A new `bite-and-switch’ approach for the design of an imprinted polymer-recognition material useful for the development of a sensor for creatine. The ability of polymerizable hemithiocetal formed by allyl mercaptan and o-phthalic dialdehyde to react with primary amines and form a fluorescent isoindole complex is explored. Imprinting with a methylated creatine analog that can form a reversible complex with hemithiocetal was used to make the reaction specific for creatine.