up to 45 mN m-1 upon compression before the Ag-PEG surface layer collapsed. Our results suggest that surface activity of Ag-PEG was due to hydrophobic interactions imparted by a combination of the amphiphilic polymer coating and the hydrophobic dodecanethiol ligands bound to the Ag-PEG surface. With lipid present, Ag-PEG + lipid surface pressure-area (π-A) isotherms reflected Ag-PEG incorporation within the lipid monolayers. At high Ag-PEG concentrations, the π-A isotherms of the Ag-PEG + lipid films closely resembled that of Ag-PEG alone with a minimal contribution from the lipids present. Analysis of the subphase silver (Ag) and phosphorus (P) concentrations revealed that most of the adsorbed material remained at the air/lipid/water interface and was not forced into the aqueous subphase upon compression, confirming the presence of a composite Ag-PEG + lipid film. While interactions between "water-soluble" nanoparticles and lipids are often considered to be dominated by electrostatic interactions, these results provide further evidence that the amphiphilic character of a nanoparticle coating can also play a significant role.

Change in Chirality of Semiconducting Single-Walled Carbon Nanotubes Can Overcome Anionic Surfactant Stabilization: A Systematic Study of Aggregation Kinetics.

Single-walled carbon nanotubes' (SWNT) effectiveness in applications is enhanced by debundling or stabilization. Anionic surfactants are known to effectively stabilize SWNTs. However, the role of specific chirality on surfactant-stabilized SWNT aggregation has not been studied to date. The aggregation behavior of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalized with three anionic surfactants-sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium deoxycholate (SDOCO)-was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and di-valent (CaCl2) electrolytes as well as a 2.5 mg TOC/L Suwannee River humic acid (SRHA) were used as background chemistry. Overall, SDBS showed the most effectiveness in SWNT stability, followed by SDOCO and SDS. However, the relatively larger diameter (7,6) chiral tubes compromised the surfactant stability, compared to (6,5) chiral enrichment, due to enhanced van der Waals interaction. The presence of di-valent electrolytes overshadowed the chirality effects and resulted in similar aggregation behavior for both the SWNT samples. Molecular modeling results enumerated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of SRHA under 10 mM monovalent and mixed electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilization of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure.

Single-walled carbon nanotubes increase pandemic influenza A H1N1 virus infectivity of lung epithelial cells.

BACKGROUND: Airborne exposure to nanomaterials from unintended occupational or environmental exposures or as a consequence of product use may lead to adverse health effects. Numerous studies have focused on single-walled carbon nanotubes (SWCNTs) and their ability to cause pulmonary injury related to fibrosis, and cancer; however few studies have addressed their impact on infectious agents, particularly viruses that are known for causing severe disease. Here we have demonstrated the ability of pristine SWCNTs of diverse electronic structure to increase the susceptibility of small airway epithelial cells (SAEC) to pandemic influenza A H1N1 infection and discerned potential mechanisms of action driving this response. METHODS: Small airway epithelial cells (SAEC) were exposed to three types of SWCNTs with varying electronic structure (SG65, SG76, CG200) followed by infection with A/Mexico/4108/2009 (pH1N1). Cells were then assayed for viral infectivity by immunofluorescence and viral titers. We quantified mRNA and protein levels of targets involved in inflammation and anti-viral activity (INFß1, IL-8, RANTES/CCL5, IFIT2, IFIT3, ST3GAL4, ST6GAL1, IL-10), localized sialic acid receptors, and assessed mitochondrial function. Hyperspectral imaging analysis was performed to map the SWCNTs and virus particles in fixed SAEC preparations. We additionally performed characterization analysis to monitor SWCNT aggregate size and structure under biological conditions using dynamic light scattering (DLS), static light scattering (SLS). RESULTS: Based on data from viral titer and immunofluorescence assays, we report that pre-treatment of SAEC with SWCNTs significantly enhances viral infectivity that is not dependent on SWCNT electronic structure and aggregate size within the range of 106 nm - 243 nm. We further provide evidence to support that this noted effect on infectivity is not likely due to direct interaction of the virus and nanoparticles, but rather a combination of suppression of pro-inflammatory (RANTES) and anti-viral (IFIT2, IFIT3) gene/protein expression, impaired mitochondrial function and modulation of viral receptors by SWCNTs. CONCLUSIONS: Results of this work reveal the potential for SWCNTs to increase susceptibility to viral infections as a mechanism of adverse effect. These data highlight the importance of investigating the ability of carbon-nanomaterials to modulate the immune system, including impacts on anti-viral mechanisms in lung cells, thereby increasing susceptibility to infectious agents.

