DETERMINATION METHOD AND ELECTROCHEMICAL DEVICE FOR ELECTROCHEMICAL TEST STRIP

An method for determining sample volume sufficiency of an electrochemical test strip having a reaction portion and two electrodes, wherein parts of the two electrodes are respectively disposed on the reaction portion, includes: placing a sample on the reaction portion; applying a first voltage to the sample for a first time period to drive a first current between two electrodes; applying a second voltage to the sample for a second time period to drive a second current between the two electrodes; calculating an absolute value of the ratio of a value of the first current to a value of the second current as a sample volume index; and comparing the sample volume index with a predetermined index range to determine if a volume of the sample is insufficient to measure accurately at least one characteristic of the sample.

CROSS REFERENCE TO RELATED APPLICATIONS

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 104131375 filed in Taiwan, Republic of China on Sep. 23, 2015, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of Invention

The invention relates to a method and device for determining sample volume sufficiency of a test strip and, in particular, to a method and device for determining sample volume sufficiency of an electrochemical test strip.

Related Art

Electrochemical analysis method is commonly used in the substance determination or concentration determination. It develops into a test-and-know sensor due to its rapid and convenient determination, and it is commonly a testing strip. The electrochemical analysis method can be applied to many fields, such as environment, agriculture, medicine or biochemistry. In environmental determination, the electrochemical analysis method can be used for detecting heavy metal contaminants such as mercury (Hg), lead (Pb) and cadmium (Cd), and it is a heavy metal determination method with high sensitivity and requiring low concentration. In agriculture, the electrochemical analysis method has developed into a simple and inexpensive sensor with which farmers can sample soil and water in fields for monitoring the heavy metal contents in the cultivated soil and the irrigation water anytime and anywhere. Moreover, it may be used for detecting antibiotic or pesticide residues in food, fruits or vegetables. In medicine, the electrochemical analysis method succeeds in applying to the test strip as the domestic blood-glucose meter.

The test strip described in the disclosure is designed with the principle of electrochemical detection technology, and it is called an electrochemical test strip. In general, the test strip has two electrodes and a space for accommodating a sample (reaction portion) so the sample and the reagent on the electrode surface (or the reagent partially contacting the electrodes) can generate corresponding electrochemical reaction, and thus a current value depending on the concentration of the sample can be detected. In other words, the concentration of the sample can be deduced from the current value. The sample changes with the application field of the testing strip. For example, the sample may be soil or water from the environment, an ingredient, a fruit, a vegetable, or a blood sample for blood glucose detection.

However, the conventional electrochemical testing strip does not have high threshold for the trigger current value generated by the electrochemical reaction, so the sensing procedure easily starts soon after the switch is turned on but an determination for the abnormal condition may not be effectively executed before the sensing procedure (unless the test strip is fully damaged or seriously defective). Therefore, the user may obtain sensing data generated by the abnormal electrochemical test strip. Further, when the user operates the measurement device having an electrochemical test strip, the sample may not fully cover two electrodes (reaction portion) while injected into the electrochemical test strip due to unfamiliar operation or other factors, for example a thick sample. Therefore, the detected value may have a deviation. A conventional method for determining sample volume sufficiency determines whether the sample exists between two electrodes. If not, a closed circuit cannot form for conduction. However, this method cannot find out the distribution of the sample on the electrodes (reaction portion) so the abnormal condition of the sample injection cannot be effectively detected and causes a mistake result which results in a misjudgment by a user. Especially, when the test strip is applied to the medicine field, for example a blood glucose test strip, the abnormal reading result may be dangerous to the user's health and safety.

Currently, the ex-factory electrochemical test strip lacks a mechanism or a design for effectively detecting abnormal conditions, such as a design for detecting resistance of the circuit of the test strip or detecting the enzyme content of the reagent. Therefore, not only the value is unable to be shown completely, but the user is not aware of the abnormal condition of the test strip and continues using the abnormal test strip.

