Ilsoon Lee

Nanometal-decorated exfoliated graphite nanoplatelet based glucose biosensors with high sensitivity and fast response.

We report the novel fabrication of a highly sensitive, selective, fast responding, and affordable amperometric glucose biosensor using exfoliated graphite nanoplatelets (xGnPs) decorated with Pt and Pd nanoparticles. Nafion was used to solubilize metal-decorated graphite nanoplatelets, and a simple cast method with high content organic solvent (85 wt %) was used to prepare the biosensors. The addition of precious metal nanoparticles such as platinum (Pt) and palladium (Pd) to xGnP increased the electroactive area of the electrode and substantially decreased the overpotential in the detection of hydrogen peroxide. The Pt-xGnP glucose biosensor had a sensitivity of 61.5+/-0.6 microA/(mM x cm(2)) and gave a linear response up to 20 mM. The response time and detection limit (S/N=3) were determined to be 2 s and 1 microM, respectively. Therefore, this novel glucose biosensor based on the Pt nanoparticle coated xGnP is among the best reported to date in both sensing performance and production cost. In addition, the effects of metal nanoparticle loading and the particle size on the biosensor performance were systematically investigated.

Identification of a Novel Benzimidazole That Inhibits Bacterial Biofilm Formation in a Broad-Spectrum Manner

ABSTRACT Bacterial biofilm formation causes significant industrial economic loss and high morbidity and mortality in medical settings. Biofilms are defined as multicellular communities of bacteria encased in a matrix of protective extracellular polymers. Because biofilms have a high tolerance for treatment with antimicrobials, protect bacteria from immune defense, and resist clearance with standard sanitation protocols, it is critical to develop new approaches to prevent biofilm formation. Here, a novel benzimidazole molecule, named antibiofilm compound 1 (ABC-1), identified in a small-molecule screen, was found to prevent bacterial biofilm formation in multiple Gram-negative and Gram-positive bacterial pathogens, including Pseudomonas aeruginosa and Staphylococcus aureus, on a variety of different surface types. Importantly, ABC-1 itself does not inhibit the growth of bacteria, and it is effective at nanomolar concentrations. Also, coating a polystyrene surface with ABC-1 reduces biofilm formation. These data suggest ABC-1 is a new chemical scaffold for the development of antibiofilm compounds.

Cell Adhesive Behavior on Thin Polyelectrolyte Multilayers: Cells Attempt to Achieve Homeostasis of Its Adhesion Energy

Linearly growing ultrathin polyelectrolyte multilayer (PEM) films of strong polyelectrolytes, poly(diallyldimethylammonium chloride) (PDAC), and sulfonated polystyrene, sodium salt (SPS) exhibit a gradual shift from cytophilic to cytophobic behavior, with increasing thickness for films of less than 100 nm. Previous explanations based on film hydration, swelling, and changes in the elastic modulus cannot account for the cytophobicity observed with these thin films as the number of bilayers increases. We implemented a finite element analysis to help elucidate the observed trends in cell spreading. The simulation results suggest that cells maintain a constant level of energy consumption (energy homeostasis) during active probing and thus respond to changes in the film stiffness as the film thickness increases by adjusting their morphology and the number of focal adhesions recruited and thereby their attachment to a substrate.

Multilayer mediated forward and patterned siRNA transfection using linear-PEI at extended N/P ratios

Gene delivery from a substrate depends, in part, on the vector-nucleic acid complex that is bound to the surface and the cell adhesive properties of the surface. Here, we present a method to deliver patterns of small interfering RNA (siRNA) that capitalize on a forward transfection method (transfection by introducing siRNA transfection reagent complexes onto plated cells); herein denoted as multilayer mediated forward transfection (MFT). This method separates the substrate-mediated delivery from the cell adhesive properties of the surface. pH responsive layer-by-layer (LbL) assembled multilayers were used as the delivery platform and microcontact printing technique (microCP) was used to pattern nanoparticles of transfection reagent-siRNA complexes onto degradable multilayers. Efficient MFT depend on optimal formulation of the nanoparticles. 25 kDa linear polyethylenimine (LPEI) was optimized as the siRNA transfection reagent for normal forward transfection (NFT) of the nanoparticles. A broad range of LPEI-siRNA nitrogen/phosphate (N/P) ratios (ranging from 5 to 90) was evaluated for the relative amounts of siRNA incorporated into the nanoparticles, nanoparticle size and NFT efficiencies. All the siRNA was incorporated into the nanoparticles at N/P ratio near 90. Increasing the amount of siRNA incorporated into the nanoparticles, with increasing N/P ratio correlated with a linear blue shift in the ultraviolet/visible (UV/vis) absorbance spectrum of the LPEI-siRNA nanoparticles. NFT efficiency greater than 80% was achieved with minimal cytotoxicity at N/P ratio of 30 and siRNA concentration of 200 nM. Similarly, MFT efficiency 60% was achieved for LPEI-siRNA nanoparticles at N/P ratios greater than 30.

