Microfluidic electrochemical device for measuring volumetric flow rate

Abstract

The invention relates to a microfluidic electrochemical device comprising microfluidic channels 11a, 11b, 11c and electrochemical cells 14a, 14b, 14c, said electrochemical cells comprising working electrode pairs WE1, WE2, a counter electrode CE and a reference electrode REF, said working electrode pairs WE1, WE2 being separated by an inter-electrode distance La, Lb, Lc in the direction of flow of the fluid through the microfluidic channels. The microfluidic electrochemical device comprises a galvanic electrochemical measurement system, and the galvanic electrochemical measurement system is configured to polarize the working electrode pair. Each electrode generates a current signal via an oxidation reaction or a reduction reaction with the electroreactive fluid or an oxidation reaction or a reduction reaction with a chemical substance associated with a redox pair in the fluid. The microfluidic electrochemical device determines the average volumetric flow rate of the fluid through the microfluidic channel, in particular from the inter-electrode distance and the time delay between the current signals generated by the working electrode pair.

Description

Technical Field

[0001] The present invention relates to the field of microfluidic electrochemical devices and methods for measuring the volumetric flow rate of a fluid that is electroactive or contains one or more electroactive substances in a microfluidic channel. In general, the present invention also relates to an apparatus for determining quantitative sweat parameters of a human or animal subject. Background Art

[0002] Sweat is secreted by the sweat glands in the skin, discharged through the skin pores, and evaporates from the epidermis. Sweating plays an important role in the subject's organism as it enables the body to regulate temperature through perspiration. Excessive sweating can cause the subject to become dehydrated, impairing their ability to perform physically and having deleterious consequences on their health. Similarly, excessive drinking can lead to hyponatremia, fatigue, confusion, coma, and even death of the subject.

[0003] Various devices for measuring microflow velocity in situ are known in the prior art, in particular thermal flow sensors or even Coriolis effect microflow meters. In practice, these devices are expensive, exhibit unresolved reliability issues, and are usually integrated into bulky units. More particularly, microfluidic devices have been developed to measure the microflow velocity of sweat discharged by a human or animal subject circulating in a microfluidic channel. Measuring sweat microflow velocity allows the evaluation of quantitative sweating parameters of a subject, so as to, for example, monitor the hydration level of the subject, thereby preventing water imbalance in the body, especially in athletes and the elderly, or even diagnose hypohidrosis, which is a sweating disorder characterized by insufficient sweat production, and hypohidrosis can be caused by: pathologies that may impair sweat gland function (diabetes, alcoholism, Parkinson's disease, Ross syndrome, Sjogren's syndrome, small cell lung cancer, etc.), skin causes (burns, inflammation, infection, skin lesions, etc.), medical causes (e.g., anticholinergic therapy) and genetic causes (e.g., hypohidrotic ectodermal dysplasia).

[0004] Known microfluidic devices have the advantage of being able to easily collect sweat with very high temporal resolution and without evaporating the sweat in the microfluidic channels. Colorimetric techniques are generally preferred due to the ease of manufacturing the relevant devices. However, their main disadvantage relates to the irreversible nature of the method. Once the microfluidic channels are filled with sweat, these devices are permanently altered by the dye and cannot be used again. This situation is comparable to detection techniques based on electrical transduction signals such as resistance, conductance, capacitance or impedance. In order to estimate the sweat microflow rate, their implementation involves monitoring the filling rate with the help of electrodes arranged along the microfluidic channels. Once filled, the microfluidic channels can no longer be used.

[0005] Document FR 3103901 A1 describes in particular a method for measuring the sweat flow rate based on the intrinsic expression of hydrogen peroxide H2O2, nitric oxide NO or nitrite ions NO2 present in the sweat flow. - The delay between the temporal changes in the concentration current signal. Summary of the invention

[0006] The idea of ​​the present invention is to provide a microfluidic electrochemical device for measuring the volumetric flow rate of a fluid in a microfluidic channel without having to determine the concentration of the electroactive chemical species contained in the fluid flow.

[0007] Another idea of ​​the present invention is to provide a flexible device adhered to the skin for determining quantitative sweat parameters of a subject based on continuous in situ measurement of the volumetric flow rate of sweat flowing in a microfluidic channel.

[0008] The object of the present invention is to provide such a device which has the additional advantages of saving space, simple design and low cost.

[0009] According to one embodiment, the present invention provides a microfluidic electrochemical device for measuring the flow velocity and / or volume flow rate of a fluid, wherein the fluid includes a solvent, and the microfluidic electrochemical device includes:

[0010] - at least one microfluidic channel configured to allow said fluid to flow along a flow direction;

[0011] - at least one electrochemical cell disposed in the at least one microfluidic channel, the electrochemical cell comprising a first working electrode and at least one second working electrode spaced apart from the first working electrode by an inter-electrode distance in the flow direction, at least one counter electrode and at least one reference electrode; and

[0012] - an electrochemical current measurement system configured to bias the first working electrode at a first electrode potential and bias the second working electrode at a second electrode potential, so that each of the first working electrode and the second working electrode generates a current signal through an oxidation reaction or a reduction reaction of a solvent or an oxidation reaction or a reduction reaction with at least one chemical substance that forms a redox pair with the solvent;

[0013] The electrochemical current measurement system is configured to determine the flow velocity and / or volume flow rate of the fluid in the microfluidic channel based on the inter-electrode distance between the first working electrode and the second working electrode and the time delay between a change in the current signal generated by the first working electrode and a change in the current signal generated by the second working electrode.

[0014] Such microfluidic electrochemical devices can be integrated into many microsystems for in situ measurement of volume flow rate and / or flow velocity of fluids in microfluidic channels, for example, lab-on-a-chip microfluidic platforms or micro-volume total analysis systems (μTAS).

[0015] Microfluidic electrochemical devices are simple to manufacture and easy to industrialize because there are no moving parts and no assumptions need to be made about the hydrodynamic state of the flow of the fluid in the microfluidic channel. Determining the flow velocity and / or volume flow rate is not relevant to determining the concentration of the chemical species generated or contained in the fluid, but only to the response time between changes in the current signal of the working electrode pair.

[0016] According to some embodiments, such a microfluidic electrochemical device may include one or more of the following features.

[0017] According to one embodiment, the solvent is water H2O (l) .

[0018] Water can act as a reducing chemical in the O2 / H2O redox couple and as a + It acts as the oxidizing chemical in the H2 / H2 redox couple.

[0019] According to one embodiment, the fluid is sweat from a human or animal subject.

[0020] According to one embodiment, the first electrode potential allows water H2O (l) Oxidized to molecular oxygen O 2(aq) , and the second electrode potential allows molecular oxygen O2 dissolved in the generated water H2O to be reduced to water H2O.

[0021] By applying appropriate potentials to the first working electrode and the second working electrode, water H2O on the first working electrode is selected. (l) The oxidation reaction and molecular oxygen O on the second working electrode 2(aq) The reduction reaction allows the amplitude of the current signal detected at each of the working electrodes to be controlled without having to measure these amplitudes, but in a manner that maintains a sufficient signal-to-noise ratio to allow changes in the current signal to be easily detected.

