title: Isotropically etched radial micropore for cell concentration, immobilization, and picodroplet generation.
abstract: To enable several on-chip cell handling operations in a fused-silica substrate, small shallow micropores are radially embedded in larger deeper microchannels using an adaptation of single-level isotropic wet etching. By varying the distance between features on the photolithographic mask (mask distance), we can precisely control the overlap between two etch fronts and create a zero-thickness semi-elliptical micropore (e.g. 20 microm wide, 6 microm deep). Geometrical models derived from a hemispherical etch front show that micropore width and depth can be expressed as a function of mask distance and etch depth. These models are experimentally validated at different etch depths (25.03 and 29.78 microm) and for different configurations (point-to-point and point-to-edge). Good reproducibility confirms the validity of this approach to fabricate micropores with a desired size. To illustrate the wide range of cell handling operations enabled by micropores, we present three on-chip functionalities: continuous-flow particle concentration, immobilization of single cells, and picoliter droplet generation. (1) Using pressure differentials, particles are concentrated by removing the carrier fluid successively through a series of 44 shunts terminated by 31 microm wide, 5 microm deep micropores. Theoretical values for the concentration factor determined by a flow circuit model in conjunction with finite volume modeling are experimentally validated. (2) Flowing macrophages are individually trapped in 20 microm wide, 6 microm deep micropores by hydrodynamic confinement. The translocation of transcription factor NF-kappaB into the nucleus upon lipopolysaccharide stimulation is imaged by fluorescence microscopy. (3) Picoliter-sized droplets are generated at a 20 microm wide, 7 microm deep micropore T-junction in an oil stream for the encapsulation of individual E. coli bacteria cells.
authors.affiliation: Sandia National Laboratories, PO Box 969, Livermore, CA 94551, USA.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Perroud
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Meagher
authors.forename: Michael P
authors.initials: MP
authors.lastname: Kanouff
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Renzi
authors.forename: Meiye
authors.initials: M
authors.lastname: Wu
authors.forename: Anup K
authors.initials: AK
authors.lastname: Singh
authors.forename: Kamlesh D
authors.initials: KD
authors.lastname: Patel
mesh_terms: D000818:Animals; D002460:Cell Line; D003584:Cytological Techniques; D004867:Equipment Design; D004926:Escherichia coli / Q000166:cytology; D008264:Macrophages / Q000166:cytology; D051379:Mice; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D016062:Porosity; D015203:Reproducibility of Results