In order to implement cell surgery on a chip-based system, we have been developing microneedle arrays capable of introducing desired biomolecules (nucleic acids, proteins, antibodies, etc.) into living cells and the parallel extracting biomolecules expressed in the cells. This paper presents a novel and simple bath fabrication process for out-of-plane, hollow silicon dioxide (SiO2) microneedles in array. The micromachining technique involves standard photolithography and 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 an isotropic XeF2 etching process for leaving SiO2 microneedle structures. This allows a good degree of flexibility with respect to different needle designs such as needle sizes, shapes, and spacing between each needle with a one-mask process. An array of microneedles with a circler tip shape (an inner diameter of 3.5 μm, an outer diameter of 6.0 μm, and a height of 90 μm) were successfully fabricated.