SUMMARY OF THE INVENTION

An aspect of the disclosure is to provide a method and device for determining the sample volume sufficiency of an electrochemical test strip while using the electrochemical test strip to avoid a misjudgment by a user.

A method for determining sample volume sufficiency of an electrochemical test strip having a reaction portion and two electrodes, wherein parts of the two electrodes are respectively disposed on the reaction portion, includes the steps of: placing a sample on the reaction portion of the electrochemical test strip; applying a first voltage to the sample for a first time period to drive a first current between the two electrodes; applying a second voltage to the sample for a second time period to drive a second current between the two electrodes; calculating an absolute value of the ratio of a value of the first current to a value of the second current as a sample volume index; and comparing the sample volume index with a predetermined index range to determine if a volume of the sample is insufficient to measure accurately at least one characteristic of the sample; wherein the first voltage and the second voltage have opposite directions.

In one embodiment, the volume of the sample is determined to be insufficient as the value of the sample volume index is out of the predetermined index range, and the volume of the sample is determined to be sufficient as the value of the sample volume index is within the predetermined index range.

In one embodiment, the method further includes the steps of: sending a normality message as the value of the sample volume index is within the predetermined index range; and sending an error signal as the value of the sample volume index is out of the predetermined index range.

In one embodiment, a positive correlation exists between the predetermined index range and the ratio of a first area to a second area, and a negative correlation exists between the predetermined index range and the ratio of the square root of the first time period to the square root of the second time period, wherein the first area indicates the area of the part of one electrode, and the second area indicates the area of the part of the other electrode.

In one embodiment, the predetermined index range is calculated based on the following equation:

wherein a first area A1indicates the area of the part of one electrode, a second area A2indicates the area of the part of the other electrode, t1indicates the first time period, t2indicates the second time period, and C indicates a tolerance ratio of the electrochemical test strip.

In one embodiment, the first time period and the second time period are between 0.5 seconds and 5 seconds.

In one embodiment, the predetermined index range is between 1.02 and 2.2.

In one embodiment, an absolute value of the first voltage is equal to that of the second voltage and between 0.1 volt and 1 volt.

In one embodiment, the method further includes the step of interrupting power for a third time period after the step of placing the sample on the reaction portion of the electrochemical test strip.

In one embodiment, the first time period is equal to the second time period.

In one embodiment, the first time period is not equal to the second time period.

An electrochemical device for determining sample volume sufficiency of an electrochemical test strip having a reaction portion and two electrodes, wherein parts of the two electrodes are respectively disposed on the reaction portion, includes a strip accommodating region, a power supply unit, a current sensing unit, and a processing unit. The strip accommodating region is used for accommodating the electrochemical test strip. The power supply unit applies a first voltage to a sample for a first time period to drive a first current between the two electrodes, and applies a second voltage to the sample for a second time period to drive a second current between the two electrodes. The current sensing unit is used for obtaining a value of the first current and a value of the second current. The processing unit is used for calculating an absolute value of the ratio of the value of the first current to the value of the second current as a sample volume index, and for comparing the sample volume index with a predetermined index range to determine if a volume of the sample is insufficient to measure accurately at least one characteristic of the sample. The first voltage and the second voltage have opposite directions.

In one embodiment, the volume of the sample is determined to be insufficient as the value of the sample volume index is out of the predetermined index range, and the volume of the sample is determined to be sufficient as the value of the sample volume index is within the predetermined index range.

In one embodiment, the processing unit sends a normality message as the value of the sample volume index is within the predetermined index range, and sends an error signal as the value of the sample volume index is out of the predetermined index range.

In one embodiment, a positive correlation exists between the predetermined index range and the ratio of a first area to a second area, and a negative correlation exists between the predetermined index range and the ratio of the square root of the first time period to the square root of the second time period, wherein the first area indicates the area of the part of one electrode, and the second area indicates the area of the part of the other electrode.

