Huang,,, Ye Ruquan *
Nano? Micro-Ritter. (2020) 12: 157
https://doi.org/ 10. 1007/s40820-020-00496-0
The highlight of this article
1. The preparation methods and engineering strategies of laser-induced graphene are summarized.
2. The sensor based on LIG is summarized, and its design principle and working mechanism are emphatically introduced.
3. The integration of optical sensor and signal transmission and the development prospect of intelligent sensing system are discussed.
brief Introduction of the content
The team of Professor Ye Ruquan from the Department of Chemistry of City University of Hong Kong focused on the design principle and working mechanism, and summarized the progress of LIG technology in sensor application. The first author of the thesis is Huang, a doctoral student in the Department of Chemistry, City University of Hong Kong. Firstly, the preparation principle of LIG and LIG complex is briefly introduced, including the regulation of morphology and composition, the control of physical and chemical characteristics and so on. Then based on the design principle and working mechanism (chemical sensor with specific binding and non-specific binding, mechanical sensor based on piezoresistive effect, etc. ), LIG sensor is summarized. Finally, the author discusses the influence of LIG and its future development.
Graphic reading guide
Preparation and related mechanical properties of I LIG
Polyimide film and so on can be made of co? Laser can be converted into graphene without mask, and LIG with arbitrary shape can be prepared by computer control software. By changing the preparation atmosphere, precursor and laser parameters, including laser scanning speed, working mode, frequency and pulse number per point, the physical and chemical characteristics of LIG can be regulated. Not only infrared laser, visible light, ultraviolet light and other lasers can also successfully prepare LIG. The preparation of LIG by infrared laser is mainly due to photothermal effect. Instantaneous high temperature is the fracture and recombination of chemical bonds of precursors, accompanied by the generation of gas, which is one of the reasons for the high porosity of LIG.
For ultraviolet laser, the conversion of LIG is mainly a photochemical reaction, because ultraviolet light has short wavelength and high energy, which can directly break chemical bonds. For visible light laser, photothermal effect and photochemical reaction may coexist. Compared with screen printing, 3D printing and lithography, laser-induced preparation of graphene shows its unique advantages of simple preparation process, low cost, high efficiency and environmental protection. Because of the flexibility of the precursor (organic thin film) and the easy transfer of LIG to the substrate with both mechanical properties and ductility, LIG has been widely used in sensors, especially wearable devices.
Figure 1. (a)PI a) Schematic diagram of converting PI into LIG. (b) Scanning electron microscope and HRTEM images of b)LIG. The scale is 10 micron and 5 nautical miles. (Contact angles of LIG in different atmospheres. (d) SEM image of fibrous light.
Figure 2. Mechanical properties of LIG and its composites. (a) Boron-doped LIG in bending state. (b) Capacitance retention of boron-doped LIG capacitors with different bending radii. (c-d) The test of LIG supercapacitor under different tensile strength. (e)LIG is mixed with cement. (f) Gas sensor based on lightweight cement composite material.
Chemical sensor based on LIG
Chemical sensors are widely used in the detection of food safety, pollutants in aquaculture and drinking water, air quality around hazardous gas emission industry and metabolites such as glucose, lactic acid and dopamine. The working mechanism of chemical substance detection usually depends on the changes of electrical signals such as resistance, capacitance and charge transfer resistance caused by stimulation. The detection of this chemical substance can be divided into two categories, one is based on the specific binding of the chemical substance to LIG surface, and the other is based on the non-specific binding.
2. 1 specific binding chemical sensor
Specific binding chemical sensors usually modify the surface of LIG, such as antibodies, enzymes and aptamers. Because of the precise combination between the identification element and the target chemical substance, this kind of sensor usually shows extraordinary sensing selectivity. When the recognition element is combined with the target chemical, the signals such as electrode surface capacitance and interface transmission resistance will change, which is related to the concentration of the target chemical. By detecting the changes of related electrical signals, the concentration of corresponding chemical substances can be deduced.
Figure 3. Preparation technology and sensing performance of specific binding chemical sensor based on LIG. Using the specific binding mechanism between chemical substances and modified LIG, a variety of substances from small molecules to biomolecules and even pathogens were successfully detected.
Figure 4. Various specific binding photochemical sensors. Schematic diagram of (a) thrombin sensor, (b) bisphenol A sensor and (c) enzyme glucose sensor. (d) Schematic diagram of AuNPs-LIG-based sensor for detecting Escherichia coli O 157:H7. (e) Nyquist diagram of E.coli sensor. (f) Calibration curve of impedance response and concentration.
2.2 Non-specific binding chemical sensor
Nonspecific binding chemical sensors also play an important role in chemical sensors, and the cost of nonspecific binding sensors is usually lower than that of specific binding sensors. Chemical redox reaction and physical properties are the information sources of nonspecific binding chemical sensors.
2.2. 1 chemical redox reaction
Chemical redox reactions are usually used to detect solutes or gases. Detection can be qualitative or quantitative. For example, different analytes often have different redox potentials, so the identification of redox potentials is helpful to distinguish different analytes. At the same time, the current density related to redox reaction is positively correlated with the concentration of analyte. By calibrating the current density at a specific potential, information about the analyte concentration can be provided.
Figure 5. Glucose sensor based on chemical redox reaction. (a) Current response of continuous addition of different glucose concentrations. (b) Calibration curve of glucose sensor.
