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We demonstrated an ultra-sensitive terahertz virus detection method combined with virus-sized gold nanogaps filled with Al2O3. Large-area high-density 20 nm-gap rectangular loop structures, containing a resonant frequency in the terahertz range, were fabricated on a 4-inch wafer using atomic layer lithography. When target viruses with a 60 nm diameter were located on the nanogaps, we observed a significant redshift of the resonant peak already with an average number of about 100 viruses per unit loop due to the strong field confinement and enhancement near the gap. Furthermore, when the virus was tightly attached to an etched gap like a bridge connecting metals, its sensitivity is doubled compared to the unetched gap, which resulted in 400% more resonance frequency shift per single virus particle than our previous work. Full-wave simulations and theoretical calculations based on modal expansions were in good agreement with the experiments, revealing that the resonant transmission spectrum was mostly determined by the change in refractive index in a two-dimensional-like optical hotspot near the nanogap. A further step could be taken to increase sensitivity by tuning nanogap-loops to the absorption frequencies associated with the intermolecular vibrational modes of the viruses and fingerprinting them as well.

Most microbial detection techniques require pretreatment, such as fluorescent labeling and cultivation processes. Here, we propose novel tools for classifying and identifying microorganisms such as molds, yeasts, and bacteria based on their intrinsic dielectric constants in the THz frequency range. We first measured the dielectric constant of films that consisted of a wide range of microbial species, and extracted the values for the individual microbes using the effective medium theory. The dielectric constant of the molds was 1.24–1.85, which was lower than that of bacteria ranging from 2.75–4.11. The yeasts exhibited particularly high dielectric constants reaching 5.63–5.97, which were even higher than that of water. These values were consistent with the results of low-density measurements in an aqueous environment using microfluidic metamaterials. In particular, a blue shift in the metamaterial resonance occurred for molds and bacteria, whereas the molds have higher contrast relative to bacteria in the aqueous environment. By contrast, the deposition of the yeasts induced a red shift because their dielectric constant was higher than that of water. Finally, we measured the dielectric constants of peptidoglycan and polysaccharides such as chitin, α-glucan, and β-glucans (with short and long branches), and confirmed that cell wall composition was the main cause of the observed differences in dielectric constants for different types of microorganisms.

We demonstrate the development of an effective technique to remove the poly methyl methacrylate (PMMA) layer used for transferring graphene synthesized by a chemical vapor deposition (CVD). This was achieved utilizing electron-beam bombardment and following developing processes, prior to the use of conventional organic solvents. Field-effect transistors were fabricated on the transferred graphene in order to explore their Dirac points and carrier motilities in the ambient condition - the results were then compared with those from the conventional wet chemical treatment. It was found that the Dirac points were located close to the zero gate bias when compared to those from the acetone and the acetic acid treatments. Most significantly, the field-effect mobility reached as high as 6770 cm2/Vs and 7350 cm2/Vs on average for holes and electrons, respectively, which is more than seven times improvement in comparison to conventional acetone treatments for CVD-grown graphene devices.

Phytochromes are photoreceptors that regulate many aspects of plant growth and development in response to red/far-red light signals from the environment. In this study, we analyzed chromophore ligation and photochromism of missense phytochrome mutants in the Per-Arnt-Sim (PAS)-related domain (PRD). Among the 14 mutants analyzed, the Gly768Asp mutant of Avena phytochrome A showed aberrant photochromism and dark reversion, suggesting that amino acid residues in the C-terminal domain affect the photochemical properties of the photosensory N-terminal domain.

In this study, we developed hybrid humidity sensing methods by incorporating silk fibroin protein onto metamaterials, operating in the terahertz (THz) frequencies; the resonant frequency shifted but saturated at a specific thickness due to the limited sensing volume of the metamaterial. From the saturated value, we extracted the dielectric constant for the silk films. We also observed additional resonance shifts when we applied humid air to silk-coated metamaterials, due to the increased water molecule numbers on the film. Frequency shifts depend linearly on relative humidity. Also, in situ THz spectroscopy measurements reveal that the time response is instantaneous within our detection limit, especially upon exposure to humid air, whereas the small slowly decaying component appeared when we applied dry air. The time taken by the slow component in the drying process was 10-50 s, depending on film thickness. This could optimize humidity sensors as a fast and efficient detection tool to measure air humidity.