Patent Publication Number: US-6904945-B2

Title: Multi-channel fluid dispenser

Description:
The present invention relates to the production of miniaturized high-density arrays of samples of biological substances (oligonucleotides, DNA, etc), often known as “biochips”, so that they can be treated. 
     Such arrays are tools that are particularly useful in the field of molecular biology, as borne out, in particular, by the publications “High-density oligonucleotides arrays” (A. P. Blanchard et Al. —Biosensors &amp; Biolectronics, Vol. 11, No. 6/7, pp. 686-690, 1996) and “Array of hope” (E. S. Lander—Nature Genetics Supplement, Vol. 21, January 1999). 
     The invention relates more specifically to a multi-duct fluid dispenser making it possible to withdraw liquid from a plurality of cavities formed in a reservoir platter then to deposit an array of microdrops thereof on to a receiving platter as to constitute a “biochip”. 
     The dispenser according to the invention is of the type comprising:
         a plurality of flexible ducts arranged in a convergent bundle, the first ends of which are intended to be immersed in the cavities of the reservoir platter and the second ends of which are assembled in a miniaturized array,   means of filling the ducts, from their first ends, with the liquid contained in the cavities, and   means of expelling a drop of liquid from the second end of each duct toward the receiving platter.       

     A device of this type is described in document WO 98/29736. The ducts are formed of a bundle of capillary filaments gathered together onto an impression head. They are all controlled together. 
     Documents U.S. Pat. No. 4,058,146 and EP 0 955 084 propose similar embodiments, but the expulsion of liquid is therefore done by simple contact with the receiving platter. The same is true of the device described in document U.S. Pat. No. 4,621,665 but, in this case, there is no change in format between the reservoir platter and the receiving platter. 
     The present invention aims to provide a dispenser that constitutes an improved version of the aforementioned systems of the prior art. 
     In order to achieve this objective, this dispenser according to the invention is characterized in that:
         the ducts are formed in a plurality of flexible plates so as to converge from their first ends toward their second ends;   these plates are joined together by their part that comprises the second ends of the ducts;   each plate comprises two polymer sheets sealed together and of which at least one is endowed with an array of convergent grooves forming the ducts,   each duct has a first narrowing near its second end and a second narrowing at said end; and   said expelling means comprise a piezoelectric actuator arranged on an exterior wall of the duct, between its two narrowings, and the purpose of which is to deform said at this point so as to reduce the thickness of the duct.       

     Advantageously, the dispenser according to the invention also has the following main characteristics.
         The reservoir platter is sealed closed by a lid through which the ducts pass and the filling means are arranged in such a way as to raise the pressure in the space lying between the lid and the cavities.   The filling means comprise a bellows connecting the lid and its platter at their periphery.   The expelling means comprise a second piezoelectric actuator identical to the first one and arranged facing it on the other exterior wall of the duct.   The piezoelectric actuator is formed as a stack which comprises, starting from the exterior wall of the duct, a lower metal electrode, an insulating layer, a layer of piezoelectric material, a further insulating layer and an upper metal electrode.   The expelling means are designed in such a way as to be able to act on each duct individually.       

    
    
     
       Other characteristics of the invention will become apparent from the description which follows, given with reference to the attached drawing in which: 
         FIGS. 1 and 2  depict, viewed from the front and from the side respectively, a dispenser according to the invention, 
         FIG. 3  shows, arranged side by side and to scale, a reservoir platter and a receiving platter; 
         FIG. 4  is a view in section of a duct, and 
         FIG. 5  shows, in section, the structure of the actuator associated with each duct. 
     
    
    
