Sweat diagnostics

Sweat diagnostics is an emerging non-invasive technique used to provide insights to the health of the human body. Common sweat diagnostic tests include testing for cystic fibrosis[1] and illicit drugs.[2] Most testing of human sweat is in reference to the eccrine sweat gland which in contrast to the apocrine sweat gland, has a lower composition of oils.[3]

Sweat diagnostics
Purposetest for Eccrine sweat gland(mostly)

Although sweat is mostly water,[3] there are many solutes which are found in sweat that have at least some relation to biomarkers found in blood. These include: sodium (Na+), chloride (Cl−), potassium (K+), ammonium (NH+
4), alcohols, lactate, peptides & proteins.[4][5] Development of devices, sensing techniques and biomarker identification in sweat continues to be an expanding field for medical diagnostics and athletics applications.

The use of smart biosensors for on-skin sweat analysis has been described as internet-enabled Sudorology (iSudorology) by Brasier et al. in 2019. It describes the lab-independent detection of molecular, next-generation digital biomarkers in sweat.[6]

History

Some of the earliest, published studies[7] on sweat composition date back to the 19th century. Further studies[8][9][10] in the 20th century began to solidify understanding of the physiology and pharmacology of the eccrine sweat gland. In-vivo and in-vitro studies from this time period, and even those continuing today, have identified numerous structural nuances and new molecules present within sweat. The first commercially adopted use for sweat diagnostics included testing of sodium and chloride levels in children for the diagnosis of cystic fibrosis. Today, one of the most popular devices for this testing is the Macroduct Sweat Collection System from ELITechGroup.[11]

General evidence

More recently, numerous studies have identified the plausibility of sweat as an alternative to blood analysis.[12][13] The potential substitution for sweat versus blood analysis has many potential benefits. For example, sweat can be: extracted in a non-invasive manner via iontophoresis; extracted with little-to-no pain; and monitored continuously.[14] There are downfalls to the technology, however. For example, demonstration of successful and reliable sweat extraction and analysis on a cohesive device has yet to be demonstrated. Furthermore, although some biomarker partitioning mechanisms are well understood and well studied, partitioning of other useful biomarkers (cytokines, peptides, etc.) are less understood.[4]

Current research

Patches

Patches have been demonstrated to be a promising detection platform for sweat diagnostics.[15][16][17] Simple, long-term collection devices which check for drugs of abuse or alcohol are already on the market and operate on the following principle: a user applies the patch which then collects sweat over a period of hours or days, then the patch is analyzed utilizing techniques such as GC-MS which are accurate but have the drawback of lack of continuous measurements and high costs. For example, sweat diagnostic products for illicit drugs and alcohol are manufactured and supplied by PharmChem and AlcoPro, respectively. Recently several efforts[18] have been made to develop low cost polymer based continuous perspiration monitoring devices and are in early stages of commercialization.[19]

More recently, several startup companies such as Xsensio or Eccrine Systems have begun developing products targeted towards the consumer, healthcare and athletics market for sweat diagnostics. Ultimately, it is the hope that these devices will have the ability to detect changes in human physiology within minutes without the need for repeated sample collection and analysis.[20]

Temporary tattoos

Temporary tattoo-based sweat diagnostic tools[21] have been demonstrated by Dr. Joseph Wang's group from University of California, San Diego. Their work includes sweat diagnostics for sodium, lactate, ammonium, pH and biofuel opportunities.[22]

