ASSAY METHOD USING MAGNETIC PARTICLES

The invention is directed to a method for assaying a target analyte in a biological sample in liquid medium, comprising the following steps: (a.) contacting the biological sample with first magnetic particles (10) bearing a first receptor (101) specific to a first site of attachment of the target analyte (20) so as to form first complexes by the bonding of first magnetic particles (10) with the target analyte (20), this contacting being accompanied, when an interfering analyte (30) is present in the sample, by the formation of interfering complexes by the non-specific bonding of said interfering analyte (30) to the first magnetic particles (10); (b.) applying a first magnetic field, and maintaining it, so as to locally combine all of the complexes formed in step a., and where appropriate to agglomerate interfering complexes with one another to form interfering aggregates; (c.) negating the magnetic field applied in step b. and adding second magnetic particles (11) to the liquid medium that bear a second receptor (111) specific to a second site of attachment of the target analyte (20); (d.) measuring a first quantity representative of the amount of interfering aggregates in the liquid medium, for identifying the presence or absence of said interfering aggregates; (e.) applying a second magnetic field so as to form second complexes (61) by the bonding of the first complexes with second magnetic particles (11); and (f.) measuring a second quantity representative of the collective amount of interfering aggregates and of second complexes (61) in the liquid medium so as to determine the amount of second complexes (61) formed in step e. as a function of the first quantity, for deducing therefrom the amount of target analyte (20) present in the biological sample and, where appropriate, the amount of interfering analyte.