Ultra Dense DNA Microarray Design Using Magnetoresistive Detectors

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Abstract
Microelectronic chip-based systems are available for a wide variety of applications. Many of these systems rely on NON-INTEGRATED optical detection schemes to collect data from the chips. A magnetoresistive detection format, however, can be completely integrated. This paper presents some basic concepts for optimizing micron-sized magnetoresistive sensors for single nucleotide polymorphism (SNP) analysis and DNA diagnostics. Magnetoresistive sensors are nano-fabricated thin film resistors whose resistance changes as a function of magnetic field. The magnetic DNA assay replaces the EXTERNAL optical reader apparatus with an INTEGRATED magnetoresistive sensor at each “pixel” of the array. The EXTERNAL light source can be replaced by an INTEGRATED magnetic field generation strap, or by a simple external coil. Magnetoresistive pixel sizes could presently be ~ 3 microns on a side, and decrease to ~ 100 nm with technological improvements. It is shown that, taking reasonable values for critical parameters, a signal to noise ratio of 10,000 : 1 is achievable using 10 nm paramagnetic beads as the assay label. As early demonstrations of the feasibility of this system, data have been collected using NVE's magnetoresistive sensors (non-optimized) to easily detect single micron-sized magnetic beads. Presently NVE is working on 1 million bit arrays of magnetoresistive sensors which are being fabricated into magnetoresistive random access memory (MRAM) chips. These arrays have many similarities to what is required for the magnetoresistive DNA assay including sub-micron bit size and single bit addressability.

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