Jongcheol Hong

Response to cardiac markers in human serum analyzed by guided-mode resonance biosensor.

Cardiac markers in human serum with concentrations less than 0.1 ng/mL were analyzed by use of a guided-mode resonance (GMR) biosensor. Cardiac troponin I (cTnI), creatine kinase MB (CK-MB), and myoglobin (MYO) were monitored in the serum of both patients and healthy controls. Dose-response curves ranging from 0.05 to 10 ng/mL for cTnI, from 0.1 to 10 ng/mL for CK-MB, and from 0.03 to 1.7 μg/mL for MYO were obtained. The limits of detection (LOD) for cTnI, CK-MB, and MYO were less than 0.05, 0.1, and 35 ng/mL, respectively. Analysis time was 30 min, which is short enough to meet clinical requirements. Antibody immobilization and the hydrophilic properties of the guided-mode resonance filter (GMRF) surface were investigated by X-ray photoelectron spectroscopy (XPS) and by monitoring the peak wavelength shift and water contact angle (CA). Both assays used to evaluate the surface density of the immobilized antibodies, a sandwich enzyme-linked immunosorbent assay (ELISA) and a sandwich immunogold assay, showed that the antibodies were successfully immobilized and sufficiently aligned to detect the low concentration of biomarkers. Our results show that the GMR biosensor will be very useful in developing low-cost portable biosensors that can screen for cardiac diseases.

Prediction of the limit of detection of an optical resonant reflection biosensor

A prediction of the limit of detection of an optical resonant reflection biosensor is presented. An optical resonant reflection biosensor using a guided-mode resonance filter is one of the most promising label-free optical immunosensors due to a sharp reflectance peak and a high sensitivity to the changes of optical path length. We have simulated this type of biosensor using rigorous coupled wave theory to calculate the limit of detection of the thickness of the target protein layer. Theoretically, our biosensor has an estimated ability to detect thickness change approximately the size of typical antigen proteins. We have also investigated the effects of the absorption and divergence of the incident light on the detection ability of the biosensor.

Noncollinear correlated photon pair source in the 1550 nm telecommunication band.

We present a source of noncollinear correlated photon pairs in the standard 1550 nm telecommunication band. They are generated by a spontaneous parametric down-conversion process and emitted in a cone because of type-I noncollinear phase matching. Within the band, the source gives a completely flexible choice of the frequencies of the photon pairs, and correlation properties related to spatial momentum as well as energy and time can easily be utilized.We characterize the source by measuring the spatial intensity distribution of the down-converted light and by performing coincidence counting.

Enhancement of Performance of Si Nanocrystal Light-Emitting Diodes by Using Ag Nanodots

Effects of Ag nanodots on silicon nanocrystal (nc-Si) light-emitting diodes (LEDs) are investigated. The electrical property of the nc-Si LED with Ag nanodots was enhanced compared to that of the nc-Si LED without ones. This was attributed to the increase in the electric field due to the formation of Ag nanodots at the contact interface, indicating that the current could flow more efficiently from the indium tin oxide layer to n-SiC film. The formation of Ag nanodots with a size of 3~6 nm was confirmed by using a high-resolution transmission electron microscope analysis. Moreover, light output power of the nc-Si LED with Ag nanodots was enhanced

Sensitivity response to coating material thickness for an optical resonant reflective biosensor based on a guided mode resonance filter

Sensitivity is a very important parameter for biosensor applications. We have numerically and experimentally studied the sensitivity and linewidth responses of optical resonant reflective biosensors to the thickness of high refractive index materials coating the grating layer used to create a guided mode. Zero sensitivity, which may create serious problems in biosensors, is obtained when the coating material has a relatively low refractive index and a thin coating thickness (near the cutoff condition in which a high index layer is no longer capable of acting as a waveguide). The sensitivity and linewidth are greatly influenced by the thickness of the coating material. The thickness also has an optimal state, which is a very important factor for designing highly sensitive optical resonant reflective biosensors using a guided mode resonance filter.

