Method for detecting an analyte contained in an individual's bodily fluid and corresponding device

Abstract

Method for detecting an analyte using a biochemical sensor and corresponding device. The invention relates to a method for detecting an analyte using a biochemical sensor (2), the sensor consisting of working electrodes coated with a reactive material capable of reacting with the analyte, the working electrodes being in contact with an interstitial fluid in which the analyte is located, the method comprising the following steps: a) supplying voltage to the working electrodes during a second time period following a first time period during which the working electrodes are not supplied with voltage while being in contact with the interstitial fluid; b) measuring an intensity I(t) at each working electrode during the second time period; c) interrupting the supply of voltage to the working electrode at the end of the second time period;d) treatment comprising obtaining a first value P=I(t1) corresponding to the first peak of I(t) during the second time period and obtaining a second value F=I(t2) corresponding to a point F of I(t) from which I(t) exhibits a decrease of less than 20%, the intensity I(t) between P inclusive and F inclusive being characteristic of a quantity of analyte put into reaction during the first time period.;

Description

Title of the invention: Method for detecting an analyte contained in a bodily fluid of an individual and corresponding device technical field

[0001] The invention relates to a method and device for detecting an analyte contained in a body fluid of an individual, and preferably glucose contained in the interstitial fluid of an individual. The invention relates in particular to the detection of such an analyte by means of a biochemical sensor, preferably an enzymatic one, the sensor consisting of electrodes coated with a reactive material capable of reacting with the analyte. STATE OF THE ART

[0002] It is known to measure the concentration of an analyte using an electrochemical sensor. Such a sensor converts information about a chemical reaction into an electrical signal. As such, the sensor comprises at least one working electrode coated with a material capable of reacting with the analyte.

[0003] A known technique for measuring the quantity of analyte is amperometry, a technique in which the working electrode is powered to cause a chemical reaction at the working electrode, the current flowing through the electrode is measured and depends on the concentration of analyte.

[0004] Amperometric measurement must be able to measure the quantity of analyte with the greatest possible precision, particularly when it comes to measuring glucose in diabetic users.

[0005] Traditional glucose sensors are based on the oxidation of glucose by oxygen in the presence of glucose oxidase (GOx) coating a working electrode. Such a sensor is described, for example, in the document Clark et al. (Clark Jr, LC, & Lyons, C., 1962, Electrode Systems for continuons monitoring in cardiovascular surgery, Annals of the New York Academy of Sciences, 102(1), 29-45).

[0006] This type of sensor has undergone several developments but none has made it possible to measure the analyte with high precision, particularly when it comes to measuring the glucose level of a diabetic individual. Description of the invention

[0007] The invention proposes to overcome at least one of these drawbacks.

[0008] To this end, the invention proposes, according to a first aspect, a method for detecting an analyte by means of a biochemical sensor, the sensor consisting of working electrodes coated with a reactive material capable of reacting with the analyte, the working electrodes being in contact with an interstitial fluid in which is the analyte, the process comprising the following steps:

[0009] a) supplying voltage to the working electrodes during a second time period following a first time period during which the working electrodes are not supplied while being in contact with the interstitial fluid;

[0010] b) measurement of an intensity I(t) at the level of each working electrode during the second time period;

[0011] c) interruption of the voltage supply to the working electrode at the end of the second time period;

[0012] d) treatment of I(t) comprising obtaining a first value P=I(ti) corresponding to the first peak of I(t) during the second time period and obtaining a second value F=I(t2) corresponding to a point F of I(t) from which I(t) exhibits a decrease of less than 20%, the intensity I(t) between P inclusive and F inclusive being characteristic of a quantity of analyte put into reaction during the first time period.

