Publications by authors named "Gi Hun Seong"

54 Publications

PVP-stabilized PtRu nanozymes with peroxidase-like activity and its application for colorimetric and fluorometric glucose detection.

Colloids Surf B Biointerfaces 2021 Apr 24;204:111783. Epub 2021 Apr 24.

Department of Bionano Engineering, Center for Bionano Intelligence Education and Research, Hanyang University, Ansan, 426-791, South Korea. Electronic address:

Nanozymes have significant advantages over natural enzymes. The intrinsic peroxidase-like activity of Pt-based nanomaterials can be enhanced by alloying with other transition metals, such as Ru, that have great catalytic activity. In this study, we used polyvinylpyrrolidone (PVP) to synthesize well-dispersed and homogeneous nanostructures. PVP-stabilized Pt-Ru nanozymes (PVP/PtRu NZs) were synthesized and characterized. The PVP/PtRu NZs had an average size of 3.54 ± 0.84 nm and exhibited an intense peroxidase-like activity. The PVP/PtRu NZs were used as peroxidase mimics for colorimetric and fluorometric glucose determination by the glucose oxidase and PVP/PtRu NZs cascade reaction. In the colorimetric assay, the linearly detectable range was 0.25-3.0 mM, with an R and limit of detection (LOD) of 0.988 and 138 μM, respectively. In the fluorometric assay, a linear relationship was found when the glucose concentration was between 5.0 and 300 μM (R = 0.997), with an LOD of 1.11 μM. Compared to the colorimetric assay, the fluorometric assay had greater sensitivity and a lower detection limit for the determination of glucose. Moreover, the PVP/PtRu NZs had high storage stability over a month and great recovery values in human serum and artificial urine, with a range of 94-106 %. From these results, PVP/PtRu NZs are expected to be used as promising peroxidase mimics in various fields such as biosensing, pharmaceutical processing, and the food industry.
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http://dx.doi.org/10.1016/j.colsurfb.2021.111783DOI Listing
April 2021

Cell-based electrochemical cytosensor for rapid and sensitive evaluation of the anticancer effects of saponin on human malignant melanoma cells.

Bioelectrochemistry 2021 Mar 31;140:107813. Epub 2021 Mar 31.

Department of Bionano Engineering, Center for Bionano Intelligence Education and Research, Hanyang University, Ansan 426-791, South Korea. Electronic address:

Discovering new anticancer agents and analyzing their activities is a vital part of drug development, but it requires a huge amount of time and resources, leading to the increasing demands for more-effective techniques. Herein, a novel and simple cell-based electrochemical biosensor, referred to as a cytosensor, was proposed to investigate the electrochemical behavior of human skin malignant melanoma (SK-MEL28) cells and the anticancer effect of saponin on cell viability. To enhance both electrocatalytic properties and biocompatibility, gold nanoparticles were electrochemically deposited onto a conductive substrate, and poly-L-lysine was further added to the electrode surface. Electric signals from SK-MEL28 cells on the electrodes were obtained from cyclic voltammetry and differential pulse voltammetry. The cathodic peak current was proportional to the cell viability and showed a detection range of 2,880-40,000 cells per device with an excellent linear cell number-intensity relationship (R= 0.9952). Furthermore, the anticancer effect of saponin on SK-MEL28 cells was clearly established at concentrations higher than 20 μM, which was highly consistent with conventional assays. Moreover, the developed electrochemical cytosensor for evaluating anticancer effects enabled rapid (<2 min), sensitive (LOQ: 2,880cells/device), and non-invasive measurements, thus providing a new avenue for assessing the anticancer drugs in vitro.
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http://dx.doi.org/10.1016/j.bioelechem.2021.107813DOI Listing
March 2021

Functionalized ultra-fine bimetallic PtRu alloy nanoparticle with high peroxidase-mimicking activity for rapid and sensitive colorimetric quantification of C-reactive protein.

Mikrochim Acta 2021 Mar 9;188(4):119. Epub 2021 Mar 9.

Department of Bionano Engineering, Center for Bionano Intelligence Education and Research, Hanyang University, Ansan, 426-791, South Korea.

The in situ synthesis is reported of citric acid-functionalized ultra-fine bimetallic PtRu alloy nanoparticles (CA@PtRu ANPs) through a simple one-pot wet chemical method. The cost-efficient CA@PtRu ANPs with an average diameter of 3.2 nm revealed to have enhanced surface area, peroxidase-like activity, high stability, and adequate availability of functional groups to bind biomolecules. Along with nanoparticle surface area, the surface charge has also significantly affected the peroxidase-like activity and the colloidal suspension stability. As an excellent immobilization matrix and peroxidase mimic, the CA@PtRu ANPs were utilized to develop non-enzymatic colorimetric immunoassay for rapid, selective, and sensitive quantification of C-reactive protein (CRP) biomarkers. In this immunoassay, CA@PtRu ANPs serve as enzyme mimic that significantly amplifies the color signals, and amine-functionalized silica-coated magnetic microbeads (APTES/SiO@FeO) act as CRP-recognizing capture probes. The absorbance curves of colorimetric immunoassay were measured in wavelengths between 550 and 750 nm, and the maximum absorbance at 652 nm was used to establish a linear relationship between absorbance and CRP concentrations. The developed colorimetric immunoassay showed rapid and sensitive quantification of CRP levels from 0.01 to 180 μg mL with a LOD of 0.01 μg mL. Moreover, the mean recovery of CRP from spiked human serum samples lies between 97 and 109% (n = 3), which indicates that the proposed nanozyme-linked immunoassay has the potential to be used in rapid point-of-care applications.
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http://dx.doi.org/10.1007/s00604-021-04775-4DOI Listing
March 2021

Determination of glycated albumin using a Prussian blue nanozyme-based boronate affinity sandwich assay.

