Thin film heater and analytical instrument

The present invention relates to a thin film heater (2) including a thin film heat-producing resistor, and a first and a second thin film electrodes (22, 24) electrically connected to the thin film heat-producing resistor to apply voltage to the thin film heat-producing resistor. In the thin film heater (2), at least part of the thin film heat-producing resistor is light transmissive. Preferably, the first thin film electrode (22), the thin film heat-producing resistor and the second thin film electrode (24) are laminated in the film thickness direction in the mentioned order. The present invention further provides an analytical instrument (X) provided with the thin film heater (2).

TECHNICAL FIELD

The present invention relates to a thin film heater, and an analytical instrument to be mounted in use to an analytical apparatus for analyzing a sample.

BACKGROUND ART

As an example of method for analyzing a sample, reaction liquid obtained by the reaction of the sample and a reagent is analyzed by an optical technique. Such an analysis is performed by mounting an analytical instrument for providing a reaction field to an analytical apparatus including an optical system capable of emitting and receiving light (See Patent Document 1, for example). In this case, to reduce the analysis error and enhance the reliability of the analysis result, it is desirable that the temperature of the analytical instrument (particularly reaction liquid) is controlled so that the sample reacts with the reagent substantially at the same temperature in each time of the measurement.

As shown inFIG. 10A, in a conventional method for controlling the temperature of the reaction liquid, an analytical instrument9is placed on a heat block91whose heat capacity is larger than that of the reaction liquid90, and the temperature of the heat block91is controlled to control the temperature of the reaction liquid90(See Patent Documents 2 and 3, for example). In this method, the temperature of the reaction liquid is monitored by a temperature sensor92embedded in the heat block91. When the temperature of the reaction liquid drops below a predetermined temperature, the heat block91is heated to raise the temperature of the reaction liquid via the heat block91. As shown inFIG. 10B, in another method, the analytical instrument9is placed on a heating element93having a high temperature follow ability, and the temperature of the reaction liquid is controlled directly by the heating element93(See Patent Document 4, for example). In this method again, the temperature of the reaction liquid90is controlled by driving the heating element93in accordance with the monitoring results obtained by the temperature sensor92.

In these temperature controlling methods, to raise the temperature of the reaction liquid90, it is necessary to heat the heat block91or drive the heating element93. Therefore, the power consumption is relatively large. Further, when the amount of the reaction liquid90is small as is in a microdevice, it is difficult to locally heat the region in which the reaction liquid90is retained by the heating medium such as the heat block91or the heating element93. Therefore, to raise the temperature of the reaction liquid90with high responsiveness, the heating medium91,93needs to be considerably larger than the region to be heated (the region directly below the reaction liquid90in the figures). Therefore, as compared with the heat quantity conducted from the heating medium91,93, the heat quantity utilized for raising the temperature of the reaction liquid90is small, so that the efficiency of use of the energy is low.

In this way, the conventional temperature control methods have a drawback that the power consumption is large. Therefore, it is difficult to apply the conventional temperature control methods to a small analytical apparatus driven by a small battery (like those generally used at home) incorporated as an internal power source in the apparatus. Even when the conventional methods are applied to such a small analytical apparatus, the operating time of the analytical apparatus becomes considerably short, so that the application is not practical. The operating time can be increased by increasing the capacity of the internal power source. In this case, however, the size of the analytical apparatus increases, whereby the portability is deteriorated. Although power may be supplied from an external power source, the use of external power source requires an adapter for connecting the analytical apparatus to the power source. Therefore, in the case of an analytical apparatus for portable use, the adapter needs to be carried, which deteriorates the portability and makes it difficult to use the apparatus away from home.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an analytical instrument which is capable of heating a liquid component retained in the analytical instrument to a target temperature efficiently with small power consumption and without increasing the size of the analytical apparatus and to provide a thin film heater which can be applied to the analytical instrument.

