Kyungwha Chung

Near-infrared light-responsive nanomaterials for cancer theranostics.

Early diagnosis and effective cancer therapy are required, to properly treat cancer, which causes more than 8.2 million deaths in a year worldwide. Among various cancer treatments, nanoparticle-based cancer therapies and molecular imaging techniques have been widely exploited over the past decades to overcome current drawbacks of existing cancer treatments. In particular, gold nanoparticles (AuNPs), carbon nanotubes (CNTs), graphene oxide (GO), and upconversion nanocrystals (UNCs) have attracted tremendous attention from researchers due to their near-infrared (NIR) light-responsive behaviors. These nanomaterials are considered new multifunctional platforms for cancer theranostics. They would enable on-demand control of drug release or molecular imaging in response to a remote trigger by NIR light exposure. This approach allows the patient or physician to adjust therapy precisely to a target site, thus greatly improving the efficacy of cancer treatments, while reducing undesirable side effects. In this review, we have summarized the advantages of NIR light-responsive nanomaterials for in vivo cancer treatments, which includes NIR triggered photothermal therapy (PTT) and photodynamic therapy (PDT). Furthermore, recent developments, perspectives, and new challenges of NIR light-responsive nanomaterials are discussed for cancer theranostic applications.

Plasmonic Solar Cells: From Rational Design to Mechanism Overview

Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. This review provides a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. The working principle is first addressed in terms of the combined effects of plasmon decay, scattering, near-field enhancement, and plasmonic energy transfer, including direct hot electron transfer and resonant energy transfer. Then, we summarize recent developments for various types of plasmonic solar cells based on silicon, dye-sensitized, organic photovoltaic, and other types of solar cells, including quantum dot and perovskite variants. We also address several issues regarding the limitations of plasmonic nanostructures, including their electrical, chemical, and physical stability, charge recombination, narrowband absorption, and high cost. Next, we propose a few potentially useful approaches that can improve the performance of plasmonic cells, such as the inclusion of graphene plasmonics, plasmon-upconversion coupling, and coupling between fluorescence resonance energy transfer and plasmon resonance energy transfer. This review is concluded with remarks on future prospects for plasmonic solar cell use.

Nanogap-based dielectric-specific colocalization for highly sensitive surface plasmon resonance detection of biotin-streptavidin interactions

We have performed highly sensitive surface plasmon resonance (SPR) detection by colocalizing the evanescent near-fields and target molecular distribution. The colocalization is based on oblique metal evaporation to form nanogaps of a size under 100 nm without using electron-beam lithography. The concept was demonstrated by detecting siloxane-based biotin/streptavidin interactions. 50-nm nanogaps produced the largest amplification of optical signatures and two orders of magnitude enhancement of sensitivity over conventional thin film-based measurements. The enhancement is associated with efficient overlap of localized near-fields and target. Colocalized detection scheme is expected to provide clues to molecular sensitivity for SPR biosensing.

The Role of High-Mobility Group Box-1 in Renal Ischemia and Reperfusion Injury and the Effect of Ethyl Pyruvate

PURPOSE High mobility group box-1(HMGB1) was identified as a DNA-binding protein that functions as a cofactor for proper transcriptional regulation in somatic cells. Extracellular HMGB1 acts as a potent proinflammatory cytokine that contributes to the pathogenesis of diverse inflammatory and infectious disorders. Ethyl pyruvate (EP), a stable aliphatic ester derived from pyruvic acid, was first described as a pharmacological inhibitor of HMGB1 secretion. We designed this study to identify changes in HMGB1 expression in rat kidney tissues after ischemia reperfusion injury and effects of EP on the expression of HMGB1. MATERIALS AND METHODS Sprague-Dawley rats (200-300 g) were subjected to 40 minutes of renal warm ischemia. The animals were divided into 3 groups: sham group without warm ischemia, EP group (EP given before ischemia), and ischemic control group. Kidneys were harvested and serum creatinine and TNF-alpha measured at 6 hours, 1 day, 3 days, and 5 days after reperfusion. We performed immunohistochemical staining of HMGB1. RESULTS Serum creatinine and TNF-alpha level were elevated in the ischemic control group and the EP injection group. In the EP injection group, serum creatinine and TNF-alpha levels were lower than the ischemic control group. In the 40-minute ischemia-reperfusion model, HMGB1 expression increased at 6 hours after reperfusion and decreased gradually at 1, 3, and 5 days after reperfusion. HMGB1 expression was more distinct at the outer medullary area. intraperitoneal EP injection had no effect on HMGB1 expression. CONCLUSION From these results, we deduced that the preventive effect of EP on rat kidney ischemia-reperfusion injury was not due to the decreased expression of HMGB1 but the prevention of HMGB1 release.

Systematic Study on the Sensitivity Enhancement in Graphene Plasmonic Sensors Based on Layer-by-Layer Self-Assembled Graphene Oxide Multilayers and Their Reduced Analogues

The use of graphene in conventional plasmonic devices was suggested by several theoretic research studies. However, the existing theoretic studies are not consistent with one another and the experimental studies are still at the initial stage. To reveal the role of graphenes on the plasmonic sensors, we deposited graphene oxide (GO) and reduced graphene oxide (rGO) thin films on Au films and their refractive index (RI) sensitivity was compared for the first time in SPR-based sensors. The deposition of GO bilayers with number of deposition L from 1 to 5 was carried out by alternative dipping of Au substrate in positively- and negatively charged GO solutions. The fabrication of layer-by-layer self-assembly of the graphene films was monitored in terms of the SPR angle shift. GO-deposited Au film was treated with hydrazine to reduce the GO. For the rGO-Au sample, 1 bilayer sample showed a higher RI sensitivity than bare Au film, whereas increasing the rGO film from 2 to 5 layers reduced the RI sensitivity. In the case of GO-deposited Au film, the 3 bilayer sample showed the highest sensitivity. The biomolecular sensing was also performed for the graphene multilayer systems using BSA and anti-BSA antibody.

