Sang Nyon Kim

Structure of a Peptide Adsorbed on Graphene and Graphite

Noncovalent functionalization of graphene using peptides is a promising method for producing novel sensors with high sensitivity and selectivity. Here we perform atomic force microscopy, Raman spectroscopy, infrared spectroscopy, and molecular dynamics simulations to investigate peptide-binding behavior to graphene and graphite. We studied a dodecamer peptide identified with phage display to possess affinity for graphite. Optical spectroscopy reveals that the peptide forms secondary structures both in powder form and in an aqueous medium. The dominant structure in the powder form is α-helix, which undergoes a transition to a distorted helical structure in aqueous solution. The peptide forms a complex reticular structure upon adsorption on graphene and graphite, having a helical conformation different from α-helix due to its interaction with the surface. Our observation is consistent with our molecular dynamics calculations, and our study paves the way for rational functionalization of graphene using biomolecules with defined structures and, therefore, functionalities.

Biotemplated Metal Nanowires Using Hyperthermophilic Protein Filaments

The fabrication of multifunctional nanostructures with complex geometries is necessary for advancement in the field of nanoelectronics and nanosensors. This is evident by the limited ability of present systems to handle optimum current loads, meet smaller device configurations, and provide integration. Electron transport in nanostructures has received a lot of attention for these reasons. Fortunately, nature offers a diverse assortment of self-assembling biomolecular templates for the construction of circuits, electrodes, and wires. These includeDNA,viruses, proteins, andpeptides that self-assemble into supramolecular structures, possess unique architectures (rods, spheres, filaments), and serve as scaffolds for nanoparticle synthesis andassembly. For example,DNAstrands have been used to template metal nanowires or two-dimensional (2D) nanogrids; the tobacco mosaic virus has been decorated with small gold nanoparticles and peptide nanotubes or protein functionalized carbon nanotubes have been mineralized with copper, gold, and silver. These biotemplated structures highlight the unique structures obtainable through the use of biomolecular templates. Moreover, biotemplating enables one to acquire nano–bio hybrids exhibiting electrical properties ranging from insulator to conductor with the conductivity close to bulkmetals, mainly due to the fact that electron transport through the metal nanowires formed fromvariousbiotemplates is governedby the metal domain-to-domain interface and/or grain boundaries. In the case of crystalline nanowires, the absence of a grain boundary or interface results in high conductivity and failure current density.

A tunable CMOS read-out integrated circuit for carbon nanotube-based bio-sensors

A robust and tunable read-out integrated circuit architecture is presented for carbon nanotube-based bio-sensor with nano-amperes current measurement at 1ms to 16 minutes intervals. The circuit contains an on-chip 8-bit analog-to-digital convertor and a trans-impedance amplifier with tunable control parameters to accommodate not easily controlled single-walled nanotube sensor fabrication with a wide distribution of resistance ranges. For one of the prepared carbon nanotube devices, the current estimation accuracy is within 0.38 nA for a carbon nanotube sensor with expected effective resistance range between 5–30 MΩ This corresponds to current measurements between 5–45 nA. This CMOS instrumentation core has an approximate area of 639 μm2 and consumes 33 mW at 5 MHz sampling rate.

Selective vapor phase sensing of small molecules using biofunctionalized field effect transistors

This work details a proof of concept study for vapor phase selective sensing using a strategy of biorecognition elements (BRE) integrated into a zinc oxide field effect transistor (ZnO FET). ZnO FETs are highly sensitive to changes to the environment with little to no selectivity. Addition of a biorecognition element retains the sensitivity of the device while adding selectivity. The DNA aptamer designed to bind the small molecule riboflavin was covalently integrated into the ZnO FET and detects the presence of 116 ppb of riboflavin in a nitrogen atmosphere by a change in current. The unfunctionalized ZnO FET shows no response to this same concentrations of riboflavin, showing that the aptamerbinding strategy may be a promising strategy for vapor phase sensing.

DNA aptamer functionalized zinc oxide field effect transistors for liquid state selective sensing of small molecules

In this work, we show the use of single stranded DNA aptamers as selective biorecognition elements in a sensor based on a field effect transistor (FET) platform. Aptamers are chemically attached to the semiconducting material in the FET through the use of linker molecules and confirmed through atomic force microscopy and positive target detection. Highly selective sensing of a small molecule, riboflavin is shown down to the nano-molar level in zinc oxide FET and micro-molar level in a carbon nanotube FET. High selectivity is determined through the use of negative control target molecules with similar molecular structures as the positive control targets with little to no sensor response. The goal of this work is to develop a sensor platform where biorecognition elements can be used to functionalize an array of transistors for simultaneous sensing of multiple targets in biological fluids.

Assembly of Single Wall Carbon Nanotube-Metal Nanohybrids Using Biomolecular Components

Biomaterials such as nucleic acids and proteins can be exploited to create higher order structures. The biomolecular components such as DNA and peptides have been used to assemble nanoparticles with high fidelity. Here, we use DNA and peptides, and their preferential interaction with inorganic and carbon nanomaterials to form homogeneous hybrids. The enhanced binding of Pt ions to both DNA and peptide functionalized nanoparticles mediates the assembly of carbon nanotubes functionalized with DNA with peptide coated gold nanoparticles.

Measuring SWNT depth in electroactive polymer nanocomposite films using electric force microscopy

Although a number of hypotheses have been presented to explain the enhanced electromechanical performance observed in electroactive polymer nanocomposite materials, many of the underlying mechanisms responsible for this behavior remain unclear. In this report, electric force microscopy (EFM) is used to investigate the near surface morphology of an electroactive polyimide-based nanocomposite film containing SWNTs in an effort to gain insight into the electrical interactions occurring at the polymer-electrode interface. As a means of measuring the proximity of SWNTs to this interface, the depths of SWNTs buried beneath a processing-induced polymer skin layer are determined using EFM measurements derived from a sample standard. In this way, evaluation of the ability for embedded SWNT structures to behave as extensions of surface electrodes is possible, a scenario that could potentially reduce the applied field required to elicit electromechanical actuation.

Deoxyribonucleic Acid (DNA) based BioTransistors

In this paper, we report the first results on DNA based thin film field effect transistors (TFFET). The DNA molecules are extracted from Salmons milt and roe sacs and purified to 96%. DNA based thin films are obtained using different techniques including spin coating, molecular beam deposition (MBD), pulse laser deposition (PLD)...etc. An increase in the overall charge carrier mobility was achieved by blending the DNA molecules with conductive polymers such as PEDOT:PSS as well as conductive nanoparticles such as single wall carbon nanotubes. MOSFETs with bottom gate, bottom contact structures using DNA based thin films as the semi-conductive layer have been developed.

DNA Mediated Solubilization of Single Wall Carbon Nanotubes

DNA has been recognized as an efficient dispersion agent that individually exfoliate and chirality-fractionate single wall carbon nanotubes (SWCNTs) according to their diameter and metallicity. Amongst, single stranded d(GT)n DNA has been known to efficiently disperse individual-level nanotube and mediate their subsequent chirality separation, when eluted from an anion exchange column at various salt concentrations. However, the cost for typical synthetic oligomer, ranging ~25,000

DNA-Conductive polymer blends for applications in Biopolymer based field effect transistors (FETs)

/g, hinders the bulk-scale solubilization and separation of SWCNTs. In this paper, we present a solubilization and separation study of SWCNTs by using salmon sperm DNA (SaDNA), which costs 20