Young Wook Chang

A carbon nanotube metal semiconductor field effect transistor-based biosensor for detection of amyloid-beta in human serum.

We have developed a carbon nanotube (CNT) film-based biosensor with a metal semiconductor field effect transistor structure (MESFET). A gold top gate was deposited on the middle of the CNT channel and probe antibodies were immobilized on the gold top gate with an antibody-binding protein, protein G or Escherichia coli outer membrane (OM) with autodisplayed Z-domains of protein A. These CNT-MESFET biosensors exhibited a higher sensitivity than the CNT-FET biosensor with probe antibodies immobilized using a chemical linker, since the orientation of immobilized antibodies was controlled by the antibody-binding proteins. In addition, nonspecific binding was effectively inhibited by E. coli OM. Using the CNT-MESFET biosensors with E. coli OM containing Z domain, we detected amyloid-β (Aβ) in human serum, one of the biomarkers for early diagnosis of Alzheimers disease. Aβ at the level of 1 pg/mL in human serum could be measured in real-time and without labeling, which was lower than a limit of detection for plasma Aβ using an enzyme-linked immune sorbent assay. These results suggested that our CNT-MESFET biosensors might be applicable for an early diagnosis of Alzheimers disease.

Electrically refreshable carbon-nanotube-based gas sensors

We report electrically refreshable carbon-nanotube (CNT)-based gas sensors with a field effect transistor (FET) structure. The sensors can be refreshed by applying a negative gate voltage pulse in NO2 and a positive gate voltage pulse in NH3. Furthermore, the temporal response of the conductance to the gate voltage pulse is observed to be dependent on the gas species, but independent of gas concentration. These results show the possibility of distinguishing gas species using CNT-FET sensors.

Carbon Nanotube-Based Dual-Mode Biosensor for Electrical and Surface Plasmon Resonance Measurements

We have developed carbon nanotube-based dual-mode biosensors with a metal semiconductor field effect transistor structure on a quartz substrate. DNA hybridization occurring on the Au top gate can be detected by simultaneously measuring the change in the electrical conductance and the surface plasmon resonance (SPR). Since electrical and SPR measurements offer high sensitivity and reliability, respectively, this dual-mode biosensor is expected to provide both of these features.

Development of SPR biosensor for the detection of human hepatitis B virus using plasma-treated parylene-N film

A plasma-treated parylene-N film was presented for the immobilization of proteins through physical adsorption. The changes in surface properties of the parylene-N film after plasma-treatment were analyzed using contact angle microscopy and AFM. To demonstrate the high protein-immobilization efficiency of the plasma-treated parylene-N film, the immobilization efficiencies of differently modified surfaces were compared using model proteins with different surface charges, such as streptavidin (pI=5, negatively charged at pH 7), horseradish peroxidase (pI=6.6, nearly neutral at pH 7), and avidin (pI=10, positively charged at pH 7). The application of the plasma-treated parylene-N film as an SPR biosensor was also tested by immobilizing model proteins. An SPR biosensor based on the plasma-treated parylene-N film was developed for the detection of the human hepatitis virus surface antigen (HBsAg), and the plasma-treated parylene-N film was estimated to improve the sensitivity of SPR biosensor as much as 1000-fold by enhancing immobilization of receptor antibodies.

A capacitive biosensor based on an interdigitated electrode with nanoislands

A capacitive biosensor based on an interdigitated electrode (IDE) with nanoislands was developed for label-free detection of antigen-antibody interactions. To enable sensitive capacitive detection of protein adsorption, the nanoislands were fabricated between finger electrodes of the IDE. The effect of the nanoislands on the sensitive capacitive measurement was estimated using horseradish peroxidase (HRP) as a model protein. Additionally, a parylene-A film was coated on the IDE with nanoislands to improve the efficiency of protein immobilization. By using HRP and hepatitis B virus surface antigen (HBsAg) as model analytes, the effect of the parylene-A film on the capacitive detection of protein adsorption was demonstrated.

