Seongchan Kim

Biosensors based on graphene oxide and its biomedical application

Abstract Graphene oxide (GO) is one of the most attributed materials for opening new possibilities in the development of next generation biosensors. Due to the coexistence of hydrophobic domain from pristine graphite structure and hydrophilic oxygen containing functional groups, GO exhibits good water dispersibility, biocompatibility, and high affinity for specific biomolecules as well as properties of graphene itself partly depending on preparation methods. These properties of GO provided a lot of opportunities for the development of novel biological sensing platforms, including biosensors based on fluorescence resonance energy transfer (FRET), laser desorption/ionization mass spectrometry (LDI-MS), surface-enhanced Raman spectroscopy (SERS), and electrochemical detection. In this review, we classify GO-based biological sensors developed so far by their signal generation strategy and provide the comprehensive overview of them. In addition, we offer insights into how the GO attributed in each sensor system and how they improved the sensing performance.

One‐Pot Synthesis of Multifunctional Au@Graphene Oxide Nanocolloid Core@Shell Nanoparticles for Raman Bioimaging, Photothermal, and Photodynamic Therapy

The paper reports a facile one-pot synthesis of core@shell nanoparticles (NPs) composed of Au core and graphene oxide nanocolloid (GON) shell. Unique properties of Au NPs and GON can be incorporated into a single nanohybrid structure to provide desirable functions for theranosis such as localized surface plasmon resonance, Raman scattering, amphiphilic surface, and photothermal conversion. Synthesis of Au@GON NPs is achieved by simple one-pot reaction in aqueous phase utilizing GON as a reducing and stabilizing agent without any additional reducing agent. The zinc phthalocyanine, a photosensitizer, loaded Au@GON NPs show excellent multifunctional properties for combinational treatment of photothermal and photodynamic therapy in addition to Raman bioimaging with low cytotoxicity.

Deoxyribozyme-loaded nano-graphene oxide for simultaneous sensing and silencing of the hepatitis C virus gene in liver cells

The multifunctional DNAzyme (Dz) delivery system is developed based on nano-sized graphene oxide (nGO) for simultaneous detection and knockdown of the target gene. The Dz/nGO complex system allowed convenient monitoring of HCV mRNA in living cells and silencing of the HCV gene expression by Dz-mediated catalytic cleavage concurrently.

Reduction in hospital stay of chronic schizophrenic patients after long-term clozapine treatment.

The present study aimed to elucidate the effectiveness of clozapine treatment in reducing the disabling period of chronically ill schizophrenic patients by investigating their rehospitalization status. Of 232 schizophrenic patients with a history of clozapine use who were recruited from the clinic at Seoul National University Hospital, 117 were selected who had been followed up for more than 1 year with respect to rehospitalization. To obtain information about the period before the clozapine change, a chart review of these 117 patients was conducted. The number and length of hospitalizations of the patients significantly decreased after clozapine treatment compared to the same period before clozapine treatment. The hospital days per year of the patients were also decreased significantly after clozapine introduction. By analysing 38 patients who were followed up for more than 5 years, it was suggested that the decrease in the number and length of hospitalizations was substantially sustained for up to 5 years after clozapine treatment. This study showed that the number and length of hospitalizations are significantly decreased by long-term clozapine treatment and that this effect can positively affect the social outcome of schizophrenic patients.

MicroRNA‐Responsive Drug Release System for Selective Fluorescence Imaging and Photodynamic Therapy In Vivo

Photodynamic therapy (PDT) is a noninvasive strategy to treat diseases by light-triggered activation of a photosensitizer (PS). One aim of the recent researches on PDT is to overcome the limitation of conventional PDT by improving selective activation of PS on targeted region. Here, a microRNA (miRNA)-responsive drug activation system is developed which focuses on the role of endogenous miRNA as an internal cancer specific stimulus for initiating drug release in cancer treatment. The present system consists of PS chlorin e6 (Ce6) conjugated to peptide nucleic acid (PNA) having complementary sequence to cancer specific miRNA and dextran coated reduced graphene oxide nanocolloid (Dex-RGON). In the presence of oncogenic miR-21 in cancer cells, Ce6-PNA drug gets hybridized with miR-21, resulting in the release of Ce6-PNA from Dex-RGON and subsequent recovery of Ce6 fluorescence and activation of Ce6 as a photosensitizer under near IR irradiation. It is demonstrated that the Ce6-PNA/Dex-RGON complex shows sequence-specific fluorescence in response to miR-21 and selective cytotoxic effect for tumor growth inhibition. The present study will pave a new way for utilizing PDT in cancer treatment with tightly regulated activation of a photosensitizer by oncogenic miRNA as an internal stimulus to reduce potential risk associated with conventional PDT.