Anal Chim Acta 2020 Oct 20;1134:41-49. Epub 2020 Aug 20.

Department of Bionano Engineering, Hanyang University, Ansan, 426-791, South Korea. Electronic address:

Nanozymes are effective substitutes for natural enzymes and offer multiple advantages. Here, synthesized Prussian blue nanoparticles (PBNPs) exhibited excellent peroxidase-like activity, catalyzing the oxidation of 3,5,3',5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide within 1 min. Oxidized TMB (TMB) underwent a color change from transparent to blue and then yellow by a stop solution. Moreover, the TMB could be reduced on an indium tin oxide electrode, generating an electrochemical current, indicating that TMB can be used as a colorimetric and electrochemical indicator. The PBNPs modified with 3-aminophenylboronic acid (APBA) captured glycated albumin (GA) with a boronate affinity sandwich assay. As boronic acid binds to glycoproteins using cis-diol bonding, it can be used to detect GA. The APBA-modified PBNPs (PBBA) were involved with a sandwich complex formation and employed as nanozymes for the quantitative analysis of GA using colorimetric and electrochemical methods. Both methods showed strong linearities for different concentrations of GA. The results show that PBBA is a suitable alternative for natural enzymes and can be applied to sensitive determination of GA.
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http://dx.doi.org/10.1016/j.aca.2020.08.015DOI Listing
October 2020

One-pot synthesized citric acid-modified bimetallic PtNi hollow nanospheres as peroxidase mimics for colorimetric detection of human serum albumin.

Mater Sci Eng C Mater Biol Appl 2020 Nov 23;116:111231. Epub 2020 Jun 23.

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea. Electronic address:

The combination of Pt with low-cost transition metal is an effective way to diminish the bulk utilization of costly Pt and to design new nanostructured materials with improved enzyme-like activity. In the present work, citric acid-functionalized platinum-nickel hollow nanospheres (CA@PtNi hNS) were synthesized through a simple one-pot wet chemical method, which involves the galvanic replacement reaction between the Ni nanoparticles and the Pt precursor that leads to the formation of hollow nanostructures. Transmission electron spectroscopic images revealed the uniformity of the CA@PtNi hNS, with an average diameter of 10.3 ± 2 nm. Moreover, zeta potential, FTIR, and XPS measurements confirmed the existence of citric acid in the CA@PtNi hNS. During synthesis, the use of citric acid not only facilitates monodispersity but also provides a negative surface charge (-11 mV) to the CA@PtNi hNS that electrostatically attracts the 3,3',5,5'-Tetramethylbenzidine (TMB) substrate. As-prepared CA@PtNi hNS possessed excellent peroxidase-like activity due to rich Pt surfaces, large surface area, and heterogeneous interaction between Pt and Ni atoms. Furthermore, a nanozyme-linked immunosorbent assay (NLISA) for human serum albumin (HSA) detection was developed by replacing the enzyme in a standard enzyme-linked immunosorbent assay with CA@PtNi hNS. The CA@PtNi hNS based-NLISA showed sensitive detection of HSA concentrations ranging from 0 to 400 ng mL with a LOD of 0.19 ng mL and an average of 112% recovery of HSA from the spiked human plasma samples. The outcomes of the present study confirm the applicability of CA@PtNi hNS as substitutes for natural enzymes.
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http://dx.doi.org/10.1016/j.msec.2020.111231DOI Listing
November 2020

Electrochemical Immunoassay for Determination of Glycated Albumin using Nanozymes.

Sci Rep 2020 06 11;10(1):9513. Epub 2020 Jun 11.

Department of Bionano Engineering, Hanyang University, Ansan, 426 - 791, South Korea.

We developed a new nanozyme-based electrochemical immunoassay method for the monitoring of glycated albumin (GA) known to reflect short-term glycaemic levels. For this study, we synthesized urchin-like Pt nanozymes (uPtNZs) and applied them to colorimetric and electrochemical assays for sensitive determination of GA in total human serum albumin (tHSA) using 3,3',5,5'-tetramethylbenzidine (TMB) and thionine as substrates, respectively. The uPtNZs showed peroxidase-mimic activity in the presence of hydrogen peroxide. Boronic acid (BA)-agarose bead was used to capture GA through specific cis-diol interactions. uPtNZs were modified with GA antibody (GA-Ab) to form sandwich complexes with GA/BA-agarose bead. The amount of Ab-uPtNZ/GA/BA-agarose bead complex increased with increasing percentage of GA in 50 mg/mL tHSA. The colorimetric assay exhibited linearity from 0.02 to 10% (10 µg/mL - 5 mg/mL) GA with an LOD of 0.02% (9.2 µg/mL). For electrochemical assay, GA was detected from 0.01 to 20% (5 µg/mL - 10 mg/mL) with an LOD of 0.008% (3.8 µg/mL). The recovery values of measured GA in human plasma samples were from 106 to 107%. These results indicate that electrochemical assay using uPtNZs is a promising method for determining GA.
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http://dx.doi.org/10.1038/s41598-020-66446-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7289889PMC
June 2020

Early Impairment of Chopsticks Skills in Parkinsonism Suggests Progressive Supranuclear Palsy.

J Clin Neurol 2020 Apr;16(2):254-260

Department of Neurology, Hallym University Sacred Heart Hospital, Hallym University College of Medicine, Anyang, Korea.

