Real-time selective recognition of cells is an important capability for medicine, molecular biology, and environmental science. We report here a cell-selective polymer film, obtained via polymerization of a thin film of fanctionalized monomers, in contact with a target cell. Under controlled conditions, the replica maintains exceptional structural memory of both shape and surface functionality of the initial bacterial cell. High selectivity is observed between bacteria featuring different cell surfaces (Gram-positive vs negative), shapes (rods vs spheres), and cell arrangements (single cells vs short chains vs clusters). Interfacing to a quartz crystal microbalance provides real-time, selective detection of bacteria at environmentally relevant concentrations of less than 500 cells/mL, an improvement of 100-fold in response time and 10(6) fold in sensitivity over current methods.