Method for analyzing sample solution and apparatus for analyzing sample solution

Disclosed is a method for analyzing a sample solution, including introducing a sample solution 50 through a sample introduction part 6 and developing the sample solution 50 to a developing layer 2 through a capillary phenomenon to analyze an analyte contained in the sample solution 50, the sample introduction part 6 being provided on one side of a test strip 100 and the developing layer 2 being provided on the other side of the test strip 100, wherein the test strip 100 is disposed in such a development posture that the downstream region of the developing layer faces downward during the development. By this method, the developing rate is less susceptible to the viscosity of the sample solution 50 and thus has a small difference even among sample solutions 50 differing in viscosity. As a result, the analytical accuracy and reliability can be improved.

TECHNICAL FIELD

The present invention relates to a method for analyzing a sample solution, including developing a sample solution to a developing layer in a test strip through a capillary phenomenon to analyze an analyte contained in the sample solution, and to an apparatus for analyzing a sample solution using this method for analyzing a sample solution.

BACKGROUND ART

With expansion of home care and community medicine (doctors' offices, clinics, etc.) and growing numbers of early diagnoses and highly urgent clinical laboratory tests, etc., even persons other than clinical laboratory test experts have demanded, in recent years, an analysis apparatus capable of simply and rapidly performing highly precise measurement. Thus, an analysis apparatus intended for POCT (Point of Care Testing) is in the limelight, which is capable of performing highly reliable measurement in a short time without complicated procedures. In general, POCT is a generic name for “near-patient” tests such as tests conducted in practitioners' or specialists' offices, wards, and outpatient clinics. This method attracts attention as being highly useful for improving the quality of clinical practice because the doctor can make an on-the-spot judgment on test results, perform rapid treatment, and even monitor a treatment process or prognosis. The POCT can reduce costs required for transportation of samples or for facilities or costs required for unnecessary tests, compared with tests conducted in the central laboratories of hospitals or the like, and can allegedly cut back on total amounts of test costs. The POCT market has rapidly expanded in the U.S. with progress in the streamlining of hospital management and is expected to grow worldwide, including Japan.

Dry analysis devices typified by chromatographic test strips as immunosensors are capable of analyzing an analyte in a test solution only by simple procedures such as dropwise addition of a sample solution (e.g., blood or urine) to be measured onto the analysis device, without the need of preparing reagents, and are very useful for a convenient and rapid analysis. Therefore, a large number of such devices are now put in practical use as a representative of POCT. Moreover, the market demands more highly precise measurement in a shorter time, in addition to measurement that can be achieved anytime and anywhere by anyone. Also, analysis apparatuses have been proposed, which specialize in optical reading from the analysis devices.

Hereinafter, a conventional method for measuring an immunochromatographic test strip will be described. When a sample solution containing a cellular component is analyzed by a conventional approach, a structure which removes the cellular component in advance or a structure having a cellular component separating member provided in a chromatographic test strip is required. However, such a method disadvantageously requires a time for removing the cellular component in advance or disadvantageously requires the sample solution in non-small amounts in consideration of samples absorbed in the cellular component separating member. Thus, as disclosed in Japanese Patent Nos. 3655283 and 3813150, a method has been proposed, which includes contracting a cellular component and then developing a sample solution.

FIGS. 10(a) and10(b) are an exploded perspective view and a perspective view, respectively, of a conventional immunochromatographic test strip.FIGS. 11(a) and11(b) are respectively a cross-sectional view of the immunochromatographic test strip, whereinFIG. 11(a) is a diagram showing an image of red blood cells in a gap portion after blood introduction, andFIG. 11(b) is a diagram showing an image of the mixed state of plasma and a labeling reagent in the gap portion after plasma introduction.

An immunochromatographic test strip (hereinafter, simply referred to as a test strip)100using an antigen-antibody reaction includes: a gap portion8formed by a transparent space forming member7which is provided on one side in the longitudinal direction of the test strip100, has an air vent10, and holds a cell shrinkage reagent9capable of being eluted due to a sample solution50; a developing layer2which is provided to extend from the central part in the longitudinal direction of the test strip100to the other side of the test strip and develops the sample solution50through a capillary phenomenon; a developing layer support1which is provided in the whole area in the longitudinal direction of the test strip100; a labeling reagent holding part3which contains a substance (e.g., a colloidal gold labeling reagent) specifically binding to an analyte contained in the sample solution50flowing to the upstream region of the developing layer2; a reagent-immobilized part4which immobilizes the analyte bound with the labeling reagent; a liquid absorption part19which finally absorbs the sample solution50; a transparent liquid-impermeable sheet5which covers the developing layer2; and so on. Reference numeral6inFIGS. 10 and 11depicts a sample introduction part which introduces a sample solution therethrough, and this sample introduction part is formed by an opening at the end of the gap portion8. The amount of the labeling reagent immobilized on the reagent-immobilized part4can be measured to thereby determine the concentration of the analyte in the sample solution50.

In this context, as shown inFIGS. 10(b) and11(a), the test strip100is kept in a horizontal posture, while the sample solution is introduced to the sample introduction part6and subjected to a reaction or development.

