Daesan Kim

Atomistic simulation of structural phase transformations in monocrystalline silicon induced by nanoindentation

Structural phase transformations of silicon during nanoindentation were investigated in detail at the atomic level. The molecular dynamics simulations of nanoindentation on the (100) and (111) surface of single crystalline silicon were simulated, and this supported the theoretical prediction of the anisotropic behaviour of structural phase transformations. Simulations showed that microscopic aspects of phase transformation varied according to the crystallographic orientation of the contact surface and were directly linked to the slip system of silicon. In the transformed region along the centreline, the crystalline structure of Si-II and the amorphous structure were observed when silicon was loaded in the [100] and [111] directions, respectively. Simultaneously, metastable phases with fourfold coordination, such as Si-III and Si-XII, were formed by the inhomogeneous distortion in the slip direction of silicon and observed along the direction. Additionally, our results indicated that the deviatoric stress added to the hydrostatic pressure induced by loading was an indispensable factor for the structural phase transformation to Si-II during nanoindentation on the (100) surface.

Bioelectronic tongue using heterodimeric human taste receptor for the discrimination of sweeteners with human-like performance.

The sense of taste helps humans to obtain information and form a picture of the world by recognizing chemicals in their environments. Over the past decade, large advances have been made in understanding the mechanisms of taste detection and mimicking its capability using artificial sensor devices. However, the detection capability of previous artificial taste sensors has been far inferior to that of animal tongues, in terms of its sensitivity and selectivity. Herein, we developed a bioelectronic tongue using heterodimeric human sweet taste receptors for the detection and discrimination of sweeteners with human-like performance, where single-walled carbon nanotube field-effect transistors were functionalized with nanovesicles containing human sweet taste receptors and used to detect the binding of sweeteners to the taste receptors. The receptors are heterodimeric G-protein-coupled receptors (GPCRs) composed of human taste receptor type 1 member 2 (hTAS1R2) and human taste receptor type 1 member 3 (hTAS1R3), which have multiple binding sites and allow a human tongue-like broad selectivity for the detection of sweeteners. This nanovesicle-based bioelectronic tongue can be a powerful tool for the detection of sweeteners as an alternative to labor-intensive and time-consuming cell-based assays and the sensory evaluation panels used in the food and beverage industry. Furthermore, this study also allows the artificial sensor to exam the functional activity of dimeric GPCRs.

A portable and multiplexed bioelectronic sensor using human olfactory and taste receptors

A multiplexed bioelectronic sensor was developed for the purpose of rapid, on-site, and simultaneous detection of various target molecules. Olfactory and taste receptors were produced in Escherichia coli, and the reconstituted receptors were immobilized onto a multi-channel type carbon nanotube field-effect transistor. This device mimicked the human olfactory/taste system and simultaneously measured the conductance changes with high sensitivity and selectivity following treatment with various odor and taste molecules commonly known to be indicators of food contamination. Various pattern recognition of odorants and tastants was available with a customized platform for the simultaneous measurement of electrical signals. The simple portable bioelectronic device was suitable for efficient monitoring of food freshness and is expected to be used as a rapid on-site sensing platform with various applications.

Detection of aquaporin-4 antibody using aquaporin-4 extracellular loop-based carbon nanotube biosensor for the diagnosis of neuromyelitis optica.

Here we propose a carbon nanotube (CNT) field-effect transistor (FET) functionalized with aquaporin-4 (AQP4) extracellular loop peptides for the rapid detection of AQP4 antibody without pretreatment. Neuromyelitis optica (NMO) is a rare disease of the central nerve system that affects the optic nerves and the spinal cord. NMO-IgG, a serum antibody in patients, is highly specific for NMO and targets AQP4. We synthesized AQP4 extracellular loop peptides, known as primary autoimmune target in NMO, and immobilized them onto CNT-FET. The sensor showed p-type FET characteristics after the functionalization of peptides. The sensor was able to detect antibody with a detection limit of 1 ng l(-1). Moreover, AQP4 antibody in human serum was detected without any pretreatment. These results indicate that the biosensor can be used for rapid and simple detection of NMO antibody.

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.

