Abstract:
Provided is an apparatus for detecting biopolymers (DNA) capable of total analysis including non-reacted samples without complicated operations such as washing. 
     A DNA probe is fixed to one of electrodes and direct current voltage is placed between the electrodes, so that it becomes possible to separate complementary strand sample DNA and non-complementary strand sample DNA. By analyzing from a ratio in the whole reaction system, it is possible to obtain clearer results. Further, by using electrophoresis by gel together, it is possible to separate reacted samples and non-reacted samples to perform measurements therefor in the same reaction field.

Description:
PRIORITY INFORMATION 
     This application claims priority to Japanese Application Serial No. 364370/2000, filed Nov. 30, 2000. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus for detecting biopolymers capable of detecting the presence of biopolymers such as DNA, RNA and protein in a sample and measuring an existing amount or a concentration thereof, and to a cartridge used for the detection. 
     As technologies for detecting DNA, such technology has been generally used, in which DNA is modified with a radioactive material, a fluorescence dyestuff or the like by use of technologies of RI (radioactive isotope), fluorescence or the like and excited by a stimulus from the outside for detection of response by luminescence. Also an electric charge detecting method for electrochemically determining DNA based on an oxidation-reduction potential by use of an intercalating agent, which is specifically bonded to a duplex of DNA, has been devised. Further, there is a method of using a surface plasmon resonance phenomenon as a method without modification and the like. With respect to a method of fixing DNA to an electrode, there is a method of utilizing an action that a monolayer of free thiol radicals located on the end of DNA is self-organized on the surface of gold using a thiol modified DNA probe. 
     In conventional DNA detecting technologies, methods of using RI or fluorescence have been needed to modify DNA. 
     SUMMARY OF THE INVENTION 
     An apparatus for detecting biopolymers in accordance with the present invention includes: a voltage supply unit for placing electric voltage between two electrodes of a cartridge which stores biopolymers between the electrodes; a holding unit for holding the cartridge; an irradiation unit for irradiating light onto the cartridge held by the holding unit; and a light receiving unit for receiving the light irradiated by the irradiation unit onto the cartridge held by the holding unit. 
     The voltage supply unit can selectively supply alternating current voltage and direct current voltage so that biopolymers can be attracted to one electrode or both electrodes. 
     The holding unit can two-dimensionally move the cartridge on a plane perpendicular to an optical axis of the light irradiated by the irradiation unit so that the presence of a biopolymer on each location in the cartridge can be detected. 
     Since the irradiation unit can irradiate light having a specified single wavelength, sensitivity for detecting can be improved. 
     The apparatus for detecting biopolymers further includes an arithmetic unit for calculating an existing amount, a base length, a concentration, a hybridization ratio and a hybridization amount of a biopolymer from a quantity of light received by the light receiving unit so that various kinds of feature amounts for the biopolymer can be determined. 
     The apparatus for detecting biopolymers further includes a heater which applies heat to the electrodes of the cartridge for disassociating biopolymers hybridized in the cartridge to single strands, so that each presence of a complementary strand biopolymer and a non-complementary strand biopolymer can be detected. 
     Also, a cartridge in accordance with the present invention includes: a pillar-shape base unit capable of accommodating a biopolymer solution, the base unit having a first electrode on the inside of a bottom face, transparent sides at least in a portion and a top face opened; and a cap unit which has a second electrode on the outside of a bottom face and is inserted in the base unit from the top face to the middle of the base unit to be fixed. 
     Since biopolymer probes are fixed on the first electrode or the second electrode, a complementary strand biopolymer and a non-complementary strand biopolymer can be separately detected. 
     Further, the cross section of the pillar-shape base unit is a square and the cross section of the cap unit is a round shape. Therefore, since a light incident plane is a plane surface, it is possible to suppress light scattering and easily insert the cap unit into the base unit. 
     Also, the cartridge further includes a solution reservoir on an upper portion of the base unit for collecting a biopolymer solution overflowed from said pillar-shape portion to prevent the solution from flowing out so that it is possible to prevent the solution from flowing out to the outside. 
     In the apparatus for detecting of the present invention, a sample DNA is injected between electrodes facing each other. In this technology, since an existing amount of DNA can be physically measured, a concentration thereof and the like can be also determined. Further, by applying an external force by an electric field between the facing electrodes to attract single strand probe DNA fixed on the surface of the electrode and non-hybridized sample DNA to the electrode where the probe DNA is not fixed, it becomes possible to detect a gene without washing. 
