US20200158680A1

US20200158680A1 - Sweat simulation collection and sensing systems

Info

Publication number: US20200158680A1
Application number: US16/743,101
Authority: US
Inventors: Joshua A. Hagen; Jason C. Heikenfeld; Ian Papautsky; Linlin Hou; Rajesh Naik; Nancy Kelley - Loughnane; Morley Stone; John Busbee; Xiao Wang
Original assignee: University of Cincinnati
Current assignee: University of Cincinnati
Priority date: 2012-04-04
Filing date: 2020-01-15
Publication date: 2020-05-21
Also published as: CN104334274A; EP2834007A2; EP3539471A1; CA2869469A1; CN107884560A; AU2017201480A1; US20220412914A1; CN107884561A; AU2013243541A1; AU2013243541B2; EP2834007B1; JP2015513104A; CN104334274B; WO2013152087A3; US20150057515A1; EP3539478A1; WO2013152087A2; US11460430B2

Abstract

Biological chemicals, potentially found in blood are measured by collecting sweat and determining the concentration or meaning of the selected chemical in sweat. The sweat can be collected using a time based, interval collector 10 and analyzed using an external device. It can also be collected on a one time basis, using a flexible, chemical capacitor 50, or on a continuous basis using a chemical, field effect transducer 98.

Description

RELATED APPLICATION

The present application claims priority to U.S. Ser. No. 61/620,069 filed Apr. 4, 2012, the disclosure of which is hereby incorporated herein by reference in its entirety. The present application further claims priority to International Application No. PCT/US13/35092 filed Apr. 3, 2013, and International Application Publication No. WO 2013/152087 published Oct. 10, 2013, the disclosures of which are hereby incorporated herein by reference in their entireties. The present application further claims priority to U.S. Ser. No. 14/388,416 filed Sep. 26, 2014, and U.S. Application Publication No. US 2015/0057515 published Feb. 26, 2015, the disclosures of which are hereby incorporated herein by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention was made with government support under SAPGrant No. 1008512 awarded by U.S. Air Force Research Labs. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Biomarkers or chemicals carried in the blood can provide significant information which enables one to diagnose ailments, health status, toxins, performance, and other physiological attributes even in advance of any physical sign. Determining the concentration of biomarkers such as electrolytes Interleukin-1α, Interleukin-1β, Interleukin-6, Tumor Necrosis Factor α, Interleukin-8, Vasoactive Intestinal Peptide, Neuropeptide Y, Substance P, Calcitonin-Gene-Related-Peptide, Orexin-A, as well as many, many other biomarkers, provides useful insight into the health of a test patient. For example, pro-inflammatory and anti-inflammatory cytokines as well as neurotransmitters such as neuropeptide-y are associated with many applications, including cardiac stress tests, stroke diagnosis, fatigue and post-traumatic-stress-disorder. Blood tests have been developed for all of these different biomarkers, however blood testing requires that blood be drawn and subsequently analyzed. As another example, direct measurement of electrolytes such as sodium and potassium provides an assessment of hydration. This is currently clinically diagnosed with a blood draw. In addition to being invasive, many biomarkers (such as stress) can be influenced by the blood draw itself. Other test fluids have also considered for determining biomarkers in blood, for example, saliva, urine and breath have all been considered but are awkward and highly prone to contamination. Utilizing implantable sensors to analyze blood is expensive and invasive and presents significant risks.
Sweat is now recently known to carry these biomarkers. However, analyzing sweat for biomarkers raises several questions including how can it be collected, tested, and how does the information on biomarkers obtainable from sweat relate to the biomarker in the blood system.

SUMMARY OF THE INVENTION

The present invention premised on the realization that sweat can be effectively collected and analyzed on a continuous or discontinuous basis to effectively provide an indication of the concentration of biomarkers in the blood system.
More particularly in one embodiment, the present invention provides a sweat collection system which allows a plurality of sweat samples to be collected over a discrete time period to allow analysis of biomarkers versus time. Further by measuring for multiple biomarkers one or more of which being a reference biomarker, one can establish ratios of the amounts of biomarkers in a test sample to provide a reliable indication of the concentration or meaning of the non-reference biomarkers in the blood system.
Further, according to the present invention, sweat can be collected and analyzed utilizing electrochemical bio-assays such as a chemical, field effect transducer (Chem-FET), ion-selective electrode analysis, and impedance spectroscopy. This can be combined with an iontophoresis electrode and a cholinergic agent such as pilocarpine to induce sweating in a non-physically active subject, which can then be collected and analyzed using the electrochemical bio-assay.
In one particular embodiment, the electrochemical bio-assay can be worn as a patch with the data collected over a prolonged period of time and transmitted in response to an external device such as a cell phone or the like, using RFID technology or Bluetooth technology as well as many other technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention we further appreciate in light of the following detailed descriptions and drawings in which:

