Detection and manipulation of biomolecules by magnetic carriers.
ABSTRACT The detection and manipulation of single molecules on a common platform would be of great interest for basic research of biological or chemical systems. A promising approach is the application of magnetic carriers. The principles are demonstrated in this contribution. It is shown that paramagnetic beads can be detected by highly sensitive magnetoresistive sensors yielding a purely electronic signal. Different configurations are discussed. The capability of the sensors to detect even single markers is demonstrated by a model experiment. In addition, the paramagnetic beads can be used as carriers for biomolecules. They can be manipulated on-chip via currents running through specially designed line patterns. Thus, magnetic markers in combination with magnetoresistive sensors are a promising choice for future integrated lab-on-a-chip systems.
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ABSTRACT: We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecular-beam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with tCr=9 Å, at T=4.2 K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.Physical Review Letters 12/1988; 61(21):2472-2475. · 7.94 Impact Factor
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ABSTRACT: Commercially available superparamagnetic nanospheres are commonly used in a wide range of biological applications, particularly in magnetically assisted separations. A new and potentially significant technology involves the use of these particles as labels in magnetoresistive assay applications. In these assays, magnetic bead labels are used like fluorescent labels except that the beads are excited and detected with magnetic fields rather than with photons. A major advantage of this technique is that the means for excitation and detection are easily integrable on a silicon circuit. A preliminary study of this technique demonstrated its basic feasibility, and projected a sensitivity of better than 10-12 Molar (Baselt et al ., Biosensors and Bioelectronics, 13, 731 (1998)). The present paper examines the theoretical signal to noise ratio of this type of assay for the special case of a single magnetic bead being detected by a single giant magnetoresistive (GMR) detector. Assuming experimentally observed and reasonable parameters for the magnetic label and the sensitivity of the GMR detector, the signal toJournal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2000; 18(4):1125-1129. · 1.43 Impact Factor
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ABSTRACT: We present a comparative analysis of a magnetoresistive biosensor to standard fluorescent DNA detection. The biosensor consists of giant magnetoresistive (GMR) type Cu/Ni(80)Fe(20) multilayers in the second antiferromagnetic coupling maximum. Each of the 206 elements of the magnetoresistive biosensor is patterned into a spiral-shaped line that can cover the area of a typical DNA spot (70 microm diameter). The probe DNA is assembled on top of the sensor elements in different concentrations ranging from 16 pg/microl to 10 ng/microl. Complementary biotin-labeled analyte DNA is hybridized to the probe DNA at a concentration of 10 ng/microl. A number of different commercially available magnetic microspheres are investigated to determine the most appropriate markers. The experimental comparison shows that the relative sensitivity of the magnetoresistive biosensor is superior to the fluorescent detection at low probe DNA concentrations.Biosensors and Bioelectronics 06/2004; 19(10):1149-56. · 5.44 Impact Factor