MAP4-regulated dynein-dependent trafficking of BTN3A1 controls the TBK1-IRF3 signaling axis

Significance Type I IFN signaling is the most important innate immune response induced by viral infection. However, it is not completely known how the components of type I IFN signaling are spatiotemporally coordinated to elicit effective immune responses upon stimulation. We identified microtubule-associated protein 4 (MAP4) and butyrophilin 3A1 (BTN3A1) as novel regulators of the type I IFN signaling pathway triggered by cytosolic nucleic acids. In response to nucleic acid stimulation, BTN3A1-mediated transport of TANK-binding kinase 1 (TBK1) along microtubules facilitated the localization of TBK1 to IFN-regulatory factor 3 (IRF3) on punctate perinuclear structures, promoting IRF3 phosphorylation and IFN-β secretion. BTN3A1 activity was controlled by an upstream regulator, MAP4. Our findings could be translated into a novel therapeutic approach to a broad spectrum of nucleic acid-mediated inflammatory and viral diseases. The innate immune system detects viral nucleic acids and induces type I interferon (IFN) responses. The RNA- and DNA-sensing pathways converge on the protein kinase TANK-binding kinase 1 (TBK1) and the transcription factor IFN-regulatory factor 3 (IRF3). Activation of the IFN signaling pathway is known to trigger the redistribution of key signaling molecules to punctate perinuclear structures, but the mediators of this spatiotemporal regulation have yet to be defined. Here we identify butyrophilin 3A1 (BTN3A1) as a positive regulator of nucleic acid-mediated type I IFN signaling. Depletion of BTN3A1 inhibits the cytoplasmic nucleic acid- or virus-triggered activation of IFN-β production. In the resting state, BTN3A1 is constitutively associated with TBK1. Stimulation with nucleic acids induces the redistribution of the BTN3A1–TBK1 complex to the perinuclear region, where BTN3A1 mediates the interaction between TBK1 and IRF3, leading to the phosphorylation of IRF3. Furthermore, we show that microtubule-associated protein 4 (MAP4) controls the dynein-dependent transport of BTN3A1 in response to nucleic acid stimulation, thereby identifying MAP4 as an upstream regulator of BTN3A1. Thus, the depletion of either MAP4 or BTN3A1 impairs cytosolic DNA- or RNA-mediated type I IFN responses. Our findings demonstrate a critical role for MAP4 and BTN3A1 in the spatiotemporal regulation of TBK1, a central player in the intracellular nucleic acid-sensing pathways involved in antiviral signaling.

Highly efficient gene silencing and bioimaging based on fluorescent carbon dots in vitro and in vivo

Small interfering RNA (siRNA) is an attractive therapeutic candidate for sequence-specific gene silencing to treat incurable diseases using small molecule drugs. However, its efficient intracellular delivery has remained a challenge. Here, we have developed a highly biocompatible fluorescent carbon dot (CD), and demonstrate a functional siRNA delivery system that induces efficient gene knockdown in vitro and in vivo. We found that CD nanoparticles (NPs) enhance the cellular uptake of siRNA, via endocytosis in tumor cells, with low cytotoxicity and unexpected immune responses. Real-time study of fluorescence imaging in live cells shows that CD NPs favorably localize in cytoplasm and successfully release siRNA within 12 h. Moreover, we demonstrate that CD NP-mediated siRNA delivery significantly silences green fluorescence protein (GFP) expression and inhibits tumor growth in a breast cancer cell xenograft mouse model of tumor-specific therapy. We have developed a multifunctional siRNA delivery vehicle enabling simultaneous bioimaging and efficient downregulation of gene expression, that shows excellent potential for gene therapy.

BANF1, PLOD3, SF3B4 as Early-stage Cancer Decision Markers and Drivers of Hepatocellular Carcinoma

