Development of Carbon Nanotube Field-Effect Transistor Arrays for Detection of HER2 Overexpression in Breast Cancer

We developed a carbon nanotube biosensor platform that was deployed at the National Cancer Institute and successfully detected the HER2 oncogene in real cancer cells at clinically relevant levels. HER2 is a receptor protein that resides on the surface of certain cancer cells and is associated with higher aggressiveness in breast cancers. Overabundance of HER2 at the chromosomal, cell surface, and intermediate gene expression levels can all indicate a dangerous HER2 status. At the present, testing for HER2 status requires labor-intensive laboratory procedures using expensive reagents. Cost remains the major barrier to widespread screening. We propose an integrated electronic testing platform based on direct label-free gene detection. The system would integrate the various labor-intensive processes that are usually performed by skilled laboratory technicians. The heart of the system is an array of carbon nanotube field-effect transistors that can detect unlabelled nucleic acids via their intrinsic electric charges. We developed a scalable fabrication technique for carbon nanotube biosensor arrays, hardware and software for data acquisition and analysis, theoretical models for detection mechanism, and protocols for immobilization of peptide nucleic acid probes and hybridization of nucleic acids extracted from cells. We demonstrated detection of HER2 from real cell lines which express cancer genes, thereby lowering the technological barrier towards commercialization of a low-cost gene expression biosensor. The system is suitable for lab-on-a-chip integration, which could bring rapid, low-cost cancer diagnoses into the clinical setting

Self-Healing Nanocomposites—Advancements and Aerospace Applications

Self-healing polymers and nanocomposites form an important class of responsive materials. These materials have the capability to reversibly heal their damage. For aerospace applications, thermosets and thermoplastic polymers have been reinforced with nanocarbon nanoparticles for self-healing of structural damage. This review comprehends the use of self-healing nanocomposites in the aerospace sector. The self-healing behavior of the nanocomposites depends on factors such as microphase separation, matrix–nanofiller interactions and inter-diffusion of polymer–nanofiller. Moreover, self-healing can be achieved through healing agents such as nanocapsules and nanocarbon nanoparticles. The mechanism of self-healing has been found to operate via physical or chemical interactions. Self-healing nanocomposites have been used to design structural components, panels, laminates, membranes, coatings, etc., to recover the damage to space materials. Future research must emphasize the design of new high-performance self-healing polymeric nanocomposites for aerospace structures

Fabrication and characterisation of DNA-templated copper nanowires

PhD ThesisThis thesis describes four approaches developed towards the fabrication of conductive 1-dimensional copper nanostructures, or nanowires, using a DNA-templating strategy. Cu-DNA nanowires are of interest for miniaturised interconnects in microprocessors. The chemical identity of the nanowires was characterised using X-ray Photoelectron Spectroscopy (XPS) and powder X-ray Diffraction (XRD) methods. Structural investigations were performed using Fourier-Transform Infra-Red (FTIR) Spectroscopy n+ and Atomic Force Microscopy (AFM) to study the Cu -DNA interaction mode(s) and nanowire size/morphologies, respectively. The electrical properties of nanowires were elucidated using Electrostatic Force Microscopy (EFM), Conductive-AFM (C-AFM) and a two-probe semiconductor device analyser for recording current-voltage (i-V) relationships. One method describes a non-aqueous route to the formation of 1-D Cu nanostructures. + This was achieved by doping of surface-immobilised DNA (the template) with Cu ions from Cu(CHCN).PF followed by chemical reduction to the zero-valent metal using 346 phenylsilane and organic solvent, under inert conditions. Metallic copper was confirmed to have formed on DNA and copper hydroxide (Cu(OH)) was also identified as a 2 surface overlayer on this material. The final structures were ~6 nm in height and show complete coverage of the template. The material was polycrystalline due to observations of a densely packed series of Cu nanoparticles along the template axis. However, electrical studies indicated these structures to be highly resistive. Thermal annealing of the templated material resulted in a considerable structural transformation, from tightly packed particles to the formation of a sporadic array of larger clusters well separated along the structure length. 2+ Another approach involved an aqueous solution-based synthesis, whereby Cu from Cu(NO) and ascorbic acid were added to a solution of DNA. This resulted in 32 nanowires, ~7 nm in height, which were mostly continuous in morphology and 2+ noticeably absent of inter-particle boundaries. The Cu :DNA(phosphate) ratio (n) was found to be critical for the formation of smooth nanowires (n= 0.05) as opposed to aggregated assemblies of material (n> 0.1). Chemical characterisation of the reaction product confirmed the presence of metallic copper as well as a surface layer of Cu(OH) Nanowires were confirmed to be conductive and i-V measurements gave a2. conductivity value of 0.94 Scm ; the first recorded conductance for copper templated on DNA, over micron length scales. Attempts were made to passivate the nanowires formed in solution by attachment of thiol molecules (p-mercaptobenzoic acid) onto the copper surface. This modification 0 resulted in the formation of a Cu(I)-thiolate layer on Cu and significantly protected the nanowires from oxidation, resulting in the formation of almost pure metallic Cu -1 nanowires. The electrical conductivity (1.01 Scm ) was similar to that obtained for the -1 unprotected wires (0.94 Scm ). This suggested that, although the degree of oxidation was minimised significantly, other factors must be more accountable for causing resistance in these wires such as surface and/or grain boundary scattering. Finally, a physical-based approach towards metallisation of DNA was performed using a vacuum deposition method. This was achieved by suspending single molecules of DNA between two electrodes, across a trench etched into the substrate. This was followed by metallisation of the sample by evaporation of copper in a sealed vacuum chamber. Electron Microscopy data showed that nanowires lay taut across the trench and were highly continuous in coverage. This process resulted in a working two- terminal nanowire device which was conductive due to nanowire(s) bridging between insulating gaps

