An inorganic-organic hybrid optical sensor for heavy metal ion detection based on immobilizing 4-(2-pyridylazo)-resorcinol on functionalized HMS

► We report an optical sensor prepared by immobilizing 4-(2-pyridylazo)-resorcinol on the functionalized HMS via N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride. ► The optical sensor can distinguish the low concentration of heavy metal ions from light metal ions by naked-eye. ► The optical sensor has a high sensitivity and excellent reusability for ultra-trace levels of Cu2+ even in real sample. ► The optical sensor that uses a 3D wormhole mesoporous material as carrier shows higher sensitivity.