In one embodiment, the predetermined index range is calculated based on the following equation:

wherein a first area A1indicates the area of the part of one electrode, a second area A2indicates the area of the part of the other electrode, t1indicates the first time period, t2indicates the second time period, and C indicates a tolerance ratio of the electrochemical test strip.

In one embodiment, the first time period and the second time period are between 0.5 seconds and 5 seconds.

In one embodiment, the predetermined index range is between 1.02 and 2.2.

In one embodiment, an absolute value of the first voltage is equal to that of the second voltage and between 0.1 volt and 1 volt.

In one embodiment, before the power supply unit applies the first voltage, power is interrupted for a third time period.

In one embodiment, the first time period is equal to the second time period.

In one embodiment, the first time period is not equal to the second time period.

As mentioned above, the method and device for determining sample volume sufficiency of an electrochemical test strip use the sample to generate currents having opposite directions by the electrochemical reaction. Namely currents are driven from the second electrode to the first electrode and from the first electrode to the second electrode. As a result, the first current value and the second current value are obtained. The absolute value of the ratio of the first current value to the second current value is regarded as the sample volume index, and then the value of the sample volume index is compared with the predetermined index range. The sample volume sufficiency is determined by comparing the value of the sample volume index with the predetermined index range to avoid a misjudgment by a user. The determination method of the disclosure does not need to actually calculate the areas covered by the sample on the first electrode and the second electrode, but defines the sample volume index and the predetermined index range instead. It can omit complex steps of calculating the areas covered by the sample on the first electrode and second electrode, and as accurate as possible determine whether the sample volume is sufficient or not.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.

In this embodiment, the electrochemical testing strip employs the electrochemical determination technology, and directly called the “testing strip” hereinafter for convenient illustration. Furthermore, the testing strip of this embodiment can be applied to many fields, such as environment determination, food determination, or medical blood-glucose detection, which are not limited thereto. For the convenient understanding, the following embodiments take the electrochemical testing strip applied to the blood-glucose detection as examples for the illustration.

FIG. 1is a flow chart of the steps of the method for determining the sample volume sufficiency of an electrochemical test strip according to an embodiment. Referring toFIG. 1, the above mentioned method is abbreviated to the determination method in the embodiment for convenient illustration. The determination method includes the following steps of: placing a sample on the reaction portion of the electrochemical test strip (step S20); applying a first voltage to the sample for a first time period to drive a first current between the two electrodes (step S30); applying a second voltage to the sample for a second time period to drive a second current between the two electrodes (step S40); calculating an absolute value of the ratio of a value of the first current to a value of the second current as a sample volume index (step S50); comparing the sample volume index with a predetermined index range to determine if a volume of the sample is insufficient to measure accurately at least one characteristic of the sample (step S60); sending an insufficient filling message or an error signal as the value of the sample volume index is out of the predetermined index range (step S62); and sending a normality message as the value of the sample volume index is within the predetermined index range (step S64). The first time period and the second time period may be uninterrupted.

First, provide an electrochemical test strip1.FIG. 2is an exploded view of the electrochemical test strip according to an embodiment. Referring toFIG. 2, the electrochemical test strip1of the embodiment may include an upper cover layer11, an interlayer12, a substrate layer13, a first electrode14, and a second electrode15. The substrate layer13is an electrical insulation substrate. The material of the substrate layer13may be polyvinyl chloride, polystyrene, polyester, polycarbonate, polyether, polyethylene, polypropylene, polyethylene terephthalate, silicon dioxide, or aluminium oxide, but it is not limited thereto. In the embodiment, the materials of the first electrode14and the second electrode15may be carbon, metal, alloy, or other electrically conductive materials, and the electrodes have designate patterns printed by the screen printing method. Moreover, relative positions, shapes and sizes of the first electrode14and the second electrode15are not limited. One end of the substrate layer13has a reaction portion131, and a part of the first electrode14and a part of the second electrode15are disposed on or cover the reaction portion131. The reaction portion131of the embodiment contains a chemical reagent which at least has an electron transfer substance and may have other substances: an enzyme that reacts with the sensing object, a macromolecule, a stabilizer or the like.

