WO2023275496A1 - Method for detecting an analyte contained in a bodily fluid of an individual and corresponding device - Google Patents

Abstract

The invention relates to a method for detecting an analyte by means of a biochemical sensor (2), the sensor consisting of working electrodes covered by a reactive material able to react with the analyte, the working electrodes making contact with an interstitial fluid in which the analyte is found, the method comprising the following steps: • a) supplying with voltage the working electrodes during a second time period consecutive to a first time period during with the working electrodes are not supplied while nonetheless making contact with the interstitial fluid; • b) measuring a current 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) processing, this comprising obtaining a first value P=l(t ₁) corresponding to the first peak of I(t) in the course of 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 smaller than 20%, the current I(t) between P inclusive and F inclusive being characteristic of an amount of analyte involved in reaction during the first time period.

Description

DESCRIPTION

TITLE OF THE INVENTION: Method for detecting an analyte contained in a bodily fluid of an individual and corresponding device

TECHNICAL AREA

The invention relates to a method and a device for detecting an analyte contained in a bodily 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 enzymatic, the sensor consisting of electrodes covered with a reactive material capable of reacting with the analyte.

STATE OF THE ART

It is known to measure the concentration of an analyte by means of an electrochemical sensor. Such a sensor makes it possible to convert information relating to a chemical reaction into an electrical signal. As such, the sensor comprises at least one working electrode covered with a material capable of reacting with the analyte.

A known technique for measuring the amount of analyte is amperometry, a technique in which the working electrode is energized to cause a chemical reaction at the working electrode, the current flowing through the electrode is measured and depends analyte concentration.

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

Traditional glucose sensors are based on the oxidation of glucose by oxygen in the presence of glucose oxidase (GOx) covering a working electrode. Such a sensor is for example described in the document Clark et al. (Clark Jr, LC, & Lyons, C., 1962, Electrode Systems for continuous monitoring in cardiovascular surgery, Annals of the New York Academy of sciences, 102(1), 29-45). This type of sensor has undergone several developments but none has made it possible to measure the analyte with great precision, in particular when it comes to measuring the glucose level of a diabetic individual.

DISCLOSURE OF THE INVENTION

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

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 covered with a reactive material capable of reacting with the analyte, the working electrodes being in contact with an interstitial liquid in which the analyte is located, the method comprising the following steps: a) supplying voltage to the working electrodes for a second time period following a first time period for which the working electrodes are not energized while in contact with the interstitial fluid; b) measurement of an intensity l(t) at the level of each working electrode during the second time period; c) interruption of the voltage supply to the working electrode at the end of the second time period; d) processing of l(t) comprising obtaining a first value P=l(ti) corresponding to the first peak of l(t) during the second time period and obtaining a second value F= l(t2) corresponding to a point F of l(t) from which l(t) has a decrease of less than 20%, the intensity l(t) between P included and F included being characteristic of a quantity of reacted analyte during the first time period.

The invention is advantageously completed by the following characteristics, taken alone or in any of their technically possible combination:

- the processing of l(t) comprises obtaining (E43) a third value D=l(t3) corresponding to a stabilized value of l(t), the value D being characteristic of a quantity of analyte placed reacting instantaneously during the second time period, D preferably being the last value of the curve l(t) measured; - the method comprises determining a duration for the first time period during which the working electrode is not energized, and this according to the amplitude of l(t) measured in the range between F and D during the first time period elapsed, then repeating steps a) b) c) and d) by applying said first time period thus determined;

- the method comprises a determination of a duration for the second time period, and this according to the level of l(t) measured in the range between F and D, said duration corresponding to the duration for l(t) to stabilize c ie exhibits a decrease of less than 5%, then repeating steps a), b), c) and d) by applying said second time period thus determined;

- the method comprises a step of selecting the intensity in a range between P inclusive and F inclusive or of the intensity in a range between F inclusive and D inclusive, the method comprising a step of obtaining a quantity of analyte from 1(t) in the range thus selected;

- the step of obtaining a quantity of analyte comprises the use of a combination of values between the values P and F or/and F and D;

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

- the processing of l(t) is implemented at the end of the second time period.

The invention proposes according to a second aspect a device for detecting an analyte contained in a bodily fluid comprising an electrochemical sensor comprising a working electrode, the device comprising a control unit configured to implement a method according to the first aspect of the invention.

The invention is advantageous in that the processing of the intensity curve makes it possible to obtain an accurate measurement of the quantity of analyte.

PRESENTATION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

- Figure 1 illustrates a device for measuring an analyte according to the invention; - Figure 2 illustrates steps of a method for detecting an analyte according to the invention;

- Figure 3 illustrates an intensity curve obtained during a method according to the invention.

