For tumor DNA, separate detector probes, labeled with fluorescein isothiocyanate, mix with the saliva sample after the latter has been centrifuged to remove cells and stabilized with RNAse. Then, anti-fluorescein antibody conjugated to horseradish peroxidase binds the detector probes, horseradish peroxidase substrate is added, and the amperometric signal generated by the subsequent redox reaction is measured. EFIRM requires just a 40 µL sample, according to Wong. Unlike polymerase chain reaction (PCR)-based assays, he stressed, “This is direct detection.”