FIAflexTM system is using Time-resolved Fluorescence Immunoassay (TR-FIA) that is suggested as more sensitive than conventional fluorometric method. TR-FIA uses Europium Ion (Eu3+) as fluorescent particles. Eu3+ shows an extended fluorescence lifetime and stable fluorescent signal, which enables the fluorescent emission to be read at a time well after any background fluorescence has decayed. Thus the background noise is decreased and the assay sensitivity is significantly improved.