Experimental–computational study of carbon nanotube effects on mitochondrial respiration: in silico nano-QSPR machine learning models based on new Raman spectra transform with Markov–Shannon entropy invariants

[Abstract] The study of selective toxicity of carbon nanotubes (CNTs) on mitochondria (CNT-mitotoxicity) is of major interest for future biomedical applications. In the current work, the mitochondrial oxygen consumption (E3) is measured under three experimental conditions by exposure to pristine and oxidized CNTs (hydroxylated and carboxylated). Respiratory functional assays showed that the information on the CNT Raman spectroscopy could be useful to predict structural parameters of mitotoxicity induced by CNTs. The in vitro functional assays show that the mitochondrial oxidative phosphorylation by ATP-synthase (or state V3 of respiration) was not perturbed in isolated rat-liver mitochondria. For the first time a star graph (SG) transform of the CNT Raman spectra is proposed in order to obtain the raw information for a nano-QSPR model. Box–Jenkins and perturbation theory operators are used for the SG Shannon entropies. A modified RRegrs methodology is employed to test four regression methods such as multiple linear regression (LM), partial least squares regression (PLS), neural networks regression (NN), and random forest (RF). RF provides the best models to predict the mitochondrial oxygen consumption in the presence of specific CNTs with R2 of 0.998–0.999 and RMSE of 0.0068–0.0133 (training and test subsets). This work is aimed at demonstrating that the SG transform of Raman spectra is useful to encode CNT information, similarly to the SG transform of the blood proteome spectra in cancer or electroencephalograms in epilepsy and also as a prospective chemoinformatics tool for nanorisk assessmentXunta de Galicia; GRC2014/049Xunta de Galicia; R2014/03

Mathematical Analysis in Characterization of Carbon Nanotubes (CNTs) as possible Mosquito Repellents

Mosquitoes are a great threat to human health to date and are a subject of interdisciplinary research involving scientists from many areas. Recently much attention has been put to novel approaches to mosquito repellent products that involve the use of novel materials, such as carbon nanomaterials, where it is essential to determine their properties. This research discusses the full molecular characterization of carbon nanotubes (CNTs) produced by electrolysis in molten salts. Each CNT has its mathematical representation due to its hexagonal lattice structure. Multi-wall carbon nanotubes (MWCNTs) are considered. The focus is on determining their structural parameters: innermost and outermost diameters, chiral indices m and n, number of walls, and unit cell parameters. Corresponding frequency parts of Raman spectra of four experimentally produced CNTs are elaborated, and Python programming and Mathematica are employed for the most accurate (m,n) assignment. Determining the chirality of these samples enables the calculation of other structural properties, which are performed now, including their graph representation. The latter enables the evaluation of different distance-based topological indices (Wiener, Balaban, Sum-Balaban, Harary index, etc.) to predict some index-related properties of the molecules

Electrical Properties of Single-Walled Carbon Nanotube Networks Produced by Langmuir-Blodgett Deposition

This thesis investigates the use of the Langmuir-Blodgett (LB) deposition technique as a means for building up ultra-thin networks of single-walled carbon nanotubes (SWCNTs) on various substrates. Transfer from a water subphase is successfully demonstrated for a range of SWCNTs and the electrical properties of the networks are discussed in detail. In contrast to the majority of literature on LB networks of SWCNTs, transfer is completed without the addition of surfactants to the nanotube material. However, and as expected, improved deposition is achieved when SWCNTs are functionalised (through thermal oxidation) with carboxylic acid groups, decreasing their hydrophobicity. In-plane electrical data reveal preferential alignment of the nanotubes along the direction of dipping. Comprehensive studies of the current dependence on temperature and the field dependence of conductivity are presented for sorted metallic and semiconducting nanotubes in an attempt to reveal the dominant conduction mechanisms. For metallic nanotubes, typical metallic conductivity is observed with an increasing resistance with increasing temperature. The metallic nanotube temperature coefficient of resistance is 0.001/K. At high electricfield strengths (>10^6 V/m), conduction in semiconducting SWCNT networks is dominated by the Poole-Frenkel effect. Transistor structures are presented with SWCNTs as the active semiconducting layer. The best device shows p-type depletion mode behaviour with an on/offratio of around 8 and a carrier mobility of 0.3 cm^2/Vs

Gas sensing with carbon nanotube networks

PhDCarbon nanotubes are an exciting new material with exemplary mechanical and electronic properties. Carbon nanotubes can be either metallic or semiconducting; either type has properties which rival conventional materials. The one-dimensional electronic nature of these materials leads to extreme sensitivity to the local energy landscape, a desirable property for a sensing element. Production of carbon nanotubes currently has no method of growing nanotubes with a speci c electronic property, any di erentiation occurs through processing a heterogenous ensemble. Recently, networks of carbon nanotubes have shown attractive properties for electronic applications. The self-selecting current path has properties averaged from the ensemble of nanotubes providing repeatability in addition to exibility and transparency. This thesis is a study of the transport properties of thin and thick networks of single-walled carbon nanotubes and their electrical response to oxygen adsorption in both a simple resistive geometry and as the gate layer in a nanotube-metal-oxide-silicon capacitor. The thickness of network was found to determine the electrical characteristics of the network ensemble, thin networks displaying semiconducting transport characteristics, thick networks becoming more metallic. The response of the nanotube networks to oxygen exposure was found to be dependent on UV treatment. UV-desorbed networks exhibited an increased conductance upon oxygen-exposure, adsorbed networks exhibited a decrease in conductance upon further oxygen-exposure. Thinner, more semiconducting nanotube networks exhibited a greater change in conductance upon oxygen exposure. The nanotube-metal-oxide-semiconductor capacitor also showed a greater change in at-band capacitance for thin nanotube networks. The capacitance of the nanotube device at the nanotube network at-band voltage is shown to be in uenced by both oxygen and nitrogen gases. The origin of the behaviour of the at-band voltage is attempted to be understood and future work is suggested.

Electrophoretic deposition of carbon nanotubes on silicon substrates

This dissertation research describes the feasibility study and investigation of Electrophoretic Deposition (EPD) of carbon nanotubes (CNTs) for applications in semiconductor research. In recent years, the EPD technique has been considered as an economical, room temperature, solution based wet coating technique for thin and thick CNT films on arbitrary substrates. In this study, fabrication of uniform coatings of acid-treated CNTs has been pursued on bare silicon substrates by EPD from aqueous and organic suspensions. Research endeavors are extended to examine EPD of CNTs on silicon substrates with various surface coatings such as metal (aluminum), insulator layers (silicon dioxide and silicon nitride) and self-assembled polar organosilane (APTES) molecules. Microstructural imaging, spectroscopic analysis and characterization of the morphology of the CNT films have also been reviewed in relation to the deposition parameters such as inter-electrode electric field, deposition duration and APTES concentration. For research and development involving advanced spectroscopic analysis, Surface Enhanced Raman Spectroscopy (SERS) studies have been conducted on horizontally aligned EPD fabricated porous CNT networks coated with silver nanoparticles (AgNPs). The acquired Raman spectra of AgNP-CNT hybrid nanostructures display significant enhancement in the Raman intensity values of Rhodamine6G (R6G) analyte by several orders of magnitude with respect to the reference sample. Improvement in the Raman signals has pushed the detection limit to as low as 1 × 10^-12 M. The experimental results, reported in this dissertation, thus establish the novelty of EPD in the fabrication of the AgNP coated porous CNT substrate for routine SERS analysis of different target analytes