We have successfully developed minimally-invasive needle-free bubble injector designed for the usage in air. The novelty is that the minimally-invasiveness of injection whose resolution is less than 10 μm, and hence cellular-scale injection can be possible without any pain. The novelty of the present techniques are (1) unique robust thick structure at the tip of the narrowed glass capillary for operation in air, (2) damper structure produce closed space to fill in reagent which enabled the injector to be used in air and (3) construction part to support inner probe to make self-aligned coaxial positioning for accurate injection. The injector can be used for any kind of materials with various hardness, owing to the strong impact of cavitation phenomenon when the high-speed micro-bubbles are collapsed. The fine adjustment of injection can be controlled by the number of applied electric pulses. The developed injector can be used for wide range of biomedical study, especially in gene therapy. This technique has advantages over the conventional electroporation or ultrasound operation in terms of localization of injection and ability of transportation of material.