Bong Jin Hong

Light-Harvesting Metal–Organic Frameworks (MOFs): Efficient Strut-to-Strut Energy Transfer in Bodipy and Porphyrin-Based MOFs

A pillared-paddlewheel type metal-organic framework material featuring bodipy- and porphyrin-based struts, and capable of harvesting light across the entire visible spectrum, has been synthesized. Efficient-essentially quantitative-strut-to-strut energy transfer (antenna behavior) was observed for the well-organized donor-acceptor assembly consituting the ordered MOF structure.

Successful stabilization of graphene oxide in electrolyte solutions: Enhancement of biofunctionalization and cellular uptake

Aqueous dispersions of graphene oxide are inherently unstable in the presence of electrolytes, which screen the electrostatic surface charge on these nanosheets and induce irreversible aggregation. Two complementary strategies, utilizing either electrostatic or steric stabilization, have been developed to enhance the stability of graphene oxide in electrolyte solutions, allowing it to stay dispersed in cell culture media and serum. The electrostatic stabilization approach entails further oxidation of graphene oxide to low C/O ratio (~1.1) and increases ionic tolerance of these nanosheets. The steric stabilization technique employs an amphiphilic block copolymer that serves as a noncovalently bound surfactant to minimize the aggregate-inducing nanosheet-nanosheet interactions. Both strategies can stabilize graphene oxide nanosheets with large dimensions (>300 nm) in biological media, allowing for an enhancement of >250% in the bioconjugation efficiency of streptavidin in comparison to untreated nanosheets. Notably, both strategies allow the stabilized nanosheets to be readily taken up by cells, demonstrating their excellent performance as potential drug-delivery vehicles.

DNA microarrays on nanoscale-controlled surface

We have developed new surface to ensure a proper spacing between immobilized biomolecules. While DNA microarray on this surface provided each probe DNA with ample space for hybridization with incoming target DNAs, the microarray showed enhanced discrimination efficiency for various types of single nucleotide polymorphism. The high discrimination efficiency holds for all tested cases (100:<1 for internal mismatched cases; 100:<28 for terminal mismatched ones). In addition, by investigating influence of hybridization temperature and washing condition on the fluorescence intensity and the discrimination efficiency with and without controlled mesospacing, it was observed that the nanoscale-controlled surface showed good discrimination efficiency in a wide range of temperature (37–50°C), and hybridization behavior on the surface was in agreement with the solution one. Intriguingly, it was found that washing process after the hybridization was critical for the high discrimination efficiency. For the particular case, washing process was so efficient that only 30 s washing was sufficient to reach the optimal discrimination ratio.

Modular Polymer‐Caged Nanobins as a Theranostic Platform with Enhanced Magnetic Resonance Relaxivity and pH‐Responsive Drug Release

Magnetic resonance imaging (MRI) can provide detailedhigh-resolution, tomographic information of disease tissue inreal time and in vivo. Hence, it has become a powerfuldiagnostic tool for detecting the stages of primary andrecurrent solid tumors and for the assessment of suitabletreatment regimens. Therefore, MRI is a suitable techniquefor use in conjunction with theranostic platforms for the post-treatment evaluation of solid tumors.MRI studies are often conducted by using paramagneticGd

Acid-Degradable Polymer-Caged Lipoplex (PCL) Platform for siRNA Delivery: Facile Cellular Triggered Release of siRNA

An acid-degradable polymer-caged lipoplex (PCL) platform consisting of a cationic lipoplex core and a biocompatible, pH-responsive polymer shell has been developed for the effective delivery of small interfering RNA (siRNA) through a combination of facile loading, rapid acid-triggered release, cellular internalization, and effective endosomal escape. In vitro testing of this degradable PCL delivery platform reveals ∼45- and ∼2.5-fold enhancement of enhanced green fluorescent protein knockdown in cancer cells in comparison to either free siRNA or siRNA-loaded non-acid-degradable lipoplex formulations, respectively.

DNA microarrays on a dendron-modified surface improve significantly the detection of single nucleotide variations in the p53 gene

