Noncovalent sidewall functionalization of single-walled carbon nanotubes for protein immobilization

Scaling laws for nanoFET sensors

The sensitive conductance change of semiconductor nanowires and carbon nanotubes in response to the binding of charged molecules provides a novel sensing modality which is generally denoted as nanoFET sensors. In this paper, we study the scaling laws of nanoplate FET sensors by simplifying nanoplates as random resistor networks with molecular receptors sitting on lattice sites. Nanowire/tube FETs are included as the limiting cases where the device width goes small. Computer simulations show that the field effect strength exerted by the binding molecules has significant impact on the scaling behaviors. When the field effect strength is small, nanoFETs have little size and shape dependence. In contrast, when the field effect strength becomes stronger, there exists a lower detection threshold for charge accumulation FETs and an upper detection threshold for charge depletion FET sensors. At these thresholds, the nanoFET devices undergo a transition between low and large sensitivities. These thresholds may set the detection limits of nanoFET sensors, while they could be eliminated by designing devices with very short source-drain distance and large width.

Theoretical Evidence for the Stronger Ability of Thymine to Disperse SWCNT than Cytosine and Adenine: self-stacking of DNA bases vs their cross-stacking with SWCNT

Self-stacking of four DNA bases, adenine (A), cytosine (C), guanine (G) and thymine (T), and their cross-stacking with (5,5) as well as (10,0) single walled carbon nanotubes (SWCNTs) were extensively investigated with a novel hybrid DFT method, MPWB1K/cc-pVDZ. The binding energies were further corrected with MP2/6-311++G(d,p) method in both gas phase and aqueous solution, where the solvent effects were included with conductor-like polarized continuum model (CPCM) model and UAHF radii. The strongest self-stacking of G and A takes displaced anti-parallel configuration, but un-displaced or "eclipsed" anti-parallel configuration is the most stable for C and T. In gas phase the self-stacking of nucleobases decreases in the sequence G>A>C>T, while because of quite different solvent effects their self-stacking in aqueous solution exhibits a distinct sequence A>G>T>C. For a given base, cross-stacking is stronger than self-stacking in both gas phase and aqueous solution. Binding energy for cross-stacking in gas phase varies as G>A>T>C for both (10,0) and (5,5) SWCNTs, and the binding of four nucleobases to (10,0) is slightly stronger than to (5,5) SWCNT by a range of 0.1-0.5 kcal/mol. The cross-stacking in aqueous solution varies differently from that gas phase: A>G>T>C for (10,0) SWCNT and G>A>T>C for (5,5) SWCNT. It is suggested that the ability of nucleobases to disperse SWCNT depends on relative strength [Formula: see text] of self-stacking and cross-stacking with SWCNT in aqueous solution. Of the four investigated nucleobases thymine (T) exhibits the highest [Formula: see text] which can well explain the experimental finding that T more efficiently functionalizes SWCNT than C and A.

Computer modeling in biotechnology: a partner in development

Computational modeling can be a useful partner in biotechnology, in particular, in nanodevice engineering. Such modeling guides development through nanoscale views of biomolecules and devices not available through experimental imaging methods. We illustrate the role of computational modeling, mainly of molecular dynamics, through four case studies: development of silicon bionanodevices for single molecule electrical recording, development of carbon nano-tube-biomolecular systems as in vivo sensors, development of lipoprotein nanodiscs for assays of single membrane proteins, and engineering of oxygen tolerance into the enzyme hydrogenase for photosynthetic hydrogen gas production. The four case studies show how molecular dynamics approaches were adapted to the specific technical uses through (i) multi-scale extensions, (ii) fast quantum chemical force field evaluation, (iii) coarse graining, and (iv) novel sampling methods. The adapted molecular dynamics simulations provided key information on device behavior and revealed development opportunities, arguing that the "computational microscope" is an indispensable nanoengineering tool.