[0013] The invention is advantageously complemented by the following features, taken alone or in any technically possible combination thereof:

[0014] - the processing of I(t) includes obtaining (E43) a third value D=I(t3) cor corresponding to a stabilized value of I(t), the value D being characteristic of a quantity of analyte put into reaction instantaneously during the second time period, D being preferably the last value of the measured I(t) curve;

[0015] - the method includes determining a duration for the first period temporal period during which the working electrode is not powered, and this according to the amplitude of I(t) measured in the range between F and D during the first elapsed time period, then repetition of steps a) b) c) and d) by applying said first time period thus determined;

[0016] - the method includes determining a duration for the second period temporal, and this according to the level of I(t) measured in the range between F and D, said duration corresponding to the time for I(t) to stabilize, i.e. to show a decrease of less than 5%, then repetition of steps a), b), c) and d) by applying said second temporal period thus determined;

[0017] - the method includes a step of selecting the intensity within a range between the P included and F included or intensity in a range between F included and D included, the process comprising a step of obtaining an amount of analyte from I(t) in the range thus selected;

[0018] - the step of obtaining a quantity of analyte includes the use of a com combination of values ​​between values ​​P and F or / and F and D;

[0019] - the processing of I(t) is implemented during the second time period of so as to disconnect the working electrodes from the voltage supply once the second value F is detected;

[0020] - the processing of I(t) is implemented at the end of the second time period.

[0021] The invention, according to a second aspect, proposes a device for detecting an analyte contained in a body fluid comprising an electrochemical sensor including a working electrode, the device comprising a control unit configured to implement a process according to the first aspect of the invention.

[0022] The invention is advantageous in that the processing of the intensity curve makes it possible to obtain a precise measurement of the quantity of analyte. PRESENTATION OF THE FIGURES

[0023] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0024] - [Fig.1] illustrates a device for measuring an analyte according to the invention;

[0025] - Figure 2 illustrates steps in a method for detecting an analyte according to the invention;

[0026] - Figure 3 illustrates an intensity curve obtained during a process according to the invention.

[0027] In all figures, similar elements bear identical references. DETAILED DESCRIPTION Device

[0028] Figure 1 illustrates a device 1 for measuring an analyte contained in an individual's body fluid, preferably glucose contained in an individual's interstitial fluid. Such a device 1 notably comprises an electrochemical sensor 2 including a working electrode 3, a reference electrode 4, and preferably a counter electrode 5 which stabilizes the chemical reaction occurring at the working electrode when the electrodes are energized.

[0029] The electrodes (i.e. the working electrode 3, the counter electrode 4 and preferably the reference electrode 4) are configured to be implanted in the dermis of a user by one or more microneedles 6 so as to be in contact with the interstitial fluid of the individual.

[0030] For example, the microneedle 6 can be metallic, so that the microneedle constitutes the electrode. A metallic track can also be deposited on a microneedle 6 manufactured to form the electrode. In practice, the microneedle 6 has a metallic surface that can be electrically connected to the outside of the microneedle 6. Several electrodes can be manufactured on the same microneedle 6 by electrically insulating the metallic surface of each electrode of the other metallic surface(s).

[0031] In another embodiment of the invention, each electrode can be mounted on a different micro-needle 6.

[0032] The device 1 also includes a control unit 7. The control unit 7 is electrically connected to the electrodes. The control unit 7 may include a processor, memory, an electrical acquisition module, and an electrical control module, particularly for driving the electrochemical sensor 2. The control unit 7 is further configured to supply power to the working electrode 3 of the sensor 2 so that it forms a circuit with the reference electrode 4 and optionally the counter electrode 5.

[0033] Each working electrode 3 is coated with a material capable of reacting with the analyte to be detected and whose quantity is to be measured. This may be glucose oxidase (GOx) or any other type of enzyme or reagent capable of reacting with glucose. A redox mediator may optionally be used.

[0034] The device 1 includes a bracelet 8 or a strap enabling it to be attached to a limb and a housing 9. The housing 9 includes a display screen (not shown) and the control unit 7 is disposed in the housing 9. Detection method

[0035] A method for detecting an analyte using device 1 is implemented by the control unit 7 and is described below in relation to [Fig.2].

[0036] In a preliminary step (step E0), the sensor 2 is positioned on an individual so that the electrodes 3, 4, 5 are in contact with the interstitial fluid containing the analyte. The device 1 is in particular placed around the wrist of an individual, the device 1 preferably being a watch.

[0037] The following describes the detection of glucose by means of at least one working electrode 3 coated with glucose oxidase (GOx).

