Hall Sensor Based CMOS Immunosensor
Octavian Florescu, Amy Wu and Bernhard Boser
Our goal is to develop a CMOS platform capable of quickly and accurately detecting the presence of micron-sized paramagnetic beads in a solution. Integrated microcoils are used to excite the paramagnetic beads, whose remnant relaxation fields are detected by an array of Hall sensors. The number of sensors detecting the presence of a bead is representative of the concentration of these beads.
The signal from the bead decays with the cube of the distance from the bead to the sensor plane. However, the Hall sensors, the magnetic microcoils, and the backend signal processing circuitry are all integrated on one chip, so this high level of integration makes it possible to keep the beads in close proximity to the sensor surface (~5 µm) thus enabling a high SNR for a wide noise bandwidth.
By applying this technology to immunodiagnostics, the goal is to develop and verify diagnostic assays with improved protocol simplicity with respect to ELISA, the current immunoassay standard. The high level of integration would enable this assay to be used in a point of care or at-home setting, in the absence of additional laboratory resources.
In this proposed immunoassay protocol, the reporting elements are the paramagnetic beads and the washing of the non-specific interactions is done magnetically.
Figure 1: Field generated by paramagnetic bead
Figure 2: Hall sensor: (a) design of Hall sensor; (b) layout of Hall sensor array with integrated microcoils
Figure 3: Proposed immunoassay protocol
- Besse et al., "Detection of a Single Magnetic Microbead Using a Miniaturized Silicon Hall Sensor," Applied Physics Letters, Vol. 80, No. 22, June 2002, pp. 4199-4201.
- Baselt et al., "A Biosensor Based on Magnetoresistance Technology," Biosensors & Bioelectronics, Vol. 13, 1998, pp. 731-739.