Biomedical subjects

So-Jung Park

Publications and source records attributed to So-Jung Park.

10 recordsLinked to original sources

PubMed2005

Hole-induced quenching of triplet and singlet excitons in conjugated polymers.

Quantitative information on the mechanisms and rates of hole (radical cation)-induced quenching of triplet and singlet excitons in the conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] has been acquired by a new technique, fluorescence-voltage time-resolved single molecule spectroscopy (FV-TR-SMS). FV-TR-SMS measures the fluorescence intensity of a single conjugated polymer molecule that is embedded in a capacitor-like device while simultaneously modulating the bias on the device and the irradiation intensity. The results demonstrate that triplet excitons are efficiently quenched by holes in conjugated polymers for hole densities >10(16) charges/cm(3), while singlet excitons are quenched with a much lower efficiency. Detailed kinetic analysis shows that the greater efficiency for quenching of triplets by holes (compared to that for singlets) is due to a >10(6) times longer exciton lifetime for triplets. In fact, the results suggest that while singlet quenching is less efficient due to a much shorter singlet lifetime, the rate constant for the quenching of singlets by holes actually exceeds that for triplets by several orders of magnitude.

Journal Article↗

PubMed2005

Polymer-DNA hybrids as electrochemical probes for the detection of DNA.

The syntheses of several norbornene block copolymers containing oligonucleotide and ferrocenyl side chains and their use in the electrochemical detection of DNA are described. Two kinds of DNA-containing block copolymers with either ferrocenyl or dibromoferrocenyl groups were prepared via ring-opening metathesis polymerization (ROMP). Based on these two distinct ferrocene derivatives, a triblock copolymer labeling strategy was developed. With this strategy, the identity of DNA target can be determined by the E1/2s of the ferrocenyl moieties and the ratio of peak currents. These polymers exhibit predictable and tailorable electrochemical properties, high DNA duplex stability, and unusually sharp melting transitions, which are highly desirable characteristics for DNA detection applications. Significantly, single-base mismatches could be easily detected using two distinct block copolymers as dual-channel detection probes in an electrochemical DNA detection format.

DNA↗

PubMed2005

Single-molecule spectroscopy of conjugated polymers.

The molecular structure, photochemistry, and device physics of conjugated polymers have been investigated by single-molecule spectroscopy (SMS), using the unique ability of this technique to unravel complex spectra and dynamics. Surprisingly efficient and directional electronic energy funneling was observed for conjugated polymer molecules due to highly ordered conformations. Furthermore, recent studies on the SMS of conjugated polymers embedded in electronic devices demonstrate that SMS is a powerful tool for studying the photophysics and charge-transfer processes of conjugated polymers, giving new insights into the complex interactions among excited and charged species that exist in a device environment.

Journal Article↗

PubMed2004

Charge injection and photooxidation of single conjugated polymer molecules.

The complex, coupled mechanisms of charge transfer and oxidative damage in organic electronic devices (such as organic light-emitting diodes (OLED), solar cells, etc.) have been elucidated by a new technique that combines single-molecule spectroscopy with charge injection from a metal electrode. The experiments employed a sandwich device architecture (Au/TPD/MEH-PPV:PMMA/SiO2/ITO), essentially a modified OLED with a charge-blocking layer (SiO2) to suppress charge injection at the ITO electrode. The fluorescence (photoluminescence) of isolated MEH-PPV conjugated polymer molecules imbedded in the device was observed to exhibit diverse time- and electrical bias-dependent effects. These include: (i) fluorescence quenching due to interactions between MEH-PPV and holes in the TPD hole-transport layer; (ii) fluorescence quenching, or "photobleaching", due to chemical defects at MEH-PPV generated by photooxidation; and (iii) a novel process, reductive "repair" of the oxidative chemical defects by externally injected carriers. These results demonstrate a very different mechanism for photobleaching of organic conjugated materials than is generally assumed to operate and, furthermore, suggest an intimate relationship among photobleaching, charge transport, and persistent photoconductivity in organic materials.

Journal Article↗

PubMed2004

A new curcumin derivative, HBC, interferes with the cell cycle progression of colon cancer cells via antagonization of the Ca2+/calmodulin function.

