Ultrasensitive Detection of Methylmercaptan Gas Using Layered Manganese Oxide Nanosheets with a Quartz Crystal Microbalance Sensor

Abstract

Methylmercaptan (MM) is a marker of periodontal disease; however, the required sensitivity for MM is parts per billion, which has been challenging to realize with a simple sensor. Here, we report the capability to detect MM at concentrations as low as 20 ppb using layered manganese oxide nanosheets with a quartz crystal microbalance sensor. The sensing capabilities of the manganese oxide nanosheets are promoted by adsorbed water present on and between the nanosheets. The strong adsorption of MM to the sensor, which is necessary for the high sensitivity, leads to significant hysteresis in the response on cycling due to irreversible adsorption. However, the sensor can be readily reset by heating to 80 °C, which leads to highly reproducible response to MM vapor at low concentrations. A key aspect of this sensor design is the high selectivity toward MM in comparison to other compounds such as ethanol, ammonia, acetaldehyde, acetic acid, toluene, and pyridine. This layered nanosheets design for high-sensitivity sensors, demonstrated here for dilute MM, holds significant promise for addressing needs to identify sulfur compounds associated for environmental protection and medical diagnostics.

A Quartz Crystal Microbalance Based Portable Gas Sensing Platform for On-Demand Human Breath Monitoring

“…We used the QCM with a methyl mercaptan gas adsorption film developed by Tokura et al [27], which was made of manganese oxide nanosheets. The materials of the gas adsorption film were prepared based on the method presented in [27] and were ion-exchanged for enhancing sensitivity.…”

“…According to the literature [27], this film has the following three properties: (i) 20 ppb of methyl mercaptan gas can be detected in a static system, which is the level required for the detection of periodontitis and other visceral diseases (see Table S.1). (ii) The film has high selectivity for methyl mercaptan gas, and (iii) the sensitivity of the film becomes high at high humidity, which is ideal for the monitoring of breath.…”

“…We convert the frequency of the QCM sensors to the gas concentrations using an adsorption isotherm identified by calibration experiments. Specifically, we use a modified version of Freundlich's adsorption isotherm [42] since the methyl mercaptan gas chemically adsorbs on the gas adsorption film (see [27] for details). Freundlich's adsorption isotherm is given by…”

“…Further, the detection limit of the QCM sensors can be very low. For example, Roto et al [29] fabricated ammonia gas sensors, whose limit of detection (LOD) was 550 ppb, and Tokura et al [27] developed gas sensors that can detect methyl mercaptan at 20 ppb, which is lower than other gas sensors for sulfur gas [30]- [33]. A multi-gas sensor array was also developed to enable the simultaneous sensing of nitric oxide at 5 ppb and aceton at 5 ppm [26].…”

Peptide Modified ZnO Nanoparticles as Gas Sensors Array for Volatile Organic Compounds (VOCs)

“…One of the simplest configurations in gas sensing is represented by quartz crystal microbalances (QCMs). These sensors have the potential for sensitive and selective target gas detection due to the ability to measure mass change, on the surface of the sensor itself, after interaction between the sensitive film and the gas (Tokura et al, 2017 ). The sensing surface of QCMs can be easily modified with organic compounds taking advantage of the measurement run at room temperature.…”