Abstract:
An electrochemical test strip is provided, including a substrate, an electrode structure and an insulative film. The electrode structure is formed on the substrate, including a first electrode and a second electrode. The second electrode includes a first end, a second end, an extension portion, and a bent portion. The extension portion connects the first end with the bent portion, and the bent portion is connected to the second end. The extension portion and the first electrode define a space therebetween for receiving the bent portion. The insulative film covers at least a part of the electrode structure and forms an opening. A sample fluid enters the electrochemical test strip through the opening, and the sample fluid sequentially contacts the first electrode and the second electrode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/586,907, filed on Jan. 16, 2012, the entirety of which is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electrochemical test strip, and in particular relates to an electrochemical test strip with an underfill detection function. 
         [0004]    2. Description of the Related Art 
         [0005]    Referring to  FIG. 1 , a conventional electrochemical test strip comprises a set of identifying electrodes D, insulated from each other. When a sample is injected into the strip and through a set of reaction electrodes E to the set of identifying electrodes D along a direction A, the set of identifying electrodes D are electrically conducted through the sample to form a circuit. The circuit can be electrically connected to an instrument for determining fill or under fill of the sample. 
         [0006]    However, the conventional electrochemical test strip requires at least two pins for the additional set of identifying electrodes, thus reducing the number of available pins and obstructing the expansion for other functions. 
         [0007]    Further more, a conventional electrode structure comprises a reaction area between an upper electrode and a lower electrode (face to face structure) for determining the hematocrit ratio by flowing speed. When the sample contacts the reagent in the reaction area, the electronic signal between the upper and lower electroedes starts to highly increase by the chemical reaction between the sample and the reagent, when the sample contacts electrode without reagent, the electronic signal starts to highly decrease, and the time interval between the highly increasing and decreasing times of the electronic signal can be used to calculate flowing speed and the hematocrit ratio of the sample. However, the electrodes of the face to face structure could be conducted to each other by compressing the strip, and the flowing speed could be affected by the coating of the reagent on the reaction area. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention provides an electrochemical test strip, comprising a substrate, an electrode structure, and an insulative layer. The substrate comprises a test end. The electrode structure is formed on the substrate, comprising: a first electrode and a second electrode. The second electrode comprises a first end, a second end, an extension portion and a bent portion, wherein the extension portion is connected between the first end and the bent portion, the bent portion is connected to the second end, and the extension portion and the first electrode define a space therebetween for receiving the bent portion. The insulative layer covers at least a part of the electrode structure and forms an opening, wherein a sample is injected through the opening into the electrochemical test strip and sequentially contacts the first electrode and the second electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a schematic view of identifying electrodes and reaction electrodes of a conventional electrochemical test strip; 
           [0011]      FIG. 2  is an exploded diagram of an electrochemical test strip according to an embodiment of the invention; 
           [0012]      FIG. 3   a  is a schematic view showing a substrate and an electrode structure of an electrochemical test strip according to another embodiment of the invention; 
           [0013]      FIG. 3   b  is a schematic view showing a substrate and an electrode structure of an electrochemical test strip according to another embodiment of the invention; 
           [0014]      FIG. 3   c  is a schematic view showing a substrate and an electrode structure of an electrochemical test strip according to another embodiment of the invention; 
           [0015]      FIG. 3   d  is a schematic view showing a substrate and an electrode structure of an electrochemical test strip according to another embodiment of the invention; 
           [0016]      FIG. 3   e  is a schematic view showing a substrate and an electrode structure of an electrochemical test strip according to another embodiment of the invention; 
           [0017]      FIG. 4  is a sectional schematic view showing a substrate and an electrode structure of an electrochemical test strip according to another embodiment of the invention; 
           [0018]      FIG. 5   a  is a schematic view showing a sample injection direction of an electrochemical test strip according to another embodiment of the invention; 
           [0019]      FIG. 5   b  is a schematic view showing a sample injection direction of an electrochemical test strip according to another embodiment of the invention; 
           [0020]      FIG. 6  is a schematic view showing variation of an electrical current when detecting underfill of a sample in an electrochemical test strip according to an embodiment of the invention; 
           [0021]      FIG. 7   a  is a schematic view showing variation of electronic signals with different hematocrit (HCT) ratios of samples; 
           [0022]      FIG. 7   b  is a schematic view showing variation of an electronic signal between second and third electrodes according to a testing voltage; 
           [0023]      FIGS. 8   a  and  8   b  are flowcharts of an embodiment of the method for testing a sample by an electrochemical test strip; and 
           [0024]      FIGS. 9   a  and  9   b  are sectional schematic views showing an electrode structure of an electrochemical test strip for testing a sample. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring to  FIG. 2 , an embodiment of an electrochemical test strip comprises a substrate  110 , an electrode structure  120  and an insulative layer  140 . The electrode structure  120  is formed on the substrate  110  which comprises a test end  143  and a connection end  144 . The insulative layer  140  covers at least a part of the electrode structure  120  and an opening  141  is formed in the insulative layer  140  corresponding to the test end  143 . An uncovered area of the insulative layer  140  relative to the electrode structure  120  is as a reaction area  142 . Specifically, the electrode structure  120  may comprise non-metal material such as carbon. In some embodiments, the electrode structure  120  may comprise non-metal and metal materials, wherein the metal material may be gold, silver, palladium, platinum, nickel, copper, molybdenum, cobalt, chromium, zinc, tin, plumbum, or titanium. However the electrode structure  120  may only comprise metal material. 