Nanodisc-Based Bioelectronic Nose Using Olfactory Receptor Produced in Escherichia coli for the Assessment of the Death-Associated Odor Cadaverine

Cadaverine (CV), a death-associated odor, is an important target molecule for various sensor applications, including the evaluation of food spoilage. In this study, we developed an oriented nanodisc (ND)-functionalized bioelectronic nose (ONBN), based on carbon nanotube transistors and nanodiscs embedded with an olfactory receptor produced in Escherichia coli (E. coli) for detection of CV. To fabricate ONBN devices, a trace-amine-associated receptor 13c (TAAR13c) binding to CV was produced in E. coli, purified, reconstituted into NDs, and assembled, in the desired orientation, onto a carbon- nanotube-based field-effect transistor with floating electrodes. The ONBN showed high performance in terms of sensitivity and selectivity. Moreover, the ONBN was used to measure CV in diverse real-food samples for the determination of food freshness. These results indicate ONBN devices can be utilized to evaluate the quality of food samples quantitatively, which should enable versatile practical applications such as food safety and preservative development. Moreover, the ONBN could provide a useful tool for detection of corpses, which could be practically used in disaster responses.

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.

A triangle study of human, instrument and bioelectronic nose for non-destructive sensing of seafood freshness

Because the freshness of seafood determines its consumer preference and food safety, the rapid monitoring of seafood deterioration is considered essential. However, the conventional analysis of seafood deterioration using chromatography instruments and bacterial colony counting depends on time-consuming and food-destructive treatments. In this study, we demonstrate a non-destructive and rapid food freshness monitoring system by a triangular study of sensory evaluation, gas chromatography-mass spectroscopy (GC-MS), and a bioelectronic nose. The sensory evaluation indicated that the acceptability and flavor deteriorated gradually during post-harvest storage (4 °C) for 6 days. The GC-MS analysis recognized the reduction of freshness by detecting a generation of dimethyl sulfide (DMS) from the headspace of oyster in a refrigerator (4 °C) at 4 days post-harvest. However, the bioelectronic nose incorporating human olfactory receptor peptides with the carbon nanotube field-effect transistor sensed trimethylamine (TMA) from the oyster at 2 days post-harvest with suggesting early recognition of oysters’ quality and freshness deterioration. Given that the bacterial species producing DMS or TMA along with toxins were found in the oyster, the bacterial contamination-driven food deterioration is rapidly monitored using the bioelectronic nose with a targeted non-destructive freshness marker.

Nanoscale Hybrid Systems based on Carbon Nanotubes for Biological Sensing and Control

This paper provides a concise review on the recent development of nanoscale hybrid systems based on carbon nanotubes (CNTs) for biological sensing and control. CNT-based hybrid systems have been intensively studied for versatile applications of biological interfaces such as sensing, cell therapy and tissue regeneration. Recent advances in nanobiotechnology not only enable the fabrication of highly sensitive biosensors at nanoscale but also allow the applications in the controls of cell growth and differentiation. This review describes the fabrication methods of such CNT-based hybrid systems and their applications in biosensing and cell controls.

Human-like smelling of a rose scent using an olfactory receptor nanodisc-based bioelectronic nose

We report a strategy for the human-like smelling of a rose scent utilizing olfactory receptor nanodisc (ND)-based bioelectronic nose devices. In this strategy, a floating electrode (FE)-based carbon nanotube (CNT) field effect transistor (FET) was functionalized with human olfactory receptor 1A2 (hOR1A2)-embedded NDs (hOR1A2NDs). The hOR1A2NDs responded to rose scent molecules specifically, which were monitored electrically using the underlying CNT-FET. This strategy allowed us to quantitatively assess the contents of geraniol and citronellol, the main components of a rose scent, as low as 1 fM and 10 fM, respectively. In addition, it enabled us to selectively discriminate a specific rose odorant from other odorants. Significantly, we also demonstrated that the responses of hOR1A2NDs to a rose scent could be strongly enhanced by enhancer materials like a human nose. Furthermore, the method provided a means to quantitatively evaluate rose scent components in real samples such as rose oil. Since our method allows one to quantitatively evaluate general rose scent ingredients just like a human nose, it could be a powerful strategy for versatile basic research and various applications such as fragrance development.