Optically and biologically active mussel protein-coated double-walled carbon nanotubes

Development and Optimization of Water-Soluble Double-Walled Carbon Nanotubes by Effective Surface Treatment of Inner Walls

Carbon nanotubes are a significant class of nanomaterials with distinctive properties that have led to their application in a variety of fields, such as polymer composites, medicine, electronics, and material science. However, their nonpolar nature and insolubility in polar solvents limit their applications. To address this issue, highly functionalized and water-soluble double-walled carbon nanotubes (DWNTs) were developed by selectively oxidizing the inner walls of the DWNTs using oleum and nitric acid. The impact of reaction time on the chemical functionalization of DWNTs was investigated under two different reaction durations of 2 and 24 h. The presence of highly oxygenated functional groups resulted in high water solubility, which was confirmed by high- and low-frequency Raman spectroscopy, high-resolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) method, and optical spectroscopy. The conductivity of highly water-soluble W-DWNTs (24 h) was 122.65 × 10² S cm^-1. After annealing for 12 h at 140 °C, the W-DWNTs retained 72% of their conductivity (88.79 × 10² S cm^-1).

Zwitterionic peptide-functionalized highly dispersed carbon nanotubes for efficient wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) have displayed great potential as catalyst carriers due to their nanoscale structure and large specific surface area. However, their hydrophobicity and poor dispersibility in water restrict their applications in aqueous environments. Herein, the dispersibility of MWCNTs was significantly enhanced with a chimeric protein MPKE which consisted of a zwitterionic peptide unit and a mussel adhesive protein unit. The MPKE could be easily attached to MWCNTs (MPKE-MWCNTs) by a simple stirring process due to the versatile adhesion ability of mussel adhesive unit. As expected, the MPKE-MWCNTs displayed outstanding dispersibility in water (>7 months), as well as in alkaline solutions (pH = 12) and organic solvents (DMSO and ethanol) due to the hydrophilicity of the zwitterionic peptide unit. Moreover, the MPKE-MWCNTs were used as silver nanoparticle carriers for the reduction of 4-nitrophenol in wastewater, with the normalized rate constant k_nor up to 32.9 s^-1 mmol^-1. Meanwhile, they also exhibited excellent biocompatibility and antibacterial activity, which were favorable for wastewater treatment. This work provides a facile strategy for MWCNT modification, functionalization and applications in aqueous environments.

Characteristics and therapeutic applications of antimicrobial peptides

The demand for novel antimicrobial compounds is rapidly growing due to the phenomenon of antibiotic resistance in bacteria. In response, numerous alternative approaches are being taken including use of polymers, metals, combinatorial approaches, and antimicrobial peptides (AMPs). AMPs are a naturally occurring part of the immune system of all higher organisms and display remarkable broad-spectrum activity and high selectivity for bacterial cells over host cells. However, despite good activity and safety profiles, AMPs have struggled to find success in the clinic. In this review, we outline the fundamental properties of AMPs that make them effective antimicrobials and extend this into three main approaches being used to help AMPs become viable clinical options. These three approaches are the incorporation of non-natural amino acids into the AMP sequence to impart better pharmacological properties, the incorporation of AMPs in hydrogels, and the chemical modification of surfaces with AMPs for device applications. These approaches are being developed to enhance the biocompatibility, stability, and/or bioavailability of AMPs as clinical options.

Graphene oxide-functionalized long period fiber grating for ultrafast label-free glucose biosensor

A label-free glucose biosensor is constructed successfully based on the long period fiber grating (LPFG) functionalized with graphene oxide (GO)-glucose oxidase (GOD) via the chemical crosslink method. GO coated on the surface of LPFG can immobilize GOD by the plentiful binding sites because of its favorable combination of exceptionally high surface-to-volume ratio. The structure and characterization of GOD-GO-modified LPFG are studied by the optical microscope, Fourier transformation infrared spectrometer (FTIR), Raman spectroscopy, scanning electron microscope (SEM) and atomic force microscopy (AFM), respectively. The reaction between GOD and glucose create gluconic acid and H₂O₂, which will lead to an evident shift of LPFG transmission spectrum due to the greater change of the surrounding refractive index (SRI). The GOD-GO-modified LPFG sensor shows a linear response with a response coefficient of 0.77 nm/(mg/mL). This biosensor has good selectivity and can be used for the detection of practical sample. The GOD-GO-modified LPFG biosensor has great prospect in the pharmaceutical research and medical diagnosis fields.

Biomedical applications of carbon nanomaterials: Drug and gene delivery potentials

One of the major components in the development of nanomedicines is the choice of the right biomaterial, which notably determines the subsequent biological responses. The popularity of carbon nanomaterials (CNMs) has been on the rise due to their numerous applications in the fields of drug delivery, bioimaging, tissue engineering, and biosensing. Owing to their considerably high surface area, multifunctional surface chemistry, and excellent optical activity, novel functionalized CNMs possess efficient drug-loading capacity, biocompatibility, and lack of immunogenicity. Over the past few decades, several advances have been made on the functionalization of CNMs to minimize their health concerns and enhance their biosafety. Recent evidence has also implied that CNMs can be functionalized with bioactive peptides, proteins, nucleic acids, and drugs to achieve composites with remarkably low toxicity and high pharmaceutical efficiency. This review focuses on the three main classes of CNMs, including fullerenes, graphenes, and carbon nanotubes, and their recent biomedical applications.

