Patent Publication Number: US-2005140971-A1

Title: Microchemical system chip and microchemical system

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application is a Continuation application of International Application PCT/JP03/03073 (not published in English) filed Mar. 14, 2003, the entire contents of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD  
      The present invention relates to a microchemical system chip and a microchemical system, and in particular relates to a microchemical system chip which can be used in microchemical systems that enable high-precision ultramicroanalysis to be carried out in very small spaces, which enables measurement to be carried out conveniently in any chosen location, and which in particular can be used when implementing absorptiometry or fluorescence analysis, and to a microchemical system using such a microchemical system chip.  
     BACKGROUND ART  
      In recent years, integration technology for carrying out chemical reactions in very small spaces has attracted attention in view of the speeding up of chemical reactions, and the need to carry out reactions using very small amounts, on-site analysis and so on, and research into this technology has been carried out with vigor throughout the world.  
      Microchemical systems, which are one example of such chemical reaction integration technology, are systems whose objective is to carry out any of mixing, reaction, separation, extraction and detection on a sample contained in a sample solution (a liquid-borne sample) in a very fine channel formed in a small glass substrate or the like. A microchemical system may have only a single function such as being for only separation of liquid-borne samples, or may have a combination of a plurality of functions. Examples of reactions carried out in microchemical systems are diazotization reactions, nitration reactions, and antigen-antibody reactions, and examples of extraction/separation are solvent extraction, electrophoretic separation, and column separation.  
      As an electrophoresis apparatus that is for only separation out of the above functions and is for analyzing extremely small amounts of proteins, nucleic acids or the like, one constituted from a channel-formed plate-shaped member that is comprised of two glass substrates joined together and has therein a channel having a channel cross section of approximately 100 μm×approximately 100 μm has been proposed (see, for example, Japanese Laid-open Patent Publication (Kokai) No. H08-178897). Because the member is plate-shaped, breakage is less likely to occur than in the case of a glass capillary tube having a circular or polygonal cross section, and hence handling is easier.  
      In such a microchemical system, because the amount of the liquid-borne sample is very small, a highly sensitive detection method is essential. Methods commonly used as such a detection method are absorptiometry in which the amount of absorption by a substance is measured, and fluorescence analysis in which the wavelength or intensity of fluorescence emitted by a substance is measured.  
      The above absorptiometry is a method in which detecting light is passed into a liquid-borne sample in a channel having a channel cross section of approximately 100 μm×approximately 100 μm in a direction orthogonal to the channel, and the amount of absorption by the liquid-borne sample is measured using a measuring instrument based on the detecting light transmitted through the liquid-borne sample. In this case, the optical path length of the detecting light through the channel is short at 100 μm, which is not sufficient for measuring the amount of absorption by the liquid-borne sample.  
      To make the optical path length over which the detecting light passes through the liquid-borne sample in the channel sufficiently long, it has thus been proposed to measure the amount of absorption by the liquid-borne sample of light introduced along the channel (see, for example, Anal. Chem. 1996, 68, 1040; Japanese Laid-open Patent Publication (Kokai) No. H09-288090).  
      Moreover, the above fluorescence analysis is carried out by measuring the wavelength or intensity of fluorescence emitted from a liquid-borne sample upon exciting light being incident on the liquid-borne sample in a tubular cell. In this fluorescence analysis, the exciting light used for exciting the fluorescent substance becomes noise if incident on a measuring optical system during the fluorescence analysis measurements, whereby the measurement sensitivity drops; the exciting light is thus introduced from a direction orthogonal to the tubular cell, and the measuring instrument is installed in a direction orthogonal to both the optical path of the exciting light and the tubular cell, whereby measurement can be carried out without the exciting light being incident on the measuring instrument.  
      However, with the above absorptiometry, so that the detecting light can be introduced along the channel in the channel-formed plate-shaped member, the detecting light is led to the vicinity of the channel through an optical fiber, an optical waveguide or the like rather than through open space, but in this case the detecting light exiting from the end of the optical fiber, the optical waveguide or the like will spread out through diffraction, and hence the amount of the detecting light introduced into the channel may be insufficient.  
      Moreover, with the above fluorescence analysis, so that the intensity of fluorescence can be measured well even for a sample solution having a low liquid-borne sample concentration, an introducing lens for efficiently introducing the exciting light onto the liquid-borne sample, and a light-receiving lens for efficiently receiving the fluorescence emitted by the liquid-borne sample are installed, but these lenses are large in size, and hence the apparatus cannot be made small in size.  
      Moreover, in the case that the channel-formed plate-shaped member has a plurality of channels therein, and measurement is carried out simultaneously on liquid-borne samples flowing through these channels, because the lenses are large in size, the channels must be provided separated from one another, and hence it is difficult to make the apparatus small in size. Furthermore, the distance between each channel and the corresponding light-receiving lens is large, and hence cross-talk in which the fluorescence emitted from the liquid-borne sample flowing through each channel influences the fluorescence emitted from the liquid-borne sample flowing through neighboring channels will arise.  