       FIGS. 1 and 2  show at  10  a reservoir platter, made of glass or rigid plastic, provided with a plurality of cavities  12  arranged in a two-dimensional array, in each of which cavities there is a biological liquid  14  samples of which need to be deposited, in the form of microdrops, onto a miniaturized receiving platter  16 , also made of glass or rigid plastic (nylon). 
     It will immediately be seen on referring to  FIG. 3  because, for obvious reasons, this is not visible in  FIGS. 1 and 2 , that the two platters are of very different sizes. Typically, the reservoir platter  10  has a surface area of about 100 cm 2  (12.5 cm×8.5 cm) and has 384 cavities  12 , of a volume of around 100 μl, arranged in a two-dimensional array of 16 columns of 24 rows and about 4.5 mm apart, between centers. By contrast, the receiving platter  16  does not have cavities and has a surface area of about 1 cm 2  only (1.2 cm×0.8 cm). 
     In order to withdraw liquid contained in the cavities  12  and spray an array of microdrops thereof onto the receiving platter  16 , the device according to the invention has a plurality of flexible transfer plates  18  joined together. These plates are made of polyimide, for example, and have a thickness of the order of 50 to 150 μm. 
     Each plate  18  has a lower part in the form of an isosceles trapezium  20 , forming a fluid interface, the long base of which is roughly the same length as the width I 1  of the reservoir platter  10  and is crenellated in such a way as to end in as many end portions  22  as the reservoir platter has columns of cavities  12 , namely  16  in the example described. The crenellations are sized in such a way that the portions  22  can enter the cavities  12 . 
     The trapezium-shaped fluid interface  20  is extended, from its short base, via a rectangular part  24  the length of which corresponds roughly to the width I 2  of the receiving platter  16 . 
     Each flexible plate  18  is provided with a bundle of ducts  26  which originate in each of its end portions  22  and terminate, parallel to one another, in the upper part  24 . Typically, in the exemplary embodiment described, the ducts  26  are then 0.5 mm apart, between centers. 
     The device according to the invention has as many identical plates  18  as the reservoir platter  10  has rows, namely  24  in the example described, the end portions  22  of each plate being intended to fit in one of the columns of the platter. 
     The flexible plates  18  are gathered together, at their upper part, parallel to one another, into a frame  28  to form an impression head the length of which roughly corresponds to the length L 2  of the receiving platter  16  and the width of which, as already mentioned, roughly corresponds to its width I 2 . 
     It goes without saying that the plates could also have a base of a length that corresponds to the length L 1  of the reservoir platter  10 . 
     As  FIGS. 1 and 2  show, the reservoir platter  10  is sealed closed by a lid  30  through which the flexible plates  18  pass, also with sealing. The sealing around the periphery is provided by a bellows  32 , the purpose of which will become apparent later on. 
     Reference will now be made to  FIG. 4  which shows, on a larger scale, the way in which the flexible plates  18  and their ducts  26  are made. It can be seen that these plates are formed of two thin sheets of plastic  34  and  36  of which one, the upper sheet  34  in the figure, has been pre-scored, by any method well known to those skilled in the art, to define the outline of the ducts  26  and which are then joined together with a laminating process, also well known to those skilled in the art. 
     Typically, the sheets  34  and  36  have a thickness of 25 to 50 μm and the total volume of the ducts is about 0.5 to 3 μl. 
     In their rectangular part  24 , the plates  18  comprise, fixed to their upper sheet  34 , facing each duct  26 , a piezoelectric actuator  38  whose purpose is to deform the sheet at this point so as to reduce the thickness of the duct. 
     Above the actuator  38 , the duct  26  opens to the outside of the sheet via a narrowing that forms the spout  40 , whereas, on the other side, the duct has a narrowing  42 . In the example described, the spout  40  and the narrowing  42  have the same depth, from 10 to 40 μm, and the same width, from 40 to 90 μm. The dimensions of the narrowing may even be smaller than those of the spout. 
       FIG. 5  shows that the actuator  38  is formed of a stack which comprises, starting from the sheet  34 , a lower metal electrode  44 , an insulating layer  46 , a layer of piezoelectric material  48 , a further insulating layer  50  and an upper metal electrode  52 . The two electrodes are associated with electrical conductors  54  for controlling the actuator. 
     The electrodes  44  and  52  are deposited by evaporation, while the insulating layers  46  and  50  are deposited by plasma and the piezoelectric layer  48  is deposited by magnetron-enhanced vapor deposition. 
     As depicted in  FIG. 1 , the electrical conductors powering the various actuators  38  end at a control circuit  56  which, under the command of a computer  58 , energizes them. 
     In operation, the assembly formed by the assembled transfer plates  18  is placed above the reservoir platter  10  whose cavities  12  contain the liquids  14  that are to be transferred onto the receiving platter  16 . Alignment is performed in such a way that having passed through the lid  30 , each of the end portions  22  of the transfer plates  18  lies vertically above a cavity  12 . When the ends of the plates are immersed in the liquid, this liquid is drawn up into the various ducts  26  through a capillary effect. 
     It is then necessary to press on the lid  30  in order to compress the bellows  32  so as to raise the pressure in the chamber by a few millibar, the pressure being read off a pressure gauge  60 . Because of this rise in pressure, the liquid continues to rise up inside the ducts  26 , passes through the narrowings  42 , and comes to a halt at the spouts  40 , through a surface tension effect. 
     In order to eject the liquid toward the receiving platter  16 , all that is then required is for the computer  58  to be commanded to apply to the terminals of the electrodes  44  and  52  of each actuator  38  an electrical impulse that causes narrowing of the corresponding duct  26 . Some of the liquid contained therein, prevented from flowing back by the narrowing  42 , is thus ejected through the spout  40  and sprayed on to the receiving platter  16 , at a clearly defined point. 
     The receiving platter  16  can thus receive an array of microdrops of liquid formed at the same number of rows and columns as the reservoir platter but, as already mentioned, at a greatly reduced scale. Typically, in the example described, the microdrops may have a volume from 20 pl to 1 nl. 
     Since the plates  18  contain a volume of liquid far greater than that of the ejected microdrops, several receiving platters  16  can then be used one after another. 
     In an alternative form of embodiment that has not been depicted, the ducts  26  could be subjected to the effect of two identical actuators  38  arranged face to face on the outside of each of the sheets that form the flexible plates. Such an arrangement allows better control over the direction in which the drops are ejected. 
     This description has been given with reference to a flexible plate formed of two sheets sealed together. As an alternative, the plates could be formed of three sheets, the central sheet of which would be pierced with through-openings forming the ducts. 
     There is thus produced a liquid dispenser that has the following main advantages:
         because the impression head  24  and the fluid interface  20  are combined as a single piece, the plates  18 , the path of the liquid is perfectly uniform and only a minimum amount of dead volume remains;   because the plates  18  are flexible, it is easier to adapt the device to suit reservoir platters  10  and receiving platters  16  of different sizes;   because the flexible plates  18  are formed of two polymer sheets assembled by lamination rather than bonding, any contamination with adhesive of the liquids flowing through the ducts is eliminated;   because each duct  26  can be controlled individually by an impulse that ejects a single microdrop, the uniformity in terms of volume of the microdrops can be guaranteed.