Micromachined Capillary Arrays for DNA Injection

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The purpose of this research is to fabricate micro capillary arrays for DNA injection to living cells by using micromachnining technology. The injection device is composed of the regular array of capillaries. Capillaries were pushed against cells and pierced them. Genetic substances such as DNA can be injected into cells through hollow capillaries. Capillaries are typically 1-5 micrometers in diameter, 0.5-1 micrometers in thickness, 20-50 micrometers in height and a few tens of micrometers in pitch between them. Major achievements of the research are :(1) We established the micromachining process for the capillary array. Thin holes of 5 micrometers in diameter and 100-200 micrometers in depth were etched in the silicon substrate by ICP-RIE (inductive coupled plasma-reactive ion etching). Then the inner surface of holes was thermally oxidized (0.5-1 micrometers in thickness). Etching of the silicon substrate from the backside revealed the bottom holes. The oxide layer at the bottom was removed by the short etching of buffered HF to make an open capillary. Further etching of the silicon substrate made capillaries protrude for 20-30 micrometers in height. Finally, a glass cover was anodically bonded on the top surface serving as a liquid reservoir and an external connector to a pipe and a pump.(2) The fabricated device was set against cultured tobacco cells. DNA solution was injected through piercing capillaries. We confirmed the production of a coded enzyme in cells.(3) We also fabricated a cell-capturing device to hold cells in a regular array with the same pitch of the injection device. The device had thinner through holes than the cell diameter. Cells suspended in liquid were captured on the holes by sucking the liquid through them from the backside.