New biochip development based on the detection of single superparamagnetic microspheres using integrated spin valve sensors

Summary form only given. Biomolecules such as the enzyme horseradish peroxidase and the protein streptavidin immobilized on superparamagnetic magnetic labels (2 /spl mu/m encapsulated microconed iron oxide (15%) poly(styrene-co-maleic acid) microspheres (Micromer(R)-M, Micromod), 20-40 biomolecules per label) were detected using spin valve sensors (2/spl times/6 /spl mu/m/sup 2/, MR/spl sim/5%). Using an on-chip field of 15 Oe (external field) MR signals of /spl sim/100 /spl mu/V were obtained when single 2 /spl mu/m particles were placed over the spin valve sensor. Sensor saturation occurs near /spl sim/1 mV with a noise level of /spl sim/10 /spl mu/V. The moment of the 2 /spl mu/m diameter microspheres at 15 Oe was estimated at 5.10/sup -12/ emu and the calculated maximum MR signal for one microsphere directly on top of the sensor was /spl sim/400 /spl mu/V (this assumes zero space between the microsphere and sensor surface). The microspheres were focussed at the sensor site and moved to and from the sensor by integrating the sensors within Al current line structures. The lines were tapered in diameter from 150 /spl mu/m to 5 /spl mu/m at the sensor area to enable (10-20 mA current) the positioning of small numbers of beads at sites (5/spl times/15 /spl mu/m/sup 2/) adjacent to the sensor. Single microspheres could then be moved over the sensor by switching the current line off and back to the current line by switching the current line on.