Method and apparatus for the processing and/or analysis and/or selection of particles, in particular biological particles

Abstract

Methods and apparatus are described for the processing particles in which the particles suspended in a first fluid are introduced under laminar flow conditions into at least one first microchamber or first region, in which a second fluid is introduced under laminar flow conditions into at least one second region or second microchamber, in such a way as not to mix with the first fluid, and in which at least one field of force acting on the particles is activated in the microchamber(s), to provoke a shift of the particles alone in a predetermined direction and to transfer the same in suspension into the second fluid.

Claims

1. A method for carrying out complex experimental protocols on particles kept suspended in a fluid, comprising: (i) introducing said particles suspended in a first process fluid into a first region of space delimited by a first microchamber; (ii) activating at least one first non-uniform field of force acting exclusively on said particles to shift said particles only into a second process fluid contained in a second region of space delimited by a second microchamber so as to suspend said particles in the second process fluid; (iii) activating at least one second non-uniform field of force acting exclusively on said particles to shift said particles only back into the first process fluid contained in the first region of space, wherein: the first and second process fluids are in a condition of stationary state when activating the at least one first and second non-uniform fields of force and remain substantially immobile during shifting of the particles, the first and second process fluids are different process fluids, and the second process fluid interacts with said particles.

2. The method according to claim 1, further comprising (iv) analyzing said particles with sensors located in the first microchamber.

3. A method for realizing particles having a complex predetermined structure starting from first particles with a simple structure, comprising: (i) introducing said first particles suspended in a first process fluid contained in a first microchamber; (ii) activating at least one first non-uniform field of force acting exclusively on said first particles to shift only said first particles with the simple structure into a second process fluid confined contained in a second microchamber so as to suspend said first particles in the second process fluid; and (iii) repeating n number of times activating at least one F.sub.2-F.sub.n non-uniform field of force acting exclusively on said first particles to shift said first particles to L.sub.3-L.sub.n process fluids contained in CH.sub.3-CH.sub.n microchamber arranged in sequence, until said first particles are suspended in a final process fluid, wherein said first particles are contacted by a plurality of different process fluids in which they are/have been suspended, at least some of said process fluids being able to interact with said first particles in a way selected from the group consisting of: coating, growing, and soaking.

4. The method according to claim 3, further comprising: (iv) analyzing said first particles with sensors located in the microchamber containing said final fluid in a confined way.

5. The method according to claim 4, wherein steps (ii) and (iii) are carried out in such a way as to expose a number N of particles to at least one predetermined reagent contained in, or consisting in, one said process fluid for TI, . . . TN different times; and wherein said step (iv) measures dynamically, with relation to time, characteristics of said particles measurable by said sensors.

6. The method according to claim 4, wherein steps (ii) and (iii) are performed in such a way as to expose a predetermined number of particles, individually or in a group, to at least one predetermined reagent contained in, or consisting in, one said process fluid which reagent is able to interact with any substances secreted by said particles; and wherein said step (iv) comprises analyzing with said sensors the process fluid within which the cell to be analyzed is suspended to identify said secreted substance and said analysis being carried out in the vicinity of said cell to be analyzed.

7. The method according to claim 6, further comprising (v) encapsulating at least some said particles in porous/gelatinous substances to keep back any substances secreted by said particles or at least to slow down their diffusion in the process fluid in which said particles are suspended so as to prevent the overlapping of signals generated by said sensors in reply to the presence of different particles.

8. The method according to claim 4, further comprising (vi) selecting, in response to a signal detected by said sensors, the particles to which the generation of said signal is related; said selection being carried out applying only to the particles related to the generation of said signal said force F generated by said field of forces to transport said particles into a defined and different confined region of space.