Development of Electronic DNA Hybridization Detection Using Carbon Nanotube Field Effect Transistor Arrays

Spurred by the Human Genome Project, deoxyribonucleic acid (DNA) microarrays are indispensable tools in molecular biology. In particular, they are used in the genetic profiling of human diseases, which includes identifying genes that are expressed in certain cancers. Genotyping allows more accurate identification and consequently, improved treatment. This technique has the potential to revolutionize the diagnosis of many other human ailments and be an important tool in the arsenal of modern medicine. At present however, microarray experiments involve complex protocols, often employing fluorescent labeling as well as sophisticated detection instruments. These systems are thus only affordable by very few large laboratories and pharmaceutical companies. In this work, we propose and demonstrate the feasibility of using a low-cost and improved alternative. We designed and fabricated biochips based on carbon nanotube field effect transistor arrays to detect the presence of specific DNA sequences, e.g. expressed genes, in a solution of DNA or RNA in the same manner as microarrays. The ultimate goal is to optimize the system to make it suitable for point-of-care applications. Our design utilizes CVD-grown carbon nanotube mats on a substrate of silicon oxide and metal contacts patterned using conventional microlithography. The carbon nanotube mats are covered by a thin oxide upon which single stranded DNA 'probe' molecules are immobilized. When exposed to a solution containing the complementary sequence, Watson-Crick hybridization leads to the binding of the complementary 'target' strands. Since DNA's are electrically charged through the excess electron of the phosphate backbone, this process results in the incorporation of additional negative charges at the transistor gate. This effectively causes a change in the conductance of the nanotube channel and a shift in the device threshold voltage. The voltage shift reflects the amount of extra charges deposited on the gate and based on this, the amount of captured target DNA can be precisely quantified. We demonstrated electronic label-free detection of specific DNA binding or hybridization at the sensitivity level of 10−100 nM, and specificity limited by chemical protocols. Comparing other label-free schemes, we believe our approach is advantageous in terms of simplicity and compatibility with current microarray protocols

Cutting Edge Nanotechnology

The main purpose of this book is to describe important issues in various types of devices ranging from conventional transistors (opening chapters of the book) to molecular electronic devices whose fabrication and operation is discussed in the last few chapters of the book. As such, this book can serve as a guide for identifications of important areas of research in micro, nano and molecular electronics. We deeply acknowledge valuable contributions that each of the authors made in writing these excellent chapters

Carbon nanotube field-effect sensors for single-molecule detection

This thesis describes a detection system for single molecules based on individual single-walled carbon nanotube field-effect sensors. The sensitivity, spatial confinement and transducer gain of the sensor is derived from a conductance controlled electrochemically created defect, which is also chemically reactive. An automated microfluidic system is designed to enable long and stable measurements of the carbon nanotube device in aqueous environment with temperature control of ±0.1°C. A probe DNA can be covalently attached to the defect through an amide bond and the conductance is modulated when a target DNA binds to the probe. As a result, the conductance shows a traditional random telegraph signal and fluctuates between a hybridized and melted state. By monitoring the conductance as a function of temperature, the kinetics and thermodynamics can be extracted, which are comparable to previous fluorescent correlation spectroscopy studies using optical fluorescent resonant energy transfer. By studying the fluctuation amplitude as a function of charge proximity, buffer concentration and solution potential, it is shown that the sensor is based on a field-effect. The sensor has a temporal resolution of 200 μs and a signal to noise ratio of 3-8 when continuously measuring for 30 seconds. By further reducing the parasitics, the sensor has the capabilities to detect biomolecule kinetics down to microsecond resolution, which could make it an attractive tool for single-molecule experiments with fast kinetics

