A platform based on a metal-organic framework (MOF) bearing free carboxylic acid groups has been developed for tumor cell capture and potential drug screening applications. A zinc-based MOF expressing uncoordinated carboxylic acids (ZnMOF-COOH) was grown on a ZnO substrate. Post-synthetic modification (PSM) of the acid groups gave a composite material that expressed peptide linkages and allowed the immobilization of anti-epithelial cell adhesion molecule (anti-EpCAM) antibody. This strategy offers a universal method for the controllable immobilization of antibodies and even enzymes on the surface of a MOF. The resulting immunotrapper exhibited excellent capture ability, demonstrating high efficiency and selectivity towards EpCAM-positive tumor cells. The promotion of tumor cell adhesion is attributed to the 3-dimentional (3D) structure of the composite, which revealed spine-like microstructures.