Sample preparing arrangement and a method relating to such an arrangement

The present invention relates to an arrangement ( 10, 20 ) for preparing samples ( 15, 27 ), submergible in a liquid medium. The arrangement comprises a section provided with a device ( 13, 23 ) for controllable generation of a magnetic field through influence of a control signal, said magnetic field being generated to trap at least part of said samples ( 15, 27 ).

DETAILED DESCRIPTION OF THE PARTICULAR EMBODIMENTS The basic idea of the present invention is to create an enclosure or a crater (a well), provided with a lid, which can be opened and closed by a “lid”. A user can control the lid and the device is intended to be submerged in a liquid medium. By operating the lid, the enclosed volume becomes separated from the surroundings. That means, the liquid stored in the crater, particles suspended therein, and/or material that adheres to the craters inner surface are not affected by subsequent changes that occur in the surroundings while the lid is closed. These changes might be a different chemical composition of the liquid, light shining on the crater chip, or other solids in the surrounding liquid. The lid may or may not be completely liquid-tight, but mixing of the liquid outside a crater with the liquid contained inside a well will be dramatically slowed. Hence, solids and liquids will be well separated between inside and outside, by the lid. FIGS. 2 and 3 illustrate a first example of an arrangement according to the invention. FIG. 2 illustratess an enlarged schematic view of a part of chip 19 comprising a number of sample collecting arrangements 10 . Each sample collecting arrangement comprises a cavity (crater, pocket, well) 12 provided in a substrate 11 and means 13 to control the cap (lid, cover) 14 . Each control means 13 is connected to controller 18 ( FIG. 3 ) through connections 17 . FIG. 3 is a schematic cross-section through the device 10 . However, the device 10 is shown in a stage where samples 15 are collected and the crater 12 is closed by means of the lid or closure 14 . The samples in this particular case are magnetic particles of diameter(s) much smaller than the diameter of the lid, covered with appropriate chemical(s) In this embodiment, the lid control means 13 comprise electrically actuated coils and the lid 14 is a magnetizeable bead. By making many craters 12 , all with individually controlled lids 14 , different types of mixing of solids dispensed in a liquid and/or liquids can be achieved at the same time. As different liquids/solids are introduced to the outside of the craters only user-selected craters with open lids will be reached for the mixing by the liquids/solids external to the closed craters. The dimensions and the shapes of each crater 12 can of course vary within a large interval both with respect to its diameter and depth. The craters can have circular cross-section, e.g. having about 50 &mgr;m deep with the diameters of approximately 100 &mgr;m. It is relatively easy to produce craters with dimensions ranging from few Jim and larger and with depth ranging from few &mgr;m and up to several hundreds of &mgr;m, having, e.g. square shapes. The material of the substrate can be silicon and the manufacturing process may include micro-machining, similar to the process of making microprocessors or memories chips. A device may contain from several hundreds of craters on a single piece of silicon, providing a so-called chip. Of course tens of thousands of craters on commercial units can be arranged. Preferably, the lid is a micro-bead introduced in a liquid. The lid-actuation mechanism, i.e. the closing and the opening of each of the craters is performed using switchable magnetic fields that influence the motion of the introduced beads. The magnetic fields are created using the coils 13 deposited around each crater. The coils 13 surrounding each of the craters are made of an electrically conducting material. In the preferred embodiment the conductor is made of aluminium, A 1 , but any electrical conductor can be used. Preferably, each coil is accessible through electrically conducting leads so that a current of different strength can be applied separately to each coil. The current amplitude and the number of windings in the coil are proportional to the strength of the magnetic field, which can thus be varied. Clearly, it is possible to change the number of windings in the coils surrounding each crater as well as their width and thickness within a broad range of dimensions. Preferably but not exclusively, coils can have from 2 and up to 10 windings. In an alternative embodiment, instead of the coils 13 , the control means can be substituted by a magnetically active material surrounding each crater and direct the beads using external magnets that will create magnetic fields counteracting the field created by the material deposited around each crater 12 . Preferably, the craters are etched in the silicon surface and the lid is provided by a large magnetic particle 14 in the liquid. Thus, particle 14 can be attracted to the crater of choice when the coil of this