External ears for non-invasive and stable monitoring of volatile organic compounds in human blood

Sci Rep. 2021 Jun 10;11(1):10415. doi: 10.1038/s41598-021-90146-1.


Volatile organic compounds (VOCs) released through skin (transcutaneous gas) has been increasing in importance for the continuous and real-time assessment of diseases or metabolisms. For stable monitoring of transcutaneous gas, finding a body part with little interference on the measurement is essential. In this study, we have investigated the possibility of external ears for stable and real-time measurement of ethanol vapour by developing a monitoring system that consisted with an over-ear gas collection cell and a biochemical gas sensor (bio-sniffer). The high sensitivity with the broad dynamic range (26 ppb-554 ppm), the high selectivity to ethanol, and the capability of the continuous measurement of the monitoring system uncovered three important characteristics of external ear-derived ethanol with alcohol intake for the first time: there is little interference from sweat glands to a sensor signal at the external ear; similar temporal change in ethanol concentration to that of breath with delayed peak time (avg. 13 min); relatively high concentration of ethanol relative to other parts of a body (external ear-derived ethanol:breath ethanol = 1:590). These features indicated the suitability of external ears for non-invasive monitoring of blood VOCs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alcohol Dehydrogenase / chemistry
  • Alcohol Drinking
  • Biosensing Techniques*
  • Blood Gas Monitoring, Transcutaneous*
  • Breath Tests
  • Ear, External / chemistry
  • Enzymes, Immobilized / chemistry
  • Ethanol / chemistry
  • Gases / blood*
  • Humans
  • Volatile Organic Compounds / blood*


  • Enzymes, Immobilized
  • Gases
  • Volatile Organic Compounds
  • Ethanol
  • Alcohol Dehydrogenase