Publications by authors named "Bong Gill Choi"

57 Publications

Highly Concentrated, Conductive, Defect-free Graphene Ink for Screen-Printed Sensor Application.

Nanomicro Lett 2021 Mar 8;13(1):87. Epub 2021 Mar 8.

Department of Chemical Engineering, Kangwon National University, Samcheok, Gangwon-do, 25913, Republic of Korea.

Highlights: Ultrathin and defect-free graphene ink is prepared through a high-throughput fluid dynamics process, resulting in a high exfoliation yield (53.5%) and a high concentration (47.5 mg mL). A screen-printed graphene conductor exhibits a high electrical conductivity of 1.49 × 10 S m and good mechanical flexibility. An electrochemical sodium ion sensor based on graphene ink exhibits an excellent potentiometric sensing performance in a mechanically bent state. Real-time monitoring of sodium ion concentration in sweat is demonstrated. Conductive inks based on graphene materials have received significant attention for the fabrication of a wide range of printed and flexible devices. However, the application of graphene fillers is limited by their restricted mass production and the low concentration of their suspensions. In this study, a highly concentrated and conductive ink based on defect-free graphene was developed by a scalable fluid dynamics process. A high shear exfoliation and mixing process enabled the production of graphene at a high concentration of 47.5 mg mL for graphene ink. The screen-printed graphene conductor exhibits a high electrical conductivity of 1.49 × 10 S m and maintains high conductivity under mechanical bending, compressing, and fatigue tests. Based on the as-prepared graphene ink, a printed electrochemical sodium ion (Na) sensor that shows high potentiometric sensing performance was fabricated. Further, by integrating a wireless electronic module, a prototype Na-sensing watch is demonstrated for the real-time monitoring of the sodium ion concentration in human sweat during the indoor exercise of a volunteer. The scalable and efficient procedure for the preparation of graphene ink presented in this work is very promising for the low-cost, reproducible, and large-scale printing of flexible and wearable electronic devices.
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http://dx.doi.org/10.1007/s40820-021-00617-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006523PMC
March 2021

3D Hierarchical Nanotopography for On-Site Rapid Capture and Sensitive Detection of Infectious Microbial Pathogens.

ACS Nano 2021 03 27;15(3):4777-4788. Epub 2021 Jan 27.

Division of Nano-Bio Sensors/Chips Development, National NanoFab Center (NNFC), Daejeon 34141, Republic of Korea.

Effective capture and rapid detection of pathogenic bacteria causing pandemic/epidemic diseases is an important task for global surveillance and prevention of human health threats. Here, we present an advanced approach for the on-site capture and detection of pathogenic bacteria through the combination of hierarchical nanostructures and a nuclease-responsive DNA probe. The specially designed hierarchical nanocilia and network structures on the pillar arrays, termed 3D bacterial capturing nanotopographical trap, exhibit excellent mechanical reliability and rapid (<30 s) and irreversible bacterial capturability. Moreover, the nuclease-responsive DNA probe enables the highly sensitive and extremely fast (<1 min) detection of bacteria. The bacterial capturing nanotopographical trap (b-CNT) facilitates the on-site capture and detection of notorious infectious pathogens ( O157:H7, , , and ) from kitchen tools and food samples. Accordingly, the usefulness of the b-CNT is confirmed as a simple, fast, sensitive, portable, and robust on-site capture and detection tool for point-of-care testing.
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http://dx.doi.org/10.1021/acsnano.0c09411DOI Listing
March 2021

Flexible nanopillar-based immunoelectrochemical biosensor for noninvasive detection of Amyloid beta.

Nano Converg 2020 Sep 1;7(1):29. Epub 2020 Sep 1.

Division of Nano-Bio Sensor/Chip Development, National NanoFab Center (NNFC), Daejeon, 34141, Republic of Korea.

The noninvasive early detection of biomarkers for Alzheimer's disease (AD) is essential for the development of specific treatment strategies. This paper proposes an advanced method for fabricating highly ordered and flexible nanopillar-based electrochemical biosensors by the combination of soft/photolithography and metal evaporation. The nanopillar array (NPA) exhibits high surface area containing 1500 nm height and 500 nm diameter with 3:1 ratio. In regard with physical properties of polyurethane (PU) substrate, the developed NPA is sustainable and durable to external pressure such as bending and twisting. To manipulate the NPA surface to biocompatible, the gold was uniformly deposited on the PU substrate. The thiol chemistry which is stably modified on the gold surface as a form of self-assembled monolayer was employed for fabricating the NPA as a biocompatible chip by covalently immobilize the antibodies. The proposed nanopillar-based immunoelectrochemical biosensor exhibited good and stable electrochemical performance in β-amyloid (Aβ) detection. Moreover, we successfully confirmed the performance of the as-developed sensor using the artificial injection of Aβ in human tear, with sensitivity of 0.14 ng/mL and high reproducibility (as a standard deviation below 10%). Our findings show that the developed nanopillar-based sensor exhibits reliable electrochemical characteristics and prove its potential for application as a biosensor platform for testing at the point of care.
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http://dx.doi.org/10.1186/s40580-020-00239-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7462961PMC
September 2020

Antibacterial Nanopillar Array for an Implantable Intraocular Lens.