9. The method according to claim 5, wherein the characteristic of said particles measurable by said sensors is one of the uptake of reagent, the variation of properties of the particles linked to reagent uptake, and variation of properties of the particles with time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an embodiment of a washing method realised according to the invention compatible with the use of forces acting on the particles in only one direction;

(2) FIG. 2 shows an embodiment of a washing method according to the invention which requires the manipulation of particles in two dimensions;

(3) FIG. 3 shows an embodiment of a particle incubation method which requires the manipulation of particles in two dimensions;

(4) FIG. 4 shows a first apparatus realised according to the present invention;

(5) FIG. 5 shows a second apparatus realised according to the present invention.

DETAILED DESCRIPTION

(6) The aim of the present invention is to supply a method and an apparatus for carrying out multiple operations typically performed on a macroscopic scale with test tubes and centrifuges, but performing them in such a way as to have one or more of the following advantages: miniaturisation; lower consumption of reagents; greater delicacy on the cells/particles; greater efficiency of recovery of the processed cells; greater control of the incubation/washing time; greater automation; integration of various steps of the process in a single integrated device; extraction of particular characteristic information on the individual cells (e.g. dynamics of reagent uptake, variations of volume, lysis) which are impossible with other methods.

(7) The method of the invention is based on the use of a non uniform field of force (F) with which to attract single particles or groups of particles (BEADS) towards positions of stable equilibrium (CAGES). This field may be, as an illustrative example without limitation, a field of dielectrophoresis (DEP), negative (NDEP) or positive (PDEDP), or an electrophoretic field (EF), an optophoretic field, etc.

(8) The identification of the effects on the particle resulting from its immersion in a second buffer may concern one of the following aspects, or combinations of the same: the identification of fluorescence the identification of absorbance, transmittance or other optical properties; the identification of variations of volume or other physical properties; the identification of impedenziometric properties; the identification of lysis of the particle.

(9) Each of these observations may be carried out optionally at the level of a single cells, and with time resolution such as to appreciate the variation dynamics of the parameters studied.

(10) Moreover, this information may be used not only to characterise the effects of the buffer on the particles, but to make a selective recovery of the particles with definite characteristics.

(11) For this purpose the measurement of the impedance variation is principally used, and/or the measurement of the variation of light intensity, transmitted, diffused or emitted in fluorescence.

(12) Generation of Forces

(13) There are various methods for generating forces to shift particles, as described previously in the state of the art.

(14) For the sake of simplicity, below is considered purely as an example, and therefore without limitation for the purposes of the present invention, the use of closed cages with negative dielectrophoresis as the activating force for the description of the methods and apparatus (for which it is necessary to use a cover acting as an electrode) of the invention. To experts of the sector with ordinary skills it is clear that is possible to generalise the methods and apparatus described below for the use of different activating forces, and different types of particles.

(15) The common characteristics of the forces which allow particles to be manipulated according to the present invention is linked to the fact that these forces act mainly on the particle, moving the latter but notor to a very limited extentthe liquid in which it is immersed.

(16) The use of one or the other force is relevantly indifferent, unless fluorescent markers are involved. In these cases it is preferable to use forces based only on electric fields, so as not to cause photo-bleaching of the fluorophors, which could occur when applying the lighting otherwise necessary using optical or electro-optical methods.

(17) Sensors Used

(18) Also for the sake of simplicity, reference will be made below only to the case of optical sensors, which allow the measurement of the optical power acting on a photodiode integrated with the electrodes. To experts of the sector with ordinary skills it is clear that is possible to generalise, in the various cases, the methods and apparatus described below also for the alternative or combined use of integrated impedenziometric sensors.

(19) It is also clear to the expert of the sector with ordinary skills in which cases the use of integrated sensors is beneficial and in which cases they are not necessary.

(20) Method for Washing Particles

(21) Reference is made to FIG. 1 and FIG. 2.

(22) The method exploits the fact that when two liquids (L1, L2), even of a type that generally mix together, are introduced into at least one microchamber (for example CH1, FIG. 1), in such a way as to realise a laminar flow for each liquid during the phase in which it is introduced into a predetermined region of the microchamber, the two liquids do not mix, apart from a very negligible mixing, for the purposes of the invention, being due to a slow process of diffusion, which process in any case begins only once the microchamber CH1 is filled and when a condition of stationary state has been reached in the two liquids.

