Study of diffusion processes in microfluidic chips using super-resolution terahertz solid immersion microscopy

Abstract

In recent years, terahertz (THz) technologies have found wide application in biophotonics and the chemical industry for analysing substance composition, measuring water concentration and state in tissues and solutions, and investigating metabolic markers. This stems from the ability of THz radiation to interact with molecular energy levels and its high absorption, and thus sensitivity to polar molecules such as water. A promising direction in biology and medicine is studying biological processes within the small volumes of microfluidic chip cells. Although THz technologies offer great potential here, they are limited by the low spatial resolution of conventional THz optical systems and the narrow channel widths of microfluidic chips. To address this, the study employed a THz optical system based on the solid immersion effect, comprising a high-resistance silicon hemisphere (hypohemispherical lens) in close contact with a flat silicon window. A polydimethylsiloxane microfluidic chip was placed on the window surface, with imaging performed by moving the window in two lateral directions. Continuous-wave imaging at 0.6 THz distinguished liquids differing in active substance concentration by as little as 0.5–2.0%. A pulsed version of the microscope measured spectral responses of common microfluidic compounds and certain hydrogels across 0.2–1.0 THz. Diffusion of compounds in a nanocrystalline cellulose (NCC)-based hydrogel was studied, clearly visualising the process and enabling evaluation of diffusion coefficients. These results demonstrate the potential of super-resolution THz microscopy for quantitative study of diffusion in microfluidic systems, opening new avenues for investigating biological objects and transport processes in liquid media.

Speaker

Vera V. Koroleva
Prokhorov General Physics Institute RAS, Bauman Moscow State Technical University
Russia

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