crater is energised by electric current to produce magnetic field for spatial attraction. Before sealing off the crater of choice, however, it is also possible to attract smaller magnetic particles into the crater. To attract the smaller magnetic particles 15 to the crater we energize the coil by leading electric current through it. When the coil is energized, a magnetic field is established. This field will attract the magnetic particle 15 from the liquid. These smaller particles have higher mobility in the liquid compared to the mobility of larger particles and will thus reach crater faster than the larger lids. The large lid-particle will cap the crater at a later stage. Preferably, as large particles commercially available magnetic particles such as ferromagnetic or super-paramagnetic having about 100 micrometers in size can be used, while the size of the smaller particles is much smaller than the crater's size. There are other dimensions and particle types on the market and the invention is applicable to a broad range of particle sizes, shapes and materials. To open a closed crater, a repelling field is generated either externally or by inverting the direction of the current flowing through the coil. It is also possible to terminate the current through the coil, whereby the particle may be released due to shear force from the flowing liquid or due to gravitational forces if the craters are positioned “upside down”. The simple actuation of the crater lid using current controlled magnetic field(s) and the large number of craters on a chip makes it necessary that the chip is operated automatically through controlling arrangement. The chip is preferably provided with an interface device that establishes electrical connection with the chip and provides the handling of the surrounding fluid with the beads and chemicals. After use the chip may be removed for cleaning and reuse or disposal. The interface device will be connected to a computer equipped with suitable software to control the sequence of operations on the craters and the liquid handling system. The software will also provide an interface for the user to establish the process sequence and to plan the states of the crater lids in each sequence. Detection of a magnetic capping bead can also be done. It is important to obtain feedback on which craters are capped. The presence of a magnetic capping bead, in place over a crater, can be detected by the change in inductance in the electric circuit, which produces the attractive magnetic field. The bead acts like a magnetic yoke in a transformer, increasing the inductance. A resonant, or other, circuit can then detect this inductance change. The presence of the capping bead can be detected by various other schemes, like the decrease of electromagnetic radiation to a detector inside the crater or by changes of capacitance between electrodes inside the crater or near the crater rim. Another possible application along similar lines is the detection of changes of inductance when a small magnetic sphere passes through the opening into a well. Using the arrangement according to the invention it is possible to determine whether a sphere is entering the well or if it is leaving the well. This is determined using the direction of externally controlled magnetic field (either by changing the direction of the electric current flowing through a coil or flipping an external magnetic field creating device by other means). Such a sphere may contain particular molecular coating, which will react with the liquid in that well or with the coating adsorbed on the walls of the crater. Given one knows the number of spheres in each well and the density of the respective coatings quantitative data on the number of reaction between the coating on the wall and the coating on a small bead can be obtained by simply counting the spheres. Following non-limiting examples are given for simplifying the understanding of the invention: According to a first example liquid A containing magnetic beads is introduced. User selected craters 12 are energized and hence capped. The remaining beads are flushed away with a cleaning liquid. Now liquid B is introduced, containing small (much smaller than the capping beads) particles, called X, made of a material interesting to the user. Only uncapped craters will accept X. Then, more magnetic beads are introduced and selected craters are capped, trapping X. Cleaning liquid will flush all excess away. A liquid containing chemical reagent Y can then be introduced and some craters are opened. X and Y are allowed to mix and react, but only in the user-selected areas. This reaction can be followed using sensing techniques, which can easily be incorporated into the system, for example using optical techniques. Other possible novel detection techniques easily incorporated into the present embodiment are mentioned below. In a second example, a substance is attached to the craters inner surface. In a repeating sequence some craters are closed by the beads and the others are exposed to a reactive chemical A. After the reaction the chemical is flushed and some craters are