     Further, by use of this method, clearer results can be obtained since both of reacted one and non-reacted one are targeted for the measurement. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a structure of an apparatus for detecting biopolymers according to one embodiment in the present invention. 
         FIG. 2  is a view showing a structure of a cartridge according to one embodiment in the present invention. 
         FIG. 3  is a general view showing an apparatus for detecting biopolymers according to one embodiment in the present invention. 
         FIG. 4  is a schematic view showing a structure of an apparatus for detecting biopolymers using plate-shape cartridges. 
         FIGS. 5A and 5B  are views showing a plate-shape cartridge in detail. 
         FIG. 6  is a general view showing an apparatus for detecting biopolymers using the plate-shape cartridges. 
         FIG. 7  is a view showing behaviors of DNA when direct current voltage is applied. 
         FIG. 8  is a view showing behaviors of DNA when alternating current voltage is applied. 
     
    
    
     DETAILED DESCRIPTION 
     Hereunder, referring to drawings, preferred embodiments will be described in details. 
       FIG. 1  is a schematic view showing a structure of an apparatus for detecting biopolymers according to one embodiment of the present invention. The apparatus includes an optical system to measure optical energy and the like, such as absorbance, transmittance and reflectance, and an optical system to detect a modified part when DNA is modified with an organic material or an inorganic material, such as a fluorescent material and a radio active material. 
     The optical system to measure optical energy and the like, such as absorbance, transmittance and reflectance, includes a laser, an optical source, a slit, a filter, a diffraction grating, a light receiving unit and the like. A controller  3  is connected to a computer  1  having a display  2 . Light generated from a laser and optical source  4  controlled with the controller  3  is passed through an optical source slit  6  after wavelength selection with a filter  5 . The light is passed through an incidence slit  7  and converted to have wavelengths of 260 nm and 280 nm at a diffraction grating  8 . Further, the light is passed through an ejection filter  10  placed just before a cartridge  11 , the details of which are shown in FIG.  2 ). Optical energy is decreased in the cartridge  11  depending on an existing amount of DNA since DNA absorbs the light. That is, optical energy after the decrease is obtained at a light receiving unit  12 . Any desired measurement location can be selected using an XY stage  13 , and reading can be conducted in a scanning manner. Analysis of the result is carried out with the computer  1 , and a distribution of the DNA existing amount can be determined by measuring how much the quantity of optical energy received at the light receiving unit is decreased from incident light at some place. The transmittance is obtained as a ratio of a quantity of light to that in the case of no presence of DNA under the condition that the cartridge  11  is fully filled with the solution. The reflectance is, in the same manner, obtained as a ratio of a quantity of reflected light to that in the case of no presence of DNA. In order to measure this reflectance, an optical system to receive the reflected light is needed. The absorbance is obtained by subtracting transmittance from reflectance. Temperature inside the cartridge can be controlled by a cartridge fixed portion  14  provided with an electric heater that is connected to a power source  15 . Thus, the temperature during reaction or measurement can be controlled, and the reactivity at each temperature, such as a dissociation temperature for single strands, for example, can be measured. 
     The optical system to detect a modified part when DNA is modified with an organic material or an inorganic material, such as a fluorescent material or a radio active material, includes a laser, a light source, a pinhole, a lens and the like. Light generated from a laser and light source  16  is condensed with a lens  22  after passing through a filter  21  for wavelength selection and is passed through a pinhole  23  at the focal point. The light passed through the pinhole  23  is again condensed with the lens  24  having the focal point at a measuring portion. The light indicating a material excited by the condensed light is advanced to the lens  24  and is advanced through a polarized beam splitter  17  to a light receiving unit  18  side. The light having a selected wavelength by passing through a filter  20  is passed through a pinhole  19  at the focal point to reach the light receiving unit  18 . A distribution of modified parts is analyzed based on signals from the light receiving unit  18 . 