Physical characteristics
By using the physical characteristics of LIG interacting with the measured object, such as resistance, thermal conductivity, electrical conductivity or impedance, the corresponding response is detected. For example, with the increase of ion concentration in solution, the interfacial transmission resistance will decrease. By constructing the relationship between ion concentration and interfacial transmission resistance, it can be used to detect the ion concentration of unknown solution. However, because other ions can also produce similar effects, this detection method is not suitable for the concentration detection of multi-component solutions.
Figure 6. Nonspecific binding sensor based on intrinsic and extrinsic physical characteristics. (a) Hydrogen sensor based on resistance change. Energy band analysis of hydrogen acting on LIG (I) and catalytic reaction of hydrogen on LIG/Pd (II). (b) Resistance reaction and H? The relationship between concentration. (c) Response of gas sensor based on thermal conductivity of various gases. (d) The response amplitude of a gas sensor with a bending radius of 7 mm to air. The diagram shows the response of the gas sensor to air after 0 and 1000 bending cycles. (e) Response of nitrate sensor to nitrate concentration. The figure shows the equivalent circuit of the sensor immersed in the solution. (f) Comparison between actual temperature and measured temperature.
Iilig mechanical sensor
Mechanical sensors are widely used in fine motion detection, sign language translation and robot grasping. The mechanical sensor based on LIG is usually based on piezoresistive effect, which can detect the resistance change caused by shape deformation caused by excitation. When LIG is in the state of tension, bending and vibration, its resistance will change. By monitoring the resistance of LIG and combining with machine learning, the physical state of the equipment can be determined. At the same time, recording the time-resolved changes of LIG resistance caused by heartbeat, pulse and vocal cord vibration can be used to detect heart rate and distinguish sound.
Figure 7. (a) Schematic diagram of the process of converting 3D printed PEEK gears into LIG. (2) The working mechanism of bidirectional bending and stretching of Peeklig intelligent components. (c) Variation of sensor resistance with applied strain. (d) Bending response time and recovery time. (e) The relationship between gear wear and circuit resistance. The illustration shows three different wear degrees of intelligent gears: (i) no wear, (II) partial wear and (III) severe wear.
By recording piezoresistive effect in time sequence, LIG-based mechanical sensors can be used to detect various signals in real time, such as heartbeat, movement and sound.
Figure 8. Electroencephalogram, electrocardiogram and electromyography measurement.
Four prospects
Since LIG was discovered in 20 14, the progress of LIG synthesis technology has significantly improved the properties of graphene and increased the versatility of application. For example, the wavelength of laser extends from infrared to visible light or even ultraviolet, which improves the spatial resolution of LIG structure to 12? The preparation strategies of m .LIG composites, such as in-situ modification and in-situ modification, can improve the physical properties of LIG, such as mechanical strength and electrical conductivity, and can also improve the chemical properties of LIG by adding functional materials. The low cost and simple synthesis of LIG technology have promoted the development of a series of LIG sensors, making them one of the potential candidate technologies for industrial production.
Through the reasonable design of the sensing mechanism, all kinds of stimuli, from various chemicals to sound, movement and temperature, have been successfully detected. Due to the high specific surface area and chemical stability of LIG, these sensors usually show high sensitivity and stability. In addition, LIG's high conductivity makes it an ideal sensor to convert stimulus signals into electrical signals. LIG originally made of polymer is usually flexible, and transferring it to other substrates (such as elastomer or cement) can give it elasticity or rigidity, which makes LIG can be used in different scenes, such as wearable electronic devices and intelligent buildings. The development of LIG sensor has developed from a single detection element to an integrated system. By combining the wireless transmission and microcontroller module with the Internet of Things, the real-time continuous detection of the tested object is realized.
As a graphic and printable manufacturing technology, LIG-based sensor opens up a new way for developing integrated miniaturized devices. However, LIG technology still has some room for improvement in practical application. For example, in some cases, the bonding strength between the LIG layer and the precursor is insufficient. Although it can be avoided in some ways, such as functionalization with viscous polymers or transfer of LIG to elastomers, the consumption of chemicals and additional manufacturing steps are not ideal for production. Some LIG sensors have not been tested in vivo or in the field, which may not reflect the feasibility, stability and durability of the sensors in the actual situation. However, this is very important for practical application, because the interference from the environment and the change of laboratory conditions may affect the sensitivity and reliability of the sensor. Nevertheless, with the joint efforts of researchers all over the world, the diversity of LIG in various sensors has been satisfactory. With the development of the future, LIG sensor will find a new world in a wide range of applications.
Brief introduction of the author
Ye ruquan
The reporter of this article
Assistant Professor, City University of Hong Kong
Main research area
Applications of laser-induced graphene technology in catalysis, water treatment, energy conversion and sensors; The rational design of interfaces and catalysts for catalytic reactions such as carbon dioxide reduction and water decomposition can improve energy utilization efficiency.
Main research results
Published more than 20 papers in NAT and other high-impact academic journals as the first author or correspondent. Commun。 Mater ，ACS Nano，ACC。 Chemistry. Research, Angew. Chemistry. It was edited by … and has obtained international patents and 6 patents granted by the United States. He has won the National Outstanding Self-funded International Student Award and the Excellent Thesis Award of Young Engineers/Researchers of Hong Kong Institution of Engineers.
Author: original author
Yangtze River Delta Laser Alliance reprinted in Chen Changjun