Terahertz sensing breakthrough
Image: A spiral bull's-eye structure is fundmental to the new plasmonic sensor.
Japan-based researchers have developed an easy-to-use, tunable biosensor tailored for the terahertz range.
The sensor was used to distinguish between different tissues in mouse organs, expanding the possibilities for terahertz applications in biological analysis and future diagnostics.
While researchers hope to combine plasmonics with emerging terahertz technologies for non-invasive detection and analysis, the ability to detect biological samples is challenging due to long THz wavelengths.
Now, Yukio Kawano and colleagues at Tokyo Tech's Laboratory for Future Interdisciplinary Research of Science and Technology and researchers at Tokyo Medical and Dental University have overcome this barrier by designing a frequency-tunable plasmonic-based THz device.
As Kawano highlights, a key feature of the device is its spiral bull's eye structure, with smoothly varied grooves.
Images of the spiral plasmonic structure: (a) The spiral bull's eye structure, (b) Double-corrugated devices, and (c) Eight-tip Siemens-star aperture at the centre of the spiral bull's eye structure.
"The groove period continuously changes with the diameter direction, resulting in continuously frequency-tunable characteristics," he says.
The new design incorporates a so-called Siemens-star aperture, which enables a user-friendly way of selecting the desired frequency by simply changing the rotation of the spiral plasmonic structure.
"The device also increases the electric field intensity at the subwavelength aperture, thus significantly amplifying the transmission," adds Kawano.
In preliminary experiments to assess how well the new device could visualise biological tissues, the researchers obtained THz transmission spectra for various mouse organs.
Terahertz transmission spectra of bio-samples using the spiral bull's eye structure: THz medical examination of sections of mice organ tissues for skin, heart, kidney, lung, spleen, brain, and femur.
The spectra were measured by rotating the spiral bull's eye structure, and revealed different transmission peaks characteristic of the organ tissues.
To probe further, Kawano and colleagues also conducted THz mapping of mouse tails.
By comparing images obtained with and without their new design, the study showed that the spiral bull's eye led to a markedly improved ability to distinguish between different tissues such as hair, skin and bone.
Terahertz mapping of the mouse-tail samples using a conventional setup (upper image) and the spiral bull's eye structure (lower image). The hair (yellow and red), skin (light blue), and bone (dark blue) were clearly distinguishable using the spiral bull's eye.
The findings suggest that the improved performance is due to the device’s tunability.
Further investigations are planned to test the new device using various mouse organ tissues.
The findings open up a new direction for plasmonic-based THz imaging of biological samples, which may eventually lead to the development of improved, non-invasive diagnostic imaging tools.
Research is published in Nature Scientific Reports.