(23) As illustrated in FIG. 1, an apparatus is used including a single microchamber CH1 having an inlet orifice or input I1 and an outlet orifice or output O1 located at the opposite ends of the microchamber CH1, the floor or base of which, parallel to the plane of the sheet in FIG. 1, is composed of a substratum (chip) provided with an array of electrodes, eventually provided with sensors.

(24) When the electrodes are energised, and the force (F) is activated which acts only on the particles (BEADS) present in suspension in the first liquid but leaves substantially immobile both the first and the second liquid, the particles (BEADS) are transferred (FIG. 1d) from the first liquid (L1) to the second (L2).

(25) For example the first liquid could be a culture medium, and the second a physiological solution.

(26) The operation may be repeated again, transferring the particles into further liquids (L3, . . . LN) in a way corresponding to multiple washing as usually carried out with test tubes and centrifuges.

(27) However, with centrifuges the starting buffer is diluted in the destination buffer, for which reason it is often necessary to perform two or three washes so as to obtain a relative absence of the original liquid.

(28) In the present invention, the contamination of the destination buffer (L2, . . . Ln) may be greatly limited if the movement of the particles (BEADS) is relatively rapid with respect to the times of diffusion of the molecules between the initial and the destination buffer. These diffusion times may be made relatively long with suitable stratagems, for example the one illustrated in FIG. 2, which shows the use, for the execution of the method of the invention, of an apparatus including two microchambers CH1, CH2, each provided with a floor having an array of electrodes that may be selectively energised and that are hydraulically connected to each other by a restriction or orifice G1,2 and each of which includes an inlet orifice or feed I1, I2, and an outlet orifice or discharge O1, O2, located at opposite ends of each microchamber CH1, CH2 and in a direction perpendicular to the one passing through the orifice G1,2.

(29) While in the case of the apparatus in FIG. 2 the liquids L1 and L2 may be introduced in laminar movement in predetermined regions of the microchambers CH1, CH2 until the microchamber CH1 is totally filled with the liquid L1 and the microchamber CH2 with the liquid L2, then activating the electrodes so as to transfer the particles from the liquid L1 (and from the respective microchamber CH1) into the liquid L2 and the respective microchamber CH2, guiding them along the orifice G1,2, where there is the interface between the liquids L1, L2 which is small and therefore limits diffusive phenomena to a minimum, in the case of the apparatus in FIG. 1 it is first necessary to introduce the liquid L2 into the microchamber CH1, operating in laminar movement, through the orifice I1, without totally filling the microchamber CH1, but only a first region of the same (for example about half the volume of the microchamber CH1) situated close to I1 and, later, introduce through the same orifice I1 the liquid L1 with the suspended particles, still operating in laminar movement, so that the liquid L1 pushes the liquid L2 to occupy a second region of the microchamber CH1 situated near the outlet orifice O1, while the liquid L1 (with the suspended particles) occupies the first region of the microchamber CH1.

(30) In any case, the particles suspended in the washing liquid L2 may be recovered by extracting the liquid L2 from the microchamber or region of the microchamber that it occupies, still working in laminar movement, through the orifice O1 (FIG. 1) or O2 (FIG. 2).

(31) The method described substantially contemplates the phases of: Introducing, in laminar flow conditions, first particles suspended in a first fluid (for example composed of a liquid, or a semi-liquid), into a first region of at least one microchamber. Introducing, in laminar flow conditions, at least one second fluid (for example a liquid or a semi-liquid) into at least one second region of said at least one microchamber, so as not to mix said at least one second fluid with said at least one first fluid. Activating in said at least one microchamber at least one field of force (F) acting on said particles, to provoke a shift of the particles alone towards said at least one second region of said at least one microchamber containing said at least one second fluid so as to suspend said particles in said second fluid.

