Fullerene nC60 Research Articles

Impact of heavy metal cations on deposition and release of clay colloids in saturated porous media

AbstractWhile the facilitated transport of heavy metals by colloids such as clay particles has been widely recognized, the influence of heavy metals on transport of the colloids has received much less attention. This study conducted saturated column experiments to systematically examine influence of multivalent heavy metal cations on transport of natural clay colloids and fullerene nC60 nanoparticles in glass bead porous media. Results showed that the presence of Cd2+ in the solution can cause more deposition of clay colloids in glass beads compared to Ca2+ at a given ionic strength (IS), and the subsequent release by IS reduction was less, demonstrating that the presence of Cd2+ increased the irreversibility of attachment. When the glass beads were initially adsorbed with Ca2+ and Cd2+, the release of clay colloids was significantly reduced due to strong cation bridge between the clay colloids and collector surfaces via the heavy metal cations. The release of clay colloids was significantly increased upon reduction of solution IS if the Na+ was used to exchange for the Ca2+ or Cd2+ before the IS reduction. Additional experiments showed that the nC60 nanoparticles that were deposited in the presence of Fe3+ and Cu2+ cannot be released by reduction of solution IS. However, the nanoparticle release occurred when the Ca2+ was used to exchange for the Fe3+ and Cu2+. Our work was the first to reveal the influence of heavy metal cations on the irreversibility of colloid attachment, and the findings have important implication to fabrication of functional nanomaterials for stabilization of heavy metals in soil and development of mathematic models for accurate prediction of cotransport of heavy metals and colloids in subsurface environments.

Humic acid induced weak attachment of fullerene nC60 nanoparticles and subsequent detachment upon reduction of solution ionic strength in saturated porous media

Sand column experiments were performed under saturated conditions to investigate impact of humic acid (HA) on attachment of nC60 nanoparticles (NPs) in NaCl and CaCl2 at ionic strengths (ISs) from 1 mM to 100 mM and subsequent detachment via reducing solution IS. The attachment increased with increasing IS due to reduced repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy and accordingly increased retention in primary energy wells. More attachments occurred in CaCl2 compared to NaCl because Ca2+ exhibited greater charge screen ability and served as a bridging agent between the NPs and sand surfaces. The presence of HA significantly reduced nC60 NPs attachment on sand surfaces (especially on nanoscale physical heterogeneities) in 10 mM NaCl and 1 mM CaCl2 because of enhanced electrostatic and steric repulsions. Interestingly, although the HA did not cause reduction of attachment in 100 mM NaCl and 10 mM CaCl2 compared to the case in absence of HA, the HA caused weak attachment of nC60 on sand surfaces and then much more significant detachment by decreasing IS. The HA did not alter both attachment and detachment in 100 mM CaCl2, because the Ca2+ at the high concentration caused formation of very stable complex of HA and NPs, and strong interaction of the complex with the sand surfaces via cation bridge. Our study highlighted that the HA can not only enhance the transport of NPs by inhibiting attachment as revealed in the literature, but also by the continuous capture and release of the NPs from surfaces in subsurface environments.

Detachment of fullerene nC60 nanoparticles in saturated porous media under flow/stop-flow conditions: Column experiments and mechanistic explanations

This study was aimed at investigating the detachment of fullerene nC60 nanoparticles (NPs) in saturated sand porous media under transient and static conditions. The nC60 NPs were first attached at primary minima of Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energy profiles in electrolyte solutions with different ionic strengths (ISs). The columns were then eluted with deionized water to initiate nC60 NP detachment by decreasing solution IS. Finally, the flow of the columns was periodically interrupted to investigate nC60 NP detachment under static condition. Our results show that the detachment of nC60 NPs occurred under both transient and static conditions. The detachment under transient conditions was attributed to the fact that the attractions acting on the nC60 NPs at primary minima were weakened by nanoscale physical heterogeneities and overcome by hydrodynamic drags at lower ISs. However, a fraction of nC60 NPs remained at shallow primary minima in low flow regions, and detached via Brownian diffusion during flow interruptions. Greater detachment of nC60 NPs occurred under both transient and static conditions if the NPs were initially retained in electrolyte solutions with lower valent cations due to lower attractions between the NPs and collectors. Decrease in collector surface chemical heterogeneities and addition of dissolved organic matter also increased the extent of detachment by increasing electrostatic and steric repulsions, respectively. While particle attachment in and subsequent detachment from secondary minima occur in the same electrolyte solution, our results indicate that perturbation in solution chemistry is necessary to lower the primary minimum depths to initiate spontaneous detachment from the primary minima. These findings have important implications for predicting the fate and transport of nC60 NPs in subsurface environments during multiple rainfall events and accordingly for accurately assessing their environmental risks.

