Chemists in Canada have developed optical sensors by filling the channels of photonic crystal fibres with luminescent materials. 

Photonic crystal fibres (PCFs) are optical fibres made from long threads of glass that have regularly-spaced air channels running through them. 

Tito Scaiano and co-workers at the University of Ottawa exploited the tubular structure of PCFs. They filled PCF channels with a solution of a pH-sensitive organic compound called coumarin 6, by simple capillary action. Coumarin 6 is strongly blue-green fluorescent at neutral pH, when excited with light of wavelength 436 nanometres.

The fluorescence decreases in acidic conditions. The researchers monitored the fluorescence of coumarin 6 inside the PFC channels. When the tip of the PCF was exposed to an acidic solution, the researchers measured a decrease in fluorescence. They said this suggests that PCFs filled with a pH-sensitive material could be used as acid-base sensors. 

The researchers also filled the PCF channels with a solution of cadmium selenide quantum dots and observed the changes in fluorescence when the fibre tip was dipped in a quencher. 

The team plans to extend this work to new applications. 'Interdisciplinary collaborations with physicists, engineers or biologists would be interesting to increase the potential applications of these new materials,' said Scaiano. 

Caroline A Moore