Continuous outbreaks of avian influenza (AI) in recent years with increasing threat to animals and human health have warranted the urgent need for rapid detection of pathogenic AI viruses.In this study,an piezoelectric immunosensor based on a quartz crystal microbalance (QCM) electrode was developed as a new application for sensitive,specific and rapid detection of avian influenza virus H5N1.Polyclonal antibodies against AI virus H5N1 surface antigen HA (Hemagglutinin) were oriented on the gold microelectrode surface through self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA).Target H5N1viruses were then captured by the immobilized antibody,resulting in a change in the frequency and resistance of the QCM electrode surface at the same time.Magnetic nanobeads with diameter of 30 nm,which were modified with anti-H5 antibody through biotin-streptavidin binding,were used for further amplification of the binding reaction of the antibody-antigen (virus).Both binding of target AI H5N 1 and magnetic nanobeads onto the QCM electrode surface were further confirmed by atomic force microscopy.The piezoelectric immunosensor could detect the target AI H5N1 virus at a titer higher than 0.128 HA unit within 2 h.The response of the antibody-antigen (virus) interaction was shown to be virus titer-dependent,and a linear relation between the titer of H5N1 virus and frequency shift,and resistance change was found respectively.No significant interference was observed from non-target viruses.(The H5N1 used in the study was inactivated virus.)