The adsorption–desorption process of bovine serum albumin on carbon nanotubes

Stability Study of Graphene Oxide-Bovine Serum Albumin Dispersions

In this work, a stability study of dispersions of graphene oxide and graphene oxide functionalized with polyethylene glycol (PEG) in the presence of bovine serum albumin is carried out. First, a structural characterization of these nanomaterials is performed by scanning electron microscopy, atomic force microscopy, and ultraviolet visible spectroscopy, comparing the starting nanomaterials with the nanomaterials in contact with the biological material, i.e., bovine fetal serum. The different experiments were performed at different concentrations of nanomaterial (0.125-0.5 mg/mL) and BSA (0.01-0.04 mg/mL), at different incubation times (5-360 min), with and without PEG, and at different temperatures (25-40 °C). The SEM results show that BSA is adsorbed on the surface of the graphene oxide nanomaterial. Using UV-Vis spectrophotometry, the characteristic absorption peaks of BSA are observed at 210 and 280 nm, corroborating that the protein has been adsorbed. When the time increases, the BSA protein can be detached from the nanomaterial due to a desorption process. The stability of the dispersions is reached at a pH between 7 and 9. The dispersions behave like a Newtonian fluid with viscosity values between 1.1 and 1.5 mPa·s at a temperature range of 25 to 40 °C. The viscosity values decrease as the temperature increases.

Deposition behavior of lignin on solid surfaces assessed by stagnation point adsorption reflectometry

The deposition behavior of lignin on a solid surface was studied using stagnation point adsorption reflectometry (SPAR) comprehensively. In this study, the light absorption coefficient of lignin (τ = 20 476 m-1) at 633 nm wavelength was considered to define a new imaginary refractive index (k) used in the SPAR technique for adsorption analysis. The inclusion of k in the adsorption model yielded an adsorbed amount (Γ) of 1.11 mg m-2, leading to the quality factor (Q f) of 31.71 mg m-2. At a lower concentration, the deposition of lignin on the surface was increased, and it generated a maximum sticking coefficient of β = 0.71 at 25 mg L-1 on the surface. At the concentration range of 35 and 45 mg L-1, lignin formed clusters and its deposition dropped. The use of Quartz crystal microbalance (QCM) and SPAR techniques also confirmed that the proportion of water in the deposited lignin adlayer was greater when a lower concentration (5-25 mg L-1) of lignin solution was used for adsorption. The findings of this study revealed the potential use of the SPAR technique for evaluating the deposition performance of lignin-based materials on varied surfaces, which would facilitate the development of coating and composite applications for lignin.

Protein Adsorption on SiO2-CaO Bioactive Glass Nanoparticles with Controllable Ca Content

Bioactive glass nanoparticles (BGNs) are emerging multifunctional building blocks for various biomedical applications. In this study, the primary aim was to develop monodispersed binary SiO2-CaO BGNs with controllable Ca content. We successfully synthesized such spherical BGNs (size ~110 nm) using a modified Stöber method. Our results showed that the incorporated Ca did not significantly affect particle size, specific surface area, and structure of BGNs. Concentrations of CaO in BGN compositions ranging from 0 to 10 mol% could be obtained without the gap between actual and nominal compositions. For this type of BGNs (specific surface area 30 m2/g), the maximum concentration of incorporated CaO appeared to be ~12 mol%. The influence of Ca content on protein adsorption was investigated using bovine serum albumin (BSA) and lysozyme as model proteins. The amount of adsorbed proteins increased over time at the early stage of adsorption (<2 h), regardless of glass composition and protein type. Further incubation of BGNs with protein-containing solutions seemed to induce a reduced amount of adsorbed proteins, which was more significant in BGNs with higher Ca content. The results indicate that the Ca content in BGNs is related to their protein adsorption behavior.

