Abstract: A method and flow system for controlling the flow of a liquid in a flow system, the liquid flow comprising particles and being led into a channel thereof. The method comprises the steps of enveloping the liquid flow by a flow of carrier liquid, hydrodynamically focussing the particles in the liquid flow providing a measurement signal of the liquid flow from an observation area in the channel, and dividing the liquid flow at a branching point into two or more outlets in response to the measurement signal. The division of the liquid comprises introducing a control liquid from at least one control channel at a merging point or merging area in the channel. The amount of control liquid is controlled by at least one electro-kinetic pump, the pump effect of which is controlled in response to the measurement signal.

Abstract: With a method of controlling the flow in a flow system where a liquid flow contains a particle concentration, the liquid flow is surrounded by a carrier liquid. The liquid flow and carrier liquid are led into a central channel in which there is provided an observation area (4) where measurements of the liquid flow are effected. The result of the measurements are used to lead the liquid flow into one of several channels, in that control liquids are introduced into the liquid flow before this reaches the channels, the control liquids being derived from a capillary pump structure which pumps on the basis of an electro-kinetic effect, e.g. an electro-osmotic effect. In a preferred embodiment, the pump structure consists of two capillary structures, to each of which an electrical field can be applied. Depending on the strength of the field, the amount of control liquid will be able to be controlled so that the liquid flow with the particle concentration can be led to one of two channels.

Abstract: A micro flow system is provided for separating particles, comprising a microfabricated member having a flow channel (5) defined therein for guiding a flow of a fluid containing the particles through the flow channel, first inlet means (2) positioned at one end of the flow channel for entering the fluid into the flow channel, first outlet means (7) positioned at the other end of the flow channel for discharging the fluid from the flow channel, the flow of the fluid containing the particles being controlled in such a way that one particle at the time passes a cross section of the flow channel, the member being positioned in a field that is substantially perpendicular to a longitudinal axis of the flow channel so that particles residing in the flow channel and being susceptible to the field across the flow channel are deflected in the direction of the field.