Patent ID: 7446524

Claim:
A method for detecting magnetic particles contained in a fluid provided in an extended gap opening formed in a channel base material supported on at least a portion of a substrate where a magnetic field sensor is also supported on at least a portion of said substrate but without said channel base material being across said magnetic field sensor from said substrate so as to form sides of said extended gap opening there that extends past said magnetic field sensor in at least one direction, there being an electrical conductor supported on said substrate positioned at least in part at said sensor location so as to be in direct contact with at least some surface of said magnetic field sensor positioned at least in part along, and between projections at said sides of, said extended gap opening, said method comprising: introducing said fluid with said magnetic particles contained therein into said extended gap opening so as to be present at a vicinity about said magnetic field sensor; supplying a selected first electrical current in said electrical conductor and said magnetic field sensor while monitoring that voltage occurring across said magnetic field sensor; and supplying a magnetic field from a source other than said magnetic particles in a selected direction such that said magnetic field is present in said extended gap opening.