Incorporation of acrylate based spiropyran monoliths in micro-fluidic devices for photo-controlled electroosmotic flow

Abstract

Spiropyran photochromic compounds can be switched using light exposure between a non-polar spiro form (SP) and a zwitterionic merocyanine form (MC) that is subject to protonation (MC-H+). It has recently been demonstrated by Walsh et al. that, under acidic conditions, electroosmotic flow (EOF) generated in vinyl based spiropyran monoliths can be modulated using light irradiation. In this paper, we report a spiropyran-modified acrylate based monolith which is particularly sensitive to protonation in the MC form, producing a positively charged surface that converts to the unpolar SP form by exposure to white light. When the MC-H+ form is dominant, it produces a charged surface which enables a relatively high flow rate (up to 1.6 μl/min) to be generated under electroosmotic conditions. Upon exposure to white light, the concentration of MC-H+ decreases due to the photo-conversion to the uncharged SP form, with up to 20% reduction of the EOF. The process is reversible, and removal of the light source results in a flow increase back to the original rate. The ability to alter flow rates in micro-fluidic channels using light has very significant implications, as it could dramatically simplify the manner in which micro-flow systems are controlled.