Abstract:
An apparatus for reverse iontophoresis has a base, an electrode provided on the base, an electrolytic gel provided on the electrode adapted for contacting a first part of a specimen, and for extracting a molecule from a first part of the specimen, a sensor chip placed underneath the electrolytic gel and having a pigment membrane containing a pigment that changes color by reaction with the molecule, a light source irradiating light on the pigment membrane, and a light sensor receiving a reflection of the light from the pigment membrane

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application P2002-308574 filed on Oct. 23, 2002; the entire contents of which are incorporated by reference herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an apparatus for measuring a specific molecule included in a specimen and in particular to an apparatus and a method for reverse iontophoresis configured to extract the specific molecule electrically.  
           [0004]    2. Description of the Related Art  
           [0005]    Measuring blood sugar is a representative example for measuring a specific molecule concentration included in a specimen and especially in a living body. An existing method for measuring blood sugar is as follows. At first, blood is collected from vein with a syringe or by pricking part of the body with a needle and squeezing the body part to collect a blood sample. The collected blood is deposited on an optical sensor to react with pigments and enzymes as catalysts. Thereafter, by measuring absorbance of the reacted solvent, a concentration of the blood sugar included in the specimen is obtained as disclosed in Guilbault et al., “Advances in Biosensors” JAI Press, 1991, Vol. 1, pp 258-289. However, the existing method for measuring blood sugar using the syringe causes injury and pain.  
           [0006]    On the other hand, an iontophoresis method recently became wide spread. An ionized molecule or a water-soluble molecule is introduced into the living body through the skin by iontophoresis as disclosed in published Japanese Patent Application H11-76428. In addition, a reverse iontophoresis method has also been studied recently. By the reverse iontophoresis method, the specific molecule is extracted from the living body through the skin with an electric current. Therefore, applying the reverse iontophoresis method to extract glucose from the living body without injury was attempted. However, the amount of extracted glucose by the reverse iontophoresis method is too small to analyze molecular concentration.  
         SUMMARY OF THE INVENTION  
         [0007]    An aspect of present invention inheres in an apparatus for reverse iontophoresis configured such that it is contacted with a specimen having a base, an electrode provided on the base, an electrolytic gel provided on the electrode adapted for contacting a first part of the specimen, and for extracting a molecule from the first part of the specimen, a sensor chip placed underneath the electrolytic gel and having a pigment membrane containing a pigment that changes a color by reaction with the molecule, a light source irradiating light on the pigment membrane, and a light sensor receiving a reflection of the light from the pigment membrane.  
           [0008]    Another aspect of the present invention inheres in a method for reverse iontophoresis including placing an electrolytic gel on an electrode connected to an anode of a power supply, contacting a first part of a specimen with the electrolytic gel and electrically connecting a second part of the specimen to a cathode of the power supply, applying a voltage between the first part and the second part by the power supply and extracting a molecule from the specimen to the electrolytic gel and transferring the molecule from the electrolytic gel to a pigment membrane, changing the color of the pigment membrane by reacting the molecule with the pigment membrane, irradiating a light on the pigment membrane and measuring a change in intensity of the light caused by the change in color of the pigment membrane. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    [0009]FIG. 1 is a sectional diagram of an apparatus for reverse iontophoresis in accordance with an embodiment of the present invention.  
         [0010]    [0010]FIG. 2 is a diagram of an apparatus for reverse iontophoresis in accordance with an embodiment of the present invention.  
         [0011]    [0011]FIG. 3A is a plan view of a sensor chip in accordance with an embodiment of the present invention and FIG. 3B is a cross section of the sensor chip in a direction of a line I-I shown in FIG. 3A in accordance with an embodiment of the present invention.  
         [0012]    [0012]FIG. 4 is a diagram of an apparatus for reverse iontophoresis in accordance with other embodiment of the present invention.  
