Magnetic nanoclusters (MNCs) were synthesized in a one-pot process, carboxylic MNCs and dual-functional protein were prepared and used to capture hepatitis B virus surface antibodies (anti-HBs) in simulated diseased oral mucosal transudate (OMT) samples. The specific substrate of dual-functional protein, dual-labeled double-chained DNA molecules, based on Fluorescence Resonance Energy Transfer (FRET), was used to amplify the detection signal and the detection limit of 0.1 ng mL(-1) of anti-HBs monoclonal antibodies was achieved. Combination MNCs with dual-functional protein enables the noninvasive detection of hepatitis B virus (HBV) surface antibodies in OMT samples, showing promise as a diagnostic tool for the OMT diagnosis of infectious diseases with sensitive, specific and facile capabilities.