According to a first aspect of the present invention, there is provided a thin film heater comprising a thin film heat-producing resistor, and a first and a second thin film electrodes electrically connected to the thin film heat-producing resistor to apply voltage to the thin film heat-producing resistor.

According to a second aspect of the present invention, there is provided an analytical instrument to be mounted in use to an analytical apparatus. The analytical instrument comprises at least one reaction vessel for causing reaction between a sample and a reagent, and a thin film heater which produces heat upon energization to heat an inside of said at least one reaction vessel. The thin film heater includes a thin film heat-producing resistor, and a first and a second thin film electrodes electrically connected to the thin film heat-producing resistor to apply voltage to the thin film heat-producing resistor.

For instance, at least part of the thin film heat-producing resistor is light transmissive. In this case, the thin film heat-producing resistor may be entirely transparent or formed with at least one through-hole or cutout for transmitting light.

For instance, the thin film heat-producing resistor may have a thickness of 20 to 300 nm. When the thickness is unduly small, the manufacture is difficult, which is disadvantageous in terms of the productivity and the manufacturing cost. When the thickness is unduly large, it may be difficult to obtain the intended resistance (amount of heat).

Preferably, the first thin film electrode, the thin film heat-producing resistor and the second thin film electrode are laminated in the film thickness direction in the mentioned order to form a heating laminate.

For instance, at least part of the heating laminate may be light transmissive. In the analytical instrument according to the present invention, the heating laminate is light transmissive at least at a portion corresponding to the reaction vessel. The heating laminate may be entirely transparent or formed with at least one through-hole or cutout for transmitting light.

When at least part of the heating laminate is light transmissive, it is preferable that the thin film heater further comprises a transparent substrate for supporting the heating laminate.

For instance, the heating laminate has a thickness of not more than 200 μm, and preferably, not more than 100 μm. When the thickness of the heating laminate is unduly large, the incorporation of the heating laminate in an analytical instrument hinders the size reduction of the analytical instrument.

In the analytical instrument according to the present invention, the thin film heat-producing resistor includes a portion which surrounds at least part of the periphery of the at least one reaction vessel as viewed in the film thickness direction.

For instance, the analytical instrument may be disk-shaped as a whole. In this case, the thin film heater is also disk-shaped as a whole.

For instance, the analytical instrument according to the present invention may further comprise a liquid receiving portion formed at the center thereof for retaining sample to be supplied to the at least one reaction vessel. In this case, a plurality of reaction vessels may be arranged along a common circumference around the liquid receiving portion, and the thin film heat-producing resistor has an annular shape including a through-hole at a location corresponding to the liquid receiving portion.

For instance, the analytical instrument according to the present invention comprises a first transparent member formed with a plurality of flow paths and a second transparent member bonded to the first transparent member to cover the flow paths. In this case, the heating laminate is provided on a surface of the first or the second transparent member. Preferably, the heating laminate is provided on a surface of the second transparent member which is opposite from a surface to which the first transparent member is bonded.

For instance, the analytical instrument may further comprise a third transparent member for covering the heating laminate. Preferably, the third transparent member is in the form of a cap capable of enclosing the second transparent member and the heating laminate between the third transparent member and the first transparent member.

For instance, the analytical instrument according to the present invention is mounted in use to an analytical apparatus provided with a first and a second probes for coming into contact with the first and the second thin film electrodes. In this case, the first and the second thin film electrodes are partially exposed for allowing the first and the second probes to come into contact with the first and the second thin film electrodes.

Preferably, the analytical instrument is so designed that the first and the second probes are capable of coming into contact with the first and the second thin film electrodes from a same side.

The analytical instrument according to the present invention may be a microdevice which uses a sample of not more than 400 μL, for example. For instance, when the analytical instrument includes a plurality of flow paths, the capacity of each of the flow paths may be 300 to 800 nL.