Specifically, when blood as an example of the sample solution50is introduced to the sample introduction part6, the sample solution50reacts with the cell shrinkage reagent9in the gap portion8. Then, the sample solution50flows through the developing layer2and elutes a colloidal gold labeling reagent in the labeling reagent holding part3. Next, by this elution of the labeling reagent, a colloidal gold-labeled antibody and an analyte (antigen) contained in the sample solution cause a binding reaction during which the reaction solution further flows through the developing layer2and arrives at the reagent-immobilized part4. Then, the complex of the colloidal gold-labeled antibody and the antigen binds to an antibody immobilized in the developing layer2. Through these processes, a color of the colloidal gold appearing in the reagent-immobilized part4can be detected by visual observation or using an optical detector to thereby confirm the presence or concentration of the analyte in the sample solution50. In the test strip100, the gap portion8formed by the space forming member7holds the cell shrinkage reagent9, which in turn contracts red blood cells as a cellular component in blood into a size smaller than the pores of the developing layer2. As a result, the whole blood is favorably developed to the developing layer2.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, the conventional method for analyzing a sample solution as shown inFIGS. 10 and 11has a large difference (variations) in the developing rate of a sample solution50(e.g., blood) travelling in a developing layer2in a test strip100supported in a horizontal posture, due to the viscosity of the sample solution50(e.g., a hematocrit having positive correlation with the viscosity of blood). Thus, blood having a larger viscosity is disadvantageously much slower in developing rate than blood having a smaller viscosity. As a result, not only does the development time or analysis time become longer, but also the whole amount of a sample solution50(e.g., blood having an exceedingly large viscosity) may not arrive at a reagent-immobilized part4yet even when the analysis time is set to a certain amount of extra time added to a development time with respect to a sample solution50having a standard viscosity. Moreover, the amount of the analyte passing through the reagent-immobilized part4within the analysis time is larger at a faster developing rate and smaller at a slower developing rate. Therefore, the larger amount of the analyte flowing is measured with higher sensitivity, whereas the smaller amount of the analyte flowing is measured with lower sensitivity. Thus, this difference in measurement sensitivity deteriorates the analytical accuracy or reliability.

Moreover, in the conventional method for analyzing a sample solution, blood on the developing layer2side aspirated in a gap portion8(i.e., red blood cells11′ at this site) sufficiently reacts with a cell shrinkage reagent9as shown inFIG. 11(a), whereas blood on the sample introduction part6side (i.e., red blood cells11at this site) insufficiently reacts with the cell shrinkage reagent9. This causes variations in the reaction state between blood and the reagent. Thus, blood insufficiently reacted with the cell shrinkage reagent9is developed to the developing layer2. As a result, the analytical accuracy is disadvantageously deteriorated.

Moreover, when the sample solution50is plasma as shown inFIG. 11(b), the influence of red blood cells can be eliminated. However, the concentration of a labeling reagent eluted into plasma aspirated in the gap portion8is disadvantageously higher on the developing layer2side and lower on the sample introduction part6side. This causes variations in the reaction between plasma and the labeling reagent. Thus, plasma insufficiently reacted with the labeling reagent is disadvantageously developed to the developing layer2.

An object of the present invention is to solve the problems of the conventional method and to provide a method for analyzing a sample solution and an apparatus for analyzing a sample solution, which can not only reduce an analysis time but also minimize deterioration in precision caused by different viscosities of sample solutions. Another object of the present invention is to provide a method for analyzing a sample solution and an apparatus for analyzing a sample solution, which secures a time sufficient for the reaction between a sample solution and a reagent (e.g., a cell shrinkage reagent) and achieves highly precise measurement of the sample solution even in trace amounts through a uniform reaction between the sample solution and the reagent.

Means for Solving the Problems

To attain the object, a method for analyzing a sample solution according to the present invention includes introducing a sample solution through a sample introduction part and developing the sample solution to a developing layer through a capillary phenomenon to analyze an analyte contained in the sample solution, the sample introduction part being provided on one side of a test strip and the developing layer being provided so that the downstream region of the developing layer extends to the other side of the test strip, wherein the test strip is disposed in such a development posture that the downstream region of the developing layer faces downward during the development.

By this method, since the test strip is disposed in such a development posture that the downstream region of the developing layer faces downward during the development, the developing rate of the sample solution is increased by means of gravity, compared with a test strip disposed in a horizontal posture even during development. As a result, the development time and analysis time can be reduced. In addition, since a force is added by means of gravity to the sample solution to move to the downstream region of the developing layer, the developing rate is less susceptible to the viscosity of the sample solution and thus has a small difference even among sample solutions differing in viscosity, compared with a test strip kept in a horizontal posture. As a result, a sample solution arrives in almost equal amounts at a predetermined site (e.g., a reagent-immobilized part) in the developing layer, regardless of the viscosity, when measurement is performed with the analysis time set to a certain amount of extra time added to a development time with respect to a sample solution having a standard viscosity. Thus, the amount of the analyte passing through the reagent-immobilized part within the analysis time does not differ among sample solutions. As a result, the analytical accuracy or reliability can be improved.

Moreover, in the method for analyzing a sample solution according to the present invention, the test strip is disposed in an introduction posture suitable for introducing the sample solution to the sample introduction part during the sample solution introduction, and the test strip is then shifted to such a development posture that the downstream region of the developing layer faces downward during the development.

By this method, since the sample can be introduced in an introduction posture that permits easy introduction of the sample solution to the sample introduction part during the sample solution introduction, improved convenience can be offered to a user.

Moreover, the method for analyzing a sample solution according to the present invention further includes arranging a reagent on the one side of the test strip, mixing the reagent with the introduced sample solution, and developing the sample solution thus mixed with the reagent to the developing layer to analyze an analyte contained in the sample solution, wherein the test strip is disposed in such a reaction posture that the one side of the test strip is positioned lower than the other side of the test strip during or after the introduction of the sample solution to the sample introduction part, and the test strip is then shifted to such a development posture that the other side of the test strip is positioned lower than the one side of the test strip. In this context, the reagent is any reagent such as a cell shrinkage reagent or a labeling reagent.