Background And Purpose: Chopsticks are a primary eating utensil in East Asia, but systematic assessments of chopsticks skills in parkinsonian disorders is lacking. We aimed to identify any differences in chopsticks skills in the early stages of Parkinson's disease (PD) and atypical parkinsonism (AP), including progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and corticobasal syndrome (CBS).

Methods: We consecutively recruited 111 patients with PD and 74 with AP (40 with PSP, 30 with MSA, and 4 with CBS) who were in a drug-naïve state. The motor and cognitive functions of the patients were evaluated using a standardized protocol. Everyday chopsticks skills were evaluated using a chopsticks questionnaire developed in-house. The chopsticks skills test (CST) involved counting the number of pills that the subject was able to carry using chopsticks between two dishes separated by 20 cm within 20 seconds.

Results: Patient responses to the questionnaire indicating poor chopsticks skills ("I cannot pick up some of the food items" or "I cannot use chopsticks anymore") were present in 23.0% of AP patients and 30% of PSP patients, compared to only 5.6% of PD patients [odd ratio (OR)=5.07 and OR=7.29, ≤0.001 in both]. The performance in the CST was worse in PSP than in PD (<0.001). The CST results were correlated with hand motor skills including in the coinrotation test, timed figure-tapping test, and motor Unified Parkinson's Disease Rating Scale scores in all of the patient groups (<0.001). In PSP, a decline in visuospatial function and frontal executive function was associated with a poor performance in the CST in addition to poor motor performance (<0.05).

Conclusions: Impairments in chopsticks skills were more common in PSP than in PD during the early stages of parkinsonism. This suggests that early functional impairment of chopsticks skills can be used as a warning sign for PSP.
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http://dx.doi.org/10.3988/jcn.2020.16.2.254DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7174121PMC
April 2020

Pattern formation of metal-oxide hybrid nanostructures via the self-assembly of di-block copolymer blends.

Nanoscale 2019 Oct 25;11(40):18559-18567. Epub 2019 Jul 25.

Electronic Convergence Materials Division, Korea Institute of Ceramic Engineering & Technology (KICET), 101 Soho-ro, Jinju 52851, Republic of Korea.

The templated self-assembly of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) can effectively create ultrafine, well-ordered nanostructures in the range of 5-30 nm. However, the self-assembled BCP patterns remain limited to possible morphological geometries and materials. Here, we introduce a novel and useful self-assembly method of di-BCP blends capable of generating diverse hybrid nanostructures consisting of oxide and metal materials through the rapid microphase separation of A-B/B-C BCP blends. We successfully obtained various hybridized BCP morphologies which cannot be acquired from a single di-BCP, such as hexagonally arranged hybrid dot and dot-in-hole patterns by controlling the mixing ratios of the solvents with a binary solvent annealing process. Furthermore, we demonstrate how the binary solvent vapor annealing process can provide a wide range of pattern geometries to di-BCP blends, showing a well-defined spontaneous one-to-one accommodation in dot-in-hole nanostructures. Specifically, we show clearly how the self-assembled BCPs can be functionalized via selective reduction and/or an oxidation process, resulting in the excellent positioning of confined silica nanodots into each nanospace of a Pt mesh. These results suggest a new method to achieve the pattern formation of more diverse and complex hybrid nanostructures using various blended BCPs.
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http://dx.doi.org/10.1039/c9nr04038bDOI Listing
October 2019

In-vivo half-life and hypoglycemic bioactivity of a fusion protein of exenatide and elastin-based polypeptide from recombinant Saccharomyces cerevisiae.

J Biotechnol 2019 Sep 3;303:16-24. Epub 2019 Jul 3.

Department of Bionanotechnology, Graduate School, Hanyang University, Ansan, Gyeonggi-do, 15588, Republic of Korea; Immunoforge, Ltd., Seoul, 08826, Republic of Korea. Electronic address:

Exenatide (Ex) is a 39-amino acid peptide of glucagon-like peptide-1 (GLP-1) receptor agonist that was approved by the FDA in 2005 as a Type II diabetes treatment. It shows a 53% homology with GLP-1 but has an extended half-life (ca. 2.4 h) relative to GLP-1 (ca. 2-3 min). In this study, to further extend its in vivo half-life, we constructed a fusion protein (Ex-(EBP)-6xHis) using a biocompatible and inert elastin-based polypeptide (EBP) as a fusion partner. Valine was inserted into the guest position of the pentapeptide (VPGXG), no linker sequence was inserted in between the EBPs, and (EBP)-6xHis tag was attached to the C-terminus of exenatide. By using a recombinant Saccharomyces cerevisiae expression system, the fusion protein was expressed and secreted to the broth and purified by Ni-NTA affinity chromatography. Compared with the native exenatide, the physical half-life of the fusion protein was ca. 3.7-fold extended while approximately 72% of the in-vitro insulin secreting activity was maintained. However, the biological half-life measured by a glucose tolerance test (GTT) and the hypoglycemic test in mice was not significantly different from that of the native form. The effects of EBPylation on bioactivity and half-life of the fusion protein are similar to those of PEGylation. The result suggests that the bioactivity and half-life should be carefully balanced to obtain optimal fusion proteins. We expect that EBPylation using an optimal repeat number of EBP can be an alternative to chemical modification for therapeutic biobetters with extended half-life.
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http://dx.doi.org/10.1016/j.jbiotec.2019.06.304DOI Listing
September 2019

Hierarchical multi-level block copolymer patterns by multiple self-assembly.

