A magnetic microchip for controlled transport of attomole levels of proteins

Abstract

A novel method of controlled transport of proteins immobilized on micrometre-sized magnetic beads in a lab-on-a-chip environment is presented. Bead motion is controlled by lithographically made magnetic elements forming transportation lines in combination with an applied in-plane rotating magnetic field. In this way, transport of attomole amounts of proteins is controlled with micrometre precision. Also, the activity of proteins immobilized on the beads is demonstrated by injecting antibodies into the system. A critical step in developing the method was to reduce sticking forces between beads and substrate during transportation of proteins. Charge interaction was found to be of minor importance compared to hydrophobic forces. To achieve a reliable transport of biologically active proteins, both substrate and beads were coated with polyethylene glycol (PEG) and the protein covered beads were suspended in buffer with surfactants. The described system fulfils all the important unit operations of a microfluidic platform and, as a further advantage, presents less need for microchannels and electric wiring.

Flow enhanced non-linear magnetophoretic separation of beads based on magnetic susceptibility

“…The FNLM separator was assembled from a 60 micro-magnet array (MMA) that was embedded in a transparent micro-fluidic chamber. Figure 2b presents a schematic of the topview of the separator in which the grey rectangular regions represent staggered arrays of micro-magnets 24 that are divided by 200 µm wide magnet-free channels. Figure 2c presents a 65 microscopic image of the edge of a MMA in which circular micro-magnets can be clearly identified.…”

Microstripes for transport and separation of magnetic particles

“…7,8 The magnetic transportation of a larger quantity of particles has been demonstrated by use of periodic arrays of soft magnetic ellipsoids 9,10 and of hard magnetic circular disks. 11,12 The latter authors have also studied the particle transportation as function of the frequency f of the harmonically varying applied magnetic field and have demonstrated theoretically and experimentally that a particle will not be transported when f exceeds a critical value that depends on the magnetic moment and the hydrodynamic size of the particle.…”

Improved bacteria detection by coupling magneto-immunocapture and amperometry at flow-channel microband electrodes

“…In addition, operation under flow conditions improves immunocapture, enzymatic reactions and electrochemical detection by minimising mass transport limitations, contributing to shorter assay time. At least one work reports on a flow-through immunomagnetic separator designed to capture bacteria from large volume samples (>50 ml) (Rotariu et al, 2005) and an increasing number of publications describe the automation of MP manipulation, recovery, and/or detection (Herrmann et al, 2008;Hervas et al, 2009;Peyman et al, 2009;Yoon et al, 2009;Berti et al, 2009;Johansson et al, 2010). However, only a few cases describe the application to immunocapture and detection of whole bacterial cells (Chandler et al, 2001;Straub et al, 2005;Qiu et al, 2009;Ramadan et al, 2010).…”