Abstract:
An apparatus analyzes liquid samples automatically and continuously by mixing certain reagents within a common arrangement of membrane pumps, mixing chambers and connecting conduits formed in a silicon wafer and evaluating the reaction results with the help of suitable sensors on the silicon wafer, the silicon wafer being of 100 orientation and the structure thereof having been formed by anisotropic etching. Immediately before and after the pump chamber of trapezoidal cross section, there are conduits of a v-shaped or trapezoidal cross section which have a nonlinear flow resistance.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus for analyzing liquid samples automatically and continuously by mixing certain reagents with the use of membrane pumps, mixing chambers and conduits and evaluating the reaction results with the help of suitable sensors. 
     In the state of the art, apparatuses are known which use, for this task, different types of pumps, including also membrane pumps, which deliver a certain volume in a particular time and, with that, bring about the mixing ratio necessary for the chemical reaction. 
     Furthermore, pump arrangements are known which mix particularly small amounts of reagents. Manufacturing technologies are used for this purpose which can be considered to be in the field of micromechanics. The active element is a micropump, which is responsible for delivering the sample or a reagent necessary for the analysis. This micropump consists of a driving mechanism and a valve arrangement. 
     In Gerlach and Warmus, Technical University Ilmenau, Design Considerations on the Dynamic Micropump, ACTUATOR 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, a membrane in a silicon wafer, which is constructed as a piezo dimorphic system, is used as driving mechanism. The valves are direction-dependent, pyramidshaped flow resistances, which are disposed in a second silicon wafer. The use of two wafers, which must be positioned precisely and are connected to one another, is a disadvantage. Due to tolerances, the metering of precise amounts is not achieved. 
     A different construction, described in Buestgens et al., Micromembrane Pump Manufactured by Molding, ACTUATOR 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, uses as valve an elastic membrane, which is clamped between two carrier plates. The propulsion is accomplished in this case by heating and deformation. The need to manufacture several carrier parts, which must be joined together accurately positioned, is a disadvantage here also. The heating of the membrane represents a limitation for certain reagents. The amount delivered can also be controlled only with difficulty. 
     An arrangement, described in Temmel et al., A Micromechanical System for Liquid Dosage and Nebulization, ACTUATOR 96, 5th International Conference on New Actuators, Jun. 26-28, 1996, Bremen, Germany, also uses several individual parts which must be joined together positionally accurate with respect to one another. The system is driven by electrostatic forces which deform a membrane. The valves are constructed as gates which produce a direction-dependent flow resistance. The amount delivered is controlled. The expensive manufacturing process, especially when an arrangement with several dozen pumps is being considered, is also a disadvantage. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the invention to provide an apparatus for analyzing liquid samples automatically and continuously, which is defined by a large number of pumps, valves, mixing and reaction chambers in the same shaped part, which can be produced with high precision. 
     This objective is accomplished owing to the fact that a structure is provided in a silicon wafer of 100 orientation by anisotropic etching which, together with a glass covering layer mounted by anodic bonding, results in an arrangement of pumps, valves, mixing chambers and reactors. As a driving mechanism, the pumps use a piezo dimorphic system which is formed by mounting a piezo plate or a piezo-active layer on the glass covering layer or on the bottom of the pump chamber. 
     The pump chamber is rectangular with a trapezoidal cross section. Directly in front of and behind the pump chamber there are conduits of a triangular or trapezoidal cross section which present a nonlinear flow resistance. The mode of functioning is that, up to a certain flow velocity v, laminar flow exists and, when this flow velocity is exceeded, this laminar flow changes over into turbulent flow. With that, there is a sudden change in the flow resistance. 
     The geometry of the inlet and outlet ducts is different, so that the point at which linear and nonlinear flow sets in is different. If now the membrane is deflected with a steady pulse, the amplitude of which changes with the duration, the times at which there is a changeover from laminar to turbulent flow are different in the inlet and outlet ducts. With that, a direction-dependent flow resistance results over average time and brings about a volume flow over the whole of the arrangement. The volume flows in the one direction or the other, depending on whether the pulse is increasing or decreasing over time. For metering precisely the amount of liquid delivered, measurement conduits, adjoining the pump chamber and representing a defined flow resistance, can be accommodated in the silicon wafer. Liquid pressures, arising at the two ends of the measurement conduit, are a measure of the amount flowing through the measurement duct. 
     The pressure difference can therefore be used as a variable for regulating the pump frequency or the pump amplitude in order to adjust the amount delivered precisely. Several pumps can act at the outlet side on a common chamber which, corresponding to the manufacturing technology for the 100 oriented silicon wafers, is also configured rectangularly with a trapezoidal cross section. Due to the asymmetric inlet into this chamber, swirling of the various reagents takes place. With that, mixing and a stable chemical reaction are produced. 