In the present invention, when the first thin film electrode, the thin film heat-producing resistor and the second thin film electrode are described as transparent, the term “transparent” is not limited to the state in which all the light rays in the visible light range are transmitted but also include the state in which the light of a particular wavelength is not absorbed or hardly absorbed, i.e., the optically transparent state with respect to a particular wavelength. For instance, in the analytical instrument of the present invention, when the light of a wavelength which is used for the analytical analysis using the analytical instrument is not absorbed by the heating laminate or is hardly absorbed by the heating laminate, the heating laminate is described as “transparent” even when it is not visually transparent.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1-3show a microdevice X which is formed with a plurality of thin flow paths and which is in the form of a transparent disk as a whole. The microdevice X includes a substrate1, a thin film heater2and a cap3.

As better shown inFIGS. 2 and 3, the substrate1has a periphery formed with a step to have a reduced thickness, and a liquid receiving portion10, a plurality of flow paths11and a common flow path12are formed in the substrate1. As a whole, however, the substrate is in the form of a transparent disk.

The liquid receiving portion10serves to retain a sample to be introduced into each of the flow paths11. The liquid receiving portion10comprises a columnar recess formed at the center of the substrate1.

The flow paths11are utilized for moving a sample and extend from the liquid receiving portion10toward the periphery of the substrate1. The flow paths11extend radially as a whole. Each of the flow paths11includes a reaction vessel13for causing reaction between the sample and a reagent, so that a plurality of reaction vessels13are provided in the substrate1. The reaction vessels13are positioned at the same distance from the liquid receiving portion13and arranged along a common circumference in the substrate1. Each of the reaction vessels13is formed with a reagent portion14. The reagent portion14is in a solid state to be soluble when a sample is supplied thereto. The reagent portion develops a color upon reaction with a detection target component contained in the sample. In this embodiment, a plurality of kinds of reagent portions14which differ from each other in component or composition are provided so that the microdevice X can measure a plurality of items.

The common flow path12is utilized for discharging gas existing in the flow paths11to the outside. The common flow path12comprises an annular groove formed at a the periphery of the substrate and communicates with the flow paths11.

The substrate1having the above-described structure can be formed by molding an acrylic resin such as polymethyl methacrylate (PMMA) or a transparent resin such as polydimethylsiloxane (PDMS). By appropriately designing the shape of a mold, the liquid receiving portion10, the flow paths11and the common flow path12can be formed at the same time in the resin molding process.

The thin film heater2serves to heat the inside of each of the reaction vessels13and includes a sub substrate20and a heating laminate21.

The sub substrate20is in the form of a transparent disk which is slightly smaller than the substrate1. The sub substrate20is formed with through-holes20A and20B. The through-hole20A is utilized for discharging the gas existing in the common flow path12of the substrate1to the outside and formed at a peripheral portion of the sub substrate20so as to communicate with the common flow path12. The through-hole20B is utilized for introducing a sample into the liquid receiving portion10of the substrate1and formed at the center of the sub substrate20so as to communicate with the liquid receiving portion10.

The heating laminate21generates heat due to the electrical resistance when power is supplied. The heating laminate21is arranged on the sub substrate20and formed with through-holes21A and21B at locations corresponding to the through-holes20A and20B of the sub substrate20. As shown inFIG. 4, the heating laminate comprises a thin film anode22, a thin film heat-producing resistor23and a thin film cathode24which are laminated in the mentioned order on the sub substrate20.

As shown inFIGS. 2 and 3, the through-hole21A serves to allow the gas existing in the common flow path12of the substrate1to be discharged to the outside. The through-hole21B serves to allow the sample to be introduced into the liquid receiving portion10of the substrate1.

As shown inFIGS. 2-5, the thin film anode22, the thin film heat-producing resistor23and the thin film cathode24are formed with through-holes22A-24A and22B-24B, and have a generally annular configuration partially cut away by the provision of the cutouts22C-24C. The through-holes22A-24A constitute the through-hole21A of the heating laminate21, whereas the through-holes22B-24B constitute the through-hole21B of the heating laminate21.

