Dong-guk Cho

Real-time monitoring of geosmin and 2-methylisoborneol, representative odor compounds in water pollution using bioelectronic nose with human-like performance.

A bioelectronic nose for the real-time assessment of water quality was constructed with human olfactory receptor (hOR) and single-walled carbon nanotube field-effect transistor (swCNT-FET). Geosmin (GSM) and 2-methylisoborneol (MIB), mainly produced by bacteria, are representative odor compounds and also indicators of contamination in the water supply system. For the screening of hORs which respond to these compounds, we performed CRE-luciferase assays of the two odorants in heterologous cell system. Human OR51S1 for GSM and OR3A4 for MIB were selected, and nanovesicles expressing the hORs on surface were produced from HEK-293 cell. Carbon nanotube field-effect transistor was functionalized with the nanovesicles. The bioelectronic nose was able to selectively detect GSM and MIB at concentrations as low as a 10 ng L(-1). Furthermore, detection of these compounds from the real samples such as tap water, bottled water and river water was available without any pretreatment processes.

Ultra-high responsivity, silicon nanowire photodetectors for retinal prosthesis

In this paper, a novel silicon nanowire photodetector on a flexible substrate is presented for replacing the function of photoreceptors in the retina to restore vision for the blind. An extremely high surface-to-volume-ratio characteristic of nanowire is capable of developing highly-sensitive photonic sensors. Therefore, a nanowire photodetector can be used as a stand-alone visual perception device without an external camera. The nanowire photodetector is first fabricated on a rigid substrate, and then transferred to a flexible substrate to fit the curvature of an eyeball. Experimental results using the fabricated silicon nanowire photodetector show very high photosensitivity and photoresponsivity for a wide range of light intensities and wavelengths. Mechanical bending tests are performed, and the results show that the optical performance of the flexible photodetector is well-preserved after repeated bending of 200 times. The presented performance evaluation results indicate the first viable alternative to using a camera for image acquisition.

Synthetic nanowire/nanotube-based solid substrates for controlled cell growth

The behaviour of cells can be controlled by various microenvironments such as nanostructured cell-culture substrates with controlled nanotopography and chemical properties. One of promising substrates for controlled cell growth is a solid substrate comprised of synthetic one-dimensional nanostructures such as polymer nanofibers, carbon-based nanotubes/nanofibers, and inorganic nanowires. Such nanotube/nanowire structures have a similar dimension as extracellular matrix fibers, and their nanotopography and chemical properties can be easily controlled, which expands their possible applications in controlling the growth and differentiation of cells. This paper provides a concise review on the recent applications of solid substrates based on synthetic nanowires/nanotubes for controlled cell growth and differentiation.

Nanovesicle-based platform for the electrophysiological monitoring of aquaporin-4 and the real-time detection of its antibody

Aquaporin-4 (AQP4) water channel protein transports water molecules across cell membranes bidirectionally and involves in a neurological disorder, neuromyelitis optica (NMO) caused by anti-AQP4 antibodies. Here, we developed a platform based on nanovesicle-carbon nanotube hybrid nanostructures for the real-time detection of anti-AQP4 antibodies and the electrophysiological monitoring of AQP4 activities. Using the hybrid device, we could detect anti-AQP4 antibodies with a high sensitivity and estimate the binding constants under different osmotic conditions. The results show AQP4 had a better affinity to anti-AQP4 antibodies under hyper-osmotic conditions than normal conditions. Furthermore, our device can be utilized to study the real-time cellular responses related with AQP4 such as those to different osmotic stresses. This nanovesicle-based platform can be a simple but versatile tool for basic research about AQP4 and related biomedical applications such as disease diagnostics.

Magnetically-refreshable receptor platform structures for reusable nano-biosensor chips.

We developed a magnetically-refreshable receptor platform structure which can be integrated with quite versatile nano-biosensor structures to build reusable nano-biosensor chips. This structure allows one to easily remove used receptor molecules from a biosensor surface and reuse the biosensor for repeated sensing operations. Using this structure, we demonstrated reusable immunofluorescence biosensors. Significantly, since our method allows one to place receptor molecules very close to a nano-biosensor surface, it can be utilized to build reusable carbon nanotube transistor-based biosensors which require receptor molecules within a Debye length from the sensor surface. Furthermore, we also show that a single sensor chip can be utilized to detect two different target molecules simply by replacing receptor molecules using our method. Since this method does not rely on any chemical reaction to refresh sensor chips, it can be utilized for versatile biosensor structures and virtually-general receptor molecular species.

Long-term In vivo Biocompatibility Evaluation of MEMS Retinal Tack for Retinal Prosthesis

In this paper, long-term (1 year) in vivo biocompatibility evaluation of silicon retinal tack is presented. Such a long-term in vivo experiment of biocompatibility has not been reported so far in the retinal prosthesis research field. Microscopic histological examinations of retina indicate no inflammatory infiltrates, and scanning electron microscope (SEM) images reveal neither chemical reactions nor mechanical fractures of the device. In addition, for the necessity of soft and elastic retinal tack, poly-methyl-methacrylate (PMMA) retinal tack is fabricated and mechanically characterized. The results indicate that PMMA retinal tack is also suitable for mechanical fixation of micro-electrode array and an in vivo experiment is in progress.

Nanoscale anomalous noise source switching with a trap-free current transition in a PEDOT:PSS film

We imaged localized charge traps in a PEDOT:PSS film by using a scanning noise microscopy (SNM) system and observed anomalous noise source switching behaviors affecting the electrical characteristics of the film. The SNM system enabled us to measure the localized electrical current and noise maps of a PEDOT:PSS film with nanoscale resolution. The measured maps of the currents and noises were utilized to calculate effective charge trap densities in the film. As a result, we found non-homogeneous distributions of currents and effective charge trap densities on the localized area of the film due to the non-uniform distribution of PEDOT-rich and PSS-rich grains. At a low bias voltage, we observed high current levels and high charge trap densities in PEDOT-rich grains, while PSS-rich grains showed low-current levels and charge trap densities. Interestingly, the charge trap densities in both grains showed a noise source switching behavior with respect to the applied bias voltages, and the behavior strongly affected their electrical characteristic such as the trap-free transition of currents. These results indicate that the charge traps in a PEDOT:PSS film play an important role in the electrical characteristics of the films. Our observations provide a valuable insight on the understanding of the electrical characteristics of PEDOT:PSS films and an important guideline for its practical applications.

Quantitative electrophysiological monitoring of anti–histamine drug effects on live cells via reusable sensor platforms

We demonstrated the quantitative electrophysiological monitoring of histamine and anti-histamine drug effects on live cells via reusable sensor platforms based on carbon nanotube transistors. This method enabled us to monitor the real-time electrophysiological responses of a single HeLa cell to histamine with different concentrations. The measured electrophysiological responses were attributed to the activity of histamine type 1 receptors on a HeLa cell membrane by histamine. Furthermore, the effects of anti-histamine drugs such as cetirizine or chlorphenamine on the electrophysiological activities of HeLa cells were also evaluated quantitatively. Significantly, we utilized only a single device to monitor the responses of multiple HeLa cells to each drug, which allowed us to quantitatively analyze the antihistamine drug effects on live cells without errors from the device-to-device variation in device characteristics. Such quantitative evaluation capability of our method would promise versatile applications such as drug screening and nanoscale bio sensor researches.