FIG. 1 is a top plan view of a time based, sweat collection system, according to the present invention;

FIG. 2 is a cross-sectional view partially broken away of the sweat collection system of FIG. 1;

FIGS. 3A-3E are cross-sectional views of a portion of an arm of a collection system as shown in FIG. 1 showing sweat progressing through the collection arm to the collection pad over a period of time, with the sweat shown as stippled shading.

FIG. 4 is an exploded view of an alternate embodiment of the present invention.

FIG. 5 is a circuit diagram of the device shown in FIG. 4.

FIG. 6 is an exploded view of a second alternate embodiment of the present invention.

FIG. 7 is a diagrammatic top plan view of the sweat collector used in the device shown in FIG. 6.

FIG. 8 is a diagrammatic cross-sectional view partially broken away of the assembled device shown in FIG. 6.

FIG. 9 is a circuit diagram of the device shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention sweat is used to determine concentrations or meaning of biomarkers in blood in a non-invasive manner As shown in FIG. 1, a sweat collector 10 that permits chronological sweat storage of a plurality of samples includes a central sweat collection member 12 having a sweat collecting central base 14 leading to a central fluid transporting core 16 leading to a plurality of arms 18. Core 16 further leads to a top portion 20 (only shown in FIG. 2) which allows for evaporation or storage of the sweat which therefore provides for continued fluid flow.
The sweat collector member 12 can be formed from any material which will readily transport sweat. Generally, a fibrous web, such as a cellulosic web, is particularly suitable for use in this application. It can be treated with a hydrophilic substance which will promote fluid flow. However, any material which will readily allow aqueous fluid flow can be used as the sweat collection member.
Sweat collection member 12 rests on a sweat porous adhesive layer 22 which permits the collector 10 to be adhered to an individual's skin 23. Separating the base 12 from the arms 18 is a water impervious flexible film 24 which has a central opening 26 corresponding with the central core 16 of the sweat collection member 12.
The radially extended arms 18 rest on the upper surface of the plastic film 24. Each arm leads to a gate member 28 which in turn extends radially outward to a bridge member 30 and finally to a collection pad 32. The arms 18, gates 28, bridges 30, and collection pads 32 are all covered with a vapor porous membrane 34 (not shown in FIG. 1, shown in FIG. 2) which also has a central opening 36 that allows the core 16 to extend through, leading to an upper fluid transporting disk 20 which simply allows fluid evaporation and flow which promotes the continued migration of sweat from the skin through the collection member 12. Disk 20 can further be coated with a super absorbent hydro gel (not shown) to further facilitate fluid flow. Alternately the disk 20 may be covered with a vapor porous membrane like that of vapor porous membrane 34. Various components of the sweat collector 10 can be arranged in multiple ways, some even excluded, so long as they satisfy the operating principles of the present invention. Furthermore, this type of sweat collector 10, may also prove useful for simple chronological collection and storage of other fluids, ranging from saliva to non-biological fluids such as river water in environmental sampling applications.
As shown in FIG. 3, the gates 28 act to delay fluid flow to the collection member 32. Each gate is slightly different from all other gates as explained below. Each of the different gates, delay the fluid flow for a different period of time so that the sweat reaches each of the collection pads at different times, thereby providing discrete chronological sweat samples at times T₁-T₁₂as shown, with the shown 12 times being exemplary only and non-limiting. The gate 28 can be formed from a variety of different materials. One particular material suited for this application is a water soluble polymeric film member which inhibits fluid flow but gradually dissolves in the presence of a fluid like sweat. Once it dissolves, it permits sweat to flow past the gate to fill the bridge 30 and the pad 32. The different gates 28 can be formed from different thicknesses of the water soluble film or the polymeric composition of the film can be adjusted in each of the gates to establish different dissolution rates. This can be done for example by choosing film with different molecular weights. One preferred material is polyethylene oxide. The water solubility of these films can be adjusted by changing the molecular weight of the polyethylene oxide with the lower molecular weight films being more soluble. Alternately, the thickness of the film can be adjusted, with a thinner film being dissolved more quickly than a thicker film. Once the gate 28 dissolves, the sweat will pass over the gate. The gate 28 may fully dissolve, or it may simply become sweat permeable, achieved for instance with a cloth or cellulose fiber film that has been embedded with polyethylene oxide polymer.