Nanoscale 2019 Apr;11(17):8433-8441

Electronic Convergence Materials Division, Korea Institute of Ceramic Engineering & Technology (KICET) 101 Soho-ro, Jinju 52851, Republic of Korea.

Uniform, well-ordered sub-20 nm patterns can be generated by the templated self-assembly of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ). However, the self-assembled BCP monolayers remain limited in the possible structural geometries. Here, we introduce a multiple self-assembly method which uses di-BCPs to produce diverse morphologies, such as dot, dot-in-honeycomb, line-on-dot, double-dot, pondering, dot-in-pondering, and line-on-pondering patterns. To improve the diversity of BCP morphological structures, we employed sphere-forming and cylinder-forming poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) BCPs with a high χ. The self-assembled mono-layer and double-layer SiOx dot patterns were modified at a high temperature (∼800 °C), showing hexagonally arranged (dot) and double-hexagonally arranged (pondering) SiOx patterns, respectively. We successfully obtained additional new nanostructures (big-dot, dot-in-honeycomb, line-on-dot, pondering, dot-in-pondering, and line-on-pondering types) through a second self-assembly of cylinder-forming BCPs using the dot and pondering patterns as guiding templates. This simple approach can likely be extended to the multiple self-assembly of many other BCPs with good functionality, significantly contributing to the development of various nanodevices.
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http://dx.doi.org/10.1039/c9nr00774aDOI Listing
April 2019

An Isolated Skull Lesion in Syphilis.

Headache 2018 Jul 20;58(7):1122-1124. Epub 2018 May 20.

Department of Neurology, Dongtan Sacred Heart Hospital, College of Medicine, Hallym University, Hwaseong, Gyeonggi-Do, Republic of Korea.

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http://dx.doi.org/10.1111/head.13319DOI Listing
July 2018

Determination of glycated albumin using boronic acid-derived agarose beads on paper-based devices.

Biomicrofluidics 2018 Jan 1;12(1):014111. Epub 2018 Feb 1.

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

Self-monitoring of glycated albumin (GA), a useful glycemic marker, is an established method for preventing diabetes complications. Here, the paper-based lateral flow assay devices were developed for the sensitive detection of GA and the total human serum albumin (tHSA) in self-monitoring diabetes patients. Boronic acid-derived agarose beads were packed into a hole on a lateral flow channel. These well-coordinated agarose beads were used to capture GA through specific cis-diol interactions and to enhance the colorimetric signals by concentrating the target molecules. The devices exhibited large dynamic ranges (from 10 g/ml to 10 mg/ml for GA and from 10 mg/ml to 50 mg/ml for tHSA) and low detection limits (7.1 g/ml for GA and 4.7 mg/ml for tHSA), which cover the range of GA concentration in healthy plasma, which is 0.21-1.65 mg/ml (0.6%-3%). In determining the unknown GA concentrations in two commercial human plasma samples, the relative percentage difference between the values found by a standard ELISA kit and those found by our developed devices was 2.62% and 8.80%, which are within an acceptable range. The measurements of GA and tHSA were completed within 20 min for the total sample-to-answer diagnosis, fulfilling the demand for rapid analysis. Furthermore, the recovery values ranged from 99.4% to 110% in device accuracy tests. These results indicate that the developed paper-based device with boronic acid-derived agarose beads is a promising platform for GA and tHSA detection as applied to self-monitoring systems.
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http://dx.doi.org/10.1063/1.5021395DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5796828PMC
January 2018

Electrochemical Detection of Hydroxylamine via Au-Pt Alloy Nanoparticle-modified Single-walled Carbon Nanotube Electrodes.

Anal Sci 2017 ;33(9):993-998

Department of Bionano Engineering, Hanyang University.

In the present study, we developed an electrochemical sensor for highly sensitive detection of hydroxylamine using Au-Pt alloy nanoparticles. Au-Pt alloy nanoparticles were electrochemically deposited on a working electrode made of single-walled carbon nanotubes. The framework composition in the Au-Pt alloy nanoparticle was easily controlled by adjusting the Au:Pt composition ratio in the precursor solution. Morphological and chemical characterizations of the resulting Au-Pt alloy nanoparticles were performed using field emission scanning electron microscopy, X-ray diffraction, and energy dispersion X-ray spectroscopy. When the Au:Pt ratio in the precursor solution was 1:5, the ratio of Au:Pt atom in alloy nanoparticle was about 6:4. AuPt alloy nanoparticles were found to have the optimum synthetic ratio for hydroxylamine detection. The electrocatalytic performance of Au-Pt alloy nanoparticles in the presence of hydroxylamine was also characterized using cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In the chronoamperometric detection of hydroxylamine, the sensor exhibited a detection limit of 0.80 μM (S/N = 3) and a high sensitivity of 184 μA mM cm. Moreover, the amperometric response of the sensor in 1 mM hydroxylamine was stable for a long time (450 s). Long-term stability tests showed that the current responses to hydroxylamine were 96, 91 and 85% of the initial signal value after storage for 5, 10, and 20 days, respectively.
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http://dx.doi.org/10.2116/analsci.33.993DOI Listing
January 2018

Electrochemical Fabrication of Nanostructures on Porous Silicon for Biochemical Sensing Platforms.

Anal Sci 2016 ;32(6):681-6

Department of Bionano Engineering, Hanyang University.