In all the figures, similar elements bear identical references.

DETAILED DESCRIPTION

Device

Figure 1 illustrates device 1 for measuring an analyte contained in a bodily fluid of an individual, preferably glucose contained in the interstitial fluid of an individual. Such a device 1 consists in particular of an electrochemical sensor 2 comprising a working electrode 3, a reference electrode 4 and preferably a counter electrode 5 which makes it possible to stabilize the chemical reaction occurring at the level of the working electrode when the electrodes are energized.

The electrodes (that is to say 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 micro- needles 6 so as to be in contact with the interstitial fluid of the individual.

For example, the micro-needle 6 can be metallic, so that the micro-needle constitutes the electrode. A metallic track can also be deposited on a micro-needle 6 micro fabricated so as to form the electrode. In practice, the micro-needle 6 has a metal surface which can be electrically connected to the outside of the micro-needle 6. Several electrodes can be fabricated on the same micro-needle 6, by electrically isolating the metal surface of each electrode of the other metal surface(s).

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

Device 1 also includes a control unit 7. Control unit 7 is electrically connected to the electrodes. The control unit 7 may comprise a processor, a memory, an electrical acquisition module and an electrical control module in particular for controlling the electrochemical sensor 2. The control unit 7 is further configured to power the working electrode 3 of the sensor 2 so that it forms a circuit with the reference electrode 4 and possibly the counter electrode 5.

Each working electrode 3 is covered with a material capable of reacting with the analyte which it is desired to detect and whose quantity it is desired to measure. It can be glucose oxidase (GOx) or any other type of enzyme or reagent capable of reacting with glucose. A redox mediator can optionally be used.

The device 1 comprises a bracelet 8 or a strap allowing it to be attached to a limb and a box 9. The box 9 includes a display screen (not shown) and the control unit 7 is placed in the box 9 .

Detection method

A method for detecting an analyte by means of device 1 is implemented by control unit 7 and is described below in relation to FIG. 2.

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 liquid in which the analyte is found. The device 1 is in particular arranged around the wrist of an individual, the device 1 preferably being a watch.

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

During a first time period (Ti), the working electrode 3 is not powered (step E1): it is neither connected to a power supply nor to another electrode. On the other hand, the working electrode 3 is in contact with the interstitial liquid so that the glucose reacts with the glucose oxidase GOx and GO2 present in the interstitial liquid then the product of this reaction is diffused to the working electrode 3according to the following reaction

GOx glucose + 0 ₂ — » gluconolactone + H ₂ 0 ₂ (1).

At the end of the first period T1, the working electrode is powered and is connected to at least one reference electrode to form a measurement circuit.

The working electrode 3 is in particular supplied during a second time period T2 (step E2). During this second time period T2, the intensity I(t) flowing in the working electrode is measured (step E3).

During this second time period T2, the hydrogen peroxide H ₂ 0 ₂ oxidizes according to the following reaction

Voltage

H ₂ 0 ₂ - » 0 ₂ + 2 H ⁺ + 2nd (2).

During reaction 2, l(t) is the oxidation current of hydrogen peroxide H ₂ 0 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.

Moreover, with the supply of working electrode 3, reactions 1 and 2 are cumulative and instantaneous and result in the following reaction:

GOx+Voltage glucose + 0 ₂ - » gluconolactone + 0 ₂ + 2H ⁺ + 2e (3).

Consequently, during this second period T2, two physico-chemical phenomena are observed: the consumption of the hydrogen peroxide H ₂ 0 ₂ accumulated during the first period T1 and the instantaneous consumption according to reaction 2.

The time periods T1 and T2 are for example between 1 and 270 seconds. Of course, these values can be adjusted depending on the analyte and reagent material used.

The variation of the current I(t) measured during the time periods T1 and T2 is then processed (step E4) to deduce glucose measurements therefrom (step E5). It is specified here that of course the method used can 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 power supply to the working electrode is interrupted (step E6).

In addition, the time periods T1 and T2 are repeated alternately in order to have a continuous glucose measurement (step E7).

FIG. 3 illustrates the variation of l(t) during the two consecutive time periods Ti, T2.

As presented above, during the first time period Ti, a quantity of glucose is reacted according to reaction 1. Thus, during this first time period T1 the H ₂ 0 ₂ accumulates at the level of the working electrode 3 and the amount of H ₂ 0 ₂ is characteristic of the amount of glucose reacted during this first time period T1. Then, the supply of the working electrodes 3 has the effect of triggering the reaction 2 and the measurement of l(t) measures in particular the quantity of "2e" electrons which is representative of the quantity of glucose by the reaction of the H ₂ 0 ₂ according to reaction 2 which was accumulated during the first time Ti.