Modification and Characterization of Fe₃O₄ Nanoparticles for Use in Adsorption of Alkaloids

Magnetite (Fe₃O₄) is a ferromagnetic iron oxide of both Fe(II) and Fe(III), prepared by FeCl₂ and FeCl₃. XRD was used for the confirmation of Fe₃O₄. Via the modification of Tetraethyl orthosilicate (TEOS), (3-Aminopropyl)trimethoxysilane (APTMS), and Alginate (AA), Fe₃O₄@SiO₂, Fe₃O₄@SiO₂-NH₂, and Fe₃O₄@SiO₂-NH₂-AA nanoparticles could be obtained, and IR and SEM were used for the characterizations. Alkaloid adsorption experiments exhibited that, as for Palmatine and Berberine, the most adsorption could be obtained at pH 8 when the adsorption time was 6 min. The adsorption percentage of Palmatine was 22.2%, and the adsorption percentage of Berberine was 23.6% at pH 8. Considering the effect of adsorption time on liquid phase system, the adsorption conditions of 8 min has been chosen when pH 7 was used. The adsorption percentage of Palmatine was 8.67%, and the adsorption percentage of Berberine was 7.25%. Considering the above conditions, pH 8 and the adsorption time of 8min could be chosen for further uses.

Polydopamine-wrapped carbon nanotubes to improve the corrosion barrier of polyurethane coating

Nanocomposite reinforced polyurethane (PU) coatings have been prepared by an ultrasonication method with polydopamine-wrapped carbon nanotubes (PDA@CNTs) as the nanofiller.

Spontaneously restored electrical conductivity of bioactive gel comprising mussel adhesive protein-coated carbon nanotubes

We demonstrated the pH-mediated self-healing performance of an electrically conductive gel comprising mussel adhesive proteins (MAPs) and carbon nanotubes (CNTs).

Optical sensitivity of mussel protein-coated double-walled carbon nanotubes on the iron–DOPA conjugation bond

The optical properties of semiconducting carbon nanotubes respond sensitively to external conditions.

Under the lens: carbon nanotube and protein interaction at the nanoscale

The combination of the very different chemical natures of carbon nanotubes (CNTs) and proteins gives rise to systems with unprecedented performance, thanks to a rich pool of very diverse chemical, electronic, catalytic and biological properties. Here we review recent advances in the field, including innovative and imaginative aspects from a nanoscale point of view. The tubular nature of CNTs allows for internal protein encapsulation, and also for their external coating by protein cages, affording bottom-up ordering of molecules in hierarchical structures. To achieve such complex systems it is imperative to master the intermolecular forces between CNTs and proteins, including geometry effects (e.g. CNT diameter and curvature) and how they translate into changes in the local environment (e.g. water entropy). The type of interaction between proteins and CNTs has important consequences for the preservation of their structure and, in turn, function. This key aspect cannot be neglected during the design of their conjugation, be it covalent, non-covalent, or based on a combination of both methods. The review concludes with a brief discussion of the very many applications intended for CNT-protein systems that go across various fields of science, from industrial biocatalysis to nanomedicine, from innovative materials to biotechnological tools in molecular biology research.

Double-walled carbon nanotube processing

Single-walled carbon nanotubes (SWCNTs) have been the focus of intense research, and the body of literature continues to grow exponentially, despite more than two decades having passed since the first reports. As well as extensive studies of the fundamental properties, this has seen SWCNTs used in a plethora of applications as far ranging as microelectronics, energy storage, solar cells, and sensors, to cancer treatment, drug delivery, and neuronal interfaces. On the other hand, the properties and applications of double-walled carbon nanotubes (DWCNTs) have remained relatively under-explored. This is despite DWCNTs not only sharing many of the same unique characteristics of their single-walled counterparts, but also possessing an additional suite of potentially advantageous properties arising due to the presence of the second wall and the often complex inter-wall interactions that arise. For example, it is envisaged that the outer wall can be selectively functionalized whilst still leaving the inner wall in its pristine state and available for signal transduction. A similar situation arises in DWCNT field effect transistors (FETs), where the outer wall can provide a convenient degree of chemical shielding of the inner wall from the external environment, allowing the excellent transconductance properties of the pristine nanotubes to be more fully exploited. Additionally, DWCNTs should also offer unique opportunities to further the fundamental understanding of the inter-wall interactions within and between carbon nanotubes. However, the realization of these goals has so far been limited by the same challenge experienced by the SWCNT field until recent years, namely, the inherent heterogeneity of raw, as-produced DWCNT material. As such, there is now an emerging field of research regarding DWCNT processing that focuses on the preparation of material of defined length, diameter and electronic type, and which is rapidly building upon the experience gained by the broader SWCNT community. This review describes the background of the field, summarizing some relevant theory and the available synthesis and purification routes; then provides a thorough synopsis of the current state-of-the-art in DWCNT sorting methodologies, outlines contemporary challenges in the field, and discusses the outlook for various potential applications of the resulting material.

Purification, separation and extraction of inner tubes from double-walled carbon nanotubes by tailoring density gradient ultracentrifugation using optical probes

We studied the effect of varying sonication and centrifugation parameters on double-walled carbon nanotubes (DWCNT) by measuring optical absorption and photoluminescence (PL) of the samples. We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter [Formula: see text]0.8 nm can be identified in absorption measurements. This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found. Furthermore, by comparing PL properties of samples centrifugated either with or without a gradient medium, we found that applying DGU greatly enhances the PL intensity, whereas centrifugation at even higher speeds but without a gradient medium results in lower intensities. This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut. A subsequent application of DGU leads to the extraction of the inner tubes or not if the host nanotube stayed uncut or no gradient medium was used. This work shows a pathway to avoid this phenomenon to unravel the intrinsic PL from inner tubes of DWCNT.