title: Calcium-assisted glass-to-glass bonding for fabrication of glass microfluidic devices.
abstract: Glass is a desired material for many microfluidics applications. It is chemically resistant and has desirable characteristics for capillary electrophoresis. The process to make a glass chip, however, is lengthy and inconvenient, with the most difficult step often being the bonding of two planar glass substrates. Here we describe a new glass bonding technique, which requires only washing of the glass surfaces with a calcium solution and 1-2 h of bonding at 115 degrees C. We found calcium uniquely allows for this simple and efficient low-temperature bonding to occur, and none of the other cations we tried (e.g., Na (+), Mg (2+), Mn (3+)) resulted in satisfactory bonding. We determined this bond is able to withstand high applied field strengths of at least up to 4 kV x cm (-1). When intense pressure was applied to a fluid inlet, a circular portion of the coverslip beneath the well exploded outward but very little of the glass-glass interface debonded. In combination with the directed hydrofluoric acid etching of a glass substrate using a poly(dimethylsiloxane) (PDMS) etch guide, we were able to make glass chips with better than 90% yield within 6 h. This technique is compatible with inexpensive unpolished glass and is limited in resolution by the PDMS etch guide used and the intrinsic properties of isotropic etching.
authors.affiliation: Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195, USA.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Allen
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Chiu
mesh_terms: D002118:Calcium / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D002118:Calcium