Patent ID: 6764861
Filing Date: 2004-07-20
Classification: G01N,G11C

Abstract:
A method of determining the presence or amount of an analyte in a test sample, the method comprising the steps of(1) providing a sensing device comprising (a) a plurality of magnetic sensing elements, each magnetic sensing element comprising at least one planar layer of electrically conductive ferromagnetic material having an initial state in which the material has a circular magnetic moment within the plane of the layer, each magnetic sensing element having molecules of a first specific binding member attached thereto, and (b) means to detect the change in the electrical resistance of each magnetic sensing element (2) exposing the sensing device to a fluid test medium suspected of containing an analyte and including a plurality or magnetizable particles, each magnetizable particle having molecules of a second specific binding member attached thereto, wherein the first specific binding member and the second specific binding member are selected so that the first specific binding member and the second specific binding member interact with each other or react competitively with the analyte to cause the magnetizable particles to become immobilized with respect to the magnetic sensing elements in direct or inverse relation to the amount of the analyte in the test medium, and wherein the relative size of the magnetizable particles and the magnetic sensing elements and the location of the molecules of the first specific binding member are selected so that when a particular magnetizable particle becomes immobilized with respect to a particular magnetic sensing element, the radial fringing field of the magnetizable particle is able to cause the magnetic moment of at least one layer of electrically conductive ferromagnetic material to shift from circular to radial, thereby causing a detectable change in the electrical resistance of the magnetic sensing element, (3) magnetizing the magnetizable particles, and (4) monitoring the resistance of each magnetic sensing element to detect any change in the electrical resistance of the magnetic sensing elements in response to the immobilization of the magnetizable particles in order to determine the presence or amount of the analyte test sample.