Bimetallic Multifunctional Core@Shell Plasmonic Nanoparticles for Localized Surface Plasmon Resonance Based Sensing and Electrocatalysis

Smart bimetallic core@shell nanoparticles were fabricated based on gold nanoparticles (AuNPs) decorated with pH-sensitive polymer shell. Concretely, AuNPs having poly(4-vinylpyridine) (P4VP) on the surface were first fabricated through surface-initiated atom transfer radical polymerization (SI-ATRP). Then, they were mixed with selected metal precursor solutions followed by reduction using reducing agent. The metal NPs thus introduced were uniformly distributed in P4VP polymer shells. In order to explore the diversity and viable function of the resultant nanostructures, we controlled the size of AuNP, pH, selectivity of metal precursors, etc. We investigated the structural alteration during the sequential synthetic process. The bimetallic nanostructures of AuNP@P4VP nanocomposites containing another type of metal NP at the P4VP periphery exhibit a controlled sensing property in terms of the change in the refractive index of surrounding media and a typical electrocatalytic activity for methanol oxidation reaction.

Change of melanocortin receptor expression in rat kidney ischemia-reperfusion injury.

OBJECTIVES alpha-Melanocyte stimulating hormone (alpha-MSH) may ameliorate renal ischemia-reperfusion (I/R) injury. Recent data suggest that melanocortin receptors may be related to the anti-inflammatory and immunomodulating action for alpha-MSH. We designed this experiment to determine the renal distribution of alpha-MSH receptors; melanocortin-1 receptor (MC-1R) and melanocortin-3 receptor (MC-3R). METHODS Sprague-Dawley male rats (n = 24) were randomly divided into 2 groups: the sham (n = 2) and the operation groups with warm ischemia (n = 12). Animals in the operation group were subjected to 40 minutes of warm renal ischemia. Western blotting analyses and immunohistochemistry were employed to determine expression of MC-1R and MC-3R. RESULTS Expression of MC-1R and MC-3R was decreased on 1 day after reperfusion. Immunohistochemical study confirmed the findings of Western blot analysis. CONCLUSIONS The present study demonstrated novel renal expression of MC-1R and MC-3R, especially in the outer medulla, representative of the renal I/R injury. Our current study suggested that the mechanisms of action of alpha-MSH may significantly attenuate the renal I/R injury by specific kidney-targeted effects via MC-Receptors as well as by systemic cytokine effects.

Layer-by-Layer Self-Assembled Graphene Multilayers as Pt-Free Alternative Counter Electrodes in Dye-Sensitized Solar Cells

Low cost, charged, and large scale graphene multilayers fabricated from nitrogen-doped reduced graphene oxide N-rGO(+), nitrogen and sulfur codoped reduced graphene oxide NS-rGO(+), and undoped reduced graphene oxide rGO(-) were applied as alternative counter electrodes in dye-sensitized solar cells (DSSCs). The neat rGO-based counter electrodes were developed via two types of layer-by-layer (LBL) self-assembly (SA) methods: spin coating and spray coating methods. In the spin coating method, two sets of multilayer films were fabricated on poly(diallyldimethylammonium chloride) (PDDA)-coated fluorine-doped tin oxide (FTO) substrates using GO(-) combined with N-GO(+) followed by annealing and denoted as [rGO(-)/N-rGO(+)]n or with NS-GO(+) and denoted as [rGO(-)/NS-rGO(+)]n for counter electrodes in DSSCs. The DSSCs employing new types of counter electrodes exhibited ∼7.0% and ∼6.2% power conversion efficiency (PCE) based on ten bilayers of [rGO(-)/N-rGO(+)]10 and [rGO(-)/NS-rGO(+)]10, respectively. The DSSCs equipped with a blend of one bilayer of [rGO(-):N-rGO(+)] and [rGO(-):NS-rGO(+)] on PDDA-coated FTO substrates were prepared from a spray coating and showed ∼6.4% and ∼5.6% PCE, respectively. Thus, it was demonstrated that a combination of undoped, nitrogen-doped, and nitrogen and sulfur codoped reduced graphene oxides can be considered as potentially powerful Pt-free electrocatalysts and alternative electrodes in conventional photovoltaic devices.

Multi-layered nanocomposite dielectrics for high density organic memory devices

We fabricated organic memory devices with metal-pentacene-insulator-silicon structure which contain double dielectric layers comprising 3D pattern of Au nanoparticles (Au NPs) and block copolymer (PS-b-P2VP). The role of Au NPs is to charge/discharge carriers upon applied voltage, while block copolymer helps to form highly ordered Au NP patterns in the dielectric layer. Double-layered nanocomposite dielectrics enhanced the charge trap density (i.e., trapped charge per unit area) by Au NPs, resulting in increase of the memory window (ΔVth).

Molecular overlap with optical near-fields based on plasmonic nanolithography for ultrasensitive label-free detection by light-matter colocalization

In this work, we investigate the detection sensitivity of surface plasmon resonance (SPR) biosensors by engineering spatial distribution of electromagnetic near-fields for colocalization with molecular distribution. The light-matter colocalization was based on plasmonic nanolithography, the concept of which was confirmed by detecting streptavidin biotin interactions on triangular nanoaperture arrays after the structure of the aperture arrays was optimized for colocalization efficiency. The colocalization was shown to amplify optical signature significantly and thereby to achieve detection on the order of 100 streptavidin molecules with a binding capacity below 1fg/mm2, an enhancement by more than three orders of magnitude over conventional SPR detection.