         [0026]    Referring to  FIG. 2  and  FIG. 3 , the electrode structure  120  comprises a working electrode  129  and an auxiliary electrode  130 . The auxiliary electrode  130  comprises an extension portion  131 , a bent portion  137 , a first end  123 , and a second end  125 . The extension portion  130  is connected between the first end  123  and the bent portion  137 , and the bent portion  137  is connected to the second end  125 . The first end  123  and second  125  are disposed at the connection end  144  of the substrate  110 , and a detection signal can be sent out through the first end  123  and the second end  125 . As shown in  FIG. 3   a , the working electrode  129  is extended and forms a bent structure (the lower section of  FIG. 3   a ), wherein the extension portion  131  and the working electrode  129  form a space  136  with the bent portion  137  disposed therein. 
         [0027]    The bent portion  137  in  FIG. 3   a  comprises a first section  132 , a connecting section  133 , and a second section  134 , wherein the first section  132  is connected between the extension portion  131  and the connecting section  133 , and the second section  134  is connected between the second end  125  and the connecting section  133 . The first section  132 , the second section  134 , and the connecting section  133  form a U-shaped structure, having an opening toward the extension portion  131 . Specifically, the opening of the U-shaped structure may also face toward the test end  143  depending on design requirements. 
         [0028]    The detection process will be described below. First, the first end  123  and the second end  125  are provided with a small voltage. A sample (such as blood) can be injected through the opening  141  into the reaction area  142  and sequentially move through the working electrode  129 , the first section  132 , and the second section  134  along an injection direction B.  FIG. 6  illustrates a result of the cyclic voltammetry between the first end  123  and the second end  125 . Before the sample flows into the reaction area  142 , only a background current Ia can be measured. When the sample is underfilled, the working electrode  129  and the first section  132  are covered by the sample, and only the background current Ia is measured. When the sample covers the second section  134 , the first and the second sections  132  and  134  are electrically conducted by the sample, and the sample undergoes an electrochemical reaction. With the cyclic voltammetry applied to the electrochemical test strip, an oxidation-reduction current can be produced, such that, a total current Ib of the background current and the oxidation reduction can be measured. As fill or underfill of the sample in the reaction area  142  can be determined by measuring the electrical current, a more precise result of measurement can be achieved. 
         [0029]    In some embodiments, the electrochemical test strip can be used for determining the hematocrit ratio of a sample. As shown in  FIG. 7   a , the electronic signal curves show different pattern correspond to several samples having different hematocrit ratios. The sample has higher flowing speed with lower hematocrit ratio. Thus, the hematocrit ratio of the sample can be determined by measuring a time interval during the sample flowing from an electrode (first time T 1 ) to another electrode (second time T 2 ), wherein the second time T 2  is recoded when the slope of the electronic signal exceeds to a predetermined value (as shown in  FIG. 7   b ).  FIGS. 8   a  and  8   b  shows a method for testing a sample by an electrochemical test strip as shown in  FIGS. 9   a  and  9   b , wherein the electrochemical test strip includes a first electrode  210 , a second electrode  220  insulated from the first electrode  210 , and a third electrode  230  connected to the second electrode  220 . 
         [0030]    As shown in  FIGS. 8   a  and  8   b , first, an electrochemical test strip of  FIG. 9   a  or  9   b  is inserted into an instrument (step S 10 ). A first testing voltage is then applied between the second electrode  220  and the third electrode  230  for recoding a background current value therebetween (steps S 11 ˜S 12 ). Before the sample be injected into the strip, the instrument applies a second testing voltage between the first electrode  210  and the second electrode  220 , and the instrument recodes a first time T 1  when the sample flows through the first electrode  210  to the second electrode  220  (steps S 13 ˜S 14 ). After recoding the first time T 1 , the instrument applies a third testing voltage between the second electrode  220  and the third electrode  230  for recoding a current signal between the second electrode  220  and the third electrode  230  (step S 15 ). In an embodiment of the invention, the third testing voltage may be just as same volume as what the first testing voltage is, however, the third testing voltage can also be different volume with what the first testing voltage is. 