     The mixing chamber can be used as a common reference potential for measuring the pressure or the flow through the apparatus. The outlet side of the mixing chamber is connected by means of a conduit with the reactor, which also has a v-shaped or trapezoidal cross section. The flow rate and the conduit length can be designed so that the reaction time is sufficient for evaluating the liquid by suitable sensors. With that, quasi continuous measurement is possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The concept on which the invention is based is explained in greater detail in the following description by means of an example, which is shown in greater detail in the drawings, in which 
     FIG. 1 shows an overall view of an analytical system according to the invention; 
     FIG. 2 shows an analytical system for several analyses according to the invention; 
     FIG. 3 shows a diagrammatic representation of micropump construction according to the invention in plan view; 
     FIG. 4 shows a diagrammatic representation of micropump construction according to the invention in cross sectional view; 
     FIG. 5 shows a plot of flow resistances versus volume flows; 
     FIG. 6 shows a plot of the volume flows over a time period; 
     FIG. 7 shows the control system for amounts metered; 
     FIG. 8 shows a diagrammatic representation of the mixing chamber; 
     FIG. 9 a  shows a cross section of a silicon wafer with glass covering according to the invention in conjunction with means for effecting an optical evaluation of the reaction product; 
     FIG. 9 b  shows a side view of FIG. 9 a ; and 
     FIG. 10 is a cross section of an analytical system according to the invention including means for supplying the liquids. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows the structural principle of the arrangement. There are several micropumps on an approximately 500 μm thick silicon wafer  2  with a 100 crystalline orientation. The micropumps  1  are connected by means of conduits  3  with inlet openings  4  through which the sample liquids or reagents are supplied. In this connection, the micropumps  1  act on a mixing chamber  5 , in which swirling of the reagents that have been introduced takes place. Each micropump  1  occupies an area of about 10 mm 2 . Due to the properties of the 100 oriented silicon, the connecting conduits are constructed with a triangular cross section, a structural depth of about 100 μm and are rectangular at the bends. 
     Referring to FIGS. 7 and 8, an inlet, of a measurement conduit  17  into the also rectangular mixing chamber  5  with a trapezoidal cross section, advisably is constructed so that the liquid sample is introduced at a transverse side  6  and the reagents, which are to be added, are introduced in proportionally smaller amounts at two longitudinal sides  7  of the mixing chamber  5 . From the mixing chamber  5 , the mixed product is supplied via a relatively long reaction conduit  8  to the evaluating sensors  9  for evaluating defined liquid properties as shown in FIG.  1 . The evaluating sensors  9  are located directly on the silicon wafer  2  or, in a different example, outside of the silicon wafer  2 , adjoining the outlet  10 . The length of the reaction conduit  8  is determined by a required reaction time for the mixed product in conjunction with a velocity of the volume flow before evaluation with the evaluating sensor  9 . Further micropumps  11  can be disposed on the silicon wafer  2  with a separate inlet  35  and outlet  36  in order to supply systems located, for example, in a periphery of the arrangement, with liquid. 
     Referring to FIG. 2, when a silicone wafer with a 4 inch diameter is used, a plurality of the micropumps  1 , mixing chambers  5  and evaluating sensors  9  can be disposed and used for different types of analytical procedures. In the exemplary embodiment of FIG. 2, four methods or analytical procedures A 1  to A 4  are realized with a single silicon wafer  2 . Each method takes up a quarter of the available area. The structure of the analytical system, as shown in FIG. 1, is realizable universally and redundantly without a significant cost disadvantage. The micropumps  1  which are not required are blocked at the respective inlet opening  4 . 
     Referring to FIGS. 3 and 4, the construction of a single micropump  1  is shown in plan view and cross section respectively. A pump chamber  13  is rectangular and an inlet conduit  14  and outlet conduit  15  have differing cross sections. The outlet conduit  15  leads into a further pressure measuring chamber  16  which is used to measure the pressure. The measuring conduit  17  connects the pressure measuring chamber  16  with the mixing chamber  5 . The sectional representation of FIG. 4 illustrates the construction of the pump system. All chambers  13 ,  5 , as well as the connecting conduits  3 ,  8 ,  17 , are produced by deep etching which is carried out anisotropically. The arrangement as a whole is covered by an approximately 150° Jim thick glass covering layer  18 , which is connected tightly by an anodic bonding with the silicon wafer  2 . There are electrical strip conductors  19  on the glass covering layer  18  for contacting the piezo elements  20 . The piezo elements  20 , which are glued onto the glass covering layer  18 , together with the glass covering layer  18  form a dimorphic system which warps when an electrical voltage is applied and, with that, brings about a flow of volume in the pump chamber  13 . Pressure sensors  21  are mounted on the glass covering layer  18  over the measuring chambers  16 . The pressure sensors  21  measure the warping which occurs as a function of the pressure in the pressure measuring chamber  16  and convert it into an electrically measurable signal. Advantageously, the pressure sensors  21  are constructed in piezo resistive layers. 
