A polymer nanosensor developed by Chinese scientists responds to both metal ions and temperature. 

Optical nanosensors have a wide range of applications including DNA sequence detection, thermometers, display devices and bar codes. Up to now the universal approach is to use gold, or silver nanocrystals or semiconductor quantum dots to get the desired colours. But, these have significant drawbacks as the colour they produce is not tunable, they require harsh synthesis conditions and can also be cytotoxic. 

Jinying Yuan at Tsinghua University, Beijing, made a full-colour optical nanosensor based on a porphyrin-containing ABC triblock copolymer which overcomes these problems and responds to both metal ion and temperature. This allows its use as both an ion detector and an ultra-sensitive thermometer. 

The copolymer solution can be used with a variety of metal ions which each give a different colour and allows Yuan to create a nanoarray which is capable of simultaneously conveying nine colour signals. 'We can clearly identify which metal triggered the specific colour change, and also exclude several metal ions which cannot cause the colour changes,' explains Yuan. In addition, the nanosensors undergo a remarkable colour transition in the range 35-61°C. The unexpected long range thermochromic character of these nanosensors could allow their use in ultra-sensitive thermometric arrays. 

Richard Hoogenboom, an expert in copolymers at the Radboud University, Nijmegen, Holland, was impressed by the 'amazing results'. He says he has not seen 'any examples where with one single polymer it is possible to get such a broad colour spectrum and temperature sensing regime just by adding metal ions'. 

Yuan's team are now developing a similar copolymer with porhyrin groups that form a hydrogel in water solutions as gel materials can be applied more readily than solutions. 

Anna Watson 

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