Microfluidic Chemotaxis Assay through Stable Chemical Gradient

Abstract

The diffusion-based method can create a non-flow environment for the bacteria, so chemotaxis response can be observed in gradients that evolve only by diffusion, in the absence of flow. Recently, we have reported a convenient and reliable diffusion-based microfluidic device for nonlinear gradient generation. Stable and rapid diffusion of chemicals was successfully generated by direct contact of two fluids manipulated by control of capillary action. In our design, the height of the junction channel is very critical because the junction channel play key roles in diffusion-based gradient generation and physical prevention of bacterial movement toward the chemoeffector channel in analysis of positive chemotactic response. In this study, to improve the height accuracy of the junction channel, we propose a new alternative microfabrication method using thick silicon oxide deposition and reactive ion etching. The height of the junction channel within 1% accuracy could be precisely fabricated by the newly-proposed microfabrication. As a proof-of-concept, we conducted experiments with bacterial chemoeffectors with Pseudomonas aeruginosa PAO1 based on fluorescent observation in a concentration-dependent manner. We easily achieved chemotaxis index of each chemoeffector and it was in a good agreement with our previous result while the variation of chemotaxis index is reduced to be half. We envision that our proposed fabrication will guide microfluidic fabrication to techniques for reproducibility for various field.