Embedded Single-Walled Carbon Nanotubes Locally Perturb DOPC Phospholipid Bilayers

Ultrasensitive Detection of MCF-7 Cells with a Carbon Nanotube-Based Optoelectronic-Pulse Sensor Framework

Biosensors are of vital significance for healthcare by supporting the management of infectious diseases for preventing pandemics and the diagnosis of life-threatening conditions such as cancer. However, the advancement of the field can be limited by low sensing accuracy. Here, we altered the bioelectrical signatures of the cells using carbon nanotubes (CNTs) via structural loosening effects. Using an alternating current (AC) pulse under light irradiation, we developed a photo-assisted AC pulse sensor based on CNTs to differentiate between healthy breast epithelial cells (MCF-10A) and luminal breast cancer cells (MCF-7) within a heterogeneous cell population. We observed a previously undemonstrated increase in current contrast for MCF-7 cells with CNTs compared to MCF-10A cells with CNTs under light exposure. Moreover, we obtained a detection limit of ∼1.5 × 103 cells below a baseline of ∼1 × 104 cells for existing electrical-based sensors for an adherent, heterogeneous cell population. All-atom molecular dynamics (MD) simulations reveal that interactions between the embedded CNT and cancer cell membranes result in a less rigid lipid bilayer structure, which can facilitate CNT translocation for enhancing current. This as-yet unconsidered cancer cell-specific method based on the unique optoelectrical properties of CNTs represents a strategy for unlocking the detection of a small population of cancer cells and provides a promising route for the early diagnosis, monitoring, and staging of cancer.

Carbon Nanotubes Translocation through a Lipid Membrane and Transporting Small Hydrophobic and Hydrophilic Molecules

Carbon nanotubes (CNTs) are extensively adopted in the applications of biotechnology and biomedicine. Their interactions with cell membranes are of great importance for understanding the toxicity of CNTs and the application of drug delivery. In this paper, we use atomic molecular dynamics simulations to study the permeation and orientation of pristine and functionalized CNTs in a lipid bilayer. Pristine CNT (PCNT) can readily permeate into the membrane and reside in the hydrophobic region without specific orientation. The insertion of PCNTs into the lipid bilayer is robust and independent on the lengths of PCNTs. Due to the presence of hydroxyl groups on both ends of the functionalized CNT (FCNT), FCNT prefers to stand upright in the lipid bilayer center. Compared with PCNT, FCNT is more suitable to be a bridge connecting the inner and outer lipid membrane. The inserted CNTs have no distinct effects on membrane structure. However, they may block the ion channels. In addition, preliminary explorations on the transport properties of CNTs show that the small hydrophobic molecule carbon dioxide can enter both PCNT and FCNT hollow channels. However, hydrophilic molecule urea is prone to penetrate the PCNT but finds it difficult to enter the FCNT. These results may provide new insights into the internalization of CNT in the lipid membrane and the transport properties of CNTs when embedded therein.

Interactions of Functionalized Multi-Wall Carbon Nanotubes with Giant Phospholipid Vesicles as Model Cellular Membrane System

Carbon Nanotubes (CNTs) are considered alternative materials for the design of advanced drug and gene delivery vectors. However, the mechanism responsible for the cellular membrane intake of CNTs is not well understood. In the present study, we show how multi-walled carbon nanotubes (MWCNTs) owning different surface properties, interact with giant unilamellar vesicles (GUVs), a simple model system for cellular membranes. In particular, we want to address the hydrophilic/hydrophobic interactions between MWCNTs and lipid membranes and the subsequent mechanical properties changes of the systems. In order to elucidate this interaction, we made the following chemical modifications on MWCNTs: oxidized MWCNTs (ox-MWCNTs) displaying reduced hydrophobic surface character, pristine MWCNTs (p-MWCNTs), and alkyl functionalized MWCNTs (alk-MWCNTs) exhibiting enhanced hydrophobic surface properties, were put in contact with GUVs and observed by confocal microscopy. Our observations revealed that the interaction between the CNTs and GUVs depends on the type of chemical functionalization: ox-MWCNTs remain at the membrane interacting with the polar head of the phospholipids, p-MWCNTs internalize GUVs spontaneously, and alk-MWCNTs persist inside the membrane. The mechanical properties of MWCNTs@GUVs systems were measured using the electrodeformation method, which shows an increased bending stiffness (κ) of the GUVs as MWCNTs concentration increases. High concentrations of p-MWCNTs and alk-MWCNTs induced vesicle adhesion; p-MWCNTs produced a considerable reduction in the average size of the GUVs, while alk-MWCNTs form complex stable structures inside the membrane. The statistical analyses of the experimental results are compared with available computer simulations. The picture emerging from our results is that the interaction between GUVs and MWCNTs is due mainly to hydrophobicity.