Deposition of protein-coated multi-walled carbon nanotubes on oxide surfaces and the retention in a silicon micromodel

The aggregation, deposition and porous retention of bovine serum albumin treated multi-walled carbon nanotubes (BSA-MWCNTs) are investigated using dynamic light scattering (DLS), quartz crystal microbalance with dissipation (QCM-D) and 2-dimensional silicon micromodel, respectively. The aggregation of BSA-MWCNTs is consistent with Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The critical coagulation concentration (CCC) is 175 mM NaCl and 2.7 mM CaCl₂, suggesting that Ca²⁺ causes stronger aggregation. The BSA-MWCNT deposition on SiO₂ surface is unfavorable with critical deposition concentration (CDC) of 100 mM in NaCl and 0.9 mM in CaCl₂. The deposition on the Al₂O₃ surface is favorable. Deposition rate is dominated by electrostatic forces at low ionic strength (IS), but electrostatic interaction is eliminated when IS is above CDC. Therefore the deposition rate on SiO₂ or Al₂O₃ surface starts decreasing at the CDC point due to the reduced particle diffusion. In micromodel, the amount and position of attached BSA-MWCNTs in pore space can be observed by a microscope. The retention attachment efficiency increases at higher IS. The suspended BSA-MWCNTs approach to the collector through either diffusion or interception. The attached BSA-MWCNTs narrow the pore space and then clog the pore throats. The straining process happens on the clogged pore throats.

Addressing the distribution of proteins spotted on μPADs

Adsorption is the most common approach to immobilize biorecognition elements on the surface of paper-based devices.

Carbon nanotubes: a novel material for multifaceted applications in human healthcare

Remarkable advances achieved in modern material technology, especially in device fabrication, have facilitated diverse materials to expand the list of their application fields.

Protein adsorption onto nanomaterials for the development of biosensors and analytical devices: a review

An important consideration for the development of biosensors is the adsorption of the biorecognition element to the surface of a substrate. As the first step in the immobilization process, adsorption affects most immobilization routes and much attention is given into the research of this process to maximize the overall activity of the biosensor. The use of nanomaterials, specifically nanoparticles and nanostructured films, offers advantageous properties that can be fine-tuned to maximize interactions with specific proteins to maximize activity, minimize structural changes, and enhance the catalytic step. In the biosensor field, protein-nanomaterial interactions are an emerging trend that span across many disciplines. This review addresses recent publications about the proteins most frequently used, their most relevant characteristics, and the conditions required to adsorb them to nanomaterials. When relevant and available, subsequent analytical figures of merits are discussed for selected biosensors. The general trend amongst the research papers allows concluding that the use of nanomaterials has already provided significant improvements in the analytical performance of many biosensors and that this research field will continue to grow.

Random networks of single-walled carbon nanotubes promote mesenchymal stem cell's proliferation and differentiation

Studies on the interaction of cells with single-walled carbon nanotubes (SWCNTs) have been receiving increasing attention owing to their potential for various cellular applications. In this report, we investigated the interactions between biological cells and nanostructured SWCNTs films and focused on how morphological structures of SWCNT films affected cellular behavior such as cell proliferation and differentiation. One directionally aligned SWCNT Langmuir-Blodgett (LB) film and random network SWCNT film were fabricated by LB and vacuum filteration methods, respectively. We demonstrate that our SWCNT LB and network film based scaffolds do not show any cytotoxicity, while on the other hand, these scaffolds promote differentiation property of rat mesenchymal stem cells (rMSCs) when compared with that on conventional tissue culture polystyrene substrates. Especially, the SWCNT network film with average thickness and roughness values of 95 ± 5 and 9.81 nm, respectively, demonstrated faster growth rate and higher cell thickness for rMSCs. These results suggest that systematic manipulation of the thickness, roughness, and directional alignment of SWCNT films would provide the convenient strategy for controlling the growth and maintenance of the differentiation property of stem cells. The SWCNT film could be an alternative culture substrate for various stem cells, which often require close control of the growth and differentiation properties.

Fabrication of PVDF membranes entrapped with oleic acid modified TiO2 and selective adsorption toward bovine hemoglobin

An active adsorption membrane of OA-modified TiO₂ entrapped PVDF showed selective adsorption toward BHb, that proposed application in protein separation.

Investigating linear and nonlinear viscoelastic behaviour and microstructures of gelatin-multiwalled carbon nanotube composites

The linear and nonlinear rheology of physically-crosslinked-gelatin gel-multiwalled carbon nanotube (MWNT), chemically-crosslinked-gelatin gel-MWNT, and chemically–physically-crosslinked-gelatin gel-MWNT composites, are investigated.

