| Photonic crystal is a novel functional material with periodic distribution of dielectric constant in space.The unique periodic structure endows photonic crystal with characteristic of modulating the propagation of electromagnetism wave.Responsive photonic crystal has gradually become a new type of sensing material with development potential due to its fast response and signal self-expression properties.Colloidal magnetically assembled photonic crystals?CMA-PCs?are formed from monodispersed colloidal superparamagnetic nanoparticles that self-assembled in an external magntic field.Comparing with the traditional colloidal photonic crystals self-assembly processes driven by gravitation,centrifugal force,electrophoretic deposition and capillary force,magnetic assembly method has the advantages of rapid assembly process,simple assembly operation and controllable assembly structure.Molecular imprinting is a technique to fabricate polymers with tailor-made recognition sites.Owing to the complementarity in spatial shape,size and binding sites,nanocavities in the molecularly imprinted polymers show high selective recognition for the target molecules.In the dissertation,magnetic composite nanoparticles?MCNPs?with core-shell structure were prepared via miniemulsion polymerization.CMA-PCs with visible structural color were obtained by magnetic assembly of the MCNPs suspension.In order to apply the CMA-PCs system to the analysis of specific substances,molecular imprinting techinique was introduced into the MCNPs preparation process to get magnetic molecularly imprinted nanoparticles?MMIPs?,which have magnetic nanocluster core and molecularly imprinted polymer shell structure.The synthesized MMIPs acted as photonic crystal building blocks and recognition elements as well,because the surface imprinted nanocavities could selectively identify and adsorb the target molecules.Therefore,colloidal magnetically assembled molecularly imprinted photonic crystals?CMA-MIPCs?with specific recognition and responsiveness could be directly obtained by applying a magnetic field to the MMIPs suspensions with different concentrations of target molecules.The main contents and results of the dissertation are summarized as follows:1.Miniemulsion polymerization was adopted to prepare spherical MCNPs with negative charged surface,and CMA-PCs with visible structural color were obtained under the balance of magnetic attraction and electrostatic repulsion in a magnetic field.The influences of the surfactant sodium dodecyl sulfate?SDS?concentration,the sonication time and cosurfactant cetyl alcohol?CA?on the size,morphology,polydispersity indexes,magnetite content of MCNPs and the optical property of CMA-PCs were investigated by transmission electron microscopy?TEM?,vibrating sample magnetometer?VSM?,thermal gravimetric analyzer?TGA?,zeta potential and nanometer particle analyzer and miniature fiber optic spectrometer.The optimum experimental conditions for the preparation of MCNPs were determined as follows:SDS concentration of 0.75 mg/mL,three-step sonication time as 60-30-60 s and without an addition of cosurfactant CA.MCNPs fabricated under the optimum conditions had an average size of 97.3 nm?RSD=7.10%,n=100?,and magnetite content of 43.0%.The structural color of CMA-PCs assembled under a magnetic field strength of 0.01 T was yellow.And the color could be changed from yellow to purple,covering the whole visible spectrum,by tuning the magnetic field strength?0.01-0.20 T?.Surfactant SDS concentration was a key parameter which influenced the size and magnetie content of MCNPs and then affected the optical property of CMA-PCs.As increasing SDS concentration,the structural color of CMA-PCs assembled under the same magnetic field strength blue-shifted and the adjustable color range was narrowed in the magnetic field strength range of 0.01-0.20 T.Ionic strength?IS?had an obvious effect on the optical property of CMA-PCs.As increasing ionic strength from 0.03 mmol/L to 0.75 mmol/L,the reflection wavelength shifted from 607 nm to 434 nm,indicating CMA-PCs could be used as an ionic strength sensor.2.On the basis of miniemulsion polymerization of MCNPs,molecular imprinting was introduced into the MCNPs preparation process.Under the optimum miniemulsion polymerization conditions,alkaline melamine?MEL?was added as the target molecule,methyl methacrylate as the skeleton monomer,acrylamide and methacrylic acid as the functional monomers,and the amounts of acrylamide and methacrylic acid were optimized.In the polymerization process,cross-linker ethylene glycol dimethacrylate?EGDMA?captured the target molecules due to hydrogen bonding with functional monomers in the polymer network to obtain melamine