      To simultaneously excite the liquid-borne samples in the plurality of channels in the channel-formed plate-shaped member using a single beam of exciting light, the exciting light must be introduced along the plane of the channel-formed plate-shaped member and in a direction orthogonal to the channels, but this is difficult with light propagated through open space, and hence the exciting light is led to the vicinity of the channels by an optical fiber, an optical waveguide or the like (see, for example, Anal. Chem. 1996, 68, 1040; Japanese Laid-open Patent Publication (Kokai) No. H09-288090); in this case, exciting light that has spread out through diffraction from the end of the optical fiber or optical waveguide will be introduced into channels positioned far from the end of the optical fiber or optical waveguide, and hence the fluorescence intensity obtained will drop, and thus the measurement sensitivity will drop.  
      It is an object of the present invention to provide a microchemical system chip and a microchemical system that can be reduced in size while improving the measurement sensitivity.  
     DISCLOSURE OF THE INVENTION  
      To attain the above object, in a first aspect of the present invention, there is provided a microchemical system chip for use in a microchemical system that carries out detection by absorptiometry on a product produced through processing of a sample in a liquid, the microchemical system chip characterized by comprising a transparent plate-shaped member having therein a channel through which the liquid containing the sample is passed, an introducing lens through which light is introduced onto the liquid in the channel, and a light-receiving lens through which light exiting from the channel is received, wherein at least one of the introducing lens and the light-receiving lens comprises a rod lens.  
      In the first aspect of the present invention, preferably, at least one of the introducing lens and the light-receiving lens comprises a gradient index rod lens.  
      In the first aspect of the present invention, preferably, at least one of the introducing lens and the light-receiving lens is provided inside the plate-shaped member.  
      In the first aspect of the present invention, preferably, at least one of the introducing lens and the light-receiving lens is provided on a surface of the plate-shaped member.  
      In the first aspect of the present invention, preferably, a guiding optical system is connected to each of the introducing lens and the light-receiving lens.  
      In the first aspect of the present invention, preferably, the guiding optical system comprises an optical fiber.  
      In the first aspect of the present invention, preferably, the guiding optical system comprises an optical waveguide.  
      In a second aspect of the present invention, there is provided a microchemical system chip for use in a microchemical system that carries out detection by absorptiometry on a product produced through processing of a sample in a liquid, the microchemical system chip characterized by comprising a transparent plate-shaped member having therein a channel through which the liquid containing the sample is passed, an introducing lens through which detecting light is introduced from an end of the channel into the channel in a longitudinal direction of the channel, and a light-receiving lens through which is received the introduced detecting light exiting from the other end of the channel, wherein each of the introducing lens and the light-receiving lens is provided inside the plate-shaped member and comprises a rod lens.  
      In the second aspect of the present invention, preferably, each of the introducing lens and the light-receiving lens comprises a gradient index rod lens.  
      In the second aspect of the present invention, preferably, a guiding optical system is connected to each of the introducing lens and the light-receiving lens.  
      In the second aspect of the present invention, preferably, the guiding optical system comprises an optical fiber.  
      In the second aspect of the present invention, preferably, the guiding optical system comprises an optical waveguide.  
      In the second aspect of the present invention, preferably, the plate-shaped member is made of glass.  
      In a third aspect of the present invention, there is provided a microchemical system characterized by comprising a microchemical system chip according to the first or second aspect of the present invention, introducing means for introducing detecting light onto the introducing lens, receiving means for receiving from the light-receiving lens detecting light received by the light-receiving lens, and calculating means for calculating an intensity of the received detecting light.  
      In a fourth aspect of the present invention, there is provided a microchemical system chip for use in a microchemical system that carries out detection by fluorescence analysis on a product produced through processing of a sample in a liquid, the microchemical system chip characterized by comprising a transparent plate-shaped member having therein a channel through which the liquid containing the sample is passed, an introducing lens through which exciting light is introduced into the channel from a direction orthogonal to the channel, and a light-receiving lens through which is received fluorescence emitted from the sample in the liquid flowing through the channel due to the introduced exciting light, wherein one of the introducing lens and the light-receiving lens is provided inside the plate-shaped member, and the other of the introducing lens and the light-receiving lens is provided on a surface of the plate-shaped member, and one of the introducing lens and the light-receiving lens comprises a rod lens.  
      In the fourth aspect of the present invention, preferably, the rod lens comprises a gradient index lens.  
      In the fourth aspect of the present invention, preferably, the other one of the introducing lens and the light-receiving lens comprises a rod lens.  
      In the fourth aspect of the present invention, preferably, the other one of the introducing lens and the light-receiving lens comprises a planar lens.  
      In the fourth aspect of the present invention, preferably, the other one of the introducing lens and the light-receiving lens comprises a gradient index lens.  
      In the fourth aspect of the present invention, preferably, the light-receiving lens is provided inside the plate-shaped member, and the introducing lens is provided on the surface of the plate-shaped member.  
      In the fourth aspect of the present invention, preferably, the channel comprises a plurality of channels arranged along an optical axis of the introduced exciting light, the introducing lens is provided inside the plate-shaped member, and the light-receiving lens comprises a plurality of lenses each provided on the surface of the plate-shaped member facing one of the plurality of channels.  
      In the fourth aspect of the present invention, preferably, the introducing lens comprises a gradient index lens.  
      In the fourth aspect of the present invention, preferably, the light-receiving lenses each comprise a rod lens.  