Adv Healthc Mater 2020 09 2;9(18):e2000447. Epub 2020 Aug 2.

Division of Nano-Bio Sensor/Chip Development, National NanoFab Center, Daejeon, 34141, Republic of Korea.

Postsurgical intraocular lens (IOL) infection caused by pathogenic bacteria can result in blindness and often requires a secondary operation to replace the contaminated lens. The incorporation of an antibacterial property onto the IOL surface can prevent bacterial infection and postoperative endophthalmitis. This study describes a polymeric nanopillar array (NPA) integrated onto an IOL, which captures and eradicates the bacteria by rupturing the bacterial membrane. This is accomplished by changing the behavior of the elastic nanopillars using bending, restoration, and antibacterial surface modification. The combination of the polymer coating and NPA dimensions can decrease the adhesivity of corneal endothelial cells and posterior capsule opacification without causing cytotoxicity. An ionic antibacterial polymer layer is introduced onto an NPA using an initiated chemical vapor deposition process. This improves bacterial membrane rupture efficiency by increasing the interactions between the bacteria and nanopillars and damages the bacterial membrane using quaternary ammonium compounds. The newly developed ionic polymer-coated NPA exceeds 99% antibacterial efficiency against Staphylococcus aureus, which is achieved through topological and physicochemical surface modification. Thus, this paper provides a novel, efficient strategy to prevent postoperative complications related to bacteria contamination of IOL after cataract surgery.
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http://dx.doi.org/10.1002/adhm.202000447DOI Listing
September 2020

Highly self-healable and flexible cable-type pH sensors for real-time monitoring of human fluids.

Biosens Bioelectron 2020 Feb 7;150:111946. Epub 2019 Dec 7.

Department of Chemical Engineering, Kangwon National University, Samcheok, Gangwon-do, 25913, Republic of Korea. Electronic address:

Development of sensing technology with wearable chemical sensors is realizing non-invasive, real-time monitoring healthcare and disease diagnostics. The advanced sensor devices should be compact and portable for use in limited space, easy to wear on human body, and low-cost for personalized healthcare markets. Here, we report a highly sensitive, flexible, and autonomously self-healable pH sensor cable developed by weaving together two carbon fiber thread electrodes coated with mechanically robust self-healing polymers. The pH sensor cable showed excellent electrochemical performances of sensitivity, repeatability, and durability. Spontaneous and autonomous sensor healing efficiency of the pH sensor cable was demonstrated by measuring sensitivity during four cycles of cutting and healing process. The pH sensor cable could measure pH in small volumes of real human fluid samples, including urine, saliva, and sweat, and the results were similar to those of a commercial pH meter. Taken together, successful real-time pH monitoring for human sweat was demonstrated by fabricating a wearable sensing system in which the pH sensor cable was knitted into a headband integrated with wireless electronics.
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http://dx.doi.org/10.1016/j.bios.2019.111946DOI Listing
February 2020

Development of zinc oxide-based sub-micro pillar arrays for on-site capture and DNA detection of foodborne pathogen.

J Colloid Interface Sci 2020 Mar 14;563:54-61. Epub 2019 Dec 14.

Nanobio Application Team, National NanoFab Center (NNFC), Daejeon 34141, Republic of Korea. Electronic address:

Prevention and early detection of bacterial infection caused by foodborne pathogens are the most important task to human society. Although currently available diagnostic technologies have been developed and designed for detection of specific pathogens, suitable capturing tools for the pathogens are rarely studied. In this paper, a new methodology is developed and proposed to realize effective capturing through touchable flexible zinc oxide-based sub-micro pillar arrays through genetic analysis. Zinc oxide coated pillar arrays have a high surface area, flexible, and adheres strongly to bacteria. Therefore, it contributes to enhance the bacterial capturability. An in-depth analysis on the sub-sequential capturing process at the bacterial cell-pillar interface is presented. By carefully observing the structural changes and performing numerical analysis under different reaction times, the results are presented. The resulting zinc oxide coated pillar arrays exhibited comprehensive capturability. These pillars were able to detect pathogenic bacteria due to a combination of complex structures, depletion force, and high surface electrostatics. The developed sub-micro pillars successfully captured and detected infectious foodborne bacteria of Escherichia coli in the range of 10-10 CFU/mL.
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http://dx.doi.org/10.1016/j.jcis.2019.12.008DOI Listing
March 2020

Extremely Fast Self-Healable Bio-Based Supramolecular Polymer for Wearable Real-Time Sweat-Monitoring Sensor.

ACS Appl Mater Interfaces 2019 Dec 27;11(49):46165-46175. Epub 2019 Nov 27.

Department of Chemical Engineering , Kangwon National University , Samcheok , Gangwon-do 25913 , Republic of Korea.