By this method, the test strip is disposed in such a reaction posture that the one side (where the sample introduction part or the reagent is provided) of the test strip is positioned lower than the other side of the test strip during or after the introduction of the sample solution to the sample introduction part. Accordingly, in this posture, the sample solution can be reserved favorably on the one side of the test strip. Thus, a time sufficient for the reaction between the reagent and the sample solution can be secured. As a result, a uniform reaction is achieved therebetween.

Moreover, in the method for analyzing a sample solution according to the present invention, the operation of disposing the test strip in the reaction posture after the introduction of the sample solution thereto and then the operation of shifting the test strip to the development posture are repetitively performed.

By repetitively performing the operation of disposing the test strip in the reaction posture and the operation of shifting the test strip to the development posture in this way, the reagent and the sample solution are more favorably stirred, compared with the reaction between a reagent and a sample solution in a test strip kept in a horizontal posture. As a result, a further favorable reaction can be achieved therebetween.

Moreover, the method for analyzing a sample solution according to the present invention further includes changeably arranging the posture of the test strip, detecting a position at which the sample solution arrives in the developing layer, and setting at least one of the posture of the test strip and duration of the posture based on the position.

By this method, since, according to the position at which the sample solution arrives in the developing layer, the posture of the test strip or a duration of the posture in the subsequent procedures is set, the development is further less susceptible to the viscosity of the sample solution. As a result, the analytical accuracy or reliability can be improved.

Moreover, in the method for analyzing a sample solution according to the present invention, the sample solution is blood.

Moreover, an apparatus for analyzing a sample solution according to the present invention includes a test strip having a sample introduction part which introduces a sample solution therethrough and a developing layer, the sample introduction part being provided on one side of the test strip and the developing layer being provided so that the downstream region of the developing layer extends to the other side of the test strip, the apparatus developing the sample solution in the developing layer through a capillary phenomenon to analyze an analyte contained in the sample solution, wherein the apparatus includes a test strip holding unit which holds the test strip, and a shift driving unit which shifts the test strip to an introduction posture suitable for introducing the sample solution to the sample introduction part and to such a development posture that the other side of the test strip is positioned lower than the one side of the test strip.

By this constitution, since the shift driving unit can be driven to favorably shift the test strip to the introduction posture or to the development posture and to dispose the test strip in such a development posture that the downstream region of the developing layer faces downward during the development, the development is less susceptible to the viscosity of the sample solution. As a result, the analytical accuracy or reliability can be improved.

Moreover, the apparatus for analyzing a sample solution according to the present invention further includes a reagent to be mixed with the sample solution, the reagent being provided on the one side of the test strip, wherein the shift driving unit shifts the test strip to such a reaction posture that the one side of the test strip is positioned lower than the other side of the test strip and to such a development posture that the other side of the test strip is positioned lower than the one side of the test strip.

By this constitution, since the shift driving unit can be driven to favorably shift the test strip to the reaction posture or to the development posture and to dispose the test strip in the reaction posture during the introduction of the sample solution to the sample introduction part, a time sufficient for the reaction between the reagent and the sample solution can be secured. As a result, a uniform reaction can be achieved therebetween.

Moreover, the apparatus for analyzing a sample solution according to the present invention further includes a detecting unit which detects a position at which the sample solution arrives in the developing layer in the test strip. By this constitution, the analysis can be achieved while the position at which the sample solution arrives in the developing layer is detected. As a result, the analytical accuracy or reliability can be improved.

Moreover, the apparatus for analyzing a sample solution according to the present invention further includes a controlling part which controls the posture of the test strip and duration of the posture based on the position at which the sample solution arrives in the developing layer. By this constitution, the sample solution can be controlled to be favorably developed in the developing layer. As a result, the analytical accuracy or reliability can be improved.

Moreover, in the apparatus for analyzing a sample solution according to the present invention, the shift driving unit rotates the test strip in a plane along a plane for detection of the test strip. The detecting unit is disposed so that its detection range is the plane along the plane for detection. In such a case, the deployed position of the test strip shifted to any posture can be detected favorably using one detecting unit.

Moreover, in the apparatus for analyzing a sample solution according to the present invention, the sample solution is blood.

Advantages of the Invention

According to a method for analyzing a sample solution and an apparatus for analyzing a sample solution according to the present invention, since a test strip is disposed in such a development posture that the downstream region of the developing layer faces downward during development, a sample solution can be developed in a manner less susceptible to the viscosity of the solution. As a result, the analytical accuracy or reliability can be improved.

Moreover, according to the method for analyzing a sample solution and the apparatus for analyzing a sample solution according to the present invention, since the test strip is disposed in such a reaction posture that one side of the test strip is positioned lower than the other side of the test strip during or after the introduction of the sample solution to a sample introduction part, a time sufficient for the reaction between the sample solution and the reagent can be secured. As a result, a uniform reaction can be achieved between the sample solution and the reagent. Thus, the sample solution even in trace amounts can be measured highly precisely.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a method for analyzing a sample solution and an apparatus for analyzing a sample solution according to embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1(a) and1(b) are respectively a plane view of a test strip used in a method for analyzing a sample solution according to an embodiment 1 of the present invention. A test strip100used in the method for analyzing a sample solution according to this embodiment of the present invention has the same constitution and functions as those of the immunochromatographic test strip100described inFIGS. 10(a) and10(b). In this context, the same reference numerals will be used to designate components having the same or similar functions.

