Patent ID: 8193003

Claim:
A method for detecting a target substance by binding magnetic particles to the target substance in a solution contained in a container and detecting with a magnetic sensor, a magnetic signal generated by the magnetic particles, comprising the steps of: a first step of applying a first external magnetic field for orientation to the solution as a specimen including the target substance bound to the magnetic particles; a second step of shutting off said first external magnetic field for orientation to detect a first magnetic signal; a third step of applying to the solution a second external magnetic field for orientation which second external magnetic field has an inverse polarity, as compared with the first external magnetic field and a strength of which second external magnetic field is not more than coercivity of the magnetic particles and coercivity of magnetic impurities; a fourth step for shutting off said second external magnetic field for orientation to detect a second magnetic signal; and a fifth step for obtaining a difference between the first magnetic signal and the second magnetic signal to detect the target substance with eliminating at least one of (1) a magnetic influence of the magnetic particles adhering to the container and (2) the magnetic impurities adhering to the container.