Development of Bioprobe Integrated with Microneedle for Cellular Function Analysis

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In order to realize cellular function analysis on a chip-base system, we have developed a newly designed AFM probe in which a conventional sharp tip is superseded by a hollow silicon dioxide(SiO_2) microneedle connecting the root to a fluidic microchannel embedded into a silicon(Si) cantilever beam structure. The probe will be capable not only of performing AFM measurements but also of introducing desired biomolecules(nucleic acids, proteins, etc.) into living cells and extracting biomolecules expressed in the cells.The micromachining technique of a hollow SiO_2 microneedle with a sharpened tip has been developed on the basis of a combination of an anisotropic Deep reactive ion etching(DRIE) process for producing thorough holes into a Si substrate as a needle mold followed by wet oxidation and a selective etching process for leaving a SiO_2 microneedle structure, resulting that microneedles with a tip diameter of less than 0.1 μm(5.5 μm in outer diameter and 20 μm in length) was succes … More sfully fabricated. A circular-shaped microchannel(typically 6 μm in diameter) was also successfully fabricated into a Si cantilever structure. In additon, a novel electrostatic field-assisted direct bonding technique was developed.In order to investigate the mechanical stability of a microneedle array, penetration tests were performed with a gelatin as an artificial cell. The results indicated that the microneedles were expected to be sufficiently stiff to penetrate living cells without fracture. Insertion performance into gelatin and the possibility of liquid delivery with fabricated microneedles were also investigated. The displacement required for needle insertion increased linearly with an increase in surface area at the needle tip. It was also found that increasing mechanical oscillation frequency during insertion decreased remarkably the displacement probably due to an increase in viscous resistance. Moreover, the fluid ejection tests revealed the possibility of liquid delivery by employing fabricated microneedles with an inner diameter as small as 3.5 μm. It was also founded that the flow rate increased in proportion to the fourth power of the inner diameter of the needles that is subject to the Hagen-Poiseuille's equation. Less