As shown inFIGS. 1(a) and1(b), the test strip100includes: a gap portion8formed by a transparent space forming member7which is provided on one side in the longitudinal direction of the test strip100, has an air vent10, and holds a reagent9capable of being eluted due to a sample solution; a developing layer2which is provided to extend from the central part in the longitudinal direction of the test strip100to the other side of the test strip and develops the sample solution through a capillary phenomenon; a developing layer support1which is provided in the whole area in the longitudinal direction of the test strip100; a labeling reagent holding part3which contains a labeling reagent specifically reacting with an analyte contained in the sample solution flowing to the upstream region of the developing layer2; a reagent-immobilized part4which contains an immobilized reagent capable of specifically reacting with the complex of the analyte bound with the labeling reagent; a liquid absorption part19which finally absorbs the sample solution; and a transparent liquid-impermeable sheet5which covers the developing layer2to protect the sample solution (e.g., blood) from drying and assist in uniform development. In detail, a sample introduction part6formed by an opening at the end of the gap portion8is provided on the one side of the test strip100. This gap portion8holds the cell shrinkage reagent9, and the developing layer2is provided so that the downstream region of the developing layer2extends to the other side of the test strip100. When a sample solution is introduced to the test strip100, an analyte contained in the sample solution reacts with the labeling reagent or the immobilized reagent to generate a color of the labeling reagent in the reagent-immobilized part4. This color is photographed using an image sensor23described later, and the color intensity in the reagent-immobilized part4is determined to thereby detect the concentration of the analyte.

Next, an apparatus for analyzing a sample solution according to the embodiment 1 of the present invention will be described.FIGS. 2(a) and2(b) are a plane view and a side view, respectively, schematically showing an example of the apparatus for analyzing a sample solution according to the embodiment 1 of the present invention.

As shown inFIGS. 2(a) and2(b), an apparatus120for analyzing a sample solution includes: a holder21as a test strip holding unit which holds the test strip100; a motor22as a shift driving unit which rotatably supports the holder21; the image sensor23as a detecting unit which monitors (photographs) the test strip100; and a controlling part (not shown) which controls the motor22based on the image or the like photographed by the image sensor23. In this apparatus120for analyzing a sample solution, the test strip100is supported rotatably about an axis X along the width direction of the test strip100, in the central part in the longitudinal direction of the test strip, though the present invention is not limited thereto.

The method for analyzing a sample solution according to the present invention using such an apparatus120for analyzing a sample solution will be described below with reference toFIGS. 3(a) to3(c). In this context,FIGS. 3(a) to3(c) are respectively a side view schematically showing the method for analyzing a sample solution according to the embodiment 1 of the present invention, whereinFIG. 3(a) schematically shows a state during sample solution introduction in the method for analyzing a sample solution, andFIGS. 3(b) and3(c) respectively schematically show a state during development in the method for analyzing a sample solution. For this method for analyzing a sample solution described below, it is preferable to use the apparatus120for analyzing a sample solution, though the present invention is not limited to the use of this apparatus120for analyzing a sample solution. An apparatus for analyzing a sample solution having a different constitution may be used, such as an apparatus130for analyzing a sample solution shown inFIGS. 7(a) to7(c) described later. In the description below, an angle is defined with respect to the angle) (0°) of the test strip100disposed horizontally. An angle formed by counterclockwise rotation about the central part in the longitudinal direction of the test strip100with respect to this reference line is described as +, while an angle formed by clockwise rotation thereabout is described as −.

As shown inFIG. 3(a), first, the test strip100is held by the holder21so that the test strip100stands still in a horizontal posture (introduction posture). To the sample introduction part6in this test strip100, a sample solution50is introduced, and the test strip100stands still in this horizontal posture for a predetermined time (e.g., 60 seconds) to favorably spread the sample solution50in the gap portion8in the test strip100. The introduction posture of the test strip100during the introduction of the sample solution50to the sample introduction part6is not limited to standing still in a horizontal posture, and the test strip100may take any posture as long as the posture easily permits the procedure of introducing the sample solution50without a hitch. Then, as shown inFIG. 3(b), the test strip100is inclined +90° via the holder21to take such a development posture that the downstream region of the developing layer2faces downward and the space forming member7provided with the sample introduction part6faces upward to develop the sample solution to the developing layer2. The test strip stands still in such a development posture, for example, for 240 seconds, and the degree of reaction on the test strip100is then measured using the image sensor23.

Moreover, in this development posture, the sample solution is developed in the developing layer2through a capillary phenomenon, while a force is added by means of gravity to the sample solution50to move to the downstream region of the developing layer2. Thus, the developing rate of the sample solution50is increased by means of gravity, compared with a test strip100kept in a horizontal posture. As a result, the development time or analysis time can be reduced. In addition, since the force is added by means of gravity to the sample solution50to move to the downstream region of the developing layer2, not merely is the analysis time reduced, but also the developing rate is less susceptible to the viscosity of the sample solution50and thus has a small difference even among sample solutions50differing in viscosity, compared with a test strip100kept in a horizontal posture even during development. As a result, a sample solution (e.g., blood having an exceedingly large viscosity) arrives in almost equal amounts at a predetermined site (e.g., the reagent-immobilized part4) in the developing layer2, when measurement is performed with the analysis time set to a small amount of extra time (e.g., 40 seconds) added to a development time (e.g., 200 seconds) required for a sample solution50having a standard viscosity. Thus, the amount of the analyte passing through the reagent-immobilized part4within the analysis time does not differ among sample solutions. As a result, the analytical accuracy or reliability can be improved.

