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Spiropyran derivatives have been immobilised on the surface of polystyrene microbeads using different\udimmobilisation strategies. These functionalised polymeric beads can be reversibly switched between the\udcolourless inactive spiropyran (SP) and highly coloured (purple) active merocyanine (MC) forms using\udlow power light sources, such as light-emitting diodes (LEDs). A UV LED (375 nm) is used for the SP\ud/MC conversion, and a white LED (430–760 nm) for the reverse MC/ SP conversion. The\udphotochromic behaviour of the coated beads has been characterised using different LEDs and\udreflection spectroscopy, employing optic fibres and an in-house-designed holder. Investigations into the\udmetal-ion binding behaviour of the spiropyran-modified microbeads have shown that Cu2+ ions cause\udan appreciable colour and spectral change when brought into contact with the beads in the MC form,\udsuggesting that a significant interaction is occurring. However, the Cu2+ ions can be completely expelled\udby photonic-conversion of the beads into the inactive SP form using a white LED. This sequence has\udbeen successfully repeated six times, suggesting that it is possible to cycle through activation of the\udfunctionalised beads from a non-binding to a binding form (SP / MC) using a UV LED, allow\udbinding with Cu2+ ions to occur, and subsequently, expel the bound ions and regenerate the passive SP\udsurface using a white LED. Other metals, such as calcium, do not cause any appreciable colour or\udspectral change over the same concentration range and in the presence of the same anion (final\udconcentration 7.1  104 M nitrate salt in ethanol). The system is therefore self-indicating in terms of\udwhether the active MC or inactive SP forms are present, and whether Cu2+ ions are bound to the MC\udform. In principle, therefore, these functionalised beads could form the basis of a photoswitchable\udstationary phase for metal ion binding and detection: irradiation of the stationary phase with UV LEDs\udcauses retention of guest species due to the presence of the MC form, while subsequent exposure to\udwhite LEDs causes release of guest species into the mobile phas

Polystyrene bead-based system for optical sensing using spiropyran photoswitches