(32) Optionally (if no other process steps are necessary in the integrated device): Selectively recovering said second fluid and said particles by extracting from said at least one microchamber said second fluid containing said suspended particles.
Method for the Incubation of Particles

(33) Reference is made to FIG. 3.

(34) In some ways the method is similar to the previous one, but it also contemplates the fact of returning the particles towards the starting buffer or towards a third destination buffer.

(35) This is a typical problem linked with the process steps necessary for example to mark cells with antibodies (for example for membrane receptors) eventually coupled with microbeads (for example polystyrene particles) so as to immunodecorate the cells, with fluorescent tracing agents (for example intracellular dyes such as Calcein, FITC, acridine orange, Trypan Blue), or to fix cells (e.g. with paraformaldehyde), or to lysate certain cells selectively (e.g. exposing the cells to acetic acid, which lysates the red blood cells but not the leucocytes).

(36) In these cases it is important not only to transfer the particles into a second liquid, but also to keep them in this second liquid for a definite length of time and then transfer them into a third liquid, which could also be the first (therefore returning the particles to the first liquid).

(37) According to the present invention it is therefore possible to transfer the cells into a second liquid where they are exposed to suitable reagents, and then transfer them to a further liquid without reagents.

(38) It is to be noted that, contrary to what can be done with test tubes and centrifuges, using the method of the invention it is possible to expose the particles to the reagent also for very short times.

(39) In practice, the BEAD particles suspended in the first liquid (or general fluid) L1 (FIG. 3b) are introduced in laminar movement into a first microchamber CH1 of a manipulation apparatus of the type with two microchambers having the floor composed of arrays of addressable electrodes, hydraulically connected to each other by an orifice G1,2, identical to the apparatus illustrated in FIG. 2. Next (or simultaneously), operating in conditions of laminar movement, the general fluid or liquid L2 is introduced into the second microchamber CH2 (FIG. 3c) and the electrodes are then selectively activated to create a field acting with force F on the particles in such a way as to transfer them, through the orifice G1,2, from the microchamber CH1 to the microchamber CH2 without producing the shift of the liquids L1, L2 (FIG. 3d), which at this point are in stationary conditions; and then, after a predetermined incubation time (which may also be short as preferred), the particles are transferred by the force F back into the microchamber CH1 (FIG. 3e) which may still contain the starting liquid L1, or a new liquid (fluid) L3 . . . Ln which in the meantime has been introduced into the microchamber CH1 through I1 after draining the liquid L1, for example through O1. Lastly the particles may be taken together with the liquid present in CH1 and in which they are suspended (FIG. 3f) through either O1 or I1, always operating in laminar movement.

(40) The method described substantially contemplates the phases of: Introducing, in laminar flow conditions, said particles suspended in a first fluid into a first region of at least one microchamber of an apparatus for manipulating particles; Introducing, in laminar flow conditions, at least one second fluid into at least one second region of said at least one microchamber, so as not to mix said at least one second fluid with said at least one first fluid. Activating in said at least one microchamber at least one field of force (F) acting on said particles, to provoke a shift of the particles alone in a predetermined direction into said at least one second region of said at least one microchamber containing said at least one second fluid, so as to suspend said particles in said second fluid. Activating in said at least one microchamber at least one field of force (F) acting on said particles, to provoke a shift in the opposite direction to the previous one of the particles alone so as to bring them back into said at least one first region of said at least one microchamber.

(41) Optionally, the method of the invention may also comprise the phases of: Replacing said first fluid in said at least one first region of said at least one microchamber with at least one third fluid, before bringing said particles back into said at least one first region of said at least one microchamber; Selectively recovering said particles by extracting from said at least one microchamber the fluid in which the particles are suspended.
Method for Carrying Out Complex Protocols

(42) The washing and incubation operations may be composed in sequence, realising complex protocols. For example with the following phases:

(43) 1. Shifting the cells from the liquid Li to a different destination liquid Li+1

(44) 2. Waiting a period of time Ti+1

(45) 3. Shifting the cells from the liquid Li+1 to a further liquid Li+2

(46) 4. Repeating the preceding phases 2) and 3) until the cells or particles are suspended in a liquid Li+n.