We present a method for the electrochemical patterning of gold nanoparticles (AuNPs) or silver nanoparticles (AgNPs) on porous silicon, and explore their applications in: (1) the quantitative analysis of hydroxylamine as a chemical sensing electrode and (2) as a highly sensitive surface-enhanced Raman spectroscopy (SERS) substrate for Rhodamine 6G. For hydroxylamine detection, AuNPs-porous silicon can enhance the electrochemical oxidation of hydroxylamine. The current changed linearly for concentrations ranging from 100 μM to 1.32 mM (R(2) = 0.995), and the detection limit was determined to be as low as 55 μM. When used as SERS substrates, these materials also showed that nanoparticles decorated on porous silicon substrates have more SERS hot spots than those decorated on crystalline silicon substrates, resulting in a larger SERS signal. Moreover, AgNPs-porous silicon provided five-times higher signal compared to AuNPs-porous silicon. From these results, we expect that nanoparticles decorated on porous silicon substrates can be used in various types of biochemical sensing platforms.
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http://dx.doi.org/10.2116/analsci.32.681DOI Listing
January 2018

Large-scale plasma patterning of transparent graphene electrode on flexible substrates.

Langmuir 2015 Mar 25;31(9):2914-21. Epub 2015 Feb 25.

Department of Bionano Engineering, ‡Department of Chemical Engineering, and §Department of Materials Engineering, Hanyang University , Ansan 425-791, South Korea.

Graphene, a two-dimensional carbon material, has attracted significant interest for applications in flexible electronics as an alternative transparent electrode to indium tin oxide. However, it still remains a challenge to develop a simple, reproducible, and controllable fabrication technique for producing homogeneous large-scale graphene films and creating uniform patterns with desired shapes at defined positions. Here, we present a simple route to scalable fabrication of flexible transparent graphene electrodes using an oxygen plasma etching technique in a capacitively coupled plasma (CCP) system. Ascorbic acid-assisted chemical reduction enables the large-scale production of graphene with solution-based processability. Oxygen plasma in the CCP system facilitates the reproducible patterning of graphene electrodes, which allows controllable feature sizes and shapes on flexible plastic substrates. The resulting graphene electrode exhibits a high conductivity of 80 S cm(-1) and a transparency of 76% and retains excellent flexibility upon hard bending at an angle of ±175° and after repeated bending cycles. A simple LED circuit integrated on the patterned graphene film demonstrates the feasibility of graphene electrodes for use in flexible transparent electrodes.
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http://dx.doi.org/10.1021/la504443aDOI Listing
March 2015

A single-walled carbon nanotube thin film-based pH-sensing microfluidic chip.

Analyst 2014 Apr;139(8):2011-5

Department of Bionano Engineering, Hanyang University, Ansan 425-791, South Korea.

A novel microfluidic pH-sensing chip was developed based on pH-sensitive single-walled carbon nanotubes (SWCNTs). In this study, the SWCNT thin film acted both as an electrode and a pH-sensitive membrane. The potentiometric pH response was observed by electronic structure changes in the semiconducting SWCNTs in response to the pH level. In a microfluidic chip consisting of a SWCNT pH-sensing working electrode and an Ag/AgCl reference electrode, the calibration plot exhibited promising pH-sensing performance with an ideal Nernstian response of 59.71 mV pH(-1) between pH 3 and 11 (standard deviation of the sensitivity is 1.5 mV pH(-1), R(2) = 0.985). Moreover, the SWCNT electrode in the microfluidic device showed no significant variation at any pH value in the range of the flow rate between 0.1 and 15 μl min(-1). The selectivity coefficients of the SWCNT electrode revealed good selectivity against common interfering ions.
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http://dx.doi.org/10.1039/c3an02195eDOI Listing
April 2014

Microfluidic chips for immunoassays.

Annu Rev Anal Chem (Palo Alto Calif) 2013 14;6:119-41. Epub 2013 Mar 14.

Department of Bionanoengineering, Hanyang University, Ansan 426-791, South Korea.

The use of microfluidic chips for immunoassays has been extensively explored in recent years. The combination of immunoassays and microfluidics affords a promising platform for multiple, sensitive, and automatic point-of-care (POC) diagnostics. In this review, we focus on the description of recent achievements in microfluidic chips for immunoassays categorized by their detection method. Following a brief introduction to the basic principles of each detection method, we examine current microfluidic immunosensor detection systems in detail. We also highlight interesting strategies for sensitive immunosensing configurations, multiplexed analysis, and POC diagnostics in microfluidic immunosensors.
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http://dx.doi.org/10.1146/annurev-anchem-062012-092616DOI Listing
October 2013

Potential application of antibody-mimicking peptides identified by phage display in immuno-magnetic separation of an antigen.

J Biotechnol 2012 Oct 11;161(3):213-20. Epub 2012 Jul 11.

College of Bionanotechnology, Gachon University, Seongnam, 461-701, Republic of Korea.

Phage display was performed against human IgG (hIgG) through five rounds of 'biopanning'. Each round consisted of: (1) incubating a library of phage-displayed 12-mer peptides sequences on hIgG-coated magnetic beads, (2) washing the unbound phages, and (3) eluting the bound phages. The eluted phages were either amplified to enrich the pool of positive clones or subjected to the next round without amplification. Through ELISA, four clones (F9, D1, G5, and A10) showing specific binding affinity to hIgG were identified. Among these, F9 had the highest affinity (K(d)=6.2 nM), only one order of magnitude lower than the native anti-hIgG antibody (0.66 nM). Following the DNA sequences of the selected clones, four 12-mer peptides were chemically synthesized. Among them, D1 peptide showed the highest binding affinity to hIgG via SPR biosensor measurements. This peptide was conjugated to biofunctionalized magnetic beads, and its immuno-binding ability was compared with that of the native antibody immobilized to magnetic beads. The mol-to-mol binding efficacy of the peptide-coated magnetic beads was approximately 1000-fold lower than that of the antibody-coated magnetic beads. Our results suggest a feasibility of using antibody-mimicking peptides identified by phage display technique for immuno-magnetic separation of an antigen.
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http://dx.doi.org/10.1016/j.jbiotec.2012.06.039DOI Listing
October 2012

Electrochemical determination of cadmium and lead on pristine single-walled carbon nanotube electrodes.