In detail, the interlayer12is disposed on the substrate layer13and has an injection portion121(an opening) corresponding to the reaction portion131. Thus, a space for accommodating the sample may be defined by combining the interlayer12with the substrate layer13if the interlayer12is thick enough. Therefore, in the step S20, the user can place or inject the sample through the injection portion121of the interlayer12. In the following embodiments, the sample is liquid whole blood for example. After entering the injection portion121of the interlayer12, the blood (the sample) may cover the parts of the first electrode14and the second electrode15on the reaction portion131. When the first electrode14and the second electrode15contact the sample, the subsequent electrochemical reaction occurs. The determination method of the embodiment can determine the distribution of the sample on the first electrode14and the second electrode15, namely the sample volume sufficiency.

Moreover, the details of each step in the embodiment will be more apparent from the following illustration with an electrochemical device2. That is to say, the electrochemical device2may be used to execute the determination method of the embodiment for determining sample volume sufficiency of the electrochemical test strip1. The electrochemical device2may be a detecting apparatus for the electrochemical test strip1, for example a blood glucose meter.FIG. 3is a schematic block diagram of the electrochemical device applied to the determination method shown inFIG. 1. Referring toFIGS. 1 to 3, the electrochemical device2of the embodiment includes a strip accommodating region21, a power supply unit22, a current sensing unit23, and a processing unit24. The strip accommodating region21is used for accommodating the disposable electrochemical test strip1, and the electrochemical test strip1is used for receiving a sample.

Providing the electrochemical test strip1may indicate that the user put the disposable electrochemical test strip1into the strip accommodating region21. Then, in the step S20, the sample is injected at the injection portion121of the electrochemical test strip1and the reaction portion131allows the injection of the sample. The reaction portion131of the electrochemical test strip1receives the sample.

Preferably, the determination method may further include the step S22of interrupting power for a third time period after placing the sample and before the step S30that the power supply unit22applies the first voltage V1. That is to say, the power supply unit22does not operate and just waits for 0.1 seconds to 2 seconds (the third time period) so that there is enough time for the sample filling the reaction portion131and contacting the chemical reagent in the reaction portion131. Typically, the sample is sufficient to cover the reaction portion131appropriately so as to measure accurately at least one characteristic of the sample by the electrochemical device2. At this time, the sample appropriately or fully covers the parts of the first electrode14and the second electrode15in the reaction portion131. After that, a voltage applied between the first electrode14and the second electrode15can cause the electrochemical reaction of the sample.FIG. 4is a schematic diagram showing the sample volume sufficiency of the electrochemical test strip inFIG. 3. As shown inFIG. 4, it shows one of the normal filling conditions of the sample as the sample (indicated by oblique lines inFIG. 4) fully covers the reaction portion131. Preferably, the third time period may be 0.5 seconds to 2 seconds that can be adjusted according to the sample property. For example, it takes more time for the reaction portion131to be filled with a thick sample, so the third time period may be 2 seconds at this case. However, the third time period may be 0.5 seconds if the sample has general concentration.

Then, proceed to the step S30and the step S40. The step S30is to apply a first voltage V1to the sample for a first time period t1to drive a first current (positive charge), for example, from the second electrode15to the first electrode14and thereby to obtain a first current value. At this case, the second electrode15is as a working electrode. The step S40is to apply a second voltage V2to the sample for a second time period t2to drive a second current, for example, from the first electrode14to the second electrode15and thereby to obtain a second current value. In this case, the first electrode14is as a working electrode. Moreover, the first voltage V1and the second voltage V2have opposite directions. For example, in the embodiment, the first voltage V1is a positive voltage, and the second voltage V2is a negative voltage. In some embodiments, the directions of the first voltage V1and the second voltage V2can be converse.