(47) For example the cells could be: introduced suspended in the culture medium, shifted into a region of the space occupied by a washing liquid (such as physiological solution), transferred into a region of the space containing paraformaldehyde, kept in this reagent for the time necessary to obtain the fixing and permeabilisation of the membrane, washed by transferring them to a further region of the space containing physiological solution, transferred into a region of the space containing proteins with fluorescent markers in order to recognise proteins potentially present inside the cell, washed by transferring them to a further region of the space containing physiological solution, analysed with sensors to recognise which cells express the proteins identified by the fluorescent marker.

(48) According to this aspect of the invention, a method is therefore performed for carrying out complex experimental protocols on particles kept suspended in a fluid, comprising the phases of:

(49) i) Suspending said particles in a first process fluid (Li) confined in a first region of space;

(50) ii) Selectively shifting said particles into a second process fluid (Li+1) confined in a second region of space, maintaining the first fluid and the second fluid in stationary conditions, by applying to said particles a force F obtained by activating a field of force acting exclusively on said particles;
iii) Repeating phase ii) a number n of times until said particles are suspended in a final fluid (Li+n), so as to contact with said particles a plurality of different process fluids, at least some of which are able to interact with said particles;
iv) Analysing said particles with sensors located in a region of space containing said final fluid in a confined way.
Method for Studying the Dynamics of Reaction of Particles with Reagents

(51) Contrary to what is possible also with techniques based on flow Microsystems such as the already mentioned Seger et al. LabChip, the time that the particles remain in the incubating reagent is not linked to the flow dynamics of the sample.

(52) Moreover, every single particle may be exposed to the reagent for different times, even though it is manipulated in the same device. In fact it is sufficient to locate said particle in the region of space occupied by the reagent for a certain time Ti, and then bring it back into the final destination suspension buffer.

(53) It is thus possible to expose N particles to a reagent for T1-TN different times.

(54) It is therefore possible to study characteristics dynamically (with relation to time), such as for example the uptake of the reagent or the variation of characteristics that it causes on the cell.

(55) This may occur with external optical sensors or preferably, using sensors integrated in the chip defining the floor of the microchambers CH1, . . . CHn used to keep confined the n process liquids with which to contact selectively the particles studied. The integrated sensor may be preferentially optical and/or impedenziometric. One may for example: Measure the uptake of a dye (for example trypan blue) Measure the uptake of a fluorochrome (for example FITC, acridine orange etc.) Measure the uptake of Calcein by increasing the fluorescence of a cell (Calcein is fluorescent only inside the cell); Measure the variation of volume of a cell; Check the lysis of a cell exposed to a reagent.

(56) All this information can in fact be found in an integrated way according to the method of the prior art or, better, according to the methods described in the international patent application in the name of the same Applicant, previously mentioned.

(57) This method, which is a variation of the one previously explained, therefore contemplates that the phases ii) and iii) described above are carried out in such a way as to expose a number N of particles to at least one predetermined reagent for T1, . . . TN different times; and that the phase iv) contemplates the dynamic study, with relation to time, of variable characteristics of said particles, such as for example the uptake of reagent or the variation of properties of the particles linked to reagent uptake.

(58) Method for Studying the Secretion of Particles

(59) Besides the characteristics of the cell, in terms of reagent uptake or the variation of physical properties, it is possible to study the secretion of single cells. To do this, the cells are moved towards a reaction buffer which contains substances that are modified depending on the presence of the type of molecules of which the secretion is to be studied.

