Jason Locklin and his colleagues from the University of Georgia have developed covalently bound polymer brushes that can bind metal ions when irradiated with UV light. The polymer brushes, containing spiropyran moieties, were synthesised using atom transfer radical polymerisation (ATRP). 

Spiropyrans are a group of photo-switchable organic molecules whose light induced cleavage of the spiro C-O bond results in switching between a colourless closed form and a strongly coloured open  form. The binding is completely reversible, and can be switched using visible light.   The binding also affords a drastic change in surface wettability and allows for switching between hydrophobic and hydrophilic states. 

Locklin explains 'with colorimetric sensors, problems can arise with selectivity and degradation, which gives rise to stability issues. Therefore the polymer brush geometry allows for an increase in functionality and high density of molecules in a limited area.   Also tuning of the microenvironment through copolymerization can lead to matrices with enhanced selectivity. Covalently bound polymer chains can also lead to sensors with improved stability. In addition, the changes in wettability can be used to control the motion of fluids in microfluidic channels.' All of which will contribute towards the future development of this research area.

'Developing sensors that are reversible and also extremely sensitive is one potential challenge.   The binding has to be sufficiently weak to achieve reversibility. We plan to pursue improved techniques to push the detection limit of the sensors, possibly by using fluorescence as detection strategy,' adds Locklin. 

Emma Shiells