[0038] During a first time period (Ti), the working electrode 3 is not powered (step El): it is neither connected to a power supply nor to another electrode. However, the working electrode 3 is in contact with the interstitial fluid so that glucose reacts with glucose oxidase GOx and the O2 present in the interstitial fluid. Subsequently, the product of this reaction is diffused to the working electrode 3 according to the following reaction:

[0039] giucose + q2 ^^luconolactone + H2O2

[0040] At the end of the first period Tb the working electrode is powered and is connected to at least one reference electrode to form a measurement circuit.

[0041] The working electrode 3 is in particular supplied during a second time period T2 (step E2).

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[0056] During this second time period T2, the intensity I(t) circulating in the working electrode is measured (step E3). During this second time period T2, hydrogen peroxide H2O2 is oxidized according to the following reaction Voltage / O'i H2O2 —^O2-r2H+2e ' During reaction 2,1(t) is the oxidation current of hydrogen peroxide ^2^2 when a potential of 0.65 volt (vs. the reference electrode) for example is applied to the working electrode 3 which is made of platinum. Furthermore, with the working electrode 3 supplied with power, reactions 1 and 2 are cumulative and instantaneous, resulting in the following reaction: glucose + O2 —gluconolactone + O2 + 2H + 2e"v Therefore, during this second period T2, two physicochemical phenomena are observed: the consumption of hydrogen peroxide H2O2 accumulated during the first period Ti and the instantaneous consumption according to reaction 2. The time periods Ti and T2, for example, range from 1 to 270 seconds. Of course, these values ​​can be adjusted depending on the analyte and reactive material used. The variation of the current I(t) measured during the time periods Ti and T2 is then processed (step E4) to deduce glucose measurements (step E5). It should be noted here that the method used can, of course, be applied to the detection of any analyte provided that the reagents are well chosen. At the end of the second time period T2, the supply to the working electrode is interrupted (step E6). In addition, the time periods Ti and T2 are repeated alternately in order to have a continuous measurement of glucose (step E7). Figure [Fig.3] illustrates the variation of I(t) during the two consecutive time periods Th T2. As shown above, during the first time period TH, a quantity of glucose reacts according to reaction 1. Thus, during this first time period Ti, H2O2 accumulates at the working electrode 3, and the amount of H2O2 is characteristic of the amount of glucose reacted during this first time period Th Next, the application of power to the working electrodes 3 triggers reaction 2, and the measurement of I(t) specifically measures the quantity of electrons "2e" which is representative of the amount of glucose produced by the reaction of H2O2 according to reaction 2, which was accumulated during the first time step Th Thus, at the beginning of the second time period T2, the current I(t) exhibits a The maximum, denoted P, corresponds to the first peak of I(t). At this point P, reaction 2 is predominant and reflects the H2O2 accumulated during the first time period Th.

[0057] The processing of I(t) therefore includes obtaining this first value P=I(tl) with tl being almost the instant when the second time period T2 starts (step E41). P is theoretically the maximum value of I(t) but singularities can also be detected so that it is indeed the first peak because the curve of I(t) can show other amplitude values ​​greater than that of the first peak.

[0058] As can be seen in [Fig. 3], after P, the curve I(t) decreases until it reaches a plateau and becomes stable. A stable curve is defined as one whose decrease (absolute value of the slope) is less than 5%.

[0059] During the first phase of strong decay (within a range starting from P), I(t) mainly reflects the end of the consumption of H2O2 accumulated during the first period Ti, with reaction 3 starting simultaneously. Therefore, during this first phase of decay, two phenomena coexist, one being predominant over the other: the end of H2O2 consumption. This quantity consumed provides additional information about the amount of H2O2 accumulated during the first time period Th.

[0060] The idea here is therefore to detect the end of the consumption of 7 / 2692 accumulated during the first time period Tp. At this point, a second value F=I(t2) is detected. This value F corresponds to a point in I(t) when the curve I(t) enters a second phase of very low decay compared to the first phase of decay starting at P, for example less than 20% (step E42).