         [0031]    Specifically, when the current signal has a slope exceeding a predetermined value due to the sample flowing through the second electrode  220  to the third electrode  230 , a second time T 2  is recorded (step S  16 ). The hematocrit value of the sample can be calculated according to the time period T from the first time T 1  to the second time T 2 , wherein T=T 2 −T 1  (steps S 17 ˜S 18 ). 
         [0032]    Fill or underfill of the sample in the reaction area  142  may be also determined according to the difference between the current signal and the background current value (step  19 ). If the difference between the current signal and the background current value exceeds a threshold value, the instrument may change to apply a third testing voltage between the first electrode  210  and the second electrode  220  for measuring the glucose concentration of the sample, and the glucose concentration can also be calibrated by the hematocrit value (step  20 ). Otherwise, the instrument may further prompt the user to change the electrochemical test strip if the difference between the background current value and the current signal is less than a threshold value (step  21 ). 
         [0033]    Referring to  FIGS. 3   b  to  3   e , several different bent portions  137  are provided for increasing the impedance and the potential difference between the first section  132  and the second section  134 . Namely, the chemical driving force between the first section  132  and the second section  134  can be strengthened, and the oxidation reduction current can be increased, thus enhancing the sensitivity of underfill detection.  FIG. 3   b  is another embodiment of the bent portion  137 , wherein the shape of the connecting section  133  of the bent portion  137  is changed to increase the resistance thereof. As shown in  FIG. 3   b , the connecting section  133  is connected between the first section  132  and the second section  134  and forms a U-shaped structure, wherein the U-shaped structure has an opening toward the test end  143 . Specifically, the opening of the U-shaped structure may also face toward the extension portion  131 . 
         [0034]    Referring to  FIG. 3   c , another embodiment of a connecting section  133  is connected between the first section  132  and the second section  134 , and forms a hollow U-shaped structure, wherein the hollow U-shaped structure has an opening toward the test end  143 . However, the opening of the hollow U-shaped structure may also face toward the extension portion  133 . 
         [0035]    Referring to  FIG. 3   d , another embodiment of the connecting section  133  is connected between the first section  132  and the second section  134  and forms a comb-shaped structure C, wherein the comb-shaped structure C has an opening toward the extension portion  133 . However, the opening of the comb-shaped structure C may also face toward the test end  143 . 
         [0036]    In this embodiment, the comb-shaped structure C has right angled teeth. In some embodiments, the comb-shaped structure C may have rounded or acute angled teeth. The traces of the comb-shaped structure C may have a width, ranging from 0.1 to 1 mm. However, the traces may also respectively have different widths, to provide different densities thereof. Furthermore, the comb-shaped structure C may also have a spacing width between the traces, ranging from 0.1 to 1 mm. However, the comb-shaped structure C may respectively have different spacing widths between the traces, to provide different densities thereof. In some embodiments, the comb-shaped structure C can be produced by various kinds of processes, such as screen printing, laser ablation, sputtering, or electroless plating processes, but is not limited thereto. 
         [0037]    The underfill of the sample may also be detected by using different protruding sections, thus preventing erroneous detections. Referring to  FIG. 3   e , another embodiment of the connecting section  133  is connected between the first section  132  and the second section  134 , wherein the first section  132 , the second section  134 , and the connecting section  133  form a U-shaped structure. The bent portion  137  further comprises at least one protruding section  135 , connected to the second section  134  and extended toward the test end  143 . 
         [0038]    Specifically, the shape of the protruding section  135  is not only limited to  FIG. 3   e , but can also be integrated into the aforesaid embodiments. As shown in  FIG. 4 , the protruding section  135  can also be connected to the comb-shaped structure C and extended toward the test end  143 . In some embodiments, the opening of the comb-shaped structure C may also face toward the test end  143 . 
         [0039]    In some embodiments, the opening  141  and the injection direction B are not perpendicular to the test end  143 . As shown in  FIG. 5   a , the sample can be injected from a lateral side into the strip. In  FIG. 5   b , the sample may also be injected along an oblique direction into the strip. 
         [0040]    In some embodiments, the electrochemical test strip may further comprises a metal layer between the electrode structure  120  and the substrate  110 , wherein the metal layer may include gold, silver, palladium, platinum, nickel, copper, molybdenum, cobalt, chromium, zinc, tin, plumbum, or titanium. 
         [0041]    In some embodiments, the working electrode  129 , the first section  132 , and the second section  134  of the electrochemical test strip ( FIGS. 3   a - 3   d ) may respectively correspond to the first electrode  210 , the second electrode  220 , and third electrode  230  (the  9   a,  and  9   b ) for the underfill detection and for determining the hematocrit value and the glucose concentration of the sample. 
         [0042]    The invention provides an electrochemical test strip comprising an auxiliary electrode with a bent portion to increase the resistance thereof. As the electrochemical test strip does not require different materials to produce electrodes (the electrode structure can be produced by the same material), the cost thereof can be effectively reduced. 
         [0043]    While the disclosure has been described by way of example and in terms of the preferred embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.