Significance Graphene is a two-dimensional carbon crystal with a single atomic layer, which was first discovered using the “Scotch tape method” in 2004. Compared with other carbon materials, graphene has shown unique physical and chemical properties, such as high carrier mobility (150000 cm ²·V ^-1·s ^-1), high thermal conductivity, high Young's modulus, optical transmittance, flexibility, and biocompatibility. Because of these properties, graphene has become a common material in electronic, energy storage, optical, micromachining, and biological devices.

The unique physical and chemical properties of graphene have stimulated the rapid development of graphene preparation technology. Researchers have developed a mature system of graphene preparation methods, such as mechanical/chemical exfoliation of graphite, silicon carbide epitaxial growth method, and chemical vapor deposition (CVD). According to the different applications of graphene, there are various advantages and disadvantages of different preparation methods. The mechanically exfoliated graphene has a better crystal structure, but lower preparation efficiency; the CVD method is effective to prepare high-quality graphene, but transferring graphene from metal catalytic substrates to target substrates is necessary for electronic devices; reduced graphene oxide (RGO) can be prepared in batch, but there exist several defects. The different properties of graphene are determined by the different preparation methods so that the application fields are not the same. No matter what device it is applied to, the processing of graphene is the primary technical problem to be solved. Thus, the device-based processing of graphene is a critical challenge for its practical applications.

Laser processing technology has numerous advantages such as fast processing speed, controllable processing procedure, unaffected by harsh reaction conditions, high precision and flexibility, friendly environment, and large-scale preparation. Therefore, it has become a simple and effective method for the preparation, modification, and device processing of graphene materials. Using laser processing technology, we can not only control the heteroatom species and concentration of graphene but can also induce its carbonization on polymeric substrates. In addition, the ability to pattern and structure without a mask also facilitates the development of graphene devices. Laser processing of graphene has been commonly used in optoelectronic devices, energy storage components, sensors, microelectronics, and other fields.

Recently, significant progress has been made in the development of laser-processed graphene-based sensors and actuators. As a two-dimensional material, each carbon atom of graphene is a surface atom, making it a unique sensitive material. Laser processing technology can not only achieve the patterning of graphene but can also effectively control its surface structure and heteroatom content, which is an effective means for preparing graphene-based sensors. In terms of actuators, graphene is sensitive to the stimulation of optical, electrical, and chemical fields because of its unique optical, electrical, and mechanical properties. Therefore, the actuators based on laser-processed graphene have been successfully developed and can be driven and controlled by a variety of physical and chemical fields.

In this paper, we reviewed the recent progress of laser-processed graphene and graphene derivatives, for example, graphene oxide (GO), for developing sensors and actuators. The topic is significant because laser processing of graphene and its derivatives hold great potential for developing carbon-based micro-electromechanical system (MEMS) sensors and actuators that are important for future smart devices.

Progress Recently, laser processing technologies have promoted the rapid progress of graphene-based devices, especially sensors and actuators. First, laser processing enables the preparation, modification, patterning, and structuring of graphene, revealing the great potential for manufacturing graphene-based electronic devices. Subsequently, typical laser processing strategies for graphene preparation, including laser reduction of GOs, laser-induced graphene (LIG), and laser-processed CVD graphene have been reviewed.

Second, using laser-processed graphene, sensors capable of detecting stress, pressure, chemicals, and biomolecules have been successfully developed. When developing graphene-based sensors, laser-processed graphene can act as electrode, semiconductor, dielectric, and host material. Laser processing facilitates device fabrication because it permits flexible and mask-free patterning, hierarchical structuring, and heteroatom doping. As a typical work, Ren's research group developed an epidermal electronic skin based on laser-scribed graphene that can be used as a strain sensor. The patterned epidermal electronic skin can be used to detect the finger bending motion and pulse. In addition, human breath can also be detected when the sensor is attached to masks and throats (Fig.6).

Third, graphene and its derivatives are sensitive to external stimuli, and thus can be employed to develop actuators. By full utilizing the moisture responsiveness of GO, the photothermal property, and conductivity of graphene, stimuli-responsive actuators that can dynamically deform in response to external stimuli have been reported. Ma et al. reported a laser-reduced RGO/GO bilayer humidity actuator that exhibits a fast response to humidity (Fig. 7). Wang et al. developed a light-driven actuator based on the Marangoni effect using patterned LIG tape. The actuator can achieve translation and rotation motion under photothermal actuation, providing a broad prospect for the development of light-driven microrobots (Fig. 8).

Conclusions and Prospects Graphene is promising for developing novel electronic devices; however, the lack of graphene-processing technologies compatible with the device manufacturing techniques may limit its progress. Laser processing of graphene has become a solution to address this limitation. Within the past decade, rapid progress has been made in the laser preparation of graphene, and the resultant sensors and actuators have revealed great potential for developing carbon-based MEMS devices. However, challenges in the preparation of high-quality graphene (or GO) and low laser processing efficiency still exist. The situation will soon improve because graphene preparation methods and laser processing systems have developed rapidly in recent years. Laser-processed graphene is expected to find practical applications in the near future, especially for developing smart carbon-based devices and flexible e-skins.