Patent ID: 8247241

Claim:
A method for detecting a target compound comprising: injecting a test liquid containing a target compound into a colloid solution of magnetic nano-particles having an average particle diameter of 50 nm or less to allow the target compound to bind to the magnetic nano-particles, thereby forming bound magnetic nano-particles having a diameter of 100 nm or more; concentrating the formed bound magnetic nano-particles by magnetic separation, thereby obtaining a concentrated dispersion liquid of the bound magnetic nano-particles; bringing the concentrated dispersion liquid containing the bound magnetic nano-particles and non-bound magnetic nano-particles in proximity to a magnetic sensor comprising at least a magnetoresistive (MR) element and a permanent magnet; and measuring the change in magnetic resistance to selectively detect the bound magnetic nano-particles in a dispersed state in the concentrated dispersion liquid without trapping the bound and the non-bound magnetic nano-particles, thereby indirectly detecting the target compound.