An
international team of scientists, led by the Universities of Surrey and Sussex,
has developed colour-changing, flexible photonic crystals that could be used to
develop sensors that warn when an earthquake might strike next.
The
wearable, robust and low-cost sensors can respond sensitively to light,
temperature, strain or other physical and chemical stimuli making them an
extremely promising option for cost-effective smart visual sensing applications
in a range of sectors including healthcare and food safety.
In a study published by the journal Advanced Functional Materials, researchers outline a method to produce photonic crystals containing a minuscule amount of graphene resulting in a wide range of desirable qualities with outputs directly observable by the naked eye.
Intensely
green under natural light, the extremely versatile sensors change colour to
blue when stretched or turn transparent after being heated.
Dr.
Izabela Jurewicz, Lecturer in Soft Matter Physics at the University of Surrey’s
Faculty of Engineering and Physical Sciences, said “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.â€
Alan
Dalton, Professor Of Experimental Physics at the University of Sussex’s School
of Mathematical and Physical Sciences, said: “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. Whereas nature has developed these materials over millions of years
we are slowly catching up in a much shorter period.â€
Among
their many potential applications are:
Time-temperature
indicators (TTI) for intelligent packaging – The sensors are able to give a
visual indication if perishables, such as food or pharmaceuticals, have
experienced undesirable time-temperature histories. The crystals are extremely
sensitive to even a small rise in temperature between 20 and 100 degrees C.
Finger
print analysis - Their pressure-responsive shape-memory characteristics are
attractive for biometric and anti-counterfeiting applications. Pressing the
crystals with a bare finger can reveal fingerprints with high precision showing
well-defined ridges from the skin.
Bio-sensing
– The photonic crystals can be used as tissue scaffolds for understanding human
biology and disease. If functionalised with biomolecules could act as highly
sensitive point-of-care testing devices for respiratory viruses offering
inexpensive, reliable, user-friendly biosensing systems.
Bio/health
monitoring – The sensors mechanochromic response allows for their application
as body sensors which could help improve technique in sports players.
Healthcare
safety – Scientists suggest the sensors could be used in a wrist band which
changes colour to indicate to patients if their healthcare practitioner has
washed their hands before entering an examination room.