Hyo-Sop Kim

Directed self-assembly of gold binding polypeptide-protein A fusion proteins for development of gold nanoparticle-based SPR immunosensors.

Effective immobilization of antibodies on a sensing platform and sensitivity enhancement are crucial in designing surface plasmon resonance (SPR) immunosensors. Colloidal gold nanoparticles (AuNPs) were directly assembled onto a surface of SPR Au chip via 2-aminoethanethiol for the enhancement of sensitivity as a label-free detection system. SEM image showed most AuNPs were uniformly distributed over the surface. A novel fusion protein was constructed by genetically fusing gold binding polypeptides (GBP) to protein A (ProA) as a crosslinker for effective immobilization of antibodies. The resulting GBP-ProA protein was directly self-immobilized onto both bare and AuNPs-assembled SPR chip surfaces via the GBP portion, followed by the oriented binding of human immunoglobulin G (hIgG) onto the ProA domain targeting the Fc region of antibodies and anti-hIgG in series. Furthermore, anti-Salmonella antibodies were immobilized onto both GBP-ProA layered chips for detection of Salmonella typhimurium. SPR analyses indicated the signal increases for successive binding of hIgG and anti-hIgG onto the GBP-ProA layered AuNPs-assembled chip were higher (about 92 and 30%, respectively) than that onto the identically treated bare chip. This signal enhancement in the AuNPs-assembled chip also caused a 10-fold increased sensitivity in detection of S. typhimurium compared to the bare one. These results demonstrate the direct assembly of AuNPs onto a SPR chip could enhance the signal in biomolecular interaction events, and the GBP-ProA protein could be a valuable crosslinker for simple and oriented immobilization of antibodies onto Au chip surfaces without any surface chemical modification.

Diagnostic accuracy and interobserver variability of pulsed arterial spin labeling for glioma grading

Background: Although pulsed arterial spin labeling (PASL) enables the reliable qualitative grading of brain tumors, its use in quantification for glioma grading may be hampered by the limited interobserver variability associated with low spatial resolution. Purpose: To assess the interobserver variability and diagnostic accuracy of the relative tumor perfusion signal intensity (rTPS) calculated using PASL in glioma grading. Material and Methods: Fifty-eight patients with 61 cerebral astrocytomas underwent conventional MR imaging and PASL. Receiver operating characteristic analyses were used to determine the optimum thresholds for tumor grading. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for identifying high-grade gliomas were also calculated. Cohens κ statistic was used to determine the levels of interobserver variability in the quantitative analysis of PASL. Results: The sensitivity, specificity, PPV, and NPV for determining a high-grade glioma with conventional MR imaging were 77.1, 73.1, 79.4, and 70.4%, respectively. A threshold value of 1.28 for rTPS provided a sensitivity, specificity, PPV, and NPV of 82.9, 96.2, 96.7, and 80.6%, respectively. There was a statistically significant difference in the rTPS between low- and high-grade astrocytomas (1.14 vs. 1.47, P<0.05). In the interobserver variability analysis, substantial agreement was obtained for the quantitative rTPS measurement from PASL (κ =0.72). Conclusion: Quantitative perfusion measurement with PASL can improve the diagnostic accuracy of preoperative glioma grading, as compared to the application of conventional imaging alone. However, the interobserver variability for quantification is substantial.

Sensitive detection of yeast using terahertz slot antennas

We demonstrated sensitive detection of individual yeast cells and yeast films by using slot antenna arrays operating in the terahertz frequency range. Microorganisms located at the slot area cause a shift in the resonant frequency of the THz transmission. The shift was investigated as a function of the surface number density for a set of devices fabricated on different substrates. In particular, sensors fabricated on a substrate with relatively low permittivity demonstrate higher sensitivity. The frequency shift decreases with increasing slot antenna width for a fixed coverage of yeast film, indicating a field enhancement effect. Furthermore, the vertical range of the effective sensing volume has been studied by varying the thickness of the yeast film. The resonant frequency shift saturates at 3.5 μm for a slot width of 2 μm. In addition, the results of finite-difference time-domain simulations are in good agreement with our experimental data.

Random Networks of Single-Walled Carbon Nanotubes Promote Mesenchymal Stem Cell’s Proliferation and Differentiation

Studies on the interaction of cells with single-walled carbon nanotubes (SWCNTs) have been receiving increasing attention owing to their potential for various cellular applications. In this report, we investigated the interactions between biological cells and nanostructured SWCNTs films and focused on how morphological structures of SWCNT films affected cellular behavior such as cell proliferation and differentiation. One directionally aligned SWCNT Langmuir-Blodgett (LB) film and random network SWCNT film were fabricated by LB and vacuum filteration methods, respectively. We demonstrate that our SWCNT LB and network film based scaffolds do not show any cytotoxicity, while on the other hand, these scaffolds promote differentiation property of rat mesenchymal stem cells (rMSCs) when compared with that on conventional tissue culture polystyrene substrates. Especially, the SWCNT network film with average thickness and roughness values of 95 ± 5 and 9.81 nm, respectively, demonstrated faster growth rate and higher cell thickness for rMSCs. These results suggest that systematic manipulation of the thickness, roughness, and directional alignment of SWCNT films would provide the convenient strategy for controlling the growth and maintenance of the differentiation property of stem cells. The SWCNT film could be an alternative culture substrate for various stem cells, which often require close control of the growth and differentiation properties.