Thus, at the start of the second time period T2, the current l(t) has a maximum noted P which corresponds to the first peak of l(t). At this point P, it is reaction 2 which is predominant and which is an image of the H2O2 accumulated during the first time period Ti.

The processing of l(t) therefore comprises obtaining this first value P=I (t 1 ) with t1 which is almost the instant when the second time period T2 starts (step E41 ). P is in theory the maximum value of l(t) but singularities can also be detected so that it is indeed the first peak because the curve of l(t) can present other amplitude values greater than that of the first peak.

As visible in Figure 3, after P, the curve l(t) decreases until it reaches a plateau and becomes stable. By stable curve is meant a curve which has a decrease (absolute value of the slope) of less than 5%.

During the first phase of strong decrease (in a range from P), l(t) mainly reflects the end of the consumption of H2O2 accumulated during the first period T1 with simultaneous reaction 3 which starts. Consequently, during this first phase of decrease, two phenomena coexist, one being predominant over the other, namely the end of the consumption of H ₂ 0 ₂ . This quantity which is consumed makes it possible to obtain additional information on the quantity of H ₂ 0 ₂ accumulated during the first time period T1.

The idea here is therefore to detect the end of the consumption of H ₂ 0 ₂ accumulated during the first time period T1. As such, a second value F=1(t2) is detected. This value F corresponds to a point of l(t) when the curve l(t) enters a second phase of very slight decrease relative to the first phase of decrease starting at P, for example less than 20% (step E42).

Between P included and F included, we can therefore consider that we obtain reliable information on the quantity of analyte reacted during the first reaction 1 which is not noisy by reaction 3 which has started: the quantity of H ₂ 0 ₂ accumulated during the first period T1 is for the most part consumed between these points P inclusive and F inclusive. It is noted that the reactions 2 and 3 coexist throughout the second time period T2 but follow each other to be the majority in turn. Reaction 3 corresponds to the consumption during the second time period T2 of the H ₂ 0 ₂ instantaneously generated by the GOx.

After point F, it is reaction 3 which predominates so that l(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 .

It is when l(t) becomes constant that it represents reaction 3 which is characteristic of a value of the quantity of glucose reacted instantaneously at a given moment and is representative of the known chrono-amperometric method.

Thus, the processing of l(t) comprises obtaining a third value D=l(t3) which corresponds to a stabilized value of l(t) (step E43).

So the intensity l(t) between P and F testifies to the past, that is to say the quantity of H ₂ 0 ₂ accumulated during the first period T1, while the intensity l(t) between F and D mainly represents the present and D testifying to the real image of the present.

To be sure to have stabilized l(t), the second time period T2 should be set appropriately as we will see later. In theory, the second time period T2 is set so that point D is the last measured point of l(t).

Indeed, as can be seen on the curve in Figure 3, it is at time tx that l(t) becomes stable (i.e. almost constant) so that the value D varies in a range denoted x in FIG. 3, the second time period T2 can therefore be optimized. It should be noted that without optimization, this second time period T2 is fixed long enough for the curve l(t) to stabilize during this second time period T2.

In a complementary manner, the method comprises a step of obtaining glucose from the curve l(t) 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.

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) then that between F and D (present) as explained above. In the zone between P included and F included, we have the image of the past which is mainly representative of the accumulation of H ₂ 0 ₂ . This accumulation therefore has the same effect as a magnifying glass since it sums all the accumulated values. For example, the equivalent of 100 accumulated values is measured instead of one instantaneously (magnifying effect).

Therefore, in the zone between P included and F included, glucose can be precisely evaluated whatever its concentration thanks to this magnifying glass/accumulation effect.

In addition, taking into account the area between P and F allows when a redox mediator is used to measure glucose precisely given that the redox mediator requires less voltage which potentially induces less measured current and furthermore “ could somehow slow down the reaction, hence the interest of working with the magnifying effect between P included and F included.

In a complementary way to be even more precise, the method can select (step E51) the range according to the value D. Indeed, according to the value of the current l(t) at the point D one is able to determine if it is appropriate to take into account the measurement between P and F or that of point D: depending on the case, it may indeed be that the measurement between P and F is less precise than the measurement between F and D. Indeed, we know that from a threshold value l(t) for D, this value makes it possible to detect the quantity of glucose more reliably.

For example, one can consider the value D as the value of l(t) representative of glucose when one is in hypoglycemia, take F as the value of l(t) representative of glucose when one is in euglycemia and take P as the value of l(t) representative of glucose when in hyperglycemia.

