Keehoon Won

Aptamers as molecular recognition elements for electrical nanobiosensors

AbstractRecent advances in nanotechnology have enabled the development of nanoscale sensors that outperform conventional biosensors. This review summarizes the nanoscale biosensors that use aptamers as molecular recognition elements. The advantages of aptamers over antibodies as sensors are highlighted. These advantages are especially apparent with electrical sensors such as electrochemical sensors or those using field-effect transistors. FigureFeeling proteins with aptamer-functionalized carbon nanotubes

Structural features of lignin macromolecules extracted with ionic liquid from poplar wood

1-Ethyl-3-methylimidazolium acetate ([Emim][CH₃COO]) was used for the extraction of lignin from poplar wood (Populus albaglandulosa), which was called to ionic liquid lignin (ILL) and structural features of ILL were compared with the corresponding milled wood lignin (MWL). Yields of ILL and MWL were 5.8±0.3% and 4.4±0.4%, respectively. The maximum decomposition rate (V(M)) and temperature (T(M)) corresponding to V(M) were 0.25%/ °C and 308.2 °C for ILL and 0.30%/ °C and 381.3 °C for MWL. The amounts of functional groups (OMe and phenolic OH) appeared to be similar for both lignins; approximately 15.5% and 6.7% for ILL and 14.4% and 6.3% for MWL. However, the weight average molecular weight (M(w)) of ILL (6347 Da) was determined to be 2/3-fold of that of MWL (10,002 Da) and polydispersity index (PDI: M(w)/M(n)) suggested that the lignin fragments were more uniform in the ILL (PDI 1.62) than in the MWL (PDI 2.64).

Electrochemical Regeneration of NADH Enhanced by Platinum Nanoparticles

This work was supported by the Korea Energy Management Corporation (2005-C-CD11-P-04) and the Korea Research Foundation (KRF-2006-331-D00113).

Novel water-resistant UV-activated oxygen indicator for intelligent food packaging.

For the first time, alginate polymer has been applied to prevent dyes from leaching out of colorimetric oxygen indicator films, which enable people to notice the presence of oxygen in the package in an economic and simple manner. The dye-based oxygen indicator film suffers from dye leaching upon contact with water. In this work, UV-activated visual oxygen indicator films were fabricated using thionine, glycerol, P25 TiO2, and zein as a redox dye, a sacrificial electron donor, UV-absorbing semiconducting photocatalyst, and an encapsulation polymer, respectively. When this zein-coated film was immersed in water for 24h, the dye leakage was as high as 80.80±0.45%. However, introduction of alginate (1.25%) as the coating polymer considerably diminished the dye leaching to only 5.80±0.06%. This is because the ion-binding ability of alginate could prevent the cation dye from leaching into water. This novel water-resistant UV-activated oxygen indicator was also successfully photo-bleached and regained colour fast in the presence of oxygen.

Detection of tumor markers using single-walled carbon nanotube field effect transistors.

We have developed a biosensor capable of detecting carcinoembryonic antigen (CEA) markers using single-walled carbon nanotube field effect transistors (SWNT-FETs). These SWNT-FETs were fabricated using nanotubes produced by a patterned catalyst growth technique, where the top contact electrodes were generated using conventional photolithography. For biosensor applications, SU-8 negative photoresist patterns were used as an insulation layer. CEA antibodies were employed as recognition elements to specific tumor markers, and were successfully immobilized on the sides of a single-walled carbon nanotube using CDI-Tween 20 linking molecules. The binding of tumor markers to these antibody-functionalized SWNT-FETs was then monitored continuously during exposure to dilute CEA solutions. The observed sharp decrease in conductance demonstrates the possibility of realizing highly sensitive, label-free SWNT-FET-based tumor sensors.

A novel route for immobilization of proteins to silica particles incorporating silaffin domains

In the diatom Cylindrotheca fusiformis, modified peptides called silaffin polypeptides are responsible for silica deposition in vivo at ambient conditions. Recently, it was discovered that the synthetic R5 peptide, the repeat unit of silaffin polypeptide without post‐translational modification, was capable of precipitating silica in vitro and at ambient conditions. Herein, chimeric proteins were generated by incorporating synthetic silaffin R5 peptides and related unmodified silaffin domains (R1–R7) from Cylindrotheca fusiformis onto green fluorescent protein (GFP) by recombinant DNA technology and their ability to cause silicification was also examined. GFP chimeric proteins showed silicification at very low concentrations (600–700 μg/mL) when compared with adding excess amounts of R5 peptides (10 mg/mL) as previously reported. Sensitive to pH conditions, only the GFP‐R1 chimera showed silicification activity at pH 8.0. The protein immobilization efficiencies of these chimeras were unexpectedly high ranging from 75 to 85%, with the R1 silaffin‐protein construct showing excellent immobilization efficiency and a constant molar ratio of silica to protein ranging from 250 to 350 over a wide pH range. The average silica particle sizes had a tendency to decrease as pH increased to basic conditions. This study demonstrated the production of nanoscale immobilized protein, fabricated via silaffin‐fused proteins.

