Researchers at Osaka University develop a microfluidic system that can measure the concentration of trace solutes in tiny drops of liquids using terahertz radiation, which may lead to novel lab-on-a-chip devices for monitoring environmental quality
Osaka, Japan – Scientists from the Institute of Laser Engineering at Osaka University created a prototype terahertz optical spectroscopy system with a sensing area equivalent to the cross-sectional area of just five human hairs. By measuring the shift in peak transmittance wavelength of a terahertz radiation source, the concentration of even trace dissolved contaminants in a tiny drop of water can be measured. This work may lead to portable sensors for applications such as the early detection of diseases, drug development, and water pollution monitoring.
Lab-on-a-chip technology is an exciting area of research. The ability to test patient samples at the bedside, or monitor water quality out in the field, with a portable monitoring device is very attractive. However, achieving strong sensitivity to the concentration of target analytes of interest can be difficult, especially when samples consist of very tiny volumes of liquid.
Now, a team of researchers at Osaka University has used a proprietary terahertz radiation source in a microfluidic chip containing a metamaterial structure to quantify the amount of trace contamination in water. “Using this lab-on-a chip system, we could detect minute changes in the concentration of trace amounts of ethanol, glucose, or minerals in water by measuring the shift in the resonance frequencies,” first author Kazunori Serita says.
The “I-design” consists of a metallic strip with a micrometer-sized gap sandwiched by other metallic strips. It is periodically arrayed in a row of five units, which formed a kind of “meta-atom,” in which peak optical transmittance varied based on the presence of trace contamination by dissolved molecules. This device is an application of the point terahertz source technology previously developed at Osaka University. A tiny source of terahertz light was generated by the irradiation spot of a femtosecond-pulse laser beam that induces a tightly confined electric-field mode at the gap regions. It then modifies the resonance frequency when a microchannel fabricated in the space between the metallic strips is filled with the sample solution.
“We succeeded in detecting just 472 attomoles of solutes in solutions with volumes of less than 100 picoliters, which is an order of magnitude better than existing microfluidic chips,” senior author Masayoshi Tonouchi says. This work can lead to significant improvements in portable sensing, both in terms of sensitivity and the amount of liquid required.
The article, “I-design terahertz microfluidic chip for attomole-level sensing” was published in Journal of Physics: Photonics at DOI: https://doi.org/10.1088/2515-7647/ac691d
About Osaka University
Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.