Preferably, the absolute values of the first voltage V1and the second voltage V2are equal and between 0.1 volt and 1 volt. In the embodiment, the first voltage V1is 0.3V, and the second voltage V2is −0.3V. Generally, after the current sensing unit23obtains the first current value and the second current value, the areas covered by the sample on the second electrode15and the first electrode14can be respectively calculated with the Cottrell equation depending on the first current value and the second current value. The Cottrell equation is:

i indicates current value (amp), N indicates the number of electrons when a closed circuit forms, F indicates Faraday constant (96,485 C/mol), A indicates the area of the electrode (cm2), cj0indicates the initial concentration of the reducible species j (mol/cm3), Djindicates the diffusion coefficient for species j (cm2/s), and t indicates time (second).

However, the determination method of the disclosure does not need to actually calculate the areas covered by the sample on the first electrode14and the second electrode15, but defines the sample volume index and the predetermined index range instead (the details are illustrated below). It can omit the complex steps of calculating the areas covered by the sample on the first electrode14and the second electrode15and may not limit that the working electrode is the first electrode14or the second electrode15.

The detection of the first current and the second current may refer toFIG. 5.FIG. 5is a schematic diagram showing the currents driven by taking the second electrode15as the working electrode and then taking the first electrode14as the working electrode. In detail, the power supply unit22may apply a positive voltage to the sample to make the voltage level of the first electrode14less than that of the second electrode15. Thus, the first current is driven from the second electrode15to the first electrode14. Then the power supply unit22may apply a negative voltage to the sample to make the voltage level of the second electrode15less than that of the first electrode14. Thus, the second current is driven from the first electrode14to the second electrode15. It can be seen fromFIG. 5that the stable value (dotted circle) of the first current detected from “the sufficient sample” greatly differs from that detected from “the insufficient sample”, and the stable values of the second currents detected from the sufficient sample and the insufficient sample are similar. It infers that the insufficient sample does not fully cover the second electrode15as the working electrode driving the first current, and the possible distribution may be like the sample G-1inFIG. 7.

Then, in the step S50, a sample volume index is obtained by calculating the absolute value of the ratio of the first current value to the second current value.

The step S60is to compare the sample volume index with the predetermined index range. The predetermined index range of the embodiment is obtained according to the Cottrell equation, more specifically, by calculating the areas of the first electrode14and the second electrode15, the time periods of applying the first voltage V1and the second voltage V2, and a tolerance ratio. For example, if the part of the first electrode14has a first area A1, the part of the second electrode15has a second area A2, the first voltage V1is applied for a first time period t1, the second voltage V2is applied for a second time period t2, and the electrochemical test strip1has a tolerance ratio C, the predetermined index range may be calculated based on the following equation:

As shown inFIG. 4, the first area A1of the embodiment indicates the area of the first electrode14located in the reaction portion131, and the second area A2indicates the area of the second electrode15located in the reaction portion131. Because the areas of the first electrode14and the second electrode15of the electrochemical test strips1with the same standard are constant, the ratio of the first area A1to the second area A2is also a constant value. Further, the time periods of applying the first voltage V1and the second voltage V2may be set equal, so the ratio of the square root of the first time period t1to the second time period t2is also a constant value. Preferably, the first time period t1and the second time period t2may be between 0.5 seconds and 5 seconds. Namely, in the step S30, the periods of applying the first voltage V1and the second voltage V2may be between 0.5 seconds and 5 seconds. In the embodiment, the first time period t1and the second time period t2are both 2 seconds for example. In the present disclosure, the first time period t1may be equal or not equal to the second time period t2. The predetermined index range may be defined based on the above equation for further determination in the following step.