[0022] According to one embodiment, the first electrode potential allows water H2O (l) Reduced to molecular hydrogen H 2(aq) , and the second electrode potential allows water H2O (l) Reduced to molecular hydrogen H 2(aq) .

[0023] According to one embodiment, the first electrode potential allows the solution in water H2O (l) Molecular oxygen O 2(aq) Reduced to water H2O (l) , and the second electrode potential allows H2O dissolved in water (l) Molecular oxygen O 2(aq) Reduction to water H2O (l) .

[0024] According to one embodiment, the electrochemical current measurement system is further configured to:

[0025] - during a first step, biasing the first working electrode at the first electrode potential and biasing the second working electrode at the second electrode potential;

[0026] - During the second step, the first working electrode is disconnected or the first electrode potential is set to a potential close to or equal to the zero current equilibrium potential.

[0027] According to one embodiment, the microfluidic electrochemical device further comprises an isolation support, wherein the at least one microfluidic channel is formed in the isolation support, and the first working electrode and the second working electrode are formed by metal deposits of platinum or platinum black on the isolation support.

[0028] According to one embodiment, the counter electrode is positioned downstream of the working electrode in the flow direction, and wherein the reference electrode is positioned upstream of the working electrode in the flow direction.

[0029] Therefore, the reference electrode is located upstream of the working electrode pair to maintain the stability of the reference electrode potential over time; and the counter electrode is located downstream of the working electrode pair, and therefore downstream of the reference electrode, so that the chemical substances generated on its surface neither disturb the working electrode nor the reference electrode.

[0030] Advantageously, the counter electrode has a surface area two to three times greater than the surface area of ​​the other electrodes.

[0031] According to some embodiments, the microfluidic electrochemical device may include one or more microfluidic channels. If applicable, the electrochemical unit may be arranged in one or each microfluidic channel, or in some or all of the microfluidic channels. The electrochemical units arranged in different channels may be different or the same. The redox reactions performed in the electrochemical units arranged in different channels may be different or the same.

[0032] According to one embodiment, the microfluidic electrochemical device includes a first microfluidic channel and a second microfluidic channel, wherein a first electrochemical unit and a second electrochemical unit are respectively arranged in the first microfluidic channel and the second microfluidic channel, and the distance between electrodes of the first electrochemical unit is different from the distance between electrodes of the second electrochemical unit.

[0033] According to one embodiment, the at least one electrochemical unit comprises two second working electrodes, and the two second working electrodes are respectively separated from the first working electrode by a first inter-electrode distance and a second inter-electrode distance, wherein the first inter-electrode distance is different from the second inter-electrode distance.

[0034] Preferably, the inter-electrode distance separating the working electrode pair is selected to be small enough so that changes in the subject's physiological response are negligible for the duration of the time delay between changes in the current signal of the working electrodes, and large enough to allow a decoupled operating regime of the working electrodes in at least one of the microfluidic channels.

[0035] In fact, the coupled or decoupled working state of the working electrode depends on the average flow velocity of the fluid in the microfluidic channel and the inter-electrode distance. At high flow velocity, if the inter-electrode distance is too small, the flow of the fluid that has reacted at the first working electrode is still uneven after reaching the second working electrode. This coupling state limits the time resolution of the current signal, which reduces the accuracy of the sweat volume flow rate measurement.

[0036] According to one embodiment, the electrochemical current measurement system is configured to determine the volumetric flow rate as a function of a cross-sectional surface area of ​​the microfluidic channel in the flow direction.

[0037] By configuring the inter-electrode distance differently depending on the electrochemical cell in question, the volume flow rate can thus be measured over a range of values ​​covering all conceivable physiological flow rates.

[0038] According to one embodiment, the invention provides a device intended to be placed on an investigation area of ​​the epidermis of a human or animal subject in order to measure a quantitative sweat parameter of said subject, said device comprising:

[0039] - defining a structure of a microfluidic electrochemical device, said structure comprising an inlet hole defining said investigation zone and allowing the passage of sweat from said epidermis, said at least one microfluidic channel of said microfluidic electrochemical device being connected to said inlet hole;

[0040] - an electronic processing device configured to determine said quantitative sweat parameter of said human or animal subject based on the measurement of sweat volume flow rate performed by said microfluidic electrochemical device.

[0041] The quantitative sweat parameter may be a sweat rate determined based on the total volume of sweat expelled by the subject relative to the surface area of ​​the investigation area within a given time frame.

[0042] According to one embodiment, the quantitative sweat parameter of the human or animal subject is sweat rate.

[0043] "Epidermis" is understood to mean the outer layer of the skin of humans and animals.

[0044] According to some embodiments, such a device may include one or more of the following features.

[0045] According to one embodiment, the structure is a multilayer structure including a lower layer and at least one layer stacked on the lower layer, the microfluidic electrochemical device extends parallel to the lower layer, and the lower layer includes the inlet hole.

[0046] According to one embodiment, the multilayer structure further comprises an upper layer and at least one intermediate layer located between the lower layer and the upper layer, and the microfluidic electrochemical device is formed within the thickness of the at least one intermediate layer.

[0047] The layers may be attached to each other using any suitable method, for example, by adhesive, by welding, by mechanical clamping, and the like.

[0048] Thus, by virtue of these features, the device is facilitated to manufacture, assemble and industrialize.

[0049] By virtue of these characteristics, the device adapts to possible curvatures when applied to the epidermis. Furthermore, the intermediate layer or layers also allow the thickness to be created to compensate for the thickness of the electrodes of the microfluidic electrochemical device. This ensures the water tightness of the device.

[0050] According to one embodiment, the upper layer comprises an outlet hole passing through the upper layer, and wherein the at least one microfluidic channel is connected to the outlet hole.

[0051] According to one embodiment, the first working electrode, the at least one second working electrode, the at least one counter electrode and the at least one reference electrode are arranged on the inner surface of the upper layer that closes the at least one microfluidic channel from above, and / or are arranged on the upper surface of the lower layer that closes the at least one microfluidic channel from below.

[0052] By virtue of these features, the electrodes are arranged in a reliable manner. Furthermore, the manufacture of a multilayer structure comprising these electrodes becomes easy, since the electrodes can be manufactured on a planar layer while the microfluidic electrochemical device is formed in an intermediate layer.

[0053] According to one embodiment, the apparatus further comprises a wired or wireless communication device configured to transmit one or more measurement signals generated by the microfluidic electrochemical device.

[0054] According to one embodiment, the device further comprises a gyroscope module and / or at least one accelerometer for detecting the activity state of the human or animal subject.

[0055] According to one embodiment, the device further comprises a temperature sensor configured to measure the temperature of the epidermis of the human or animal subject.

[0056] According to one embodiment, the device comprises a geo-location module.

[0057] By virtue of these features, for example, the device is configured to periodically make and transmit measurements at a configurable frequency or at a frequency dependent on the activity state detected by the device, so as to facilitate analysis of the correlation between the subject's activity state and the quantitative sweat parameters measured by the device.