magnetic molecularly imprinted nanoparticles?MEL-MMIPs?.Owing to the imprinted nanocavities in the surface of the eluted MEL-MMIPs,MEL-MMIPs could selectively recognize the target molecules rapidly.Therefore,CMA-MIPCs sensor with specific recognition and responsiveness to melamine was obtained by magnetic assembly of the MEL-MMIPs suspension.The response of CMA-MIPCs to melamine caused the increase of the surface charge density of MEL-MMIPs,which enhanced interparticle electrostatic repulsive force between MEL-MMIPs.Therefore,an increase of the lattice spacing of CMA-MIPCs led to the red-shift of the structural color.As increasing melamine concentration from 1.0×10-5 mg/mL to 1.0×10-2 mg/mL,the diffraction wavelength shifted from 420 nm to620 nm.The largest redshift could reach 200 nm,and the detection limit for melamine was1.0×10-5 mg/mL.Moreover,CMA-MIPCs had no response to the structural analogues cyanuric acid and atrazine,which showed high selectivity for melamine.3.Chloramphenicol?CAP?was chosen as the target molecule to investigate the response of CMA-MIPCs to neutral molecules.O n the basis of MEL-MMIPs preparation,chloramphenicol magnetic molecularly imprinted nanoparticles?CAP-MMIPs?with core-shell structure were synthesized by adjusting the amount of the target molecule chloramphenicol and the functional monomers acrylamide and methacrylic acid via miniemulsion polymerization.CMA-MIPCs with specific responsiveness to chloramphenicol were obtained by magnetic assembly of the CAP-MMIPs suspension.In the sensing process,the response of CMA-PCs to chloramphenicol caused the increase of the CAP-MMIPs size.The swell of the CAP-MMIPs made the magnetic nanoparticles in the inner core spread outward and weaken the shell shielding effect.Hence,the increased interparticle magnetic attraction resulted in the decrease of the lattice spacing of CMA-MIPCs and finally the blue-shift of the structural color.As increasing chloramphenicol concentration from 1.0×10-3mg/mL to 1.00 mg/mL,the largest blueshift could reach 181 nm,the detection limit for chloramphenicol was 1.0×10-3 mg/mL.Furthermore,CMA-MIPCs had no response to the structural analogue p-nitroaniline and the functional analogue tetracycline,which showed high selectivity for chloramphenicol.4.L-phenylalanine?L-Phe?was chosen as the target molecule to investigate the response of CMA-MIPCs to acidic molecules.L-phenylalanine magnetic molecularly imprinted nanoparticles?L-Phe-MMIPs?with core-shell structure were prepared by optimizing the amount of the functional monomers acrylamide and methacrylic acid via miniemuls ion polymerization.CMA-MIPCs with specific responsiveness to L-phenylalanine were obtained by magnetic assembly of the L-Phe-MMIPs suspension.The response of CMA-MIPCs to L-phenylalanine caused the increase of the surface charge density of L-Phe-MMIPs,which enhanced interparticle electrostatic repulsive force between L-Phe-MMIPs.Therefore,an increase of the lattice spacing of CMA-MIPCs led to the red-shift of the structural color.As increasing L-phenylalanine concentration from 1.0×10-4 mg/mL to 1.0×10-1 mg/mL,the largest redshift could reach 171 nm,the detection limit for L-phenylalanine was 1.0×10-4mg/mL.Moreover,CMA-MIPCs had no response to the structural analogues L-tyrosine and L-tryptophan,which showed high selectivity for L-phenylalanine.Because the CMA-MIPCs system was stabled based on the electrostatic repulsion,so t he responsiveness of the CMA-MIPCs sensor platform for small molecules has been researched by systematically investigating the imprinting and sensing results of the alkaline molecule melamine,the neutral molecule chloramphenicol and the acidic molecule L-phenylalanine,respectively.5.The combination of hydrogel solidification technology with CMA-PCs could make a new direction for the application of CMA-MIPCs sensing platform.Low-temperature induced polymerization was investigated to prepare magnetically assembled photonic crystal hydrogel film.Hydrogel polymerization and the magnetic assembly of CMA-PCs proceed simultaneously,and the reaction time of low-temperature polymerization was only 10 s,which was beneficial to the uniform distribution of the magnetically assembled photonic crystal structure in the hydrogel matrix.Meanwhile,polyacrylamide matrix has good elasticity deformation capibility,which granted the magnetically assembled photonic crystal hydrogel film with deformation response property.The introduction of CMA-PCs into the hydrogel matrix could realize a quick,convenient and large-scale preaparation of photonic crystal hydrogel film,which has a great significance in the field of physical sensor. |
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