For example, when a predetermined substance is analyzed using blood as the sample solution50, blood having a low viscosity (e.g., hematocrit (value having positive correlation with the viscosity of blood): approximately 20%) is developed at a distance of 1.3 times that of, for example, blood having a standard hematocrit of around 40%, in a test strip100kept in a horizontal posture even during development. By contrast, blood having a high viscosity (e.g., hematocrit: approximately 60%) is developed at a distance 0.7 times that of the blood in this test strip100. Therefore, the amount of the predetermined substance passing through the reagent-immobilized part4also differs therebetween. Thus, when the concentration of the predetermined substance is measured using this test strip100, the rate of deviation from the true value with respect to blood having a standard hematocrit of 40% is as large as +60% for blood having a hematocrit of approximately 20% and −60% for blood having a hematocrit of approximately 60%. By contrast, the test strip100inclined +90° so that the downstream region of the developing layer2faces downstream during the development as aforementioned exhibits a small difference in development distance between blood having a hematocrit of approximately 20% and blood having a hematocrit of approximately 60%. Therefore, the rate of deviation from the true value is also reduced almost 50%. Thus, the development is less susceptible to the viscosity of the sample solution50.

Specifically, in the test strip100kept in a horizontal posture during development, it is highly possible that a portion of the sample solution50having a large viscosity dose not arrive at the predetermined position (reagent-immobilized part4) even after a long time spent for the development. In such a case, the analytical accuracy or reliability may be reduced. By contrast, the present embodiment can minimize such a problem and can improve the analytical accuracy or reliability.

The posture of the test strip100during development (development posture) is more preferably a posture inclined +90° so that the downstream region of the developing layer2faces downward as aforementioned. However, the development posture is not limited thereto, and a development posture inclined at any angle, preferably +45 to +135°, as shown inFIG. 3(c) also has the effect of making the developing rate less susceptible to the viscosity of the sample solution. However, a posture inclined +30° or smaller or +150° or larger is not preferable because this posture hardly differs from the horizontal posture in their effects. Moreover, the time for which the test strip stands still in a horizontal posture (introduction posture) immediately after introduction and the time for which the test strip stands still in such a development posture that the downstream region of the developing layer2faces downward are not limited to the aforementioned times. The optimal times can be selected according to the property of the test strip100.

Moreover, the present embodiment also has advantages shown below, in addition to the aforementioned effect. In this context,FIGS. 4(a) and4(b) are respectively a cross-sectional side view showing the state of the test strip100after a given time from the introduction of the sample solution50in this embodiment.FIG. 4(a) is a cross-sectional side view showing as a comparative example that the test strip continues to stand still in a horizontal posture even after the introduction of the sample solution50, andFIG. 4(b) is a cross-sectional side view showing as the embodiment of the present invention that the test strip stands still in such a development posture that the downstream region of the developing layer2faces downward after the introduction of the sample solution50.

As shown inFIG. 4(a), when the sample solution50as a sample to be measured is introduced to the sample introduction part6in the test strip100disposed in a horizontal posture and then the test strip100continues to stand still in this horizontal posture, the sample solution50is developed to the downstream region of the developing layer2. During this development, the developing layer2has smaller friction on the developing layer support side (on the underside of the developing layer) than on the liquid-impermeable sheet side. Therefore, the sample solution50tends to be developed faster on the developing layer support1side due to the enhanced capillary phenomenon and developed slower on the liquid-impermeable sheet5side. Thus, in the test strip100disposed in a horizontal posture not only during introduction but also during development, the sample solution is developed nonuniformly in the thickness direction of the developing layer2(i.e., developed faster on the lower side and slower on the upper side in the thickness direction of the developing layer2). As a result, a nonuniform reaction occurs in the reagent-immobilized part4. Furthermore, this causes an indefinite boundary in the position of the development or variations in color intensity in the reagent-immobilized part. Therefore, the measurement of the degree of reaction on the test strip100using the image sensor23tends to result in deteriorated precision.

However, in the present embodiment, the test strip100shifted to the development posture (+45° to +135°) as aforementioned utilizes, in addition to the force of a capillary phenomenon, gravity further imparted thereto as a force developing the sample solution50in the direction of development, as shown inFIG. 4(b). Therefore, the sample solution50is developed to the downstream region of the developing layer1without a difference in developing rate between the developing layer support1side and the liquid-impermeable sheet5side. Accordingly, variations in the development of the sample solution50in the thickness and width directions of the developing layer2can be alleviated. As a result, the sample solution50is developed almost uniformly to the downstream region of the developing layer2. Thus, the sample solution50reacts uniformly without variations in the thickness and width directions of the developing layer2with the labeling reagent in the labeling reagent holding part3or the immobilized reagent in the reagent-immobilized part4. This also achieves uniform color intensity in the reagent-immobilized part4in the thickness and width directions. Accordingly, the measurement of the degree of reaction on the test strip100using the image sensor23is performed with higher precision, because the position of the development can be clearly observed.

FIGS. 5(a) and5(b) are respectively a side view schematically showing a state during sample solution (blood) introduction in a method for analyzing a sample solution according to an embodiment 2 of the present invention,FIG. 5(c) is a side view schematically showing a state after sample solution introduction and before development in the method for analyzing a sample solution, andFIG. 5(d) is a side view schematically showing a state during sample solution development in the method for analyzing a sample solution. Moreover,FIGS. 6(a) to6(c) are respectively an image of the behavior of red blood cells as a cellular component in a gap portion in the method for analyzing a sample solution, whereinFIG. 6(a) is a diagram schematically showing a state immediately after sample solution introduction,FIG. 6(b) is a diagram schematically showing a state after a lapse of some time after sample solution introduction, andFIG. 6(c) is a diagram schematically showing a state during sample solution development.

For the method for analyzing a sample solution according to the embodiment 1, the method for coping with the problem associated with the sample solution50development is described. However, the conventional method for analyzing a sample solution wherein the test strip100is kept in a horizontal posture even after sample solution introduction also has the problem of an insufficient reaction, because the sample solution50introduced in the test strip100is not favorably mixed with a reagent (e.g., a cell shrinkage reagent9). The embodiment of the present invention described below also copes with this problem.