Molecular dynamics simulations of carbon nanotube porins in lipid bilayers

Carbon nanotube porins embedded in lipid membranes are studied by molecular dynamics simulations.

Molecular dynamics simulation strategies for designing carbon-nanotube-based targeted drug delivery

The carbon nanotube (CNT)-based target-specific delivery of drugs, or other molecular cargo, has emerged as one of the most promising biomedical applications of nanotechnology. To achieve efficient CNT-based drug delivery, the interactions between the drug, CNT and biomolecular target need to be properly optimized. Recent advances in the computer-aided molecular design tools, in particular molecular dynamics (MD) simulation studies, offer an appropriate low-cost approach for such optimization. This review highlights the various potential MD approaches for the simulation of CNT interactions with cell membranes while emphasizing various methods of cellular internalization and toxicities of CNTs to build new strategies for designing rational CNT-based targeted drug delivery to circumvent the limitations associated with the various clinically available nonspecific therapeutic agents.

Membrane interactions and antimicrobial effects of inorganic nanoparticles

Interactions between nanoparticles and biological membranes are attracting increasing attention in current nanomedicine, and play a key role both for nanotoxicology and for utilizing nanomaterials in diagnostics, drug delivery, functional biomaterials, as well as combinations of these, e.g., in theranostics. In addition, there is considerable current interest in the use of nanomaterials as antimicrobial agents, motivated by increasing resistance development against conventional antibiotics. Here, various nanomaterials offer opportunities for triggered functionalites to combat challenging infections. Although the performance in these diverse applications is governed by a complex interplay between the nanomaterial, the properties of included drugs (if any), and the biological system, nanoparticle-membrane interactions constitute a key initial step and play a key role for the subsequent biological response. In the present overview, the current understanding of inorganic nanomaterials as antimicrobial agents is outlined, with special focus on the interplay between antimicrobial effects and membrane interactions, and how membrane interactions and antimicrobial effects of such materials depend on nanoparticle properties, membrane composition, and external (e.g., light and magnetic) fields.

Effects of charge and surface defects of multi-walled carbon nanotubes on the disruption of model cell membranes

The direct contact between multi-walled carbon nanotubes (MWCNTs) and cell membranes causes membrane disruption, potentially leading to cytotoxicity. However, the role of electrostatic forces and MWCNT properties is still open to debate. In this study, the influences of charge and MWCNT surface defects on membrane disruption were investigated by microscopy and a quartz crystal microbalance with dissipation monitoring (QCM-D). Positively/negatively charged giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs) were made as model cell membranes. Negatively charged MWCNTs disrupted the GUVs containing positively charged lipids, which confirmed the electrostatically mediated interaction. However, the mass loss was detected from the negatively charged SLBs after MWCNT exposure, which suggests the extraction of phospholipids. The defect degree of MWCNTs correlated with their adhesion amount on the membranes. Both the oxygenated functional groups and unoxidized dangling carbon bonds were active sites for MWCNT-membrane interactions. The MWCNTs were observed to be engulfed inside the GUVs. The results clearly demonstrate that phospholipid extraction by MWCNTs could occur in electrostatically repulsive conditions, and MWCNT defects were active binding sites whether or not they were oxygenated. Our findings should be helpful in the design and safe applications of carbon nanomaterials.