[0058] The measurements of the sweat volume flow rate and / or the quantitative sweat parameters can be used in various applications, for example, to monitor the hydration level of a subject to prevent body water imbalances, particularly in athletes or the elderly during exercise, especially in hot weather, or even to diagnose hypohidrosis, regardless of the cause.

[0059] Further applications may be found in various technical or environmental fields whenever flow rate measurement is required in devices or methods involving electroactive fluids or containing one or more electroactive substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The invention will be better understood and further objects, details, features and advantages thereof will appear more clearly from the following description of several specific embodiments of the invention, which description is provided by way of non-limiting illustration only, and with reference to the accompanying drawings.

[0061] [ Figure 1 ] Figure 1 is a schematic back view of a subject with a device according to one embodiment placed thereon;

[0062] [ Figure 2 ] Figure 2 is a perspective view partially showing a multi-layer structure of a device according to an embodiment;

[0063] [ Figure 3 ] Figure 3 is along Figure 2 A cross-sectional view taken along line III-III;

[0064] [ Figure 4 ] Figure 4 is an exploded view of a multi-layer structure according to an embodiment;

[0065] [ Figure 5 ] Figure 5 is a partially functional schematic diagram of a multilayer structure defining an electrochemical device in an apparatus;

[0066] [ Figure 6 ] Figure 6 It is a partial functional schematic diagram of a microfluidic electrochemical device that can be used in the device;

[0067] [ Figure 7 ] Figure 7 is a schematic top view of an electrochemical cell according to a first embodiment;

[0068] [ Figure 8 ] Figure 8 According to the second embodiment, it is similar to Figure 7 Schematic diagram of

[0069] [ Fig. 9 ] Fig. 9 is a functional schematic cross-sectional view of an electrochemical unit along a microfluidic channel according to a first embodiment;

[0070] [ Fig.10 ] Fig.10 is a set of chronoelectric current diagrams showing that according to the first embodiment, Figure 7 A method implemented by a microfluidic electrochemical device;

[0071] [ Fig.11 ] Fig.11 According to the second embodiment, it is similar to Fig. 9 Functional diagram of

[0072] [ Fig.12 ] Fig.12 According to the second embodiment, it is similar to Fig.10 A set of chronoamperographs;

[0073] [ Fig.13 ] Fig.13 is similar to the third embodiment Fig. 9 and Fig.11 Functional diagram of

[0074] [ Fig.14 ] Fig.14 is similar to the third embodiment Fig.10 and Fig.12 A set of chronoamperographs;

[0075] [ Fig.15 ] Fig.15 is a schematic functional diagram of an electronic control device that may be implemented with the device. DETAILED DESCRIPTION

[0076] The embodiments described below relate to an apparatus for determining quantitative sweat parameters of a subject by means of a microfluidic electrochemical device for continuously measuring the volume flow rate of sweat in a microfluidic channel. In general, such a microfluidic electrochemical device can be integrated into many microsystems for in situ measurement of the average flow rate of an electroactive fluid in a microfluidic channel. For example, these microsystems can be a chip lab microfluidic platform or a micro total analysis system (μTAS).

[0077] Reference Figure 1 , a device 1 for determining quantitative sweat parameters is placed on the skin 2 of a human subject, for example on their back. In a variant not shown, the device 1 may be placed on the skin of an animal subject.

[0078] Reference Figure 2 For example, the device 1 is made of a watertight material (e.g., a polymer material) in the form of a space-saving multilayer structure. The multilayer structure includes a lower layer 3 made of a flexible and biocompatible material and an isolation support 4 superimposed on the lower layer 3. Preferably, the flexible and biocompatible material is a self-adhesive material, such as polyethylene terephthalate (PET), which can be directly positioned on the skin 2 of the subject.

[0079] The microfluidic channel 11 is hollowed out from the thickness of the insulating support 4. A sampling cup 5 is made in the lower layer 3 in alignment with the circular opening 6.

[0080] Reference Figure 3 , the lower layer 3 is adhered to the skin 2 by means of an adhesive layer 7. The central part of the lower layer 3 and the adhesive layer 7 comprises a circular opening 6 which defines an investigation area 8 on the skin 2 of the subject, for example, with a diameter of a few millimeters to a few centimeters. The circular opening 6 may present any other shape, for example, an ellipse, a triangle, a rectangle, a square, a polygon, etc. The circular opening 6 forms an inlet hole 6 for guiding a sweat flow 9, in particular to transport the sweat into the microfluidic channel 11. The sweat flow 9 passes from the skin 2 of the subject through the circular opening 6 to the microfluidic channel 11.

[0081] A hydrophilic collecting element (not shown), for example, a fibrous body such as cotton or a nonwoven material, may be disposed in the circular opening 6 and the sampling cup 5. The collecting element transports the sweat produced in the investigation area 8 to the microfluidic electrochemical device 100.

[0082] According to the first embodiment, referring to Figure 4 The multilayer structure of the device 1 includes: a lower layer 3, including an inlet hole 6 allowing sweat to pass through; an upper layer 10, including an outlet hole 22; an intermediate layer 4, located between the lower layer 3 and the upper layer 10, and the microfluidic electrochemical device 100 is formed in the thickness of the isolation support 4, forming an intermediate layer 4 extending parallel to the lower layer 3.

[0083] The microfluidic electrochemical device 100 includes a microfluidic channel 11 connected at a first end to an inlet hole 6 and at a second end to an outlet hole 22. Thus, a sweat flow 9 from the subject's skin 2 is transported into the microfluidic channel 11, which guides the sweat from the inlet hole 6 to the outlet hole 22 by capillary action.

[0084] like Figure 7 or Figure 8 As shown, the microfluidic channel 11 is provided with an electrochemical unit 14 described below. The electrochemical unit 14 is provided on the inner surface of the upper layer 10 that closes the microfluidic channel 11 from above, and is located in the inner space of the microfluidic channel 11.

[0085] In terms of size, the diameter of the inlet hole 6 is a few millimeters, the length of the microfluidic channel 11 ranges between 0.5 cm and 5 cm, and its width ranges between 20 μm and 1,000 μm, the thickness of the intermediate layer 4 ranges between 10 μm and 500 μm, the width of the layers 3, 4, 10 ranges between 1 cm and 5 cm, and the length of the layers ranges between 2 cm and 10 cm.

[0086] For example, the inlet hole 6 has a diameter of 5 mm, the microfluidic channel 11 has a length of 3 cm and a width of 200 μm, the intermediate layer 4 has a thickness of 150 μm, and the layers 3, 4, 10 of the multilayer structure have a width of 3 cm and a length of 9 cm.

[0087] According to the second embodiment, referring to Figure 5 and Figure 6 , the device 1 comprises a main channel 23, which is divided into one or more microfluidic channels in the flow direction of the sweat flow 9, in this case, three parallelepiped microfluidic channels 11a, 11b, 11c parallel to each other, formed in the thickness of the isolation support 6 and separated by partitions 12. Therefore, each microfluidic channel 11a, 11b, 11c is separated from the other microfluidic channels 11a, 11b, 11c, respectively, and sweat can flow independently in the microfluidic channels. The number of microfluidic channels can be higher or lower than Figure 5 and 6 Quantity shown.