Sensors with autonomous self-healing properties offer enhanced durability, reliability, and stability. Although numerous self-healing polymers have been attempted, achieving sensors with fast and reversible recovery under ambient conditions with high mechanical toughness remains challenging. Here, a highly sensitive wearable sensor made of a robust bio-based supramolecular polymer that is capable of self-healing via hydrogen bonding is presented. The integration of carbon fiber thread into a self-healing polymer matrix provides a new toolset that can easily be knitted into textile items to fabricate wearable sensors that show impressive self-healing efficiency (>97.0%) after 30 s at room temperature for K/Na sensing. The wearable sweat-sensor system-coupled with a wireless electronic circuit board capable of transferring data to a smart phone-successfully monitors electrolyte ions in human perspiration noninvasively in real time, even in the healed state during indoor exercise. Our smart sensors represent an important advance toward futuristic personalized healthcare applications.
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http://dx.doi.org/10.1021/acsami.9b16829DOI Listing
December 2019

Preparation of ultrathin defect-free graphene sheets from graphite via fluidic delamination for solid-contact ion-to-electron transducers in potentiometric sensors.

J Colloid Interface Sci 2020 Feb 2;560:817-824. Epub 2019 Nov 2.

Department of Chemical Engineering, Kangwon National University, Samcheok 25913, Republic of Korea. Electronic address:

In this study, ultrathin and defect-free graphene (Gr) sheets were prepared through a fluid dynamics-induced shear exfoliation method using graphite. The high hydrophobicity and surface area of Gr make it attractive as a solid-contact ion-to-electron transducer for potentiometric K sensors, in which the electrodes are fabricated through a screen-printing process. The electrochemical characterization demonstrates that Gr solid contact results in a high double-layer capacitance, potential stability, and strong resistance against water layer, gases, and light. The Gr-based K sensors showed a Nernstian slope of 53.53 mV/log[K] within a linear concentration range of 10-10 M, a low detection limit of 10 M, a fast response time of ~8 s, good repeatability, and excellent long-term stability. Moreover, the Gr-based K sensors provided accurate ion concentrations in actual samples of human sweat and sports drinks.
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http://dx.doi.org/10.1016/j.jcis.2019.11.001DOI Listing
February 2020

Sustainable Boron Nitride Nanosheet-Reinforced Cellulose Nanofiber Composite Film with Oxygen Barrier without the Cost of Color and Cytotoxicity.

Polymers (Basel) 2018 May 5;10(5). Epub 2018 May 5.

Research Center for Bio-based chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Korea.

This paper introduces a boron nitride nanosheet (BNNS)-reinforced cellulose nanofiber (CNF) film as a sustainable oxygen barrier film that can potentially be applied in food packaging. Most commodity plastics are oxygen-permeable. CNF exhibits an ideal oxygen transmission rate (OTR) of <1 cc/m²/day in highly controlled conditions. A CNF film typically fabricated by the air drying of a CNF aqueous solution reveals an OTR of 19.08 cc/m²/day. The addition of 0⁻5 wt % BNNS to the CNF dispersion before drying results in a composite film with highly improved OTR of 4.7 cc/m²/day, which is sufficient for meat and cheese packaging. BNNS as a 2D nanomaterial increases the pathway of oxygen gas and reduces the chances of pinhole formation during film fabrication involving water drying. In addition, BNNS improves the mechanical properties of the CNF films (Young's modulus and tensile strength) without significant elongation reductions, probably due to the good miscibility of CNF and BNNS in the aqueous solution. Addition of BNNS also produces negligible color change, which is important for film aesthetics. An in vitro cell experiment was performed to reveal the low cytotoxicity of the CNF/BNNS composite. This composite film has great potential as a sustainable high-performance food-packaging material.
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http://dx.doi.org/10.3390/polym10050501DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6415411PMC
May 2018

Potentiometric performance of flexible pH sensor based on polyaniline nanofiber arrays.

Nano Converg 2019 Mar 18;6(1). Epub 2019 Mar 18.

Department of Chemical Engineering, Kangwon National University, 346 Joongang-ro, Samcheok, Gangwon-do, 25913, Republic of Korea.

We report potentiometric performance of a polyaniline nanofiber array-based pH sensor fabricated by combining a dilute chemical polymerization and low-cost and simple screen printing process. The pH sensor had a two-electrode configuration consisting of polyaniline nanofiber array sensing electrode and Ag/AgCl reference electrode. Measurement of electromotive force between sensing and reference electrodes provided various electrochemical properties of pH sensors. The pH sensor show excellent sensor performances of sensitivity of 62.4 mV/pH, repeatability of 97.9% retention, response time of 12.8 s, and durability of 3.0 mV/h. The pH sensor could also measure pH changes as the milk is spoiled, which is similar to those of a commercial pH meter. The pH sensors were highly flexible, and thus can measure the fruit decay on the curved surface of an apple. This flexible and miniature pH sensor opens new opportunities for monitoring of water, product process, human health, and chemical (or bio) reactions even using small volumes of samples.
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http://dx.doi.org/10.1186/s40580-019-0179-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6421353PMC
March 2019

Fast and Scalable Hydrodynamic Synthesis of MnO/Defect-Free Graphene Nanocomposites with High Rate Capability and Long Cycle Life.

