Concentration of Magnetic Beads Utilizing Light-Induced Electro-Osmosis Flow

Microfluidics and Nanofluidics, 2013

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 Ò 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 Ni 80 Fe 20 (permalloy) 5 lm 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 lm s -1 for 1 Hz rotational frequency with 5 lm pattern elements spaced with a 1 lm gap between elements.

Analytical Chemistry, 2016

The detection of single molecules in magnetic microbead microwell array formats revolutionized the development of digital bioassays. However, retrieval of individual magnetic beads from these arrays has not been realized until now despite having great potential for studying captured targets at the individual level. In this paper, optical tweezers were implemented on a digital microfluidic platform for accurate manipulation of single magnetic beads seeded in a microwell array. Successful optical trapping of magnetic beads was found to be dependent on Brownian motion of the beads, suggesting a 99% chance of trapping a vibrating bead. A tailormade experimental design was used to screen the effect of bead type, ionic buffer strength, surfactant type, and concentration on the Brownian activity of beads in microwells. With the optimal conditions, the manipulation of magnetic beads was demonstrated by their trapping, retrieving, transporting, and repositioning to a desired microwell on the array. The presented platform combines the strengths of digital microfluidics, digital bioassays, and optical tweezers, resulting in a powerful dynamic microwell array system for single molecule and single cell studies.

Lab on a Chip, 2010

This paper reports a novel microfluidic-chip based platform using ''phase-transfer magnetophoresis'' enabling continuous biomolecule processing. As an example we demonstrate for the first time continuous DNA extraction from cell lysate on a microfluidic chip. After mixing bacterial Escherichia coli culture with superparamagnetic bead suspension, lysis and binding buffers, DNA is released from cells and captured by the beads. These DNA carrying beads are continuously transported across the interfaces between co-flowing laminar streams of sample mixture, washing and elution buffer. Bead actuation is achieved by applying a time-varying magnetic field generated by a rotating permanent magnet. Flagella-like chains of magnetic beads are formed and transported along the microfluidic channels by an interplay of fluid drag and periodic magnetic entrapment. The turnover time for DNA extraction was approximately 2 minutes with a sample flow rate of 0.75 ml s À1 and an eluate flow rate of 0.35 ml s À1. DNA recovery was 147% (on average) compared to bead based batch-wise extraction in reference tubes within a dilution series experiment over 7 orders of magnitude. The novel platform is suggested for automation of various magnetic bead based applications that require continuous sample processing, e.g. continuous DNA extraction for flow-through PCR, capture and analysis of cells and continuous immunoassays. Potential applications are seen in the field of biological safety monitoring, bioprocess control, environmental monitoring, or epidemiological studies such as monitoring the load of antibiotic resistant bacteria in waste water from hospitals.

ISSCC. 2005 IEEE International Digest of Technical Papers. Solid-State Circuits Conference, 2005., 2005

IEEE Transactions on Magnetics, 2009

In this paper, we investigated a means to manipulate small magnetic beads using the magnetic fields of current-carrying wires. Narrow metallic wires were fabricated with optical lithography and vacuum deposition methods. As we applied 20-40 mA of current, the magnetic beads could be collected on the wire. Depending on the magnitude of the currents, the velocity of the beads was 2-20 m/s. In addition to the motion of the beads by the interaction with the fields, we also observed drift of the beads caused by the local heating of the wire and the resulting temperature gradient. We also demonstrated transfer of beads between wires by switching the current between the wires. We consider that this simple device can be used to transfer the beads to the locations of the sensors and that it can increase the reaction probability between beads and magnetic sensors.

Advanced Materials, 2010

Microfluidics and Nanofluidics, 2010

Functionalized magnetic beads offer promising solutions to a host of micro-total analysis systems ranging from immunomagnetic biosensors to cell separators. Immunochemical binding of functional biochemical agents or target biomolecules serves as a key step in such applications. Here we show how magnetophoretic motion of magnetic microspheres in a microchannel is harnessed to promote in situ immunochemical binding of short DNA strands (probe oligonucleotide) on the bead surface via streptavidin-biotin bonds. Using a transverse magnetic field gradient, the particles are transported across a co-flowing analyte stream containing biotinylated probe oligonucleotides that are labeled with a Cy3-fluorophore. Quantification of the resulting biotin-streptavidin promoted binding has been achieved through fluorescence imaging of the magnetophoretically separated magnetic particles in a third stream of phosphate buffered saline. Both the experimental and numerical data indicate that for a given flow rate, the analyte binding per bead depends on the flow fraction of the co-flowing analyte stream through the microchannel, but not on the fluid viscosity. Parametric studies of the effects of fluid viscosity, analyte flow fraction, and total flow rate on the extent of binding and the overall analyte separation rate are also conducted numerically to identify favorable operating regimes of a flowthrough immunomagnetic separator for biosensing, cell separation, or high-throughput applications.

Sensors and Actuators B-chemical, 2006

Manipulating biological samples in microliter droplets has vast potential in molecular diagnostics. We present a system for the two-dimensional (2D) magnetic manipulation of aqueous droplets suspended in silicone oil as a platform for on-chip bioanalysis. Superparamagnetic microparticles inside the droplets provide the means of the magnetic actuation. The droplets can be displaced, merged, mixed and separated on the chip without

2009

We present a novel microfluidic platform using laminar-flow magnetophoresis for combined continuous extraction and purification of DNA. All essential unit operations (DNA binding, sample washing and DNA elution) are integrated on one single chip. The key function is the motion of magnetic beads given by the interplay of laminar flow and time-varying magnetic field. The time for extraction was 1 minute. The device is a central part of a complete biochemical system for continuous monitoring of cell-growth in bioreactors. The novel platform allows continuous purification of DNA, but is also applicable to purification of RNA, proteins or cells, including their subsequent real-time analysis in general.

Scientific Reports

Magnetically actuated lab-on-a-chip (LOC) technologies have enabled rapid, highly efficient separation of specific biomarkers and cells from complex biological samples. Nonlinear magnetophoresis (NLM) is a technique that uses a microfabricated magnet array (MMA) and a time varying external magnetic field to precisely control the transport of superparamagnetic (SPM) beads on the surface of a chip based on their size and magnetization. We analyze the transport and separation behavior of SPM monomers and dimers on four MMA geometries, i.e., circular, triangular, square and rectangular shaped micromagnets, across a range of external magnetic field rotation frequencies. The measured critical frequency of the SPM beads on an MMA, i.e., the velocity for which the hydrodynamic drag on a bead exceeds the magnetic force, is closely related to the local magnetic flux density landscape on a micromagnet in the presence of an external magnetic field. A set of design criteria has been established ...