Methods and devices for manipulation of magnetically collected material

A method for separating a target substance having at least one characteristic determinant from a fluid medium suspected of containing said target substance, said method comprising:

• a. contacting said fluid medium with a quantity of magnetic particles having directly or indirectly immobilized on their surface a specific binding substance that binds specifically to said at least one characteristic determinant, under conditions causing binding of said at least one characteristic determinant to said specific binding substance, resulting in target substance-bearing magnetic particles;
• b. introducing said fluid medium into a separation chamber;
• c. providing a ferromagnetic element either in or adjacent to said separation chamber, and a collection surface, wherein said collection surface is selected from the group consisting of a wall of said separation chamber, a portion of said ferromagnetic element, and a wall of a collection chamber disposed in said separation chamber;
• d. applying a magnetic field which intercepts said separation chamber, said magnetic field having a first region which exerts an attractive magnetic force urging said target substance-bearing magnetic particles in said fluid medium in a direction toward said ferromagnetic element and said surface and causing said target substance-bearing magnetic particles to be collected on said surface, and a second region which exerts a repulsive force causing repulsion of said collected target substance-bearing magnetic particles away from said ferromagnetic element and said surface, said surface being movably positionable relative to said magnetic field;
• e. positioning said surface relative to said magnetic field for exposure to said first region and collecting on said surface said target substance-bearing magnetic particles attracted to said element;
• f. discharging said fluid medium from said separation chamber;
• g. introducing dispersion medium into said separation chamber;
• h. repositioning said surface relative to said magnetic field for exposure to said second region and dispersing said target substance-bearing magnetic particles repelled from said element in said dispersion medium;
• and
• i. recovering said target substance-bearing magnetic particles.

Apparatus for separating magnetic particles from a non-magnetic fluid medium containing said particles, said apparatus comprising:

• a housing for receiving said fluid medium, said housing having an interior wall area;
• a ferromagnetic element disposed either in or adjacent to said housing;
• a collection surface, wherein said collection surface is selected from the group consisting of a wall of said housing, a portion of said ferromagnetic element, and a wall of a collection chamber disposed in said housing;
• a magnetic field source providing a magnetic field which intercepts said housing, said magnetic field having a first region which exerts an attractive magnetic force urging magnetic particles in said fluid medium in a direction toward said ferromagnetic element and said surface, and a second region which exerts a repulsive force urging said magnetic particles away from said ferromagnetic element and said surface, said surface being movably positionable relative to said magnetic field to serve as a collection zone for collecting magnetic particles attracted to said element in a first position and to serve as a dispersion zone for dispersing magnetic particles repelled from said element in a second position;
• means to move said surface selectively, in said first position and said surface being in said first region and in said second position said surface being in said second region;
• and
• a chamber in said housing for confining said magnetic particles during movement of said surface from said first position to said second position, wherein said chamber comprises either said collection chamber disposed in said housing or a chamber defined by at least said surface and an interior wall area of said housing.