Anal Sci 2012 ;28(7):699-704

Department of Bionano Engineering, Hanyang University, Ansan, South Korea.

A flexible, transparent, single-walled carbon nanotube (SWCNT) film electrode was prepared by vacuum filtering methods, followed by photolithographic patterning of a photoresist polymer on the SWCNT surface. The morphology of the SWCNT film electrode surface was characterized using a field-emission scanning electron microscope coupled to an energy-dispersive X-ray spectrophotometer. The electrodes were successfully used as a mercury-free electrochemical sensor for individual and simultaneous detection of cadmium (Cd(2+)) and lead (Pb(2+)) in 0.02 M HCl by square-wave stripping voltammetry. Some important operational parameters, including deposition time, deposition potential, square-wave amplitude, and square wave-frequency were optimized for the detection of Cd(2+) and Pb(2+). The newly developed sensor showed good linear behavior in the examined concentration. For individual Cd(2+) and Pb(2+) ion detection, the linear range was found from 0.033 to 0.228 ppm with detection limits of 0.7 ppb (R(2) = 0.985) for Cd(2+) and 0.8 ppb (R(2) = 0.999) for Pb(2+). For simultaneous detection, the linear range was found from 0.033 to 0.280 ppm with a limit of detection of 2.2 ppb (R(2) = 0.976) and 0.6 ppb (R(2) = 0.996) for Cd(2+) and Pb(2+), respectively. SWCNT film electrodes offered favorable reproducibility of ± 5.4% and 4.3% for Cd(2+) and Pb(2+), respectively. The experiments demonstrated the applicability of carbon nanotubes, specifically in the preparation of SWCNT films. The results suggest that the proposed flexible SWCNT film electrodes can be applied as simple, efficient, cost-effective, and/or disposable electrodes for simultaneous detection of heavy metal ions.
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http://dx.doi.org/10.2116/analsci.28.699DOI Listing
November 2012

Effects of operating parameters on the efficiency of liposomal encapsulation of enzymes.

Colloids Surf B Biointerfaces 2012 Jun 14;94:296-303. Epub 2012 Feb 14.

Department of Chemical Engineering, Hanyang University, Ansan, Republic of Korea.

Encapsulation of active proteins in the hydrophilic core of vesicular liposomes is important for developing a therapeutic protein carrier system. The efficiency of liposomal encapsulation of proteins is generally low. A better understanding of the fundamental mechanisms of encapsulation is needed to increase this efficiency. In this study we investigated the effects of operating parameters such as phospholipid concentration, buffer pH and ionic strength, protein size and surface charge, and liposome size on the enzyme encapsulation yield. Four model enzymes of different molecular weights and isoelectric points (trypsin, horseradish peroxidase, enterokinase and hyaluronidase) were encapsulated into three different sized liposomes (125 nm, 194 nm, and 314 nm in mean diameter). Relatively inert and neutral DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) was used as the main phospholipid in the liposomes. Size exclusion chromatography was used to separate the enzyme-encapsulated liposomes from the free enzyme, and the encapsulation yield was determined from the peak area. The encapsulation yield was generally low ranging from ca. 5% to 20%, and did not depend much on the molecular weight of the enzyme encapsulated. Larger liposomes had higher encapsulation yields. The electrostatic interaction between the phospholipid and enzyme was the most significant parameter in determining the encapsulation yield. Thus adjusting buffer pH and ionic strength and adding charged phospholipids to the liposome preparation to impart electric charge to the lipid bilayer could significantly improve the yield. This approach can be used to optimize the liposomal encapsulation of clinically significant proteins.
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http://dx.doi.org/10.1016/j.colsurfb.2012.02.008DOI Listing
June 2012

Simultaneous detection of ultratrace lead and copper with gold nanoparticles patterned on carbon nanotube thin film.

Analyst 2012 Apr 7;137(8):1888-94. Epub 2012 Mar 7.

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

Highly sensitive detection of a Pb(2+)-Cu(2+) mixture using gold nanoparticles patterned on single-walled carbon nanotube (AuNP-SWCNT) film is reported. The gold nanoparticles were deposited electrochemically on carbon nanotube film using a cyclic voltammetry technique. The film showed a homogeneous size and density that could be easily controlled by the potential scanning cycle and gold precursor concentration. Square wave stripping voltammetry (SWSV) was applied to the simultaneous detection of Pb(2+) and Cu(2+) under optimized conditions. The AuNP-SWCNT electrode exhibited a high increase in sensitivity with a limit of detection of 0.546 ppb (R(2) = 0.984) and 0.613 ppb (R(2) = 0.991) for Pb(2+) and Cu(2+) ions, respectively, in a mixture of Pb(2+)-Cu(2+) solution (S/N = 3, n = 5), and a good linear response in the range from 3.31 ppb to 22.29 ppb. The electrode exhibited high reproducibility in repetitive measurements with a relative standard deviation as low as 4.2% and 2.6% for Pb(2+) and Cu(2+) ions, respectively. An interference study showed that Sb(3+), As(3+), Zn(2+), Ca(2+), and Na(+) ions did not have a significant effect. This study demonstrated an alternative approach to the rapid and reliable detection of heavy metals of environmental interest.
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http://dx.doi.org/10.1039/c2an16020jDOI Listing
April 2012

Enzyme kinetic measurements using a droplet-based microfluidic system with a concentration gradient.