      In the fourth aspect of the present invention, preferably, the light-receiving lenses each comprise a planar lens.  
      In the fourth aspect of the present invention, preferably, the light-receiving lenses each comprise a gradient index lens.  
      In the fourth aspect of the present invention, preferably, a guiding optical system is connected to each of the introducing lens and the light-receiving lens.  
      In the fourth aspect of the present invention, preferably, the guiding optical system comprises an optical fiber.  
      In the fourth aspect of the present invention, preferably, the guiding optical system comprises an optical waveguide.  
      In the fourth aspect of the present invention, preferably, the plate-shaped member is made of glass.  
      In a fifth aspect of the present invention, there is provided a microchemical system characterized by comprising a microchemical system chip according to the fourth aspect of the present invention, introducing means for introducing the exciting light into the introducing lens, receiving means for receiving from the light-receiving lens the fluorescence received by the light-receiving lens, and measuring means for measuring an intensity of the received fluorescence. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  consists of views schematically showing the construction of a microchemical system chip according to a first embodiment of the present invention; specifically:  
       FIG. 1A  is a plan view; and  
       FIG. 1B  is a sectional view taken along line Ib-Ib in  FIG. 1A ;  
       FIG. 2  is a block diagram of a microchemical system that uses the microchemical system chip  1  of  FIG. 1  and carries out absorptiometry.  
       FIG. 3  consists of views schematically showing the construction of a microchemical system chip according to a second embodiment of the present invention; specifically:  
       FIG. 3A  is a perspective view; and  
       FIG. 3B  is a sectional view taken along line IIb-IIb in  FIG. 3A ;  
       FIG. 4  is a view useful in explaining a planar lens that can be used in the microchemical system chip  2  of  FIG. 3 ;  
       FIG. 5  is a block diagram of a microchemical system that uses the microchemical system chip  2  of  FIG. 3  and carries out fluorescence analysis;  
       FIG. 6  is a view schematically showing the construction of a microchemical system chip according to a third embodiment of the present invention; and  
       FIG. 7  is a view schematically showing the construction of a microchemical system chip according to a fourth embodiment of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      The constructions of microchemical systems according to embodiments of the present invention will now be described with reference to the drawings. Note, however, that the present invention is not limited to the embodiments described below.  
       FIG. 1  consists of views schematically showing the construction of a microchemical system chip according to a first embodiment of the present invention; specifically,  FIG. 1A  is a plan view, and  FIG. 1B  is a sectional view taken along line Ib-Ib in  FIG. 1A ;  
      In  FIG. 1 , the microchemical system chip  1  according to the first embodiment of the present invention is a chip for use in absorptiometry in which the amount of absorption of detecting light introduced into a channel by a liquid-borne sample in a sample solution flowing through the channel is measured.  
      The microchemical system chip  1  is comprised of a substantially rectangular plate-shaped glass substrate  10  (plate-shaped member), and the glass substrate  10  has a U-shaped channel  11  therein. The U-shaped channel  11  is comprised of a longitudinal channel  11   a , and a pair of transverse channels  11   b  and  11   c  that are connected to the two ends of the longitudinal channel  11   a . Moreover, the glass substrate  10  has therein an inflow hole  12  that is connected to an end of the transverse channel  11   b  and opens out at one surface of the glass substrate  10 , and a discharge hole  13  that is connected to an end of the transverse channel  11   c  and opens out at the same surface of the glass substrate  10 .  
      Furthermore, the glass substrate  10  has therein two voids provided coaxially with the longitudinal channel  11   a  near the two ends of the longitudinal channel  11   a , and gradient index rod lenses  14  and  15  are housed respectively in the two voids. An optical fiber  16  that propagates detecting light emitted from a light source, not shown, is connected to the gradient index rod lens  14 , and an optical fiber  17  that leads light received by the gradient index rod lens  15  to a detector, not shown, is connected to the gradient index rod lens  15 .  
      In  FIG. 1 , each of the gradient index rod lenses  14  and  15  is preferably disposed on the longitudinal channel  11   a  side in the respective void, but does not necessarily have to be in contact with the longitudinal channel  11   a  side end face of the void; moreover, the gradient index rod lenses  14  and  15  themselves may each form a side face of the U-shaped channel  11  at a site of contact. To introduce the detecting light uniformly into the longitudinal channel  11   a , it is preferable for the detecting light exiting from the gradient index rod lens  14  to be parallel.  
      The glass substrate  10  is comprised of glass substrates  10   a  to  10   c  that are placed on one another in three layers and are bonded together; the U-shaped channel  11  is formed through a U-shaped groove being formed in the glass substrate  10   b  and the glass substrates  10   a  and  10   c  being joined to the two surfaces of the glass substrate  10   b . Moreover, through holes are formed in the glass substrate  10   a  in two positions corresponding to the two ends of the U-shaped channel  11 , whereby the inflow hole  12  and the discharge hole  13  are formed.  
      The longitudinal channel  11   a  forms an analysis cell for analyzing the liquid-borne sample, and the width and depth thereof are each 100 μm.  