Mechanistic heteroaggregation of gold nanoparticles in a wide range of solution chemistry.

Heteroaggregation behavior of gold nanospheres (AuNS) in presence of pluronic acid (PA) modified single-walled carbon nanotubes (PA-SWNTs) was systematically studied for a wide range of mono- and divalent (NaCl and CaCl(2)) electrolyte conditions. Homoaggregation rates of AuNS were also determined to delineate heteroaggregation mechanisms. Time resolved dynamic light scattering (DLS) was employed to monitor aggregation. The homoaggregation of AuNS showed classical Derjaguin-Landau-Verwey-Overbeek (DLVO) type behavior with defined reaction limited (RLCA) and diffusion limited (DLCA) aggregation regimes. PA-SWNTs homoaggregation on the one hand showed no response with electrolyte increase. AuNS heteroaggregation rates on the other hand, showed regime dependent response. At low electrolyte or RLCA regime, AuNS heteroaggregation showed significantly slower rates, compared to its homoaggregation behavior; whereas enhanced heteroaggregation was observed for DLCA regime. The key mechanisms of heteroaggregation of AuNS are identified as obstruction to collision at RLCA regime and facilitating enhanced attachment at DLCA regime manifested by the presence of PA-SWNTs. Presence of Suwannee River humic acid (SRHA) showed aggregation enhancement for both homo- and hetero-systems, in presence of divalent Ca(2+) ions. Bridging between SRHA molecules is identified as the key mechanism for increased aggregation rate. The findings of this study are relevant particularly to coexistence of engineered nanomaterials. The strategy of using nonaggregating PA-SWNTs is a novel experimental strategy that can be adopted elsewhere to further the heteroaggregation studies for a wider set of particles and surface coatings.

Single-walled carbon nanotube transport in representative municipal solid waste landfill conditions.

Single-walled carbon nanotubes (SWNTs) are being used in many consumer products and devices. It is likely that as some of these products reach the end of their useful life, they will be discarded in municipal solid waste landfills. However, there has been little work evaluating the fate of nanomaterials in solid waste environments. The purpose of this study is to systematically evaluate the influence of organic matter type and concentration in landfill-relevant conditions on SWNT transport through a packed-bed of mixed municipal solid waste collectors. The influence of individual waste materials on SWNT deposition is also evaluated. Transport experiments were conducted through saturated waste-containing columns over a range of simulated leachate conditions representing both mature and young leachates. Results indicate that SWNT transport may be significant in mature waste environments, with mobility decreasing with decreasing humic acid concentration. SWNT mobility in the presence of acetic acid was inhibited, suggesting their mobility in young waste environments may be small. SWNTs also exhibited collector media-dependent transport, with greatest transport in glass and least in paper. These results represent the first study evaluating how leachate age and changes in waste composition influence potential SWNT mobility in landfills.

Chirality affects aggregation kinetics of single-walled carbon nanotubes.

Aggregation kinetics of chiral-specific semiconducting single-walled carbon nanotubes (SWNTs) was systematically studied through time-resolved dynamic light scattering. Varied monovalent (NaCl) and divalent (CaCl(2)) electrolyte composition was used as background solution chemistry. Suwannee River humic acid (SRHA) was used to study the effects of natural organic matter on chirally separated SWNT aggregation. Increasing salt concentration and introduction of divalent cations caused aggregation of SWNT clusters by suppressing the electrostatic repulsive interaction from the oxidized surfaces. The (6,5) SWNTs, i.e., SG65, with relatively lower diameter tubes compared to (7,6), i.e., SG76, showed substantially higher stability (7- and 5-fold for NaCl and CaCl(2), respectively). The critical coagulation concentration (CCC) values were 96 and 13 mM NaCl in the case of NaCl and 2.8 and 0.6 mM CaCl(2) for SG65 and SG76, respectively. The increased tube diameter for (7,6) armchair SWNTs likely presented with higher van der Waals interaction and thus increased the aggregation propensity substantially. The presence of SRHA enhanced SWNT stability in divalent CaCl(2) environment through steric interaction from adsorbed humic molecules; however showed little or no effects for monovalent NaCl. The mechanism of aggregation-describing favorable interaction tendencies for (7,6) SWNTs-is probed through ab initio molecular modeling. The results suggest that SWNT stability can be chirality dependent in typical aquatic environment.