Chemiluminescence lateral flow immunoassay based on Pt nanoparticle with peroxidase activity.

A lateral flow immunoassay (LF-immunoassay) with an enhanced sensitivity and thermostability was developed by using Pt nanoparticles with a peroxidase activity. The Pt nanoparticles were synthesized by citrate reduction method, and the peroxidase activity of Pt nanoparticles was optimized by adjusting reaction conditions. The peroxidase activity was estimated by using Michaelis-Menten kinetics model with TMB as a chromogenic substrate. The kinetics parameters of KM and Vmax were calculated and compared with horseradish peroxidase (HRP). The thermal stability of the Pt nanoparticles was compared with horseradish peroxidase (HRP) according to the storage temperature and long-term storage period. The feasibility of lateral flow immunoassay with a chemiluminescent signal band was demonstrated by the detection of human chorionic gonadotropin (hCG) as a model analyte, and the sensitivity was determined to be improved by as much as 1000-fold compared to the conventional rapid test based on colored gold-colloids.

Effectively enhanced sensitivity of a polyaniline-carbon nanotube composite thin film bolometric near-infrared sensor

The polyaniline–carbon nanotube composite thin film bolometric near-infrared sensor exhibited more than a two orders of magnitude sensitivity enhancement over both the polyaniline thin film and carbon nanotube network NIR sensor. We also investigated the mechanism of the effectively enhanced sensitivity of the composite material and demonstrated that it is a synergistic effect due to the higher heat generation of carbon nanotubes and higher temperature coefficient of resistance of polyaniline.

Scaling behaviors for resistive memory switching in NiO nanowire devices

We investigated scaling behaviors for NiO nanowire array devices with different nanowire diameters. Plots of the reset current and the third harmonic generation signal as a function of the on-state resistance (R0) show scaling behaviors for all devices, such as NiO film devices. However, the scaling exponents of NiO nanowire devices were different from those of NiO film devices, and hence the fractal dimension estimated from the scaling exponent was smaller for the NiO nanowire devices than for the NiO film devices. This decrease in the fractal dimension was attributed to the confinement of the conducting filaments within each nanowire.

One-step electrochemical fabrication of vertically self-organized silver nanograss

Fabrication of one dimensional metal nanomaterials offers many beneficial aspects due to their unique size- and shape-dependent characteristics. However, facile fabrication of a robust one dimensional nanostructure has still remained a great challenge. Here, we developed a new synthetic route of one-step electrochemical deposition of silver nanograss without the assistance of a template. By applying an overpotential of −2.0 V (vs. Ag/AgCl) under aqueous alkaline conditions, silver nanograss with a slight tilt in a randomly oriented direction was spontaneously formed on the working electrode surface. Two applications that utilize advantageous features of this silver nanograss were demonstrated: (i) an efficient surface-enhanced Raman scattering substrate for a chemical sensor and (ii) an enzyme-less hydrogen peroxide sensor. Compared to silver nanowire arrays fabricated using anodized aluminum oxide (AAO) templates, the silver nanograss exhibited comparable hydrogen sensing due to its catalytic hydrogen peroxide reduction activity and produced a much stronger surface-enhanced Raman spectroscopy (SERS) signal due to its innate structure.

Optoelectric Properties of Gate-Tunable MoS 2 /WSe 2 Heterojunction

Two dimensional transition-metal dichalcogenides (TMDs) semiconductors are attractive materials for optoelectric devices because of their direct energy bandgap and transparency. To investigate the feasibility of transparent p-n junctions, we have fabricated heterojunctions consisting of WSe2 and MoS2 since WSe2 and MoS2 with proper electrode metals exhibit p-type and n-type behaviors, respectively. These heterojunctions showed rectifying behaviors, indicating that p-n junctions were formed. In addition, photocurrent and photovoltaic effects were observed under light illumination, which were dependent on the gate voltage. Possible origins of gate-tunability are discussed.