Retroreflective Janus Microparticle as a Nonspectroscopic Optical Immunosensing Probe

We developed retroreflective Janus microparticles (RJPs) as a novel optical immunosensing probe for use in a nonspectroscopic retroreflection-based immunoassay. By coating the metals on the hemispherical surface of silica particles, highly reflective RJPs were fabricated. On the basis of the retroreflection principle, the RJPs responded to polychromatic white light sources, in contrast to conventional optical probes, which require specific monochromatic light. The retroreflection signals from RJPs were distinctively recognized as shining dots, which can be intuitively counted using a digital camera setup. Using the developed retroreflective immunosensing system, cardiac troponin I, a specific biomarker of acute myocardial infarction, was detected with high sensitivity. On the basis of the demonstrated features of the retroreflective immunosensing platform, we expect that our approach may be applied for various point-of-care-testing applications.

Cytokine Gene Expression in Peripheral Blood Mononuclear Cells During Acute Renal Allograft Rejection

Many studies have explored the participation of cytokines and their genes in renal allograft rejection by using biopsy tissues. To screen for rejection, a biopsy is too invasive to perform without a clinical clue. Therefore, we studied the expression of cytokines that contribute to the early phase of allograft rejection by analyzing mRNA transcripts in sequential blood samples of peripheral blood mononuclear cells (PBMCs) 120 of 6 among patients transplanted before diagnosis of rejection. for comparison with 6 control recipients. The relative expression amount of cytokine genes encoding interleukin (IL) 2, IL-4, IL-10, IL-15, and interferon-γ were assessed using real-time reverse-transcription polymerase chain reactions. IL-2, IL-4, and IL-15 mRNA expressions in clinically stable prerejection phase of the rejection group were significantly higher than those of the control group. In the prerejection samples, the expression of mRNA encoding IL-10 negatively correlated with the expressions of IL-2, IL-4, and IL-15 mRNAs, which were not different from the positive correlations in the postoperative samples from the control group. The expression patterns of IL-2, IL-4, IL-10, and IL-15 genes in PBMCs after transplantation may help to identify acute rejection episodes before clinical deterioration to monitor the efficacy of immunosuppressive treatment.

Effects of anodized titanium implant coated with RGD peptides via chemical fixation on osseointegration and bone regeneration

This study was conducted to investigate the effects of an anodized titanium surface with RGD-peptides. Silane was used to immobilize the RGD peptides to the titanium surfaces. The surfaces were examined by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Crystal violet assay, XTT assay and Alkaline phosphatase (ALP) assay were performed to evaluate response of human mesenchymal stem cell. For in vivo study, twenty-four implants and four beagle dogs were used and made the dehiscence defect model (n=12 in each group). Implant stability quotient (ISQ) value was measured and evaluated by histometric analysis. Histological examination revealed an increase of bone height in the test group. There were significant differences in intra-thread bone density (ITBD) between the groups. The application of RGD peptide to the implant surface may contribute to the improvement of osseointegration quality and bone growth in a small defect area around the implant.

Water-soluble mercury ion sensing based on the thymine-Hg 2+ -thymine base pair using retroreflective Janus particle as an optical signaling probe

Herein, we report an optical sensing platform for mercury ions (Hg2+) in water based on the integration of Hg2+-mediated thymine-thymine (T-T) stabilization, a biotinylated stem-loop DNA probe, and a streptavidin-modified retroreflective Janus particle (SA-RJP). Two oligonucleotide probes, including a stem-loop DNA probe and an assistant DNA probe, were utilized. In the absence of Hg2+, the assistant DNA probe does not hybridize with the stem-loop probe due to their T-T mismatch, so the surface-immobilized stem-loop DNA probe remains a closed hairpin structure. In the presence of Hg2+, the DNA forms a double-stranded structure with the loop region via Hg2+-mediated T-T stabilization. This DNA hybridization induces stretching of the stem-loop DNA probe, exposing biotin. To translate these Hg2+-mediated structural changes in DNA probe into measurable signal, SA-RJP, an optical signaling label, is applied to recognize the exposed biotin. The number of biospecifically bound SA-RJPs is proportional to the concentration of Hg2+, so that the concentration of Hg2+ can be quantitatively analyzed by counting the number of RJPs. Using the system, a highly selective and sensitive measurement of Hg2+ was accomplished with a limit of detection of 0.027nM. Considering the simplified optical instrumentation required for retroreflection-based RJP counting, RJP-assisted Hg2+ measurement can be accomplished in a much easier and inexpensive manner. Moreover, the detection of Hg2+ in real drinking water samples including tap and commercial bottled water was successfully carried out.

Optical investigation on plasmonic effect of the nanostructured surface plasmon resonance sensor chips fabricated by Langmuir-Blodgett technique

We used the Langmuir-Blodgett (LB) method for preparation of defect-free and large-area silica-nanoparticlesmonolayer as a template for the fabrication of Au nanostructures on an Au-thinfilm for surface plasmon resonance (SPR). The dimensions of trigonal pyramid Au nanostructures were controlled by changing the particle size of the silica LB template. The nanostructured SPR chips provide the enhancement of sensitivity in SPR analysis compared to a conventional SPR chip when 20 % ethanol solution was used as an analyte. We took a theoretical approach by evaluating optical properties of the Au-nanostructures and nanostructured SPR chips in the view of plasmonic effect.

Nano-structured surface plasmon resonance sensor for sensitivity enhancement

A new nano-structured SPR sensor was devised to improve its sensitivity. Nano-scaled silica particles were used as the template to fabricate nano-structure. The surface of the silica particles was modified with thiol group and a single layer of the modified silica particles was attached on the gold or silver thin film using Langmuir-Blodgett (LB) method. Thereafter, gold or silver was coated on the template by an e-beam evaporator. Finally, the nano-structured surface with basin-like shape was obtained after removing the silica particles by sonication. Applying the new developed SPR sensor to a model food of alcoholic beverage, the sensitivities for the gold and silver nano-structured sensors, respectively, had 95% and 126% higher than the conventional one.