Amplification of direct current magnetic responses of magnetic nanobeads due to induced self-assembly of magnetic microbeads

Abstract

Detection of small concentrations of sub-200-nm-sized SPBs (superparamagnetic beads with sizes similar to target molecules) used as ‘magnetic labels’ is critical for the development of rapid, highly sensitive, and portable point of care treatment (POCT) systems. Currently, magnetoresistive (MR) biosensors are used for the detection of large concentrations of SPBs but such an approach is not suitable for monitoring small numbers of sub-200-nm SPBs due to the intrinsic noise of these electronic devices. In order to overcome this limitation of conventional MR sensors, we have developed a simple procedure for detecting small concentrations of sub-200-nm-diameter SPBs for biosensing by exploiting magnetically induced self-assembly of micrometer-sized SPBs onto nanometer targets. Here, our approach enables the physical amplification of the signal from otherwise undetectable nano-SPB targets using Hall biosensors without using the application of ac, magnetic fields or lock-in detection, thereby enabling the production of a simple POCT protocol for a wide range of applications.