Flowing label-free bacteria trapped by small magnetic fields

Trapping of biological entities suspended in flowing liquids is of high interest for lab-on-a-chip devices. Micro-magnetofluidic techniques offer a wireless, remote control, label-free, programmable, isothermal method for such trapping. We investigated trapping of nonmagnetic entities suspended in flowing fluids by uniform magnetic fields. Alignment and chain formation of bacteria and polybeads suspended in flowing ferrofluids was observed under low magnetic fields. Individual bacteria as well as bacteria clusters were trapped in flowing ferrofluids by external magnetic fields, demonstrating trapping over a broad size range. In contrast to the conventional studies of bacteria in a stationary fluid, this work demonstrates continuous label-free trapping and alignment of biological entities in flowing fluids in a simple microchannel with low cost microfluidic chip fabrication, facile sample preparation and remote isothermal control of trapping by small uniform magnetic fields. This is a new approach to noninvasive manipulation for bioassays using perfusion-based systems as well as to bioprinting, drug efficacy, cell phenotype, molecular interactions and tissue engineering studies.