Inverse opal hydrogel sensor for the detection of pH and mercury ions

An inverse opal hydrogel (IOH) sensor was constructed through colloidal templating photopolymerization of acrylic acid and pemaerythritol-triacrylate. Its dual responsive behaviours to pH and mercury ions (Hg2+) were demonstrated by detecting the shift of the diffraction wavelength. The diffraction wavelength of the IOH sensor was dramatically red-shifted when the pH was increased from 11 to 13, due to the swelling of the hydrogel. The shift of the diffraction wavelength can be directly observed by the naked eye through the colour change of the IOH. A fast response behaviour of the IOH sensor to pH was approximately completed within 3 s. Furthermore, carboxyl groups were used to detect Hg2+ as recognition groups. A low detection limit of 10 nM for Hg2+ was achieved in the optimized IOH sensor. The present work indicates the prospect of constructing multi-responsive IOH sensors using a single recognition group through the facile colloidal templating route.