         [0013]    [0013]FIG. 5 and FIG. 6 are plan views of a sensor chip in accordance with other embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified.  
         [0015]    With reference now to FIG. 1, an apparatus  1  for reverse iontophoresis in accordance with an embodiment of the present invention has a measuring device  3  and a sensor chip  2  placed on the measuring device  3 .  
         [0016]    With reference to FIG. 2, the sponsor chip  2  has a chip base  4 , a glass chip  5  placed oil the chip base  4 , and a pigment membrane  6  placed on the glass chip  5 . The pigment membrane  6  contains allochroic pigments that react with a specific molecule extracted from a specimen. In addition, the sensor chip  2  has a first on-chip electrode  11   a  and a second on-chip electrode  11   b  respectively placed on both end of chip base  4 . The glass chip  5  is made from borosilicate glass and the chip base  4  is made from plastics, for example. The pigment membrane  6  may contain a catalyst such as an enzyme to improve reactivity or a change of color. The first on-chip electrode  11   a  and the second on-chip electrode  11   b  are made from a conductive material such as aluminium (Al), gold (Au), silver (Ag), platinum (Pt) and stainless steel, for examples. Gel electrodes that provide good contact with the skin of the living body are also available for the first on-chip electrode  11   a  and the second on-chip electrode  11   b . The first on-chip electrode  11   a  and the second on-chip electrode  11   b  are replaced after use.  
         [0017]    [0017]FIG. 3A shows a plan view of the sensor chip  2  and FIG. 3B shows a cross section of the sensor chip  2  In a direction of a line I-I shown in FIG. 3A. The chip base  4  has a first locating hole  7   a  and a second locating hole  7   b  in a vertical direction to principal plane as shown in FIG. 3B. The chip base  4  also has an observation opening  8  to allow laser beam directed to the pigment membrane  6  on the glass chip  5  to pass there through. The first on-chip electrode  11   a  and the second on-chip electrode  11   b  are placed over the first locating hole  7   a  and the second locating hole  7   b  of the chip base  4  respectively.  
         [0018]    With reference again to FIG. 2, the measuring device  3  has a base  50 , a first electrode  12   a  and a second electrode  12   b  placed on the base  50 , an electrolytic gel  20  placed over the first electrode  12   a  and the second electrode  12   b . In addition, the measuring device  3  has a light source  31  which irradiates a laser beam to the pigment membrane  6  on the sensor chip  2 , a light sensor  32  receives the laser beam reflected from the pigment membrane  6  in the base  50 . The base  50  has an observation opening  9  that allows the laser beam irradiated from the light source  31  to pass there through. The observation opening  9  is located at the center of the principal plane of the base  50 . Further, a first conductive locating pin  10   a  and a second conductive locating pin  10   b  are provided on the principal plane of base  50 . The first conductive locating pin  10   a  and the second conductive locating pin  10   b  is used to fix the sensor chip  2  with the first locating hole  7   a  and the second locating hole  7   b . As is apparent, the first conductive locating pin  10   a  and the second conductive locating pin  10   b  are made from conductive material. In addition, the measuring device  3  has a power supply  30  in the base. An anode of the power supply  30  is connected to both the first electrode  12   a  and the second electrode  12   b . A cathode of the power supply  30  is connected to both the first conductive loading pin  10   a  and the second conductive loading pin  10   b . Both the first electrode  12   a  and the second electrode  12   b  can be separated from the base  50  to place the sensor chip  2  on the base  50  easily. In addition, the first electrode  12   a  and the second electrode  12   b  are movable in a vertical direction with respect to the principal plane of the base  50 .  