A test strip100used in the method for analyzing a sample solution according to this embodiment 2 is constituted in the same way as in those described inFIGS. 1(a),1(b),10(a), and10(b). Specifically, the test strip100includes: a gap portion8formed by a transparent space forming member7which has an air vent10and holds a cell shrinkage reagent9; a developing layer2which holds and immobilizes a labeling reagent and an antibody; a liquid absorption part19which finally absorbs a sample solution50; a developing layer support1which supports the developing layer2and the liquid absorption part19; and a transparent liquid-impermeable sheet5which protects the sample solution50(e.g., blood) from drying and assists in uniform development. A sample introduction part6which introduces the sample solution50therethrough is formed at the end of the gap portion8in the test strip100. Thus, the sample introduction part6formed by an opening at the end of the gap portion8is provided on one side of the test strip100. This gap portion8holds the cell shrinkage reagent9. Moreover, the developing layer2is provided so that the downstream region of the developing layer2extends to the other side of the test strip100. In this context, the air vent10formed in the space forming member7discharges the air of the gap portion8so that the sample solution50is smoothly aspirated in the gap portion8during the introduction of the sample solution50.

Next, the method for analyzing a sample solution according to this embodiment 2 will be described with reference toFIGS. 5(a) to5(d) and6(a) to6(c).

Blood is introduced as the sample solution50to the sample introduction part6at the end of the gap portion8in the test strip100. During this introduction, the test strip100may be disposed in an introduction posture suitable for introducing the sample solution50to the sample introduction part6. The introduction posture may be, for example, a posture in which the test strip100stands still horizontally as shown inFIG. 5(a) or a posture in which the sample introduction part6in the test strip100faces upward as shown inFIG. 5(b).

After the blood introduction to the sample introduction part6in the test strip100, the test strip100is put into standby mode in such a posture inclined −45° to −135° that the sample introduction part6on the one side of the test strip100is positioned lower than the downstream region of the developing layer2on the other side of the test strip100as shown inFIG. 5(c). This posture permits a sufficient reaction with the cell shrinkage reagent9as described later and hereinafter, is referred to as a reaction posture. An angle formed by this reaction posture is most preferably −90°, though the angle is not limited thereto. This angle may be any angle from −45° to −135°.

A test strip100standing still along the horizontal direction after sample solution50introduction as in the conventional method for analyzing a sample solution exhibits variations in the concentrations of blood and the cell shrinkage reagent9in the gap portion8. As a result, red blood cells insufficiently reacted with the cell shrinkage reagent9are developed to the developing layer2. By contrast, in the test strip100put into standby mode in a reaction posture inclined −45° to −135° as in the present embodiment, red blood cells11in blood introduced through the sample introduction part6are moved by means of gravity to the sample introduction part6(distantly from the developing layer2) on the one side of the test strip100as shown inFIG. 6(a), or stay in the gap portion8. This is because components of red blood cells usually have larger gravity (generally 1.095) than that (generally 1.025 to 1.029) of plasma components in human blood, though there are variations among individuals. Accordingly, a time for which the red blood cells11stay in the gap portion8can be secured. As a result, the red blood cells11in blood react uniformly without variations with the cell shrinkage reagent9and are thereby contracted into a size smaller than the pores of the developing layer2made of a porous carrier (i.e., the state of red blood cells11′ shown inFIG. 6(a)).

When the test strip100is kept in this posture, a portion of blood (represented by reference numeral12inFIG. 6(b)) is developed to the developing layer2as shown inFIG. 6(b). However, when blood held in the gap portion8becomes smaller in volume than the gap portion8, a fluid level50aof the blood is positioned lower than the end of the developing layer2so that the blood in the gap portion8does not have contact with the developing layer2any more. As a result, the blood is not developed to the developing layer2. Therefore, the test strip100is disposed in the reaction posture for 30 seconds (which probably permits a sufficient reaction) and then kept in such a posture inclined +45° to +135° (development posture) that the downstream region of the developing layer2on the other side of the test strip100is positioned lower than the sample introduction part6on the one side of the test strip100as shown inFIG. 5(d). An angle formed by this development posture is most preferably +90°, though the angle is not limited thereto. This angle may be any angle from +45° to +135°.

Accordingly, blood flows to the downstream region of the developing layer2by means of gravity as shown inFIG. 6(c) and therefore moves from the sample introduction part6side to the air vent10side in the gap portion8to come in contact with the developing layer2. As a result, blood (sample solution50) containing sufficiently contracted red blood cells11′ is developed to the developing layer2. Moreover, the residues of blood in the gap portion8can be eliminated by the effect of the gravity imparted thereto. Then, an analyte in blood reacts with the labeling reagent and an immobilized reagent. As a result, a color of the labeling reagent appears in a reagent-immobilized part4. The appearing color of the labeling reagent is measured as color intensity by a signal from an image sensor23to favorably and accurately detect the presence or concentration of the analyte.

According to the method for analyzing a sample solution according to this embodiment, since the red blood cells11in blood react sufficiently and uniformly with the cell shrinkage reagent9in the gap portion8and are then developed to the developing layer2, blood can react with the labeling reagent and a labeled antibody without clogging the developing layer2. Furthermore, since blood does not remain in the gap portion8, the sample solution50even in trace amounts can be measured highly precisely. Moreover, in this embodiment as well, the developing rate is less susceptible to the viscosity of the sample solution50by virtue of the development posture during development, as in the embodiment 1. As a result, the analytical accuracy or reliability can be improved.

In this context, an apparatus130for analyzing a sample solution shown inFIGS. 7(a) to7(c) may be used, instead of the apparatus120for analyzing a sample solution shown inFIGS. 2(a) and2(b), in the method for analyzing a sample solution according to this embodiment.