(60) If the secretion dynamics is sufficiently rapid with respect to the coefficient of diffusion of the secretion in the liquid, by analysing the liquid in the vicinity of the cell to be analysed with suitable sensors (for example optical sensors outside the chip defining the floor of the microchambers in which the reactions take place, or integrated in the chip, or impedenziometric sensors integrated in the chip), the cells that produce more or less secretion can be identified. In the prior art, numerous methods are available for revealing secreted substances. These methods may be used with few or no modifications in order to study the secretion, not of a group but, according to the invention, of single cells.

(61) As an example without limitation, one may mention the use of chemiluminescent substances, of fluorescent substances with quenching which is inhibited by the presence of a certain secretion, or substances which change colour in the presence of a certain secretion.

(62) If the diffusion of the secretion is too fast with respect to the dynamics of secretion and to the time scale for which the cells are to be analysed, it is necessary to adopt more elaborate solutions. Otherwise, the signal represented by the variation of colour, fluorescence, impedance or light intensity emitted, is not confined to an area around the cell and does not allow the separation of the signal coming from different cells.

(63) In this case, the method comprises the phase of encapsulating the cells in porous/gelatinous substances which keep the secretion longer, slowing down its coefficient of diffusion and preventing the overlapping of the signal from different cells.

(64) This method may be used for example in the selection of encapsulated cells to avoid rejection in transplants for therapeutic purposes.

(65) The method just described therefore contemplates that the phases ii) and iii) described above are performed in such a way as to expose a predetermined number of particles, individually or in a group, to at least one predetermined reagent that is able to interact with any substances secreted by said particles; while phase iv) contemplates at this point the identification of this interaction with sensors, integrated or not. Moreover, it may optionally contemplate the phase of encapsulating at least some particles in porous/gelatinous substances able to keep back any substances secreted by the particles or at least to slow down their diffusion in the fluid in which the particles are suspended so as to prevent the overlapping of signals generated by the sensors in reply to the presence of different particles.

(66) Method for Studying the Effects of the Exposure of Particles to Reagents

(67) As well as the reaction dynamics, also the dynamics of the reactions of the exposure of a cell to a determined reagent may be analysed with high time resolution and above all with low delay.

(68) By returning the single particles to a neutral buffer, the modifications generated by the exposure of the cells to the reagent may be studied after a variable period of time.

(69) As above, this may be done with external optical sensors, or preferable with integrated optical or impedenziometric sensors.

(70) For example one might want to check the expression of a reporter gene, or cellular differentiation.

(71) Method for Selecting Particles

(72) As well as observing the dynamics of reaction with a reagent, and observing the effects of the exposure to said reagent, it is possible to make an automatic selection of the cells based on the response of the same to the stimuli applied (in the form of reagents).

(73) For example this allows the selection of the cells which, from a certain point of view, are more or less affected by a determined stimulus, or series of stimuli.

(74) For example one might want to isolate the cells which absorb a smaller quantity of drugs of one type, or the cells that produce a greater quantity of a certain protein once exposed to a reagent.

(75) So, according to this aspect of the invention, the phase is contemplated of selecting, in response to a signal detected by the sensors, the particles to which the generation of the signal is related; this selection phase is then carried out applying only to the particles related to the generation of that signal the force F generated by the field of forces that may be generated by means of the selective activation of the array of electrodes defining the floor of the microchambers to transport said particles and only them into a defined confined region of space, for example composed of a predetermined microchambers CHn or of a predetermined region of volume of the same microchamber in which the sensors are situated.

(76) Method for Constructing Particles

(77) By means of the methods described so far it is clear that one can also shift a particle or a group of seed particles from a first liquid to at least one second liquid, in which said particle(s) is(are) modified for example in one of the following ways: coating itself (for example with substances present in the second liquid or which are the product of the reaction between the particle and a reagent contained in the second liquid, growing (typically in the case of biological particles, such as cells, which may for example draw nourishment or a multiplication signal from the second liquid), soaking (typically in the case of artificial porous particles, such as microspheres).