         [0019]    To set the sensor chip  2  on the measuring device  3 , the sensor chip  2  is introduced into a space between the first electrode  12   a  and the second electrode  12   b . Subsequently, the first conductive locating pin  10   a  and the second conductive locating pin  10   b  of the measuring device  3  are embedded in the sensor ship  2  through the first locating hole  7   a  and the second locating hole  7   b . Consequently, the sensor chip  2  is correctly positioned on the base  50 . In addition, the first conductive locating pin  10   a  and the second conductive locating pin  10   b  electrically contact with the first on-chip electrode  11   a  and the second on-chip electrode  11   b  respectively through the first locating hole  7   a  and the second locating hole  7   b  of the chip base  4 . Therefore, the cathode of the power supply  30  is electrically connected to both the first on-chip electrode  11   a  and the second on-chip electrode  11   b  through the first conductive locating pin  10   a  and the second conductive locating pin  10   b  respectively as shown in FIG. 1.  
         [0020]    A method for reverse iontophoresis in accordance with the embodiment of the present invention using the apparatus  1  for reverse iontophoresis is described below. As an example, a method for extracting glucose as a specific molecule from specimen  100  is represented.  
         [0021]    (a) The sensor chip  2  is placed on the measuring device  3 . The first conductive locating pin  10   a  and the second conductive locating pin  10   b  of the measuring device  3  are embedded in the sensor chip  2  through the first locating hole  7   a  and the second locating hole  7   b  Consequently, the first conductive locating pin  10   a  and the second conductive locating pin  10   b  electrically contact with the first on-chip electrode  11   a  and the second on-chip electrode  11   b  respectively as shown in FIG. 1.  
         [0022]    (b) The electrolytic gel  20  is placed on the first electrode  12   a  and the second electrode  12   b  straddling the pigment membrane  6  on the glass chip  5 . Thereafter, the first conductive locating pin  10   a  and the second conductive locating pin  10   b  are electrically connected to the cathode of the power supply  30 . The first electrode  12   a  and the second electrode  12   b  are electrically connected to the anode of the power supply  30 . Consequently, the first on-chip electrode  11   a  and the second on-chip electrode  11   b  on the chip base  4  of the sensor chip  2  are electrically connected to the cathode of the power supply  30  through the first conductive locating pin  10   a  and the second conductive locating pin  10   b . The power supply  30  generates, for example, a pulse electric field  
         [0023]    (c) One part of specimen  100  such as a skin part is pressed against the electrolytic gel  20  of the apparatus  1  for reverse iontophoresis. Further, another part of specimen  100  is pressed against the first on-chip electrode  11   a  and the second on-chip electrode  11   b . Since the first electrode  12   a  and the second electrode  12   b  are movable in a vertical direction with respect to the principal plane of the base  50 , the electrolytic gel  20  is held to the pigment membrane  6  on the sensor chip  2  as shown in FIG. 1. At this time, voltage of less than 20 volts is applied between the one part and another part of the specimen  100 . Consequently, the glucose contained under the skin of the specimen is effectively extracted to the pigment membrane  6  through the electrolytic gel  20 . The glucose reacts with the pigment contained in the pigment membrane  6  and changes the color of the pigment membrane  6 . A range of the applied voltage is 5 volts to 20 volts or a narrower range to 10 volts to 15 volts. If the applied voltage is below 5 volt, resistance of the specimen  100 , such as skin, affects a smooth flow of the electric current. Therefore, it takes an unacceptable long time to extract the glucose. In contrast, if the applied voltage is above 20 volt, damage to the specimen  100  may become a problem. For example, 0.3 mA/cm 2  of the electric current is selected to reduce damage to the specimen  100 .  
         [0024]    (d) The light source  31  such as a semiconductor laser oscillator and the light sensor  32  are placed symmetrically in the base  50  below the chip base  4  of the sensor chip  2  as shown in FIG. 1. For example, a 650 nm laser beam is irradiated on the under side of chip base  4  from the light source  31 . The irradiated 650 nm laser beam reaches the pigment membrane  6  through the observation opening  8  and the transparent glass chip  5 . At this time, the change in color of the pigment membrane  6  affects the absorbance of the pigment membrane  6 . Consequently, intensity of the reflected laser beam changes. Therefore, the glucose concentration is measured by detecting transition of the reflected laser beam intensity with the light sensor  32 .  