The tolerance ratio C of the electrochemical test strip1may vary with the sensitivity of the electrochemical test strip1. For example, if the area covered by the sample of the first electrode14and the second electrode15is 60% and the accuracy of the electrochemical device2for detecting glucose concentration of the sample is still kept, the tolerance ratio C is 40. In the embodiment, the ratio of the first area A1to the second area A2is 1.5. If the absolute values of the first voltage V1and the second voltage V2are equal and the applying time periods are set equal, the predetermined index range as the following result can be obtained with the above equation:

As a result, the predetermined index range of the embodiment is between 1.07 and 2.10. Moreover, the above mentioned equation for calculating the predetermined index range shows that a positive correlation exists between the predetermined index range and the ratio of the first area A1to the second area A2, and a negative correlation exists between the predetermined index range and the ratio of the square root of the first time period t1to the square root of the second time period t2. In some embodiments of the present invention, the predetermined index range is between 1.02 and 2.2 as the tolerance ratio C is 46.67.

After the above description defines the predetermined index range, the predetermined index range of the embodiment is between 1.02 and 2.2 for example. The predetermined index range may be stored in the processing unit24in advance, and the processing unit24executes the step S60as shown inFIG. 1. The processing unit24compares the obtained sample volume index with the predetermined index range to determine if a volume of the sample is insufficient to measure accurately at least one characteristic of the sample, e.g. the concentration of glucose in the sample of whole blood. More specifically, the processing unit24determines whether the value of the sample volume index (i.e. the absolute value of the ratio of the first current value to the second current value) is within the predetermined index range. If the result is “no”, namely the value of the sample volume index is out of the predetermined index range, the step S62is executed and the processing unit24determines that the volume of the sample is insufficient. In other words, the amount of the sample introduced into the reaction portion of the test strip is inadequate for accurate measurement. In the step S62in this embodiment, the processing unit24may send an insufficient filling message or an error signal optionally to notify the user that a new electrochemical test strip should be provided and the processes of the determination method should be restarted. If the result is “yes”, namely the value of the sample volume index is within the predetermined index range, the step S64is executed and the processing unit24determines that the volume of the sample is sufficient. In other words, the amount of the sample introduced into the reaction portion of the test strip is adequate for accurate measurement. In the step S64in this embodiment, the processing unit24may send a normality message optionally and then proceed to the following measurement for some biological characteristics of the sample.

The step S60to the step S64are illustrated below with the experimental results shown inFIG. 6A.FIGS. 6A and 6Bare schematic diagrams showing the results of sample volume index obtained by placing different samples on the electrochemical test strips. Table 1 shows the details of samples A to G shown inFIGS. 6A and 6B.

As to sample E and sample F shown in Table 1, GCS (Glucose Control Solution) indicates a control solution used for examining blood glucose meter. Low GCS indicates a low concentration of glucose in the control solution, and this experimental example uses a control solution having a glucose concentration of 30-50 mg/dL. High GCS indicates a high concentration of glucose in the control solution, and this experimental example uses a control solution having a glucose concentration of 280-420 mg/dL. Referring toFIG. 6Aand Table 1, it can be seen fromFIG. 6Athat the values of the sample volume index (i.e. the absolute values of the ratios of the first current value to the second current value) obtained from samples A-F are all within the predetermined index range, so the processing unit24determines the samples A-F with sufficient quantity and sends a normality massage at this time. However, the value of the sample volume index obtained from sample G is out of the predetermined index range, so the processing unit24determines the sample G has inadequate volume and sends an insufficient filling message or an error signal. The above description shows that the determination method is not affected by different glucose concentration or HCT percentage in the sample and may accurately determine whether the volume of the sample introduced into the reaction portion of the electrochemical test strip1is insufficient. Referring toFIG. 7, it is a schematic diagram showing the insufficient sample filling conditions of the electrochemical test strip according to an embodiment. After sample G with insufficient volume shown in Table 1 flows into the reaction portion of the electrochemical test strip1, its distribution may be like the distribution (i.e. shaded region in the drawing) of sample G-1, sample G-2or sample G-3as shown inFIG. 7. In some embodiments, assuming that the tolerance ratio is 40%, the obtained value of the sample volume index (i.e. the absolute value of the ratio of the first current value to the second current value) will be out of the predetermined index range as shown inFIG. 6Aif the area covered by the sample of the first area A1and the second area A2is less than 60%.