Next,FIGS. 7(a) to7(c) are respectively a diagram schematically showing the structure of the apparatus130for analyzing a sample solution according to the embodiment 2 of the present invention, whereinFIG. 7(a) is a perspective view of the apparatus130for analyzing a sample solution,FIG. 7(b) is a side view of the apparatus130for analyzing a sample solution immediately after blood introduction, andFIG. 7(c) is a side view of the apparatus130for analyzing a sample solution after changing an angle at which a test strip is inclined. The same reference numerals will be used to designate components having the same or similar functions as those in the apparatus120for analyzing a sample solution shown inFIGS. 2(a) and2(b).

As shown inFIGS. 7(a) to7(c), the apparatus130for analyzing a sample solution includes: a holder21as a test strip holding unit which holds a test strip100; a motor22as a shift driving unit which rotatably supports the holder21; an image sensor23which monitors (photographs) the test strip100; a controlling part (not shown) which controls the motor22based on the image or the like photographed by the image sensor23; and a case24which accommodates these holder21, motor22, image sensor23and controlling part. In this apparatus130for analyzing a sample solution, the motor22is mounted in such a posture on the inner surface of a back panel24aof the case24that a rotation axis22aof the motor is positioned horizontally. The holder21mounted to the rotation axis22aand the test strip100attached to this holder21are arranged to rotate in a plane (referred to as a plane for detection)2a(in this embodiment, in a vertical plane orthogonal to the horizon) in which the state of development in a developing layer2in the test strip100can be determined and detected. A long hole24bis formed in the top panel of the case24so that a site positioned at the upper end of the test strip100protrudes from the long hole24b. Moreover, the image sensor23is arranged to face the plane2afor detection of the developing layer2in the test strip100.

During blood introduction, the motor22is positionally controlled to dispose the holder21in a posture shown inFIG. 7(a). To this holder21, a test subject or the like loads (attaches) the test strip100. Accordingly, the test strip100is held in such a posture that the sample introduction part6protrudes from the top panel of the case24as shown inFIG. 7(a). In this state, the test subject or the like introduces blood to the sample introduction part6.

In the apparatus130for analyzing a sample solution, the test strip100is loaded, while the image sensor23is controlled to start to monitor the test strip100. When the apparatus automatically recognizes the blood introduction to the test strip100by image processing, the motor22rotates the test strip100at an angle of 180° so that the sample introduction part6in the test strip100is positioned lower than the downstream region of the developing layer2(reaction posture) as shown inFIG. 7(b). This rotation may be performed in any direction. Moreover, during this operation, the image sensor23further monitors the test strip100and detects a position50bat which blood arrives in the developing layer2as shown inFIG. 8.

The controlling part in the apparatus130for analyzing a sample solution confirms that the position50bat which blood arrives reaches a predetermined distance L or larger from the end of the test strip100provided with the sample introduction part6. After a lapse of any time, the motor22rotates the test strip100at an angle of 180° so that the test strip100is disposed in such a development posture that the downstream region of the developing layer2is positioned lower than the sample introduction part6as shown inFIG. 7(c). Then, after a lapse of a predetermined time (e.g., 5 minutes) from blood introduction, the image sensor23photographs the test strip100disposed in this development posture and measures the color intensity of the reagent-immobilized part4. As a result, the concentration of an analyte in blood is detected.

According to the apparatus130for analyzing a sample solution according to this embodiment, since the test strip100is arranged to rotate in the same plane as the plane2afor detection of the developing layer2, the surface state of the test strip100can always be monitored by one image sensor23. Moreover, in this case, since the image sensor23necessary for the measurement can also be used in the detection of timing of changing an angle at which the test strip100is inclined, another special part is unnecessary. Thus, the apparatus according to this embodiment advantageously offers reduced production cost and simplified assembly procedures.

In this context, the apparatus120for analyzing a sample solution shown inFIGS. 2(a) and2(b) may be used instead of this apparatus130for analyzing a sample solution. In this case, the test strip100during blood introduction may be disposed in the horizontal posture as shown in the solid line inFIG. 2(b) or may be disposed so that the sample introduction part6in the test strip100faces upward as shown in the imaginary line inFIG. 2(b). Thus, the test strip100is preferably disposed in a posture that permits easy blood introduction.

Next, a method for analyzing a sample solution using plasma as the sample solution will be described with reference toFIGS. 1,5, and9. This plasma used as a sample solution50is free from red and white blood cells. Therefore, a test strip100having the same constitution as that shown inFIG. 1(a) is used in this method except that the test strip100has no cell shrinkage reagent9as shown inFIG. 1(b).

FIGS. 9(a) to9(c) are respectively an image of the mixed state of plasma as a sample solution50and a labeling reagent in a gap portion8in the test strip100according to this embodiment 3, whereinFIG. 9(a) is a diagram showing the mixed state of plasma and the labeling reagent immediately after plasma introduction,FIG. 9(b) is a diagram schematically showing the mixed state after a lapse of some time after plasma introduction, andFIG. 9(c) is a diagram schematically showing a state during development.

First, plasma is introduced to a sample introduction part6at the end of the gap portion8in the test strip100. During this plasma introduction, the test strip may be disposed in an introduction posture (not shown) suitable for introducing the sample solution50to the sample introduction part6, as in the embodiment 2. The introduction posture may be, for example, a posture in which the test strip100stands still horizontally as shown inFIG. 5(a) or a posture in which the sample introduction part6in the test strip100faces upward as shown inFIG. 5(b). Then, the test strip100is put into standby mode in such a reaction posture inclined −45° to −135° that the sample introduction part6on one side of the test strip100is positioned lower than the downstream region of a developing layer2on the other side of the test strip100as shown inFIG. 5(c). An angle formed by this reaction posture is most preferably −90°, though the angle is not limited thereto. This angle may be any angle from −45° to −135°. Moreover,FIG. 9(a) shows a state at −90°.