Finally, in these ranges it is possible to measure the glucose from the current l(t) resulting from a combination of the points between P inclusive and F inclusive and/or between F inclusive and D inclusive or alternatively using only the points P, F and D. A combination is for example an average of points, a sum of points.

The determination of the P, F, D values can be done in different ways. According to one embodiment, it involves working on the points of the curve l(t): the first value P consists in sampling l(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 l(t) 10, 15 or 20 seconds after P;

D is the value of l(t) as soon as l(t) is stabilized to do this we calculate the slope of the curve and when in absolute value this slope becomes less than 5% we can consider that l(t) is stable

D is the last point of the curve l(t) at the end of the second time period T ₂ .

Furthermore, the processing of l(t) is implemented at the end of the second time period T ₂ or else during the second time period T ₂ .

The advantage of implementing the processing of l(t) during the second period T ₂ is that it is possible to dimension Ti and I ₂ to increase the frequency of the measurements. Furthermore, the processing of l(t) during the measurement makes it possible to no longer supply the working electrode as soon as the second value F is detected or when the stabilized value of l(t) is detected. This makes it possible to optimize the supply duration of the working electrode.

In a complementary way, the curve l(t) makes it possible to fix the durations T ₁ and/or T ₂ . In this case, on the first use of the sensor, initial values are fixed for Ti and T ₂ .

In particular, as we have seen, the first time period T ₁ conditions a number of values accumulated during the period when the working electrode is not powered. From then on, from the level of l(t) in the range between F and D, it is possible to fix this first time period Ti to adjust this magnifying effect (step E8). Also, the duration of the second time period T ₂ can be fixed at a duration corresponding to the moment when l(t) becomes stable (step E9). Indeed, as indicated above, it must be ensured that l(t) is stabilized at the end of the second time period T ₂ . This reduces the measurement time and potentially increases the frequency of measurements.

These values are used in the iterated steps next

Claims

1. Method for detecting an analyte by means of a biochemical sensor (2), the sensor (2) consisting of working electrodes covered with a reactive material capable of reacting with the analyte, the working electrodes being in contact with an interstitial liquid in which the analyte is located, the method comprising the following steps: a) supplying (E2) voltage to the working electrodes during a second time period (T2) consecutive to a first time period (Ti ) during which the working electrodes are not energized while being in contact with the interstitial liquid; b) measurement (E3) of an intensity l(t) at the level of each working electrode during the second time period (T2); c) processing (E4) of l(t) comprising obtaining (E41) a first value P=l(ti) corresponding to the first peak of l(t) during the second time period (T2) and l obtaining (E42) a second value F=l(t2) corresponding to a point F of l(t) from which l(t) exhibits a decrease of less than 20%, the intensity l(t) between P included and F included being characteristic of a quantity of analyte reacted during the first time period (T1); d) interruption (E6) of the voltage supply to the working electrode at the end of the second time period. 2. Method according to claim 1, in which the processing of l(t) comprises obtaining (E43) a third value D=l(t3) corresponding to a stabilized value of l(t), the value D being characteristic of a quantity of analyte reacted instantaneously during the second time period (T2), D preferably being the last value of the curve l(t) measured. 3. Method according to one of claims 1 to 2, which comprises a determination (E8) of a duration for the first time period (Ti) during which the working electrode is not powered, and this according to the amplitude of l(t) measured in the range between F and D during the first elapsed time period, then repeating steps a) b) c) and d) by applying said first time period thus determined. 4. Method according to one of claims 2 to 3, comprising a determination (E9) of a duration for the second time period, and this according to the level of l (t) measured in the range between F and D, said duration corresponding to the duration for l(t) to stabilize, that is to say 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. Method according to one of claims 2 to 4, comprising a step of selecting (E51) the intensity in a range between P included and F included or the intensity in a range between F included and D included, the method comprising a step of obtaining (E5) an amount of analyte from l(t) in the range thus selected. 6. Method according to one of claims 1 to 5, in which the step of obtaining (E5) a quantity of analyte comprises the use of a combination of values between the values P and F or/and F and D. 7. Method according to one of the preceding claims, in which the processing of l(t) is implemented during the second time period (T2) so as to disconnect the working electrodes from the voltage supply once the second F value is detected. 8. Method according to one of claims 1 to 7, in which the processing of l(t) is implemented at the end of the second time period (T2). 9. Device for detecting an analyte contained in a bodily fluid comprising an electrochemical sensor (2) comprising a working electrode (3), the device comprising a control unit (7) configured to implement a method according to one of the preceding claims.