(78) The particle is then moved into a possible third, fourth, n-th reagent, realising a complex protocol to supply at the end product particles, for example composed of layers with controlled dimensions of different materials.

(79) According to this aspect of the invention, a method is therefore provided for realising particles having a complex predetermined structure starting from first particles with a simple structure, comprising the phases of:

(80) i) Suspending said first particles in a first process fluid (Li) confined in a first region of space;

(81) ii) Selectively shifting said particles with a simple structure into a second process fluid (Li+1) confined in a second region of space, maintaining the first fluid and the second fluid in stationary conditions, by applying to said particles a force F obtained by activating a field of force acting exclusively on said particles;
iii) Repeating phase ii) a number n of times until said first particles are suspended in a final fluid (Li+n), so as to contact with said first particles a plurality of different process fluids, at least some of which are able to interact with said first particles in one of the ways chosen in the group comprising: coating, growing, soaking.
Apparatus for the Complex Processing of Particles

(82) In the case of multi-step protocols, which require a sequence of cell processing steps, it is particularly useful to realise a manipulating apparatus as schematically illustrated in FIG. 4, based on three microchambers CH1,CH2,CH3 arranged in sequence and realised as described previously for the microchambers CH1,CH2 in FIGS. 1-3, in which the central microchamber CH2 is hydraulically connected to the other two through two orifices G1,2 and G2,3 of hydraulic communication in the direction of the sequence of microchambers, which are located not only on opposite sides (in the direction of the sequence of microchambers) of the microchamber CH2, but are also offset to each other in the transverse sense, that is in a direction perpendicular to the direction of arrangement in sequence of the microchambers, being located one close to the inlet orifice I2 of the microchamber CH2 and the other close to the outlet orifice O2 of the microchamber CH2.

(83) The central microchamber (CH2) is used for washing the cells between the buffer contained in the starting microchamber (CH1) and the reagent microchamber (CH3).

(84) The first advantage of this device is that the distance between the orifices of hydraulic communication that constitute the two doors (G1,2) between the first and the second microchamber and (G2,3) between the second and the third microchamber increases the time necessary for the diffusion to contaminate the first starting liquid with the reagent in the third microchamber (CH3). Moreover, if after the passage of the cells washing buffer is flushed constantly into the second microchamber (CH2), any contamination between the reagent present in the third microchamber and the initial buffer is avoided.

(85) Preferably, during flushing, the inlets and outlets (I1,I3 and O1,O3) of the other microchambers are kept closed, so as to keep the flow confined inside the second microchamber.

(86) The liquids are preferably introduced in this order:

(87) CH1, CH3, CH2. In this way, as long as the meniscuses of the liquids L1 and L3 (that is the ones contained respectively in the microchambers CH1 and CH3) look onto the microchamber CH2, but do not touch, there is no contamination between the two due to diffusion.

(88) Arbitrarily long multi-step reactions may be also be completed with this apparatus by completely replacing the buffer in the first microchamber (CH1) while the cells are in the third microchamber (CH3) and vice-versa. In this way the reagents are multiplexed in the space.

(89) Alternatively a device may be realised in which all the reagents are injected in the initial phase and are already present at the start of the manipulation of the particles. This apparatus is shown in FIG. 5.

(90) It comprises a first and a second terminal microchamber (CH1,CHn) and a plurality of intermediate microchambers (CH2, . . . CHn1) arranged in sequence between the terminal microchambers and each of which is hydraulically connected to the microchamber immediately before and immediately after in the direction of the sequence of microchambers by means of a respective first and second orifice (G1,2; Gn1,n) of hydraulic communication in the direction of the sequence of microchambers, offset to each other in a transverse direction to the direction of the sequence of microchambers.

(91) Generalising what has been said previously, the apparatus in FIG. 5 is preferably filled firstly by filling the microchambers with an even index and secondly the microchambers with an odd index, so as to avoid contacts and contaminations until the liquids come into contact.