Is there an urgent need for breakthroughs in the feasibility and practical application of gas sensors?

The concept of sensors may not be familiar to the general public, but infrared thermometers for daily epidemic prevention, breathalyzers for detecting drunk driving, and household gas leak alarms are all common electronic measuring instruments that play an important role in people’s daily lives. Their core component is the sensor.

A sensor is a device or module that can sense a specified measured variable and convert it into a usable output signal according to a certain rule. It usually consists of a sensing element and a conversion element. Among them, gas sensors are generally used to measure the concentration of a certain gas or volatile organic compounds in the environment, mainly for monitoring oxygen content, and detecting leaks of flammable, explosive, toxic and harmful gases. They are of great significance in regulatory fields such as environmental monitoring, petrochemical production supervision, coal mine gas monitoring, and medical diagnosis.

Practical tin dioxide sensors were launched by Figaro Engineering Inc. of Japan in 1968, and have been developed for more than 50 years. Since the 1980s, China has built up certain R&D and manufacturing capabilities as well as a talent pool through basic research and technology introduction. However, there is still a gap between China and advanced countries in terms of marketization, which is mainly reflected in the preparation of sensitive materials, automation of device manufacturing, and product performance.

At present, the development of sensor technology, especially gas sensor technology, lags far behind that of communication and computer technologies. This is because sensors have a wide variety, and the market size of each type is relatively small. As special components, their development is inevitably restricted. Therefore, Europe, the United States, Japan, and China all provide key support for sensor technology R&D.

Although gas sensors seem inconspicuous, they involve multiple disciplines including physics, chemistry, biology, materials science, electronics, and information technology. The journey of a gas sensor product from a principle prototype to pilot production and then to large‑scale market promotion requires a step‑by‑step process, and each stage demands a broad and solid foundation. It is suggested that universities and basic research institutions carry out principle prototype development, solve scientific problems in material and device manufacturing, address challenges that may arise in practical applications, and evaluate the feasibility of product promotion. Enterprises, on the other hand, should focus on pilot and mass production, realize large‑scale and standardized manufacturing, reduce production costs, form an industrial chain, and improve product practicality.

In the R&D process, we must value and respect researchers, entrepreneurs, engineers, and technicians, attach importance to every talent, and implement the strategies of strengthening the country through science and technology and the spirit of craftsmanship. Meanwhile, intellectual property rights must be strictly protected to foster a sound industry‑university‑research ecosystem.

Gas sensors can be classified into many types based on the measurement target, sensing principle, and sensitive material used.

Specifically, the measurement targets of gas sensors include oxygen, flammable and explosive gases (hydrogen, methane, acetylene, etc.), toxic and harmful gases (carbon monoxide, ammonia, nitrogen dioxide, etc.), and volatile organic compounds (alcohol, acetone, etc.).

According to sensing principles, common gas sensors include resistive, catalytic combustion, electrochemical, optical, and thermal conductivity types.

Common sensitive materials for gas sensors include metal oxide semiconductors, conductive polymers, catalyst materials, solid electrolytes, and hybrid materials. Metal oxide semiconductor sensors have broad-spectrum response, reacting to most gases except a few, but their stability and selectivity need to be improved. Catalytic combustion sensors are mainly used to detect flammable gases such as hydrogen and methane, with relatively high detection concentrations. Solid electrolyte sensors are mostly used to measure oxygen, nitrogen oxides, etc., mainly for vehicle exhaust emission monitoring. Optical sensors only respond to gases that absorb characteristic light and have a wide measurement range, but are easily affected by humidity and dust. Thermal conductivity gas sensors can only be used for quantitative testing, i.e., detecting the content of known gases in a given environment.

Sensors are critical information acquisition devices, standing alongside information transmission (communication and information processing) and computer technology as the three main pillars of information technology. With the rise of the Internet of Things (IoT), the role of sensors has received increasing attention.

The IoT is an intelligent service system that connects objects, people, systems, and information resources via sensing devices according to agreed protocols, processes information from the physical and virtual worlds, and responds accordingly. The core sensing devices are sensors. Acquiring information appropriately, accurately, and efficiently at a reasonable cost is the primary problem for information systems. This requires further improvement in sensor performance as well as compatible signal interfaces. Since most gas sensors output analog signals, analog‑to‑digital conversion and compliance with interface protocols are necessary for IoT adaptation. This usually requires adding an ADC module or integrating the gas sensor, conditioning circuit, and ADC into a single chip system, which involves the compatibility of micro‑nano processing technologies for different materials. In addition, for smart mobile terminals, gas sensors must have low power consumption, small size, and acceptable cost for consumers.

The core indicators of gas sensors are the 3S and 2R: Sensitivity, Selectivity, Stability, Response, and Recovery.Higher sensitivity means a lower detection limit, which can lower the early‑warning concentration and improve safety. High selectivity avoids or reduces interference from non‑target gases and lowers the false alarm rate. Response and recovery characteristics determine the detection speed of the sensor.

Currently, the biggest problem in the application of gas sensors is insufficient stability. This is because gas detection usually involves chemical reactions, which, together with ambient atmosphere, cause gradual effects on the surface and microstructure of sensitive materials, making the stability and service life of sensors unable to meet practical requirements.

The current development trends of gas sensors are mainly reflected in three aspects:

First, miniaturization. Using silicon‑based microfabrication or multilayer ceramic co‑sintering technology, combined with thick‑film and thin‑film hybrid electronics, sensors can be miniaturized for mass production, improving consistency and interchangeability, significantly reducing volume and power consumption, and enabling applications in fields demanding low energy use and small size.

Second, application of new materials. The key to gas sensors lies in gas‑sensitive materials, which determine performance, especially selectivity and stability. The application of nanomaterials, hierarchical materials, hybrid materials, new carbon materials (carbon nanotubes, graphene, graphyne, etc.), new two‑dimensional materials, and metal–organic frameworks (MOFs) has great potential for enhancing gas sensor performance and expanding application fields.

Third, intelligence. Problems inherent in discrete sensor devices may not be solved in the short term, but can be compensated and improved through algorithms. By forming a sensor array with multiple identical or different gas sensors, processing their signals, and applying advanced algorithms, more valuable information can be obtained and the performance of measuring instruments improved.