MagArray Biochips for Protein and DNA Detection with Magnetic Nanotags: Design, Experiment, and Signal-to-Noise Ratio

Abstract

MagArray ™ chips contain arrays of magnetic sensors, which can be used to detect surface binding reactions of biological molecules that have been labeled with 10 to 100 nm sized magnetic particles. Although MagArray chips are in some ways similar to fluorescence-based DNA array chips, the use of magnetic labeling tags leads to many distinct advantages, such as better background rejection, no label bleaching, inexpensive chip readers, potentially higher sensitivity, ability to measure multiple binding reactions in homogeneous assays simultaneously and in real-time, and seamless integration with magnetic separation techniques. So far, the technology of MagArray chips has been successfully used to perform quantitative analytic bioassays of both protein and nucleic acid targets. The potential of this technology, especially for point-of-care testing (POCT) and portable molecular diagnostics, appears promising, and it is likely that this technology will see significant further performance gains in the near future. 15.1 Principle of Operation and Technological Benefits The majority of magnetic-label based biochips, or MagArrays, share a common principle of operation. At the heart of the technology stands an elaborate mag-netoresistive (MR) multilayer thin film, the resistance of which varies with the orientation and strength of the proximate magnetic field. This MR film is sputter-deposited onto a nonconducting substrate wafer and patterned into a sensor array by lithographic means. With a reasonable degree of circuit complexity, each sensor of such an array can be independently and simultaneously read out. The MR response is very fast (on the time scale of nanoseconds or less) and is a direct function of