ACS Appl Mater Interfaces 2018 Oct 5;10(41):35250-35259. Epub 2018 Oct 5.

Department of Chemical Engineering , Kangwon National University , 346 Joongang-ro , Samcheok , Gangwon-do 25913 , Republic of Korea.

The integration of metal oxides and carbon materials provides a great potential for enhancing the high energy and power densities of supercapacitors, but the rational design and scalable fabrication of such composite materials still remain a challenge. Herein, we report a fast, scalable, and one-pot hydrodynamic synthesis for preparing ion conductive and defect-free graphene from graphite and MnO/graphene nanocomposites. The use of this hydrodynamic method using Taylor-Couette flow allows us to efficiently fast shear-exfoliate graphite into large quantities of high-quality graphene sheets. Deposition of MnO on graphene is subsequently performed in a fluidic reactor within 10 min. The prepared MnO/graphene nanocomposite shows outstanding electrochemical performances, such as a high specific capacitance of 679 F/g at 25 mV/s, a high rate capability of 74.7% retention at an extremely high rate of 1000 mV/s, and an excellent cycling characteristic (∼94.7% retention over 20 000 cycles). An asymmetric supercapacitor device is fabricated by assembling an anode of graphene and a cathode of MnO/graphene, which resulted in high energy (35.2 W h/kg) and power (7.4 kW/kg) densities (accounting for the mass of both electrodes and the electrolyte) with a high rate capability and long cycle life.
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http://dx.doi.org/10.1021/acsami.8b12894DOI Listing
October 2018

Flexible nanopillar-based electrochemical sensors for genetic detection of foodborne pathogens.

Nano Converg 2018 6;5(1):15. Epub 2018 Jun 6.

Nano-bio Application Team, National NanoFab Center (NNFC), Daejeon, 34141 Republic of Korea.

Flexible and highly ordered nanopillar arrayed electrodes have brought great interest for many electrochemical applications, especially to the biosensors, because of its unique mechanical and topological properties. Herein, we report an advanced method to fabricate highly ordered nanopillar electrodes produced by soft-/photo-lithography and metal evaporation. The highly ordered nanopillar array exhibited the superior electrochemical and mechanical properties in regard with the wide space to response with electrolytes, enabling the sensitive analysis. As-prepared gold and silver electrodes on nanopillar arrays exhibit great and stable electrochemical performance to detect the amplified gene from foodborne pathogen of O157:H7. Additionally, lightweight, flexible, and USB-connectable nanopillar-based electrochemical sensor platform improves the connectivity, portability, and sensitivity. Moreover, we successfully confirm the performance of genetic analysis using real food, specially designed intercalator, and amplified gene from foodborne pathogens with high reproducibility (6% standard deviation) and sensitivity (10 × 1.0 CFU) within 25 s based on the square wave voltammetry principle. This study confirmed excellent mechanical and chemical characteristics of nanopillar electrodes have a great and considerable electrochemical activity to apply as genetic biosensor platform in the fields of point-of-care testing (POCT).
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http://dx.doi.org/10.1186/s40580-018-0147-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5988775PMC
June 2018

Heteroassembled gold nanoparticles with sandwich-immunoassay LSPR chip format for rapid and sensitive detection of hepatitis B virus surface antigen (HBsAg).

Biosens Bioelectron 2018 Jun 7;107:118-122. Epub 2018 Feb 7.

Department of Energy and Materials Engineering, Dongguk University, 30 Pildong-ro 1-gil, Seoul 04620, South Korea. Electronic address:

This study aimed to develop a more sensitive method for the detection of hepatitis B surface antigen (HBsAg) using heteroassembled gold nanoparticles (AuNPs). A single layered localized surface plasmon resonance (LSPR) chip format was developed with antigen-antibody reaction-based detection symmetry using AuNPs, which detected HBsAg at 10 pg/mL. To further improve the detection limit, a modified detection format was fabricated by fixing a secondary antibody (to form a heteroassembled sandwich format) to the AuNP monolayer, which enhanced the detection sensitivity by about 100 times. The developed heteroassembled AuNPs sandwich-immunoassay LSPR chip format was able to detect as little as 100 fg/mL of HBsAg within 10-15 min. In addition, the heteroassembled AuNPs sandwich-immunoassay LSPR chip format did not show any non-specific binding to other tested antigens, including alpha fetoprotein (AFP), C-reactive protein (CRP), and prostate-specific antigen (PSA). These findings confirm that the proposed detection strategy of heteroassembled AuNPs sandwich-immunoassay LSPR chip format may provide a new platform for early diagnosis of various human diseases.
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http://dx.doi.org/10.1016/j.bios.2018.02.019DOI Listing
June 2018

Fabrication of newspaper-based potentiometric platforms for flexible and disposable ion sensors.

J Colloid Interface Sci 2017 Dec 12;508:167-173. Epub 2017 Aug 12.