Mobile iron nanoparticle and its role in the formation of SiO2 nanotrench via carbon nanotube-guided carbothermal reduction

The detailed role of iron nanoparticles (NPs) involved with the formation of SiO2 nanotrenches is revealed. The physical movements of iron NPs, such as levitation and adsorption, turn out to be responsible for the initiation of carbothermal reduction (C (carbon nanotube, s) + SiO2(s) <--> SiO(g) + CO(g)), which results in SiO2 nanotrenches that are fully guided by carbon nanotubes. Under the chemical vapor deposition condition with 0.1% of O2 gas, iron NPs are liberally levitated from SiO2/Si substrate then adsorbed on the sidewalls of carbon nanotubes. Depending on the numbers of iron NPs attached to carbon nanotubes, two different types of nanotrenches are determined. When multiple iron NPs are assembled on carbon nanotubes and involved in carbothermal reduction, aligned nanohole type of nanotrenches is produced (Type I). On the contrary, when single iron NPs initiate the carbothermal reduction, nanotrenches having smooth pathways and high shoulders are commonly formed (Type II).

Enhancement of lipase activity in non-aqueous media upon immobilization on multi-walled carbon nanotubes

BACKGROUND

Immobilization of biologically active proteins on nanosized surfaces is a key process in bionanofabrication. Carbon nanotubes with their high surface areas, as well as useful electronic, thermal and mechanical properties, constitute important building blocks in the fabrication of novel functional materials.

RESULTS

Lipases from Candida rugosa (CRL) were found to be adsorbed on the multiwalled carbon nanotubes with very high retention of their biological activity (97%). The immobilized biocatalyst showed 2.2- and 14-fold increases in the initial rates of transesterification activity in nearly anhydrous hexane and water immiscible ionic liquid [Bmim] [PF6] respectively, as compared to the lyophilized powdered enzyme. It is presumed that the interaction with the hydrophobic surface of the nanotubes resulted in conformational changes leading to the 'open lid' structure of CRL. The immobilized enzyme was found to give 64% conversion over 24 h (as opposed to 14% with free enzyme) in the formation of butylbutyrate in nearly anhydrous hexane. Similarly, with ionic liquid [Bmim] [PF6], the immobilized enzyme allowed 71% conversion as compared to 16% with the free enzyme. The immobilized lipase also showed high enantioselectivity as determined by kinetic resolution of (+/-) 1-phenylethanol in [Bmim] [PF6]. While free CRL gave only 5% conversion after 36 h, the immobilized enzyme resulted in 37% conversion with > 99% enantiomeric excess. TEM studies on the immobilized biocatalyst showed that the enzyme is attached to the multiwalled nanotubes.

CONCLUSION

Successful immobilization of enzymes on nanosized carriers could pave the way for reduced reactor volumes required for biotransformations, as well as having a use in the construction of miniaturized biosensensor devices.

The Isolation of Basic Proteins by Solid-Phase Extraction with Multiwalled Carbon Nanotubes

Multiwalled carbon nanotubes (MWCNTs) have been employed for the first time as sorbents for the isolation of basic proteins from other protein species in biological sample matrices by solid-phase extraction (SPE). A microcolumn packed with MWCNTs was incorporated after appropriate pretreatment into a sequential injection system, which facilitates online selective sorption of basic protein species (hemoglobin and cytochrome c in this particular case). The retained protein species were afterwards separated from each other by sequential elution from the microcolumn through the employment of appropriate eluents. A 0.025 mol L(-1) phosphate buffer solution of pH 8.0 facilitated the efficient collection of hemoglobin, while a 0.5 mol L(-1) NaCl solution ensured the quantitative recovery of the retained cytochrome c. With a sample loading volume of 2.0 mL, enrichment factors of 11 and 15 were derived for hemoglobin and cytochrome c, along with retention efficiencies of 100% for both species and recovery rates of 98 and 90%, respectively. A sampling frequency of 8 h(-1) was achieved, and the precisions were 3.0% and 0.8% (RSD) for hemoglobin and cytochrome c at a concentration of 5.0 microg mL(-1). The practical applicability of this system was demonstrated by processing of human whole blood for isolation of hemoglobin, and satisfactory results were obtained by assay with SDS-PAGE.

Carbon nanotubes and glucose oxidase bionanocomposite bridged by ionic liquid-like unit: Preparation and electrochemical properties

For their biocompatibility and potential bionanoelectronic applications, integration of carbon nanotubes (CNTs) with biomolecules such as redox enzyme is highly anticipated. Therein, CNTs are expected to act not only as an electron transfer promoter, but also as immobilizing substrate for biomolecules. In this report, a novel method for immobilization of biomolecules on CNTs was proposed based on ionic interaction, which is of universality and widespread use in biological system. As illustrated, glucose oxidase (GOD) and single-walled carbon nanotubes (SWNTs) were integrated into a unitary bionanocomposite by means of ionic liquid-like unit on functionalized SWNTs. The resulted bionanocomposite illustrated better redox response of immobilized GOD in comparison of that prepared by weak physical absorption without ionic interaction. As a potential application of concept, the electrochemical detection of glucose was exemplified based on this novel bionanocomposite.

