While gas-phase atmospheric pressure plasma (APP) is a promising technology for highly-efficient and minimally-invasive gene/drug (molecule) introduction, the reduction of external gas supply and the expansion of the effective treatment area in biological fluids for in vivo treatment are still challenging. We developed a device for mm-scale plasma generation in saline without working gas supply and demonstrated the local introduction of YOYO-1 molecule (molecular weight : 1271) into cultured cells using the device. Unlike the conventional APP accounting for chemical stimuli with reactive species, plasma-induced mechanical stimulus was indicated as one of key factor(s) in the molecule introduction.