A method for updating an index in a database includes storing a plurality of changes to be made to a database index in a change table. The magnetoresistive sensor device includes a substrate having attached thereto binding sites able to selectively bind the target sample, and a magnetoresistive sensor for detecting the magnetic field of the nanoparticles coupled to the target sample. A polymer is dispersed in the fluid, this polymer having a plurality of second groups capable of attracting the first groups on the particles so that the polymer in the fluid forms a complex with the electrophoretic particles. The n elongated pad regions bound n-1 active regions of the lateral transistor where n\u22673.