The thin film anode22and the thin film cathode24are transparent and utilized for applying a voltage to the thin film heat-producing resistor23. The electrodes22and24are exposed via probe insertion ports32A and32B of the cap3, which will be described later, so that voltage application probes40and41of an analytical apparatus (not shown) can be brought into contact with the electrodes through the probe insertion ports32A and32B.

The thin film heat-producing resistor23is transparent and heated by the application of a voltage using the thin film anode22and the thin film cathode24. Herein, the term “transparent” means the state in which at least the light of a wavelength used for the analysis with the analytical instrument is not absorbed or is hardly absorbed and does not necessarily mean the visually transparent state.

Each of the thin film anode22, the thin film heat-producing resistor23and the thin film cathode24can be formed as a transparent thin film having an appropriate resistance by selecting the film forming method, the thickness or the material. The thin film heat-producing resistor23is so formed as to have a higher sheet resistance than those of the thin film anode22and the thin film cathode24.

For instance, each of the thin film anode22and the thin film cathode24has a thickness of 1 to 100 μm, whereas the thin film heat-producing resistor23has a thickness of 20 to 300 nm. As a method for forming the thin films22-24, screen printing, sputtering, CVD, vapor deposition, application or rolling may be employed. As the material of the thin films22-24, use may be made of inorganic oxide, an inorganic substance such as TiN or an organic substance such as conductive polymer. Examples of inorganic oxide include an oxide of a single element such as In2O3, ZnO, SnO2, a complex oxide obtained by compounding two or more oxides of a single element selected from the above examples, or an oxide obtained by doping an oxide of a single element or a complex oxide with a particular element. As the dopant, use may be made of B, Al2O3or Ga2O3, for example. The thin film anode22and the thin film cathode24may be formed by working a highly conductive metal (e.g. noble metal such as gold) into a thin metal film in the order of nm to have a light transmittance.

As shown inFIGS. 1-3, the cap3is formed with a sample introduction port30, a gas discharge port31and probe insertion ports32A and32B. The cap is in the form of a transparent disk as a whole.

The sample introduction port30is utilized for introducing a sample. The sample introduction port30is provided by forming a bulging portion30having an opening33A at the center of the cap3. The opening33A communicates with the liquid receiving portion10of the substrate1via the through-holes20B,21B of the sub substrate20and the heating laminate21. With this structure, the sample can be introduced into the liquid receiving portion10through the sample introduction port30(opening33A).

The gas discharge port31is utilized for discharging the gas existing in the flow paths11to the outside through the common flow path12. The gas discharge port31is a through-hole communicating with the common flow path12via the through-holes20A,21A of the sub substrate20and the heating laminate21. Before the use of the microdevice1, the gas discharge port31is closed by a sealing member31a. For instance, the sealing member31ais peeled off when the microdevice X is to be used. By peeling off the sealing member, the gas discharge port31is opened so that the flow paths11communicate with the outside through the common flow path12. Alternatively, the gas discharge port31may be opened by forming a hole in the sealing member31a. Specifically, the sealing member31amay be made of a thin film such as an aluminum foil, and a hole may be formed in the sealing member31aby piercing the sealing member31awith a needle or the like. Alternatively, the sealing member31amay be made of a thermoplastic resin having a low melting point (not higher than 100 degrees, for example), and a hole may be formed in the sealing member31aby irradiating the sealing member31awith laser beam.

The probe insertion holes32A and32B are through-holes into which the voltage application probes40and41of the analytical apparatus are to be inserted for coming into contact with the thin film anode22and the thin film cathode24of the thin film heater2.

Similarly to the substrate1, the cover3having the above-described structure can be formed by molding a transparent resin. The sample introduction port30, the gas discharge port31and the probe insertion ports32A,32B can be formed at the same time in the resin molding process.

The use and advantages of the microdevice X will be described below.