Ultrasonication study for suspending single-walled carbon nanotubes in water.

A systematic calorimetry-based technique was developed to standardize single-walled carbon nanotube (SWNT) dispersion protocol. Simple calorimetric experiments were performed to benchmark the performance of the ultra-dismembrator. Temperature profiles for the sonication period were utilized to estimate energy input to the system. Energy loss profile was generated for the ultradismembrator in use and a calibration relationship was formulated that could standardize the sonication process. The standardized protocol was used to prepare aqueous SWNT suspensions-sonicating SWNTs in a varied range of input energy (18-100 kJ) in water. SWNT mass fractions suspended for each energy input was accurately measured and the suspended SWNT samples were characterized for morphology, surface potential, cluster size and structure, and chemical functionality using high resolution transmission electron microscopy (HRTEM), electrophoresis, dynamic and static light scattering (DLS/SLS), and Raman spectroscopy. The study demonstrated that suspended mass of SWNTs increased up to 18 kJ of energy input with no further increase upon continued energy input. The physicochemical properties showed similar trend for energy input. The aggregate cluster size, surface potential behavior, as well as the Raman defect properties plateaued after the initial energy input. The significant changes observed were limited to morphological properties, i.e., shorter length, debundled, and sharp edged SWNTs and fractal cluster formation (lower D(f)) with increased input energy.

A Novel Core-Shell Microcapsule for Encapsulation and 3D Culture of Embryonic Stem Cells.

In this study, we report the preparation of a novel microcapsule of ~ 100 µm with a liquid (as compared to solid-like alginate hydrogel) core and an alginate-chitosan-alginate (ACA) shell for encapsulation and culture of embryonic stem (ES) cells in the miniaturized 3D space of the liquid core. Murine R1 ES cells cultured in the microcapsules were found to survive (> 90%) well and proliferate to form either a single aggregate of pluripotent cells or embryoid body (EB) of more differentiated cells in each microcapsule within 7 days, dependent on the culture medium used. This novel microcapsule technology allows massive production of the cell aggregates or EBs of uniform size and controllable pluripotency, which is important for the practical application of stem cell based therapy. Moreover, the semipermeable ACA shell was found to significantly reduce immunoglobulin G (IgG) binding to the encapsulated cells by up to 8.2 times, compared to non-encapsulated cardiac fibroblasts, mesenchymal stem cells, and ES cells. This reduction should minimize inflammatory and immune responses induced damage to the cells implanted in vivo becasue IgG binding is an important first step of the undesired host responses. Therefore, the ACA microcapsule with selective shell permeability should be of importance to advance the emerging cell-based medicine.

Fractal structures of single-walled carbon nanotubes in biologically relevant conditions: role of chirality vs. media conditions.

Aggregate structure of covalently functionalized chiral specific semiconducting single-walled carbon nanotubes (SWNTs) was systematically studied employing static light scattering (SLS). Fractal dimensions (Df) of two specific chirality SWNTs-SG65 and SG76 with (6, 5) and (7, 6) chiral enrichments-were measured under four biological exposure media conditions, namely: Dulbecco's Modified Eagle Medium (DMEM), Minimum Essential Medium (MEM), Roswell Park Memorial Institute (RPMI) 1640 medium, and 0.9% saline solution. The SWNTs exhibited chiral dependence on Df with SG65 showing more fractal or loosely bound aggregate structures, i.e., lower Df values (range of 2.24±0.03 to 2.64±0.05), compared to the SG76 sample (range of 2.58±0.13 to 2.90±0.08). All the Df values reported are highly reproducible, measured from multiple SLS runs and estimated with 'random block-effects' statistical analysis that yielded all p values to be <0.001. The key mechanism for such difference in Df between the SWNT samples was identified as the difference in van der Waals (VDW) interaction energies of these samples, where higher VDW of SG76 resulted in tighter packing density. Effect of medium type showed lower sensitivity; however, presence of di-valent cations (Ca(2+)) in DMEM and MEM media resulted in relatively loose or more fractal aggregates. Moreover, presence of fetal bovine serum (FBS) and bovine serum albumin (BSA), used to mimic the in vitro cell culture condition, reduced the Df values, i.e., created more fractal structures. Steric hindrance to aggregation was identified as the key mechanism for creating the fractal structures. Also, increase in FBS concentration from 1% to 10% resulted in increasingly lower Df values.