         [0025]    As described above, the method for reverse iontophoresis using the apparatus for reverse iontophoresis in accordance with the embodiment of the present invention extracts a very small quantity of the specific molecule from the specimen  100  such as skin. In addition, the method and apparatus for reverse iontophoresis detect a modicum of the change in the reflected laser beam caused by the change in color of the pigment membrane  6  reacted with the extracted specific molecule. Therefore, the method and apparatus for reverse iontophoresis of the embodiment makes an accurate measurement of the extracted specific molecule concentration.  
       OTHER EMBODIMENTS  
       [0026]    Although the invention has been described above by reference to the embodiment of the present invention, the present invention is not limited to the embodiment so described. Modifications and variations of the embodiment so described will occur to those skilled in the art, in the light of the above teachings.  
         [0027]    For example, the first on-chip electrode  11   a  and the second on-chip electrode  11   b  placed on the chip base  4  of the sensor chip  2  are electrically connected to the power supply  30  through the first conductive locating pin  10   a  and the second conductive locating pin  10   b  as shown in FIG. 1. However, the present invention is not limited to the placement of the first on-chip electrode  11   a  and the second on-chip electrode  11   b  on the chip base  4  of the sensor chip  2 . The apparatus  1  for reverse iontophoresis shown in FIG. 4 has a base electrode  14  on the base  50  as an alternative to the first on-chip electrode  11   a  and the second on-chip electrode  11   b  shown in FIG. 1. The base electrode  14  shown in FIG. 4 is placed on the principal plane of the base  50  and surrounds the sensor chip  4 . In addition, a measuring device  3   a  has a first locating pin  13   a  and a second locating pin  13   b  on the principal plane of the base  50 . The first locating pin  13   a  and the second locating pin  13   b  are embedded in the sensor chip  2   a  through the first locating hole  7   a  and the second locating hole  7   b  respectively. As shown in FIG. 5, the sensor chip  2   a  has the chip base  4 , the glass chip  5  placed on the chip base  4 , and the pigment membrane  6  placed on the glass chip  5 . The chip base  4  has the first locating hole  7   a  and the second locating hole  7   b . To set the sensor chip  2   a  on the measuring device  3   a , the sensor chip  2  is introduced into a space between the first electrode  12   a  and the second electrode  12   b . Thereafter, the first locating pin  7   a  and the second locating pin  7   b  of the measuring device  3   a  are embedded in the sensor chip  2   a  through the first locating hole  7   a  and the second locating hole  7   b . Consequently, the sensor chip  2   a  is correctly positioned on the base  50 . In addition, the cathode of the power supply  30  is electrically connected to the base electrode  14 . The anode of the power supply  30  is electrically connected to the first electrode  12   a  and the second electrode  12   b . The placement of other elements is similar to the apparatus  1  for reverse iontophoresis shown in FIG. 1.  
         [0028]    In addition, the glass chip  5  is placed on the chip base  4  in the case of both the sensor chip  2  shown in FIG. 3A and the sensor chip  2   a  shown in FIG. 5. This is because the glass chip  5  is obtained from a large glass plate divided by a scriber and thes glass chip  5  is then milled. However, a sensor chip shown in FIG. 6 which does not have the chip base  4  also be used  
         [0029]    Further, the embodiment is explained in the context of extracting cationic molecules from the specimen  100 . In contrast, the apparatus for reverse iontophoresis also extracts anionic molecules if the anode of power supply  30  is connected to the first conductive locating pin  10   a  and the second conductive locating pin  10   b  and the cathode of power supply  30  is connected to the first electrode  12   a  and the second electrode  12   b.    
         [0030]    As described above, the present invention includes many variations of embodiments. Therefore, the scope of the invention is defined with reference to the following claims.