Removal of aqueous fullerene nC60 from wastewater by alum-enhanced primary treatment

This study examined the removal of nC60 from wastewater by alum-enhanced primary treatment at different pH levels and alum dosages and identified wastewater characteristics affecting the removal. The efficiency of the removal depended on the alum dosage, pH, alkalinity, and the concentrations of suspended solids, sewage organic matter and salinity. Alum dosage and pH influenced the removal efficiency by changing the hydrolyzed aluminum species distribution at acidic and near neutral pH levels. At pH 9–10, nC60 removal was associated with the formation of magnesium (or calcium) carbonate or hydroxide precipitates. Alkalinity dramatically enhanced the nC60 removal efficiency (by up to 71%) through the formation of sodium aluminum hydroxycarbonate precipitates. Increasing the concentration of suspended solids enhanced the nC60 removal efficiency by up to 46% at 25mg/L of alum as the solids act as adsorbents and the nuclei around which flocs can grow. Increasing the concentration of sewage organic matter decreased the nC60 removal efficiency (by 17% or less) while salinity improved it, albeit only slightly so. The results of this study demonstrate that nC60 can be effectively removed from wastewater by the alum-based chemically enhanced primary treatment process under appropriate conditions and better removal can be achieved by increasing alum dosage.

Adsorption of fullerene nC60 on activated sludge: Kinetics, equilibrium and influencing factors

The increasing production and use of fullerene C60 nanomaterials raises concerns about environmental risks and human health. However, the materials’ behavior and fate during wastewater treatment are still unclear. We investigated the adsorption of aqueous nanoscale fullerene (nC60) on activated sludge by analysis of adsorption kinetics and equilibrium. The adsorption process closely followed the pseudo-second-order kinetics model, and the adsorption isotherm was well described by the Freundlich model. The adsorption process depended strongly on the activated sludge concentration and pH, but there was no significant effect by the temperature and low ionic strength. The dissolved organic matter in wastewater could obviously inhibit the adsorption process. At mixed liquor suspended solids concentrations of 1000 and 2000mg/L after 1h mixing, nC60 removal by adsorption reached 47% and 74%, respectively. Thus, adsorption could play an important role in the fate of nC60 during conventional biological wastewater treatment. The analysis of factors influencing the adsorption amounts indicated that the nC60 adsorption behavior on activated sludge was affected by the combined forces of the hydrophobic attraction, electrostatic repulsion and steric interaction.

Carbon Nanotubes Activate Store Operated Calcium Entry (SOCE) In Human Platelets Manifested by STIM1 Capping

