a chemical composition including a fluorescent polymer and a receptor that is specific for both a target biological agent and a chemical moiety including a recognition element , a tethering element , and a property - altering element is disclosed . both the fluorescent polymer and the receptor are co - located on a support . when the chemical moiety is bound to the receptor , the property - altering element is sufficiently close to the fluorescent polymer to alter the fluorescence emitted by the polymer . when an analyte sample is introduced , the target biological agent , if present , binds to the receptor , thereby displacing the chemical moiety from the receptor , resulting in an increase of detected fluorescence . assays for detecting the presence of a target biological agent are also disclosed .