Moreover, samples with different temperatures also do not influence the accuracy of the determination method. Referring toFIG. 6B, it shows the sample volume indexes of samples A to F (the details refer to Table 1) at 10° C., 23° C., and 40° C. which are injected into the electrochemical test strip1. These sample volume indexes are obtained by executing the step S30and the step S40, and they are all within the predetermined index range. Therefore, the temperature of the sample does not affect the determination results of sample volume sufficiency as shown inFIG. 6B.

The tolerance ratio may be obtained by experiment. Referring toFIGS. 8A to 8C, they are schematic diagrams showing the results of deviation value obtained by placing the same sample with different volumes respectively on the electrochemical test strips for detecting blood glucose concentration, and comparing the results with the blood glucose concentration of the sample detected by the standard equipment (YSI).FIGS. 8A to 8Conly shows the experimental results with deviation values within 10% in comparison with the result obtained by the standard equipment (YSI). As shown inFIGS. 8A to 8C, when the sample volume is less than 0.36 μL, the deviation value from the standard equipment (YSI) is greater than 10%. It infers that the accuracy of detecting blood glucose concentration reduces if the sample volume is less than 0.36 μL, which should be excluded from the normal reading range. In other words, the reaction portion131of the electrochemical test strip needs the sample of about 0.6 μL to be fully filled, and the detection fails if the sample volume is less than 0.36 μL. Accordingly, the determination tolerance ratio of the embodiment may be determined as 40%.

In another embodiment, the directions of first voltage and the second voltage can be converse. For example, the negative voltage may be applied to the sample first to drive a first current from the first electrode14to the second electrode15, and then the positive voltage is applied to the sample to drive a second current from the second electrode15to the first electrode14. The first and second currents of this embodiment and those of the above mentioned embodiment have opposite directions. However, it does not affect the absolute value of the ratio of the first current value to the second current value.

Moreover, another electrochemical device for the electrochemical test strip is provided. The electrochemical device includes a strip accommodating region, a power supply unit, a current sensing unit, and a processing unit. The strip accommodating region is used for accommodating an electrochemical test strip having a first electrode and a second electrode, and a part of the first electrode and a part of the second electrode are disposed at a reaction portion. The power supply unit applies a first voltage to the sample for a first time period to drive a first current from the second electrode to the first electrode, and applies a second voltage to the sample for a second time period to drive a second current from the first electrode to the second electrode. The current sensing unit is used for obtaining a first current value and a second current value. The processing unit is used for calculating an absolute value of the ratio of the first current value to the second current value as a sample volume index, and for comparing the sample volume index with a predetermined index range and then determining if the sample volume is insufficient to measure accurately at least one characteristic of the sample. Because the detailed elements of this electrochemical device and its executing actuation may refer to the electrochemical device2in the first embodiment, the related description is omitted here.

Similarly, the terms first and second in the disclosure are named for clear illustration but not for limitation.

In summary, the method and device for determining sample volume sufficiency of an electrochemical test strip use the sample to generate currents having opposite directions by the electrochemical reaction. Namely currents are driven from the second electrode to the first electrode and from the first electrode to the second electrode. As a result, the first current value and the second current value are obtained. The absolute value of the ratio of the first current value to the second current value is regarded as the sample volume index, and then the value of the sample volume index is compared with the predetermined index range. The sample volume sufficiency is determined by comparing the value of the sample volume index with the predetermined index range to avoid a misjudgment by a user. The determination method of the disclosure does not need to actually calculate the areas covered by the sample on the first electrode and the second electrode, but defines the sample volume index and the predetermined index range instead. It can omit complex steps of calculating the areas covered by the sample on the first electrode and second electrode, and as accurate as possible determine whether the sample volume is sufficient or not.