Opal-Like Material can Help Develop Next-Generation Smart Sensors

Taking a cue from the biomimicry of peacock feathers and butterfly wings, researchers have created a novel opal-like material that could lay the groundwork for sophisticated smart sensors.

Headed by the University of Surrey and the University of Sussex, an international research team has produced flexible, color-changing photonic crystals that can potentially be used for developing sensors that send alerts about an impending earthquake.

The low-cost, wearable, and rugged sensors can react sensitively to strain, temperature, light, or other chemical and physical stimuli, rendering them a highly viable option for low-cost, smart, visual-sensing applications in a wide range of industries, such as food safety and healthcare.

In the latest research published in the Advanced Functional Materials journal, scientists have demonstrated a new technique to create photonic crystals. These crystals comprise a tiny amount of graphene that leads to an array of preferred qualities, with outputs that can be directly visualized by the naked eye.

The highly versatile sensors are deeply green under natural light and change color to blue upon stretching, or become transparent upon heating.

This work provides the first experimental demonstration of mechanically robust yet soft, free-standing and flexible, polymer-based opals containing solution-exfoliated pristine graphene. While these crystals are beautiful to look at, we’re also very excited about the huge impact they could make to people’s lives.

Dr Izabela Jurewicz, Lecturer in Soft Matter Physics, Faculty of Engineering and Physical Sciences, University of Surrey

According to Alan Dalton, Professor of Experimental Physics at the School of Mathematical and Physical Sciences of the University of Sussex, “Our research here has taken inspiration from the amazing biomimicry abilities in butterfly wings, peacock feathers and beetle shells where the colour comes from structure and not from pigments.”

Dalton continued, “Whereas nature has developed these materials over millions of years we are slowly catching up in a much shorter period.”

The promising applications of the sensors are as follows:

• Time-temperature indicators (TTI) for smart packaging—the sensors are capable of providing a visual indication when perishables, like pharmaceuticals or food, undergo adverse time-temperature histories. The photonic crystals are highly susceptible to even a slight increase in temperature between 20 °C and 100 °C.
• Fingerprint analysis—the pressure-sensitive shape-memory properties of the fingerprints make them suitable for anti-counterfeiting and biometric applications. When the crystals are pressed with a bare finger, the fingerprints are revealed with excellent accuracy, demonstrating the skin’s well-defined ridges.
• Bio-sensing—the photonic crystals can be employed as tissue scaffolds for interpreting human disease and biology. If these crystals are functionalized with biomolecules, they could serve as extremely responsive point-of-care testing instruments for respiratory viruses, providing reliable, affordable, and easy-to-use bio-sensing systems.
• Bio/health monitoring—the mechanochromic response of the sensors makes them suitable for use as body sensors, which can help enhance techniques in sports players.
• Healthcare safety—Researchers have recommended that the sensors can be integrated into a wrist band, which changes color to alert patients if their healthcare practitioner has cleaned their hands before coming into an examination room.

The study builds on the Soft Matter Group’s (University of Surrey) expertise in polymer colloids, Materials Physics Group’s (the University of Sussex) know-how in the liquid processing of two-dimensional (2D) nanomaterials, and integrates it with the experience of the Advanced Technology Institute in optical modeling of complex materials.

The University of Sussex and the University of Surrey are working with a Sussex-based firm, Advanced Materials Development (AMD) Ltd, to market the technology.

Polymer particles are used to manufacture everyday objects such as inks and paints. In this research, we were able to finely distribute graphene at distances comparable to the wavelengths of visible light and showed how adding tiny amounts of the two-dimensional wonder-material leads to emerging new capabilities.

Joseph Keddie, Professor of Soft Matter Physics, University of Surrey

“Given the versatility of these crystals, this method represents a simple, inexpensive and scalable approach to produce multi-functional graphene infused synthetic opals and opens up exciting applications for novel nanomaterial-based photonics. We are very excited to be able to bring it to market in near future,” concluded John Lee, CEO of Advanced Materials Development (AMD) Ltd.

Journal Reference:

Jurewicz, I., et al. (2020) Mechanochromic and Thermochromic Sensors Based on Graphene Infused Polymer Opals. Advanced Functional Materials. doi.org/10.1002/adfm.202002473.