Selectivity and sensitivity in the detection of single nucleotide polymorphisms (SNPs) are among most important attributes to determine the performance of DNA microarrays. We previously reported the generation of a novel mesospaced surface prepared by applying dendron molecules on the solid surface. DNA microarrays that were fabricated on the dendron-modified surface exhibited outstanding performance for the detection of single nucleotide variation in the synthetic oligonucleotide DNA. DNA microarrays on the dendron-modified surface were subjected to the detection of single nucleotide variations in the exons 5–8 of the p53 gene in genomic DNAs from cancer cell lines. DNA microarrays on the dendron-modified surface clearly discriminated single nucleotide variations in hotspot codons with high selectivity and sensitivity. The ratio between the fluorescence intensity of perfectly matched duplexes and that of single nucleotide mismatched duplexes was >5–100 without sacrificing signal intensity. Our results showed that the outstanding performance of DNA microarrays fabricated on the dendron-modified surface is strongly related to novel properties of the dendron molecule, which has the conical structure allowing mesospacing between the capture probes. Our microarrays on the dendron-modified surface can reduce the steric hindrance not only between the solid surface and target DNA, but also among immobilized capture probes enabling the hybridization process on the surface to be very effective. Our DNA microarrays on the dendron-modified surface could be applied to various analyses that require accurate detection of SNPs.

Directed Assembly of Nucleic Acid-Based Polymeric Nanoparticles from Molecular Tetravalent Cores

Complementary tetrahedral small molecule-DNA hybrid (SMDH) building blocks have been combined to form nucleic acid-based polymeric nanoparticles without the need for an underlying template or scaffold. The sizes of these particles can be tailored in a facile fashion by adjusting assembly conditions such as SMDH concentration, assembly time, and NaCl concentration. Notably, these novel particles can be stabilized and transformed into functionalized spherical nucleic acid (SNA) structures through the incorporation of capping DNA strands conjugated with functional groups. These results demonstrate a systematic, efficient strategy for the construction and surface functionalization of well-defined, size-tunable nucleic acid particles from readily accessible molecular building blocks. Furthermore, because these nucleic acid-based polymeric nanoparticles exhibited enhanced cellular internalization and resistance to DNase I compared to free synthetic nucleic acids, they should have a plethora of applications in diagnostics and therapeutics.

Pseudo 3D Single‐Walled Carbon Nanotube Film for BSA‐Free Protein Chips

Rapid progress in genomics and proteomics has inspired many scientists to develop techniques for efficient screening of specific biological interactions, such as DNA hybridization, antigen–antibody recognition, and potential drug molecule–protein interactions. Microarray technology combined with fluorescence detection is one of the most popular tools for the high-throughput analysis of biological events and has been the cornerstone of many scientific advances. In contrast to the success of DNA microarray chip applications, protein chips have suffered from several critical issues, including loss of molecular conformation and, therefore, protein activity after immobilization on substrates. Another issue of concern is orientation control of proteins during immobilization, which is believed to have a significant influence on their biological activities. A great many improvements have been made by introducing site-specific linker molecules to the terminal groups of proteins, which preferentially adsorb onto a chemically modified substrate while the active sites of the proteins are directed towards the incoming targets. The suppression of nonspecific binding (NSB) during the assay is also one of the most important issues. Among the possible approaches to prohibiting NSB, the addition of bovine serum albumin (BSA) has been most popularly used. Conventionally, BSA is introduced after the immobilization of probe proteins in order to fill the unreacted areas of the substrate, which are potential sites for the NSB of target proteins. However, this space-filling concept is difficult to apply when the size of probe protein (or peptide) is very small because BSA treatment will significantly shield the immobilized small proteins (or peptides) and result in inefficient specific binding with the target proteins. In order to overcome this problem, Schreiber et al. have suggested an approach in which small proteins are immobilized on a preformed monolayer of BSA activated with linker molecules, such as N-hydroxysuccinimide (NHS) groups. In this case, however, another technically important chemical treatment step is required to quench the unreacted NHS-activated BSA. BSA treatments also frequently lead to ambiguous results, mostly arising from the size and intrinsic NSB characteristics of BSA itself. Therefore, the development of a BSA-free system is a necessary and a challenging subject for the realization of highly efficient protein chips. Herein, we report the successful demonstration of a BSAfree protein chip with a 1,1’-carbonyldiimidazole-activated Tween20-functionalized (CDI–Tween20) high-yield singlewalled carbon nanotube (SWNT) film: CDI–Tween20/SWCN. Tween20 has a similar chemical structure to poly(ethylene glycol) (PEG), except for a long alkyl chain moiety. Tween20 and its derivatized forms have been reported to be good “interfacing molecules” between carbon nanotubes and proteins in terms of efficiently preventing NSB and simultaneously facilitating the immobilization of proteins onto carbon nanotubes. Our strategy is to passivate CDI–Tween20 on both SWNT and bare hydroxy-terminated SiO2/Si surfaces such that no further treatment is required for NSB prevention. After the passivation, SWNTs are ready to accommodate probe proteins by covalent coupling through the CDI groups. At the same time, the reaction of CDI with hydroxyl groups of the SiO2/Si surface covalently attaches Tween20 to the surfaces where no SWNTs are present, thus effectively preventing NSB in all areas. Furthermore, SWNT substrates might help preserve protein conformation. Due to its high aspect ratio and pseudo 3D network structure, SWNT film could significantly reduce the contact area for protein immobilization, leading to minimal shape deformation of protein molecules. A schematic representation of SWNT film-based microarray protein chip preparation is shown in Figure 1a. A successful growth of the high yield of pure SWNTs was confirmed by a simple resistance measurement (5–40 kW) as well as by atomic force microscope (AFM, Digital Instruments, Nanoscope III, Figure 1b). As a new platform for protein chip application, it was necessary to confirm that the formation of protein microspots on the CDI–Tween20/SWNT substrate was reproducible and homogeneous. The spotting conditions were optimized from several test spottings (4E4 array) with Cy3–IgG (20 mgmL ) with respect to several variables such as concentration, incubation time, and washing conditions. Successful immobilization and reproducible formation of protein spots were confirmed by observing fluorescent dots with a laser scanner after 3 hours’ incubation (Figure 1c). Protein immobilization on the CDI– Tween20/SWNT surface was also investigated by AFM, which clearly showed IgG molecules (60 mgmL ) immobilized on the SWNT sidewalls (Figure 1d). Note that SWNTs grown in low yield were used for visual clarity. The optimal concentration for the immobilization of probe protein was determined from the fluorescence versus concentration curve (Figure 2 and Figure S1 in the Supporting Information). The change in fluorescence intensity was monitored from the specific bindings of Cy3–IgG (20 mgmL ) to the SpA spotted at various concentrations. Figure 2 shows that saturation occurs at around 250 mgmL . This concentration was used for the probe protein immobilizations in future experiments. For the study of specific and nonspecific interactions on BSA-free SWNT film substrates, biotin–BSA + Cy5–SA and SpA [a] H. R. Byon, Dr. B. J. Hong, Prof. J. W. Park, Prof. H. C. Choi Department of Chemistry, Pohang University of Science and Technology San 31, Hyoja-Dong, Nam-Gu, Pohang, 790-784 (Korea) Fax: (+82)5-279-3399 E-mail : choihc@postech.edu [b] Prof. Y. S. Gho Department of Life Science, Pohang University of Science and Technology San 31, Hyoja-dong, Nam-Gu, Pohang, 790-784 (Korea) Supporting information for this article is available on the WWW under http://www.chembiochem.org or from the author.

