Fabrication And Application Of Polymeric Photonic Crystal Sensors

Nature produces a series of complex multi-level structures to adapt to the changes in the environment in the long process of evolution, this provides the new idea to create functional materials with new structure. Some unique and interesting properties in nature often arise from hierarchical structuration in a variety of forms, for example, some biological feathers have bright colors, chameleons can change color with the changes of the environment. Inspired by the materials in nature, people have imitated and fabricated a variety of tunable responsive sensors with more complex properties via some convenient methods such as the colloid self-assembly. The inverse opal polymeric photonic crystal sensor based on colloidal crystal template is one of the hot research topics. Inverse opal photonic crystal is a porous material with periodicity in 3D, which not only has the general properties of porous functional materials, but also obtains some new properties like the self-response optical properties because of its periodic structure. Therefore, it attracts more and more attention in design and application of sensors.In this work, the monodisperse silica colloidal particles were synthesized by using an approach based on the St?ber method with certain modifications. And the opal colloidal crystal templates were fabricated through the vertical self-assembly method, then the templates were infiltrated with different functional monomers. After photopolymerization, the silica was removed and the inverse opal polymeric photonic crystal sensors were formed. The sensors fabricated with different functional monomers can response to different external stimuli. The results can be summarized as follows:1. The optimal reaction condition of fabrication monodisperse silica particle controlled by temperature and substrate concentration was explored. The size of the silica particles can be tuned in the range of 180–550 nm, and they were characterized by scanning electron microscopy(SEM), separately. Compared to the previous method that only changed one factor, the control effect of this method was more significant and the uniformity, stability and reproducibility were improved. Moreover, it had more advantage in the large-scale fabrication.Based on silica particles with different sizes, the colloidal crystal templates were fabricated by controlling the concentration and temperature. Based on the colloidal crystal templates, the fabrications of the inverse opal polymeric photonic crystal sensors with different photonic band gap were explored. The templates and sensors were characterized by SEM and fiber spectrometer, separately.2. Based on the unique optical properties of the inverse opal photonic crystal polymer films which are sensitive to a specific range of p H values, a novel label-free CO32- sensor has been successfully fabricated with acrylic acid as functional monomer. Due to the self-response optical properties, the sensors directly generate visually perceptible optical signals to report respond events, which are easily observable by the naked eye without any pretreatment of samples and any analytical instrumentation. The detection of CO32- in different concentration ranges could be achieved by changing the molar ratio between the functional monomer and cross-linker: when the molar ratio was 2:1, the sensor could respond to the concentrate ions from 10 to 30 m M; when the molar ratio was 5:1, the sensor could respond to the concentrate ions from 1 to 10 m M. These sensors showed different structure colors as a response to varying concentrations of CO32- under ambient conditions with a swift detecting velocity and even semi-quantitative determination on the spot.Because the sensors are sensitive to a specific range of p H values, they showed excellent interference immunity over other anions including F-, Cl-, Br-, CH3COO-, NO3-, HCO3-, S2O82-, HPO42-, C2O42- and SO42-. Moreover, they are stable and reusable.3. Based on a special enzyme catalytic reaction, a novel label-free urea sensor has been successfully fabricated with methacrylic acid as functional monomer. The sensors can detect different concentration ranges of urea by changing the molar ratio between the functional monomer and cross-linker when preparing the polymeric backbone of the photonic crystals: when the molar ratio was 2:1, the sensor could respond to the urea from 100 to 200 m M; when the molar ratio was 5:1, the sensor could respond to the urea from 10 to 40 m M; when the molar ratio was 5:1, the sensor could respond to the urea from 1 to 9 m M. Practically, the normal concentration range of urea in blood is 2.5 to 7.5 m M, the sensor can response to this concentration range of urea by a sudden leap of the color change: when the blood urea is at a normal level in human body, the sensor exhibited its original color(green); the sensor displayed a yellow color when the urea level was at the borderline concentration(7 m M). The color of the sensor turned red in higher urea concentrations(9 m M) associated with a clear-cut diagnosis of renal deficiency. For green, yellow, and red which are used internationally in traffic signals, we introduced this color variation of the sensor in an easy way to understand.Because urease is an absolute specific enzyme, the sensors showed excellent selectivity over other molecules including formamide, acetamide, methylurea and 1,3-dimethylurea, which are structurally similar to urea. Meanwhile, these sensors were stable and reusable. They were also showed good practicability to complex samples, natural lake water for example. The combination of photonic crystal technology and specific enzymatic reaction has important reference significance for the detection of other molecules.4. Based on the sensibility of azobenzene derivatives(photoresponsive molecule) to different light conditions, a photoresponsive photonic crystal sensor was fabricated with acrylamide and host–guest molecules as functional monomer. The response of the sensor under different illumination conditions(ultraviolet and visible light) was explored.