Single-walled carbon nanotube interactions with HeLa cells

This work concerns exposing cultured human epithelial-like HeLa cells to single-walled carbon nanotubes (SWNTs) dispersed in cell culture media supplemented with serum. First, the as-received CoMoCAT SWNT-containing powder was characterized using scanning electron microscopy and thermal gravimetric analyses. Characterizations of the purified dispersions, termed DM-SWNTs, involved atomic force microscopy, inductively coupled plasma - mass spectrometry, and absorption and Raman spectroscopies. Confocal microRaman spectroscopy was used to demonstrate that DM-SWNTs were taken up by HeLa cells in a time- and temperature-dependent fashion. Transmission electron microscopy revealed SWNT-like material in intracellular vacuoles. The morphologies and growth rates of HeLa cells exposed to DM-SWNTs were statistically similar to control cells over the course of 4 d. Finally, flow cytometry was used to show that the fluorescence from MitoSOXtrade mark Red, a selective indicator of superoxide in mitochondria, was statistically similar in both control cells and cells incubated in DM-SWNTs. The combined results indicate that under our sample preparation protocols and assay conditions, CoMoCAT DM-SWNT dispersions are not inherently cytotoxic to HeLa cells. We conclude with recommendations for improving the accuracy and comparability of carbon nanotube (CNT) cytotoxicity reports.

Self-Assembled Single-Walled Carbon Nanotube:Zinc–Porphyrin Hybrids through Ammonium Ion–Crown Ether Interaction: Construction and Electron Transfer

An ammonium ion-crown ether interaction has been successfully used to construct porphyrin-single-walled carbon nanotube (SWNT) donor-acceptor hybrids. The [18]crown-6 to alkyl ammonium ion binding strategy resulted in porphyrin-SWNT nanohybrids that are stable and soluble in DMF. The porphyrin-SWNT hybrids were characterized by spectroscopic, TEM, and electrochemical techniques. Both steady-state and time-resolved emission studies revealed efficient quenching of the singlet excited state of the porphyrins and free-energy calculations suggested that electron-transfer quenching occurred. Nanosecond transient absorption spectral results supported the charge-separation quenching process. Charge-stabilization was also observed for the nanohybrids in which the lifetime of the radical ion pairs was around 100 ns. The present nanohybrids were also used to reduce the hexyl viologen dication (HV2+) and to oxidize 1-benzyl-1,4-dihydronicotinamide in solution in an electron-pooling experiment. Accumulation of the radical cation (HV.+) was observed in high yields, which provided additional proof for the occurrence of photoinduced charge separation. The present study demonstrates that a hydrogen-bonding motif is a successful self-assembly method to build SWNTs bearing donor-acceptor nanohybrids, which are useful for light-energy harvesting and photovoltaic applications.

Part I: recent developments in nanoelectrodes for biological measurements

Biosensors are a type of analytical device that use biological molecules to monitor biorecognition events and interactions. Coupled with the progress in nanotechnologies over recent years, the development of a nanobiosensor based on individual nanoelectrodes and nanoelectrode arrays or nanoelectrode ensembles offers unprecedented avenues for screening and detection at ultrahigh sensitivities. These capabilities provide the basis for a paradigmatic change in biomedical diagnostics and treatment. In this review, we highlight recent developments in nanoelectrode platforms and their suitability for integrating with biological components for the fabrication of ultrasensitive nanobiosensors.

Photoinduced Electron Transfer on Aqueous Carbon Nanohorn–Pyrene–Tetrathiafulvalene Architectures

Water-soluble carbon-nanohorn-tetrathiafulvalene (CNH-TTF) nanoensembles were prepared by utilizing positively charged pyrene as an assembly medium and characterized by spectroscopy and electron microscopy. Electronic interactions within the nanoensemble were probed by optical spectroscopy, indicating electron transfer between the TTF units and CNHs after light illumination.