Enhancing DNA-Mediated Assemblies of Supramolecular Cage Dimers through Tuning Core Flexibility and DNA Length--A Combined Experimental-Modeling Study.

Two complementary small-molecule-DNA hybrid (SMDH) building blocks have been combined to form well-defined supramolecular cage dimers at DNA concentrations as high as 102 μM. This was made possible by combining a flexible small-molecule core and three DNA arms of moderate lengths (<20 base pairs). These results were successfully modeled by coarse-grained molecular dynamics simulations, which also revealed that the formation of ill-defined networks in the case of longer DNA arms can be significantly biased by the presence of deep kinetic traps. Notably, melting point studies revealed that cooperative melting behavior can be used as a means to distinguish the relative propensities for dimer versus network formation from complementary flexible three-DNA-arm SMDH (fSMDH3) components: sharp, enhanced melting transitions were observed for assemblies that result mostly in cage dimers, while no cooperative melting behavior was observed for assemblies that form ill-defined networks.

Effects of lateral spacing on enzymatic on-chip DNA polymerization

Enzymatic on-chip DNA polymerization can be utilized to elongate surface-bound primers with DNA polymerase and to enhance the signal in the detection of target DNAs on the solid support. In order to investigate the steric effect of the enzymatic reaction on the solid support, we compared the efficiency of on-chip DNA polymerization on a high-density surface with that on a spacing-controlled surface. The spacing-controlled, 9-acid dendron-coated surface exhibited approximately 8-fold higher efficiency of on-chip DNA polymerization compared with the high-density surface. The increase in fluorescence intensity during the on-chip DNA polymerization could be fit to an exponential equation, and the saturation level of the 9-acid dendron slide was 7 times higher than that of the high-density slide. The on-chip DNA polymerization was employed to measure the transcription level of nine genes related to epithelial-to-mesenchymal transition in hepatocellular carcinoma cells. Compared to the high-density surface, the dendron-coated surface exhibited a lower detection limit in the on-chip DNA polymerization and higher correlation with transcription levels as determined by quantitative real-time PCR. Our results suggest that control of the lateral spacing of DNA strands on the solid support should significantly enhance the accessibility of DNA polymerase and the efficiency of the on-chip DNA polymerization.