Versatile titanium dioxide inverse opal composite photonic hydrogel films towards multi-solvents chip sensors

Photonic crystals with orderly periodic structure and manipulated structural colors have garnered widespread attention in sensors field. However, the unsatisfactory detection range, low sensitivity and inconvenient integration highly limit their further practical applications. In this paper, by combining TiO2 inverse opal photonic crystal with polyacrylamide hydrogel, a novel organic-inorganic composite solvents responsive photonic hydrogel (SRPH) was developed. By encapsulating TiO2 inverse opal photonic crystal with high refractive index in this hydrogel, the photonic hydrogels, therefore, possess bright structural colors. Due to the discrepancy in swelling rate of SRPH film in various solvents (ethanol, dimethyl formamide, dimethyl sulfoxide, etc.), it can identify these organic solvents through the rapid change of structural colors and detect the concentrations of the solvent in a wide range. Even for solvents with similar refractive index, it can be clearly distinguished, along with the excellent repeatability. Benefiting from the wide detection range and high sensitivity, the chip sensors were then developed by integrating multiple hydrogel films into the microfluidic system, which have high efficiency in solvent naked-eye multi-identification and concentration multi-detection. The new composite photonic hydrogels provide a reference for the design of functional photonic crystals and next-generation application of sensors.