A Solid Fluorescence Sensor For Methyl Mercury:Its Preparation And Application

Methyl mercury is a strong toxic ion,which can be accumulated in the organs of animals and can cause prenatal nervous system and visceral damage.Therefore,the efficient and sensitive monitoring of Methyl mercury in organisms is of great importance.Upconversion luminescence?UCL?detection based on rare-earth upconversion nanophosphors as probes has been proved to exhibit a large anti-Stokes shift,no autofluorescence from biological samples,a remarkably deep penetration depth,and no photobleaching.However,the surface defect and large phonon groups inserted in the preparation of rare earth upconversion nanoparticles,as well as the smaller absorption section of upconversion population process,leaded to the low UCL efficiency,which is became a bottleneck of restricting its practical application.In recent years,the researchers developed many methods to improving the UCL efficiency,including the phonon energy modulation,core-shell structure design,surface plasmon resonance inducing by metal and so on.The photon modulation of the photonic crystals is one of the more effective methods to improve the UCL efficiency.The concept of photonic crystals was first put forward by Yablonovitch in1987 which is soon caused extensive concern of the research community and the in-depth research.Photonic crystal refers to the medium periodically by different refractive index of artificial crystal structure,the long range order of periodic structure of electromagnetic periodic modulation will produce a photonic band gap,the light of the specific frequency within the photonic band gap transmission is inhibited.Three-dimensional inverse opal photonic crystals,with thin wall,high connectivity and open,that not only can realize the modulation of the light,but also can effectively inhibit long-range energy transfer process of the luminescence center,improving the luminescence efficiency.In recent years,the extensive research has been carried out for the luminescence modulation in inverse opal photonic crystals,but these studies mainly focus on the modulation of down-convension luminescence,the study of the UCL modulation in the inverse opal also is less.This paper carried out the preparation of In₂O₃:Yb³⁺,Er³⁺inverse opal photonic crystals,the upconversion efficiency is improved by the special structure of inverse opal photonic crystals.On the basis,the upconversion biosensor is built to highly detect methyl mercury in serum.This thesis mainly in the following two aspects of research work:1.The In₂O₃:Yb³⁺,Er³⁺inverse opal photonic crystals are prepared by PMMA template combined with sol-gel method.First the modulation spontaneous emission in inverse opal photonic crystals is discussed,we found that the spontaneous emission of Er³⁺ions is inhibited,when the ⁴S_3/2-⁴I_15/2?⁵22 nm?transition of Er³⁺ions overlapped with the position of In₂O₃:Yb³⁺,Er³⁺inverse opal photonic crystals.Through the dependence of lifetimes and photonic band gap,we found that the modulation is not from the change of the photonic state density,but because the change of the effective refractive index in inverse opal photonic crystals.Due to the inverse opal photonic crystals with high connectivity,good openness,and with thin-wall structure?¹0 nm?,thus can effectively inhibit the long-range energy transfer processes among the rare earth ions,which can inhibit the concentration quenching,improve the upconversion luminescence efficiency.2.Based on the principle of fluorescence resonance energy transfer,when the position of rare earth Er³⁺ions luminescence overlap with the absorption position of quantum dots,the fluorescence resonance energy transfer will be occur between them,and the luminescence intensity of rare earth ions will change.In this paper we take In2O3:Yb³⁺,Er³⁺inverse opal photonic crystals as energy donor,and CdTe quantum dots as the accepter,prepared biosensor based on fluorescence resonance energy transfer for detecting methyl mercury content in the serum.Because of using the UCL as fluorescent signal,it can effectively avoid the interference of background light.And using the inverse opal photonic crystals as the carrier at the same time,can effectively improve the UCL efficiency,enlarge the fluorescent signal,and improve the detection sensitivity.