Photonic Crystal Structure Based On Magnetic Response Nanoparticles And The Application In Surface Enhanced Spectroscopy

Modern surface-enhanced spectroscopy technology can provide vibration signals related to the chemical and structural information of the detected objects,and it is considered as an ideal analytical method to detect and determine the composition of matter.Among them,Surface Enhanced Fluorescence Spectroscopy?SEF?,Surface-enhanced Raman Spectroscopy?SERS?and Surface Enhanced Infrared Absorption Spectroscopy?SEIRA?are typically used.However,the common metal solid-state enhanced substrates nowadays have the drawbacks of complicated and time-consuming preparation processes,the need to use sophisticated and expensive instruments,and inherent defects in structural design that result in spectral quenching.The periodic structure of photonic crystals forms a unique band structure,which regulates photon behavior and strong optical coupling characteristics.For example,photonic bandgap,photonic localization,and purcell effects can bring further development of surface-enhanced spectroscopy.Therefore,in this dissertation,Fe₃O₄ nanoparticles with superparamagnetic properties were prepared by green and efficient methods,and they can be self assembled into liquid photonic crystal structures by external magnetic response.In addition,the composite structure of magnetically-responsive nanoparticles and noble metal nanoparticles enabled surface plasmon resonance and photonic crystal photonic bandgap to form a coupling response,which was further applied to surface-enhanced spectroscopy techniques.This article specifically includes the following aspects:?1?We used liquid suspension of Fe₃O₄ nanoparticles as tunable liquid fluorescence enhanced substrates.By applying an external magnetic field,the Fe₃O₄ nanoparticle suspension can self-assemble into a periodic photonic crystal structure.The external magnetic field increased or decreased the distance between the Fe₃O₄ particles in a reversible manner,and further changes its optical properties.In addition,by coupling the photonic bandgap position of the liquid phase Fe₃O₄ photonic crystal to various fluorescence emission wavelengths,a reversibly regulated fluorescence enhancement was achieved.For photonic crystal systems/DMTPS-DCV organic dye molecules(concentrations of 10^–7 M,water The volume fraction fw=90%),the substrates gave a maximum fluorescence enhancement effect of 12.3 times.This work can reliably and inversely control the fluorescence enhancement factor,which is of great significance for fluorescence detection using liquid photonic crystal fluorescence enhanced substrates?non-metallic fluorescence enhanced substrates?.?2?We used a smart liquid surface-enhanced Raman?SERS?active substrate composed of triiron tetraoxide?Fe₃O₄?/gold nanoparticle?Au?composite materials for quantitative detection applications.Using the coupling of metal nanoparticles localized surface plasmon resonance?LSPR?and the unique optical properties of colloidal photonic crystals,we have prepared substrates with strong and controlled surface-enhanced Raman?SERS?activity and excellent point-to-point reproducibility.The study of the SERS performance of the substrate showed that the substrates not only had excellent enhancement effect,but also exhibited high signal repeatability.In addition,by changing the intensity of the external applied magnetic field,the distance between the particles of the self-assembled liquid photonic crystal and the electromagnetic field distribution generated by the local surface plasmon resonance of the metal nanoparticles can also be changed accordingly.Therefore,in this controlled manner,the SERS enhancement factor?EF?can be magnetically tuned in the range of10⁴ to 10⁷,up to 2 orders of magnitude.?3?We studied the distribution of the surrounding electric field intensity of the photonic crystal and noble metal composite structure by FDTD software.Through simulation,it was found that at 514 and 633 nm?source wavelength?,the photonic band gaps and local surface plasmon resonance effects were more pronounced,resulting in greater electric field enhancement.Next,we studied the effect of the spacing of different photonic crystal structures on the electric field enhancement.It was found that as the spacing of the crystal structure continues to decreased,the photonic band gap appeared blue-shifted,and the electric field intensity at the hot spot also increased.In addition,we studied the effect of the changes in intermetallic distance on its electric field enhancement capability.The results showed that the strength of the electric field between metals increased as the spacing decreased.These calculation results are of great significance for evaluating the enhancement effects of photonic crystals and noble metal composite structure SERS substrates,guiding the preparation of SERS substrates,and will help people understand the mechanism of SERS enhancement better.?4?Fe₃O₄/Au nanocomposites were synthesized by two-step method and used for SEIRA substrates.The oppositely charged Fe₃O₄ and Au nanoparticles were prepared separately,and then the complexes were obtained by electrostatic adsorption.The prepared Fe₃O₄/Au nanocomposites were used as the SEIRA substrates,and the reinforcing effect could be adjusted by the strength of the applied magnetic field.When the magnetic field strength reached 280 mT,the substrate-pair of p-mercaptobenzoic acid?MBA?can be increased by 3.3 times,and the enhancement effect of-NO₂ by p-nitrobenzoic acid?NBA?can reach 10.7 times.