Department of Chemical Engineering, Kangwon National University, Samcheok 25913, Republic of Korea. Electronic address:

Paper-based materials have attracted a great deal of attention in sensor applications because they are readily available, biodegradable, inexpensive, and mechanically flexible. Although paper-based sensors have been developed, but important obstacles remian, which include the retention of chemical and mechanical stabilities when paper is wetted. Herein, we develop a simple and scalable process for fabrication of newspaper-based platforms by coating of parylene C and patterning of metal layers. As-prepared parylene C-coated newspaper (PC-paper) provides low-cost, disposable, and mechanically and chemically stable electrochemical platforms for the development of potentiometric ion sensors for the detection of electrolyte cations, such as, H and K. The pH and K sensors produced show near ideal Nernstian sensitivity, good repeatability, good ion selectivity, and low potential drift. These disposable, flexible ion sensors based on PC-paper platforms could provide new opportunities for the development of point-of-care testing sensors, for diagnostics, healthcare, and environment testing.
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http://dx.doi.org/10.1016/j.jcis.2017.08.036DOI Listing
December 2017

High performance electrochemical glucose sensor based on three-dimensional MoS/graphene aerogel.

J Colloid Interface Sci 2017 Nov 18;506:379-385. Epub 2017 Jul 18.

Department of Chemical & Biomolecular Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea. Electronic address:

Two-dimensional (2D) nanosheets have been extensively explored as electrode materials for the development of high-performance electrochemical biosensors due to their unique structural characteristics. Nevertheless, 2D nanosheets suffer from sheet aggregation issues limiting the electrical conductivity of layered metal sulfides or hydroxides. Here, we report high-performance glucose biosensors based on a three-dimensional (3D) aerogel composed of interconnected 2D MoS and graphene sheet. 3D MoS/graphene aerogel (MGA) provides a large surface area for the effective immobilization of enzymes, and continuous framework of electrically conductive graphene sheets. Flow-injection amperometric evaluation of the glucose biosensor using a 3D MGA electrode exhibits a rapid response (∼4s), a linear detection range from 2 to 20mM, a sensitivity of 3.36μA/mM, and a low limit of detection of 0.29mM. Moreover, the interference response from oxidizable species, such as ascorbic acid, uric acid and dopamine is negligible at an operating potential of -0.45V.
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http://dx.doi.org/10.1016/j.jcis.2017.07.061DOI Listing
November 2017

MnO Nanowire/Biomass-Derived Carbon from Hemp Stem for High-Performance Supercapacitors.

Langmuir 2017 05 16;33(21):5140-5147. Epub 2017 May 16.

Department of Chemical Engineering, Kangwon National University , 346 Joongang-ro, Samcheok, Gangwon-do 25913, Republic of Korea.

Hierarchical 3D nanostructures based on waste biomass are being offered as promising materials for energy storage due to their processabilities, multifunctionalities, environmental benignities, and low cost. Here we report a facile, inexpensive, and scalable strategy for the fabrication of hierarchical porous 3D structure as electrode materials for supercapacitors based on MnO nanowires and hemp-derived activated carbon (HC). Vertical MnO wires are uniformly deposited onto the surface of HC using a one-step hydrothermal method to produce hierarchical porous structures with conductive interconnected 3D networks. HC acts as a near-ideal 3D current collector and anchors electroactive materials, and this confers a specific capacitance of 340 F g at 1 A g with a high rate capability (88% retention) of the 3D MnO/HC composite because of its open-pore system, which facilitates ion and electron transports and synergistic contribution of two energy-storage materials. Moreover, asymmetric supercapacitors fabricated using 3D HC as the anode and 3D MnO/HC as the cathode are able to store 33.3 Wh kg of energy and have a power delivery of 14.8 kW kg.
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http://dx.doi.org/10.1021/acs.langmuir.7b00589DOI Listing
May 2017

Development of Lateral Flow Assay Based on Size-Controlled Gold Nanoparticles for Detection of Hepatitis B Surface Antigen.

Sensors (Basel) 2016 Dec 16;16(12). Epub 2016 Dec 16.

Department of Chemical Engineering, Kangwon National University, Samcheok 25913, Korea.

In this study, we developed lateral flow assay (LFA) biosensors for the detection of hepatitis B surface antigens using well-controlled gold nanoparticles (AuNPs). To enhance colorimetric signals, a seeded growth method was used for the preparation of size-controlled AuNPs with a narrow size distribution. Different sizes of AuNPs in the range of 342-137.8 nm were conjugated with antibodies and then optimized for the efficient detection of LFA biosensors. The conjugation stability was investigated by UV-vis spectroscopy of AuNP dispersion at various pH values and concentrations of antibody. Based on optimized conjugation conditions, the use of 42.7 ± 0.8 nm AuNPs exhibited superior performance for the detection of LFAs relative to other sizes of AuNPs.
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http://dx.doi.org/10.3390/s16122154DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5191134PMC
December 2016

Flexible and Disposable Sensing Platforms Based on Newspaper.

ACS Appl Mater Interfaces 2016 Dec 15;8(51):34978-34984. Epub 2016 Dec 15.

