Kwang Min Shin

Direct ascorbic acid detection with ferritin immobilized on single-walled carbon nanotubes

Ferritin protein was noncovalently immobilized onto single-walled carbon nanotubes (SWNTs). This SWNT/ferritin composite was characterized using cyclic voltammetry, UV-visible spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy. The use of the SWNT/ferritin film as an amperometric biosensor was demonstrated by sensing 1.0 mM ascorbic acid in phosphate-buffered saline solution with a sensitivity of 767 μA/mg. It demonstrated that ferritin protein bound to SWNTs enhances the oxidation reaction of ascorbic acid over 11-fold.

The optimum functionalization of carbon nanotube/ferritin composites

We fabricated a covalently linked composite composed of functionalized single-walled carbon nanotubes (f-SWNT) and ferritin protein as nanoparticles. The various f-SWNTs were prepared using an acid treatment of purified SWNT for different functionalization times (30, 60, 120 and 180 min), and ferritin was immobilized on each of the f-SWNT by covalent immobilization. The specific capacitance of the f-SWNT and the electrochemical activity of the f-SWNT/ferritin composites showed a Gaussian distribution. From the electrochemical analysis, the ferritin composite with functionalized SWNT for 60 min showed the highest capacitance and electrochemical activity than other f-SWNT/ferritin composites. This result suggests the optimum value for the best performance of the electrochemical properties of f-SWNT/ferritin composites was found for a potential bioapplication.

Anomalous pH Actuation of a Chitosan/SWNT Microfiber Hydrogel with Improved Mechanical Property

Composite fibers composed of chitosan and single-wall carbon nanotubes (CNTs) have been fabricated using a wet spinning method. The dispersion was improved by the sonic agitation of the CNTs in a chitosan solution followed by centrifugation to remove tube aggregates and any residual catalyst. The mechanical behavior was investigated using a dynamic mechanical analyzer (DMA). The mechanical tests showed a dramatic increase in Youngs modulus for the chitosan/CNT composite fibers fabricated using the improved dispersion method. The strain on the microfibers was determined from tensile load measurements during pH switching in acidic or basic electrolyte solutions. The microfibers showed a general actuation behavior of expanding at pH = 2 and contracting at pH = 7 under low tensile loads. However, a reverse of this actuation behavior was exhibited under high tensile loads. This anomalous pH actuation is both new and surprising. It was explained from an analysis of the differences in sample stiffness and Poisson’s ratio under tensile load in electrolyte solutions with different pH values.

Redox Reactions of Bio Molecule for Nano-bio Battery

Metal oxide nanoparticles within the protein ferritin can act as an energy storage source in nano-bio batteries containing ferrous ferritin and a reconstituted ferritin cage containing different inorganic elements, such as Co, Mn, Ni, and Pt. These components were introduced as two ferritin half-cells with different redox potentials existing between the ferrous ferritin and the reconstituted ferritin. The reduction of ferritin was analyzed in a solution containing 3-[N-morpholino] propanesulfonic acid buffer and oxidized methyl viologen using cyclic voltammetry. The reduction and oxidation peaks of the methyl viologen occurred at potentials of −300 and −100 mV, respectively, and the reduction and the oxidation peaks of the released Fe occurred at potentials of −300 and −100 mV, respectively. The reduction of ferritin was influenced by the pH of the ferritin solution.

Polyacrylic acid/poly(vinyl sulfonic acid, sodium salt) copolymer hydrogel actuator under an electric field

Random copolymer hydrogel actuators, composed of poly(acrylic acid) and poly(vinyl sulfonic acid, sodium salt), were prepared. The swelling ratios at various temperatures and pHs, the deswelling water ratio and contraction/expansion behavior under an electric field for the hydrogel actuators were measured. The hydrogels exhibited very high swelling ratios, in the range of 8200 ~ 18000%, at 37 °C, and showed temperature/pH dependent swelling behavior. The deswelling water ratio of the CO1 hydrogel sample showed about an 80% weight reduction under a 5 V applied voltage. When the hydrogel actuator in various pH buffer solutions is subjected to an electric field, the hydrogel actuator was contracted. When the electric stimulus was removed, the hydrogel actuator was expanded on its original size. The hydrogel actuator also showed stepwise contraction/expansion behavior depending on the electric stimulus.