The test strip100standing still along the horizontal direction after plasma introduction as in the conventional method for analyzing a sample solution exhibits variations in the concentration of the labeling reagent eluted into plasma in the gap portion8. As a result, plasma insufficiently reacted with the labeling reagent is developed to the developing layer2. By contrast, in the test strip100put into standby mode in a reaction posture inclined −45° to −135° as in the present embodiment, plasma is moved by means of gravity to the sample introduction part6(distantly from the developing layer2) on the one side of the test strip100as shown inFIG. 9(a), or stays in the gap portion8. Accordingly, a time for which plasma stays in the gap portion8can be secured. As a result, plasma reacts uniformly without variations with the labeling reagent.

When the test strip100is kept in this posture, a portion of plasma is developed to the developing layer2as shown inFIG. 9(b). However, when plasma held in the gap portion8becomes smaller in volume than the gap portion8, a fluid level50aof plasma is positioned lower than the end of the developing layer2, so that the plasma in the gap portion8does not have contact with the developing layer2any more. As a result, the plasma is not developed to the developing layer2. Therefore, in this embodiment, the test strip100is disposed in the reaction posture for 30 seconds (which probably permits a sufficient reaction) and then kept in such a development posture inclined +45° to +135° that the downstream region of the developing layer2on the other side of the test strip100is positioned lower than the sample introduction part6on the one side of the test strip100as shown inFIG. 9(c). Accordingly, the plasma flows by means of gravity to the downstream region of the developing layer2as shown inFIG. 9(c) and thereby moves from the sample introduction part6side to the air vent10side in the gap portion8to come in contact with the developing layer2. As s result, plasma sufficiently reacted with the labeling reagent is developed to the developing layer2. Moreover, the residues of plasma in the gap portion8can be eliminated by the effect of the gravity imparted thereto. Then, an analyte in plasma reacts with the labeling reagent and is then immobilized in a reagent-immobilized part4. A color of the labeling reagent appearing in the reagent-immobilized part4is measured as color intensity by a signal from an image sensor23to favorably and accurately detect the presence or concentration of the analyte.

According to the method for analyzing a sample solution according to this embodiment, since plasma reacts with the labeling reagent sufficiently and uniformly in the gap portion8and is then developed to the developing layer2and since no plasma remains in the gap portion8, the sample solution50even in trace amounts can be measured highly precisely. Moreover, in this embodiment as well, the developing rate is less susceptible to the viscosity of the sample solution50by virtue of the development posture during development, as in the embodiment 1. As a result, the analytical accuracy or reliability can be improved.

In these embodiments 2 and 3, the test strip100is disposed in such a reaction posture that the sample introduction part6faces downward, and the test strip100is then shifted to such a development posture that the downstream region of the developing layer2faces downward. After a predetermined time, the image sensor23detects the presence or concentration of the analyte, as aforementioned. However, the present invention is not limited thereto, and the operation of disposing the test strip100in the reaction posture after the introduction of the sample solution50thereto and then the operation of shifting the test strip to the development posture may be performed repetitively.

By repetitively performing the operation of disposing the test strip in the reaction posture and the operation of shifting the test strip to the development posture in this way, the cell shrinkage reagent9or the labeling reagent and the sample solution50are more favorably stirred, compared with a reaction between a cell shrinkage reagent9or a labeling reagent and a sample solution50in a test strip kept in the reaction posture. As a result, the effect of providing a further favorable reaction therebetween can be achieved.

In the embodiments 1 to 3, the sample solution does not have contact with the developing layer2any more in the test strip shifted to the reaction posture, as aforementioned. However, the present invention is not limited thereto, and these embodiments are sufficiently effective even for a structure where the sample solution50always comes in contact with a portion of the developing layer2in such a way that the developing layer2extends to the sample introduction part6.

Moreover, the duration of the reaction posture may be any time, and it is preferable to select the optimum duration for each embodiment.

Furthermore, the timing of changing the posture of the test strip100(changing the angle at which the test strip100is inclined) may be detected based on the position of the fluid level of the sample solution50held in the gap portion8described inFIG. 6(b) and may be detected by any method.

Furthermore, the shift driving unit which changes the posture of the test strip100(changes the angle at which the test strip100is inclined) or a method therefor may be any unit or method. A method for measuring the lapse of time may be any method.

Furthermore, the test strip100is monitored using the image sensor23in the methods aforementioned. However, the monitoring may be performed by any method.

Furthermore, the color intensity is measured by photographing using the image sensor23and image processing in the methods aforementioned. However, the measurement may be performed by any method.

Furthermore, examples of the sample solution50that may be used include blood as well as other sample solutions including those containing cells (e.g., bacterial solutions) and body fluids (e.g., urine, serum, and saliva). Moreover, biological materials such as proteins, hormones, bacteria, and viruses contained in those sample solutions may be measured as an analyte. Specific examples of the analyte include analytes for water examination, human chorionic gonadotropin in urine, various antibodies and antigens in blood, albumin, HbAlc, estradiol, estriol, corpus luteum hormone, and bacteria or viruses contained in saliva in the mouth.

INDUSTRIAL APPLICABILITY

A method for analyzing a sample solution and an apparatus for analyzing a sample solution according to the present invention achieve highly precise measurement of a sample solution even in trace amounts and is therefore suitable particularly when rapid, convenient, accurate and highly precise measurement of an analyte is required.