Nanobio Application Team, National NanoFab Center (NNFC) , Daejeon 34141, Republic of Korea.

The flexible sensing platform is a key component for the development of smart portable devices targeting healthcare, environmental monitoring, point-of-care diagnostics, and personal electronics. Herein, we demonstrate a simple, scalable, and cost-effective strategy for fabrication of a sensing electrode based on a waste newspaper with conformal coating of parylene C (P-paper). Thin polymeric layers over cellulose fibers allow the P-paper to possess improved mechanical and chemical stability, which results in high-performance flexible sensing platforms for the detection of pathogenic E. coli O157:H7 based on DNA hybridization. Moreover, P-paper electrodes have the potential to serve as disposable, flexible sensing platforms for point-of-care testing biosensors.
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http://dx.doi.org/10.1021/acsami.6b10298DOI Listing
December 2016

High performance flexible pH sensor based on polyaniline nanopillar array electrode.

J Colloid Interface Sci 2017 Mar 9;490:53-58. Epub 2016 Nov 9.

Department of Chemical Engineering, Kangwon National University, Samcheok 25913, Republic of Korea. Electronic address:

Flexible pH sensor technologies have attracted a great deal of attention in many applications, such as, wearable health care devices and monitors for chemical and biological processes. Here, we fabricated flexible and thin pH sensors using a two electrode configuration comprised of a polyaniline nanopillar (PAN) array working electrode and an Ag/AgCl reference electrode. In order to provide nanostructure, soft lithography using a polymeric blend was employed to create a flexible nanopillar backbone film. Polyaniline-sensing materials were deposited on a patterned-nanopillar array by electrochemical deposition. The pH sensors produced exhibited a near-Nernstian response (∼60.3mV/pH), which was maintained in a bent state. In addition, pH sensors showed other excellent sensor performances in terms of response time, reversibility, repeatability, selectivity, and stability.
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http://dx.doi.org/10.1016/j.jcis.2016.11.033DOI Listing
March 2017

Protein-directed assembly of cobalt phosphate hybrid nanoflowers.

J Colloid Interface Sci 2016 Dec 24;484:44-50. Epub 2016 Aug 24.

Nano-bio Application Team, National Nanofab Center, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea. Electronic address:

The understanding and controlling of biomimetic hybrid materials are a key objective in bio-nanotechnology, materials chemistry, and colloid science fields. Biomaterials, such as, enzyme, DNA, RNA, and proteins have become important templates for the construction of inorganic-organic hybrid nanoflowers. From this perspective, we present a simple approach to synthesize protein and metal hybrid flower-like structure using bovine serum albumin (BSA) and cobalt phosphate, and the results of our study on the formation mechanism involved. The time dependent growing stage and formation mechanism were analyzed by electron microscopes and spectroscopic techniques. The protein-directed assembly method for preparation of hybrid nanoflowers described in this work could be used to fabricate other bio-metal hybrid materials with possible applications in biosensors, bioanalytical devices, and industrial biocatalyst fields.
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http://dx.doi.org/10.1016/j.jcis.2016.08.059DOI Listing
December 2016

Fabrication of Flexible, Redoxable, and Conductive Nanopillar Arrays with Enhanced Electrochemical Performance.

ACS Appl Mater Interfaces 2016 Aug 22;8(34):22220-6. Epub 2016 Aug 22.

Department of Chemical Engineering, Kangwon National University , Samcheok 25913, Republic of Korea.

Highly ordered and flexible nanopillar arrays have received considerable interest for many applications of electrochemical devices because of their unique mechanical and structural properties. Here, we report on highly ordered polyoxometalate (POM)-doped polypyrrole (Ppy) nanopillar arrays produced by soft lithography and subsequent electrodeposition. As-prepared POM-Ppy/nanopillar films show superior electrochemical performances for pseudocapacitor and enzymeless electrochemical sensor applications and good mechanical properties, which allowed them to be easily bent and twisted. Regarding electrochemical characteristics for pseudocapacitive electrodes, the POM-Ppy/nanopillar electrodes are capable of delivering high areal capacitance of 77.0 mF cm(-2), high rate performance, and good cycle life of ∼100% retention over 3500 cycles even when bent. Moreover, the study suggests that the POM-Ppy/nanopillar electrodes have an excellent electrocatalytic activity toward hydrogen.
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http://dx.doi.org/10.1021/acsami.6b06579DOI Listing
August 2016

Graphene growth from reduced graphene oxide by chemical vapour deposition: seeded growth accompanied by restoration.

Sci Rep 2016 Mar 10;6:22653. Epub 2016 Mar 10.

Department of Chemistry, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea.

