Patent Application
20150276650
1. Field of the Invention
The present disclosure relates to a method for fast measurement of a specimen concentration, particularly a method accelerating equilibrium of chemical reactions.
2. Descriptions of the Related Art
The health of modern people with varied dietary habits and life styles has been widely influenced by chronic diseases, particularly high blood sugar, hypertension and hyperlipidemia, all of which are early signs of chronic diseases. Accordingly, how to measure physiological data routinely has become common sense of modern people.
As the major tool to measure physiological data currently, the electrochemical sensor system on the basis with an enzymatic amperometric method is used to test analytes in a specimen such as glucose level or cholesterol level. The electrochemical sensor system is based on the theory that an enzymatic reagent with a specific ingredient reacts with an analyte in a specimen, for example, glucose oxidase reacts with glucose in a specimen rather than other carbohydrates or cholesterol oxidase reacts with cholesterol in a specimen without interference of other substances. According to this characteristic, a measuring voltage is applied on the electrode to generate an electrochemical current (also known as Cottrell current) and calculate a concentration of the analyte in the specimen by referring to the Cottrell equation.
In the above descriptions, a sensing strip should be provided with an electrode test region consisting of two parallel electrodes (not shown in figures), i.e., a first conductive electrode and a second conductive electrode, on which an enzymatic reagent with a specific ingredient for development of chemical reactions between the enzymatic reagent and a specimen is coated. As shown in
However, other substances held in an actual specimen such as uric acid or vitamin C contributes to a non-faradic current, N (as shown in
Accordingly, how to effectively reduce time in measuring a specimen concentration deserves to be studied by the persons skilled in the art.
The present disclosure presents a method for fast measurement of a specimen concentration in a short time. The method needs a sensing strip with an electrode test region on which an enzymatic reagent with a specific ingredient is coated and comprises steps as follows:
Step 1: Place a specimen on the electrode test region of the sensing strip;
Step 2: Apply a high voltage on the electrode test region for a period in order to accelerate equilibrium of a non-faradic current;
Step 3: Apply a measuring voltage less than the high voltage or the same as the high voltage in Step 2 on the electrode test region to generate an electrochemical current finally reaching a steady current, which implies electrochemical current equilibrated with the non-faradic current disappearing, and measure the steady current for calculating a specimen concentration.
In the present disclosure, the high voltage in Step 2 is kept between the lowest potential to create redox reaction on the specimen and 5 Volt.
In the present disclosure, the high voltage in Step 2 is applied for 0.01 second to 1 second.
In the present disclosure, the measuring voltage in Step 3 is kept between 0.05 Volt and 0.42 Volt (oxidation voltage).
In the present disclosure, a total current including faradic and non-faradic currents generated on the electrode test region reaches a steady current in a short time to reach a steady current, the short time is 3 seconds or below 3 seconds.
In the present disclosure, the specimen can be glucose (blood sugar), uric acid or cholesterol so that an enzymatic reagent coated on the electrode test region has a distinct ingredient.
The present disclosure is beneficial to measurement of a specimen concentration completed in a short time by means of a high voltage applied for fast equilibrium of electrochemical current and consuming of any reaction with non-faradic current.
The technical measures and effects of the present disclosure are presented in preferred embodiments and accompanying drawings for descriptions of above purposes.
Please refer to
As shown in the figures, the method for fast measurement of a specimen concentration needs at least a sensing strip (not shown in figures) with an electrode test region which includes, without limitation, a specific enzymatic reagent coating by referring to a specimen to be measured. For example, the enzymatic reagent can be glucose oxidase (urate oxidase or cholesterol oxidase) when a specimen is glucose (uric acid or cholesterol). No matter which ingredient is included in the reagent, the sensing strip is provided with an electrode test region on its surface. The present disclosure described with a specimen such as glucose herein includes, without limitation, a method for fast measurement of a specimen concentration comprises steps as follows:
Step 1: Place a specimen on the electrode test region of the sensing strip (S1);
Step 2: Apply a high voltage on the electrode test region for a period in order to accelerate equilibrium of a non-faradic current (as shown in
Step 3: Apply a measuring voltage less than the high voltage or the same as the high voltage in Step 2 on the electrode test region to generate an electrochemical current finally reaching a steady current, which implies electrochemical current equilibrated with the non-faradic current disappearing, and measure the steady current for calculating a specimen concentration (as shown in
Glucose+GOD(ox)->Gluconic acid+GOD(red);
GOD(red)+Med(ox)->GOD(ox)+Med(re)+2H+; and
2Med(re)->2Med(ox)+2e−
In the redox reactions, GOD(OX), the oxidation state of glucose oxidase (GOD) in normal status, reacts with glucose and is reduced to GOD(red), the reducing state. With electrons transferred to Mediator (Med(ox)) concurrently, Mediator (Med) is oxidized for generation of a reaction current, i.e., faradic current, F. However, other substance in the specimen such as uric acid or vitamin C, each of which interferes in a voltage applied on the electrode and induces a current, i.e., non-faradic current, N. In Step 2, the high voltage is intended to accelerate equilibrium of the reaction, consuming the non-faradic current quickly.
Including a faradic current and a non-faradic current initially, a total current generated in the electrode test region and finally becoming a steady current in Step 3 implies the electrochemical current equilibrated with non-faradic current disappearing. Therefore, the measured steady current is the faradic current, F, which is also known as Cottrell current and substituted into the following equation to calculate a specimen concentration.
i(t)=K·n·F·A·C·D0.5·t−0.5
where the definitions of all parameters are shown as follows. (a) i: measured instantaneous current or faradic current; (b) K: constant; (c) n: count of electrons transferred; (d) F: Faraday constant; (e) A: electrode test region's surface area; (f) C: specimen concentration; (g) D: reagent's diffusion coefficient; (h) t: time for a default voltage applied on the electrode test region. As mentioned above, a specimen concentration is calculated with the measured faradic current and other data substituted into the equation.
In the present disclosure, the high voltage applied in Step 2 for one period is kept between an oxidation potential and 5 Volt. As shown in
In the present disclosure, the measuring voltage which is less than the high voltage or the same as the high voltage in Step 2 and applied on the electrode test region in Step 3 initially should be kept at a normal level between 0.05 Volt and 0.42 Volt later.
Based on experimental data, the statistics presented hereinafter are used to explain the present disclosure is effective in keeping a steady current compared with a conventional method. In experiments, the glucose solutions were classified into three specimens with distinct concentration values, 50 mg/dl (specimen 1), 85 mg/dl (specimen 2) and 180 mg/dl (specimen 3), and tested in a conventional method as well as the method in the present disclosure. According to the conventional method, the three specimens were tested 5 times each for measurement of current values: no voltage applied from T=0 to T=1 sec. (time=0 to time=1 sec.); 0.42 Volt applied from T=1 sec to T=3 sec. According to the method of the present disclosure, the three specimens were tested 5 times each for measurement of current values: a high voltage of 2 Volt applied from T=0 to T=0.1 sec; a lower voltage of 0.42 Volt applied from T=0.1 sec to T=3 sec. The current values were measured at T=0.5 sec, T=1.0 sec, T=2.0 sec and T=3.0 sec in both types of experiments.
The above descriptions are preferred embodiments which do not limit the scope of a method for fast measurement of a specimen concentration; any equivalent change or improvement without departing from spirit of the present disclosure should be incorporated in claims herein.
