1,3-Dichloro-9,9-dimethyl-7-(phosphonooxy)-2(9H)-acridinone has been used as a component of an optical fiber nanobiosensor to detect telomerase as general cancer biomarker at single cell level followed by in vitro sandwich ELISA. This compound is also used in nanoparticle-based optical biosensors for the direct detection of organophosphate chemical warfare agents and pesticides.