exposed to another chemical B. So there will be craters that have been exposed to A and B, some to A, some to B, and some to neither. This process can be repeated with many chemicals producing very large numbers of differently modified substances residing in different locations (craters) of choice. With a sequence of 10 different chemicals, for example, more than 1000 different combinations are obtained. In particular, this could be used to synthesize DNA strands or (using appropriate well-known techniques) to investigate the function(s) of different proteins. Yet another application is to lock cells in the wells filled with different chemicals and monitor the reaction of cells (cell proliferation, differentiation, spreading or others) to these chemistries. This would enable, for example a fast high throughput screening of drugs. The arrangement may also be used separately, one-by-one, for example to deliver a certain chemical or chemicals locally at a certain place or places in a reaction vessel, and monitor reaction products locally, or to deliver a drug inside a body. Another field of possible applications of the device has been triggered by something generally referred to as a “low throughput screening” (LTS). LTS is often used when the amount of required information is smaller but in addition one wants to obtain some quantitative information about concentrations of analyses or number of reactions that occur during certain time at certain amounts of reagents. The idea behind LTS has much in common with another timely idea often used to day: an “electronic tongue”. Electronic tongue is a device that enables one to determine components in a liquid. These components can then be associated with certain tastes (sweet, sour, salt, etc. or combinations thereof). To determine the content of simple liquids in a liquid mixture, for example % of sugar dissolved in a cup of tea along with the amount of tea used to prepare this cup, and even perhaps different tea blends used. To acquire knowledge about all these requires performing several experiments with constituents that react differently to different tea blends and to different amounts of tea from each blend that has been used, as well as to the amounts of sugar being dissolved in this tea. All these can be made by LTS methods using our equipment and choosing appropriate reagents different for each crater and letting these first to react with a “standard” samples (“learning the tongue” to recognise certain non-mixed liquids) and later exposing these samples to mixtures of different tea blends with or without sugar. Appropriate data processing from the outcome compared with the results obtained on standard samples enables one often to obtain information about tea blends used and the amount of sugar dissolved. The device is not limited to spheres or coils for creation of magnetic fields that direct beads nor is it limited to the use of beads, and other shapes can be used. Finally it is not limited to the use of silicon technology to fabricate the crater matrices; other materials can be used for this purpose. Following are additional, non-limiting, examples of different crater preparation techniques and materials of use paired with its utilisation: The general idea behind these examples is to manipulate small particles in order to bring them to a chosen place on the surface of the substrate using magnetic field(s) as a driving force for particle manipulation. The surface of the substrate may be either patterned in a particular manner, or not. When the substrate is patterned and the pattern consists of craters some particles are used preferably as caps or lids to close each crater as described earlier. When the substrate is left without a pattern or patterned in a different manner (see below for an example) the particles can be used mainly as a way to enhance sensitivity of detection of the processes taking place in the device. The magnetic force to manipulate the particles can be created using coils as described above, but it also may be created using externally applied magnets. In the former case the field strength (and thus the magnitude of the force) is determined primarily by the number of windings in the coil and the magnitude of the electric current. In the latter case it is possible to control the magnitude of the magnetic force by appropriate choice of magnet position and strength. The substrate may be made of silicon (described above), Si, or of Si-compound, e.g. Si-oxide Si-nitride or Si-carbide, or combinations thereof. It may also consist of thin self-supporting Si, or of a Si-compound, with another film of suitable thickness (for example few micrometers), such as ZnO, evaporated onto its surface. This additional film is needed if the device is to work as an acoustic wave device for detection. The substrate may also be fabricated using other material than silicon. For example a suitable polymer, e.g. polyethylene, polyethylene glycol, polyethylene oxide, fluorine containing a polymer (PTFE-Teflon), or silicon containing a polymer, may be used as a substrate material. When patterning the substrate different