Surface-immobilized monolayers of fluorescent molecular sensors consisting of a short conjugated oligo(p-phenylene ethynylene) core end-capped with an acceptor fluorophore (analyte receptor) display significant signal amplification due to enhanced intermolecular energy transfer within the monolayer. This general phenomenon offers a superior platform for designing ratiometric fluorescent sensors. An example of how this can be used to convert a narrow-range threshold fluorescent pH indicator (fluorescein) to a broad-range ratiometric fluorescent chemosensor is described.