Structure of Carbon Nanotube Porins in Lipid Bilayers: An in Situ Small-Angle X-ray Scattering (SAXS) Study

Carbon nanotube porins (CNTPs), small segments of carbon nanotubes capable of forming defined pores in lipid membranes, are important future components for bionanoelectronic devices as they could provide a robust analog of biological membrane channels. In order to control the incorporation of these CNT channels into lipid bilayers, it is important to understand the structure of the CNTPs before and after insertion into the lipid bilayer as well as the impact of such insertion on the bilayer structure. Here we employed a noninvasive in situ probe, small-angle X-ray scattering, to study the integration of CNT porins into dioleoylphosphatidylcholine bilayers. Our results show that CNTPs in solution are stabilized by a monolayer of lipid molecules wrapped around their outer surface. We also demonstrate that insertion of CNTPs into the lipid bilayer results in decreased bilayer thickness with the magnitude of this effect increasing with the concentration of CNTPs.

Graphene mechanics: I. Efficient first principles based Morse potential

We present a computationally efficient pairwise potential for use in molecular dynamics simulations of large graphene or carbon nanotube systems, in particular, for those under mechanical deformation, and also for mixed systems including biomolecules. Based on the Morse potential, it is only slightly more complex and computationally expensive than a harmonic bond potential, allowing such large or mixed simulations to reach experimentally relevant time scales. By fitting to data obtained from quantum mechanics (QM) calculations to represent bond breaking in graphene patches, we obtain a dissociation energy of 805 kJ mol(-1) which reflects the steepness of the QM potential up to the inflection point. A distinctive feature of our potential is its truncation at the inflection point, allowing a realistic treatment of ruptured C-C bonds without relying on a bond order model. The results obtained from equilibrium MD simulations using our potential compare favorably with results obtained from experiments and from similar simulations with more complex and computationally expensive potentials.

Modification of Fatty acids in membranes of bacteria: implication for an adaptive mechanism to the toxicity of carbon nanotubes

We explored whether bacteria could respond adaptively to the presence of carbon nanotubes (CNTs) by investigating the influence of CNTs on the viability, composition of fatty acids, and cytoplasmic membrane fluidity of bacteria in aqueous medium for 24 h exposure. The CNTs included long single-walled carbon nanotubes (L-SWCNTs), short single-walled carbon nanotubes (S-SWCNTs), short carboxyl single-walled carbon nanotubes (S-SWCNT-COOH), and aligned multiwalled carbon nanotubes (A-MWCNTs). The bacteria included three common model bacteria, Staphyloccocus aureus (Gram-positive), Bacillus subtilis (Gram-positive), and Escherichia coli (Gram-negative), and one polybrominated diphenyl ether degrading strain, Ochrobactrum sp. (Gram-negative). Generally, L-SWCNTs were the most toxic to bacteria, whereas S-SWCNT-COOH showed the mildest bacterial toxicity. Ochrobactrum sp. was more susceptible to the toxic effect of CNTs than E. coli. Compared to the control in the absence of CNTs, the viability of Ochrobactrum sp. decreased from 71.6-81.4% to 41.8-70.2%, and E. coli from 93.7-104.0% to 67.7-91.0% when CNT concentration increased from 10 to 50 mg L(-1). The cytoplasmic membrane fluidity of bacteria increased with CNT concentration, and a significant negative correlation existed between the bacterial viabilities and membrane fluidity for E. coli and Ochrobactrum sp. (p < 0.05), indicating that the increase in membrane fluidity induced by CNTs was an important factor causing the inactivation of bacteria. In the presence of CNTs, E. coli and Ochrobactrum sp. showed elevation in the level of saturated fatty acids accompanied with reduction in unsaturated fatty acids, compensating for the fluidizing effect of CNTs. This demonstrated that bacteria could modify their composition of fatty acids to adapt to the toxicity of CNTs. In contrast, S. aureus and B. subtilis exposed to CNTs increased the proportion of branched-chain fatty acids and decreased the level of straight-chain fatty acids, which was also favorable to counteract the toxic effect of CNTs. This study suggests that the bacterial tolerances to CNTs are associated with both the adaptive modification of fatty acids in the membrane and the physicochemical properties of CNTs. This is the first report about the physiologically adaptive response of bacteria to CNTs, and may help to further understand the ecotoxicological effects of CNTs.