[0061] Between P inclusive and F inclusive, we can therefore consider that we obtain reliable information on the quantity of analyte put into reaction during the first reaction 1 which is not noisy by the reaction 3 which has started: the quantity of H2O2 accumulated during the first period Ti is largely consumed between these points P inclusive and F inclusive.

[0062] It is noted that reactions 2 and 3 coexist throughout the second time period T2 but alternate in order to be predominant. Reaction 3 corresponds to the consumption during the second time period T2 of the H2O2 generated instantaneously by the GOx.

[0063] After point F, reaction 3 predominates so that I(t) is the quantity of electrons produced in real time by reaction 3 and which is representative of the quantity of glucose put into reaction according to this reaction 3.

[0064] It is when I(t) becomes constant that it represents reaction 3 which is characteristic of a value of the quantity of glucose put into reaction instantaneously at a given instant and is representative of the known chrono-amperometric method.

[0065] Thus, the processing of I(t) includes obtaining a third value D=I(t3) which corresponds to a stabilized value of I(t) (step E43).

[0066] Therefore, the intensity I(t) between P and F reflects the past, that is, the quantity of H2O2 accumulated during the first period Th, while the intensity I(t) between F and D represents mainly the present, and D reflects the real image of the present.

[0067] To ensure that I(t) is stable, it is necessary to fix the second time period T2, appropriately as will be seen later. In theory, the second time period T2 is fixed so that point D is the last measured point of I(t).

[0068] Indeed, as can be seen on the curve in [Fig. 3], it is at time tx that I(t) becomes stable (i.e., almost constant) so that the value D varies within a range denoted x in [Fig. 3]. The second time period T2 can therefore be optimized. Note that without optimization, this second time period T2 is fixed for a sufficiently long period so that the curve I(t) stabilizes during this second time period T2.

[0069] Complementarily, the process includes a step of obtaining glucose from the I(t) curve in the range between P and F or in the range between F and D (step E5) according to well known correspondences taking into account potential calibration.

[0070] Indeed, if we take the whole curve in the entirety of the second time period T2: we lose precision since we mix two different pieces of information, that between P and F (past) and then that between F and D (present) as explained above.

[0071] In the area between P inclusive and F inclusive, we have an image of the past, representing mainly the accumulation of H2O2. This accumulation therefore has the same effect as a magnifying glass since it sums all the accumulated values. For example, we measure the equivalent of 100 accumulated values ​​instead of one instantaneous value (magnifying glass effect).

[0072] Therefore, in the zone between P inclusive and F inclusive, glucose can be precisely evaluated regardless of its concentration thanks to this magnifying / accumulation effect.

[0073] Furthermore, taking into account the area between P and F allows, when a redox mediator is used, for the measurement of glucose precisely, given that the redox mediator requires less voltage, which potentially induces less measured current and, moreover, "could slow down" the reaction in some way, hence the interest in working with the magnifying effect between included P and included F.

[0074] To be even more precise, the process can further select (step E51) the range based on the value of D. Indeed, depending on the value of the current I(t) at point D, it is possible to determine whether the measurement between P and F or that of point D should be taken into account: depending on the case, the measurement between P and F may be less precise than the measurement between F and D. In fact, it is known that, from a threshold value I(t) for D, this value allows the quantity of glucose more reliably.

[0075] For example, we can consider the value D as the value of I(t) representative of glucose when we are in hypoglycemia, take F as the value of I(t) representative of glucose when we are in euglycemia and take P as the value of I(t) representative of glucose when we are in hyperglycemia.

[0076] Finally, in these ranges glucose can be measured from the current I(t) resulting from a combination of points between P inclusive and F inclusive and / or between F inclusive and D inclusive or using only points P, F and D. A combination is for example an average of points, a sum of points.

[0077] The determination of the values ​​P, F, D can be done in different ways.

[0078] According to one embodiment, it involves working on the points of the curve I(t):

[0079] - the first value P consists of sampling I(t) and as soon as at least two successive samples decrease then P is detected; - the second value F is detected by calculating the slope of the curve when in absolute value this slope becomes less than 20% then F is detected; - F is the value of I(t) 10, 15 or 20 seconds after P; - D is the value of I(t) as soon as I(t) is stabilized; to do this we calculate the the slope of the curve and when its absolute value becomes less than 5% we can consider that I(t) is stable - D is the last point of the curve I(t) at the end of the second time period T2.