Anal Chem 2011 Mar 31;83(5):1603-8. Epub 2011 Jan 31.

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

In this paper, we propose a microfluidic device that is capable of generating a concentration gradient followed by parallel droplet formation within channels with a simple T-junction geometry. Linear concentration gradient profiles can be obtained based on fluid diffusion under laminar flow. Optimized conditions for generating a linear concentration gradient and parallel droplet formation were investigated using fluorescent dye. The concentration gradient profile under diffusive mixing was dominated by the flow rate at sample inlets, while parallel droplet formation was affected by the channel geometry at both the inlet and outlet. The microfluidic device was experimentally characterized using optimal layout and operating conditions selected through a design process. Furthermore, in situ enzyme kinetic measurements of the β-galactosidase-catalyzed hydrolysis of resorufin-β-d-galactopyranoside were performed to demonstrate the application potential of our simple, time-effective, and low sample volume microfluidic device. We expect that, in addition to enzyme kinetics, drug screening and clinical diagnostic tests can be rapidly and accurately performed using this droplet-based microfluidic system.
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http://dx.doi.org/10.1021/ac102472aDOI Listing
March 2011

Control of ZnO morphologies on carbon nanotube electrodes and electrocatalytic characteristics toward hydrazine.

Chem Commun (Camb) 2011 Jan 15;47(3):938-40. Epub 2010 Nov 15.

Department of Bionano Engineering, Hanyang University, Ansan 425-791, South Korea.

We controlled the morphologies of zinc oxide (ZnO) nanostructures on single-walled carbon nanotube electrodes by an electrochemical deposition method and investigated the dependence of the electrocatalytic characteristics toward hydrazine on the different morphologies. ZnO nanorods provided high electrocatalytic activity with unique electrochemical behaviours, associated with the H(+) ion generated by the electro-oxidation of hydrazine.
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http://dx.doi.org/10.1039/c0cc03848bDOI Listing
January 2011

Highly reproducible immunoassay of cancer markers on a gold-patterned microarray chip using surface-enhanced Raman scattering imaging.

Biosens Bioelectron 2011 Jan 17;26(5):2135-41. Epub 2010 Sep 17.

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

This paper reports a highly reproducible immunoassay of cancer markers using surface-enhanced Raman scattering (SERS) imaging. SERS is a highly sensitive detection method but it is limited in its ability to achieve reproducible signal enhancement because of the difficulty with precisely controlling the uniform distribution of hot junctions. Consequently, inconsistent enhancement prevents the wide exploitation of SERS detection as a bio-detection tool for quantitative analysis. To resolve this problem, we explored the use of a SERS imaging-based immunoassay. For this purpose, Raman reporter-labeled hollow gold nanospheres (HGNs), were manufactured and antibodies were immobilized onto their surfaces for targeting specific antigens. After the formation of sandwich immunocomplexes using these functional HGNs on the surfaces of gold patterned wells, the SERS mapping images were measured. For target protein markers, 12×9 pixels were imaged using a Raman mapping technique in the 0-10(-4) g/mL concentration range, and the SERS signals for 66 pixels were averaged. Here, the SERS imaging-based assay shows much better correlations between concentration and intensity than does the conventional point-based assay. The limits of detection were determined to be 0.1 pg/mL and 1.0 pg/mL for angiogenin (ANG) and alpha-fetoprotein (AFP), respectively. This detection sensitivity is increased by three or four orders of magnitude over that of conventional ELISA method. The detectable dynamic range for SERS imaging (10(-4)-10(-12) g/mL) is also much wider than that for ELISA (10(-6)-10(-9) g/mL).
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http://dx.doi.org/10.1016/j.bios.2010.09.021DOI Listing
January 2011

Electrochemical characterization of a single-walled carbon nanotube electrode for detection of glucose.

Anal Chim Acta 2010 Jun 13;671(1-2):36-40. Epub 2010 May 13.

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

We developed glucose biosensing electrodes using single-walled carbon nanotube (SWCNT) films on flexible, transparent poly(ethylene terephthalate). The homogeneous SWCNT films were fabricated by a vacuum filtration method, and the averaged resistivity and transparency of the fabricated flexible SWCNT films were 400 Omega sq(-1) and 80%, respectively. The glucose sensing electrodes were constructed by encapsulating glucose oxidase (GOx) by Nafion binder into the SWCNT film, and the variation in current response as a function of enzyme loading amount, Nafion thickness were investigated. 30 mg mL(-1) GOx and 2% Nafion was optimal for the detection of glucose. When ferrocene monocarboxylic acid (FMCA) was introduced as diffusional electron mediator, the current responses toward glucose of the Nafion/GOx/SWCNT electrodes in glucose solution containing FMCA were dramatically improved, and the developed sensor was independent of oxygen. In the application of GOx immobilized SWCNT films for glucose detection, a linear electrical response was observed for concentrations ranging from 0.25 to 3.0 mM, and the detection limit and the sensitivity were assessed to be 97 microM and 9.32 microA mM(-1) cm(-2), respectively. Moreover, according to the Lineweaver-Burk plot, the apparent Michaelis-Menten constant was calculated to be 23.8 mM, and the current responses did not interfere with coexisting electroactive species, indicating that Nafion is an effective permselective polymer barrier.
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http://dx.doi.org/10.1016/j.aca.2010.05.010DOI Listing
June 2010

On-chip immunoassay using surface-enhanced Raman scattering of hollow gold nanospheres.

