Fast and precise magnetophoresis of superparamagnetic nanoparticles on a micro-magnetic substrate in a static liquid environment

Abstract

Micro-magnet arrays coupled with external rotating magnetic fields have been reported for the manipulation of individual superparamagnetic particles in stationary microfluidics, requiring no fluidic actuation. In addition to their magnetic properties preventing particle aggregation, superparamagnetic particle size reduction advantageously increases their interaction with surrounding liquid environment. However, precise magnetophoresis of submicrometric particles is challenging, owing to their low magnetic content. We present a micro-magnetofluidic chip for fast and collective transport of superparamagnetic nanoparticles (SNPs) over centimetric distances. In our innovative approach, SNPs are captured on a line pattern on top of a micro-magnet array covered with a spacer, which allows for SNP precise positioning along the surface using a rotating external magnetic field. The impact of SNP size on magnetophoresis was explored by characterizing the velocility ranges of 100 nm and 200 nm SNPs. For 100 nm size, a critical speed of 500 µm/s was reached beyond which the particles get resuspended, whereas for the 200 nm size, our system maximum rotation speed conveys the particles at up to 1.4 mm/s without reaching a critical speed. The mobility of SNPs was investigated in different buffers commonly used for biological analysis, and shown to be enhanced in low ionic strength conditions. As an example of future application, we demonstrate nucleic acid detection by SNP accumulation enabling to concentrate the fluorescence signal. This system provides the opportunity to be easily integrated in lab-on-a-chip (LOC) devices and could help relieve current development limitations related to complex and costly fluidic actuation instrumentation.