Microcapillary-based BioMEMS systems have recently gained increasing attention with special interest in precisely positioning and electrically analyzing single cells [1-3].Existing fabrication schemes for microcapillaries include bonding of one substrate of open trench structure with another flat substrate [1,3] and introduction of thin-film materials (e.g.phosphosilicate glass (PSG)) to enclose microstructured trenches [2].Nevertheless,additional effort for consistent bonding and the difficulty to process glass are still among the major concerns for the aforementioned techniques.Here we present a novel method to fabricate microcapillaries leveraging on the phenomenon of silicon surface migration,through which microcapillaries are self-formed entirely on silicon substrate,thus eliminating the subsequent bonding step or additional material deposition.As illustrated in Fig.1a-c,rod-like trench structures are first etched on silicon substrate which is then subjected to high temperature reflow (1150 oC) in argon ambient.Silicon migration at atomic level takes place and leads to a final pipe-like microvoid (microcapillary).A conceptual microcapillary-based device for on single cell probing and analysis can be built with integration of microchannels (Fig.1d).We conducted quantitative study of the microcapillary diameter dependence on the size of the predefined trenches.Rod-like trenches were arranged as a one-dimensional grid with varying diameters yet at fixed edge-to-edge spacing (0.5 μm).Trenches with 0.7 μm and 0.8 μm diameter yielded microcapillaries with 0.8 μm and 1.1 μm opening,respectively,while those of 0.9 μm failed to form a well-defined profile (Fig.2a).Interestingly,with the extension of the trench pattern to a two-dimensional grid,microcapillary diameter could be raised up to 2.8 μm (Fig.2b,c).Moreover,microcapillaries with turns and junctions were successfully achieved with ingeniously designed trench layout (Fig.3a,c),which were filled with fluorescein-stained solution for fluidic continuity verification via fluorescent imaging (Fig.3b,d).Finally,cell impedance spectroscopy was performed to demonstrate the utility of the microcapillaries.Three identical microcapillaries were each occupied by a live-stained cell (Fig.4a),the presence of which caused significant change in the impedance spectrum across a single microcapillary,i.e.up to 30% in magnitude and 80% in phase (Fig.4b).In conclusion,surface migration of silicon produces cylindrical microcapillaries not only straight but with turns and joins as well.We believe this presented method,having convenience of fabrication and compatibility with semiconductor integration as outstanding merits,is suitable for building versatile microcapillary-based BioMEMS platforms.