Aromaticity of Carbon Nanotubes

Carbon nanotubes (CNTs) are aromatic, peri-condensed benzenoids, composed of sp2 carbon atoms; the carbons are arranged in a graphite-like, hexagonal pattern. The aromatic character of armchair and zigzag nanotubes was compared with the corresponding rectangular graphite sheets, from which CNTs may be derived. The number of Kekulé structures in (2,2)m and (4,0)m CNTs and in planar rectangular graphite sheets of equivalent size, where m denotes the number of strips making up the CNTs (1 ≤ m ≤ 5), was determined. The aromatic character of the structures was estimated by using the Swinborne-Sheldrake equation. It was found that (2,2) CNTs are more aromatic than their planar counterparts and (4,0) CNTs. (4,0) CNTs are less aromatic compared to the corresponding planar structures. Hence it is more difficult to saturate (and functionalize) armchair CNTs than the corresponding planar graphite structures and zigzag CNTs

Development of a biosensor system to detect bacteria in food systems

The development of biosensors may assist for the on-site detection of foodborne pathogens. The overall goal of this study was to develop a biosensor system for detecting Listeria innocua (non-pathogenic surrogate bacteria used as a model for pathogenic Listeria monocytogenes) in food systems. The study was divided into three main parts: (1) development of a sample collection and interface system for Listeria innocua from food samples, (2) development of a sample concentration system for the collected bacteria prior detection, and (3) development of a detection system based on a carbon nanotube potentiometric biosensor for a quantitative detection of Listeria innocua. In the second chapter, we discussed a sample collection protocol and delivery system developed for bacteria from food surfaces. Listeria innocua was used for testing and illustration. For this purpose, the surface of meat samples was inoculated with Listeria innocua at different concentrations from 10^1-10^5 CFU/mL. Then, cellulose membranes were applied to the surface of products for different times: 5, 10, 15, 20, 25, and 30 min sampling. The cellulose membranes were analyzed for their suitability for bacteria enumeration using a plating method for Listeria innocua. It was observed that sampling times between 5-10 min were the best and collection of \u3e80% of bacteria from the food’s surface was achieved. In the third chapter we discussed a microfluidic device for concentration of biological samples based on removal of liquids by hydrogel films. The performance of the device was demonstrated by concentrating 1-5 µm fluorescent beads followed by concentration of bacteria samples such as Listeria innocua. Results showed that fluorescence intensity of the beads was increased by 10 times at the end of concentration. Recovery efficiencies of 85.60 and 91.75 % were obtained for initial bacteria concentrations of 1x10^1 and 1x10^2 CFU/mL. Moreover, cell counts were observed to increase by up to 10 times at the end of concentration. This study showed that the concentrator device successfully concentrated the samples and no significant loss of living cells was observed for most of the bacteria concentrations. A carbon nanotube potentiometric biosensor for the detection of bacteria from food samples was demonstrated in the fourth chapter. The biosensor was constructed by depositing carboxylic acid (–COOH) functionalized single walled carbon nanotubes (SWCNTs) on a glassy carbon electrode (GCE), followed by the attachment of anti-Listeria antibodies to the SWCNTs between the amine groups and the –COOH by covalent functionalization using EDC/Sulfo-NHS chemistry. The performance of the biosensor was evaluated at various concentrations of L. innocua, for factors such as limit of detection, sensitivity, response time, linearity, and selectivity. In addition, the application of the complete detection system based on sample collection, concentration and detection of bacteria from food samples such as meat and milk was evaluated. Results showed that the system could successfully detect L. innocua with a linear response between electromotive force (EMF/voltage) and bacteria concentrations and a lower limit of detection of 11 CFU/mL. Additionally, similar results were obtained from the biosensor system for L. innocua from food samples

Carbon nanotubes micro-arrays: characterization and application in biosensing of free proteins and label-free capture of breast cancer cells