Controlling amine receptor group density on aluminum oxide surfaces by mixed silane self assembly

To estimate adhesion at polymer)solid interfaces, model substrates with varying )NH density on Al O were prepared by a 22 3 . . self-assembly of mixed amine terminated silanes AS and methyl terminated silanes MS . The density of )NH groups on 2 Al O was varied by changing the mol.% of AS and MS in solution. The model surfaces were characterized by means of X-ray 23 . . photoelectron spectroscopy XPS , contact angle measurements, atomic force microscopy AFM , and mechanical tests with polymers. The analysis of the competitive coadsorption kinetic model showed that MS adsorbed two times faster than AS on aluminum surfaces. The surface energetics of Al O was controlled by the mixed silane treatments from hydrophobic and low 23

Molecular self-assembly: smart design of surface and interface via secondary molecular interactions.

The molecular self-assembly of macromolecular species such as polymers, colloids, nano/microparticles, proteins, and cells when they interface with a solid/substrate surface has been studied for many years, especially in terms of molecular interactions, adsorption, and adhesion. Such fundamental knowledge is practically important in designing smart micro- and nanodevices and sensors, including biologically implantable ones. This review gives a brief sketch of molecular self-assembly and nanostructured multifunctional thin films that utilize secondary molecular interactions at surfaces and interfaces.

Intact transfer of layered, bionanocomposite arrays by microcontact printing

A novel approach is presented that allows high-quality, 3D patterned bionanocomposite layered films to be constructed on substrates whose surface properties are incompatible with existing self-assembly methods.

Cellulase Immobilized Nanostructured Supports for Efficient Saccharification of Cellulosic Substrates

Functionalized nanomaterials are promising candidates for enzyme immobilization to develop efficient industrial biocatalysts with tailor-made catalytic properties. Cellulase, a saccharifying hydrolase, can be immobilized on various nanostructured supports using different types of binding chemistries. This review examines prior cellulase immobilization strategies and promising future techniques to integrate nanotechnology with biocatalysis.

Time controlled release of arabinofuranosylcytosine (Ara-C) from agarose hydrogels using layer-by-layer assembly: An in vitro study

Experimentally induced axonal regeneration is compromised by glial scar formation arising from leptomeningeal fibroblasts cells in and around the hydrogel scaffold implanted for nerve repair. Strategies are needed to prevent such fibroblastic reactive cell layer formation for enhanced axonal regeneration. Here, we implement the technique of layer-by-layer assembled degradable, hydrogen bonded multilayers on agarose hydrogels to incorporate an anti-mitotic drug (1-β-D-arabinofuranosylcytosine (Ara-C)) within the agarose hydrogels. We show controlled release of Ara-C under physiological conditions over a period of days. The concentrations of Ara-C released from agarose at the different time points were sufficient to inhibit fibroblast growth in vitro, while not adversely affecting the viability of the neuronal cells.

Conductive oxygen barrier films using supramolecular assembly of graphene embedded polyelectrolyte multilayers

The supramolecular self-assembly of polyelectrolyte multilayers (PEMs) provides robust bottom-up strategies to assemble a broad spectrum of nanostructures on the host substrates. In this study, we discuss the formation of graphene nanoplatelet (GNP) embedded polyelectrolyte films to enhance the oxygen barrier properties of poly(ethylene terephthalate) (PET) films. Despite cheaper costs and high mechanical strength, the diffusion of small gas molecules such as oxygen through PET films remains a matter of great concern. The simple yet robust supramolecular deposition of GNP/polyelectrolyte on PET substrates significantly increases the tortuous path the oxygen molecule has to travel, making it harder to diffuse through the PET film. With permeability coefficients in the range of 10-18 cc cm/cm(2) s Pa, the coatings developed in this study show three orders of magnitude reduction as compared to the permeability coefficient of the bare PET film, significantly lower than that of ethylene vinyl alcohol (EVOH) and comparable to silicon oxide thin films used in commercial gas barrier foils. The use of GNPs in the multilayered films also helped reduce the electrical sheet resistance to about 1MΩ which is five orders of magnitude lower than the original PET substrate opening up promising opportunities for future use in semiconductor and electronics industry. Making suitable modifications in the deposition process, three configurations of GNP embedded PEM multilayers namely hydrogen bonded, electrostatic, and composite films were developed and their effect on oxygen barrier property and sheet resistance was monitored. Oxygen permeability of films was tested in accordance with ASTM D-3985 using a MOCON 2/21 ML instrument, whereas electrical sheet resistance was quantified using a Gamry Femtostat Electrochemical Impedance station.