Laser-directed graphene: paving the way for the development of sensors

With the development of the information age, sensors that can transmit and detect information have become the main way to obtain information. Sensor technology has been widely used in various fields such as industrial production, environmental detection, medical diagnosis, and bioengineering, so it is necessary to build a sensor system with a wide detection range, high sensitivity, and fast response. Recently, a two-dimensional material, graphene, has attracted more and more attention in sensor applications due to its excellent electrical conductivity, physical, optical, thermal properties and excellent structural properties. Such as the detection of physical properties such as pressure and mechanical strain and the detection of glucose, heavy metals, organic pollutants and other chemicals, as well as the detection of gas, temperature and humidity. It has been reported that graphene can already be prepared by a variety of methods, such as mechanical peeling, chemical vapor deposition (CVD), epitaxial growth, and chemical reduction of graphene oxide. However, these traditional methods of preparing graphene are often accompanied by problems such as high temperature treatment, high cost, high energy consumption, and environmental pollution. Therefore, low-cost, high-efficiency, pollution-free graphene preparation methods still attract much attention.

Recently, laser direct writing technology has attracted research applications in various fields due to its unique advantages of selectivity and local reduction, precise and rapid patterning, and the absence of masks and additional chemicals. In the process of using laser direct writing technology, the laser is used to irradiate the carbon source, and graphene is generated in situ direct writing, and the whole laser direct writing process only takes a few minutes, which greatly improves the efficiency of preparing graphene. This laser-based graphene with in-situ, high efficiency, and flexible patterning, and its thin film exhibits excellent characteristics of high surface area, high thermal stability, and high electrical conductivity, which makes it widely used in the field of sensors.

In view of this, a research team from the Institute of Photonic Chips of the University of Shanghai for Science and Technology published a review article entitled “Laser-scribed graphene for sensors: preparation, modification, applications, and future prospects” in Light:Advanced Manufacturing.

This article reviews the latest advances in sensor applications based on laser direct graphene (LSG) technology in recent years. Firstly, two synthetic routes and modifications of LSG are introduced. It then introduces the application of LSG in stress, biological, gas, temperature and humidity sensors, and also focuses on the application research of multifunctional integrated sensors. Finally, ideas on the challenges and prospects of LSG sensors are proposed.

Two synthetic routes and modifications of LSG

At present, the precursors of LSG are mainly graphene oxide and carbon-containing polymers, in the precursor of graphene oxide, graphene oxide is converted to graphene by laser reduction, and the reduction mechanism is mainly related to the photochemical and photothermal effects of lasers. For polymer precursors, graphene is generated by direct carbonization of carbon-containing polymer precursors induced by lasers. Furthermore, this paper discusses effective ways to adjust the surface morphological structure and properties of LSG, including adjusting laser parameters, the preparation environment of different gases, and doping them.

Figure 1: LSG in sensor applications. Source: Light: Advanced Manufacturing 4, 11 (2023).

LSG applications in sensors

Because LSG films exhibit high surface area, high thermal stability, and high electrical conductivity, making them very promising in sensor applications, researchers such as Yonglai Zhang inspired researchers to directly write microcircuits on graphene oxide films by femtosecond lasers in 2010, which inspired researchers to study laser direct graphene in the field of sensors.

In the past decade, the application of laser direct graphene in sensors (including stress, biological, gas, temperature and humidity sensors) has been widely studied, providing new development opportunities for tactile sensing, environmental monitoring, and medical diagnosis

Challenges and prospects

Flexible patterning and the use of various flexible substrates make LSG also have great prospects in wearable sensor applications. However, LSG-based sensors still have some challenges and room for development.

First, at present, LSG does not have strong adhesion ability in its flexible precursor (such as polyimide film), which is a big challenge for flexible sensors, and most of them use the transfer substrate method to solve this problem. The search for new precursors is therefore urgent or necessary.

Second, for stress sensors, sensitivity and sensing range are two key factors in sensor performance. However, the combination of high sensitivity and wide detection range is still difficult for stress sensors. It is hoped that new technologies can be explored to solve the problem, such as designing suitable graphene surface microstructure and doping to improve comprehensive performance.

In addition, in terms of laser type, ultrafine laser lithography can maximize the specific surface area of graphene structure, thereby achieving performance breakthroughs, which is an indispensable research direction in the future.

In the future application of LSG sensors, it is expected to further explore the integration of LSG sensors with other LSG devices, such as nanogenerators and supercapacitors, for energy supply and energy storage. In addition, the combination of LSG sensors and artificial intelligence technologies can be explored, including the use of intelligent graphic design LSGs to improve sensor performance. On the other hand, LSG-based sensors can be applied to the field of robotics, enabling them to monitor external data in real time and further improve their intelligence level. (Source: Advanced Manufacturing WeChat public account)

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