The gates 28 are in turn in fluid communication with what are referred to as bridges 30. The bridges 30 are simply fluid conduits that only allow fluid flow for a limited period of time before they become suitably impervious to fluid flow or solute diffusion. These fluid conduits 30 will allow sweat from the gates to flow to the collection pads 32. However after a certain volume of sweat has passed through the bridge 30, it will dissolve or become impermeable to further fluid flow or solute transport, interrupting the fluid path, and preventing further sweat solutes (ions, molecules, biomarkers) from being transported into or out of the collection pad 32. Thus each collection pad 32 would receive sweat sample at a time permitted by the gate 28. When the bridge 30 dissolves, it isolates the sample on pad 32 such that the biomarker information is not blended, diluted, or distorted by sweat from later collection time periods. The present invention includes all methods that achieve this same basic functionality of sampling and isolating sweat samples, storing them in a manner that properly preserves them, and sampling and storing them in a manner which the sweat sample is representative of the sweat excreted at or near the time of sampling. The sweat collector 10 can therefore utilize alternate materials that physically or chemically change in any manner that provides similar results, including but not limited to bridges made of polymers that cross-link after some time of sweat exposure to prevent fluid flow and/or gates based on a material that slowly swells and moves into fluid connection with the next fluidic component of a sweat collector.
The bridge can be any water soluble member that has an acceptable dissolution rate. In particular, the bridge can be a polyethylene oxide thread having a fibrous surface which allows capillary migration of the sweat across a polyethylene thread. Once the thread dissolves, fluid will no longer pass to the collection pad 32 as there will be a void on the upper surface of the plastic film 24 thereby preventing further fluid flow.
The pads 32 can be tested for a variety of different biomarkers. In particular it may be desirable to analyze one or more reference biomarkers to determine the amount of a reference biomarker and compare this to a non-referenced tested biomarker, where the concentration of the referenced biomarker is generally known. This permits one to use the ratio of the referenced biomarker to the tested biomarker to determine the concentration of the tested biomarker without knowing the volume of sweat being tested. Typical reference biomarkers include known methods such as those used to determine electrolyte balance. Some biomarkers found in sweat may degrade quickly due to enzymatic or other forms of decomposition or breakdown, and storage, preservation, chemical reacting, or other chemicals, materials, or components, may be included in or with the pad 32 to preserve the desired information provided by the biomarkers.
In use, the time specific sweat collector 10 is applied to an individual skin by placing the collector on the skin with the sweat porous adhesive 22 contacting the skin. Generally, the adhesive layer will have a protective release layer (not shown) which is removed prior to use. The individual then can continue with daily activity, or sports activity, or the like. Pilocarpine can be applied at the area where the collector is applied to induce sweat formation before or after the sweat collector 10 is applied, or sweat can be generated through natural occurring methods or other forms of stimulation. Components of multiple sweat collectors 10 may be stacked and connected with additional bridges or gates to increase the duration of use and total sample collections of the sweat collector 10.
Sweat, shown as stippling in FIGS. 3A-3E, will then, as generated, travel up the central core 16 extending to the plurality of arms 18 (see FIG. 3A) and then to the individual gates 28 (see FIG. 3B). A first gate will dissolve at time T1 and a second gate at time T2 and third gate at time T3 and so on. As the gates dissolve (see FIG. 3C), sweat can migrate over the surface of dissolved polyethylene oxide film. The polyethylene oxide fiber bridge 30 will allow sweat to immediately migrate to the respective collection pad 32 (See FIG. 3D). After a period of time, the bridge 30 will dissolve (See FIG. 3E), because the bridge is narrow and breaks up by capillary-breakup, there is none or not enough polymer to allow sweat to continue to the pad 32. Thus, a first pad will stop collecting sweat at time T1+X, and a second pad at T2+X, and a third pad at T3+X, and so on, with X being the time required for the bridge 30 to dissolve. The time X could also be a variable controlled, especially so if time-averaged sampling is desired. After a period of time, the collector 10 is removed and the individual pads are analyzed for certain biomolecules using standard analysis and apparatus such as mass spectroscopy, colorimetric spectroscopy, electrophoresis, or other biomarker measurement methods known by those skilled in the art. This will provide time-based information which allows one to correlate concentration of the biological molecules in the blood stream over a period of time, with either physical factors, such as periods of stress, or in relationship to the effects of drugs and the like.
As shown in FIGS. 4 and 5, an alternative embodiment of the present invention, is a one-time use sweat collector/sensor 50 referred simply to as the disposable sensor 50. This apparatus is designed to quickly generate and absorb sweat in a short period of time and allow immediate electrical detection of biomarkers. The disposable sensor 50 is either fully disposable or just portions thereof are disposable, with the primary feature being fast stimulation and sensing of sweat in a single wearable format. The disposable sensor 50 includes a chemical capacitor 66 or other biological chemical sensor and a disk 54 which acts as a reservoir of a cholinergic agent such as pilocarpine followed by an iontophoresis electrode 56, all secured to a wristband 58. As can be seen, wiring 60 leads from the wrist band to a second apparatus which controls the disposable sensor 50. The apparatus (not shown) can be, for example, a computer, a smart phone, or simply a dedicated device designed to operate and analyze the data set forth from the chem capacitor 66.
