Proceedings Article | 15 March 2000
KEYWORDS: Glasses, Particles, Microfluidics, Silicon, Microfabrication, Free space, Wet etching, Yeast, Microscopes, Adhesives
Arrays of microgrooves (groove width; 2, 3, 4, 5, 6, 7, 8, 10, 12, and 14 micrometer, groove interval; width x3, x10, and x20, one size and interval per chip) each connecting a center well and a side edge of a silicon substrate were created by photolithography and anisotropic wet etching. A penetrating hole was made by sand blast at the substrate center for the access to the center well. By tightly covering the substrate surface with a glass plate, the microgroove arrays were converted to microchannel arrays having one ends open at the side edges of the substrate. These microchannel arrays were used for cell trapping for microinjection and also used for emulsification. Poplar (Populus alba) protoplasts were used for the test of cell trapping. Cells showed a very large variation in size and irregularity in shape, and, furthermore, the protoplast preparation contained a number of cell membrane fragments and chloroplasts. Despite the cell size and shape variations and obstruction by the admixtures, many cells could be trapped by aspiration at the channel ends because of their openness to the outside free space and also their large multiplicity in parallel. The free space outside the side of the substrate allowed a free manipulation of a glass micropipette under microscopic observation using transmitted illumination. The microscopic observation direction nearly perpendicular to the movement directions of the micropipette further allowed the movement of the pipette tip nearly always in focus. These led to an easy pointing and puncturing. In addition, the cell trapping points in a line made successive approach to adjacent cells easier. Soybean oil containing 1.5 wt% polyoxyethylene(20)sorbitan monoolete as a surfactant was forced to flow into physiological saline filling the outside of the substrate through the microchannels. Regularly sized oil particles were created by this process with a variation coefficient (S.D./mean) 16% of their diameter. This variation, which is larger than those (minimum 1 - 2%) obtained in our previous trials using our previous microchannel arrays, appeared to be attributable to an irregularity of the channel ends due to microchipping by saw cutting. As an advantage over the previous ones, the present microchannel arrays allowed an easy collection of the created oil particles and also an easy change of the composition of the suspending fluid during the process. The substrate side surface is thus indicated to be useful for interfacing structures or devices microfabricated in the main substrate surface, which may be covered with a glass plate, with conventional or hand-operated tools or processes outside the substrate.
