Biomedical subjects

Nokyoung Park

Publications and source records attributed to Nokyoung Park.

6 recordsLinked to original sources

PubMed2006

Enzyme-catalysed assembly of DNA hydrogel.

DNA is a remarkable polymer that can be manipulated by a large number of molecular tools including enzymes. A variety of geometric objects, periodic arrays and nanoscale devices have been constructed. Previously we synthesized dendrimer-like DNA and DNA nanobarcodes from branched DNA via ligases. Here we report the construction of a hydrogel entirely from branched DNA that are three-dimensional and can be crosslinked in nature. These DNA hydrogels were biocompatible, biodegradable, inexpensive to fabricate and easily moulded into desired shapes and sizes. The distinct difference of the DNA hydrogel to other bio-inspired hydrogels (including peptide-based, alginate-based and DNA (linear)-polyacrylamide hydrogels) is that the crosslinking is realized via efficient, ligase-mediated reactions. The advantage is that the gelling processes are achieved under physiological conditions and the encapsulations are accomplished in situ-drugs including proteins and even live mammalian cells can be encapsulated in the liquid phase eliminating the drug-loading step and also avoiding denaturing conditions. Fine tuning of these hydrogels is easily accomplished by adjusting the initial concentrations and types of branched DNA monomers, thus allowing the hydrogels to be tailored for specific applications such as controlled drug delivery, tissue engineering, 3D cell culture, cell transplant therapy and other biomedical applications.

Catalysis↗

PubMed2005

Synthesis of cage-type molecules with pi-cavity and selective gas-phase cation complexation.

[structure: see text] Cage-type molecules composed of phenyl walls and caps were synthesized as hosts for the binding of ammonium and alkali metal cations through cation-pi interactions. The synthesis involved a key cyclization step, which was markedly dependent on the capping component. Binding studies by electrospray ionization mass spectrometry toward lithium, sodium, potassium, and ammonium cations showed that the cage-type molecules selectively form a 1:1 complex. A competitive binding study showed that cage 3c (R = Et, R' = OMe) has a preference toward lithium cation while cage 4b (R = Me, R' = OMe) has a similar preference toward both lithium and ammonium ion in the presence of others. This selectivity pattern was tentatively explained by the gate size of the cage-type compounds, not by their cavity size.

Journal Article↗

PubMed2005

Structural characterization of the molten globule state of apomyoglobin by limited proteolysis and HPLC-mass spectrometry.

A method to characterize the structural conformation of an acidic molten globule apomyoglobin (apoMb) at pH 4.2 was developed using limited proteolysis and HPLC-mass spectrometry (HPLC-MS). Endoproteinase Glu-C, which has a double maximum activity at pH 4.0 and pH 7.8 toward glutamic acid (Glu), was used as a proteolytic enzyme. Using this method enabled us to compare the proteolytic cleavages of native apoMb (at pH 8.0) and molten globule (at pH 4.2) directly. Only the first cleavage event in each molecule was considered as reflecting original structural information since the original structure of the protein can be altered after the fist cleavage. Structural changes of apoMb in various pH conditions were studied here to elucidate the local helicity of molten globule apoMb. Among 13 Glu sites, only Glu83 and Glu85 in the F-helix were cleaved at pH 8.0, which confirms that only helix F is frayed upon removal of heme group. At acidic molten globule state, rapid cleavages at Glu38, Glu52, Glu54, Glu85, and Glu148 were detected, while the remaining eight sites were protected. Glu6 and Glu18 in the A-helix, and Glu105 in the G-helix were protected due to the helicity of the secondary structures. The cleavage at Glu38 and the protection at Glu41 in the C-helix indicate that the first half of the C-helix is frayed and the second half of the C-helix is structured. Cleavage at both Glu52 and Glu54 in the D-helix proves that the D-helix is disordered. The N-terminal end of the E-helix at Glu59 was protected, and the beginning of the F-helix was protected by aid of the pH-induced C-cap of the E-helix. The cleavage at Glu148 in H suggests that the C-terminal end of the H-helix is disordered. The A-helix and the first half of the B-helix were highly stable.

Animals↗

PubMed2004

Electrochemical sensing of DNA hybridization based on duplex-specific charge compensation.

A nonlabeling voltammetric detection method for DNA hybridization has been developed, in which [Fe(CN)(6)](3-) in solution can readily approach an electrode surface covered with a charge-compensated DNA duplex layer and thus provides a strong redox-sensing current. Charge compensation for negative charges on the DNA backbone has been specifically accomplished on DNA duplexes by discouraging nonspecific binding of positively charged intercalating molecules with single strands. A pretreatment of DNA-modified electrodes with sodium dodecyl sulfate before the intercalator binding process is essential in preventing the nonspecific binding. Since ferricyanide, the only electrochemically active species, is present in the voltammetric solution, the detection signal can be amplified by increasing its concentration. Combination of the duplex-specific charge compensation with the signal amplification has achieved a remarkable signal difference: in 30 mM [Fe(CN)(6)](3-), the area ratio between cyclic voltammograms of the hybridized and unhybridized electrodes is approximately 200 when 3,6-diaminoacridine is used as the intercalator. High sensitivity of the method has been demonstrated by detecting 10 fM (100 zmol in amount) of a target probe DNA.

Biosensing Techniques↗

PubMed2003

Cylindrical compact thermal-cycling device for continuous-flow polymerase chain reaction.

A compact, thermal-cycling device for high-throughput continuous-flow polymerase chain reaction (PCR) has been developed, which consists of a flow-through capillary and a cylindrical heating-block assembly. A 3.5-m-long fused-silica capillary coils helically, with 33 turns, up around the 30-mm-diameter assembly of three equally divided thermostating copper blocks for melting, annealing, and extension. An injected PCR mixture undergoes one cycle of PCR each turn. A continuous-flow PCR of one sample and also a segmented-flow PCR of four different samples have been successfully demonstrated. The present device can easily evolve into a parallel-processing, multistation compact device and be modified to have real-time PCR capability. This solid-based compact PCR device, therefore, has a potentiality to be the format of choice when developed for a portable system.

Journal Article↗

PubMed2003

Surface modification of poly(dimethylsiloxane) microchannels.

This review looks at the efforts that are being made to modify the surface of poly(dimethylsiloxane) (PDMS) microchannels, in order to enhance applicability in the field of microfluidics. Many surface modifications of PDMS have been performed for electrophoretic separations, but new modifications are being done for emerging applications such as heterogeneous immunoassays and cell-based bioassays. These new modification techniques are powerful because they impart biospecificity to the microchannel surfaces and reduce protein adsorption. Most of these applications require the use of aqueous or polar solvents, which makes surface modification a very important topic.

Adsorption↗