Chem capacitor 66 is found on a planar support layer 52 and is partially functionalized with one or more molecules adapted to bind to one or more biomarkers being studied. As such, the capacitor 66 can be a very simple, planar capacitor or interdigitated electrodes, depending upon the number of biomarkers being detected. Support layer 52 includes a series of holes 69 permitting the pilocarpine to move through the layer 52 and sweat to flow in the opposite direction to the capacitors 66. Reference, ground, and working electrodes may also be included or excluded. Other suitable sensors include chemical field effect transistors, chemical electrical impedance spectroscopes and electrochemical potentiostats.
A general wiring diagram for the device 50 is shown in FIG. 5. In a preferred embodiment only the chem capacitor 66, disk 54, and electrode 56, are actually on the disposable portion of the sensor with the remaining circuitry are in the separate control apparatus or external device (not shown).
In use, the disposable sensor 50 would be strapped on an individual's wrist with the wristband 58. Other means to attach the sensor to a body part can also be employed such as adhesives, tape and the like. The location of the sensor is not particularly critical, and can be used at almost any portion of the body with adequate surface area and access to sweat pores.
Once attached, the wires 60 are attached to the control apparatus and the iontophoresis electrode 56 is activated, causing the pilocarpine to migrate from disk 54 through holes 69. This will cause the formation of sweat. Since the chem capacitor 66 is adjacent skin, it will immediately contact the sweat. If the biomarker is present in the sweat, this will immediately be detected by change in electrical charge or electrical impedance. Generally multiple biomarkers or chemicals will be detected. In particular, one may be the reference biomarker. The concentration or meaning of the remaining biomarkers can be estimated based on the concentration or meaning of the reference biomarker. Once used for a set period of time, the sensor is thrown away. Basically, any biological chemical present in blood can be detected. Primarily biomarkers which are indicative of physical state are of interest. These include but are not limited to electrolytes, glucose, lactate, pro-inflammatory cytokines, anti-inflammatory cytokines, catecholamines, neuropeptides, as well as any protein which may be present in blood.
A third embodiment of the present invention is shown in FIGS. 6-9. Continuous sensor 70 incorporates a sweat porous adhesive layer 72, and a sweat transportation medium 74. The sweat transportation medium includes a collection pad 76 resting on the adhesive layer 72, a transfer section 78, which leads to an evaporation or storage pad 80. Although shaded differently, the collection pad 76, the transfer section 78 and the evaporation pad 80 will normally be made from the same material. The transfer section 78 extends from the collection pad 76 and around a chem-field effect transducer 82. The sensor 70 includes an upper vapor porous covering 84, which allows sweat to evaporate, and thus continue to flow through the collection pad. The covering 84 may include a layer of a hydrogel (not shown) to store sweat and therefore be less reliant on evaporation of sweat.
The sweat transport medium 74 is designed to continually promote sweat transfer in only one direction through the collection pad 76, otherwise the collection pad would fill up and not provide a continuous analysis of newly-produced sweat. Therefore, the transfer section 78 is formed from a plurality of narrow strips, which reduces the fluid flow path from the collection pad 76 to the evaporation pad 80. The enlarged evaporation pad 80 promotes fluid flow both by its size and by evaporation. Thus the reduced flow permitted through the transfer section 78 and the fluid flow promotion caused by evaporation in the evaporation pad 80 provides a continuous flow of sweat through the collection pad 76 to the evaporation pad 80 without any reverse flow or undesirable levels of back-diffusion of solutes or biomarkers. The transport medium 74 can be any medium which will absorb and transfer aqueous fluids. This can, for example, be any woven or non-woven web, and particularly non-woven webs. Cellulosic fiber webs are particularly suitable for such uses. If solutes or biomarker buildup or concentration is excessive over time, the evaporation pad 80 may be replaced or washed with water. The evaporation pad may be any material or component that serves to remove fluid, including hydrogels that simply pull in fluid by wick and swell in size as they absorb the fluid. Therefore the evaporation pad may be more broadly considered as simply a sweat removal element.
Chem-FET 82 includes a flexible base plastic layer 92 formed from Kapton or similar suitable materials. Along a periphery 93 of the base layer 92 is an RFID antenna 94 and a control chip 96. In turn, the Chem-FET 82 includes a sensor section 98 which is connected to the chip 96 through a connection strip 100. As shown, the area 99 between the sensor section 98 and the RFID antenna 94 is open which allows pilocarpine to be located in the evaporation pad 80 or an adjacent layer (not shown) to promote sweat. An iontophoresis electrode can also be included adjacent the pilocarpine. When assembled, the sensor section 98 rests directly on the transfer section 78 analyzing sweat as it is transported from the skin. As shown by arrow 106, transport section and evaporation section 80 are on the side of sensor section 98 adjacent layer 84 and collection pad 76 is on the opposite side adjacent adhesive 72.
