Self-assembly Of Magnetically Responsive Photonic Crystals Sensor By Amphiphilic Random Copolymer

The magnetically responsive photonic crystals?MRPCs?is a kind of periodic structure material using the magnetic colloidal nanoparticles?MCNPs?as the magnetic assembly building blocks,and constructed based on the balance between the repulsive force and the magnetic attraction between adjacent particles.A magnetically molecularly imprinted photonic crystals?MMIPCs?sensor would be parpared by combination of the magnetically responsive photonic crystals with molecular imprinting technology.The sensor not only has the specific selectivity owing to molecular imprinting technology,but also has fast,reversible and controllable magnetic response of MRPCs,and the self-expression of optical signals of photonic crystals.In this thesis,MCNPs are prepared with one-step process through the miniemulsion self-assembly by an amphiphilic random copolymer,and used as building blocks to construct the MRPCs based on steric hindrance.In the preparation process of MCNPs,molecular imprinting technology were introduced to obtain magnetic molecularly imprinted nanoparticles?MMINPs?to obtain bisphenol A and melamine MMIPCs sensors.The research contents and results of this paper are as follows:?1?The MCNPs were prepared through the miniemulsion self-assembly by an amphiphilic random copolymer with one-step process,building the MRPCs based on steric hindrance.The MCNPs were obtained through ultrasonic miniemulsification and solvent volatilization process,in which oleic acid modified Fe₃O₄ nanoparticles?OA-Fe₃O₄ NPs?and nonionic amphiphilic random copolymer polystyrene-co-vinylpyrrolidone?P?St-co-VP??dispersed in chloroform as the oil phase and deionized water as the water phase.P?St-co-VP?was not only used as the emulsifier for miniemulsion,but also as the coating material for magnetic nanoclusters.The self-assembly of the magnetic nanoclusters and the random copolymer coating layer is completed simultaneously,and the polymer shell is prepared without polymerization reaction.It makes the preparation process fast,simple,convenient and easy to control,and the preparation conditions are mild.The preparation conditions of MCNPs were optimized,the molar ratio of St:VP in P?St-co-VP?as 1:9,10.0 g/L P?St-co-VP?,100 mg OA-Fe₃O₄,and ultrasonic miniemulsification for 2 minutes were chosen as the optimum conditions.The MCNPs were characterized by TEM,Zeta potential and nanometer particle analysis,TG-DSC,VSM,XRD,XPS.TEM showed that MCNPs presented a regularly spherical shape with an average particle size of about 104.6 nm?RSD=13.9%,n=100?.The zeta potential of MCNPs was 0 mV,indicating that the non-ionic coating material eliminates the surface charge of the particles.So,none of an electrostatic repulsion plays a role in magnetic assembly of PCs.The average hydrodynamic diameter was 200.5 nm,a double the diameter determined with TEM.It implied that PVP molecular chain on the particle surface stretch out in MCNPs aqeous dispersion,which give the steric hinderance among the particles.TG results showed that the magnetite content of MCNPs was 76.15%.According to VSM analysis,the saturated magnetization was up to52.60 emu/g,and the coercivity and remanent magnetization were 33.95 Oe and 3.95 emu/g,respectively,indicating that MCNPs are paramagnetic materials close to superparamagnetism.XRD proves that in OA-Fe3O4 NPs and MCNPs cores are cubic trans spinel structures of Fe₃O₄.XPS verifies that PVP on particle surface has coordination effect with Fe3O4,which ensure the stability of MCNPs.By adjusting the applied magnetic field,the reflection wavelength of MRPCs can be adjusted from 450 nm to 750 nm,which covers the entire visible spectrum.MRPCs based on steric hindrance can withstand 0.10 mol/L electrolyte and pH range of 2.0-12.0.After repeated washing for 10 times,the structural color of MRPCs remains unchanged,and the structural color could be recovered after washing