Binding of hydroxylated single-walled carbon nanotubes to two hemoproteins, hemoglobin and myoglobin

Herein, we studied the binding interactions between hydroxylated single-walled carbon nanotubes and hemoglobin and myoglobin by the use of multi-spectral techniques and molecular modeling. The ultraviolet-vis absorbance and circular dichroism spectral results indicated that the binding interactions existed between hydroxylated single-walled carbon nanotubes and hemoglobin/myoglobin. These binding interactions partially affected the soret/heme bands of hemoglobin and myoglobin. The secondary structures of hemoproteins were partially destroyed by hydroxylated single-walled carbon nanotubes. Fluorescence studies suggested that the complexes formed between hydroxylated single-walled carbon nanotubes and hemoglobin/myoglobin by hydrogen bonding, hydrophobic, and π-π stacking interactions. In addition, molecular modeling analysis well supported the experimental results.

New insight into the binding interaction of hydroxylated carbon nanotubes with bovine serum albumin

In order to understand the effects of carbon nanotubes on the structural stability of proteins, the ligand-binding ability, fibrillation, and chemical denaturation of bovine serum albumin in the presence of a multi-walled hydroxylated carbon nanotubes (HO-MWCNTs) was characterized by UV-vis, circular dichroism, fluorescence spectroscopy and molecule modeling methods at the molecular level. The experiment results indicated that the fluorescence intensity of BSA was decreased obviously in presence of HO-MWCNTs. The binding interaction of HO-MWCNTs with BSA led to the secondary structure changes of BSA. This interaction could not only affect the ligand-binding ability of BSA, but also change the rate of fibrillation and denaturation of BSA. This work gave us some important information about the structures and properties of protein induced by carbon nanotubes.

Potential-assisted adsorption of bovine serum albumin onto optically transparent carbon electrodes

This article describes the effect of the applied potential on the adsorption of bovine serum albumin (BSA) to optically transparent carbon electrodes (OTCE). To decouple the effect of the applied potential from the high affinity of the protein for the bare surface, the surface of the OTCE was initially saturated with a layer of BSA. Experiments described in the article show that potential values higher than +500 mV induced a secondary adsorption process (not observed at open-circuit potential), yielding significant changes in the thickness (and adsorbed amount) of the BSA layer obtained. Although the process showed a significant dependence on the experimental conditions selected, the application of higher potentials, selection of pH values around the isoelectric point (IEP) of the protein, high concentrations of protein, and low ionic strengths yielded faster kinetics and the accumulation of larger amounts of protein on the substrate. These experiments, obtained around the IEP of the protein, contrast with the traditional hypothesis that enhanced electrostatic interactions between the polarized substrate and the (oppositely charged) protein are solely responsible for the enhanced adsorption. These results suggest that the potential applied to the electrode is able to polarize the adsorbed layer and induce dipole-dipole interactions between the adsorbed and the incoming protein. This mechanism could be responsible for the potential-dependent oversaturation of the surface and could bolster to the development of surfaces with enhanced catalytic activity and implants with improved biocompatibility.

Real-time study of protein adsorption kinetics in porous silicon

This paper presents an optical method for real-time monitoring of protein adsorption using porous silicon self-supported microcavities as a label-free detection platform. The study combines an experimental approach with a physical model for the adsorption process. The proposed model agrees well with experimental observations, and provides information about the kinetics of diffusion and adsorption of proteins within the pores, which will be useful for future experimental designs.

Interaction of carboxylated single-walled carbon nanotubes with bovine serum albumin

Carboxylated single-walled carbon nanotubes (c-SWNTs) were synthesized prosperously in order to improve dispersion of raw carbon nanotubes. Then, bovine serum albumin (BSA) was used as the template protein to study the biocompatibility of c-SWNTs by UV-Vis, fluorescence and circular dichroism (CD) spectroscopic methods at the molecular level. Results from fluorescence spectrum showed obvious decreases in fluorescence intensity of BSA induced by c-SWNTs, indicating the occurrence of interaction between BSA and c-SWNTs. Static quenching effect of c-SWNTs was verified by linear Stern-Volmer plots and K(SV) values. Thermodynamic parameters at different temperatures demonstrated that the interaction between c-SWNTs and BSA was mainly favored by hydrophobic force. In addition, Na(+) interfered with the quenching effect of c-SWNTs, which revealed that electrostatic force played a role in binding roles of BSA to c-SWNTs simultaneously. The results of UV and synchronous fluorescence spectrum validated that hydrophobicity of amino acid residues expressly increased with the addition of c-SWNTs. The content of α-helix structure in BSA decreased by 14.06% with c-SWNTs viewed from CD spectrum. Effect of SWNTs on the conformation of BSA could be controlled by the surface chemistry of SWNTs.