[0088] In terms of size, preferably, the microfluidic channels 11a, 11b, 11c have a height ranging between 10 μm and 500 μm, a width ranging between 20 μm and 1,000 μm, and a length ranging between 0.5 cm and 5 cm. The microfluidic channels 11a, 11b, 11c have a constant cross-sectional surface area S a , S b , S c For simplicity, but without loss of generality, it is assumed that the cross-sections of the microfluidic channels 11a, 11b, and 11c have the same surface area S, namely S a =S b =S c =S.

[0089] The sweat discharged by the subject 2 in the investigation area 8 is collected by the portion of the collecting element in contact with the subject's skin 2, and then transferred to the main channel 23 by capillary action so as to flow independently in the microfluidic channels 11a, 11b, 11c of the microfluidic electrochemical device 100. Arrows 13 indicate the flow direction of the sweat in the microfluidic channels 11a, 11b, 11c. Each microfluidic channel 11a, 11b, 11c is provided with an electrochemical unit 14a, 14b, 14c, as shown in FIG. Figure 6 shown and in Figure 7 or Figure 8 Preferably, the microfluidic channels 11a, 11b, 11c lead to an outlet reservoir (not shown) connected to the outlet hole 22. The outlet reservoir retains the sweat to prevent it from returning to contact with the skin 2.

[0090] Reference Figure 7 , the electrochemical cells 14, 14a, 14b, 14c are based on a four-electrode configuration. More specifically, the electrochemical cells 14, 14a, 14b, 14c include independent working electrode pairs WE1 and WE2, counter electrodes CE and reference electrodes REF arranged in the microfluidic channels 11, 11a, 11b, 11c. The electrodes WE1, WE2, CE and REF are produced in the form of microelectrode strips parallel to each other, perpendicular to the flow direction of sweat in the microfluidic channels 11, 11a, 11b, 11c, and are implanted by microfabrication, for example, by chemical vapor deposition (CVD) and / or by photolithography. Therefore, the length of the microelectrode strips corresponds to the width of the microfluidic channels 11, 11a, 11b, 11c.

[0091] The working electrodes WE1 and WE2 can be produced in the form of micro strips made of platinum or platinum-plated platinum (also called platinum black) with a nanometer-scale thickness, for example, tens of nanometers to hundreds of nanometers, typically 200 nm. The working electrodes WE1 and WE2 are spaced apart by inter-electrode distances L, L in the direction of sweat flow in the microfluidic channels 11, 11a, 11b, 11c. a , Lb , L c As will be explained below, the inter-electrode distances L, L a , L b , L c The first working electrode is denoted by the reference numeral WE1 and the second working electrode is denoted by the reference numeral WE2. By convention, the first working electrode WE1 is located upstream of the second working electrode WE2 relative to the flow direction of the sweat of the subject 2 in the microfluidic channels 11, 11a, 11b, 11c.

[0092] A reference electrode REF, produced for example in the form of a strip of Ag / AgCl reference microelectrode with nanoscale thickness (eg 500 nm), is located upstream of the working electrode pair WE1 and WE2 in order to maintain the stability of the reference electrode potential over time.

[0093] The counter electrode CE is located downstream of the working electrode pair WE1 and WE2 and therefore also downstream of the reference electrode REF, so that the chemical substances generated on its surface do not disturb neither the working electrodes WE1 and WE2 nor the reference electrode REF, and the counter electrode is produced, for example, in the form of microstrips, for example, made of platinum, which may or may not be platinum-plated, with a nanometer-scale thickness, for example tens of nanometers to hundreds of nanometers, typically 100 nm. Advantageously, the surface of the counter electrode CE is two to three times larger than the surface area of ​​the other electrodes.

[0094] Advantageously, the microelectrodes produced in the form of microstrips are all deposited on a subnanometer adhesion layer (not shown), for example made of titanium or chromium or the like, depending on the nature of the insulating support 4 , in order to properly adhere the microstrips to the insulating support 4 .

[0095] The microfluidic electrochemical device 100 further includes an electrochemical current measuring system 15. Each of the electrodes WE1, WE2, CE, and REF is connected to the electrochemical current measuring system 15 by means of an electrical contact (not shown) that is electrically insulated from the sweat of the subject.

[0096] The electrochemical current measurement system 15 includes, for example, a potentiostat or a multipotentiostat (not shown) configured to control one, all, or some of the electrochemical cells 14, 14a, 14b, and 14c. More specifically, the electrochemical current measurement system 15 is configured to bias the first working electrode WE1 and the second working electrode WE2 of the electrochemical cells 14, 14a, 14b, and 14c at the first electrode potential E1 and the second electrode potential E2, respectively, to generate a water-soluble H2O in the sweat. (l) Related oxidation or reduction reactions (Examples 1 and 2) or even with water H2O(l) The reaction of the relevant redox couple chemical species, especially molecular oxygen O pre-dissolved in sweat 2(aq) (Example 3).

[0097] The average volume flow rate Q of sweat flowing in the microfluidic channel 11, 11a, 11b or 11c is based on the principle of "time of flight" technology (i.e., based on measuring the flow rate of electroactive chemicals detected by current through the inter-electrode distances L, L between the first working electrode WE1 and the second working electrode WE2). a , L b , L c The time required) and the volume of the microfluidic channels 11, 11a, 11b, 11c, the volume of the microfluidic channel being defined by a plane perpendicular to the plane at which the working electrodes WE1, WE2 are crimped and a plane located at the most upstream limit of each working electrode.

[0098] In the following three embodiments, the working electrodes WE1 and WE2 are respectively Fig. 9 and Fig.10 (Example 1), Fig.11 and Fig.12 (Example 2) and Fig.13 and Fig.14 (Example 3) The method shown in Figure 3 applies a bias voltage. These methods include several steps, which will be explained in more detail for each specific embodiment described below. Graphs 101, 121 and 141 show the first electrode potential E1 applied to the first working electrode WE1 as a function of time t. Graphs 102, 122 and 142 show the second electrode potential E2 applied to the second working electrode WE2 as a function of time t. When the first electrode potential E1 and the second electrode potential E2 present a "0" value on graphs 101, 102, 121, 122, 141 and 142, this corresponds to the corresponding working electrode WE1 or WE2 being disconnected (open circuit), or even corresponding to the application of a potential close to or equal to the equilibrium potential. Graphs 103, 123 and 143 show the intensity of the Faraday current measured at the first working electrode WE1 as a function of time t. Finally, graphs 104, 124 and 144 show the intensity of the Faradaic current measured at the second working electrode WE2 as a function of time t.

[0099] The values ​​of electrode potentials El and E2 provided as examples are provided in volts relative to the standard hydrogen electrode (V / SHE). By convention, the anodic intensity of the Faraday current is presented as positive values, while the cathodic intensity of the Faraday current is presented as negative values.