Preferably, the sensor section 98 is a gate-exposed SiCMOS chips having three or more identical chem-FETs per biomarker. Sub-microns SiCMOS allow for MHz impedance spectroscopy. Multi-step patterning/washing may be used to immobilize biorecognition elements. Sensors are separated spatially into subgroups of identical sensors, or large sensor arrays can be formed using techniques such as photo-initiated chemical patterning. The sensors allow for continuous monitoring of multiple physiological conditions realizing larger arrays of biomarker-specific sensors. The larger arrays can determine physiological condition through semi-specific but distinct sensors by statistical determination, eliminating the need to quantify individual biomarker levels.
In another embodiment, the sensor section 98 is an electrode, or array of electrodes, which is coated with an ion-selective material. This ion-selective material allows only one type of ion to pass through to the electrode surface, thus allowing for quantitative analysis of a single molecule type, such as sodium or potassium to name two. These ion-selective sensor arrays can determine hydration status of an individual.
It is desirable to have the chip 96, which is somewhat thicker than the printed circuitry 101, face away from the skin, but it is also desirable to form everything on one surface. The chem-FET 82 is formed by electro-deposition of the circuitry on one surface of base layer 92. The central portion 99 is then cut out. Although it is preferred to have the circuiting 101 positioned on transfer section 78, due to the flexible nature of the base layer substrate 92, the sensor section 98 can be rotated 180 degrees with the circuitry 101 positioned directly against the collection pad 76, if desired.
The chip 96 can be purchased. A variety of such chips are available on the market. One particular chip which can be used for the present invention is MLX 90129 (sold by Melexis), which is capable of up to 500 micro ampsin run mode. This chip has an internal temperature sensor. Chip 96 can also control the iontophoresis electrode if present.
In operation, this device would be attached to the skin with the adhesive layer 72. A reader, such as a smart phone, would then be strapped in close proximity to the sensor 70 on a periodic basis, for example, every few minutes, the smart phone detects and records concentrations of the selected biomolecules such as neuropeptides, cytokines, electrolyte balance, and body temperature.
The continuous sensor 70 can be modified in a wide variety of ways to provide added benefits. For example, a more robust wireless protocol such as Bluetooth can be utilized, or alternate communication or power strategies can be used. For example, the sensor can include a thin layer battery and provide its own power source, and thus not rely on RFID. Both RFID and Bluetooth can be used in conjunction where RFID can be used to charge the battery when provided the proper near field communications. In addition, an upper layer of hydrogel can be incorporated to promote a greater sweat flow. Other biomarker sensing methods and sweat transport methods may be included, so long as they provide the same capability of continuous or semi-continuous monitoring of biomarkers in sweat.
The sweat collectors of the present invention can provide a wide variety of different benefits. Time-based sweat collector 10 can be used for example in a cardiac stress test, allowing cardiac cytokine biomarker mapping versus time with no blood catheter required. lontophoretically dosing pilocarpine for less than five minutes can stimulate sweating for the duration of such a test. Sweat collector 10 can then be positioned and later analyzed using proven techniques such as mass spectrometry. The sensor 10 can be used as a non-invasive study of the chronological systemic response of a new drug treatment. It can also be used by athletes during regular athletic activity for improved sport exertion or impact studies.
The disposable sensor 50 can be used to quickly test for very specific critical biomarkers. For example, paramedics could use this device with potential stroke victims, by strapping it onto a patient's arm; there would be no need to find a vein. The device would provide sweat in 2 to 3 minutes, and detect biomarkers 1 to 2 minutes later. Three major cytokines, namely tumor necrosis factor, interleukin 1 and interleukin 6, are produced by cultured brain cells after various stimuli, such as ischemia. This provides a diagnostic test which will expedite the appropriate treatment. By selecting the appropriate biomarkers, one can even differentiate ischemic versus hemorrhagic strokes. This very specific, inexpensive sensor can also be used in a wide variety of different time critical tests.
The continuous monitor, in addition to be useful for time-based testing of athletes and in clinical studies, can also be used as a preventive control of the onset of severe depression by detecting certain cytokines and neuropeptides. It can also be used to anticipate migraine headaches, and can be used for continuous diabetes monitoring.
Both the disposable sensor as well as the continuous monitor can be used for determining hydration status rapidly and/or continuously.
This has been a description of the present invention along with a preferred method of practicing the present invention, however the invention itself should only be defined by the appended claims.