References
  1. Mishra A, Greaves R, Massie J (November 2005). "The relevance of sweat testing for the diagnosis of cystic fibrosis in the genomic era". The Clinical Biochemist. Reviews. 26 (4): 135–53. PMC 1320177. PMID 16648884.
  2. De Giovanni N, Fucci N (2013). "The current status of sweat testing for drugs of abuse: a review". Current Medicinal Chemistry. 20 (4): 545–61. doi:10.2174/0929867311320040006. PMID 23244520.
  3. Wilke K, Martin A, Terstegen L, Biel SS (June 2007). "A short history of sweat gland biology". International Journal of Cosmetic Science. 29 (3): 169–79. doi:10.1111/j.1467-2494.2007.00387.x. PMID 18489347.
  4. Sonner Z, Wilder E, Heikenfeld J, Kasting G, Beyette F, Swaile D, Sherman F, Joyce J, Hagen J, Kelley-Loughnane N, Naik R (May 2015). "The microfluidics of the eccrine sweat gland, including biomarker partitioning, transport, and biosensing implications". Biomicrofluidics. 9 (3): 031301. doi:10.1063/1.4921039. PMC 4433483. PMID 26045728.
  5. Sato K, Kang WH, Saga K, Sato KT (April 1989). "Biology of sweat glands and their disorders. I. Normal sweat gland function". Journal of the American Academy of Dermatology. 20 (4): 537–63. doi:10.1016/s0190-9622(89)70063-3. PMID 2654204.
  6. Brasier N, Eckstein J (2019). "Sweat as a Source of Next-Generation Digital Biomarkers". Digital Biomarkers. 3 (3): 155–165. doi:10.1159/000504387. PMC 7011725. PMID 32095774.
  7. Hoelscher JH (1899). "A Study in Perspiration.: Original Research in One Hundred and Thirteen Cases". Journal of the American Medical Association. 32: 1352–1360. doi:10.1001/jama.1899.92450510001003.
  8. Nyman E, Palmlöv A (1936). "The elimination of ethyl alcohol in sweat". Skandinavisches Archiv für Physiologie. 74 (2): 155–159. doi:10.1111/j.1748-1716.1936.tb01150.x.
  9. Schwartz IL, Thaysen JH (January 1956). "Excretion of sodium and potassium in human sweat". The Journal of Clinical Investigation. 35 (1): 114–20. doi:10.1172/JCI103245. PMC 438784. PMID 13278407.
  10. Sato K (1977). "The physiology, pharmacology, and biochemistry of the eccrine sweat gland". Reviews of Physiology, Biochemistry and Pharmacology. 79: 51–131. doi:10.1007/BFb0037089. ISBN 978-3-540-08326-9. PMID 21440.
  11. Pullan NJ, Thurston V, Barber S (May 2013). "Evaluation of an inductively coupled plasma mass spectrometry method for the analysis of sweat chloride and sodium for use in the diagnosis of cystic fibrosis". Annals of Clinical Biochemistry. 50 (Pt 3): 267–70. doi:10.1177/0004563212474565. PMID 23605131.
  12. Czarnowski D, Górski J, Jóźwiuk J, Boroń-Kaczmarska A (1992). "Plasma ammonia is the principal source of ammonia in sweat". European Journal of Applied Physiology and Occupational Physiology. 65 (2): 135–7. doi:10.1007/bf00705070. PMID 1396636.
  13. Cizza G, Marques AH, Eskandari F, Christie IC, Torvik S, Silverman MN, Phillips TM, Sternberg EM (November 2008). "Elevated neuroimmune biomarkers in sweat patches and plasma of premenopausal women with major depressive disorder in remission: the POWER study". Biological Psychiatry. 64 (10): 907–11. doi:10.1016/j.biopsych.2008.05.035. PMC 2610843. PMID 18657799.
  14. Banga AK, Chien YW (1988). "Iontophoretic delivery of drugs: fundamentals, developments and biomedical applications". Journal of Controlled Release. 7: 1–24. doi:10.1016/0168-3659(88)90075-2.
  15. Scutti S (29 October 2014). "Measuring Your Sweat, A Health Monitor And Diagnostic Device Is The Future Of Wearable Technology". Medical Daily.
  16. Fenner R (8 May 2015). "CoreSyte Selected as Worldwide Athletics Partner by Eccrine Systems". Business Wire.
  17. Begonia R (5 December 2014). "Kenzen Wearable Optimizes Athletic Performance with Real-Time Hydration, Lactic Acid and Glucose Analysis". PR Newswire.
  18. Jain V, Ochoa M, Jiang H, Rahimi R, Ziaie B (2019-06-17). "A mass-customizable dermal patch with discrete colorimetric indicators for personalized sweat rate quantification". Microsystems & Nanoengineering. 5 (1): 29. Bibcode:2019MicNa...5...29J. doi:10.1038/s41378-019-0067-0. PMC 6572848. PMID 31240108.
  19. US 10772560, Ziaie, Babak; Ochoa, Manuel P. & Jain, Vaibhav et al., "Skin-mounted hydration sensor and management system", published 2020-09-15, issued 2017-10-02, assigned to Purdue Research Foundation
  20. Heikenfeld J (22 October 2014). "Sweat Sensors Will Change How Wearables Track Your Health". IEEE Spectrum.
  21. Free K (13 August 2014). "A Temporary Tattoo to Track Your Workout and Charge Your Phone". Popular Mechanics.
  22. Bandodkar AJ, Jia W, Wang J (2015). "Tattoo-Based Wearable Electrochemical Devices: A Review". Electroanalysis. 27 (3): 562–572. doi:10.1002/elan.201400537.
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