Structural Colored Based Humidity Sensor Consisting of High Resolution 3D Printed Photonic Crystal Coated with Ultrathin Responsive Hydrogels.

Today, humidity sensors have become an integral part of the daily lives. In particular, humidity sensors using an electronic measuring principle have become the standard. Although these sensors have proven to be a stable measurement method, they have some disadvantages, such as their long response time or the danger of using them in explosive environments. This work introduces photonic crystals as an alternative optical measurement approach. The novel technology of ultra-fast two-photon polymerisation printing is combined with a thin-film deposition process, namely iCVD. This allows to print large area high-precision 3D templates, which are subsequently coated with a humidity responsive hydrogel thin film (p(HEMA) of 20 nm.The limits of 2PP technology are being pushed allowing the production ofs table and periodic large-area 3D structures. The flexible customization of hydrogels for ambient conditions make them exceptionally promising for a wide range of sensing applications. Additionally, optical methods for measuring humidity seem to be an excellent alternative to overcome the limitations for current state of the art humidity sensors. The optical detection of changes in ambient air humidity is achieved by observing color changes of the printed structure within the visible wavelength range.