An accurate tool enabling early diagnosis of hepatocellular carcinoma (HCC) is clinically important, since early detection of HCC markedly improves survival. We aimed to investigate the molecular markers underlying early progression of HCC that can be detected in precancerous lesions. We designed a gene selection strategy to identify potential driver genes by integrative analysis of transcriptome and clinicopathologic data of human multi-stage HCC tissues including precancerous lesions, lowand high-grade dysplastic nodules. The gene selection process was guided by detecting the selected molecules in both HCC and precancerous lesion. Using various computational approaches, we selected 10 gene elements as a candidate and, through immunohistochemical staining, showed that BANF1, PLOD3 and SF3B4 are HCC decision markers with superior capability to diagnose early-stage HCC in a large cohort of HCC patients, as compared to the currently popular trio of HCC diagnostic markers: glypican 3, glutamine synthetase, and heat-shock protein 70. Targeted inactivation of BANF1, PLOD3 and SF3B4 inhibits in vitro and in vivo liver tumorigenesis by selectively modulating EMT and cell cycle proteins. Treatment of nanoparticles containing siRNAs of the three genes suppressed liver tumor incidence as well as tumor growth rates in spontaneous mouse HCC model. We also demonstrated that SF3B4 overexpression triggers SF3b complex to splice tumor suppressor KLF4 transcript to non-functional skipped exon transcripts. This contributes to malignant transformation and growth of hepatocyte via transcriptional inactivation of p27 and simultaneously activation of Slug genes. Conclusion: The findings suggest novel molecular markers of BANF1, PLOD3 and SF3B4 indicating early-stage HCC in precancerous lesion, and also suggest drivers for understanding the development of hepatocarcinogenesis. Page 3 of 71 Hepatology Hepatology This article is protected by copyright. All rights reserved.An accurate tool enabling early diagnosis of hepatocellular carcinoma (HCC) is clinically important, given that early detection of HCC markedly improves survival. We aimed to investigate the molecular markers underlying early progression of HCC that can be detected in precancerous lesions. We designed a gene selection strategy to identify potential driver genes by integrative analysis of transcriptome and clinicopathological data of human multistage HCC tissues, including precancerous lesions, low‐ and high‐grade dysplastic nodules. The gene selection process was guided by detecting the selected molecules in both HCC and precancerous lesion. Using various computational approaches, we selected 10 gene elements as a candidate and, through immunohistochemical staining, showed that barrier to autointegration factor 1 (BANF1), procollagen‐lysine, 2‐oxoglutarate 5‐dioxygenase 3 (PLOD3), and splicing factor 3b subunit 4 (SF3B4) are HCC decision markers with superior capability to diagnose early‐stage HCC in a large cohort of HCC patients, as compared to the currently popular trio of HCC diagnostic markers: glypican 3, glutamine synthetase, and heat‐shock protein 70. Targeted inactivation of BANF1, PLOD3, and SF3B4 inhibits in vitro and in vivo liver tumorigenesis by selectively modulating epithelial‐mesenchymal transition and cell‐cycle proteins. Treatment of nanoparticles containing small‐interfering RNAs of the three genes suppressed liver tumor incidence as well as tumor growth rates in a spontaneous mouse HCC model. We also demonstrated that SF3B4 overexpression triggers SF3b complex to splice tumor suppressor KLF4 transcript to nonfunctional skipped exon transcripts. This contributes to malignant transformation and growth of hepatocyte through transcriptional inactivation of p27Kip1 and simultaneously activation of Slug genes. Conclusion: The findings suggest molecular markers of BANF1, PLOD3, and SF3B4 indicating early‐stage HCC in precancerous lesion, and also suggest drivers for understanding the development of hepatocarcinogenesis. (Hepatology 2018;67:1360‐1377).

One-Transistor–One-Transistor (1T1T) Optoelectronic Nonvolatile MoS2 Memory Cell with Nondestructive Read-Out

Taking advantage of the superlative optoelectronic properties of single-layer MoS2, we developed a one-transistor-one-transistor (1T1T)-type MoS2 optoelectronic nonvolatile memory cell. The 1T1T memory cell consisted of a control transistor (CT) and a memory transistor (MT), in which the drain electrode of the MT was connected electrically to the gate electrode of the CT, whereas the source electrode of the CT was connected electrically to the gate electrode of the MT. Single-layer MoS2 films were utilized as the channel materials in both transistors, and gold nanoparticles acted as the floating gates in the MT. This 1T1T device architecture allowed for a nondestructive read-out operation in the memory because the writing (programming or erasing) and read-out processes were operated separately. The switching of the CT could be controlled by light illumination as well as the applied gate voltage due to the strong light absorption induced by the direct band gap of single-layer MoS2 (∼1.8 eV). The resulting MoS2 1T1T memory cell exhibited excellent memory performance, including a large programming/erasing current ratio (over 106), multilevel data storage (over 6 levels), cyclic endurance (200 cycles), and stable retention (103 s).

Highly Efficient and Rapid Neural Differentiation of Mouse Embryonic Stem Cells Based on Retinoic Acid Encapsulated Porous Nanoparticle

An improved cell conversion strategy for neural differentiation of mouse embryonic stem (mES) cells is developed by incorporating functionalized mesoporous silica nanoparticle (MSN) as an efficient delivery carrier of retinoic acid (RA), which is a pleiotropic factor required for initiation of neural differentiation. Traditional RA-mediated neural differentiation methods required either preactivation of the cells to the differentiating state by embryoid body (EB) formation or repetitive treatment of the differentiation factor. Our modified cell conversion system involves only singular treatment of the RA/MSN complex, which simplified the whole process and accelerated neural induction to be finished within 6 days with high quality. With our new method, neural cells were successfully derived from mES cells with stable expression of neurite marker gene.