Design and Implementation of an Integrated Magnetic Spectrometer for Multiplexed Biosensing

Abstract

Magnetic spectroscopy allows for characterization of the magnetic susceptibility of magnetic beads across a broad frequency range. This enables differentiation and quantification of multiple beads of varying types concurrently present in the active volume of a sensor's surface. A magnetic spectrometer can be used for multi-probe tagging and identification akin to multi-color fluorescent bio-sensing. We propose a new sensing methodology to perform magnetic spectroscopy and analyze various important design parameters such as SNR and gain uniformity. We present a proof-of-concept design of a fully integrated CMOS magnetic spectrometer that can detect, quantify, and characterize magnetic materials in the 1.1 GHz to 3.3 GHz frequency range, where we demonstrate magnetic multiplexing capability using a mixture of two different kinds of magnetic beads. The sensor consumes less than 2 mW of DC power within the whole frequency range, requires no external biasing magnetic fields, is implemented in a standard CMOS process, and can be powered and operated completely from a USB interface. The magnetic spectrometer not only increases the throughput and multiplexing of biosensing experiments for a given sensor area, but also can enable additional applications, such as magnetic flow cytometry and signal-collocation assays of multiple probes.

Analysis and Design of Coupled Inductive Bridges for Magnetic Sensing Applications

“…A similar result was previously presented in [15] assuming only that the magnetic field, H 0 (r), does not change in the presence of a small magnetic perturbation. Here, we have shown how the latter holds only for small values of χ and only if the fundamental assumptions in Section II are fulfilled.…”

“…Fig. 9 overlays two previously measured data sets of the spectral properties of different beads [10], [15] on top of the expected SRF of our coupled sensor, for a different number of turns, N, and different diameters of the core inductors. The desired frequency of operation dictates the sensor size; for example, in order to measure the real part (or magnitude) of χ of iron-oxide nanoparticles up to 1 GHz, we require SRF > 5 GHz.…”

“…In reality, f Z ,in and f out slightly differ due to the distributed nature of the parasitic elements, but the approximation is very Complex frequency response of two types of magnetic beads [10] (top). Change in magnitude of χ versus frequency [15] for three beads types (bottom). reasonable for design purposes.…”

“…9.Complex frequency response of two types of magnetic beads[10] (top). Change in magnitude of χ versus frequency[15] for three beads types (bottom).…”

Giant Magnetoresistive Biosensors for Time-Domain Magnetorelaxometry: A Theoretical Investigation and Progress Toward an Immunoassay

“…Due to the above challenges in MRX, there is an urgent need to re-innovate time-domain MRX in unprocessed samples without the loss of magnetic sensitivity. Some state-of-the-art works substantially improved the temporal limit of MRX by using Hall-effect sensors and inductive microchips with a high sampling-rate analog to digital converter to capture the dynamic response2021535455. Yet, the realization on bioassay using time-domain GMR MRX hasn’t been reported to date.…”