Ultrathin optically transparent carbon electrodes produced from layers of adsorbed proteins

This work describes a simple, versatile, and inexpensive procedure to prepare optically transparent carbon electrodes, using proteins as precursors. Upon adsorption, the protein-coated substrates were pyrolyzed under reductive conditions (5% H2) to form ultrathin, conductive electrodes. Because proteins spontaneously adsorb to interfaces forming uniform layers, the proposed method does not require a precise control of the preparation conditions, specialized instrumentation, or expensive precursors. The resulting electrodes were characterized by a combination of electrochemical, optical, and spectroscopic means. As a proof-of-concept, the optically transparent electrodes were also used as substrate for the development of an electrochemical glucose biosensor. The proposed films represent a convenient alternative to more sophisticated, and less available, carbon-based nanomaterials. Furthermore, these films could be formed on a variety of substrates, without classical limitations of size or shape.

Activated carbons and carbon-containing poly(vinyl alcohol) cryogels: characterization, protein adsorption and possibility of myoglobin clearance

Adsorption of myoglobin (Mb), bovine serum albumin (BSA) and γ-globulin (GG) onto activated carbons (ACs) with different pore size distributions, and poly(vinyl alcohol) (PVA) monolithic cryogels containing AC particles was studied. The highest initial rate of Mb adsorption was observed for AC having the largest specific surface area (1939 m(2) g(-1)) and pore volume (1.82 cm(3) g(-1)). The adsorption kinetics of proteins was characterized by a bimodal shape of the distribution f(D) function of an effective diffusion coefficient. Adsorption isotherms of Mb and GG were of Freundlich type within the studied range of equilibrium concentrations (10-150 μg mL(-1)). The distributions of free energy of protein adsorption were bimodal and reflected both interactions with carbon surfaces and self-association of proteins. Adsorbed amounts of Mb were the highest among the proteins studied (up to 700 mg g(-1) carbon), which was attributed to the higher fraction of pores accessible for Mb. Incorporation of carbon particles into PVA-based cryogel resulted in macroporous monolithic composite materials (AC-PVA) exhibiting good flow-through properties. Scanning electron microscopy of the composites showed macroporous aggregates of carbon particles held together by films and bridges of PVA. The rates of adsorption and adsorbed amounts of proteins on AC-PVA were reduced compared to the pristine carbon and depended on the carbon content in the composites. Nevertheless, adsorption of Mb on AC-PVA took place even in the presence of 500-fold higher concentration of BSA. This indicated a possibility of Mb clearance from blood plasma using the PVA-carbon monoliths.

Computational, electrochemical, and spectroscopic, studies of acetycholinesterase covalently attached to carbon nanotubes

This manuscript describes results related to the characterization of electrodes modified with a composite of acetylcholinesterase covalently bound to carbon nanotubes (CNT). The characterization was performed by computational methods and complemented by cyclic voltammetry, infrared spectroscopy, and electrochemical impedance spectroscopy. In-silico simulations enabled the identification of the binding site and the calculation of the interaction energy. Besides complementing the computational studies, experimental results obtained by cyclic voltammetry showed that the addition of CNT to the surface of electrodes yielded significant increases in effective area and greatly facilitated the electron transfer reactions. These results are also in agreement with impedance spectroscopy data, which indicated a high apparent rate constant, even after the immobilization of the enzyme. These results lend new information about the physical and chemical properties of biointerfaces at the molecular level, specifically about the mechanism and consequences of the interaction of a model enzyme with CNT.