To analyze a sample, the microdevice X is mounted to an analytical apparatus (not shown). The sample may be supplied to the microdevice X in advance or supplied to the microdevice X after the microdevice X is mounted to the analytical apparatus.

The supply of the sample to the microdevice X is performed through the sample introduction port30of the cap3. The sample introduced through the sample introduction port30reaches the liquid receiving portion10through the through-holes20B,21B of the sub substrate20and the heating laminate21. However, since the gas discharge port31of the microdevice X is closed by the sealing member31a, capillary force is not exerted to the inside of each of the flow paths11. Therefore, the sample is retained in the liquid receiving portion10.

When the microdevice X is mounted to the analytical apparatus (not shown), the voltage application probes40and41of the analytical apparatus are brought into contact with the thin film anode22and the thin film cathode24through the probe insertion ports32A and32B of the cap3. The analytical apparatus (not shown) applies a voltage across the thin film anode22and the thin film cathode24of the thin film heater2via the probes40and41. As a result, the thin film heat-producing resistor23is energized to generate heat, whereby the reaction vessels13are heated. The heating of the reaction vessels13is performed under feedback control in which the temperature of the reaction vessel13is monitored to maintain the temperature of the reaction vessels13at a target temperature or by applying a predetermined voltage for a predetermined time period.

Subsequently, the gas discharge port31is opened so that the sample retained in the liquid receiving portion10flows into each of the flow paths11. As noted before, the gas discharge port31is opened by peeling off the sealing member31aor making a hole in the sealing member31a.

When the gas discharge port31is opened, the inside of each of the flow paths22communicates via the common flow path12and the gas discharge port31. As a result, capillary force is exerted on each of the flow paths11, so that the sample retained in the liquid receiving portion10moves through the flow paths11to reach the reaction vessels13. In each of the reaction vessels13, the reagent portion14is dissolved by the sample, whereby a liquid phase reaction system is established. The liquid phase reaction system is heated to a target temperature by heating the reaction vessel13by the thin film heater2. In the liquid phase reaction system, the sample reacts with the reagent. As a result, the liquid phase reaction system develops a color related with the amount of the detection target component contained in the sample, or a reaction product corresponding to the amount of the detection target component is produced. As a result, the liquid phase reaction system of the reaction vessel13shows a light transmittance (light absorbance) corresponding to the amount of the detection target component.

When a predetermined period has elapsed after the supply of the sample to each of the reaction vessels13, photometry is performed with respect to the liquid phase reaction system in the reaction vessels13in a predetermined order. In the analytical apparatus (not shown), computation necessary for the analysis of the detection target component in the sample is performed based on the photometry results of each of the reaction vessels13.

According to the present invention, the reaction vessels13are heated by the thin film heater2incorporated in the microdevice X. The design of the thin film heater2can be varied in accordance with the size, position, number or shape of the reaction vessels of the microdevice X. Therefore, only the liquid phase reaction system in the reaction vessels13can be selectively heated, so that the supplied energy can be used efficiently. Further, since the thin film heater2can be provided adjacent to the reaction vessels13, thermal energy can be efficiently transferred from the thin film heater2to the liquid phase reaction system. Therefore, the efficiency of use of the supplied energy can be enhanced, and the power consumption by the heating of the liquid phase reaction system (reaction vessels13) can be reduced. Therefore, as the internal power source for driving the thin film heater2, a small battery such as a dry cell generally used at home can be used. Even when such a small battery is used, the battery can sufficiently heat the liquid phase reaction system (reaction vessels13) without running down quickly. Therefore, even in a small analytical apparatus, the liquid phase reaction system (reaction vessels13) can be heated by utilizing the internal power source and without increasing the size of the analytical apparatus. Since the internal power source can be used, connection with an external power source is not necessary, so that an adapter is not necessary. Accordingly, in carrying the analytical apparatus, it is unnecessary to carry an adapter, whereby the portability is improved.

