A prototype terahertz optical spectroscopy system with a detection area comparable to the cross-section of just five human hairs was developed by researchers at University of Osaka‘s Institute of Laser Engineering.
The amount of pollutants dissolved even in trace amounts in a microscopic drop of water can be determined by monitoring the variation in peak transmission wavelength of a terahertz radiation source. This research could lead to wearable sensors for, among other things, monitoring water pollution, developing new medicines and early diagnosis of diseases.
A fascinating subject of study is lab-on-a-chip technology. It is very attractive to have portable monitoring equipment that can analyze patient samples at the patient’s bedside or monitor water quality outside.
However, it can be challenging to achieve great sensitivity to the concentration of the target analytes, especially when samples consist of minute volumes of liquid.
Researchers from Osaka University have now quantified the level of trace contamination in water using a proprietary terahertz radiation source in a microfluidic device with a metamaterial structure.
Using this lab-on-a-chip system, we were able to detect minute changes in the concentration of trace amounts of ethanol, glucose or minerals in water by measuring the shift in the resonance frequencies.
Kazunori Serita, lead author of the study, University of Osaka
The “I-design” consists of two metal strips, one of which has a gap of a few micrometers. It is regularly arranged in a row of five units, creating a kind of “meta-atom” whose maximum optical transmission changes depending on the amount of dissolved molecular impurity.
This gadget uses a point terahertz source technology previously developed by Osaka University. The irradiation points of a femtosecond pulse laser beam, which causes a tightly bounded electric field mode in the slit regions, produce a small source of terahertz light.
When the sample solution is poured into a microchannel constructed in the gap between the metal strips, the resonance frequency changes.
We managed to detect only 472 attomoles of solutes in solutions with volumes less than 100 picolitres, which is an order of magnitude better than existing microfluidic chips.
Masayoshi Tonouchi, senior study author, University of Osaka
This study has the potential to significantly increase wearable sensing in terms of sensitivity and the amount of fluid required.
Serita, K., et al† (2022) I-design terahertz microfluidic chip for attomole-level detection. Journal of Physics: Photonics. doi:10.1088/2515-7647/ac691d