Portable guided-mode resonance biosensor platform for point-of-care testing

It represents a viable solution for the realization of a portable biosensor platform that could screen/diagnose acute myocardial infarction by measuring cardiac marker concentrations such as cardiac troponin I (cTnI), creatine kinase MB (CK-MB), and myoglobin (MYO) for application to u-health monitoring system. The portable biosensor platform introduced in this presentation has a more compact structure and a much higher measuring resolution than a conventional spectrometer system. Portable guided-mode resonance (GMR) biosensor platform was composed of a biosensor chip stage, an optical pick-up module, and a data display panel. Disposable plastic GMR biosensor chips with nano-grating patterns were fabricated by injection–molding. Whole blood filtration and label-free immunoassay were performed on these single chips, automatically. Optical pick-up module was fabricated by using the miniaturized bulk optics and the interconnecting optical fibers and a tunable VCSEL (vertical cavity surface emitting laser). The reflectance spectrum from the GMR biosensor was measured by the optical pick-up module. Cardiac markers in human serum with concentrations less than 0.1ng/mL were analyzed using a GMR biosensor. Analysis time was 30min, which is short enough to meet clinical requirements. Our results show that the GMR biosensor will be very useful in developing lowcost portable biosensors that can screen for cardiac diseases.

A Compact Tunable VCSEL and a Built-in Wavelength Meter for a Portable Optical Resonant Reflection Biosensor Reader

This study reports a portable and precision photonic biosensor reader that can measure the concentration of a particular antigen using an optical resonant reflection biosensor (ORRB). To create a compact biosensor reader, a compact tunable vertical-cavity surface-emitting laser (VCSEL) and a compact built-in wavelength meter were manufactured. The wavelength stability and accuracy of the compact built-in wavelength meter were measured to be less than 0.02 nm and 0.06 nm, respectively. The tunable VCSEL emission wavelength was measured with the compact built-in wavelength meter, it has a fast sweep time (~ 10 seconds) and a wide tuning range (> 4 nm) that are sufficient for biosensor applications based on ORRB. The reflection spectrum of a plastic based ORRB chip was measured by the fabricated portable photonic biosensor reader using the VCSEL and wavelength meter. Although the reader is the size of a palmtop device, it could make a precise measurement of the peak wavelength on equal terms with a conventional bulky optical spectrometer.

Improvement in light emission of Si nanocrystal LED using surface plasmons

We investigate the effects of surface plasmons (SPs) by Au nanopartilces (NPs) on performance of silicon nanocrystals light-emitting diodes. The light emission was enhanced due to the localized SPs by Au NPs.

Effects of electron injection efficiency on performances of Si nanocrystal light‐emitting diodes

We have investigated the effects of electron injection efficiency on the electrical and optical performances of the nc‐Si LEDs. The current‐voltage curves of nc‐Si LED with 6‐periods of SiCN/SiC multiple electron injection layers was better than that of nc‐Si LED with single SiC electron injection layer. This can be attributed to the increase in an electron density of the 6‐periods of SiCN/SiC multiple electron layers compared to that of the single SiC electron injection layer because the electron density of SiCN layer is higher than SiC layer. Light output power of the LED with 6‐periods of SiCN/SiC multiple electron injection layers was improved by 50% compared to that of LED with single SiC electron injection layer. We show here that the use of the multiple electron injection structure could be used to realize a highly efficient nc‐Si LED.

Effects of an Undoped Si1 − x C x Buffer Layer on Performance of Si Nanocrystal Light-Emitting Diodes

We report the effects of introducing an undoped Si 1-x C x buffer layer between a silicon nanocrystal (nc-Si) active layer and an n-type SiC layer on the performance of the nc-Si light-emitting diodes (LEDs). The electrical property of an nc-Si LED with a buffer layer was greatly improved compared to that of an nc-Si LED without a buffer layer. Moreover, the light output power of the nc-Si LED with a buffer layer was enhanced by a factor of 2. By employing a buffer layer, the efficiency of electron injection into the nc-Si layer was enhanced, which resulted in an increase in the light output power. The data show that the introduction of an undoped Si 1-x C x buffer layer is a very effective way to improve the performance of nc-Si LEDs.