Real-time ultrafast humidity sensing optical sensor

A POSTECH research team led by Professor Junsuk Rho (Department of Chemical Engineering and Department of Mechanical Engineering) has developed an ultrafast humidity-responsive colorimetric sensor.

Sensors using light are already being used in our daily lives, for electrocardiogram and air quality measurement. These sensors use light to detect changes in their surroundings and convert them into digital signals.

The research team fabricated a colorimetric sensor that consists of metal-hydrogel-metal structure using a disordered metal nanoparticle layer -- a chitosan hydrogel -- and a reflecting substrate. When the external humidity changes, the resonant frequency of the sensor changes due to the characteristic of the chitosan hydrogel that swells under wet state and contracts under dry state repeatedly.

This new sensor boasts an ultrafast speed that is 10,000 times faster than the conventional Fabry-Perot interferometer based optical sensors. This fast reaction speed is thanks to the porous space between the nanoparticles that make up the sensor, much like the shell of the beetle that changes colors depending on the humidity.