AbstractAbstract 3190Carbon nanotubes (CNTs) are a promising new class of materials with many potential biomedical applications. CNTs have profound impact on the development of diagnostic biosensors, drug delivery nanosystems, imaging nanoprobes for intravascular use or other devices that come in contact with blood. Therefore, the biocompatibility/toxicity of CNTs in blood is a critical safety issue. We have previously shown that agglomerates of structurally different CNTs but not fullerene (nC60), activate human platelets by inducing extracellular Ca2+ influx (Semberova, J. et al.: Nano Lett., 2009). In addition, we demonstrated that CNT-induced Ca2+ entry in platelets could be inhibited by calcium channel blockers SKF 96365 and 2-APB. Here we investigate a mechanism of CNT-induced platelet activation. Since both unmodified CNTs and nC60 are hydrophobic and insoluble in aqueous solutions, characterization of the dispersed nanomaterial agglomerates in plasma is critical for evaluation of effects on platelets. Flow particle image analysis showed that both multiwalled carbon nanotubes (MWCNTs) M60 (>95% purity; outer diameter 60–100 nm, SES) and nC60 (99.9%; MER) form agglomerates of a similar size range in plasma: median particle size 1.0 μm (10th-90th%: 0.4–2.9) μm for M60, and 0.7 μm (0.4-1.5) μm for nC60. However, roughness and surface area are markedly higher for CNT M60 (128±28 nm; 122 m2/g) compared to fullerene nC60 (4.4±3.9 nm; 0.9 m2/g). Both Field-Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) demonstrated that MWCNTs self-assemble to fiber networks which leads in platelet rich plasma to platelet entrapment, formation of pseudopodia, aggregation, platelet plasma membrane budding and release of membrane microparticles. To test whether a surface modification of CNTs leading to increased solubility would affect activity on platelets, we prepared carboxy-MWCNTs (M60(COOH)) by refluxing pristine M60 in a concentrated 3:1 (v/v) H2SO4 and HNO3 mixture at 70°C for 2 hours; followed by washing and dialysis in water. Interestingly, we observed that M60(COOH), which dispersed well in PBS, activate human blood platelets similarly like their pristine counterparts. FESEM showed that both pristine and carboxy-modified M60 self-assemble in plasma forming rope-like structures. Numerous protuberances existed on the top surface of the M60 and M60(COOH) clusters, which were formed by the relatively long, dense net, highly tangled CNTs without specific orientation. In contrast, nC60 particles are largely devoid of these surface features and minimal platelet activation was observed. In addition, TEM analysis with DAB stained platelet dense tubular system (DTS) showed nanopenetration of CNTs through platelet membranes likely causing DTS injury. Changes in calcium concentration in the intracellular compartments were studied in Fura FF loaded platelets in the presence of streptolysin and EGTA (100μM). We demonstrated a marked decrease of calcium in the intracellular stores induced by M60 or M60(COOH), as well as by SERCA inhibitor thapsigargin (TPG). Under the same conditions, nC60 did not induce depletion of calcium from the stores, similarly to the control untreated platelets. Moreover, Laser Scanning Confocal Microscopy (LSCM) using anti STIM1 (clone 44/GOK) monoclonal antibody showed that M60 caused capping of STIM1 molecules in platelets, which indicates activation of the store operated calcium entry (SOCE). Western blotting of platelet lysates showed that the anti STIM1 antibody 44/GOK detected a band at the expected MW of about 85 kDa. This was also confirmed using a polyclonal antibody against carboxy-terminal of STIM1 and corresponding blocking peptide (ProSci, Inc.). LSCM further showed a colocalization of the STIM1 and ORAI1 molecules in platelets. Similar picture of STIM1 capping in platelets was observed after treatment with TPG. In contrast, no STIM1 capping was observed in platelets treated with fullerene nC60. In conclusion, our results showed that the MWCNTs nanopenetrate membranes of DTS and activate SOCE in human platelets. The findings and conclusions in this study have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy. Disclosures:No relevant conflicts of interest to declare.