      Each of the gradient index rod lenses  14  and  15  is comprised of a cylindrical transparent body in which the refractive index changes continuously from the center thereof outward; such a cylindrical transparent body is known as a converging light-transmitting body in which the refractive index n(r) at a position a distance r in the radial direction from the central axis is given approximately by the quadratic equation in r, 
 
 n ( r )=n 0 {1−( g   2 /2)·r 2 }, 
 
 wherein n 0  represents the refractive index on the axis, and g represents a quadratic distribution constant. 
 
      For each of the gradient index rod lenses  14  and  15 , if the length z 0  thereof is chosen to be in a range of 0&lt;z 0 &lt;π/2g, then even though the gradient index rod lens has flat end faces, the gradient index rod lens will have the same image formation characteristics as an ordinary convex lens; upon a parallel incident light beam being incident on the gradient index rod lens  14  or  15 , a focal point will be formed at a position a distance so from the end of the gradient index rod lens  14  or  15  from which the light beam exits, where 
 
 s   0 =cot( gz   0 )/ n   0   g.  
 
      The gradient index rod lenses  14  and  15  may be manufactured, for example, using the following method.  
      A rod is formed from a glass having as principal components thereof 57 to 63 mol % of SiO 2 , 17 to 23 mol % of B 2 O 3 , 5 to 17 mol % of Na 2 O, and 3 to 15 mol % of Tl 2 O, and then, in an ion exchange medium such as potassium nitrate, the rod formed from the glass (the glass rod) is subjected to ion exchange between thallium ions and sodium ions in the glass and potassium ions in the ion exchange medium, thus giving a refractive index distribution in the glass rod in which the refractive index decreases continuously from the center of the glass rod outward.  
      Because each of the gradient index rod lenses  14  and  15  has a cylindrical shape with flat end face, the gradient index rod lens  14  or  15  can easily be attached to an end face of the optical fiber  16  or  17 , and moreover the optical axis of the optical fiber  16  or  17  can easily be aligned with that of the gradient index rod lens  14  or  15 . Furthermore, the gradient index rod lenses  14  and  15  are small in size, and hence when installing each of the gradient index rod lenses  14  and  15  close to the longitudinal channel  11   a , it is not necessary to form a large hole for installing the gradient index rod lens  14  or  15 .  
      In particular, in the case of attaching a gradient index rod lens  14  or  15  having a diameter approximately the same as the diameter of the optical fiber  16  or  17  to the end face of the optical fiber  16  or  17 , the gradient index rod lens  14  or  15  can be installed merely by inserting the optical fiber  16  or  17  having the gradient index rod lens  14  or  15  attached to the tip thereof into the void provided close to the respective end of the longitudinal channel  11   a  coaxially with the longitudinal channel  11   a.    
      The gradient index rod lens  15  installed as described above efficiently receives the residual light from the detecting light that has exited from the gradient index rod lens  14  and passed through the longitudinal channel  11   a , whereby noise is reduced, and hence highly sensitive measurement is possible. The residual light received by the gradient index rod lens  15  is propagated to the detector via the optical fiber  17 .  
      According to the first embodiment of the present invention, because the gradient index rod lens  14  is attached to the tip of the optical fiber  16 , the detecting light exiting from the optical fiber  16  can be received reliably by the gradient index rod lens  15  which is the light-receiving lens, and hence the measurement sensitivity of the microchemical system chip  1  can be improved; in addition, because the gradient index rod lens  14  is disposed inside the glass substrate  10 , the microchemical system chip  1  can be reduced in size. Moreover, to measure the absorption of the detecting light by all of the liquid-borne sample in the sample solution flowing through the longitudinal channel  11   a , it is preferable for the detecting light exiting from the optical fiber  16  to be made into parallel light; the focal distance of the gradient index rod lens  14  can be adjusted merely by adjusting the length of the gradient index rod lens  14 , and hence by making the length of the gradient index rod lens  14  be the optimum length for the wavelength of the detecting light used, the detecting light can be made into parallel light before being introduced onto the liquid-borne sample flowing through the longitudinal channel  11   a.    
      Considering durability and chemical resistance, the material of the glass substrate  10  is a glass, and considering usage with biological samples such as cell samples, for example in DNA analysis, a glass having high acid resistance and alkali resistance is preferable, specifically a borosilicate glass, a soda lime glass, an aluminoborosilicate glass, a quartz glass or the like. However, if the usage is limited accordingly, then an organic material such as a plastic may be used.  
      Examples of adhesives that can be used to bond the glass substrates  10   a  to  10   c  together include organic adhesives such as acrylic adhesives and epoxy adhesives, for example, an ultraviolet-curing type, a thermosetting type, and a two-liquid-curing type, and inorganic adhesives. Alternatively, the glass substrates  10   a  to  10   c  may be fused together by heat fusion.  
