Manipulation and Detection of Magnetic Nanoparticles for Diagnostic Applications

Abstract

Abstract This review presents recent developments concerning the use of nanoscale magnetic materials in the field of biosensors and bioelectronics. Compared with optical and electrical materials, magnetic materials enjoy several advantages which have been applied to numerous bioanalytical devices. For example, biological fluids do not attenuate magnetic fields, which is advantageous both for detection and manipulation systems due to the reduction of background noise. Magnetic materials are also more stable than their fluorescent counterparts, in which photo‐bleaching is a serious impediment to quantitative analysis. This article begins with a brief tutorial on the magnetization behavior of nanoscale magnetic materials. It is followed by a discussion of how force can be applied to colloidal materials with various magnetic manipulation apparatus, with a particular emphasis on the role that size and geometry play in determining the efficiency of magnetic particle manipulation in the context of randomizing thermal energy. Design principles will be provided to demonstrate how the manipulation apparatus can achieve greater flexibility by using two sources of magnetic field, one which produces strong local magnetic field gradient and the other which produces uniform magnetic field. Next, we review recent developments on miniature magnetic field sensor devices, which are routinely applied to detect and analyze the presence of biological molecules and micro‐organisms. An outline of the different types of magnetic field sensors used in biodiagnostics is provided, however the focus is mainly on the physical principles underlying the most commonly used sensor based on magnetoresistive materials. Finally, a brief conclusion is provided on the future outlook of nanoscale magnetic materials in lab‐on‐a‐chip devices.