Study On Fluorescence-enhanced Photonic Crystal Sensing Technology Based On Quantum Dots And Its Applications

Photonic crystals(Ph Cs)are a new kind of optical materials whose dielectric constant varies periodically in space.By controlling the photonic band gap,the propagation of photons in photonic crystals can be controlled.Due to its unique optical characteristics,photonic crystals are often combined with other materials to construct a variety of highly efficient and sensitive chemical sensors.The fluorescence intensity is enhanced by“optical blocking effect”of photonic crystals,which is the photonic band gap of photonic crystals overlaps with the emission spectrum of quantum dots.The optical blocking effect of photonic crystals causes intense bragg diffraction of light at a particular frequency.The light signal can not be transmitted in photonic crystals,which is collected and enhanced in the fixed direction.The following two new detection methods are designed based on the enhancement of fluorescence signal by photonic crystals.The main contents are as follows:(1)In Chapter 2,monodisperse Si O₂ microspheres with different sizes are prepared,whose relative deviation of the particle size and the adhesion rate are less than 5%.A room temperature photoluminescence(RTP)quantum dots doped with Mn are fabricated on Si O₂ photonic crystals based on the“optical blocking effect”,the method is applied to the determination of chloramphenicol in the milk solution.The surface of Zn S:Mn room temperature phosphorescent quantum dots are modified by mercaptopropionic acid which is rich in carboxyl group,which can collide with chloramphenicol(containing electron donor groups such as-NO₂,-Cl and carbonyl)through electrostatic interaction and lead to electron energy transfer and phosphorescent quenching.Compared with traditional organic fluorescent dyes,Zn S:Mn QDs has longer lifetime and better light stability,and can effectively avoid the interference of background fluorescence and diffraction light.When Zn S:Mn QDs is combined with Si O₂ photonic crystals,the room temperature phosphorescence signal can be enhanced by 7.4 times.The method can detect chloramphenicol rapidly and sensitively in the concentration range of 100.0-2000.0 n M,and the detection limit is64.8 n M.(2)In Chapter 3,mesoporous Si O₂ microspheres(MSN)with different core-shell structures is prepared by seed growth method,which has good dispersibility.A fluorescence enhanced mesoporous photonic crystal(CDs-Ph Cs)sensing system is prepared by coating carbon dots on mesoporous photonic crystals,which is applied to the determination of UO₂²⁺in solution.Due to the strong electrostatic interaction between UO₂²⁺and carbon dots when the molecules are close enough,the electrons transfer from the surface of carbon dots to UO₂²⁺,which leads to the quenching of the fluorescence signal.In this system,mesoporous silica has large specific surface areas and regular channels,which can effectively disperse carbon dots and prevent the fluorescence quenching caused by the accumulation of carbon dots.In addition,the fluorescence signal of the carbon dots is increased by 325 times through the“light blocking effect”,which can sensitively detect UO₂²⁺.The method can detect UO₂²⁺rapidly and efficiently in the concentration range of 62.5-600.0 n M,and the detection limit is 5.4 n M.