techniques may be used depending on the substrate material and the pattern. Thus, Si and Si-compounds are suitably patterned applying well-known techniques from the semiconductor fabrication. When patterning polymers one can use known techniques like polymer stamping or moulding. The patterns on the substrate are not limited to craters. For example when using the device as an acoustic wave detector one may produce matrices consisting of many interdigitated patterns needed for acoustic wave generation and detection. FIGS. 4 and 5 show one example of such a device. The coils can be patterned using well-known techniques such as electroplating, vapour deposition or sputter. In the following, few non-limiting examples of how similar techniques based on the magnetic manipulation of beads can be used to enhance detection sensitivity of chemical reactions are described: A single site of a matrix of the Surface Acoustic Wave, SAW, devices is shown in FIGS. 4 and 5 Each device 20 , comprises an arrangement 22 for generating acoustic waves and magnetic field control means 23 on a substrate or carrier 21 . The arrangement for generation and detection of acoustic waves comprises two finger-shaped, reversed arranged conductors 221 and 222 provided on both sides of the control means 23 . The control means 23 is arranged as a coil connected to a controller (not shown) as described in conjunction with foregoing embodiment. The coil and the arrangement for generating acoustic waves are covered with an insulating layer 24 ( FIG. 5 ), made of, e.g. glass or plastic, or a biomolecular layer. Onto this insulating layer, (biomolecular) “receptors” 25 can be adsorbed. The receptors, 25 , can be used in their native state and adsorb spontaneously onto a suitably prepared insulating layer, 24 . They may also be pre-adsorbed onto small magnetic beads, 23 , and the whole complex (magnetic bead-receptor) can be attracted to the surface of the SAW—device by magnetic field created by letting the current pass through the coil 23 . The beads&plus;receptors attenuate the acoustic wave, 29 , many times stronger compared to the case when native receptors are attached to the insulating layer 24 and thus much lower concentrations of adsorbates at the surface are needed when the receptor-bead complexes are adsorbed. Another advantage of such configuration is that it allows for the regeneration of the device. It may be possible to manufacture the surface of the insulating layer, 24 , inert to receptors themselves, so that the receptor and bead complex is attached to the surface by magnetic forces acting on a bead. Once the investigation is completed the magnetic field can be removed (or the direction of the field changed using external magnet) causing the receptor and bead complex to desorb. This will leave the surface in its as-prepared state ready for another investigation. If one wishes to study the reaction between these receptors and appropriate “donors”, 27 , the latter may be introduced in their native stage ( 27 ), or coupled to a magnetic bead 28 . Again, coupling the donors to magnetic beads allows for larger attenuation of acoustic wave when the acceptor-donor reaction has occurred (irrespective from whether this reaction caused additional donor-derived beads to be adsorbed on the surface or whether it caused the desorption of the reaction product−receptor &plus;bead/donor &plus;bead) which decreases the necessary number of reaction needed for a given sensitivity of the device. Since the beads influence the propagation of acoustic waves stronger than do the molecules, which react, to each other one obtains manifold enhancement of the detection of the chemical reaction involving these molecules. One particular, but far from the only one, example of such reaction is the antibody-antigene reaction. Another example would be DNA-complementary DNA (or PNA) reaction. The reaction may occur spontaneously over many sites of the matrix, leaving other sites unreacted. By separately applying the magnetic field so as to remove particles from each site one obtains (i) a pattern over sites where reaction did take place, and (ii) a quantitative information about the number of reaction that did take place at each site (see, FIG. 6 A- 6 C). Another way to use the matrix with interdigitated electrodes is as a capacitor; a certain number of electrode pairs will be considered as a single site and will constitute a capacitor. One prepares each site of the matrix differently, i.e. using different chemistries. By directing beads, with specific molecules attached to them, to these sites using magnetic field, or withdrawing particles from these sites, one is able to perturb the dielectric constant of a layer close to the surface and therefore produce large changes of the capacitance of the device compared to attachment of only (bio)molecules. The invention is not limited the shown embodiments but can be varied in a number of ways without departing from the scope of the appended claims and the arrangement and the method can be implemented in various ways depending on application, functional units, needs and requirements etc.