We report on a promising approach for the label-free analysis of DNA molecules with electromagnetic surface waves in the terahertz (THz) region. A metallic mesh with a polyvinylidene difluoride membrane is employed for THz transmission analysis. The metallic mesh with opening holes provides a sharp dip structure in a THz transmission spectrum, which is sensitive to a small change of the refractive index of a sample on the metallic mesh surface. The optical properties of a small amount of DNA molecules cannot be investigated by a free-space THz measurement because of the low absorption coefficients of such samples. However, metallic mesh-based THz measurement revealed the difference in optical properties between single- and double-stranded DNA molecules on the basis of refractive index, as estimated from a dip frequency shift of the metallic mesh. Therefore, our metallic-based THz technique provides a dramatically enhanced sensitivity, and demonstrates the potential of our approach of the analysis of biologically relevant DNA samples.

Administering appropriate antimicrobial therapy as early as possible is important for rescuing bacteremic patients. Therefore, rapid antimicrobial susceptibility tests in positive blood culture specimens have been diligently sought. Adenosine triphosphate (ATP) bioluminescence-based methods have been used for rapid antimicrobial susceptibility tests. However, blood culture specimens have not been examined in many studies, possibly due to abundant intracellular ATP in blood corpuscles resulting in false-susceptible results. In this study, we developed a rapid ATP bioluminescence-based method for detecting antibiotic resistance starting from positive blood culture. To minimize background ATP originating from blood corpuscles, specimens were centrifuged and the supernatant diluted with broth, and an ATP-eliminating reagent was then added to the bacterial suspension at the beginning of incubation. This newly devised procedure reduced the background ATP by more than five orders of magnitude. In a pilot study using levofloxacin, no false-susceptible results were observed in 15 clinical specimens. Furthermore, the results indicated that the rapid method provided additional information about bacterial activities with high resolution, in contrast to the less-thorough findings with the conventional turbidity method. Therefore, our approach will contribute to the treatment of infectious diseases as a rapid antimicrobial susceptibility test.

This paper describes a real-time transmission-type Terahertz (THz) microscope, with palm-size THz camera and compact quantum cascade laser (QCL). The THz camera contains 320x240 microbolometer focal plane array which operates at 30 Hz frame rate and has lock-in imaging function as well as integration functions such as frame integration and spatial filter. These functions are found very powerful in improving signal-to-noise ratio. QCL is installed in compact Stirling cycle cooler. A variety of QCLs covers frequency range from 1.5 to 5 THz and provides time-average power of 0.5~2 mW. The illumination area for sample is changed by adjusting one lens in the illumination optics. Performances of the THz microscope, such as signal-to-noise ratio and so on, were measured and are found consistent with the calculations. THz images taken with the THz microscope are finally presented.

The sol-gel transition temperature of gelatin is determined using viscoelasticity measurement and terahertz time-domain spectroscopy. From the results of the viscoelasticity measurement, the sol-gel transition temperature is determined to be 30–32 °C, and it strongly depended on the concentration. However, terahertz time-domain spectroscopy indicates a particular transition temperature of 36 °C. A distinction of these transition temperatures is attributed to the difference in the structural changes detected by these measurements.

In this study, we have evaluated the hydration properties of water-soluble polymers by terahertz spectroscopy. In particular, we focused on polyvinylpyrrolidone which has potential use for a wide range of applications as a biomaterial. The dielectric loss of samples obtained by the terahertz spectroscopy was found to strongly depend on the molecular weight of the polymers and the density of the solution. We revealed that the hydration number per monomer depends on the molecular weight of the polymer. It is also deduced that the hydration number is affected by the conformation of the polymer in the solution.