Barrier properties of poly(vinyl alcohol) membranes containing carbon nanotubes or activated carbon.

Carbon nanotube addition has been shown to improve the mechanical properties of some polymers. Because of their unique adsorptive properties, carbon nanotubes may also improve the barrier performance of polymers used in contaminant containment. This study compares the barrier performance of poly(vinyl alcohol) (PVA) membranes containing single-walled carbon nanotubes (SWCNTs) to that for PVA containing powdered activated carbon (PAC). Raw and surface-functionalized versions of each sorbent were tested for their abilities to adsorb 1,2,4-trichlorobenzene and Cu(2+), representing the important hydrophobic organic and heavy metal contaminant classes, as they diffused across the PVA. In both cases, PAC (for 1,2,4-trichlorobenzene) and functionalized PAC (for Cu(2+)) outperformed SWCNTs on a per mass basis by trapping more of the contaminants within the barrier membrane. Kinetics of sorption are important in evaluating barrier properties, and poor performance of SWCNT-containing membranes as 1,2,4-TCB barriers is attributed to kinetic limitations.

Removal of bisphenol A and 17α-ethinyl estradiol from landfill leachate using single-walled carbon nanotubes.

In this study, the adsorption of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) from landfill leachate onto single-walled carbon nanotubes (SWCNTs) was investigated. Different leachate solutions were prepared by altering the pH, ionic strength, and dissolved organic carbon (DOC) in the solutions to mimic the varying water conditions that occur in leachate during the various stages of waste decomposition. The youngest and oldest leachate solutions contained varying DOC and background chemistry and were represented by leachate Type A (pH = 5.0; DOC = 2500 mg/L; conductivity = 12,500 µS/cm; [Ca(2+)] = 1200 mg/L; [Mg(2+)] = 470 mg/L) and Type E (pH = 7.5; DOC = 250 mg/L; conductivity = 3250 µS/cm; [Ca(2+)] = 60 mg/L; [Mg(2+)] = 180 mg/L). These solutions were subsequently combined in different ratios to produce intermediate solutions, labeled B-D, to replicate time-dependent changes in leachate composition. Overall, a larger fraction of EE2 was removed as compared to BPA, consistent with its higher log K(OW) value. The total removal of BPA and EE2 decreased in older leachate solutions, with the adsorptive capacity of SWCNTs decreasing in the order of leachate Type A > Type B > Type C > Type D > Type E. An increase in the pH from 3.5 to 11 decreased the adsorption of BPA by 22% in young leachate and by 10% in old leachate. The changes in pH did not affect the adsorption of EE2 in the young leachate, but did reduce adsorption by 32% in the old leachate. Adjusting the ionic strength using Na(+) did not significantly impact adsorption, while increasing the concentration of Ca(2+) resulted in a 12% increase in the adsorption of BPA and a 19% increase in the adsorption of EE2. DOC was revealed to be the most influential parameter in this study. In the presence of hydrophilic DOC, represented by glucose in this study, adsorption of the endocrine disrupting compounds (EDCs) onto the SWCNTs was not affected. In the absence of SWCNTs, hydrophobic DOC (i.e., humic acid) adsorbed 15-20% of BPA and EE2. However, when the humic acid and SWCNTs were both present, the overall adsorptive capacity of the SWCNTs was reduced. Hydrophobic (π-π electron donor-acceptor) interactions between the EDCs and the constituents in the leachate, as well as interactions between the SWCNTs and the EDCs, are proposed as potential adsorption mechanisms for BPA and EE2 onto SWCNTs.