Research Spotlight: The next big thing is actually small

Recent developments in materials, surface modifications, separation schemes, detection systems and associated instrumentation have allowed significant advances in the performance of lab-on-a-chip devices. These devices, also referred to as micro total analysis systems (µTAS), offer great versatility, high throughput, short analysis time, low cost and, more importantly, performance that is comparable to standard bench-top instrumentation. To date, µTAS have demonstrated advantages in a significant number of fields including biochemical, pharmaceutical, military and environmental. Perhaps most importantly, µTAS represent excellent platforms to introduce students to microfabrication and nanotechnology, bridging chemistry with other fields, such as engineering and biology, enabling the integration of various skills and curricular concepts. Considering the advantages of the technology and the potential impact to society, our research program aims to address the need for simpler, more affordable, faster and portable devices to measure biologically active compounds. Specifically, the program is focused on the development and characterization of a series of novel strategies towards the realization of integrated microanalytical devices. One key aspect of our research projects is that the developed analytical strategies must be compatible with each other; therefore, enabling their use in integrated devices. The program combines spectroscopy, surface chemistry, capillary electrophoresis, electrochemical detection and nanomaterials. This article discusses some of the most recent results obtained in two main areas of emphasis: capillary electrophoresis, microchip-capillary electrophoresis, electrochemical detection and interaction of proteins with nanomaterials.

Screening the cytotoxicity of single-walled carbon nanotubes using novel 3D tissue-mimetic models

Single-walled carbon nanotubes (SWNTs) are promising candidates for a wide range of biomedical applications due to their fascinating properties. However, safety concerns are raised on their potential human toxicity and on the techniques that need to be used to assess such toxicity. Here, we integrate for the first time 3D tissue-mimetic models in the cytotoxicity assessment of purified (p-) and oxidized (o-) SWNTs. An established ultrasound standing wave trap was used to generate the 3D cell aggregates, and results were compared with traditional 2D cell culture models. Protein-based (bovine serum albumin) and surfactant-based (Pluronic F68) nanotube dispersions were tested and compared to a reference suspension in dimethyl sulfoxide. Our results indicated that p- and o-SWNTs were not toxic in the 3D cellular model following a 24 h exposure. In contrast, 2D cell cultures were significantly affected by exposure to p- and o-SWNTs after 24 h, as assessed by high-content screening and analysis (HCSA). Finally, cytokine (IL-6 and TNF-α) secretion levels were elevated in the 2D but remained essentially unchanged in the 3D cell models. Our results strongly indicate that 3D cell aggregates can be used as alternative in vitro models providing guidance on nanomaterial toxicity in a tissue-mimetic manner, thus offering future cost-effective solutions for toxicity screening assays under the experimental conditions more closely related to the physiological scenario in 3D tissue microenvironments.

Differential toxicity of copper (II) oxide nanoparticles of similar hydrodynamic diameter on human differentiated intestinal Caco-2 cell monolayers is correlated in part to copper release and shape

The potential toxic effects of copper oxide (CuO) nanoparticles (NPs) were studied on differentiated Caco-2 cell monolayers, a classical in vitro model of human small intestine epithelium. Two types of CuO NPs, with different specific surface area, different sizes as raw material but the same hydrodynamic diameter in suspension, differentially disturbed the monolayer integrity, were cytotoxic and triggered an increase of the abundance of several transcripts coding for pro-inflammatory cytokines and chemokines. Specific surface area was not a major variable explaining the increased toxicity when intestinal epithelium is exposed to rod-shaped CuO NPs, compared with spherical CuO NPs. The results suggest that release of Cu(II) cations and shape of these CuO NPs are likely to be implicated in the toxicity of these CuO NPs.

Nanomolar Detection of Glutamate at a Biosensor Based on Screen-Printed Electrodes Modified with Carbon Nanotubes

The amperometric glutamate biosensor based on screen-printed electrodes containing carbon nanotubes (CNT), and its integration in a flow injection analysis system, is described herein. The sensor was fabricated by simply adsorbing enzyme glutamate oxidase (GlutOx) on a commercial substrate containing multi-wall CNT. The resulting device displayed excellent electroanalytical properties toward the determination of L-glutamate in a wide linear range (0.01-10 μM) with low detection limit (10 nM, S/N≥3), fast response time (≤5 s), and good operational and long-term stability. The CNT modified screen-printed electrodes have a potential to be of general interest for designing of electrochemical sensors and biosensors.

