Papers by Author: Brett Paull

Abstract: This paper presents a fast fabrication process of microfluidic channels with quartz substrates. Microchannels were ablated on the surface of quartz samples with a CO₂ laser. Double sided Pressure Sensitive Adhesive (PSA) was applied to bond the samples with scribed microchannels to flat glass sheets. Dimensions of the fabricated channels were characterised with optical microscopy and laser profilometry. The recorded data was modelled with a BoxBehnken experiment design using Response Surface Methodology. Characterisation included also the measurement of optical transmission through the processed glass and measurement of flow rate through the fabricated channels. With an average width of 165 µm and depth of 280µm, fabricated channels had appropriate dimensions for a range of microfluidic applications. A significant width of the laser processed channels provided 100% transmission for a wide range of the optical spectrum. These fabricated channels were also shown to not significantly retard the fluid flow rate thus making these channels applicable for integration into numerous detection systems for chemical separation applications.

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 [1]. 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.