[0080] Furthermore, the processing of I(t) is implemented at the end of the second time period T2 or during the second time period T2.

[0081] The advantage of implementing the processing of I(t) during the second period T2 is that it allows Ti and T2 to be sized to increase the measurement frequency. Furthermore, processing I(t) during the measurement allows the working electrode to be de-energized as soon as the second value F is detected or when the stabilized value of I(t) is detected. This optimizes the duration of the working electrode's energization.

[0082] In addition, the I(t) curve allows the durations Ti and / or T2 to be set. In this case, at the first use of the sensor, initial values ​​are set for Ti and T2.

[0083] In particular, as we have seen, the first time period Ti determines the number of values ​​accumulated during the period when the working electrode is not powered. Therefore, starting from the level of I(t) in the range between F and D, we can fix this first time period Ti to adjust this magnifying effect (step E8). Similarly, we can fix the duration of the second time period T2 to a duration corresponding to the moment when I(t) becomes stable (step E9). Indeed, as indicated above, we must ensure that I(t) is stabilized at the end of the second time period T2. This allows for a reduction in measurement time and potentially an increase in the frequency of measurements.

[0084] These values ​​are used in the subsequent iterated steps

Claims

Demands

1. A method for detecting an analyte using a biochemical sensor (2), the sensor (2) consisting of working electrodes coated with a reactive material capable of reacting with the analyte, the working electrodes being in contact with an interstitial fluid in which the analyte is located, the method comprising the following steps: a) supplying (E2) a voltage to the working electrodes during a second time period (T2) following a first time period (Ti) during which the working electrodes are not supplied with voltage while being in contact with the interstitial fluid; b) measuring (E3) an intensity I(t) at each working electrode during the second time period (T2);c) processing (E4) of I(t) comprising obtaining (E41) a first value P=I(ti) corresponding to the first peak of I(t) during the second time period (T2) and obtaining (E42) a second value F=I(t2) corresponding to a point F of I(t) from which I(t) exhibits a decrease of less than 20%, the intensity I(t) between P inclusive and F inclusive being characteristic of a quantity of analyte reacted during the first time period (Ti); d) interruption (E6) of the voltage supply to the working electrode at the end of the second time period.

2. A method according to claim 1, wherein the treatment of I(t) comprises obtaining (E43) a third value D=I(t3) corresponding to a stabilized value of I(t), the value D being characteristic of an amount of analyte reacted instantaneously during the second time period (T2), D being preferably the last value of the measured I(t) curve.

3. A method according to any one of claims 1 to 2, comprising a determination (E8) of a duration for the first time period (Ti) during which the working electrode is not powered, according to the amplitude of I(t) measured in the range between F and D during the first elapsed time period, and then repeating steps a) b) c) and d) by applying said first time period thus determined.

4. A method according to any one of claims 2 to 3, comprising a determination (E9) of a duration for the second time period, according to the level of I(t) measured in the range between F and D, said duration corresponding to the time for I(t) to stabilize, i.e., to present a decrease of less than 5%, then repetition of steps a), b), c) and d) by applying said second time period thus determined.

5. A method according to any one of claims 2 to 4, comprising a step of selecting (E51) the intensity in a range between inclusive P and F or the intensity in a range between inclusive F and D, the method comprising a step of obtaining (E5) an amount of analyte from I(t) in the range so selected.

6. A method according to any one of claims 1 to 5, wherein the step of obtaining (E5) an amount of analyte comprises the use of a combination of values ​​between the values ​​P and F and / or F and D.

7. A method according to any one of the preceding claims, wherein the processing of I(t) is implemented during the second time period (T2) so as to disconnect the working electrodes from the voltage supply once the second value F is detected.

8. A method according to any one of claims 1 to 7, wherein the processing of I(t) is carried out at the end of the second time period (T2).

9. Device for detecting an analyte contained in a body fluid comprising an electrochemical sensor (2) including a working electrode (3), the device comprising a control unit (7) configured to implement a method according to one of the preceding claims.

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