METHOD AND FLUIDIC MICROSYSTEM FOR THE DIELECTROPHORETIC MANIPULATION OF SUSPENDED PARTICLES

Abstract

The invention relates to a method for operating a fluidic microsystem (100) for the dielectrophoretic manipulation of suspended particles (1) having a particle diameter in a suspension liquid (2), wherein the microsystem (100) comprises: —a channel (10) having a longitudinal direction; —an electrode device (20) having an electrode (21), the longitudinal extent of which deviates from the longitudinal direction of the channel (10) and which has individually controllable electrode segments (22) for producing dielectrophoretic forces which act on the particles (1), each electrode segment (22) having a deflection angle α, relative to the longitudinal direction of the channel (10), and a segment length (s.sub.i), which determine a segment offset (D.sub.i) perpendicular to the longitudinal direction of the channel (10); and—a control device (30). The method comprises: —producing a flow of the suspension liquid (2) with a flow velocity so that the particles (1) successively pass through an interaction region of the electrode (21), which interaction region is spanned by the electrode segments (22); and—activating the electrode segments (22) in order to deflect the particles (1) onto predetermined motion paths (4, 5), which are determined by a superposition of flow forces in the flow of the suspension liquid (2) and of the dielectrophoretic forces at the electrode segments (22). During the passage of each particle, each of the electrode segments (22) which are passed by the particle (1) is activated in a clocked manner for a predetermined activation duration, according to the desired motion path (4, 5), the activation duration of each electrode segment (22) being determined by the quotient of the segment length (s.sub.i) of the electrode segment (22) and the flow velocity. The electrode segments (22) are dimensioned such that the segment offset (D.sub.i) of each electrode segment (22) is less than the particle diameter. For the deflection of each particle (1), at least two successive electrode segments (22) cooperate.

Claims

1-18. (canceled)

19. A method for operating a fluidic microsystem for dielectrophoretic manipulation of suspended particles having a predetermined particle diameter in a suspension liquid, wherein the fluidic microsystem comprises: a channel having a longitudinal direction, an electrode device having an elongate electrode, a longitudinal extension of which deviating from a longitudinal direction of the channel and which has a plurality of individually activatable electrode segments for generating dielectrophoretic forces acting on the suspended particles, wherein each electrode segment has a deflection angle relative to the longitudinal direction of the channel and a segment length, which determine a segment offset transverse to the longitudinal direction of the channel, and a control device by way of which the electrode segments can be activated, wherein the method comprises the steps: generating a flow of the suspension liquid with a flow velocity in the channel, so that the suspended particles in succession pass an interaction region of the elongate electrode which is spanned by the electrode segments, activating the electrode segments in order to deflect the suspended particles in the channel onto predetermined movement paths which are determined by a superposition of flow forces in the flow of the suspension liquid and the dielectrophoretic forces generated at the electrode segments, wherein as each particle passes, each of the electrode segments which the particle passes in succession is activated in a clocked manner by the control device in dependence on a desired movement path in each case for a predetermined activation time, wherein the activation time of each electrode segment is determined by a quotient of the segment length of the electrode segment and the flow velocity, and the electrode segments are so dimensioned that the segment offset of each electrode segment is smaller than the particle diameter, and in each case at least two successive electrode segments cooperate for a deflection of each particle.

20. The method according to claim 19, wherein segment lengths of the electrode segments are less than or equal to 10 times the particle diameter.

21. The method according to claim 19, wherein segment lengths of the electrode segments are less than or equal to twice the particle diameter.

22. The method according to claim 19, wherein deflection angles of the electrode segments are less than 10°.

23. The method according to claim 19, wherein deflection angles of the electrode segments are less than 5°.

24. The method according to claim 19, further comprising the steps position detection for determining at least one particle position of each particle, and activation of the electrode segments in dependence on the at least one particle position of each particle.

25. The method according to claim 24, wherein the position detection comprises monitoring of the interaction region of the electrode with a microscope device with which the electrode segments which the particle passes in succession are detected directly.

26. The method according to claim 24, wherein the position detection comprises observing of a monitoring region upstream of the interaction region of the electrode with a microscope device, wherein the monitoring region is spaced apart from each of the electrode segments by a predetermined channel length and the electrode segments which the particle passes in succession are determined from an observation time of the particles in the monitoring region, channel lengths and the flow velocity.

27. The method according to claim 19, further comprising the step detection of at least one particle property of each particle, wherein activation of the electrode segments takes place in dependence on the at least one particle property.

28. The method according to claim 27, wherein the channel is divided downstream of the interaction region of the electrode into multiple subchannels, and each of the suspended particles is moved into one of the subchannels by the activation of the electrode segments in dependence on the at least one particle property.

29. The method according to claim 19, wherein the flow velocity of the suspension liquid is set at a predefined constant value by a control loop.

30. The method according to claim 19, wherein a distribution of the particles is chosen such that multiple particles are located in the interaction region of the electrode, wherein, when averaged over time, not more than one of the particles is located at each electrode segment.

