Abstract
The remarkable advantages micro-chip platforms offer over cumbersome, time-consuming equipment currently in use for bio-analysis are well documented. In this research, a micro-chip that includes a unique magnetic actuator (MA) for the manipulation of superparamagnetic beads (SPBs), and a magnetoresistive sensor for the detection of SPBs is presented. A design methodology, which takes into account the magnetic volume of SPBs, diffusion and heat transfer phenomena, is presented with the aid of numerical analysis to optimize the parameters of the MA. The MA was employed as a magnetic flux generator and experimental analysis with commercially available COMPEL™ and Dynabeads® demonstrated the ability of the MA to precisely transport a small number of SPBs over long distances and concentrate SPBs to a sensing site for detection. Moreover, the velocities of COMPEL™ and Dynabead® SPBs were correlated to their magnetic volumes and were in good agreement with numerical model predictions. We found that 2.8 μm Dynabeads® travel faster, and can be attracted to a magnetic source from a longer distance, than 6.2 μm COMPEL™ beads at magnetic flux magnitudes of less than 10 mT. The micro-chip system could easily be integrated with electronic circuitry and microfluidic functions, paving the way for an on-chip biomolecule quantification device.
Highlights
Superparamagnetic beads (SPBs) have attracted a lot of interest for sorting, separating, purifying and detecting biomolecules in assays [1,2,3,4,5,6,7,8,9,10,11,12]
We describe a design framework for the optimization of the magnetic actuator (MA) by numerical analysis, taking into account the diffusion of SPBs, and factors such as the magnetic volume of the SPBs based on the magnetite/iron oxide content of the SPB, volume susceptibilities at working fields instead of saturation fields, since the susceptibilities at low magnetization fields are higher than susceptibilities at magnetizations approaching saturation, and heat transfer phenomena due to Joule heating
The coefficient of attraction (Catt ), which is the product of the volume susceptibility of an SPB and the magnetic volume of an SPB: Catt = Vmag × χ
Summary
Superparamagnetic beads (SPBs) have attracted a lot of interest for sorting, separating, purifying and detecting biomolecules in assays [1,2,3,4,5,6,7,8,9,10,11,12]. A large number of magnetic micro-devices have been developed in recent times for on-chip manipulation of SPBs [3,13,14,15] In these devices, the magnetic force used to manipulate SPBs is provided by micrometer sized electromagnets, soft-ferromagnetic structures, or some combination of both. Domain wall motion in nanometer thick permalloy patterns has been used to precisely transport SPBs to a target location [16,17] as well for detection of SPBs [18,19,20,21,22] These devices employ bulky off-chip electromagnets or permanent magnets as magnetic field generators, which must be aligned to features on the micro-device.
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