Cation identity dependence of crown ether photonic crystal Pb sensing

We quantitatively modeled the volume phase transition of a hydrogel containing a crystalline colloidal array with a crown ether ligand which binds Pb. The hydrogel volume response and the wavelength diffracted depend on the Pb concentration and on both the ionic strength and the valence of the nonbinding ionic species. We successfully modeled the response of this hydrogel Pb sensor to ionic strength and the cation valence of the added salts.