Fabrication of high-aspect-ratio micro pipettes and fiber probes by sacrificial boundary etch process

This paper presents a novel fabrication process to realize high-aspect-ratio micro pipettes and fiber probes which can be used for biological applications. The basic fabrication process employs hydrofluoric acid (HF) to etch the outer layer of the end of capillary tubes and optical fibers as previously reported by other researchers. However, we invented a "sacrificial boundary etching" technique that can be used to shape micron size tubes and fibers into sharp pipettes or probe tips with controllable tip angle. The tip profile and the length of its taper can be controlled by the initial height of the HF inside a glass tube, which is used as a sacrificial material in shaping the tip profile. Our experimental results showed that capillary tubes and optical fibers can be sharpen into tips with angle as small as 2.1° and with tip diameter of ranging from 300 nm to 5 μm (the initial tube and fiber diameter being 125 μm). If the aspect-ratio (AR) of a pipette is defined as the ratio between the length of its taper distance and the length of its base diameter, the AR for our fabricated pipette can be as high as 10. We also conducted experiments by using the fabricated pipettes to perform microinjection of fluid into cells and fluid ejection to substrates for potential micro-spotting applications.