| Nov 21, 2024 |
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(Nanowerk Spotlight) The burgeoning demands for health care and human-machine interfaces call for the next generation of multifunctional and flexible integrated sensor systems. Principally, flexible sensors are categorized as physical, chemical, and electrophysiological types. Judicious integration of them renders multifunctional flexible sensor systems with skin-like compliance and reliable performances, while also brings formidable challenges in fabrication.
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The emerging laser-induced graphene (LIG) technology features versatile and cost-effective fabrication of carbon patterns from various polymeric films. As the backbone material for flexible sensors, LIG exhibits good conductivity, flexibility and biocompatibility.
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More importantly, tunable physical and chemical properties, along with mask-less fabrication of LIG, play vital roles in facilely developing multifunctional flexible or stretchable sensor systems for versatile applications.
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In a recent review article published in ACS Nano (“Toward Integrated Multifunctional Laser-Induced Graphene-Based Skin-Like Flexible Sensor Systems”), researchers from Zhejiang University present a comprehensive overview of recent advances in LIG-based flexible sensors and their system integrations from basic material and structural design to various applications (Figure 1).
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| Figure 1. Research trend of LIG-based sensors in recent ten years. (Reprinted with permission from American Chemical Society) (click on image to enlarge)
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First, the fabrication methods of LIG using different laser sources from various media with controllable dimensions is elaborated. The transfer techniques of LIG to stretchable platforms are highlighted. The second section critically discusses three categories of LIG-based sensors including physical, chemical, and electrophysiological sensors. In the third section, various emerging LIG-based sensor systems are described for human health monitoring and plant growth detection.
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In addition, the signal cross-talk issues in flexible LIG-based multifunctional sensor systems are discussed together with the presentation of relevant solutions. Finally, the future trends of integrated LIG-based sensor systems are provided.
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By leveraging the LIG technology, multimodal sensor systems are constructed to meet the needs in our daily lives (Figure 2). They typically incorporate heterogeneous sensor modules with additional signal processing, transmission, or display units on a thin film.
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“In spite of the enormous progress made in the design and fabrication of LIG sensors, challenges still exist,” says Prof. Kaichen Xu, first and corresponding author of this publication. “Scenarios of multimodal monitoring systems pose higher standards to these wearable platforms, including immunity to crosstalk, cross-scale fabrication and conformal attachment.”
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| Figure 2. Features and applications of LIG-based integrated multifunctional flexible sensor systems. (Reprinted with permission from American Chemical Society) (click on image to enlarge)
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Potential solutions to deal with these issues lie in material, structural design, fabrication and algorithm. For instance, LIG with high special resolution and small size are beneficial for brain–computer interfaces and strain-insensitive sensors. By subtractive laser engraving or combing with photolithography, the spatial resolution of LIG could been improved to ∼10-15 μm. In addition, the synthesis of specific LIG precursors, which undergo mild chemical reactions during laser irradiation, is another way to downscale the porosity and linewidth of LIG.
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With submillimeter LIG patterns, it is crucial to balance area and efficiency during fabrication. Distinct from traditional single-beam laser writing strategy, parallel multibeam writing or plane exposure are potential laser fabrications to drastically boost the production rate of complex LIG structures in large-area sensor systems.
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These improvements might extend LIG-based integrated flexible sensor systems to higher complexity and functionality. Future efforts through the close collaborations among interdisciplinary researchers should be able to push forward the technique of LIG into practical wearable applications.
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Provided by Zhejiang University as a Nanowerk exclusive
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