Modular photoinduced electron transfer (PET) sensors bearing two phenylboronic acid groups, a pyrene group and alkylene linkers, from trimethylene to octamethylene, have been prepared and evaluated. The diboronic acid systems with tetramethylene 3444 pentamethylene 3555 and hexamethylene 3666 linkers display the greatest enhancement in binding relative to monoboronic acid 4 with D-glucose. The diboronic acid system with the hexamethylene 3666 linker is particularly D-glucose selective and sensitive. Whilst the diboronic acid systems with the longer heptamethylene 3777 and octamethylene 3888 linkers display the greatest enhancement in binding relative to monoboronic acid 4 with D-galactose. All saccharide titrations were performed in methanolic aqueous solution.