HBC (4-[3,5-Bis-[2-(4-hydroxy-3-methoxy-phenyl)-ethyl]-4,5-dihydro-pyrazol-1-yl]-benzoic acid) is a recently developed curcumin derivative which exhibits potent inhibitory activities against the proliferation of several tumor cell lines. In the present study, we identified Ca2+/calmodulin (Ca2+/CaM) as a direct target protein of HBC using phage display biopanning. Ca2+/CaM-expressing phages specifically bound to the immobilized HBC, and the binding was Ca2+ dependent. Moreover, flexible docking modeling demonstrated that HBC is compatible with the binding cavity for a known inhibitor, W7, in the C-terminal hydrophobic pocket of Ca2+/CaM. In biological systems, HBC induced prolonged phosphorylation of ERK1/2 and activated p21(WAF1) expression, resulting in the induction of G0/G1 cell cycle arrest in HCT15 colon cancer cells. These results suggest that HBC inhibits the cell cycle progression of colon cancer cells via antagonizing of Ca2+/CaM functions.

Amino Acid Sequence↗

PubMed2002

Bio-barcodes based on oligonucleotide-modified nanoparticles.

By utilizing oligonucleotide-modified Au nanoparticles encoded with sequences that act as biobarcodes, one can screen for multiple target polyvalent proteins simultaneously in one solution. This novel concept was demonstrated with two types of detection formats, a homogeneous assay and one based on oligonucleotide microarrays. With such an approach, one can prepare an extraordinarily large number of barcodes from synthetically accessible oligonucleotides (e.g., a 12-mer sequence offers 4(12) possible barcodes).

Biosensing Techniques↗

PubMed2002

Array-based electrical detection of DNA with nanoparticle probes.

A DNA array detection method is reported in which the binding of oligonucleotides functionalized with gold nanoparticles leads to conductivity changes associated with target-probe binding events. The binding events localize gold nanoparticles in an electrode gap; silver deposition facilitated by these nanoparticles bridges the gap and leads to readily measurable conductivity changes. An unusual salt concentration-dependent hybridization behavior associated with these nanoparticle probes was exploited to achieve selectivity without a thermal-stringency wash. Using this method, we have detected target DNA at concentrations as low as 500 femtomolar with a point mutation selectivity factor of approximately 100,000:1.

Antigens, Bacterial↗

PubMed2002

Protein nanoarrays generated by dip-pen nanolithography.

Dip-pen nanolithography was used to construct arrays of proteins with 100- to 350-nanometer features. These nanoarrays exhibit almost no detectable nonspecific binding of proteins to their passivated portions even in complex mixtures of proteins, and therefore provide the opportunity to study a variety of surface-mediated biological recognition processes. For example, reactions involving the protein features and antigens in complex solutions can be screened easily by atomic force microscopy. As further proof-of-concept, these arrays were used to study cellular adhesion at the submicrometer scale.

3T3 Cells↗

PubMed2002

In vitro antiinflammatory activity of kalopanaxsaponin A isolated from Kalopanax pictus in murine macrophage RAW 264.7 cells.

In the present study, effects of various hederagenin monodesmosides isolated from the stem bark of Kalopanax pictus Nakai, such as hederagenin, 5-hederin, kalopanaxsaponin A, kalopanaxsaponin 1, and sapindoside C, have been evaluated on lipopolysaccharide (LPS)-induced nitric oxide (NO), prostaglandin E2 (PGE2) and tumor necrosis factor-alpha (TNF-alpha) release by the macrophage cell line RAW 264.7. Among the tested monodesmosides, kalopanxsaponin A was the most potent inhibitor of NO production, and it also significantly decreased PGE2 and TNF-alpha release. Consistent with these observations, the expression level of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 enzyme was inhibited by kalopanxsaponin A in a concentration-dependent manner. Thus, this study suggests that kalopanaxsaponin A-mediated inhibition of iNOS, COX-2 expression, and TNF-alpha release may be one of the mechanisms responsible for the anti-inflammatory effects of the stem bark of Kalopanax pictus Nakai.

Animals↗

PubMed2001

Directed Assembly of Periodic Materials from Protein and Oligonucleotide-Modified Nanoparticle Building Blocks C.A.M. acknowledges DARPA, NSF, ARO, and NIH for support of this research. R.L.L. acknowledges the NIH. The DND-CAT Synchrotron Research Center is supported by E.I. Dupont de Nemours & Co., The Dow Chemical Company, the U.S. National Science Foundation through Grant DMR-9304725, and the State of Illinois through the Department of Commerce and the Board of Higher Education Grant IBHE HECA NWU 96. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Energy Research under Contract No. W-31-102-Eng-38.

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Journal Article↗