What is a Ferrofluid?
Ferrofluids are suspensions of magnetic nanoparticles in a solution. These nanoparticles typically have diameters between 40 and 140 nm, giving them colloidal properties. Colloids are homogenous mixtures that due to their size, do not settle out into their components and cannot be separated by filtration. Colloids also react with diffusion control kinetics, which means that the high rate of diffusion eliminates the need for constant mixing during a reaction.
Ferrofluids are also unique in that they have a high magnetic moment, and under the influence of a magnetic field, will form small chains of North-South nanoparticles. These chains have synergistic magnetic properties, making them readily separable in low magnetic gradients ( > 3-4 kGauss/cm).
Ferrofluids at BioMagnetic Solutions
Our Ferrofluids are manufactured by first forming crystalline cores of magnetite of about 100 nm, which are subsequently coated with multilayers of bovine or human serum albumin. Monoclonal antibodies or other proteins such as streptavidin or other common capture agents are then covalently coupled to the albumin protein, allowing for cell capture.
Our manufacturing process produces nanoparticles that are 84% magnetic mass, whereas other nanoparticles of similar size are typically only 8%. This means that our ferrofluids are highly magnetic, and can be separated out of solution using only a low gradient magnet, no need for high-gradient columns!
Applications of XpresSepTM Ferrofluid
The antibodies or capture agents such as streptavidin (SA) or rat anti-mouse Ig (RAM) that are conjugated onto the ferrofluids can be used to selectively bind to target cell receptors. Once the ferrofluid has bound to the cells, the separation process is as simple as diluting the solution to the separation concentration and putting the sample tube in the Multipole Cell Separator, where the ferrofluid will pull the targeted cells to the magnet. Cells that are not magnetically labeled can be removed by aspiration or by pouring out the solution, and the magnetically targeted cells can be removed from the magnet and resuspended into solution.
Our ferrofluids are biodegradable, non-toxic, and do not interfere with downstream analysis of cells such as microscopy or flow cytometry!
Magnetic Contrast Agents
The composition of these ferrofluids mean that the materials shift the NMR spectra of hydrogens, lending themselves to many important applications in the biotech industry. Our ferrofluid has been used in the construction of immune-based assays with high sensitivity. This was done by incubating biotinylated capture monocolonal antibody and a signal monoclonal antibody with the cell sample for 7 - 10 minutes followed by the addition of streptavidin ferrofluid. The ferrofluid binds in less than four minutes, after which it can be separated into a monolayer in a magnet. The monolayered ferrofluid can readily be freed of signal antibody without resuspension and where signal can be read directly from that monolayer. The monolayered ferrofluid is then processed as a coated cup.
Clinical Scale Separations
Our clinical scale separator, X-GRAFFETM (in development) is capable of processing up to 8 x 109 cells in a single separation. In a separation using X-GRAFFETM, ferrofluid-labeled cells are never suspended after initial separation for the removal of bystander entrained cells. Instead, we developed a method called "meniscus scrubbing" that removes bystander cells from the captured cells magnetically separated. This process has significant advantages, including an increase in yield without decreasing cell viability, and an increase in purity compared to resuspension methods!
Our XpresSepTM Protein A Ferrofluid (coming soon!) can be used in antibody purification and concentration. Protein A is conjugated onto the albumin coating, which grabs antibodies, which are then eluted off using an elution buffer. Our Protein A Ferrofluid can be recycled, allowing for greater amounts of antibody separation.
Simultaneous Isolation and Activation of T Cells (SIATTM)
Following a separation using our XpresSepTM Ferrofluids, the targeted T cells can then be activated by cross-linking CD28 to the CD3 on the ferrofluids, and can be expanded in culture with the addition of IL-2.