Understanding the underlying mechanisms involved in graphene growth via chemical vapour deposition (CVD) is critical for precise control of the characteristics of graphene. Despite much effort, the actual processes behind graphene synthesis still remain to be elucidated in a large number of aspects. Herein, we report the evolution of graphene properties during in-plane growth of graphene from reduced graphene oxide (RGO) on copper (Cu) via methane CVD. While graphene is laterally grown from RGO flakes on Cu foils up to a few hundred nanometres during CVD process, it shows appreciable improvement in structural quality. The monotonous enhancement of the structural quality of the graphene with increasing length of the graphene growth from RGO suggests that seeded CVD growth of graphene from RGO on Cu surface is accompanied by the restoration of graphitic structure. The finding provides insight into graphene growth and defect reconstruction useful for the production of tailored carbon nanostructures with required properties.
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http://dx.doi.org/10.1038/srep22653DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4785362PMC
March 2016

Hierarchical porous microspheres of the [email protected] with enhanced electrocatalytic performance for electrochemical biosensors.

Biosens Bioelectron 2017 Mar 29;89(Pt 1):612-619. Epub 2016 Jan 29.

Department of Chemical Engineering, Kangwon National University, Samcheok 245-711, Republic of Korea. Electronic address:

The integration of organic and inorganic building blocks into hierarchical porous architectures makes potentially desirable electrocatalytic materials in many electrochemical applications due to their combination of attractive qualities of dissimilar components and well-constructed charge transfer pathways. Herein, we demonstrate the preparation of the hierarchical porous [email protected] ([email protected]) microspheres by one-step hydrothermal method to achieve high electrocatalytic performance for enzyme-free biosensor applications. The obtained [email protected] microspheres are consisted of the interconnected networks of CoO and graphene sheets, and thus provide large accessible active sites through porous structure, while graphene sheets offer continuous electron pathways for efficient electrocatalytic reaction of CoO. These structural merits with synergy effect of CoO and graphene lead to a high performance of enzyme-free detection for glucose: high sensitivity, good selectivity, and remarkable stability.
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http://dx.doi.org/10.1016/j.bios.2016.01.075DOI Listing
March 2017

Polyoxometalate-grafted graphene nanohybrid for electrochemical detection of hydrogen peroxide and glucose.

J Colloid Interface Sci 2016 Apr 22;468:51-56. Epub 2016 Jan 22.

Department of Chemical Engineering, Kangwon National University, Samcheok 25913, Republic of Korea. Electronic address:

The electrochemical performances of electrochemical biosensors largely depend on electrode characteristics, such as size, composition, surface area, and electron and ion conductivities. Herein, highly efficient electrocatalytic polyoxometalate (POM) was directly deposited on polymeric ionic liquid (PIL)-functionalized reduced graphene oxide (rGO) in a simple manner. The nano-sized POM with PIL functional groups was uniformly distributed on the surface of rGO sheets. The unique nanostructure of the resultant POM-g-rGO nanohybrids enabled well-defined multiple redox reaction of POMs and rapid electron transfer. In particular, as-prepared nanohybrids demonstrated high electrocatalytic activity for the electrochemical detection of H2O2 and glucose molecules in flow-injection biosensor device with high sensitivity, rapid response time, and low detection limit.
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http://dx.doi.org/10.1016/j.jcis.2016.01.047DOI Listing
April 2016

Nanopillar films with polyoxometalate-doped polyaniline for electrochemical detection of hydrogen peroxide.

Analyst 2016 Feb;141(4):1319-24

Department of Chemical Engineering, Kangwon National University, Samcheok 25913, Republic of Korea.

Design and fabrication of electrodes is key in the development of electrochemical sensors with superior electrochemical performances. Herein, an enzymeless electrochemical sensor is developed for detection of hydrogen peroxide based on the use of highly ordered polyoxometalate (POM)-doped polyaniline (PANI) nanopillar films. The electrodeposition technique enables the entrapment of POMs into PANI during electropolymerization to produce thin coatings of POM-PANI. Electrochemical investigations of the POM-PANI/nanopillar electrode showed well-defined multiple pairs of redox peaks and rapid electron transfer. The nanopillar structure facilitated the diffusion of the electrolyte and thus, enhanced the redox reaction. In particular, the POM-PANI/nanopillar electrode was incorporated into a flow injection biosensor and it demonstrates its electrocatalytic activity to detect hydrogen peroxide with high sensitivity, rapid response time, and low detection limit.
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http://dx.doi.org/10.1039/c5an02134kDOI Listing
February 2016

Hierarchical core/shell structure of [email protected] composites grown on carbon fiber paper for application in pseudocapacitors.

Phys Chem Chem Phys 2015 Nov 21;17(44):29874-9. Epub 2015 Oct 21.

Department of Nano Bio Research, National NanoFab Center (NNFC), Daejeon 305-806, Republic of Korea.

Hierarchical core/shell structured arrays of [email protected] (PANI) nanosheets are successfully deposited on the surface of carbon fiber paper (CFP) by a two-step method of a redox reaction-assisted deposition of MnO2 and post electrodeposition of PANI. The CFP is used as a three-dimensional (3D) current collector to ensure 3D transport of ions and electrons with a large surface area. In addition, the electrodeposition technique enables conformal and thin coating of a layer of PANI across the entire MnO2 nanosheet. The [email protected] on the CFP shows a unique architecture for efficient ion diffusion pathways in hierarchical porous structures and rapid electron transfer through PANI coated layers. The [email protected]/CFP can be applied as a binder- and carbon-free electrode for supercapacitors. Evaluation of the electrochemical performance revealed that the as-prepared electrodes have a high value of specific capacitance (437 F g(-1) at 1 A g(-1)), high rate capability (62.4% retention at 15 A g(-1)), and good cycle life (∼100% at sequential current densities of 1 and 5 A g(-1) over 3000 cycles).
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http://dx.doi.org/10.1039/c5cp04761gDOI Listing
November 2015

Three-Dimensional Expanded Graphene-Metal Oxide Film via Solid-State Microwave Irradiation for Aqueous Asymmetric Supercapacitors.