31. A fluidic microsystem configured for the dielectrophoretic manipulation of particles having a predetermined particle diameter in a suspension liquid, comprising: a channel having a longitudinal direction, an electrode device having an elongate electrode, the longitudinal extension of which deviating from the longitudinal direction of the channel and which has a plurality of individually activatable electrode segments for generating dielectrophoretic forces acting on the particles, wherein each electrode segment has a deflection angle relative to the longitudinal direction of the channel and a segment length, which determine a segment offset transverse to the longitudinal direction of the channel, and a control device by way of which the electrode segments can be activated, wherein the channel is configured to receive a flow of the suspension liquid with a flow velocity such that the suspended particles pass in succession through an interaction region of the electrode which is spanned by the electrode segments, wherein the control device is configured to activate the electrode segments in order to deflect the particles in the channel onto predetermined movement paths which are determined by a superposition of flow forces in the flow of the suspension liquid and the dielectrophoretic forces generated at the electrode segments, the control device is configured, as the particles pass, to activate in a clocked manner each of the electrode segments which one of the particles passes in succession in dependence on a desired movement path in each case for a predetermined activation time, wherein the activation time of each electrode segment is determined by a quotient of the segment length of the electrode segment and the flow velocity, the electrode segments are so dimensioned that the segment offset of each electrode segment is smaller than the particle diameter, and the control device is configured to activate the electrode segments so that in each case at least two successive electrode segments cooperate for the deflection of each particle.

32. The fluidic microsystem according to claim 31, wherein segment lengths of the electrode segments are less than or equal to 10 times the particle diameter.

33. The fluidic microsystem according to claim 31, wherein segment lengths of the electrode segments are less than or equal to 100 μm.

34. The fluidic microsystem according to claim 31, wherein segment lengths of the electrode segments are less than or equal to 10 μm.

35. The fluidic microsystem according to claim 31, which comprises a position detection device with which at least one particle position of each particle can be detected, wherein the control device is configured to activate the electrode segments in dependence on the at least one particle position of each particle.

36. The fluidic microsystem according to claim 35, wherein the position detection device comprises a microscope device which is arranged to observe the interaction region of the electrode and to directly detect the electrode segments which the particle passes in succession.

37. The fluidic microsystem according to claim 35, wherein the position detection device comprises a microscope device which is arranged to observe an monitoring region upstream of the interaction region of the electrode with a microscope device, wherein the monitoring region is spaced apart from each of the electrode segments by a predetermined channel length, and the control device is configured to determine the electrode segments which the particle passes in succession from an observation time of the particles in the monitoring region, channel lengths and the flow velocity.

38. The fluidic microsystem according to claim 31, wherein the control device is configured to activate the electrode in dependence on at least one particle property.

39. The fluidic microsystem according to claim 38, wherein the channel divides into multiple subchannels downstream of the interaction region of the electrode, wherein the control device is configured to move each of the particles into one of the subchannels by activation of the electrode in dependence on the at least one particle property of the particle.

40. The fluidic microsystem according to claim 31, comprising a control loop with which the flow velocity of the suspension liquid can be set at a predefined constant value.

Description

[0058] Further details and advantages of the invention are described hereinbelow with reference to the accompanying drawings, in which:

[0059] FIG. 1: shows a schematic illustration of features of embodiments of the method according to the invention and of the fluidic microsystem according to the invention; and

[0060] FIGS. 2 and 3: show schematic illustrations of conventional fluidic microsystems.

[0061] Features of embodiments of the invention will be described by way of example hereinbelow with reference to the sorting of biological cells into two subchannels at a Y-branch of a channel of a fluidic microsystem. It is emphasised that the application of the invention is not restricted to this example but is correspondingly possible in a different manipulation of particles, for example for their displacement onto one of more than two movement paths in the channel, for example in order for a redistribution or for a change of the particle spacings. Instead of the manipulation of biological cells, a manipulation of other, in particular non-biological particles can be provided according to the invention. When implementing the invention in practice, sizes and forms of the parts of the microsystem in particular can be chosen in dependence on the requirements of the concrete application. Details of the structure and operation of fluidic microsystems, in particular the generation of high-frequency electric fields for electrode activation, and of the detection of particle properties, for example by the processing of measured data of a microscope, are not described because they are known per se from the prior art.

[0062] FIG. 1 shows, in a schematic plan view, the channel 10 of the fluidic microsystem 100 having an electrode device 20, a control device 30 and a microscope device 40. The channel 10 extends linearly in a longitudinal direction z up to a branch into two subchannels 11, 12. The channel 10 has, for example, a rectangular cross section with a width in the range of from 20 μm to 1000 mm and a height in the range of from 5 μm to 1 mm. The planar lower side is also referred to as the channel bottom 13 and the planar upper side as the cover surface (not shown). In the channel there are cells 1, 1A, which are suspended in a suspension liquid 2. On actuation of a pump device 14, a flow of the suspension liquid is generated in the channel 10 in a flow direction that coincides with the longitudinal direction z.