Adsorption of Glucose Oxidase to 3-D Scaffolds of Carbon Nanotubes: Analytical Applications

This study is the first to focus on the potential use of carbon nanotube (CNT) scaffolds as enzyme immobilization substrates for analytical purposes. Besides all the well-known advantages of CNT, three-dimensional scaffolds can significantly increase the amount of enzymes adsorbed per unit area, preserve the catalytic activity of the adsorbed molecules, and allow effective exposure to substrates present in the adjacent medium. Additionally, our results indicate that the sensitivity of analytical probes based on enzyme-loaded CNT scaffolds is proportional to the thickness of the scaffold providing 3-fold sensitivity improvements with respect to the control surfaces.

Recent applications of carbon-based nanomaterials in analytical chemistry: critical review

The objective of this review is to provide a broad overview of the advantages and limitations of carbon-based nanomaterials with respect to analytical chemistry. Aiming to illustrate the impact of nanomaterials on the development of novel analytical applications, developments reported in the 2005-2010 period have been included and divided into sample preparation, separation, and detection. Within each section, fullerenes, carbon nanotubes, graphene, and composite materials will be addressed specifically. Although only briefly discussed, included is a section highlighting nanomaterials with interesting catalytic properties that can be used in the design of future devices for analytical chemistry.

Ferritin immobilization on patterned poly(2-hydroxyethyl methacrylate) brushes on silicon surfaces from colloid system

In this paper, we describe a graft polymerization/solvent immersion method for generating poly(2-hydroxyethyl methacrylate) (PHEMA) brushes in various patterns. We used a novel fabrication process, involving very-large-scale integration and oxygen plasma treatment, to generate well-defined patterns of polymerized PHEMA on patterned Si(100) surfaces. We observed brush- and mushroom-like regions for the PHEMA brushes, with various pattern resolutions, after immersing wafers presenting lines of these polymers in MeOH and n-hexane, respectively. The interaction between PHEMA and ferritin protein sheaths in MeOH and n-hexane (good and poor solvent for PHEMA, respectively) was used to capture and release ferritins from fluidic system. The “tentacles” behaver for PHEMA brushes was found through various solvents in fluidic system. Using high-resolution scanning electron microscopy, we observed patterned ferritin Fe cores on the Si surface after pyrolysis of the patterned PHEMA brushes and ferritin protein sheaths, which verify the “tentacles” behaver for PHEMA brushes.

Adsorption of Proteins to Thin-Films of PDMS and Its Effect on the Adhesion of Human Endothelial Cells

This paper describes a simple and inexpensive procedure to produce thin-films of poly(dimethylsiloxane). Such films were characterized by a variety of techniques (ellipsometry, nuclear magnetic resonance, atomic force microscopy, and goniometry) and used to investigate the adsorption kinetics of three model proteins (fibrinogen, collagen type-I, and bovine serum albumin) under different conditions. The information collected from the protein adsorption studies was then used to investigate the adhesion of human dermal microvascular endothelial cells. The results of these studies suggest that these films can be used to model the surface properties of microdevices fabricated with commercial PDMS. Moreover, the paper provides guidelines to efficiently attach cells in BioMEMS devices.

Adsorption kinetics of catalase to thin films of carbon nanotubes

The adsorption conditions used to immobilize catalase onto thin films of carbon nanotubes were investigated to elucidate the conditions that produced films with maximum amounts of active catalase. The adsorption kinetics were monitored by spectroscopic ellipsometry, and the immobilized catalase films were then assayed for catalytic activity. The development of a volumetric optical model used to interpret the ellipsometric data is discussed. According to the results herein discussed, not only the adsorbed amount but also the initial adsorption rates determine the final catalytic activity of the adsorbed layer. The results described in this paper have direct implications on the rational design and analytical performance of enzymatic biosensors.