ACS Appl Mater Interfaces 2015 Oct 1;7(40):22364-71. Epub 2015 Oct 1.

Department of Chemical Engineering, Kangwon National University , Samcheok 245-711, Republic of Korea.

Carbon-based electrochemical double-layer capacitors and pseudocapacitors, consisting of a symmetric configuration of electrodes, can deliver much higher power densities than batteries, but they suffer from low energy densities. Herein, we report the development of high energy and power density supercapacitors using an asymmetric configuration of Fe2O3 and MnO2 nanoparticles incorporated into 3D macroporous graphene film electrodes that can be operated in a safe and low-cost aqueous electrolyte. The gap in working potential windows of Fe2O3 and MnO2 enables the stable expansion of the cell voltage up to 1.8 V, which is responsible for the high energy density (41.7 Wh kg(-1)). We employ a household microwave oven to simultaneously create conductivity, porosity, and the deposition of metal oxides on graphene films toward 3D hybrid architectures, which lead to a high power density (13.5 kW kg(-1)). Such high energy and power densities are maintained for over 5000 cycles, even during cycling at a high current density of 16.9 A g(-1).
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http://dx.doi.org/10.1021/acsami.5b06187DOI Listing
October 2015

Bio-inspired Hierarchical Nanowebs for Green Catalysis.

Small 2015 09 8;11(34):4292-7. Epub 2015 Jun 8.

Department of Chemistry, Hanyang University, 17 Haengdang dong, Seoul, 133-791, South Korea.

Bio-inspired 3D hierarchical nanowebs are fabricated using silicon micropillars, carbon nanotubes (CNT), and manganese oxide. The Si pillars act as artificial branches for growing CNTs and the secondary metal coating strengthens the structures. The simple but effective structure provides both chemical and mechanical stability to be used as a green catalyst for recycling waste polymers into raw materials.
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http://dx.doi.org/10.1002/smll.201403717DOI Listing
September 2015

Low-current field-assisted assembly of copper nanoparticles for current collectors.

Faraday Discuss 2015 ;181:383-401

School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, Shaanxi, P. R. China.

Current collectors are essential features of batteries and many other electronic devices being responsible for efficient charge transport to active electrode materials. Three-dimensional (3D), high surface area current collectors considerably improve the performance of cathodes and anodes in batteries, but their technological implementation is impeded by the complexity of their preparation, which needs to be simple, fast, and energy efficient. Here we demonstrate that field-stimulated assembly of ∼3 nm copper nanoparticles (NPs) enables the preparation of porous Cu NP films. The use of NP dispersions enables 30× reduction of the deposition current for making functional 3D coatings. In addition to high surface area, lattice-to-lattice connectivity in the self-assembly of NPs in 3D structures enables fast charge transport. The mesoscale dimensions of out-of-plane features and the spacing between them in Cu films made by field-stimulated self-assembly of NPs provides promising morphology for current collection in lithium ion batteries (LIBs). Half-cell electrochemical models based on self-assembled films show improved specific capacity, total capacity, and cycling performance compared to traditional flat and other 3D current collectors. While integration of active electrode material into the 3D topography of the current collector needs to be improved, this study indicates that self-assembled NP films represent a viable manufacturing approach for 3D electrodes.
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http://dx.doi.org/10.1039/c4fd00263fDOI Listing
October 2015

High density decoration of noble metal nanoparticles on polydopamine-functionalized molybdenum disulphide.

J Colloid Interface Sci 2015 Aug 8;451:216-20. Epub 2015 Apr 8.

Department of Chemical Engineering, Kangwon National University, Samcheok 245-711, Republic of Korea. Electronic address:

Here, we report a highly stable colloidal suspension of nanoparticles (i.e., Pt and Au)-deposited MoS2 sheets, in which polydopamine (PD) serves as surface functional groups. The adoption of polydopamine coating onto the MoS2 surface enables homogeneous deposition of nanoparticles in an aqueous solution. As-synthesized nanohybrids are thoroughly characterized by transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction (XRD) measurement. These intensive investigations reveal that noble metal nanocrystals are uniformly distributed on the surface of ultrathin MoS2 sheets (∼4 layers). Moreover, as-prepared Au/PD/MoS2 nanohybrids can be applied as a heterogeneous catalyst for reduction of 4-nitrophenol to 4-aminophenol, and they exhibit an excellent catalytic activity.
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http://dx.doi.org/10.1016/j.jcis.2015.03.062DOI Listing
August 2015
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