Fluidic encapsulation in SU-8 μ-reservoirs with μ-fluidic through-chip channels

A process has been developed that allows encapsulation of an aqueous solution within a micrototal analysis system (μ-TAS) device. This device, a microtransdermal glucose sensor called B-FIT is cast in the photopolymer SU-8. A 50 nl μ-reservoir is filled and sealed by means of bonding two cured SU-8 surfaces using a thin layer of uncured SU-8. The μ-reservoir is bound by two membranes of 5 and 20-40 μm thick. Upon electrolysis of the encapsulated fluid by applying 2.6 V (or more, depending on the desired rate of fluid release) to two electrodes within the μ-reservoir, expansion of the created gas instantly ruptures the 5 μm membrane in a controlled fashion at a scoring mark that was fabricated by thinning the 5 μm membrane to 2-3 μm by reactive ion etching. The fluid exits the μ-reservoir and moves up the adjacent μ-capillaries through the entire chip. The technique of encapsulating fluid within MEMS devices offers possibilities for drug delivery systems.