An anticipatory governance approach to carbon nanotubes

Carbon nanotubes (CNTs) are novel materials with remarkable properties; possible beneficial applications include aircraft frames, hydrogen storage, environmental sensors, electrical transmission, and many more. At the same time, precise characterization of their potential toxicity remains elusive, in part because engineered nanostructures pose challenges to existing assays, predictive models, and dosimetry. While these obstacles are surmountable, their presence suggests that scientific uncertainty regarding the hazards of CNTs is likely to persist. Traditional U.S. policy approaches implicitly pose the question: "What level of evidence is necessary and sufficient to justify regulatory action?" In the case of CNTs, such a strategy of risk analysis is of limited immediate utility to both regulators essaying to carry out their mandates, and users of CNTs seeking to provide an appropriate level of protection to employees, customers, and other stakeholders. In contrast, the concept of anticipatory governance suggests an alternative research focus, that is: "Given the conflicted character of the data, how should relevant actors respond?" Adopting the latter theoretical framework, this article argues that currently available data support treating CNTs "as if" they are hazardous, while simultaneously highlighting some systemic uncertainties in many of the experiments carried out to date. Such a conclusion implies limiting exposure throughout product lifecycles, and also points to the possible applicability of various conceptual tools, such as life-cycle and multicriteria decision analysis approaches, in choosing appropriate courses of action in the face of prolonged uncertainty.

Oxidation reactions mediated by single-walled carbon nanotubes in aqueous solution

How single-walled carbon nanotubes (SWCNT) function in redox reactions may be related to their behaviors in the induction of oxidative stress. Herein, oxidation of several biologically relevant reducing agents in the presence of SWCNT was studied in aqueous solutions. The selected reductants included a common indicator for intracellular reactive oxygen species (ROS) (2,7-dichlorodihydrofluorescein), small antioxidants (vitamin C, Trolox, and cysteine), and a high-molecular-weight ROS scavenger (bovine serum albumin). The unmodified or carboxylated SWCNT acted as both the oxidants and the catalysts in reactions. Moreover, they accelerated the oxidation reactions mediated by horseradish peroxidase, a representative member of the enzyme family actively involved in balancing oxidative stress. These diverse roles in redox reactions may serve the chemistry basis for SWCNT to induce oxidative stress in biological systems as potential environmental pollutants.

Driving Forces and Consequences of the Adsorption of Proteins to Carbon Nanotubes

Different strategies used to biofunctionalize CNTs with proteins, from direct physical adsorption on pristine CNTs to chemical treatments to achieve covalent interaction, are described. The discussion is focused on the consequences of the adsorption process on the structure and properties of both proteins and CNTs. On this base, recent developments in CNTs-proteins based biosensors (electrochemical and optical) and drug delivery systems are reviewed.

Determination of a setup correction function to obtain adsorption kinetic data at stagnation point flow conditions

This paper is the first report on the characterization of the hydrodynamic conditions in a flow cell designed to study adsorption processes by spectroscopic ellipsometry. The resulting cell enables combining the advantages of in situ spectroscopic ellipsometry with stagnation point flow conditions. An additional advantage is that the proposed cell features a fixed position of the "inlet tube" with respect to the substrate, thus facilitating the alignment of multiple substrates. Theoretical calculations were performed by computational fluid dynamics and compared with experimental data (adsorption kinetics) obtained for the adsorption of polyethylene glycol to silica under a variety of experimental conditions. Additionally, a simple methodology to correct experimental data for errors associated with the size of the measured spot and for variations of mass transfer in the vicinity of the stagnation point is herein introduced. The proposed correction method would allow researchers to reasonably estimate the adsorption kinetics at the stagnation point and quantitatively compare their results, even when using different experimental setups. The applicability of the proposed correction function was verified by evaluating the kinetics of protein adsorption under different experimental conditions.

Optical Properties of Single-Wall Carbon Nanotube Films Deposited on Si/SiO(2) Wafers

The paper describes a set of simple experiments performed to develop an optical model to describe Si/SiO(2) substrates coated with two transparent films of carbon nanotubes. The final goal is to use such optical model to investigate the interaction of proteins with carbon nanotubes. Experiments were performed to assess light reflection as a function of the wavelength or angle of incidence using two substrates (same material, different amounts) composed of oxidized carbon nanotubes. The experimental results indicate that the selected carbon nanotubes layers are anisotropic and significantly different from each other. Experiments performed by spectroscopic ellipsometry (as a function of the wavelength and incident angle) enabled the development of an Effective Medium Approximation model consisting in a two-fraction phase (arc-evaporated carbon and void space). Furthermore, the model enabled calculating the amount of protein adsorbed on the surface of the carbon nanotubes film.