       FIG. 2  is a view showing a structure of a cartridge according to one embodiment of the present invention. A cartridge  11  includes a cap unit  25  and a base unit  27 . In the cap unit  25 , at a top face thereof, an inner cylinder  25   b  having a bottom face opened and a smaller cross section is coaxially joined to an outside pillar  25   a  having a bigger cross section. An electrode  26  is provided on the outside of the whole bottom face of the inner cylinder  25   b . The base unit  27  has a round shape electrode  28  on the inside of the bottom face of a hollow square pillar  27   a  having a square cross section. A top face of the square pillar  27   a  is opened so that a DNA solution is injected and the cap unit  25  can be inserted. Further, a solution reservoir  27   b  is provided on an upper portion of the square pillar  27   a  to prevent the DNA solution from flowing out to the outside when some of the DNA solution overflows from the square pillar  27   a . With respect to the cartridge  11 , there are ones where DNA probes are fixed to both electrodes, DNA probes are fixed to one of the electrodes and DNA probes are fixed to neither electrode. The cartridge  11  is inserted into a cartridge insertion portion of the apparatus. The apparatus has electrodes to generate an electric field in the cartridge  11  so that direct current voltage and/or alternating current voltage supplied from a power source can be placed between the electrodes in the cartridge  11 . 
     Detection is carried out by measuring optical energy such as absorbance, transmittance and reflectance of light having a wavelength of 260 nm. The measurement is carried out by comparison in a plurality of ranges or scanning in a tiny range. Based on a distribution of the obtained optical energy such as absorbance, transmittance and reflectance, a distribution of DNA existing between the electrodes can be obtained to determine an existing amount, a concentration, a hybridization ratio, a hybridization efficiency of DNA and the like. 
       FIG. 7  is a view showing DNA behaviors when direct current voltage is applied. When direct current voltage is applied between an electrode  71  and an electrode  72 , DNA is drawn in a direction of the electric field and attracted to one of the electrodes, electrode  72  in this case. For this reason, when probe DNA  73  is fixed on the electrode  71  and direct current voltage applied between the electrodes after hybridization reaction, complementary strand sample DNA  75 , which was hybridized, is fixed to the electrode  71  to be prolonged, but non-complementary strand sample DNA  76 , which was not hybridized, is attracted to the electrode  72  side to be a shrunk state. By measuring the DNA amount at each location in this state, the amount and the base length of the hybridized complementary strand sample DNA  75  and the amount of the non-complementary strand sample DNA  76 , which was not hybridized, can be determined. Specifically, the base length can be determined by measuring where the end of DNA is prolonged and exists. 
       FIG. 8  is a view showing DNA behaviors when alternating current voltage is applied. When alternating current voltage is applied between an electrode  77  and an electrode  78 , DNA is drawn, in a prolonged state, from the location before the application of voltage to the closer electrode at some range of frequency and voltage, 1 MHz and 106 V/m in the present apparatus. In the present embodiment, a sample DNA  79  existing at a location closer to the electrode  77  becomes elongated at the location closer to the electrode  77 . A sample DNA  80  existing at a location closer to the electrode  78  becomes elongated at the location closer to the electrode  78 . By separately and repeatedly using direct current voltage and alternating current voltage as voltage applied to the cartridge  11 , it is possible to control the location of DNA. In the present apparatus, direct current voltage is applied between the electrodes at each of the stage of attracting DNA between electrodes at the time of injection of a sample, the stage of attracting sample DNA to the probe side before hybridization reaction and the stage of separating sample DNA forming a duplex with the probes and non-reacted sample DNA after hybridization reaction. Alternating current voltage is applied when DNA is stretched in a separated state at the time of measuring the base length and the like. 
       FIG. 3  is a general view of apparatus for detecting biopolymers according to one embodiment of the present invention. A rotary cartridge inserting part  30  is provided in the main unit  29  of the apparatus. The plurality of cartridges  11  are loaded thereon, and a cover unit  31  of the apparatus is closed. Therefore, DNA detection can be continuously conducted by automatically changing the cartridges  11  to be subjected to the measurement. 
       FIG. 4  is a schematic view showing a structure of the apparatus for detecting biopolymers using a plate-shape cartridge, the details of which is shown in FIG.  5 . An optical system to measure optical energy and the like, such as absorbance, transmittance and reflectance, includes a laser and a light source, a slit, a filter, a diffraction grating, a light receiving unit and the like. Light generated from a laser and light source  35 , after wavelength selection with a filter  36 , is passed through a light source slit  37 . The light is passed through an incident slit  38  and converted to have wavelengths of 260 nm and 280 nm with a diffraction grating  39 . Further, the light is passed through an ejection slit  41  placed just before the cartridge. Optical energy is decreased in a plate-shape cartridge  42  depending on an existing amount of DNA since DNA absorbs the light. That is, optical energy after the decrease is obtained at a light receiving unit  45 . Any desired measurement location can be selected using an XY stage  43 , and reading can be conducted in a scanning manner. Analysis of the result is carried out with a computer  32 , and a distribution of the DNA existing amount can be determined by measuring how much the quantity of optical energy received at the light receiving unit  45  is decreased from incident light at some place. 