      Furthermore, as guiding optical systems, instead of the optical fibers  16  and  17 , for example optical waveguides formed using a flame hydrolysis method may be used. In the flame hydrolysis method, for example, two glass fine particle layers for a lower cladding and a core respectively are deposited on a surface of the glass substrate  10   b  through flame hydrolysis of silicon tetrachloride and germanium tetrachloride, and then the fine particle layers are modified into transparent glass layers by heating at a high temperature. Next, a core portion having a circuit pattern is formed through photolithography and reactive etching. After that, an upper cladding is formed through flame hydrolysis of silicon tetrachloride. An example of formation of optical waveguides using this method is in J. Lightwave Tech., Vol. 17 (5), 771 (1999). In the above, if the glass substrate  10   b  and the core portion have suitable refractive indices, then the lower cladding need not be formed. Moreover, an optical waveguide may also be formed by removing a portion of the glass substrate  10   b  where the optical waveguide is to be formed by etching or the like to a suitable depth in advance coaxial with a center line passing through the center of the longitudinal channel  11   a  and the gradient index rod lens  14  or  15 , and then carrying out flame hydrolysis.  
      The above description of the material of the glass substrate, the adhesive, and the method of forming optical waveguides also applies to the other embodiments described below.  
       FIG. 2  is a block diagram of a microchemical system that uses the microchemical system chip  1  of  FIG. 1  and carries out absorptiometry.  
      In  FIG. 2 , detecting light emitted from a light source  20  is introduced via the optical fiber  16  onto the microchemical system chip  1  having the liquid-borne sample therein. The detecting light received by the gradient index rod lens  15  in the microchemical system chip  1  is received by an optical receiver  21  via the optical fiber  17 , and is then received by a received light intensity calculator  22 . The intensity of the detecting light received by the optical receiver  21  is calculated by the received light intensity calculator  22 , and the calculated value is recorded by a recorder  23 .  
      With the absorptiometry apparatus of  FIG. 2 , the intensity of the detecting light after passing through the longitudinal channel  11   a  of the microchemical system chip  1  containing a liquid-borne sample of a known concentration is measured in advance, and then the intensity of the detecting light after passing through the longitudinal channel  11   a  of the microchemical system chip  1  containing a targeted liquid-borne sample is compared with these intensities, whereby the concentration of the targeted liquid-borne sample can be calculated.  
      To measure the amount of absorption of the detecting light by a liquid-borne sample in a sample solution of low concentration, it is important to make the distance over which the detecting light passes through the targeted liquid-borne sample long, and hence generally the targeted liquid-borne sample is put into a cell of approximately 10 mm square, and thus measurement is carried out with the distance d over which the detecting light passes through the liquid-borne sample being 10 mm.  
       FIG. 3  consists of views schematically showing the construction of a microchemical system chip  2  according to a second embodiment of the present invention; specifically,  FIG. 3A  is a perspective view, and  FIG. 3B  is a sectional view taken along line IIb-IIb in  FIG. 3A .  
      In  FIG. 3 , the microchemical system chip  2  according to the second embodiment of the present invention is a chip for use in fluorescence analysis in which fluorescence emitted upon a liquid-borne sample in a sample solution flowing through channels absorbing exciting light introduced into the channels is measured.  
      The microchemical system chip  2  is comprised of a substantially rectangular plate-shaped glass substrate  30  (plate-shaped member), and the glass substrate  30  has therein three channels  31   a  to  31   c  that are arranged parallel to one another and each extend along the plane of the glass substrate  30  in a direction of short sides of the glass substrate  30 . Furthermore, the glass substrate  30  has, for each of the channels  31   a  to  31   c , an inflow hole  32  that is connected to one end of the channel  31   a ,  31   b  or  31   c  and opens out at one surface of the glass substrate  30 , and a discharge hole  33  that is connected to the other end of the channel  31   a ,  31   b  or  31   c  and opens out at the same surface of the glass substrate  30 .  
      Furthermore, the glass substrate  30  has a void in one of the short sides thereof near to the center of that short side, the void extending in the direction of long sides of the glass substrate  30 , and a gradient index rod lens  34  is housed in the void. An optical fiber  35  that propagates exciting light from a light source, not shown, is connected to the gradient index rod lens  34 . Gradient index rod lenses  36  that condense fluorescence emitted by the liquid-borne sample flowing through the channels  31   a  to  31   c  are disposed in one surface of the glass substrate  30  in positions facing onto the channels  31   a  to  31   c , and optical fibers  37  that lead the fluorescence condensed by the gradient index rod lenses  36  to a detector, not shown, are connected to the gradient index rod lenses  36 .  
      The glass substrate  30  is comprised of glass substrates  30   a  to  30   c  that are placed on one another in three layers and are bonded together; the glass substrate  30   b  has therein three grooves that pass right through the glass substrate  30   b , extend in the direction of the short sides of the glass substrate  30   b , and are formed parallel to one another; the channels  31   a  to  31   c  are formed through the glass substrate  30   a  being joined to one surface of the glass substrate  30   b  and the glass substrate  30   c  being joined to the other surface of the glass substrate  30   b . The channels  31   a  to  31   c  are used for mixing, agitation, synthesis, separation, extraction, detection or the like of the liquid-borne sample.  
      The gradient index rod lenses  36  may be replaced with planar lenses. As a result, gradient index rod lenses  36  will no longer project out from the glass substrate  30 , and hence the microchemical system can be reduced in size.  
      Examples of such planar lenses are ones formed in the glass substrate  30  using an ion exchange method or the like, and ones formed by building up a lens medium into a spherical shape on the surface of the glass substrate  30  using an ink jet method, a resist dissolution method or the like.  
      Moreover, three channels  31   a  to  31   c  are provided in the microchemical system chip  2 , but the number of channels is not limited thereto.  