Computing the Fundamental Interactions Between Carbon Nanotubes and Pulmonary Surfactant Proteins

Molecular dynamic computation is one of the most direct and detailed approaches for investigating protein and carbon nanotube interaction at the atomic level. Molecular dynamic computation can address the events occurring in a protein’s structure and on the surface of the carbon nanotube. Molecular dynamic computation can also explain the structural changes in protein, including (i) secondary and tertiary structure changes, (ii) orientation and reorientation of the protein before and after adsorption, (iii) behavior of each amino acid residual group, (iv) hydrogen-bonding, (v) pi-pi stacking of carbon atoms of proteins and carbon nanotube, and other things as well. These fundamental properties have to address the adsorption of protein on a carbon nanotube surface, and estimates of this process are produced by molecular dynamic computations. Also, molecular dynamic computation is an attractive method for 3D imaging in bio-nanotechnology because it can give a complete trajectory over time (tens or hundreds of nanoseconds) of all atoms of protein interacting with carbon nanotubes and thus clarify their behavior in a given environment. This work presents the fundamental understanding of the human pulmonary surfactant proteins SP-A, SP-B, SP-C, and SP-D and their interaction with a single-walled carbon nanotube. This is accomplished using nanoscale molecular dynamic computation. Atomistic molecular dynamic simulation is performed and a trajectory over 100 ns is computed. Results show that all four pulmonary surfactant proteins are adsorbed on the surface of a carbon nanotube. The main driving force of interaction is the Van der Waals force of attraction. From the root mean square deviation of all four protein trajectories, stability is achieved. Both hydrophobic and hydrophilic residues of proteins are adsorbed on the surface of a carbon nanotube. These results will be helpful in developing nano-electro-chemical biosensors in the future

Nitrogen doped carbon nanomaterials for biosensing applications

Tesis (Doctorado en Nanociencias y Nanotecnología)"The doping of carbon nanostructures with elements such as nitrogen and boron adds useful characteristics to the already remarkable features exhibited by nanocarbons. These new properties can be used for tackling several obstacles encountered for nanotechnology based applications, specially in biotechnology, where biocompatibility and sensitivity are crucial parameters for biosensing applications development. In this thesis work, we report the synthesis of nitrogendoped graphitic nanoribbons, along with their characterization by SEM and TEM. Raman and XPS spectroscopy results are also shown, and electrical characterization results are presented as well. Our results demonstrate how the presence of nitrogen produces novel morphologic, chemical and physical properties on graphitic nanoribbons, which in turn make the nanomaterial a promising candidate for bioelectronics research. Additionaly, we present results of theoretical and experimental research on interactions of doped carbon nanomaterials and biomolecules. Our theoretical findings suggest strong effects of doping on the stability of interactions between graphene and dopamine, whereas our experimental results suggest improved electrical properties for nitrogen-doped carbon nanotubes based biodevices when compared with undoped ones. This thesis shows, from theoretical and experimental studies, that doping of carbon nanostructures can be useful for sensing of biomolecules.

Oligonucleotide guanosine conjugated to gallium nitride nano-structures for photonics.

In this work, I studied the hybrid system based on self-assembled guanosine crystal (SAGC) conjugated to wide-bandgap semiconductor gallium nitride (GaN). Guanosine is one of the four bases of DNA and has the lowest oxidation energy, which favors carrier transport. It also has large dipole moment. Guanosine molecules self-assemble to ribbon-like structure in confined space. GaN surface can have positive or negative polarity depending on whether the surface is Ga- or N-terminated. I studied SAGC in confined space between two electrodes. The current-voltage characteristics can be explained very well with the theory of metal-semiconductor-metal (MSM) structure. I-V curves also show strong rectification effect, which can be explained by the intrinsic polarization along the axis of ribbon-like structure of SAGC. GaN substrate property influences the properties of SAGC. So SAGC has semiconductor properties within the confined space up to 458nm. When the gap distance gets up to 484nm, the structure with guanosine shows resistance characteristics. The photocurrent measurements show that the bandgap of SAGC is about 3.3-3.4eV and affected by substrate properties. The MSM structure based on SAGC can be used as photodetector in UV region. Then I show that the periodic structure based on GaN and SAGC can have photonic bandgaps. The bandgap size and the band edges can be tuned by tuning lattice parameters. Light propagation and emission can be tuned by photonic crystals. So the hybrid photonic crystal can be potentially used to detect guanosine molecules. If guanosine molecules are used as functional linker to other biomolecules which usually absorb or emit light in blue to UV region, the hybrid photonic crystal can also be used to tune the coupling of light source to guanosine molecules, then to other biomolecules