Meta-Atoms, Terahertz, Microfluidic Biosensing

Researchers have developed a nonlinear optical crystal-based compact terahertz (THz)-microfluidic chip with several I-design meta-atoms for attomole (amol)-level sensing of trace amounts of solution samples.

The I-design meta-atoms consist of metallic strips with micrometer-sized gaps sandwiched by other metallic strips, periodically arrayed in a row of 1 × 5 units. A point THz source (locally generated by optical rectification at the irradiation spot of a femtosecond-pulse laser beam) induces a tightly confined electric-field mode at the gap regions. It modifies the resonance frequency when a microchannel fabricated along the space between the metallic strips is filled with solutions.

Using the microfluidic biosensing chip, the researchers could detect minute changes in the concentration of trace amounts of ethanol- and glucose-water solutions and mineral water by measuring the shift in the resonance frequencies. They detected 472 amols of solutes in solutions less than 100 picoliters using an effective sensing area of 0.10 λTHz × 0.57 λTHz, which indicates an improvement of approximately one order of magnitude compared to the performance of existing chips. This technique compactifies THz-microfluidic chips with high sensitivity. It would accelerate the development of microfluidics integrated with THz technology, such as lab-on-a-chip devices and THz micro total analysis systems.

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