Programmable hierarchical photonic crystal arrays activated by post-hydrolysis for highly sensitive biochemical pH sensing

Water is closely linked with our life and pH monitoring is of great significance to biochemistry, environment and industry. Herein, utilizing a controllable post-hydrolysis modification strategy, multilayered photonic crystal based pH sensors consist of mesoporous TiO2 and partially hydrolyzed poly(acrylamide-N,N’-methylene bis(acrylamide)) (P(AM-MBA)) layers are proposed. Varying pH from 4.0 to 8.5, the portable sensor transforms its color from violet to red with a linearly increased wavelength of 199 nm as the stopband generates ∼7 nm shift per 0.1 pH unit. The sensor exhibits repeatable response to pH change with a short sensing time of 0.8 s. Through goal-directed molecular regulations by the post-hydrolysis strategy, innovative dot-matrix sensor arrays with multiple sensing elements are created and present distinct color difference maps under diverse pH circumstances. And color based radar maps and PCA analysis greatly promote the detection accuracy and reliability. The dot-matrix sensors provide convenience for color-blind crowd and are applicable for use in human perspirations, suggesting promising potential in clinical applications. Furthermore, quartz crystal microbalance studies reveal the effect of the molecular regulation involving functional group and segment structure modifications on the sensing performance of the polymer based photonic materials, showcasing high reference values for future polymer-related researches.