Koichi Fujiwara

Electron Microscopic Studies of Viruses Labeled with Magnetite

We were able to develop a method with which to successfully and specifically detect virus particles under the electron microscope by using magnetite. This method was devised on the principle that magnetite‐labeled antibody or magnetite coupled with protein A selectively bind virus or antibody‐treated virus particles on the electron microscope grid by the action of an electromagnet. Another advantage characterizing the technique is the possibility of detection of a small number of virus particles. This is done through a process of concentration and purification of the reaction complexes trapped rigidly by magnetic force.

Sensitive Detection of Viral Antigens with a New Method, "Laser Magnet Immunoassay"

A new method, “laser magnet immunoassay” (LMIA), has been developed for sensitive detection of viral antigens. Target viruses captured on microbeads were made to react with antibodies labeled with magnetite particles. In a magnetic field, magnetically labeled antigens dispersed in water were attracted to and concentrated at one point on the surface, resulting in the lifting up of a small surface area. A laser beam which was incident on the point reflected, making an interference fringe. The intensity of the fringe indicates the amount of the magnetite conjugated with antigen. A very low concentration of antigens, such as 5 particles of influenza virus and 0.1 pg/ml of human immunodeficiency virus (HIV) p24 antigen in human serum, could be detected by this method. Application of this method to diagnoses of viral diseases in early stages is discussed.