The present invention generally relates to the use of magnetic fields. More specifically, the present invention relates to the magnetic separation of particles in a solution.
Laboratories often require a technique to separate particles in a solution. Target particles, such as proteins and the like, may be separated from a solution by a technique known as magnetic separation.
In general, magnetic separation of biological particles, such as target proteins, involves coating small magnetically susceptible paramagnetic or ferromagnetic materials, such as micro-beads with a chemical-specific substance that is known to chemically bond with the target proteins. The coated micro-beads are introduced into a well containing a solution of the target proteins and unwanted biological molecules. The target proteins chemically bond to the coating of the micro-beads. Magnets are placed near the well to apply magnetic fields in the well and the solution.
The micro-beads, including the target proteins chemically bonded to the coating of the micro-beads, are attracted to the magnets in accord with the direction and strength of the magnetic fields generated by the magnets. Placement of the magnets determines where in the well the micro-beads with the target proteins will collect, i.e., if the magnets are placed along the side of the well, the micro-beads will collect to the side wall of the well. Once the micro-beads have been collected at the desired location, the well is rinsed, removing the solution and unwanted particles. The collected micro-beads with the target proteins chemically bonded to the coating of the micro-beads remain in the well as long as the magnetic fields are applied.
Once the well has been rinsed, a xe2x80x9ccleanxe2x80x9d solution, without unwanted particles, is introduced into the well. A chemical is mixed with the xe2x80x9ccleanxe2x80x9d solution to break the chemical bonds between the target proteins and the coating of the micro-beads, resulting in a well with isolated target proteins. Additionally, the micro-beads may be removed by disabling/removing the magnetic fields from the well.
Molecular biological magnetic separation is well known, and until relatively recently, this process was performed using large tubes of fluids (e.g., 15-50 ml tubes) and micro-beads. Recent molecular magnetic separation techniques typically involve the use of 96-well micro-plates, that is, a tray having 96 wells, arranged in an 8xc3x9712 matrix, with each well capable of holding 250-500 micro-liter (xcexcl) of liquid. A variety of placement methods for magnets to apply the desired magnetic fields may be employed on these micro-plates. One method is to place small magnets, having predetermined magnetic fields, between micro-plate receiving orifices, so that the micro-beads collect along the walls of the wells as described by Li, et al., U.S. Pat. No. 4,988,618. Another method is to place an apparatus with magnetic pins into the wells with the micro-beads collecting on the pins as described by Ekenberg, et. al., U.S. Pat. No. 5,567,326. Another method is to have a base for a micro-plate with cylindrical magnets positioned for insertion from the base of the micro-plate into the spaces between the wells of the micro-plate with the micro-beads collecting along the walls of the wells as described by Yu, U.S. Pat. No. 5,779,907.
As molecular magnetic separation techniques advance the number of wells increase. In high throughput applications, typically involving automated systems, 384-well to 1536-well micro-plates are utilized to increase capacity and throughput. In such systems, each 384-well micro-plate is arranged as 16xc3x9724 wells, while each 1536-well micro-plate is arranged as 32xc3x9748 wells, effectively increasing the volume of the conventional 96-well micro-plate by 4 and 16 times respectively.
As the number of wells increase, the spaces between the individual wells in micro-plates are relatively small, making the magnetic separation methods of Li, Ekenberg, and Yi difficult, if not impracticable. However, magnets are still required to separate the target particles from the solution contained in micro-plates.