Claims

What is claimed is:

1. A method, comprising:

collecting a volume of sweat from an area of skin of an individual;

determining a concentration of a first solute in the volume of sweat without quantifying the volume of sweat;

determining a concentration of a second solute in the volume of sweat to establish a ratio of the first solute to the second solute.

2. The method of claim 1, wherein the first solute and the second solute are selected from the group consisting of: an electrolyte, glucose, lactate, a pro-inflammatory cytokine, an anti-inflammatory cytokine, a catecholamine, a neuropeptide, and a protein.

3. The method of claim 1, further comprising:

using the ratio to estimate a concentration of the first solute in a blood sample of the individual, wherein the second solute is a reference biomarker.

4. A method, comprising:

collecting a volume of sweat from an area of skin of an individual;

measuring a concentration of a first solute in the volume of sweat;

measuring a concentration of a reference solute in the volume of sweat; and

establishing a ratio of the first solute to the reference solute.

5. The method of claim 4, further comprising:

using the ratio to estimate a concentration of the first solute in a blood sample of the individual.

6. The method of claim 4, further comprising:

using the ratio to estimate a concentration of the first solute in a blood sample of the individual without quantifying the volume of sweat.

7. The method of claim 4, further comprising:

using the ratio to indicate a physiological meaning of the concentration of the first solute in a blood system of the individual.

8. The method of claim 4, further comprising:

using the ratio to indicate a response by the individual to a drug treatment.

9. The method of claim 4, wherein the reference solute is chosen from the following: an electrolyte, sodium, potassium, a protein, lactate, a cytokine, a catecholamine, and a neuropeptide.

10. The method of claim 4, wherein the concentration of the first solute and the concentration of the second solute are measured by one of the following: a mass spectroscopy technique, a colorimetric spectroscopy technique, an electrophoresis technique, an ion-selective electrode sensor, a chem-FET sensor, a biorecognition sensor, and an electrochemical sensor.

11. The method of claim 4, further comprising a step prior to collecting the volume of sweat, the step comprising:

stimulating the area of skin to cause the generation of sweat by one of the following: introducing a cholinergic agent into the skin using an iontophoresis electrode, or applying a cholinergic agent to the skin.

12. A method, comprising:

collecting a volume of sweat from an area of skin of an individual;

measuring a concentration of a first biomarker in the volume of sweat;

measuring a concentration of a second biomarker in the volume of sweat;

establishing a ratio of the first biomarker to the second biomarker; and

using the ratio to determine a response by the individual to a drug treatment.