to remove the electrolytes,which proves the stability and reproducibility of MRPCs.?2?The MMINPs were prepared through the miniemulsion self-assembly by an amphiphilic random copolymer with one-step process to build the MMIPCs sensor.The nonionic amphiphilic random copolymer P?St-co-VP??1:9?was used as the emulsifier in miniemulsion system,the coating material of magnetic nanoparticles,and the molecular imprinting material.Surface imprinted BPA-MMINPs were obtained towing to the hydrogen bond between Bisphenol A and PVP in random copolymer P?St-co-VP?,and the imprinting sites were fixed by P?St-co-VP?self-assembly aggregates.After removing the template molecules,BPA-MMIPCs sensor was constructed.In the process of P?St-co-VP?self-assembly,when BPA added is an important parameter.It was found that BPA was added too early,the imprinting sites were buried deeply in MCNPs,and the template molecules were eluted out difficultly.When BPA was added too late,the self-assembly of P?St-co-VP?was almost completed,which resulted in little and unstable imprinting sites.With BPA concentration changed from 0.001 g/L to 0.400 g/L,the structural color of BPA-MMIPCs sensor shifted from green to deep red,and the reflection spectrum shifted from 540 nm to 700 nm.The fitting equation of the BPA concentration?C?and the reflection wavelength???of the BPA-MMIPCs was?=52.34×logC+717.86?R²=0.9966?.Therefore,the quantitative detection of BPA could be carried out,and the the detection limit of BPA-MMIPCs sensor for BPA was 0.001 g/L?based on S/N=3?.Compared with the magnetic non-imprinted photonic crystals sensor,the imprinting factor of BPA-MMIPCs sensor was 4.29.The selectivity factors for estradiol,estriol,and diethylstilbestrol are 18.00,6.30,and 5.25,respectively,showing a high selectivity.The response time of the sensor was less than 30 seconds.After 10 cycles of response/elution,the BPA-MMIPCs sensor still has a good ability to identify BPA,which proves the stability and reproducibility of the BPA-MMIPCs sensor.The response mechanism of BPA-MMIPCs sensor was discussed.This sensor was applied to the determination of actual samples such as mineral water,tap water,lake water and plastic bottle.It was found that 0.0241 mg/L of BPA was detected in the lake water,and the none of BPA was detected in the other samples.The recovery was btween 84%and 103%with RSD less than 5.6%,indicating that the BPA-MMIPC is applicable.?3?In order to explore the applicability of the MMIPCs,melamine?Melamine,MEL?was selected as template molecule,and melamine magnetic molecularly imprinted nanoparticles?MEL-MMINPs?were prepared by using the miniemulsion self-assembly by amphiphilic random copolymer.The melamine magnetically molecularly imprinted photonic crystals?MEL-MMIPCs?sensor were constructed using the MEL-MMINPs,and the sensitivity of the sensor has been further improved.With the increase of melamine concentration from 1.0×10-6 g/L to 1.0 g/L,the structural color of MEL-MMIPCs sensor shifted from purple to dark red,and the reflection wavelength shifted from 497 nm to 709nm,covering the entire visible spectrum.The fitting equation of the MEL concentration?C?and the reflection wavelength???was?=29.21×logC+709.83?R²=0.9995?.Therefore,the quantitative determination of MEL could be carried out,and the detection limit of MEL-MMIPCs sensor for MEL was 2.14×10^-77 g/L?based on S/N=3?.Compared with BPA-MMIPCs sensors,MEL-MMIPCs sensors have a wider linear range and more sensitivity.Compared with magnetic non-imprinted photonic crystals,the MEL-MMIPCs sensor had an imprinting factor of 5.09,and selectivity factors for analogs cyanuric acid and atrazine was 8.76 and 5.75,respectively.MEL-MMIPCs had the higher selectivity than BPA-MMIPCs sensors.The response time of the sensor was less than 30 seconds also.After 10 cycles of response/elution,the MEL-MMIPCs sensor still has a good ability to identify MEL,which proves the stability and reproducibility of the MEL-MMIPCs sensor.