Significance The emerging technologies such as the Internet of Things and wearable technology in recent decades have brought great changes and convenience with better healthcare and manufacturing and higher safety, security, and efficiency for the whole society. As an essential important link in these systems, sensors provide key value proposition and play a pivotal role. Take wearable electronics as examples , the market value of wearable technology has doubled in the past five years. Sensors have provided core functions for many different products during the development of wearable electronics, and they will continue to play a key role in future generation of products. For example, smartwatches and skin patches are built based on the fitness tracking and daily activity data, and are used for medical measurement. Virtual, augmented, and mixed reality devices rely on a set of sensors (e.g. inertial measurement unit, depth induction, force/pressure sensors) to enable users to interact with the content and environment. Moreover, the transition from traditional human-computer interaction to a natural user interface will also depend on further advances in sensors. Other products in different areas, such as autonomous vehicles, air detector, and smart clothing, are similar and depend on a set of core sensors that can interact with the body or the surrounding environment. Some of these sensor systems have been gradually commercialized and expanded to more industrial, agricultural, military, environmental, and safety applications. In particular, the COVID-19 pandemic in 2020 has also brought increased attention to sensors owing to their promising applications in tracking early onset and potential virus contacts, and remote patient monitoring of isolated patients. In short, the sensor remains a fundamental component of the entire product line, which has been required to be thinner, lighter, smaller, more flexible, and sensitive in the new application systems.

Based on the important role of sensors, many preparation methods such as vapor deposition, lithography, nano-imprint lithography as well as printing have been developed. Each technology has its unique advantages and adapts to different scenarios. At the same time, their disadvantages that cannot be ignored also need to be addressed. For instance, chemical and physical vapor deposition methods, including thermal evaporation, vacuum evaporation, magnetron sputtering, and molecular beam epitaxy, can produce high-quality materials and devices with good performance, but these technologies usually require expensive equipment and specific operating environment. Moreover, it is difficult for these techniques to be compatible with flexible substrates and realize low-cost industrialized mass production. In addition, photolithography and nano-imprint lithography are suitable for precision device fabrication. However, they often face the challenges of low processing efficiency, low output, high cost due to the complex processing process, high design cost of mask, and long processing cycle. In comparison, printing is a very attractive technology for low-cost large scale production. But in most cases, the presence of mask limits the precision and resolution of the prepared micro/nano-sized devices. Therefore, with the increasing demand for flexible, wearable, miniaturized, precise, integrated, and customized sensors, the new processing method with higher precision and more flexibility manners is needed to achieve controllable preparation.

To meet the developmental requirements of sensors, various processing techniques mentioned above are utilized to optimize and improve the sensor mainly from the aspects of the electrode, sensing material, and whole device. In recent decade, laser micro-nano fabrication has been gradually developed and popular in the field of manufacturing. The laser micro-nano fabrication changes the material state and property through the laser-material interaction and realizes the well-control of shape and property across scales. With the advantages of large processing speed, high precision, strong controllability, easy integration, and high compatibility with materials, the sensor fabricated by laser has ushered in a new development in structure regulation and performance optimization. However, it still faces challenges and difficulties in mass production and efficiency promotion in practical applications.

Progress The laser processing technologies for the fabrication of sensors and sensing systems of different stimulus sources are summarized ( Fig. 2). Firstly, three laser processing modes widely used in sensor production including laser induced heating, reaction, and delamination are introduced. The convenience and advantages of laser processing compared with those of the traditional processing technology can be clearly understood in the section of laser processing modes ( Fig. 3). Then, based on the existing research results, the sensor systems prepared by laser are classified into ultraviolet, gas, humidity, temperature, strain/stress, biology, and environmental monitoring sensors. It is easily found that the advantages of laser micro-nano fabrication are mainly reflected in the following three aspects. 1) Laser micro-nano fabrication has broadened the preparation approaches of electrodes and sensing materials. It can realize in-situ or non-in-situ preparation of conductive electrodes and sensing materials by laser reduction, sintering, annealing, ablation, pulse deposition, laser induced carbonization, and hydrothermal reaction as well as other specific laser processing technologies, which provide alternative strategies for material preparation. 2) Laser micro-nano fabrication simplifies the assembly process of the whole device. The laser direct writing technology can realize in situ selective process in specific areas or specific materials, leading to great convenience for device construction. Moreover, the whole sensor on flexible substrates can even be prepared by one-step laser fabrication through digital design. 3) Laser micro-nano fabrication contributes to promote sensor performance. Sensing material, as a key part of a single sensor, can be modified and regulated by laser processing, thus providing the possibility of performance optimization. With these optimizations and improvements, the sensors become softer, smaller, and more customized and have higher integration. Finally, we also analyze the problems existing in sensors fabricated by laser micro-nano fabrication, such as insufficient researches on laser-material interaction, limited processing accuracy and efficiency enhancement, and low level of device integration.

Conclusions and Prospect Laser micro-nano fabrication has gradually become a common and popular technology for sensing system preparation and integration. To sum up, the sensor fabricated by laser still needs in-depth and detailed exploration to promote the development of commercialization and industrialization of the sensor.