[0063] The electrode device 20 comprises the electrode 21, which is divided into a plurality of electrode segments 22. In the example shown, the electrode 21 has the form of a linear strip which is formed by the linear electrode segments 22 arranged in series. Only the electrode 21 on the channel bottom 13 is shown in FIG. 1. A further electrode (not shown) having the same size and form and orientation relative to the channel 10, or alternatively a planar counter-electrode, is preferably arranged on the cover surface. The longitudinal extension of the electrode 21 forms with the longitudinal direction z of the channel 10 a deflection angle α.sub.l, which because of the linear electrode form forms the deflection angle α.sub.l of each electrode segment 22. The electrode segments 22 have a segment length s.sub.i in the longitudinal direction z of the channel 10 and a segment offset D.sub.i transverse to the longitudinal direction z of the channel 10. Accordingly, each electrode segment 22 has an associated interaction length l.sub.i. The interaction length (detection length) L of the electrode 21 as a whole is given by the sum of the individual interaction lengths l.sub.i of the electrode segments 22 and their mutual spacings. In the example shown, all the electrode segments 22 have the same interaction lengths Ii.

[0064] The electrode 21 is divided into the electrode segments 22 in order to be able to operate with a maximum cell density at a minimum deflection angle, whereby a stepwise deflection of the cells with a minimal width of the segment offset D.sub.i (sorting window) is possible. Ideally, the division is such that the width of the segment offset D.sub.i is in the order of magnitude of the cell diameter. The individual electrode segments 22 can be switched on and off again in succession, so that only the electrode segment 22 at which the cell to be sorted is located is ever active. Even cells that are following behind very closely can thus be handled independently of the preceding cell. In a concrete embodiment there are provided, for example, 20 electrode segments 22 each having a segment length s.sub.i of 20 μm and a deflection angle at of 3°, wherein an interaction length L of the electrode 21 as a whole of 0.2 mm is obtained. The width of the electrode 21 is, for example, 10 μm.

[0065] The control device 30 comprises an electrode voltage source 31 and a computer unit 32. The electrode voltage source 31, the microscope device 40 and the pump device 14 are controlled by means of the computer unit 32. The computer unit 32 is further designed to analyse image data of the microscope device 40, to detect particle properties of the cells 1, 1A and to generate a sorting decision in dependence on the detected particle properties. The electrode voltage source 31 is designed to generate high-frequency electric voltages for activating the electrode 21. According to the invention, each electrode segment 22 is activated individually. To that end, the electrode voltage source 31 has a group of output channels, the number of which is equal to the number of electrode segments 22. Each output channel is connected to one of the electrode segments 22 of the electrode 21 and to one of the electrode segments of the electrode (not shown) on the cover surface of the channel 10.

[0066] The microscope device 40 comprises, for example, a transmitted-light or fluorescence microscope which is arranged to acquire images in a monitoring region upstream of the interaction region of the electrode 21. The cover surface of the channel 10 is transparent in the monitoring region. At the same time, the microscope device 40 forms a position detection device with which the particle position of the cells 1, 1A can be detected. To that end, the passage of the cells 1, 1A through the monitoring region and the associated observation time are detected. In conjunction with the flow velocity in the channel 10 and the segment lengths l.sub.i, the time intervals at which the particles 1, 1A pass the electrode segments 22 are obtained.

[0067] In the time segment between the observation time and the reaching of the first electrode segment 22, the computer unit 32 performs the analysis of the image data of the microscope device 40, the detection of particle properties of the cells 1, 1A, such as, for example, size, shape, co-localisation of fluorescent-stained membrane proteins, and the sorting decision.

[0068] For cell sorting in the channel 10, the cells 1, 1A suspended in the suspension liquid 2, such as, for example, cell culture medium, buffer solution, etc., flow through the monitoring region of the microscope device 40 to the electrode device 20. A particle property and the time interval of the passage past the electrode segments 22 are associated with each cell. By application of high-frequency electric voltages, the electrode segments 22 are activated for activation times equal to the respective time intervals of the passage. If a field is not generated at an electrode segment 22 (the electrode 21 is locally inactive), the cells are freely able to pass the electrode segment 22. If a field is generated at an electrode segment 22 (the electrode 21 is locally active), the cells are prevented from passing by negative dielectrophoresis and are deflected onto a different movement path according to the electrode geometry and the hydrodynamic propulsion. As a result of the division of the electrode 21 into the electrode segments 22 with a relatively small deflection angle α.sub.i, the effective detection length of the electrode 21 is minimised, so that even cells 1, 1A that follow one another closely can be individually sorted and can reach the subchannels 11, 12 correctly separated.

[0069] In contrast to methods described hitherto (e.g. [8]), the use of the described sorting function allows very dense cell samples to be processed. In combination with a parallelisation (which is simple to carry out) of the system, the same throughput can therefore be achieved with significantly lower flow velocities, which facilitates optical image acquisition and the handling of dead times potentially caused by the image processing. In addition, the complex microfluidic control elements that are necessary at high flow velocities are not required, which further reduces the complexity of the method and thus improves the compactness, costs and operability of the system considerably.

[0070] The features of the invention that are disclosed in the preceding description, the drawings and the claims can be of importance for the implementation of the invention in its various embodiments both individually and in combination or sub-combination.