       FIG. 4  is a view useful in explaining a planar lens that can be used in the microchemical system chip  2  of  FIG. 3 .  
      In  FIG. 4 , first, one surface of a glass substrate  40   a  having the same shape and size as the glass substrate  30   a  shown in  FIG. 3  is masked with a metal mask having therein an opening corresponding to a lens region, then the glass substrate  40   a  is immersed in a KNO 3  molten salt to carry out ion exchange treatment between potassium ions and sodium ions on the exposed portion, and then the metal mask is removed, whereby a planar lens  40  having a predetermined refractive index distribution can be formed. The planar lens  40  is convex on the inside of the glass substrate  40   a , and also bulges out slightly on the outside of the glass substrate  40   a.    
      In the microchemical system chip  2  of  FIG. 3 , by replacing the glass substrate  30   a  with such a glass substrate  40   a  having planar lenses  40  therein, as described above gradient index rod lenses  36  will no longer project out from the glass substrate  30 , and hence the microchemical system can be reduced in size.  
      According to the second embodiment of the present invention, because the gradient index rod lens  34  is attached to the tip of the optical fiber  35 , the exciting light exiting from the optical fiber  35  can be received reliably by each of the channels  31   a  to  31   c , and hence the measurement sensitivity of the microchemical system chip  2  can be improved; in addition, because the gradient index rod lens  34  is disposed inside the glass substrate  30 , the microchemical system chip  2  can be reduced in size. Moreover, because the gradient index rod lenses  36  that receive fluorescence emitted by the liquid-borne sample in the channels  31   a  to  31   c  are attached to a surface of the glass substrate  30 , the gap between each of the channels  31   a  to  31   c  and the corresponding gradient index rod lens  36  can be shortened, and hence the fluorescence collecting efficiency is improved, and thus highly sensitive measurement becomes possible. Moreover, because the gradient index rod lenses  36  are cylindrical in shape and small in size, the gradient index rod lenses  36  can be arranged with small gaps therebetween on the surface of the glass substrate  30 , and hence the microchemical system can be reduced in size.  
      Note that in  FIG. 3 , the fluorescence collected by the gradient index rod lenses  36  is led to the detector by the optical fibers  37 , but photoelectric converters for detecting the fluorescence may instead be disposed at the focal positions of the gradient index rod lenses  36 .  
       FIG. 5  is a block diagram of a microchemical system that uses the microchemical system chip  2  of  FIG. 3  and carries out fluorescence analysis.  
      In  FIG. 5 , exciting light emitted from a laser light source  50  is first introduced via the optical fiber  35  into the channels  31   a  to  31   c  of the microchemical system chip  2  containing the liquid-borne sample, whereby fluorescence is emitted from the liquid-borne sample in each of the channels  31   a  to  31   c . The fluorescence is then received by each of the gradient index rod lenses  36 , and the received fluorescence is received by an optical receiver  51  via the optical fibers  37 , and is analyzed by a signal processor  52 , and the results are recorded by a recorder  53 .  
      With the microchemical system described above, exciting light of a wavelength that will be absorbed by the liquid-borne sample, which is the substance to be subjected to the measurement, is incident on the liquid-borne sample, and fluorescence thus emitted by the liquid-borne sample is measured, whereby identification or quantification of the liquid-borne sample is carried out. For the amount of light absorbed by the liquid-borne sample, if the intensity of the exciting light incident on the liquid-borne sample is represented by I 0  (the incident light intensity), the intensity of the exciting light transmitted by the targeted liquid-borne sample is represented by I (the transmitted light intensity), a represents a coefficient, the concentration of the liquid-borne sample is represented by c, and the distance over which the exciting light is transmitted through the liquid-borne sample is represented by d, then the following equation (1) holds (Lambert-Beer law). 
 
 A=− log( I/I   0 )= acd   (1) 
 
      Here, A represents the absorbance, and I/I 0  represents the internal transmittance.  
      Assuming that the amount of fluorescence emitted through the light being absorbed is proportional to the amount of light absorbed, then the fluorescence intensity F is represented by: 
 
 F=K′ ( I   0   −I )= KI   0 (1 −e   −acd )φ  (2) 
 
 Here, K represents a constant that depends on the apparatus, for example the area of incidence of the liquid-borne sample, the size and response of the optical receiver  51  and so on, and φ represents the fluorescence yield, i.e. the ratio of the total amount of fluorescence to the amount of exciting light absorbed. For a liquid-borne sample of low concentration, the following equation thus holds (“Kiki Bunseki” (“Instrumental Analysis”), written by Tanaka and Iida, Shokabo Publishing, 1985, p 51). 
 
 F=KI   0   φacd  (when acd&lt;0.05)  (3) 
 
      From equation (3), the fluorescence intensity is proportional to the liquid-borne sample concentration c, and hence if a line showing the relationship between F and c (a calibration line) is determined in advance, then an unknown liquid-borne sample concentration can be found out.  