Circulating tumor cells (CTCs) are cells released into the bloodstream from primary tumors and are suspected to be one of the main causes behind metastatic spreading of cancer. The ability to capture and analyze circulating tumor cells in clinical samples is of great interest in prevailing patient prognosis and clinical management of cancer. Carbon nanotubes, individual rolled-up graphene sheets, have emerged as exciting materials for probing the biomolecular interactions. With diameter of about 1 nm, they can attach themselves to cell surface receptors through specific antibodies and hold a great potential for diagnostic cellular profiling. Carbon nanotubes can be either semiconducting or metallic, and the electronic properties of either type rivals the best known materials. Small size of nanotubes and the ability to functionalize their surface using 1-Pyrenebutanoic Acid, Succinimidyl Ester (PASE), enables a versatile probe for developing a platform for capture and analysis of cancer biomarkers and circulating tumor cells. Although nanotubes have previously been used to electrically detect a variety of molecules and proteins, here for the first time we demonstrate the label free capture of spiked breast cancer cells using ultra-thin carbon nanotube film micro-array devices in a drop of buffy coat and blood. A new statistical approach of using Dynamic Time Warping (DTW) was used to classify the electrical signatures with 90% sensitivity and 90% specificity in blood. These results suggest such label free devices could potentially be useful for clinical capture and further analysis of circulating tumor cells. This thesis will go in-depth the properties of carbon nanotubes, device fabrication and characterization methodologies, functionalization protocols, and experiments in buffy coats and in blood. Combination of nano and biological materials, functionalization protocols and advanced statistical classifiers can potentially enable clinical translation of such devices in the future

Kekulé Structures of Fullerene C70

Despite that, besides Buckminsterfullerene C60, fullerene C70 is the next most stable structure, there are considerable differences in structural properties of these two most common fullerenes. The paper reports on numerous mathematical properties of the set of Kekulé structures of C70. Of over 50,000 Kekulé structures of fullerene C70, only 2780 Kekulé valence structures are distinct, while all the others are symmetry related. The subset of distinct Kekulé valence structures was examined and classified into six classes according to the degree of freedom (df), varying from df = 5 to df = 11. Enumeration of conjugated circuits R1, R2 and R3 points to two symmetry related dominant Kekulé structures having the maximal number of 20 R1. There are 16 distinct symmetry unrelated Kekulé structures of C70 that have no conjugated circuits R1 at all

Two essays in computational optimization: computing the clar number in fullerene graphs and distributing the errors in iterative interior point methods

Fullerene are cage-like hollow carbon molecules graph of pseudospherical sym- metry consisting of only pentagons and hexagons faces. It has been the object of interest for chemists and mathematicians due to its widespread application in various fields, namely including electronic and optic engineering, medical sci- ence and biotechnology. A Fullerene molecular, Γ n of n atoms has a multiplicity of isomers which increases as N iso ∼ O(n 9 ). For instance, Γ 180 has 79,538,751 isomers. The Fries and Clar numbers are stability predictors of a Fullerene molecule. These number can be computed by solving a (possibly N P -hard) combinatorial optimization problem. We propose several ILP formulation of such a problem each yielding a solution algorithm that provides the exact value of the Fries and Clar numbers. We compare the performances of the algorithm derived from the proposed ILP formulations. One of this algorithm is used to find the Clar isomers, i.e., those for which the Clar number is maximum among all isomers having a given size. We repeated this computational experiment for all sizes up to 204 atoms. In the course of the study a total of 2 649 413 774 isomers were analyzed.The second essay concerns developing an iterative primal dual infeasible path following (PDIPF) interior point (IP) algorithm for separable convex quadratic minimum cost flow network problem. In each iteration of PDIPF algorithm, the main computational effort is solving the underlying Newton search direction system. We concentrated on finding the solution of the corresponding linear system iteratively and inexactly. We assumed that all the involved inequalities can be solved inexactly and to this purpose, we focused on different approaches for distributing the error generated by iterative linear solvers such that the convergences of the PDIPF algorithm are guaranteed. As a result, we achieved theoretical bases that open the path to further interesting practical investiga- tion

Polymeric Carbon Nanocomposites - Preparation, Characterization, and Properties

Excellent thermal properties of carbon nanomaterials such as carbon nanotubes and newly discovered graphene make them the filler of choice for the development of thermal management materials. Graphene has been viewed as “ unrolled single-walled carbon nanotube and as a wonder material with many superlatives to its name ” thus there is an excessive interest in developing new synthetic routes towards large scale production of high quality graphene nanosheets. In this dissertation, we report different methods that could further exfoliate the commercially available expanded graphite to nanometer sized carbon structures, “carbon nanosheets ”, for their use in highly thermal conductive polymeric nanocomposites. Initially, an overview of recent advances in the development of thermal conductive polymeric/carbon nanocomposites is provided. Then, the “ carbon nanosheets ” from the specific processes will carefully be characterized by spectroscopic techniques and the effectiveness of the processing methods is demonstrated in terms of polymeric carbon nanocomposites thermal diffusivity. While the focus of this manuscript will be on the enhancement of thermal diffusivity we will also discuss the chemical modification and functionalization of these “ carbon nanosheets ” with matrix polymer. Finally, the critical research opportunities and challenges in the development of functional graphene nanocomposites for thermal management materials will be discussed