The present invention is not limited to the foregoing embodiment and may be varied in design in various ways. For instance, firstly, the analytical instrument according to the present invention does not necessarily need to be structured as a microdevice. Secondly, the analytical instrument is not limited to one designed to perform the sample analysis by an optical method but may be designed to perform the sample analysis by an electrochemical method. Thirdly, the analytical instrument is not limited to one provided with a plurality of reaction vessels. The heater of the analytical instrument according to the present invention may have such structures as shown inFIGS. 6-9.

The heater5shown inFIG. 6is similar in structure to the foregoing thin film heater2(SeeFIGS. 4 and 5) in that the heater includes a thin film anode52, a thin film heat-producing resistor53and a thin film cathode54. However, the heater5differs from the thin film heater2(SeeFIGS. 4 and 5) in that the thin film anode52and the thin film cathode54are electrically connected selectively to the portions (ends) of the thin film heat-producing resistor53at which a cutout53is formed.

In the heater5shown inFIG. 6, the thin film anode52is connected to the lower surface54of the thin film heat-producing resistor53, whereas the thin film cathode54is connected to the upper surface55of the thin film heat-producing resistor53. However, the thin film anode52and the thin film cathode54may be connected to a same surface of the thin film heat-producing resistor53.

The heater6shown inFIGS. 7A and 7Bincludes a heating laminate61having a configuration obtained by eliminating the cutouts22C-24C (SeeFIGS. 4 and 5) from the heating laminate21of the thin film heater2. Specifically, the heating laminate61includes a thin film anode62, a thin film heat-producing resistor63and a thin film cathode64each of which is shaped like a doughnut. The dimension (difference between the inner diameter and the outer diameter) of each of the thin films62-64is smaller than that of the thin films22-24(SeeFIGS. 4 and 5) of the thin film heater2so that the thin films62-64selectively cover the portion provided with the reaction vessels13.

Since the area to be heated is relatively small in this structure, efficient heating is possible, and the running cost can be reduced. Further, since the dimension of the thin films62-64is small, the cost for the material can also be reduced.

The heater7shown inFIGS. 8A and 8Bhas a structure obtained by adding a plurality of through-holes71D to the heater6shown inFIG. 6. Specifically, the through-holes71D are provided in the heating laminate71at locations corresponding to the reaction vessels13. Each of the through-holes71D is made up of through-holes72D,73D and74D respectively formed in the thin film anode72, the thin film heat-producing resistor73and the thin film cathode74at locations corresponding to the reaction vessel13.

With this structure, since the through-holes71D are provided in the heating laminate71at locations corresponding to the reaction vessels13, the heating laminate71and hence the thin films72-74do not need to be transparent. Therefore, the material for forming the heating laminate71and the thin films72-74can be selected from a wide range, whereby the manufacturing cost can be reduced.

Similarly to the heater7shown inFIG. 8, the heater8shown inFIGS. 9A and 9Bincludes a plurality of through-holes81D in the heating laminate81at locations corresponding to the reaction vessels13. The through-holes81D are provided by forming a plurality of through-holes82D in the thin film anode82at locations corresponding to the reaction vessels13and forming a plurality of cutouts83D and84D respectively in the thin film heat-producing resistor83and the thin film cathode84at locations corresponding to the reaction vessels13. With this structure, the heating of each of the reaction vessels13by the heating laminate81is performed not at the entire circumference of the reaction vessel13but at a portion adjacent to the common flow path12. It is to be noted that the thin film anode82may have the same configuration as that of the thin film heating resistor83and the thin film cathode84.

In the heaters6-8shown inFIGS. 7-9, each of the thin films may be partially cut away similarly to the thin film heater2shown inFIGS. 4 and 5. Further, similarly to the heater5shown inFIG. 6, the thin film heat-producing resistor may be partially cut away, and the thin film anode and the thin film cathode may be electrically connected selectively to the opposite ends of the thin film heat-producing resistor, respectively.