      To carry out fluorescence measurement on a liquid-borne sample in a sample solution of low concentration, as shown by equation (3), it is important to make the amount of exciting light absorbed by the liquid-borne sample large. The exciting light is thus made to be incident on the liquid-borne sample after being narrowed down by a lens. Moreover, to collect the fluorescence emitted by the liquid-borne sample as much as possible, a condensing lens is placed upstream of the detector. In this case, the smaller the volume of the liquid-borne sample emitting the fluorescence, the more efficiently the fluorescence can be condensed; introducing the exciting light onto the liquid-borne sample after narrowing down the exciting light using a lens is thus important in fluorescence measurement on a liquid-borne sample in a sample solution of low concentration.  
      In the case that it is not necessary to carry out measurement using all of the channels  31   a  to  31   c  simultaneously, because as shown by equation (3) the larger the amount of exciting light incident on the liquid-borne sample the larger the amount of fluorescence emitted by the liquid-borne sample, by making the exciting light not be parallel light but rather focusing the exciting light to a point in one of the channels out of the channels  31   a  to  31   c , a large amount of exciting light can be supplied into that channel, and hence the measurement sensitivity can be improved. Moreover, by focusing the exciting light to a point in one of the channels, the fluorescence emission point becomes smaller in size, and hence the amount of fluorescence condensed by the gradient index rod lens  36  can be made larger, and thus the measurement sensitivity can be improved yet further.  
       FIG. 6  is a view schematically showing the construction of a microchemical system chip according to a third embodiment of the present invention.  
      For the microchemical system chip  3  according to the third embodiment of the present invention shown in  FIG. 6 , component elements the same as ones of the microchemical system chip  2  shown in  FIG. 3  are represented by the same reference numerals as in  FIG. 3 , and redundant repeated description will be omitted; in the following, a description will be given of only the differences.  
      In the microchemical system chip  3 , there is one channel  31 , and exciting light entering from a gradient index rod lens  34  is focused to a point in the channel  31 . Moreover, a lens for condensing fluorescence emitted by a liquid-borne sample in the channel  31  is a planar lens  40 , and a photoelectric converter  60  that converts the light condensed by the planar lens  40  into an electrical signal is installed close to the glass substrate  30 .  
      According to the third embodiment of the present invention, a planar lens  40  as shown in  FIG. 4  is used as a lens for condensing fluorescence emitted by the liquid-borne sample in the channel  31 , and hence there are no longer any projections on the glass substrate  30 , and thus the microchemical system can be reduced in size.  
      In the third embodiment of the present invention, only one set of a channel  31 , a gradient index rod lens  34 , an optical fiber  35  and a planar lens  40  is provided on the side of one of the short sides of the glass substrate  30 , but two sets each of a channel  31 , a gradient index rod lens  34 , an optical fiber  35  and a planar lens  40  may be provided opposite one another on the two sides of the glass substrate  30 .  
       FIG. 7  is a view schematically showing the construction of a microchemical system chip according to a fourth embodiment of the present invention.  
      For the microchemical system chip  4  according to the fourth embodiment of the present invention shown in  FIG. 7 , component elements the same as ones of the microchemical system chip  3  shown in  FIG. 6  are represented by the same reference numerals as in  FIG. 6 , and redundant repeated description will be omitted; in the following, a description will be given of only the differences.  
      The microchemical system chip  4  differs to the microchemical system chip  3  according to the third embodiment shown in  FIG. 6  in that the relationship between the exciting light and the fluorescence is reversed, a mask  80  is formed on a surface of the glass substrate  30  on the side on which there are planar lenses  40 , but is not formed on the surfaces of the planar lenses  40  themselves, and two sets each of a channel  31 , a gradient index rod lens  34 , an optical fiber  35 , and a planar lens  40  are provided opposite one another on the two sides of the glass substrate  30 .  
      According to the microchemical system chip  4 , exciting light emitted from a light source, not shown, is made into spatially parallel light  70  by a collimator, not shown, and the spatially parallel light  70  is incident on the planar lenses  40  which are disposed on the surface of the glass substrate  30  in positions facing onto the channels  31 , and is focused into each channel  31  by the corresponding planar lens  40 . Fluorescence emitted by the liquid-borne sample at the focal position in each channel  31  is condensed by a gradient index rod lens  34  installed close to that channel  31 , and led by an optical fiber  35  to a detector, not shown. The optical fibers  35  in the microchemical system chip  4  preferably have a large core so that as much of the fluorescence as possible can be led to the detector.  
      With the microchemical system chip  4 , spatially parallel light  70  incident at places other than the planar lenses  40  would become noise in the fluorescence analysis, and hence the mask  80  is formed on the surface of the glass substrate  30  to intercept such spatially parallel light  70 .  
      According to the fourth embodiment of the present invention, the exciting light must be made into spatially parallel light  70  by a collimator or the like, and hence the microchemical system increases in size in this respect; nevertheless, each gradient index rod lens  34  for condensing the fluorescence can be installed extremely close to the respective channel  31  from which the fluorescence is emitted, and hence the fluorescence collecting efficiency can be improved, and thus the measurement sensitivity can be improved, while the apparatus can be reduced in size.  
      In the fourth embodiment of the present invention, the exciting light is led in as spatially parallel light  70 , but the exciting light may instead be led separately to each planar lens  40  using a guiding optical system such as an optical fiber.  