Nanochips and medical applications

Ο όρος «νανοτσιπ» αναφέρεται σε ένα ολοκληρωμένο κύκλωμα (τσιπ) με νανοϋλικά και δομές στη νανοκλίμακα (1-100nm). Ένα ολοκληρωμένο κύκλωμα είναι μια συλλογή ηλεκτρονικών εξαρτημάτων, όπως τρανζίστορ, δίοδοι, πυκνωτές και αντιστάσεις. Τα σημερινά τρανζίστορ είναι στη νανοκλίμακα, αλλά μπορούν να τροποποιηθούν με νανοδομές για την κατασκευή βιοαισθητήρων που μπορούν να πραγματοποιούν ανίχνευση βιομορίων, όπως ιόντα, μόρια DNA, αντισώματα και αντιγόνα με μεγάλη ευαισθησία. Υλικά και Μέθοδοι: Πραγματοποιήθηκε συστηματική αναζήτηση βιβλιογραφίας με χρήση των ηλεκτρονικών βάσεων δεδομένων PubMed, Google Scholar και Scopus για την ανάπτυξη και χρήση νανοτσίπ σε ιατρικές εφαρμογές. Για τον προσδιορισμό των σχετικών εργασιών, τα κριτήρια συμπερίληψης αναφέρονται σε άρθρα στην αγγλική γλώσσα, άρθρα βιβλιογραφικού περιεχομένου ή/και έρευνών. Τα κριτήρια αποκλεισμού ήταν άρθρα εφημερίδων, περιλήψεις συνεδρίων και επιστολές. Αποτελέσματα: Τεχνικές in-vivo και in-vitro έχουν χρησιμοποιηθεί για την ανίχνευση μορίων DNA, ιόντων, αντισωμάτων, σημαντικών πρωτεϊνών και καρκινικών δεικτών, όχι μόνο από δείγματα αίματος αλλά και από ιδρώτα, σάλιο και άλλα βιολογικά υγρά. Διαγνωστική εφαρμογή των νανοτσίπ αποτελεί και η ανίχνευση πτητικών οργανικών ενώσεων μέσω τεστ εκπνεόμενης αναπνοής. Υπάρχουν και αρκετές θεραπευτικές εφαρμογές αυτών των συσκευών ημιαγωγών όπως τσιπ διασύνδεσης εγκεφάλου-υπολογιστή για παραλυτικές ή επιληπτικές καταστάσεις, κατασκευή «βιονικών» οργάνων όπως τεχνητός αμφιβληστροειδής, τεχνητό δέρμα και ρομποτικά προθετικά άκρα για ακρωτηριασμένους ή ρομποτική χειρουργική. Συμπέρασμα: Η χρήση των νανοτσίπ στην ιατρική είναι ένας αναδυόμενος τομέας με αρκετές θεραπευτικές εφαρμογές όπως η διάγνωση, η παρακολούθηση της υγείας και της φυσικής κατάστασης και η κατασκευή «βιονικών» οργάνων.Background: The term “nanochip” pertains to an integrated circuit (chip) with nanomaterials and components in the nano-dimension (1-100nm). An integrated circuit is essentially a collection of electronic components, like transistors, diodes, capacitors, and resistors. Current transistors are in the nanoscale but can also be modified with nanostructures like nanoribbons and nanowires to manufacture biosensors that can perform label-free, ultrasensitive detection of biomolecules like ions, DNA molecules, antibodies and antigens. Materials and Methods: A systematic literature search was conducted using the electronic databases PubMed, Google Scholar and Scopus for the development and use of nanochips in medical applications. For the identification of relevant papers, the inclusion criteria referred to articles in the English language, review and/or research articles. The exclusion criteria were newspaper articles, conference abstracts and letters. Results: In-vivo and In-vitro techniques have been used for detection of DNA molecules, ions, antibodies, important proteins, and tumor markers, not only from blood samples but also from sweat, saliva and other biological fluids. Another diagnostic application of nanochips is detection of volatile organic compounds via a breath test. There are also several therapeutic applications of these semiconductor devices like brain-computer interface chips for paralytic or epileptic conditions, manufacture of “bionic” organs like artificial retinas, artificial skin and robotic prostheses for amputees or robotic surgery. Conclusion: The use of nanochips in medicine is an emerging field with several therapeutic applications like diagnostics, health and fitness monitoring, and manufacture of “bionic” organs