Design and performance of GMR sensors for the detection of magnetic microbeads in biosensors

Rapid, femtomolar bioassays in complex matrices combining microfluidics and magnetoelectronics

“…we have described such a BARC ® chip having a 64-element array of giant magnetoresistive (GMR) sensors (Rife et al, 2003), that can be incorporated in a microfluidic cell (Fig. 6a).…”

“…Magnetoelectronic bead counting is accomplished on a BARC ® chip as described previously (Rife et al, 2003). All beads captured above a GMR sensor contribute to the measured resistance with a linear response from ~1 to 1000 Dynabeads.…”

“…However, we find microbead labels offer two significant advantages over smaller labels that far outweigh any disadvantages from the size mismatch. First, it is far simpler to detect low numbers of microbeads than molecular fluorophores, chromophores, or nanoparticles, with individual microbeads readily counted with routine optical microscopy (Lee et al, 2000;Mulvaney et al, 2004) or magnetic detection (Rife et al, 2003;Rife and Whitman, 2004). Second, and more significantly, we find that if a controlled laminar flow is maintained at the capture surface, fluidic drag forces can be applied to the microbead labels to preferentially remove nonspecifically bound labels and thereby dramatically improve the assay performance (Rife and Whitman, 2004).…”

Continuous-flow ferrohydrodynamic sorting of particles and cells in microfluidic devices

“…The label-based methods are manually intensive and time-consuming. The magnetic moments of these beads, even from the same batch, can vary dramatically due to their manufacturing procedure, making scaling of the method scaling difficult (Hafeli et al 1997;Miller et al 2001;Rife et al 2003;Mihajlovic et al 2007;Shevkoplyas et al 2007).…”

Microparticle photometry in a CMOS microsystem combining magnetic actuation and in situ optical detection

“…for detection or further processing [4][5][6]. In most cases, the actuation is achieved by attracting the magnetic particles towards a wire or a microcoil, where they serve as magnetic labels that can be detected via magnetoresistive effects [7][8][9]. Further methods of choice are the optical detection of fluorescently labeled particles or the observation via a microscope [3,6].…”