Spiropyran modified micro-fluidic chip channels as photonically controlled self-indicating system for metal ion accumulation and release

In this paper, we show how through integrating the beneficial characteristics of micro-fluidic devices and spiropyrans dyes, a simple and very innovative chip configured as an on-line photonically controlled self-indicating system for metal ion accumulation and release can be realised. The micro-fluidic device consists of five independent 94 μm depth, 150 μm width channels fabricated in polydimethylsiloxane. The spiropyran 1′-(3-carboxypropyl)-3,3′-dimethyl-6-nitrospiro-1-benzopyran-2,2′-indoline is immobilised by physical adsorption into a polydimethylsiloxane matrix and covalently on the ozone plasma activated polydimethylsiloxane micro-channel walls. When the colourless, inactive, spiropyran coating absorbs UV light it switches to the highly coloured merocyanine form, which also has an active binding site for certain metal ions. Therefore metal ion uptake can be triggered using UV light and subsequently reversed on demand by shining white light on the coloured complex, which regenerates the inactive spiropyran form, and releases the metal ion. When stock solutions of several metal ions (Ca2+, Zn2+, Hg2+, Cu2+, Co2+) are pumped independently through the five channels, different optical responses were observed for each metal, and the platform can therefore be regarded as a micro-structured device for photo-controlled self-indicating metal ion complexation, accumulation and release.