Preparation of ORMOSIL particles with controlled amounts of binary organic functional groups and their application to colorimetric sensors for cadmium ion

Binary functional ORMOSIL particles were prepared by the one pot process using organosilane mixtures of mercaptopropyltrimethoxysilanes and vinyltrimethoxysilanes. Colorimetric cadmium ion sensors were then prepared by immobilizing α,β,γ,δ–tetrakis(1-methylpyridinium-4-yl)porphine-p-toluenesulfonate molecules in ORMOSIL particles containing a controllable amount of mercaptopropylsilanes that served as binding sites. The relative amount of mercaptopropyl and vinyl functionalities in particles were controlled by adjusting molar ratios of organosilanes and thereby the amount of immobilized TMPyP molecules was easily controlled, which allowed a facile control of the detection range and sensitivity toward Cd ion detection. A particle sensor grid capable of colorimetric detection of Cd ions in a concentration range from 10 ppb to 5 ppm was constructed by combining three cadmium sensors with a different amount of mercaptopropylsilanes and showed distinctive visible color changes in a different concentration range of cadmium ions. Recycled sensor particles exhibited almost the same sensing performance as freshly prepared ones.