Research Of Stimulus Responsive Photonic Crystal Sensor For Small Molecule Detection

Photonic crystal(Ph C)is made of periodic arrangement of materials with different dielectric constants,which can effectively control the direction of optical propagation due to the structure of the photonic band gap(PBG).Based on such excellent optical properties,the sensor constructed by Ph C shows unique advantages in the field of analytical detection and has a good application prospect.The stimulus responsive materials can respond to the changes in the external environment,and they can be introduced into the Ph C array to prepare the responsive photonic crystal(RPh C).According to the stimuli in the external environment,RPh C can be divided into three types,including physical,chemical and biological responsive photonic crystals.When RPh C is stimulated by the external environment,the internal structure of photonic crystal will be changed,and this makes the wavelength or intensity of Bragg diffraction peak change.This can transform the stimulus signal of the external environment into optical signal and output it.Based on this,this paper develops several kinds of RPh C sensors with simple operation,high sensitivity and good selectivity by using Ph C as signal conversion element and introducing stimulus responsive materials or groups to realize rapid and sensitive detection of target analytes.The details are as follows:In Chapter 2:A molecularly imprinted photonic hydrogel(MIPH)is described for the optical determination of L-Histidine(L-His).The inverse opal structure of MIPH was obtained by placing silica particles in molecularly imprinted polymer on a glass slide.After fully etched through hydrofluoric acid,this inverse opal structure brings about high specific surface and plentiful binding sites for L-His.If L-His is absorbing by the modified MIPH,its average effective refraction coefficient is increased.The detection limit of this method is 10 Pm,and the response time towards L-His is as short as 60 s.Compared with traditional hydrogel materials,the MIPH does not need to modify special chemical groups,and can detect target molecules with the change of the optical signal of the Ph C,which has a good application prospect in the field of analysis and detectionIn Chapter 3:A RPh C film sensor for the ultrasensitive and label-free detection of uranyl ions(UO₂²⁺)has been proposed,which is easy to construct and does not need to combine with hydrogel.The RPh C film is non-p H sensitive because it is obtained by the self-assembly of methyl methacrylate-acrylonitrile co-polymeric nanospheres(PMMA-AN).These nanospheres are modified with amidoxime groups which have a good coordination ability with UO₂²⁺.The bindings between nanospheres and UO₂²⁺change the refractive index and disturb the face centered cubic structure of the film,that leads to a decrease of the diffraction peak intensity of the RPh C film.The sensor works in the range of 10 p M to 100?M for UO₂²⁺determination.Moreover,the sensor shows a good selectivity for UO₂²⁺,and can also perform the determination of UO₂²⁺in real sample.The RPh C film sensor shows great potential in label-free and ultrasensitive detection of UO₂²⁺.Be different from the previous detection method,this work is based on the intensity variation of diffraction peak,which provides a novel way for the application of RPh C in the field of detection.In Chapter 4:A self-healing smart 2D Ph C hydrogel film that combines the optical property of photonic crystal and the dynamic regeneration property of boronate ester bond has been prepared for glucose and related saccharides.The boronate ester bond formed through phenylboronic acid and dopamine results in the self-healing property of hydrogel network,which can effectively improve the reliability and lifetime of hydrogel.And due to the high bonding capacity between1,2-or 1,3-diol and phenylboronic acid,the smart hydrogel film has a good recognition ability for glucose and other related saccharides.The reaction between the monosaccharides and the phenylboronic acid group breaks the original boronate ester bond,this will lead to a decrease in cross-linking density of the 2D Ph C hydrogel film,and further makes the film swell and the diameter of the Debye diffraction ring decrease.The film shows good reuse and responsive ability for saccharides.For example,the glucose can be recognized by the film in the range of0.5 to 12 m M.The film also has good response to glucose in urine,which shows a good potential application value in primary diagnosis of diabetes.This kind of smart Ph C hydrogel material is expected to functionalized with other responsive ability through the introduction of specific dynamic covalent bonds,showing a broad application prospect.In Chapter 5:By taking the polyacrylamide hydrogel as the first network and nucleic acid hydrogel as the second network,a new kind of double-network Ph C nucleic acid hydrogel(DN-hydrogel)has been constructed.Because the C-rich sequences of DNA in the nucleic acid hydrogel would fold to form an i-motif structure in an acidic environment,which leads to the volume contraction of the DN-hydrogel and the increase in the diameter of Debye diffraction rings of Ph C.And the DN-hydrogel can be restored to their initial state in weakly alkaline environment because of the reversibility of i-motif structure.In addition,the C-rich sequence can also specifically bind with Ag⁺to form C-Ag⁺-C complex,making the DNA strand form hairpin like structure,so the presence of Ag⁺will also cause the volume contraction of the DN-hydrogel.Since Cysteine can seize Ag⁺from the C-Ag⁺-C complex,the DN-hydrogel can revert to its initial state in Cysteine solution.The triple response of p H,Ag⁺and Cysteine can be realized through the DN-hydrogel,and the response concentration of Ag⁺and Cysteine can reach 0.5?M,which provides a new idea for the development of intelligent optical materials.In Chapter 6:Eu³⁺doped PMMA composite microspheres were synthesized by emulsion polymerization,and Eu³⁺doped Ph C films were further prepared by vertical deposition.Due to the slow photonic effect of photonic crystals,when the photonic band gap of Ph C matches the emission peak of Eu³⁺,the fluorescence emission intensity of Eu³⁺will be significantly enhanced.Based on this,a series of Ph C films with different photonic band gap were prepared by adjusting the particle size of PMMA composite microspheres,and Eu³⁺luminescence performance was successfully regulated.The experimental results show that the fluorescence emission intensity of films with Ph C structure is stronger than that of films with non-Ph C structure.When the Ph C substrate with photonic band gap of 589 nm is used as the base,the enhancement multiple of Eu³⁺fluorescence emission intensity can reach up to 3.2.In addition,the Eu³⁺doped Ph C film can also be used for sensitive detection of Fe³⁺in solution by using the characteristics of fluorescence resonance energy transfer.At the same time,the film also has good selectivity and identification ability.