[0100] Example 1

[0101] In the first embodiment, referring to Fig. 9 The electrode potential difference between the first working electrode WE1 and the counter electrode CE is set such that the first working electrode WE1 is biased at the first electrode potential E1, typically 1.6 V / SHE, thereby allowing water H2O according to the following redox half-equation (l) to be oxidized to molecular oxygen O 2(aq) :

[0102] 6H2O (l) →O 2(aq) +4H3O + (aq) +4e -

[0103] Correspondingly, the electrode potential difference between the second working electrode WE2 and the counter electrode CE is set such that the second working electrode WE2 is biased at the second electrode potential E2, typically -0.3 V / SHE, thereby allowing oxygen O generated on the surface of the working electrode WE1 and dissolved in sweat according to the following redox half-reaction equation 2(aq) to be reduced to water H2O (l) :

[0104] O 2(aq) +4H3O + (aq) +4e - →6H2O (l)

[0105] Referring to Fig.10 , the method for biasing the first working electrode WE1 and the second working electrode WE2 includes two consecutive steps over time t.

[0106] During the first step, before time t0 (i.e., for t < t0), the first electrode potential E1 applied to the first working electrode WE1 can be close to the initial equilibrium potential, or the first working electrode WE1 can even be disconnected. In the subsequent assumption, as shown in Chart 101, the first electrode potential E1 typically exhibits a zero "0" value. The detected anodic intensity i 氧化 is zero, as shown in Chart 103.

[0107] Meanwhile, as shown in Chart 102, the second electrode potential E2 applied to the second working electrode WE2 is set to be lower than the initial equilibrium potential and sufficient to reduce dissolved oxygen O 2(aq) value. As shown in Chart 104, the cathodic intensity i 还原 is proportional to the concentration of molecular oxygen O 2(aq) previously dissolved in sweat; if the initial concentration is zero, the cathodic intensity i 还原 is zero.

[0108] During the second step starting from time t0, as shown in graph 101, the first electrode potential E1 applied to the first working electrode WE1 is fixed at water H2O (l) The oxidation wave begins to produce a considerable amount of molecular oxygen O 2(aq) In other words, the molecular oxygen O near the surface of the first working electrode WE1 2(aq) The total concentration of molecular oxygen O previously dissolved in sweat 2(aq) The concentration of anode is much greater. 氧化 is the oxygen O generated on the surface of the first working electrode WE1 2(aq) The amount of , therefore, is set by the first electrode potential E1 applied to the first working electrode WE1. Once the capacitive current associated with the potential jump is cancelled, the anode strength i 氧化 is constant over time, because the assumed redox reaction at the first working electrode WE1 is not limited by mass transport, since the reactant is water H2O (l) The capacitive current associated with the potential switching is not shown in the figure, only the Faraday current is considered.

[0109] Once the bias voltage is applied to the first working electrode WE1 at time t0, dissolved oxygen O is generated near the first working electrode WE1. 2(aq) The anode intensity i measured at the first working electrode WE1 is 氧化 Since water H2O (l) In Figure 103, the anode strength i 氧化 The increase in is schematically shown by a step function or a Heaviside function. Under the influence of the sweat flow, molecular oxygen O 2(aq) The concentration gradient forms a concentration front driven by convection downstream of the first working electrode WE1.

[0110] At the same time, the second working electrode WE2 is biased at a constant second electrode potential E2. The second working electrode WE2 continuously records the 2(aq) Reduction to water H2O (l) The cathodic intensity i of the generated Faraday current 还原 Therefore, at time t0+Δt, when the molecular oxygen O generated on the surface of the first working electrode WE1 2(aq) When the concentration front passes above the surface of the second working electrode WE2, due to the oxygen O 2(aq) Reduction to water H2O (l) , the detected cathode intensity i 还原 The decrease (in relative terms) is indicated in the diagram 104. The duration Δt corresponds to the generation of molecular oxygen O at the first working electrode WE1. 2(aq)The time required for the front to travel to the second working electrode WE2 under the influence of the sweat flow through the microfluidic channel 11, 11a, 11b or 11c at a flow velocity V.

[0111] The second step ends at a time t1 after the time t0, from which the first working electrode WE1 is again biased to a first electrode potential E1 close to the initial equilibrium potential, or even disconnected, as shown in the diagram 101. The first working electrode WE1 can then be re-biased, so that the method can be repeated as often as necessary in order to determine the average volume flow rate Q at more or less closely successive successive times.

[0112] The method described in this paper is simple and easy to industrialize, because it does not require moving parts and does not require assumptions about the fluid dynamics of the sweat flow in the microfluidic channel. The scheme is independent of determining the concentration of the chemical species generated or contained in the sweat, but only of the response time Δt between the current signals of the working electrode pair WE1 and WE2. In particular, water H2O is chosen (l) Oxidation reaction and molecular oxygen O 2(aq) The reduction reaction allows the amplitude of the detected current signal to be directed to each working electrode WE1, WE2 so as to maintain a sufficient signal-to-noise ratio, thereby allowing changes in the current signal to be easily detected.

[0113] Example 2

[0114] In the second embodiment, referring to Fig.11 , setting the electrode potential difference between the first working electrode WE1 and the counter electrode CE so that the first working electrode WE1 is biased at the first electrode potential E1, typically -0.8 V / SHE, thereby allowing water H2O to be oxidized according to the following redox half equation (l) Reduced to molecular hydrogen H 2(aq) :

[0115] 2H2O (l) +2e - →H 2(aq) +2OH - (aq)

[0116] Accordingly, the electrode potential difference between the second working electrode WE2 and the counter electrode CE is set so that the second working electrode WE2 is biased at a second electrode potential E2 equal to the first electrode potential E1. Similar to the first working electrode WE1, therefore, the second working electrode WE2 is configured to convert water H2O in sweat into (l) Reduced to molecular hydrogen H 2(aq) .

[0117] Reference Fig.12, A method for applying a bias voltage to a first working electrode WE1 and a second working electrode WE2 includes two consecutive steps over time t.

[0118] During the first step, before time t0, i.e., for t < t0, the first electrode potential E1 applied to the first working electrode WE1 can be close to the initial equilibrium potential, or the first working electrode WE1 can even be disconnected. In the subsequent assumption, as shown in Chart 121, the first electrode potential E1 generally exhibits a zero "0" value, such that the detected cathodic intensity i 还原 is zero, as shown in Chart 123.

[0119] Meanwhile, as shown in Chart 112, the second electrode potential E2 applied to the second working electrode WE2 is lower than the initial equilibrium potential to reduce water in the sweat to molecular hydrogen H 2(aq) . As shown in Chart 124, the cathodic intensity i 还原 is constant.

[0120] During the second step starting from time t0, as shown in Chart 111, the first electrode potential E1 applied to the first working electrode WE1 is lower than the initial equilibrium potential, thereby starting to reduce water in the sweat to molecular hydrogen H 2(aq) . Due to the increase in pH brought about by the reduction of water H2O (l) at the first working electrode WE1, the detected cathodic intensity i 还原 decreases (in relative terms). In Chart 123, the decrease in the growth of the cathodic intensity i 还原 is schematically shown by a step function or a Heaviside function. Under the influence of the flow, the partially hydrolyzed sweat is carried by convection downstream of the first working electrode WE1.

