Method and apparatus for the separation and quantification of particles
The invention pertains to a method and apparatus to separate and quantify particles using time-variable force fields. The force fields can be for dielectrophoresis (positive or negative), electrophoresis, or electrohydrodynamic. In one aspect, the fields are translated and/or modified in space at a speed substantially comparable to the speed of translation of the fastest particles in the sample. The translation and/or modification of the force fields can also occur with varying speed. In another aspect, the field is translated and/or modified in a first direction at high speed. In another aspect, the quantity or size of the particles is determined by an indirect measurement of the speed of movement after varying the force field by means of a relationship between the speed of movement and the volume of the particles. This invention also pertains to an apparatus to produce appropriate field configurations necessary for the selective movement of particles.
1. A method to separate a sample of particles comprising at least first and second particles, comprising:
i. generating a first distribution in the space of a first force field characterized by a first set of points of stable equilibrium for the first and second particles;
ii. generating at least a second distribution in the space of a second force field characterized by a second set of points of stable equilibrium for the first and second particles, wherein the first and second distributions of forces are such that:
a) a first point of stable equilibrium of one of the first and second sets of points of stable equilibrium is included inside a basin of attraction of a single second point of stable equilibrium of the other one of the first and second sets of points of stable equilibrium, and
b) said second point of stable equilibrium is not contained in a basin of attraction of said first point of stable equilibrium; and
iii. alternating between the first and second distributions at a frequency substantially comparable to the inverse of the settling-time of the first particles at a new point of stable equilibrium, but greater than the inverse of the settling-time of the second particles to obtain a net movement of only the first particles.
2. A method to separate a sample of particles comprising at least first and second particles, the first particles being larger than the second particles, comprising:
i. generating a first distribution in the space of a force field characterized by a first set of points of stable equilibrium for said first and second particles;
ii. generating at least a second distribution in the space of a force field characterized by a second set of points of stable equilibrium for said first and second particles, wherein said first and second distributions are such that:
a) a first point of stable equilibrium of one of the first and second sets of points of stable equilibrium is included inside a basin of attraction of a single second point of stable equilibrium of the other one of the first and second sets of points of stable equilibrium,
b) said second point of stable equilibrium is not contained in a basin of attraction of said first point of stable equilibrium, and
c) the size of the basin of attraction of the first point of stable equilibrium is greater or less than the size of the basin of attraction of said single second point of stable equilibrium containing it; and
iii. alternating between the first and second distributions at a frequency comparable to the inverse of the settling-time of the first and second particles, so as to move the first and second particles from one point of equilibrium to a next point of equilibrium until the size of the particles is compatible with that of the basin of attraction so as to obtain a net overall movement of the second particles greater than a net overall movement of the first particles.
3. The method as in claim 1 , wherein said first and second sets of points of stable equilibrium are generated by at least one set of electrodes of increasing or decreasing width distributed with a constant step of spatial repetition.
4. The method as in claim 1 , wherein said first and second sets of points of stable equilibrium are generated by at least one set of electrodes of constant width distributed with a non-constant step of spatial repetition.
5. The method as in claim 1 , wherein said first and second sets of points of stable equilibrium are generated by at least one set of electrodes of increasing or decreasing width distributed with a non-constant step of spatial repetition.
6. The method as in claim 1 , wherein said first and second sets of points of stable equilibrium are generated by at least one set of electrodes of constant dimensions distributed with a constant step of spatial repetition, supplied with voltages of non-constant amplitude.
7. The method as in claim 2 , wherein said first and second sets of points of stable equilibrium are generated by an array of electrodes and by at least one cover electrode facing said array of electrodes and angled with respect thereto so as to have an increasing or decreasing distance between the electrodes and the cover electrode.