The detection and manipulation of single molecules on a common platform would be of great interest for basic research of biological or chemical systems. A promising approach is the application of magnetic carriers. The principles are demonstrated in this contribution. It is shown that paramagnetic beads can be detected by highly sensitive magnetoresistive sensors yielding a purely electronic signal. Different configurations are discussed. The capability of the sensors to detect even single markers is demonstrated by a model experiment. In addition, the paramagnetic beads can be used as carriers for biomolecules. They can be manipulated on-chip via currents running through specially designed line patterns. Thus, magnetic markers in combination with magnetoresistive sensors are a promising choice for future integrated lab-on-a-chip systems.
[Show abstract][Hide abstract] ABSTRACT: Super-paramagnetic microbeads are widely used for cell isolation. Evaluation of the binding affinity of microbeads to cells using optical microscopy has been limited by its small scope. Here, magnetic property of microbeads was first investigated by using synchrotron radiation (SR) in-line x-ray phase contrast imaging (PCI). The cell line mouse LLC (Lewis lung carcinoma) was selected for cell adhesion studies. Targeted microbeads were prepared by attaching anti-VEGFR2 (vascular endothelial growth factor receptor-2) antibody to the shell of the microbeads. The bound microbeads were found to better adhere to LLC cells than unbound ones. PCI dynamically and clearly showed the magnetization and demagnetization of microbeads in PE-50 tube. The cells incubated with different types of microbeads were imaged by PCI, which provided clear and real-time visualization of the cell isolation. Therefore, PCI might be considered as a novel and efficient tool for further cell isolation studies.
PLoS ONE 09/2012; 7(9):e45597. DOI:10.1371/journal.pone.0045597 · 3.23 Impact Factor
"In addition, the magnetic fields do not screen by biologic content and bacterial growth medium. Magnetic beads with functionalized surfaces are widely used as carriers for manipulation, separation, and biomolecular sensing (Brzeska et al. 2004; Gijs 2004; Karle et al. 2010; Karle et al. 2011; Safarik and Safarikova 2004). In the past few years, many approaches have been developed for the on-chip manipulation and transport of functionalized magnetic beads using micro-fabricated current-carrying wires and coils (Deng et al. 2001; Ramadan et al. 2006; Wirix-Speetjens et al. 2005). "
[Show abstract][Hide abstract] ABSTRACT: We demonstrate on-chip manipulation and trapping of individual microorganisms at designated positions on a silicon surface within a microfluidic channel. Superparamagnetic beads acted as microorganism carriers. Cyanobacterium Synechocystis sp. PCC 6803 microorganisms were immobilized on amine-functionalized magnetic beads (Dynabead® M-270 Amine) by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)–N-hydroxysulfosuccinimide coupling chemistry. The magnetic pathway was patterned lithographically such that half-disk Ni80Fe20 (permalloy) 5 μm elements were arranged sequentially for a length of 400 micrometers. An external rotating magnetic field of 10 mT was used to drive a translational force (maximum 70 pN) on the magnetic bead carriers proportional to the product of the field strength and its gradient along the patterned edge. Individual microorganisms immobilized on the magnetic beads (transporting objects) were directionally manipulated using a magnetic rail track, which was able to manipulate particles as a result of asymmetric forces from the curved and flat edges of the pattern on the disk. Transporting objects were then successfully trapped in a magnetic trapping station pathway. The transporting object moves two half-disk lengths in one field rotation, resulting in movement at ~24 μm s−1 for 1 Hz rotational frequency with 5 μm pattern elements spaced with a 1 μm gap between elements.
Microfluidics and Nanofluidics 01/2012; 14(1-2). DOI:10.1007/s10404-012-1046-z · 2.53 Impact Factor
"On the contrary, the use of microfabricated electromagnets allows to create strong local magnetic field gradients that can easily be either switched on and off or modulated by controlling the intensity of the current powering the micro-coils (Choi et al. 2001;d e Vries et al. 2005; Smistrup et al. 2005; Dubus et al. 2006; Ramadan et al. 2006a, b; Smistrup et al. 2006). Moreover, by using several integrated micro-electromagnets (Deng et al. 2001; Brzeska et al. 2004; Lee et al. 2004; Liu et al. 2007), modulable magnetic field profiles for effective manipulation and positioning of magnetic carriers can easily be achieved. Although these efforts have to some extent addressed several challenges related to the magnetic manipulation in microfluidic channels, there are still many remaining issues related to magnetic bead confinement with micron or even sub-micron resolution, as required for the development of ultrasensitive biosensors. "
[Show abstract][Hide abstract] ABSTRACT: Efficient manipulation and capture of magnetic carriers in fluid stream require appropriate magnetic confinement devices whose
performances are strongly dependent on the nature of the magnetic carriers. In this sense, we have performed a systematic
investigation of the magnetic capture efficiencies for five commercially available superparamagnetic particles pumped along
rectangular microfluidic channels using microelectromagnetic traps composed of planar circular current-carrying microwires
and cylindrical ferromagnetic posts. In addition, in order to obtain a quantitative description of particle movement, we have
implemented a numerical model for the dynamics of magnetic objects subjected to magnetic field gradients in conventional continuous-flow
microfluidic devices. Fully 3D trajectories of the particles, effective cross-sectional areas of the microchannel as well
as micro-electromagnet trapping efficiencies are compared to experimental measurements and a very good agreement is obtained.
Finally, a simple and effective analytical model to determine the critical velocity, i.e. when the magnetic trapping device
is no longer able to capture and hold 100% of the magnetic superparamagnetic particles, is also presented.
Microfluidics and Nanofluidics 08/2008; 5(3):373-381. DOI:10.1007/s10404-007-0249-1 · 2.53 Impact Factor
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