Abstract
The correlation between gas concentrations in human breath and diseases has been increasingly revealed in recent years, triggering the need for cheap and easy-to-use gas sensors that can detect diseases in their early stages. The gas sensors used in these clinical applications need to be portable and sensitive, and preferably provide on-demand measurements for prompt diagnosis. In this paper, we propose a portable and cost-effective sensor platform that can quickly identify gas concentrations in human breath. Specifically, we combined quartz crystal microbalance (QCM) sensors with a single board computer, Raspberry Pi, to enable real-time data processing and display of the sensor data. A web server was operated on the single board computer, and thus, on-demand visualization of the sensor data was possible using a web browser. A gas quantification protocol was also proposed based on Freundlich’s adsorption isotherm. We demonstrated the real-time monitoring of methyl mercaptan (MM) gas over the internet using the developed small sensor device, which can easily be handled in one hand. The limit of detection (LOD) for MM gas was 107 ppb when the sensors were operated for 20 minutes after gas injection. The developed gas sensing platform is unmatched in terms of size and cost compared with analytical devices though less sensitive. These advantages would allow for wide distribution of the developed device to hospitals and individuals in large quantities, leading for behavioral changes for preventive care.
Highlights
Since the concept of the Internet of Things (IoT) was proposed by Ashton [1] in 1999, a considerable amount of small and cheap sensors were developed to enable ubiquitous sensing [2]
We propose a portable quartz crystal microbalance (QCM) gas sensing platform capable of monitoring gas concentrations in human breath using web browsers on mobile tablets (Fig. 1)
Gas molecules in human breath are initially bound to the surface of the QCM sensors, which are small thin films attached to quartz crystal resonators driven by the Colpitts oscillator circuits [36]
Summary
Since the concept of the Internet of Things (IoT) was proposed by Ashton [1] in 1999, a considerable amount of small and cheap sensors were developed to enable ubiquitous sensing [2]. We propose a portable QCM gas sensing platform capable of monitoring gas concentrations in human breath using web browsers on mobile tablets (Fig. 1). The gas sensing platform consists of three parts: QCM sensors, a frequency counter circuit, and a small single-board computer, Raspberry Pi, for frequency logging and data transmission to mobile devices through the internet (Fig. 2). Gas molecules in human breath are initially bound to the surface of the QCM sensors, which are small thin films attached to quartz crystal resonators driven by the Colpitts oscillator circuits [36] This causes a small change in molecular mass at the films and results in the deviation of the oscillation frequency. Individuals in large quantities and can be used as one of the tools for preventive self check up, which would save on the insurance and social security cost
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