Anal Chem 2010 Jun;82(12):5290-5

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

A surface-enhanced Raman scattering (SERS)-based gradient optofluidic sensor has been developed for a fast and sensitive immunoassay. In this work, a novel microfluidic sensor with functional internal structures has been designed and fabricated. This sensor is composed of three compartments consisting of the gradient channel that serially dilutes the target marker, the injection and mixing area of antibody-conjugated hollow gold nanospheres and magnetic beads, and the trapping area of sandwich immunocomplexes using multiple solenoids. Quantitative analysis of a specific target marker is performed by analyzing its characteristic SERS signals. This SERS-based gradient optofluidic sensor can replace the set of microwells or microtubes used in manual serial dilutions that have been traditionally used in enzyme-linked immunosorbent assay (ELISA)-type assays. The limit of detection for rabbit immunoglobin (IgG) is estimated to be 1-10 ng/mL. This novel SERS-based optofluidic immunoassay system is expected to be a powerful clinical tool for the fast and sensitive medical diagnosis of a disease.
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http://dx.doi.org/10.1021/ac100736tDOI Listing
June 2010

Electrochemical patterning of transparent single-walled carbon nanotube films on plastic substrates.

Langmuir 2010 Jun;26(11):9136-41

Department of Bionano Engineering, Hanyang University, Ansan 426-791, South Korea.

We report a new patterning method for single-walled carbon nanotubes (SWCNTs) films on flexible, transparent poly(ethylene terephthalate) using electrochemical etching in an aqueous electrolyte solution. Electrochemical etching of the SWCNT films patterned with photoresist polymer was accomplished in a three-electrode system, and the electrochemically patterned SWCNT films were then characterized by scanning electron microscopy (SEM) and Raman spectroscopy. The voltammetry curve showed that SWCNTs underwent drastic oxidation above an applied potential of 1.315 V with the generation of gas bubbles, and the oxidation current became constant above 2.6 V due to the mass transfer limit. SEM images showed that the networks of SWCNTs in the area protected with the photoresist polymer had no damage and vivid connections were obvious, while the connections and shapes of SWCNTs in the area exposed to electrochemical etching were indistinct and slightly damaged. In the Raman spectra of the area protected with the photoresist polymer and the exposed SWCNT area, the intensity ratio of the D-line to the G-line increased from 0.077 to 1.136, which indicated that the ordered carbons of the SWCNT film gradually became amorphous carbons due to electrochemical etching. For optimal patterning, the electrochemical etchings of SWCNT films were performed under various conditions (the applied potential, pH of the electrolyte solution, and electrolyte concentration). An applied potential of 3.0 V in 0.1 M NaCl electrolyte solution (pH 7.0) was optimal for homogeneous electrochemical patterning of SWCNT films. In an electrochemiluminescence reaction, the SWCNT films patterned by this technique could be used successfully as flexible and transparent electrodes.
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http://dx.doi.org/10.1021/la904642kDOI Listing
June 2010

Edge-directed [(M2)2L4] tetragonal metal-organic polyhedra decorated using a square paddle-wheel secondary building unit.

Chem Commun (Camb) 2010 Mar 15;46(12):2049-51. Epub 2010 Feb 15.

Department of Chemistry and Applied Chemistry, Hanyang University, Ansan, Kyunggi-do, 426-791, Korea.

A general strategy was developed for edge-directed self-assembly of tetragonal metal-organic polyhedra (MOPs) having a C(4) symmetry Cu(II)(2)(COO)(4) paddle-wheel as a secondary building unit, using C(2) symmetric dicarboxylic ligands as pincer-type primary building units.
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http://dx.doi.org/10.1039/b925335aDOI Listing
March 2010

Electrochemical patterning of gold nanoparticles on transparent single-walled carbon nanotube films.

Chem Commun (Camb) 2009 Oct 10(37):5549-51. Epub 2009 Aug 10.

Department of Applied Chemistry, Hanyang University, Ansan 425-791, South Korea.

We report a simple, low cost, electrochemical deposition method to pattern gold nanoparticles on flexible, transparent, single-walled carbon nanotube (SWCNT) films, and demonstrate the application of the gold-patterned SWCNT films as surface-enhanced Raman spectroscopy substrates and biosensing electrodes for non-enzymatic glucose detection.
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http://dx.doi.org/10.1039/b906939aDOI Listing
October 2009

Patterning of single-walled carbon nanotube films on flexible, transparent plastic substrates.

Langmuir 2010 Jan;26(1):598-602

Department of Applied Chemistry, Hanyang University, Ansan 425-791, South Korea.

We report a simple patterning method for single-walled carbon nanotubes (SWCNTs) films on flexible, transparent poly(ethylene terephthalate) using an O(2)-plasma technique in a capacitively coupled plasma (CCP) system. The homogeneous SWCNT films in a large area were fabricated by the vacuum filtration method. The plasma patterning process of SWCNT films includes conventional photolithography and subsequent O(2)-plasma treatment. During the plasma treatment, SWCNTs underneath the patterned photoresist polymer are protected from etching and damage by O(2)-plasma while the exposed SWCNTs are destroyed. The morphological changes and the effect of plasma treatment on the chemical properties of SWCNT films were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The physical properties of SWCNT films such as transparency and conductivity were systematically characterized under various plasma conditions. In an electrochemiluminescence reaction, the SWCNT films patterned by the CCP system-based O(2)-plasma treatment could be used as flexible and transparent electrodes.
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http://dx.doi.org/10.1021/la9021273DOI Listing
January 2010