Electrical properties of polyaniline nanofibre synthesized with biocatalyst

Polyaniline (PANI) nanofibres were synthesized using a biocatalyst (recombinant Coprinus cinereus peroxidase) instead of toxic chemical oxidants. Relatively uniform nanofibres with 50?100?nm diameter were easily obtained with this method, and the doping state of the PANI nanofibre could be controlled either with 1N camphorsulfonic acid (CSA) or with 30% NH4OH. Doped (or dedoped) PANI nanofibres were deposited on pre-patterned Au electrodes for electrical characterization. Completely dedoped PANI behaves as an insulator, while a larger current, by more than four?orders of magnitude, was observed from doped PANI nanofibres. A?weak p-type gate effect was observed for PANI nanofibre devices as well. As one could expect from the easy doping nature of PANI, PANI nanofibre devices show high sensitivity toward dedoping (NH3) gases, thereby demonstrating the possibility of using enzyme-synthesized PANI nanofibre devices as sensitive chemical sensors.

Electrochemical Regeneration of NADH Using Conductive Vanadia-Silica Xerogels

Electrically conductive sol‐gel matrices have been first introduced in order to enhance the efficiency of electrochemical NADH regeneration systems for biocatalysis. Vanadia‐silica mixed gels as conductive sol‐gels were synthesized using vanadium (V) oxytripropoxide (VOTP) and tetramethyl orthosilicate (TMOS) as precursors. Direct electrochemical reductions of NAD+ were carried out in the presence of vanadia‐silica xerogels using unmodified platinum electrodes. Vanadia‐silica gels from higher ratios of VOTP to TMOS could effectively improve electrochemical generations of NADH from NAD+. Direct electrochemical regenerations of NADH were coupled to the synthesis of l‐glutamate from α‐ketoglutarate catalyzed by glutamate dehydrogenases (GDH). In this case, vanadia‐silica gels were used as matrices for enzyme encapsulation, as opposed to serving as additives. When GDH were entrapped in “nonconductive” silica gels, synthesized using only TMOS, in the control experiment, the initial supply of NADH exhausted quickly and a final conversion of 30% was obtained. However, the use of conductive vanadia‐silica gels with encapsulated GDH resulted in complete conversion of α‐ketoglutarate to l‐glutamate. A turnover number of a cofactor was also enhanced 3‐fold by the application of conductive vanadia‐silica gels.

Wood mimetic hydrogel beads for enzyme immobilization

Wood component-based composite hydrogels have potential applications in biomedical fields owing to their low cost, biodegradability, and biocompatibility. The controllable properties of wood mimetic composites containing three major wood components are useful for enzyme immobilization. Here, lipase from Candida rugosa was entrapped in wood mimetic beads containing cellulose, xylan, and lignin by dissolving wood components with lipase in [Emim][Ac], followed by reconstitution. Lipase entrapped in cellulose/xylan/lignin beads in a 5:3:2 ratio showed the highest activity; this ratio is very similar to that in natural wood. The lipase entrapped in various wood mimetic beads showed increased thermal and pH stability. The half-life times of lipase entrapped in cellulose/alkali lignin hydrogel were 31- and 82-times higher than those of free lipase during incubation under denaturing conditions of high temperature and low pH, respectively. Owing to their biocompatibility, biodegradability, and controllable properties, wood mimetic hydrogel beads can be used to immobilize various enzymes for applications in the biomedical, bioelectronic, and biocatalytic fields.

Immobilization of iron storage protein on a gold electrode based on self-assembled monolayers.

Ferritin is a globular protein consisting of 24 subunits to form a hollow shell and is capable of storing iron in the cavity. Findings that the naturally existing iron core of ferritin can be readily extracted and replaced with a variety of electroactive materials make ferritin suitable for biosensor and biofuel cell applications. The immobilization of ferritin on the electrode surface is essential for various bioelectronic applications. In this work, based on self-assembled monolayers, ferritin was immobilized on a gold electrode through two different methods: chemisorption of thiolated ferritin onto bare gold electrodes and covalent binding of ferritin to succinimidyl alkanedisulfide-modified Au electrodes. Effects of experimental conditions on the ferritin immobilization were investigated. The ferritin immobilized on the gold electrode was characterized by atomic force microscopy and cyclic voltammetry.