[0121] Meanwhile, the second working electrode WE2 is biased at a constant second electrode potential E2. The second working electrode WE2 continuously records the cathodic intensity i 2(aq) of the faradic current generated by the reduction of water in the sweat to molecular hydrogen H 还原 . Thus, as shown in Chart 114, at time t0 + Δt, when the partially hydrolyzed sweat flows over the surface of the second working electrode WE2, the detected cathodic intensity i 还原 increases (in relative terms), i.e., because the concentration of hydronium ions H3O + (aq) is lower upstream of the first working electrode WE1. The duration Δt corresponds to the depleted hydronium ions H3O generated at the first working electrode WE1 + (aq)The time required for the sweat flow front to travel to the second working electrode WE2 under the influence of the sweat flow passing through the microfluidic channels 11, 11a, 11b, 11c at a flow velocity V.

[0122] Under the influence of the sweat flow in the microfluidic channel 11, 11a, 11b, 11c at a flow velocity V, the volume of sweat that has undergone an increase in pH due to the action of the first electrode travels from the first working electrode WE1 to the second working electrode WE2.

[0123] The second step ends at a time t1 after the time t0, from which the first working electrode WE1 is again biased to a first electrode potential E1 close to the initial equilibrium potential, or even disconnected, as shown in the diagram 121. The first working electrode WE1 can then be re-biased so that the method can be repeated as often as necessary in order to determine the average volume flow rate Q at the immediately following consecutive time instants.

[0124] The method described in this paper is simple and can be easily industrialized because it does not require moving parts and does not require assumptions about the fluid dynamics. The scheme is in no way related to determining the concentration of chemical substances generated or contained in sweat, but only to the response time Δt between the changes in the current signal of the working electrode pair WE1 and WE2.

[0125] Example 3

[0126] In the third embodiment, referring to Fig.13 , the electrode potential difference between the first working electrode WE1 and the counter electrode CE is set so that the first working electrode WE1 is biased at the first electrode potential E1, typically -0.3 V / SHE, thereby allowing only oxygen O initially dissolved in the aqueous solution under examination according to the following redox half equation 2(aq) , when it contains the solution, it is reduced to water H2O (l) :

[0127] O 2(aq) +4H3O + (aq) +4e - →6H2O (l)

[0128] Accordingly, the electrode potential difference between the second working electrode WE2 and the counter electrode CE is set so that the second working electrode WE2 is biased at the second electrode potential E2 equal to the first electrode potential E1. Therefore, similar to the first working electrode WE1, the second working electrode WE2 is configured to convert oxygen dissolved in sweat into oxygen. 2(aq) The part of H2O is reduced to the unreduced water H2O at the first working electrode WE1. (l) .

[0129] Reference Fig.14 , a method for applying a bias voltage to a first working electrode WE1 and a second working electrode WE2 includes two consecutive steps over time t.

[0130] During the first step, before time t0, i.e., for t < t0, the first electrode potential E1 applied to the first working electrode WE1 can be close to the initial equilibrium potential, or the first working electrode WE1 can even be disconnected. In the subsequent assumption, as shown in Chart 141, the first electrode potential E1 generally exhibits a zero "0" value, such that the detected cathodic intensity i 还原 is zero, as shown in Chart 143.

[0131] Meanwhile, as shown in Chart 142, the second electrode potential E2 applied to the second working electrode WE2 is lower than the initial equilibrium potential to reduce molecular oxygen O 2(aq) to water H2O(l) . The cathodic intensity i 还原 is constant because it is proportional to the concentration of molecular oxygen O 2(aq) previously dissolved in sweat, as shown in Chart 144.

[0132] As shown in Chart 141, during the second step starting from time t0, the first electrode potential E1 applied to the first working electrode WE1 is lower than the initial equilibrium potential, thus starting to reduce all or some of the molecular oxygen O 2(aq) dissolved in sweat. As a result of the reduction of oxygen O 2(aq) to water H2O (l) , the cathodic intensity i 还原 detected at the first working electrode WE1 decreases (in relative value). In Chart 143, the decrease in the growth of the cathodic intensity i 还原 is schematically shown by a step function or a Heaviside function. The hydrolyzed part of the depleted oxygen O 2(aq) in sweat is carried downstream of the first working electrode WE1 by convection under the influence of the flow.

[0133] Meanwhile, the second working electrode WE2 is kept biased at a constant second electrode potential E2. The second working electrode WE2 continuously records the cathodic intensity i 2(aq) of the Faraday current generated by the reduction of molecular oxygen O (l) to water H2O 还原 . Thus, as shown in Chart 144, at time t0 + Δt, when the depleted molecular oxygen O 2(aq) sweat flow passes over the surface of the second working electrode WE2, the detected cathodic intensity i 还原 increases (in relative value), i.e., it approaches zero because the molecular oxygen O 2(aq)The concentration of is zero, or at least, lower than upstream of the first working electrode WE1. The duration Δt corresponds to the depletion of dissolved molecular oxygen O 2(aq) The time required for the sweat flow to travel from the first working electrode WE1 to the second working electrode WE2 under the influence of the sweat flow passing through the microfluidic channel 11, 11a, 11b or 11c at a flow velocity V.

[0134] The second step ends at a time t1 after the time t0, from which the first working electrode WE1 is again biased to a first electrode potential E1 close to the initial equilibrium potential, or even disconnected, as shown in the diagram 141. The first working electrode WE1 can then be re-biased so that the method can be repeated as often as necessary in order to determine the average volume flow rate Q at the immediately following consecutive time instants.

[0135] The method described in this paper is simple and can be easily industrialized because it does not require moving parts and does not require assumptions about the fluid dynamics. The scheme is in no way related to determining the concentration of chemical substances generated or contained in sweat, but only to the response time Δt between the changes in the current signal of the working electrode pair WE1 and WE2.

[0136] In the above three embodiments, the inter-electrode distances L and L separating the working electrodes WE1 and WE2 can be used to determine the distances. a , L b , L c , and the flow velocity V and volume flow rate Q of sweat flowing in the flow direction 13 through a cuboid parallelepiped shaped microfluidic channel 11, 11a, 11b or 11c having a constant cross-sectional surface area S are determined based on the duration Δt characteristic of the delay of the transient response of the second working electrode WE2 relative to the first working electrode WE1 monitored by chronoamperometry.

[0137] Under the reservations described below, the average linear flow velocity V and the average volume flow velocity Q of the sweat flow flowing in the microfluidic channel (e.g., the microfluidic channel labeled 11 and whose inter-electrode distance is labeled L) can be estimated according to the following equations:

[0138] V=L / Δt

[0139] Q=S x V=L x S / Δt

[0140] Under the same reservation, by using the inter-electrode distance L a , L b , L c These equations are also valid in the microfluidic channels 11 a , 11 b , 11 c , respectively, instead of the inter-electrode distance L.

