Measurement of volatile organic compounds (VOCs) released from a human body holds great potential for non-invasive and convenient assessment of metabolisms or disease screening. Here, we introduce a biochemical monitoring system for external ear-derived ethanol vapor. The monitoring system consisted of an over-ear gas collection cell and a biochemical gas sensor (bio-sniffer) for ethanol. The bio-sniffer for ethanol was composed of a bifurcated optical fiber, which was connected to a UV-LED (λ = 340 nm), a photomultiplier tube, and an alcohol dehydrogenase (ADH) immobilized membrane. Gaseous ethanol was oxidized through an ADH-catalyzed reaction with the reduction of co-enzyme, β- nicotinamide adenine dinucleotide (NAD). Ethanol was finally measured by detecting the autofluorescence of a product of this reaction, a reduced form of NAD (NADH), at the wavelength of 490 nm. Characterization of the monitoring system demonstrated the high sensitivity with a broad dynamic range (26 ppb – 554 ppm), high selectivity to ethanol, and capability of continuous measurement, which allowed us to monitor external ear-derived ethanol vapor after drinking alcohol. The experiment revealed that there was little interference from sweat in sensor signals at the external ear and a similar temporal change of ethanol concentration to that of breath. These features indicate the suitability of external ears for non-invasive blood VOCs monitoring and the high degree of usefulness of the developed monitoring system.
Trace acetone contained in the human-derived vapor is a potential indicator of lipid metabolisms. Exhaled breath and skin gas contain various kinds of volatile chemicals. Thus, major analytical systems implement chromatographical separation techniques to measure only target chemicals without interference. Such systems are suitable for clinical lab analysis but not for monitoring personal health status. Optical biosensors are suitable for measuring human-derived vapor in a real-time manner because of their high selectivity and sensitivity. Here we report an acetone vapor imaging technique based on secondary alcohol dehydrogenase (S-ADH) immobilized on a laser-patterned hydrophilic polytetrafluoroethylene (PTFE) mesh. The S-ADH catalyzes the reduction of acetone to 2-propanol with concurrent oxidation of coenzyme nicotinamide adenine dinucleotide (NADH) to NAD+. The NADH can be excited by 340 nm of ultraviolet light and emits visible fluorescence at around 490 nm. Acetone concentration can be transduced to a decrement in fluorescence intensity by combining the NADH fluorescence property and S-ADH reaction. S-ADH was immobilized on a breathable hydrophilic PTFE mesh fabricated with laser patterning. In the experiment, fluorescence intensity distribution changing by application of acetone vapor to the S-ADH immobilized mesh was captured by the camera. Fluorescence intensity rapidly decreased at the application point. The decrement was correlated to acetone vapor concentration. The high selectivity against acetone was also observed at typical concentrations and components of volatiles in human breath. Those characteristics will enable the developed technique to measure acetone in human samples in the future.
Volatile organic compounds in exhaled breath and transdermal gas reflect biochemical information such as conditions of diseases and activities metabolisms. In the laboratories, such volatile markers were measured by large analytical systems like gas chromatography-mass spectrometry. If a sensor for volatile markers could be developed that could be used as easily as a wearable device, it could provide early screening for signs of disease and metabolic abnormalities. We have been developing optical biosensors for volatile markers based on nicotinamide adenine dinucleotide (NADH)-dependent enzymes. The NADH has a fluorescence (excitation 340 nm, emission 490 nm) and can be utilized to monitor enzyme reactions. Various kinds of volatile markers including ethanol, acetaldehyde, acetone, 2-propanol and etc could be measured by this technique. Gas imaging was also possible by employing fluorescence imaging optics. Here we introduce gas sensors and imaging systems using a bio-fluorometric technique for human volatile marker sensing.
A bio-optic gas-imaging system (sniff-cam) with enzyme immobilized mesh demonstrates a spatiotemporal gasimaging
for human volatiles (i.e., ethanol, acetaldehyde, etc. after drinking). A bio-fluorometric technique was applied to
improve the sensitivity of the gas visualization system. The bio-fluorometric sniff-cam for ethanol was constructed with
alcohol dehydrogenase (ADH) immobilized mesh and the NADH imaging unit (UV-LED array and highly sensitive
CMOS), thus imaging human ethanol in the gas phase not only exhaled air but also transcutaneous vapor after drinking.
The sniffer system would be useful for detecting the volatile biomarkers.
Gas-phase biosensors (Bio-sniffers, Sniff-cam) have been investigated not only for human volatiles (acetone, methyl mercaptan, trimethylamine, ethanol, isopropanol, etc.) but also for residential harmful VOCs (formaldehyde, toluene, nicotine) causing sick-house syndrome, etc. The biofluorometric bio-sniffers constructed with UV-LED and PMT shows good sensitivity and selectivity for continuous monitoring of target VOCs (formaldehyde, ethanol, acetaldehyde, acetone, isopropanol, etc.). The sniff-cam with enzyme immobilized mesh demonstrates a spatiotemporal gas-imaging for human volatiles (i.e. ethanol, acetaldehyde, etc. after drinking). As novel non-invasive biosensing approaches, the gas-phase biosensors for human and environmental VOCs will be introduced in this contribution. The bio-sniffer for acetone vapor was developed using S-ADH (secondary alcohol dehydrogenase) reverse reaction by detecting NADH fluorometric system. The S-ADH was possible to continuous measure gaseous acetone from less than 1 ppb to 20ppm with a good selectivity based on the enzyme specificity. The device allows to use the evaluation of the acetone concentration in exhaled air from healthy subjects and diabetes patients (type I and II). The novel biofluorometric sniff-cam for ethanol was also fabricated with ADH (alcohol dehydrogenase) immobilized mesh and the NADH visualization unit (UV-LED sheet array and high sensitive CCD), thus imaging human ethanol vapor not only exhaled air but also skin gas after drinking. The sniffer-device would be useful for conventional detecting the volatile biomarkers.
A fluorometric acetone biosniffer (biochemical gas sensor) for assessment of lipid metabolism utilizing reverse reaction of secondary alcohol dehydrogenase was constructed and evaluated. The biosniffer showed highly sensitivity and selectivity for continuous monitoring of gaseous acetone. The measurement of breath acetone concentration during fasting and aerobic exercise were also investigated. The acetone biosniffer provides a novel analytical tool for noninvasive evaluation of human lipid metabolism and it is also expected to use for the clinical and physiological applications such as monitoring the progression of diabetes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.