Self-powered triboelectric nanogenerator sensor for detecting humidity level and monitoring ethanol variation in a simulated exhalation environment

Abstract

Respiration stands as a vital process reflecting physiological and pathological human health status. Exhaled breath analysis offers a facile, non-invasive, swift, and cost-effective approach for diagnosing and monitoring diseases by detecting concentration changes of specific biomarkers. In this study, we employed Polyethylene oxide/copper (I) oxide composite nanofibers (PCNFs), synthesized via the electrospinning method as the sensing material to measure ethanol levels (1-200 ppm) in an exhaled breath simulator environment. The integrated contact-separation triboelectric nanogenerator was utilized to power the self-powered PCNFs exhaled breath sensor. The PCNFs-based gas sensor demonstrates promising results with values of 0.9 and 3.2 for detecting 5 ppm and 200 ppm ethanol, respectively, in the presence of interfering gas at 90% relative humidity (RH). Notably, the sensor displayed remarkable ethanol selectivity, with ratios of 10:1 to methanol and 25:1 to acetone. Response and recovery times for 200 ppm ethanol at 90 RH% were rapid, at 2.7 s and 5.8 s, respectively. The PCNFs-based exhaled breath sensor demonstrated consistent and stable performance in practical conditions, showcasing its potential for integration into wearable devices. This self-powered breath sensor enabling continuous monitoring of lung cancer symptoms and facilitating compliance checks with legal alcohol consumption limits.

Figure 1

Synthesis procedures of exhaled breath sensors: (a) Polyethylene Oxide Nanofiber (PNFs) Sensor, and (b) Polyethylene Oxide/Copper (I) Oxide Composite Nanofibers (PCNFs) Sensor.

Figure 2

The experimental set-up comprises an exhaled breath simulator intended to evaluate the performance of PCNFs sensors across various environments containing different ethanol concentrations (1, 2, 5, 20, 50, 100, 200 ppm) at 90 RH% through two distinct modes: (a) employing an external power source via µAuto-lab system, and (b) utilizing a triboelectric nanogenerator for self-powering.

Figure 3

(a) Schematics of integrated FTO/Kapton TENG- powered- sensor; (b) Open-circuit voltage (V_OC) of the FTO/Kapton TENG operating under various working frequencies ranging from 1 to 4 Hz; (c) The voltage amplitude diversity of the FTO/Kapton TENG vs external load resistance; (d) The evolution of power and current of FTO/Kapton TENG versus external load resistance.

Figure 4

Top view FESEM images of (a) polyethylene oxide/copper (I) oxide composite nanofibers (PCNFs); and (b) polyethylene oxide nanofibers (PNFs) at different magnifications (I) 5 kx, (II) 10 kx, (III) 50 kx.

Figure 5

(a) EDS of PCNFs at different magnifications (I) 5 kx, (II) 50 kx. (b) XRD pattern of PCNFs.

Figure 6

(a) Variation in PCNFs current with relative humidity ranging from 30 to 99%; (b) Response values of PCNFs and PNFs at relative humidity ranging from 30 to 99%; (c) Variation in PCNFs current with ethanol concentrations of 50, 100, 150 and 200 ppm; (d) Response values of PCNFs and PNFs at ethanol concentrations of 50, 100, 150 and 200 ppm; (e) Variation in PCNFs current with ethanol concentrations of 1, 2, 5, 20, 50, 100, and 200 ppm at 90% RH; (f) Response values of PCNFs and PNFs with ethanol concentrations of 1, 2, 5, 20, 50, 100, and 200 ppm at 90% RH.

Figure 7

(a) Schematic illustration of humidity adsorption process on the PCNFs sensor, and (b) Proton hopping mechanism for H⁺ transfer through surface-adsorbed humidity.

Figure 8

(a) Stability of the PCNFs sensor response to 5 ppm and 200 ppm ethanol concentrations at 90 RH% environments from the day of fabrication to every 7 days over 4 week; (b) Repeatability of the PCNFs sensor response to 200 ppm ethanol at 90 RH% for 6 repetitions; (c) Selectivity of the PCNFs sensor against ethanol, methanol, acetone, hydrogen, methane, carbon monoxide, and moisture.

Figure 9

(a) Variation of the output voltage of the PCNFs sensor with relative humidity levels ranging from 20 to 99%; (b) Changes in output voltage and response values of the PCNFs sensor with relative humidity levels ranging from 20 to 99%; (c) Variation of the output voltage of the PCNFs sensor with ethanol concentrations of 50, 100, 150, and 200 ppm; (d) Changes in output voltage and response values of the PCNFs sensor with ethanol concentrations of 50, 100, 150, and 200 ppm; (e) Variation of the output voltage of the PCNFs sensor with ethanol concentrations of 1, 2, 5, 20, 50, 100, and 200 ppm at 90% RH (Inset: response and recovery time in 200 ppm ethanol at 90 RH%); (f) Changes in output voltage and response values of the PCNFs sensor with ethanol concentrations of 1, 2, 5, 20, 50, 100 and 200 ppm at 90% RH.

Figure 10

(a) Schematic of a natural human breath test. (b) The change in the output voltage of the PCNFs sensor when exposed to natural human breath; (c) The response and recovery time of the PCNFs sensor to natural human breath.