[0141] In the context of the envisaged dynamic application, in order to monitor the physiological state of the subject in real time, it is advantageous that the device 1 measures the values ​​of the volumetric flow rate Q of sweat at closely successive moments to determine the quantitative sweating parameters of the subject, consistent with the expected sweating rate, for example, once a minute. Then, integrating any real-time changes in the volumetric flow rate Q of sweat allows the determination of the total sweat flow value discharged by the subject within a given time frame t.

[0142] The quantitative sweat parameter may be a sweat rate determined based on the total volume of sweat expelled by the subject relative to the surface area of ​​the investigation area 8 within a given time frame t.

[0143] The inter-electrode distances L and L separating the working electrodes WE1 and WE2 are a , L b , L c is chosen to be small enough so that changes in the subject's physiological response are negligible over the duration Δt, and large enough to allow decoupled operating conditions of the working electrodes WE1 and WE2 in one or each microfluidic channel 11, 11a, 11b, 11c for measuring the volume flow Q.

[0144] In fact, depending on the average linear flow velocity V of the sweat in the microfluidic channel 11, 11a, 11b or 11c, the concentration gradient generated near the first working electrode by generating the electroactive chemical substance (Example 1) or by depleting the electroactive chemical substance already present in the sweat (Examples 2 and 3) is carried through the inter-electrode distance L, L a , L b , L c Afterwards, it may become uniform or non-uniform at the height of the microfluidic channel 11, 11a, 11b or 11c. In particular, when the linear flow velocity V of the sweat is given, the concentration gradient has no time to dissipate at the height of the microfluidic channel 11a, 11b or 11c before reaching the second working electrode WE2, and the operations of the two working electrodes WE1 and WE2 are linked. This coupling state limits the time resolution of the current signal, which disrupts the measurement of the volume flow rate Q of the circulating sweat in the microfluidic channel 11a, 11b or 11c. By adjusting the distances L, L between the electrodes, the measurement of the volume flow rate Q of the circulating sweat can be achieved. a , L b , L c The relative values ​​of the durations t1–t0 and the expected value of the average linear flow velocity V make it easy to avoid this obstacle.

[0145] According to the first embodiment, Figure 6 As shown, the distance L between different electrodes a , L b , L cThe separated first and second working electrode pairs WE1 and WE2 can be used in the separated parallel microfluidic channels 11a, 11b, 11c. Preferably, the inter-electrode distance L separating the working electrodes WE1 and WE2 is a , L b , L c Depending on the microfluidic channel 11a, 11b or 11c considered, for example, L a <L b <L c .

[0146] As a variation, according to Figure 8 In the second embodiment shown, the second working electrode array, in this case the first second working electrode WE2 (1) and the second working electrode WE2 (2) , can be implemented in the same microfluidic channel 11, 11a, 11b, 11c. According to some embodiments not shown, the second working electrode array can include more than two second working electrodes. The rest of the description will be limited to describing the second working electrode array implemented in the microfluidic channel marked as 11. Such an array can also be implemented in microfluidic channels 11a, 11b, 11c.

[0147] In the microfluidic channel 11, each second working electrode WE2 (1) WE2 (2) The inter-electrode distance L is different from that of the first working electrode WE1. (1) , L (2) Working electrodes WE1, WE2 (1) WE2 (2) The duration t1–t0 is electronically adjusted by feeding back the average linear flow velocity value V measured at the previous measurement moment.

[0148] Therefore, the volume flow rate Q can be determined within a wide range of values ​​because the volume flow rate Q can be measured in each of the microfluidic channels 11, 11a, 11b and 11c or in several of them while retaining only the distance L between the electrodes. a , L b , L c , L (1) , L (2) Consistent volume flow rate Q measurement. Advantageously, the inter-electrode distance L a , L b and L c , L (1) , L (2) Millimeter level.

[0149] The above-described method for measuring the volume flow rate Q of sweat can be automatically implemented using the electronic processing device 16 , which is preferably integrated in the device 1 .

[0150] Reference Fig.15 , an embodiment of the electronic processing means 16 will now be described, which may be integrated into the device 1 , for example in the form of an electronic board 17 .

[0151] exist Figure 5 and Figure 6 In the embodiment shown with a plurality of microfluidic channels 11a, 11b, 11c, the electrochemical cells 14a, 14b, 14c are connected to an analog-to-digital converter 18, which itself powers a processor 19. For example, the processor 19 is programmed to implement the above-described method for measuring the volume flow rate Q of sweat.

[0152] exist Figure 8 In the embodiment shown, the first working electrode WE1 and the second working electrode WE2 are provided with different inter-electrode distances L. (1) and L (2) Positioned second working electrodes WE2 (1) WE2 (2) is implemented in the same microfluidic channel 11, consisting of a first working electrode WE1 and a second working electrode WE2 (1) WE2 (2) Each pair formed by one of the forms an electrochemical cell 14 connected to an analog-to-digital converter 18, which itself supplies a processor 19. For example, the processor 19 is programmed to implement the method described above for measuring the volume flow rate Q of sweat.

[0153] An energy source 20, such as a battery, supplies power to the electronic processing device 16. A wired or wireless communication module 21 may also be provided to transmit the results of the sweat volume flow rate Q measurement to a memory or a post-processing device.

[0154] Electronic processing device 16 optionally includes other functional modules, such as gyroscope and / or accelerometer modules for detecting the orientation and movement of subject 2 and for quantifying its activity level, and / or a temperature sensor for measuring the temperature of the epidermis of subject 2. In fact, it is worth knowing the skin temperature because of the correlation between temperature and sweat rate.

[0155] Some elements of the device 1, in particular the electronic processing means 16, can be produced in various forms, in an integral or distributed manner, by means of hardware and / or software components. Hardware components that can be used include application specific integrated circuits (ASICs) and field programmable gate arrays (FPGAs). Software components can be written in various programming languages, such as C, C++, Java or VHDL. This list is not exhaustive.

[0156] Although the present invention has been described in conjunction with several specific embodiments, it is apparent that the present invention is not limited thereto in any way, and that the present invention includes all technical equivalents of the described means and combinations thereof if they fall within the scope of the present invention.

[0157] Use of the verb "comprise" and "include" and their conjugations does not exclude the presence of elements or steps other than those stated in a claim.

