Free-standing colloidal membranes (nanofrits) with varied thickness and nanopore size are fabricated and modified with pH-responsive poly(2-(dimethylamino)ethyl methacrylate) brushes. The polymer-modified nanofrits demonstrate excellent gating behavior for molecular diffusion: in the presence of acid, the diffusion rate of positively charged species significantly decreases. Increasing the polymer length and membrane thickness and decreasing the nanopore size leads to the complete acid-controlled gating of the membranes.