     The inlet conduit  14  and outlet conduit  15  act as resistances to the volume flowing. The special feature of the flow resistances in the microregion is that at a certain flow velocity laminar flow changes over into a turbulent flow. The flow resistance increases suddenly, as shown in FIG. 5, from a value R l  to a value R t . Due to the different geometries of the inlet conduit  14  and the outlet conduit  15 , the transition from R l  to R t  takes place at different flow velocities. If now the piezo element  20  is triggered with a relatively steep flank, there is a rapid volume change in the pump chamber  13  and this volume change leads to a liquid stream of high velocity. In the inlet conduit  14  with a smaller cross section, this liquid flow leads to a sudden increase in resistance, whereas the flow resistance in the outlet conduit  15  remains largely constant. The fluid flow produced in the pump chamber  13  is divided differently depending on the flow resistances. In the embodiment of FIG. 3, the bulk of the fluid flows through the outlet conduit  15 . The dimorphic system formed from the piezo element  20  and the glass covering layer  18  is reset with a relatively flat pulse flank. The volume change in the pump chamber  13  is correspondingly slow. It is avoided that the flow in the inlet conduit  14  becomes turbulent, so that the flow resistance here remains almost constant. Thus, the division of the volume flowing is different than in the case of the rapid volume change of the pump chamber  13 , although here also the greater part of the volume flows through the outlet conduit  15 , however, with the reverse algebraic sign. 
     Referring to FIG. 6, graphs of the chamber volume, inlet volume flow  o V a  and outlet volume flow  o V b  over time illustrate that the fluid flows predominantly in one direction over the whole length of a saw tooth-shaped triggering pulse; this is equivalent to a pumping action. During a time period T lowering , the time during which the chamber volume is decreased rapidly resulting in a steep negative slope in the chamber volume graph, a significantly greater amount of the outlet volume flow  o V b  exists than inlet volume flow  o V a  due to the existence of the turbulent flow in the inlet conduit  14  as oppose to the laminar flow in the outlet conduit  15 . During a time period T lifting , the time period during which the chamber volume is increasing at a slower rate than the decrease of the volume chamber, only a slightly greater amount of the outlet volume flow  o V b  exists than inlet volume flow  o V a  due to the existence of laminar flow in both the inlet conduit  14  and the outlet conduit  15 . Thus, the net effect over a complete pump cycle, T lowering  and T lifting , is that fluid flows from the inlet conduit  14 , through the pump chamber  13 , and out the outlet conduit  15 . 
     The measurement conduit  17  is dimensioned so that there is no transition to turbulent flow in any case. With that, depending on the volume flowing, there is a pressure difference, which at the same time is a measure of the amount flowing through the conduit. The specially constructed pressure measuring chamber  16  records the warping of the glass covering layer  18 . The mixing chamber  5 , which follows the measuring conduit  17 , also has pressure sensors  21  on the glass covering  18 , which record the warping, so that two pressure signals  22  and  23 , depicted in FIG. 7, represent the pressure difference. 
     As shown in FIG. 7, the two pressure signals  22  and  23  are compared with one another. The resulting difference signal  24  is converted into a signal which is supplied to a servo component  12  for the output of the micropump  1 . For this purpose, the difference signal  24  produces a change in the voltage amplitude or in the frequency of the signal applied to the piezo element  20 . In this way, a regulating circuit is formed which permits the reagents for the analytical process to be metered accurately even under changing environmental conditions. 
     FIG. 8 shows an example of the construction of a mixing chamber  5  in which six different reagents can be added to the sample. 
     It is advantageous for the evaluation of optical properties to integrate also the cuvettes, necessary for this, in the silicon wafer  2 . FIGS. 9 a  and  9   b  show an example, for which light from a light-emitting diode  40  is coupled into and out of a cuvette conduit  42  for the purpose of determining the extinction of light effected by the reaction product, i.e., the attenuation of the light beam in the cuvette channel. The reflection at the inclined chamber walls  37 , at the chamber bottom  38  and at the glass covering layer  18  is used for this purpose. Spectral selectivity can be achieved by inserting spectral filters  39 , such as interference filters, into the beam path. The light is measured by a photo element  41  which preferably is constructed as a phototransistor. 
     Referring to FIG. 10, for the overall arrangement of the analytical system, it is advisable to use the upper side  25  of the silicon wafer  2  for contacting the electrical signals and the underside  26  of the wafer for supplying the sample or the reagent. The wafer  2  is mounted for this purpose on a chip carrier  27 , for example, by gluing  28 . The chip carrier  27  receives hollow needles  29 , which are inserted mechanically rigidly and connected with appropriate reservoirs  30 . At a short distance above the upper side of the silicon wafer  2  there is a carrier plate  31  for the electrical contacts  32 , which act elastically on the contact surfaces  33  of the piezo elements  20  or on the pressure sensors  21 . In this way, the sensitive silicon wafer  2  is protected. The overall arrangement thus permits the system to be operated under harsh conditions. 
     The invention is described and presented above by means of selected distinguishing features. Of course, the invention is not limited to this representation. Rather, all distinguishing features can be used alone or in any combination, even independently of their combination in the claims.