[0158] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A microfluidic electrochemical device (100) for measuring a volume flow rate (Q) of a fluid, wherein the fluid comprises a solvent, and wherein the microfluidic electrochemical device (100) comprises: - at least one microfluidic channel (11, 11a, 11b, 11c) configured to allow said fluid to flow along a flow direction (13); - at least one electrochemical unit (14, 14a, 14b, 14c) arranged in the at least one microfluidic channel (11, 11a, 11b, 11c), the electrochemical unit (14, 14a, 14b, 14c) 14c) comprises a first working electrode (WE1) and at least one second working electrode (WE2, WE2 (1) WE2 (2) ), at least one counter electrode (CE) and at least one reference electrode (REF), wherein the at least one second working electrode (WE2, WE2 (1) WE2 (2) ) is separated from the first working electrode (WE1) by an inter-electrode distance (L) in the flow direction (13) a , L b , L c , L (1) , L (2) );and - an electrochemical current measurement system (15) configured to apply a bias voltage to the first working electrode (WE1) at a first electrode potential (E1) and to apply a bias voltage to the second working electrodes (WE2, WE2) at a second electrode potential (E2) (1) WE2 (2) ) applying a bias voltage so that each of the first working electrode and the second working electrode generates a current signal through an oxidation reaction or a reduction reaction of the solvent or an oxidation reaction or a reduction reaction with at least one chemical substance that forms a redox pair with the solvent; The electrochemical current measurement system (15) is configured to measure the current based on the inter-electrode distance (L a , L b , L c , L (1) , L (2) ) and the change of the current signal generated by the first working electrode (WE1) and the change of the current signal generated by the second working electrode (WE2, WE2 (1) WE2 (2) ) is used to determine the volume flow rate (Q) of the fluid in the microfluidic channel (11, 11a, 11b, 11c) based on the time delay (Δt) between the changes in the current signal generated by the microfluidic channel (11, 11a, 11b, 11c).

2. The microfluidic electrochemical device (100) according to claim 1, wherein: The solvent is water H2O.

3. The microfluidic electrochemical device (100) according to claim 2, wherein: The fluid is sweat from a human or animal subject.

4. The microfluidic electrochemical device (100) according to claim 2 or 3, wherein: The first electrode potential (E1) allows water H2O to be oxidized into molecular oxygen O2, and the second electrode potential E2 allows molecular oxygen O2 dissolved in the generated water H2O to be reduced into water H2O.

5. The microfluidic electrochemical device (100) according to claim 2 or 3, wherein: The first electrode potential (E1) allows water H2O to be reduced into molecular hydrogen H2, and the second electrode potential (E2) allows water H2O to be reduced into molecular hydrogen H2.

6. The microfluidic electrochemical device (100) according to claim 2 or 3, wherein: The first electrode potential (E1) allows molecular oxygen O2 dissolved in water H2O to be reduced to water H2O, and the second electrode potential (E2) allows molecular oxygen O2 dissolved in water H2O to be reduced to water H2O.

7. The microfluidic electrochemical device (100) according to any one of claims 1 to 6, wherein: The electrochemical current measurement system (15) is also configured to: - during a first step, biasing the first working electrode (WE1) at the first electrode potential (E1) and biasing the second working electrode (WE2) at the second electrode potential (E2); - During the second step, the first working electrode (WE1) is disconnected or the first electrode potential (E1) is set close to or equal to the zero current equilibrium potential.

8. The microfluidic electrochemical device (100) according to any one of claims 1 to 7, further comprising an isolation support (4), wherein the at least one microfluidic channel (11, 11a, 11b, 11c) is formed in the isolation support (4), and the first working electrode (WE1) and the at least one second working electrode (WE2, WE2 (1) WE2 (2) ) is formed by a metal deposit of platinum or platinum black on the isolation support (6).

9. The microfluidic electrochemical device (100) according to any one of claims 1 to 8, wherein: The counter electrode (CE) is positioned in the flow direction (13) between the working electrodes (WE1, WE2, WE2 (1) WE2 (2) ), and wherein the reference electrode (REF) is positioned in the flow direction (13) at the working electrodes (WE1, WE2, WE2 (1) WE2 (2) ) upstream.

10. The microfluidic electrochemical device (100) according to any one of claims 1 to 9, comprising a first microfluidic channel and a second microfluidic channel (11a, 11b), a first electrochemical unit and a second electrochemical unit (14a, 14b) being respectively arranged in the first microfluidic channel and the second microfluidic channel (11a, 11b), and an inter-electrode distance (L) of the first electrochemical unit (14a) a ) is different from the inter-electrode distance (L) of the second electrochemical unit (14b) b ).

11. The microfluidic electrochemical device (3) according to any one of claims 1 to 9, wherein: The at least one electrochemical unit (14a) comprises two second working electrodes (WE2 (1) WE2 (2) ), the two second working electrodes are respectively separated from the first working electrode (WE1) by a first inter-electrode distance (L (1) ) and the distance between the second electrode (L (2) ), the first inter-electrode distance (L a (1) ) is different from the second inter-electrode distance (L (2) ).

12. The microfluidic electrochemical device (100) according to any one of claims 1 to 11, wherein: The electrochemical current measurement system (15) is configured to determine the volume flow rate (Q) as a function of the cross-sectional surface area (S) of the microfluidic channel (11, 11a, 11b, 11c) in the flow direction (13).

13. A device (1) intended to be placed on an investigation area (8) of the epidermis of a human or animal subject in order to measure a quantitative sweat parameter of said subject, said device (1) comprising: - a structure defining a microfluidic electrochemical device (100) according to any one of claims 1 to 12, said structure comprising an inlet hole (6) defining said investigation area (8) and allowing the passage of sweat from said epidermis, said at least one microfluidic channel (11, 11a, 11b, 11c) of said microfluidic electrochemical device (100) being connected to said inlet hole; and - an electronic processing device (16) configured to determine the quantitative sweat parameter of the human or animal subject based on the measurement of the sweat volume flow rate (Q) performed by the microfluidic electrochemical device (100).

14. The device (1) according to claim 13, wherein: The quantitative sweat parameter of the human or animal subject is sweat rate.

15. The device (1) according to claim 13 or 14, wherein: The structure is a multi-layer structure, comprising a lower layer (3) and at least one layer stacked on the lower layer (3), the microfluidic electrochemical device (100) extends parallel to the lower layer (3), and the lower layer (3) comprises the inlet hole (6).

16. The device (1) according to claim 15, wherein The multilayer structure further comprises an upper layer (10) and at least one intermediate layer (4) located between the lower layer (3) and the upper layer (10), and the microfluidic electrochemical device (100) is formed within the thickness of the at least one intermediate layer (6).

17. The device (1) according to claim 16, wherein The upper layer (10) has an outlet hole (22) passing through the upper layer (10), and wherein the at least one microfluidic channel (11, 11a, 11b, 11c) are connected to the outlet hole (22).

18. The device (1) according to any one of claims 16 or 17, wherein: The first working electrode (WE1), the at least one second working electrode (WE2, WE2 (1) WE2 (2) ), the at least one counter electrode (CE) and the at least one reference electrode (REF) are arranged on the inner surface of the upper layer (10) that closes the at least one microfluidic channel (11, 11a, 11b, 11c) from above, and / or are arranged on the upper surface of the lower layer (3) that closes the at least one microfluidic channel (11, 11a, 11b, 11c) from below.

19. The device (1) according to any one of claims 13 to 18, further comprising a communication device (21) configured to transmit one or more measurement signals generated by the microfluidic electrochemical device (100).

20. The device (1) according to any one of claims 13 to 19, further comprising a gyroscope module and / or at least one accelerometer for detecting the activity state of the human or animal subject.

21. The device (1) according to any one of claims 13 to 20, further comprising a temperature sensor configured to measure the temperature of the epidermis (2) of the human or animal subject.

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