Carbon Nanotubes Activate Platelets by Facilitating Extracellular Ca2+ Influx

Due to a unique combination of their physico-chemical properties, carbon nanotubes (CNTs) are among the principal materials used in biomedical nanotechnologies. Superior mechanical characteristics like elasticity (CNTs 1012Pa vs. steel 108Pa) and tensile strength (CNTs 100 GPa vs. steel 2 GPa) make CNTs very attractive candidates as materials for plastic composites for various biomedical applications including devices for collection, processing, and storage of blood transfusion products. Moreover, CNTs have a profound impact on the development of diagnostic biosensors, drug delivery nanosystems, or imaging nanoprobes for intravascular use. Thus the investigation of CNT activities on platelets is a critical safety issue. We studied the effects of PBS suspensions of structurally different purified CNT materials from different manufacturers (Nanolab, NanoAmor, SES, MER) on human platelets (PLTs) and compared their effects to amorphous carbon black nanoparticles (ACB; > 99%, mean size 30 nm, Aldrich), C60 fullerene (nC60; 99.9%), fullerenol C60(OH)24 (both from MER Corp.), and NIST standard polystyrene nanobeads (PNBs; 20nm and 200nm; Duke Scientific Corp.). Using aggregometry of human platelet rich plasma (PRP), we found that CNT materials induced PLT aggregation in a concentration dependent manner. Single wall CNTs (SWCNTs) at 100 μg/mL showed PLT-aggregation 34 ± 10%, similarly to most tested multiwall CNTs (MWCNTs), which was significantly higher compared to ACB 15 ± 4%; p = 0.03. In contrast, fullerene nC60, fullerenol C60OH24, PNBs, or vehicle (PBS) did not cause any significant PLT aggregation (4 ± 0.5%; positive control collagen 100%). Interestingly, the thicker MWCNTs of d = 60nm (MWCNT60) exhibited significantly higher aggregating activity (27 ± 6%) compared to MWCNTs of d = 15nm (13 ± 3%; p = 0.007). Moreover, the bamboo structured MWCNTs showed only very low aggregating activity (7 ± 6%) compared to the corresponding hollow MWCNTs (33 ± 15%; p = 0.001). The PLT aggregation response (MA, AUC) induced by CNTs was proportional to the extracellular Ca2+concentration and was completely inhibited by 100 μM EDTA. The activation-dependent Ca2+ channel blocker SKF 96365 at 100 μM caused a significant inhibition (64 ± 16%) of MWCNT60-induced PLT-aggregation response. In contrast, no inhibitory effect on CNT-induced PLT-aggregation response was observed with 2-APB (20 μM; IP3 receptor inhibitor), NF 449 (1 μM; P2X1 blocker), MRS 2500 (5 nM; P2Y1 blocker), or TBHQ (20 μM; SERCA3 blocker). The effect of CNTs on intracellular free Ca2+ concentration [Ca2+]i was studied using a ratio fluorometry in platelets loaded with a Ca2+-sensitive probe FURA-2AM. Changes in fluorescence in individual platelets (n=100) were monitored using an epifluorescence/contrast phase microscope with a low light-level CCD camera/microphotometer assembly. We demonstrated that in contrast to ACB or PNBs, MWCNTs induced in platelets a rapid concentration dependent elevation of [Ca2+]i. For example, MWCNT60 at 100 μg/mL caused a 107 ± 4 nM increase in [Ca2+]i in platelets. No response was observed in Ca2+ free buffer. In addition, the flow cytometric analysis demonstrated that CNT-induced PLT activation led to surface exposure of CD62P and CD63 and a release of CD62P+ and CD63+ platelet membrane microparticles (MPs). In conclusion, we demonstrated that CNTs activate platelets and cause a platelet release reaction, aggregation, and release of MPs. The PLT-activating effect of CNTs is structure dependent: the hollow and thicker (60 nm) MWCNTs were most potent. A likely mechanism is that CNTs induce extracellular Ca2+ influx with involvement of activation-dependent Ca2+ channels. Our results warrant further studies on blood compatibility of CNT materials for biomedical applications. Caution needs to be applied when considering CNT materials as additives for plastics for transfusion devices and other devices that come in contact with blood. The findings and conclusions in this study have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any Agency determination or policy.

P.441 Serological, epidemiological and molecular aspects of hepatitis B virus infection in the largest Afro-Brazilian isolated community

This study was aimed at investigating the detachment of fullerene nC60 nanoparticles (NPs) in saturated sand porous media under transient and static conditions. The nC60 NPs were first attached at primary minima of Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energy profiles in electrolyte solutions with different ionic strengths (ISs). The columns were then eluted with deionized water to initiate nC60 NP detachment by decreasing solution IS. Finally, the flow of the columns was periodically interrupted to investigate nC60 NP detachment under static condition. Our results show that the detachment of nC60 NPs occurred under both transient and static conditions. The detachment under transient conditions was attributed to the fact that the attractions acting on the nC60 NPs at primary minima were weakened by nanoscale physical heterogeneities and overcome by hydrodynamic drags at lower ISs. However, a fraction of nC60 NPs remained at shallow primary minima in low flow regions, and detached via Brownian diffusion during flow interruptions. Greater detachment of nC60 NPs occurred under both transient and static conditions if the NPs were initially retained in electrolyte solutions with lower valent cations due to lower attractions between the NPs and collectors. Decrease in collector surface chemical heterogeneities and addition of dissolved organic matter also increased the extent of detachment by increasing electrostatic and steric repulsions, respectively. While particle attachment in and subsequent detachment from secondary minima occur in the same electrolyte solution, our results indicate that perturbation in solution chemistry is necessary to lower the primary minimum depths to initiate spontaneous detachment from the primary minima. These findings have important implications for predicting the fate and transport of nC60 NPs in subsurface environments during multiple rainfall events and accordingly for accurately assessing their environmental risks.