The Self-Assembly Composite Photonic Crystal: Toward Easy Humidity Detection by a Smartphone

We report a self-assembly composite photonic crystal with humidity-controlled structure color, towarding to easy humidity detection by a smartphone. As the key issue, the composite photonic sensor is developed via quasi-coating the silica colloidal photonic crystal (SPC) with hydrophilic metal-organic-framework (MOF). Thus the sensor combines the complementary adsorption properties between SPC and MOF, so that realizes a sensitive humidity sensor with wide dynamic detection range. The performance of the sensor was validated via water vapor testing, that its reflection spectrum shifts similar to 9 nm towards to longer wavelength with the concentration from 500ppm to 20000ppm under room temperature. The humidity-controlled structure color of the sensor paves a way for smartphone detection, so that a simple yet powerful smartphone spectrometer is established to analyze the reflection spectrum of the sensor. Thus, a lab-on-a-phone humidity measurement platform is developed. Thanks to the portability, low-cost and user-friendliness, this platform is promising to be a powerful tool for humidity IoT application, from personal health monitoring to environment monitoring.