      In each of the second to fourth embodiments of the present invention described above, an optical fiber  35  is connected to each gradient index rod lens  34 , but an optical waveguide may be used instead of the optical fiber  35 . The optical fiber or optical waveguide propagating the exciting light preferably has a single mode at the frequency of the exciting light. In the case of carry out detection on a very small amount of a liquid-borne sample using fluorescence analysis, it is preferable to narrow down the exciting light as much as possible, and thus increase the energy used in the fluorescence reaction. In this case, the exciting light used for producing the fluorescence preferably has a Gaussian distribution; exciting light exiting from a single mode optical fiber or optical waveguide will always have a Gaussian distribution, and hence such a single mode optical fiber or optical waveguide is suitable for making the focal point of the exciting light small. It is thus preferable to use an optical fiber or optical waveguide that propagates the exciting light with a single mode.  
     Industrial Applicability  
      As described in detail above, according to a microchemical system chip of the present invention, at least one of an introducing lens and a light-receiving lens is comprised of a rod lens; as a result, the lens can easily be held and the optical axis of the lens can easily be adjusted, and moreover the lens can be reduced in size, whereby the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, at least one of the introducing lens and the light-receiving lens may be comprised of a gradient index rod lens; as a result, the lens can be made yet smaller in size, and moreover because such a gradient index rod lens has flat end faces, adjustment of the optical axis of the lens can be made yet easier.  
      According to the microchemical system chip of the present invention, at least one of the introducing lens and the light-receiving lens may be provided inside a plate-shaped member; as a result, propagation of light between a channel and the at least one of the introducing lens and the light-receiving lens can be carried out reliably, and hence the measurement sensitivity can be improved, while the system can be reduced in size.  
      According to the microchemical system chip of the present invention, at least one of the introducing lens and the light-receiving lens may be provided on a surface of the plate-shaped member; as a result, propagation of light between the channel and the at least one of the introducing lens and the light-receiving lens can be carried out reliably.  
      According to the microchemical system chip of the present invention, a guiding optical system may be comprised of an optical fiber; as a result, the detecting light can be propagated to the vicinity of the channel in the plate-shaped member reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, the guiding optical system may be comprised of an optical waveguide; as a result, the detecting light can be propagated to the vicinity of the channel in the plate-shaped member reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to a microchemical system chip of the present invention, each of an introducing lens and a light-receiving lens is provided inside a plate-shaped member and is comprised of a rod lens; as a result, detecting light can be propagated reliably along a channel over a sufficient length for detection, and the detecting light that has passed through the channel can be propagated reliably to the light-receiving lens, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, each of the introducing lens and the light-receiving lens may be comprised of a gradient index rod lens; as a result, each lens can be made yet smaller in size, and moreover because such a gradient index rod lens has flat end faces, adjustment of the optical axis of each lens can be made yet easier, and hence each lens can be installed in the plate-shaped member easily.  
      According to the microchemical system chip of the present invention, a guiding optical system may be comprised of an optical fiber; as a result, the detecting light can be propagated to the vicinity of the channel in the plate-shaped member reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, the guiding optical system may be comprised of an optical waveguide; as a result, the detecting light can be propagated to the vicinity of the channel in the plate-shaped member reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, the plate-shaped member may be made of glass; as a result, durability and chemical resistance can be improved.  
      According to a microchemical system of the present invention, the measurement sensitivity for absorptiometry can be improved, and moreover the microchemical system can be reduced in size.  
      According to a microchemical system chip of the present invention, one of an introducing lens and a light-receiving lens is comprised of a rod lens; as a result, the lens can easily be held and the optical axis of the lens can easily be adjusted, and moreover the lens can be reduced in size, whereby the microchemical system can be reduced in size. In addition, one of the introducing lens and the light-receiving lens is provided inside a plate-shaped member; as a result, propagation of light between a channel and the one of the introducing lens and the light-receiving lens can be carried out reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, the rod lens may be comprised of a gradient refractive index lens; as a result, the lens can be reduced in size, and hence the system can be reduced in size, and moreover because such a gradient refractive index lens has flat end faces, adjustment of the optical axis of the lens can be made easier, and hence the lens can be installed in the plate-shaped member easily.  
      According to the microchemical system chip of the present invention, exciting light may be introduced into a plurality of channels from one lens; as a result, the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, the introducing lens may be comprised of a gradient index rod lens; as a result, the lens can be reduced in size, whereby the microchemical system can be reduced in size, and moreover because such a gradient index rod lens has flat end faces, adjustment of the optical axis of the lens can be made yet easier, and hence the lens can be installed in the plate-shaped member easily.  
      According to the microchemical system chip of the present invention, guiding optical systems may each be comprised of an optical fiber; as a result, the exciting light can be propagated to the vicinity of the channels in the plate-shaped member reliably, and moreover received fluorescence can be propagated reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to the microchemical system chip of the present invention, the guiding optical systems may each be comprised of an optical waveguide; as a result, the exciting light can be propagated to the vicinity of the channels in the plate-shaped member reliably, and moreover the received fluorescence can be propagated reliably, and hence the measurement sensitivity can be improved, while the microchemical system can be reduced in size.  
      According to a microchemical system of the present invention, the measurement sensitivity for fluorescence analysis can be improved, and moreover the microchemical system can be reduced in size.