     An optical system to detect a modified part when DNA is modified with an organic material or an inorganic material, such as a fluorescent material or a radio active material, includes a laser and a light source, a pinhole, a lens and the like. Light generated from a laser and light source  47  is condensed with a lens  49  after passing through a filter  48  for wavelength selection and is passed through a pinhole  50  at the focal point. The light is turned to the plate-shape cartridge  42  with a reflecting mirror  51  and is again condensed with the lens  53  having the focal point at a measuring portion. The light indicating a material excited by the condensed light is advanced to the lens  53  and is advanced through a polarized beam splitter  52  to a light receiving unit  56 . The light having a selected wavelength by passing through a filter  54  is passed through a pinhole  55  at the focal point to reach the light receiving unit  56 . Analysis of the distribution of modified parts is conducted with a computer  32  based on signals from the light receiving unit  56 . Temperature inside the cartridge can be controlled by a cartridge fixed portion  44  provided with an electric heater that is connected to a power source  46 . Thus, the temperature during reaction or measurement can be controlled, and the reactivity at each temperature, such as a dissociation temperature for single strands, for example, can be measured. 
       FIGS. 5A and 5B  are views showing a plate-shape cartridge in details. A plate-shape cartridge shown in  FIG. 5A  has a structure, in which storing ditches  59  having micro widths and depths are provided on a plate, and electrodes  57  and  58  are provided on the both sides of each of the storing ditches  59 . When the absorbance, the transmittance and the like are measured, a transparent bottom face is needed. As for the measurement, optical energy such as absorbance, transmittance and reflectance and the like is measured. The conventional detection by fluorescence can be carried out. 
       FIG. 5B  is a view showing plate-shape cartridges having gel. By putting gel  65  in the middle of the storing ditches and heating electrodes  61  and  62 , it is possible to conduct a time lag measurement. Single-strand DNA probes are fixed to one electrode  61  beforehand and a sample DNA solution is injected in each of wells  63  located on the side of the electrode  61 , to which the probes are fixed, for hybridization reaction. Measurement is performed for non-reacted sample DNA by conventional electrophoresis. When DNA and modified materials in gel portion  65  have completely flowed out into the well  64  located on the side of the electrode  62  facing the electrode  61 , the electrode  61  is heated to dissociate DNA existing around the electrode  61  to single strands, and the measurement is again performed by conventional electrophoresis. By this way, it is possible to determine a base length distribution and an existing amount of complementary strand DNA and a base length distribution and an existing amount of non-complementary strand DNA in the sample DNA. 
     In the measurement and the detection, it is possible to use unmodified sample DNA, but it is possible to obtain higher sensitivity by modifying DNA with an organic material or an inorganic material, such as a fluorescent dyestuff, for excitation from an outside stimulus. 
       FIG. 6  is a general view of the apparatus of detecting biopolymers having plate-shape cartridges. A plurality of plate-shape cartridges  42  are loaded in a main unit  66  of the apparatus so that the electrodes of the cartridge are connected to be in contact with one electrode  67  and the other electrode  68 . The cartridges are scanned in one time with a scanning part  69 . Usually, hybridization or electrophoresis is conducted while a lid  70  is closed. 
     Note that the present invention is not limited to the embodiment mentioned above. 
     In the embodiment mentioned above, the cross section of the cartridge is a square, but other shapes such as a hexagon may be acceptable. It is desirable that the cartridge has transparent and parallel planes in order to avoid scattering of light passing therethrough. 
     Moreover, dissociation temperature for single strands of DNA can be determined by varying temperature of the electrodes and by measuring an amount of hybridized DNA or non-hybridized DNA at each temperature. 
     In accordance with the present invention, the presence and an existing amount or a concentration of a biopolymer such as DNA, RNA and protein and the like in a sample can be simply determined.