A magnetic sensor for the identification of a chemical or biological species to which are bonded small magnetized particles, by means of a characteristic signature produced by said magnetized particles, comprising: a substrate having a surface on which is formed a plurality of species binding sites; a regular array of MTJ cells formed below said substrate surface, wherein each MTJ cell includes a free layer having an easy axis and a hard axis and a threshold switching field; an MTJ cell selection and resistance measuring circuit for addressing each said MTJ cell in said array and determining variations in the resistance of each said cell and generating a signal indicating said variations; and characterized in that there is: a signal analysis algorithm for identifying a particular correlation between cell resistance variations among two or more substantially neighboring MTJ cells in said regular array, wherein said correlation is configured to detect the presence of two clusters of MTJ resistance variations of approximately equal amplitude but of opposite sign and wherein said clusters are laterally disposed about a vertical axis aligned along said hard axis of a free layer of an MTJ cell in said array, wherein said resistance variations have been determined through the application of said cell selection and resistance measuring circuit; and wherein, said signal analyzing algorithm can distinguish between a single bound magnetized particle and a cluster of magnetized particles by means of stored criteria that recognize the presence of a said cluster by the number and distribution of magnetized particles therein; and wherein said correlation is the signature of a magnetic particle that is magnetized by an externally imposed magnetic field and whereby the presence of said signature is indicative of the presence of a species bonded to said surface, on which species said magnetized particle is bonded. a substrate having a surface on which is formed a plurality of species binding sites; a regular array of MTJ cells formed below said substrate surface, wherein each MTJ cell includes a free layer having an easy axis and a hard axis and a threshold switching field; an MTJ cell selection and resistance measuring circuit for addressing each said MTJ cell in said array and determining variations in the resistance of each said cell and generating a signal indicating said variations; and characterized in that there is: a signal analysis algorithm for identifying a particular correlation between cell resistance variations among two or more substantially neighboring MTJ cells in said regular array, wherein said correlation is configured to detect the presence of two clusters of MTJ resistance variations of approximately equal amplitude but of opposite sign and wherein said clusters are laterally disposed about a vertical axis aligned along said hard axis of a free layer of an MTJ cell in said array, wherein said resistance variations have been determined through the application of said cell selection and resistance measuring circuit; and wherein, said signal analyzing algorithm can distinguish between a single bound magnetized particle and a cluster of magnetized particles by means of stored criteria that recognize the presence of a said cluster by the number and distribution of magnetized particles therein; and wherein said correlation is the signature of a magnetic particle that is magnetized by an externally imposed magnetic field and whereby the presence of said signature is indicative of the presence of a species bonded to said surface, on which species said magnetized particle is bonded. a signal analysis algorithm for identifying a particular correlation between cell resistance variations among two or more substantially neighboring MTJ cells in said regular array, wherein said correlation is configured to detect the presence of two clusters of MTJ resistance variations of approximately equal amplitude but of opposite sign and wherein said clusters are laterally disposed about a vertical axis aligned along said hard axis of a free layer of an MTJ cell in said array, wherein said resistance variations have been determined through the application of said cell selection and resistance measuring circuit; and wherein, said signal analyzing algorithm can distinguish between a single bound magnetized particle and a cluster of magnetized particles by means of stored criteria that recognize the presence of a said cluster by the number and distribution of magnetized particles therein; and wherein said correlation is the signature of a magnetic particle that is magnetized by an externally imposed magnetic field and whereby the presence of said signature is indicative of the presence of a species bonded to said surface, on which species said magnetized particle is bonded.