Construction And Multiplexed Detection Of Core-Shell Fluoride Upconversion Fluorescence Probe

Trace detection technology has been widely used in environmental science,material analysis,biomedicine.In recent years,with the further improvement of trace analysis requirements,fluorescence analysis with high selectivity and high sensitivity has become the most popular detection method for trace analysis.Compared with traditional fluorophores,upconversion nanomaterials have the advantages of long light penetration depth,long life and less damage to the samples,so they have high application value in fluorescence sensing.However,the commonly used F?rster resonance energy transfer（FRET）detection process of upconversion probes occurs only when the distance between donor and acceptor is less than 10 nm,and the size of upconversion nanoparticles is usually tens of nanometers,which leads to the problem of low energy transfer efficiency of upconversion fluorescent probes.In addition,in order to meet the growing demand for high-throughput analysis,multiplexd fluorescence detection technique for simultaneous identification and quantification of multiple chemical substances and biomolecules is highly desirable.Based on the above problems,this thesis aims at enhancing the energy transfer efficiency of the nanoprobes by optimizing the structure of upconversion nanoparticles and constructing core/multishell nanoparticles with orthogonal emission performance to achieve multiplexed detection with independent channel.The NO₂^-nanoprobe with efficient FRET process was constructed by designing core-shell structure to modulate the distribution region of activator ions in nanoparticles.The core-shell structure NaYb F₄@NaYF₄:Yb³⁺,Er³⁺upconversion nanoparticles were prepared,which limited the activator Er³⁺ions to the surface of nanoparticle,which significantly shortened the energy transfer distance between the donor and the acceptor,and could provide the maximum energy to the acceptor.The theoretical FRET efficiency of the NaYb F₄@NaYF₄:Yb³⁺,Er³⁺→NR sensing system was calculated by Monte Carlo simulation,which could reach 93.8%.The 100%Yb³⁺doping in the core can increase the absorption of excitation energy,so the optimal doping concentration of Er³⁺in the shell was increased to 4%,and the upconversion fluorescence intensity was enhanced over～4.5times compared to the common NaYF₄:20%Yb³⁺,2%Er³⁺nanoparticles.The FRET efficiency of the NaYb F₄@NaYF₄:Yb³⁺,Er³⁺@Si O₂@NR probe was calculated to be91.9%,which was much higher than that of the NaYF₄:Yb³⁺,Er³⁺@Si O₂@NR probe（27.7%）.Moreover,the NO₂^-concentration detection of the well-designed nanoprobe showed a much lower detection limit of 0.6 ng/m L and higher selectivity.The core/multishell upconversion nanoparticles were constructed to obtained orthogonal emissions,and realized multiplexed fluorescence detection with independent sensing channels.The core/multishell NaYF₄:Yb³⁺,Tm³⁺@NaYF₄:Yb³⁺,Nd³⁺@Na Lu F₄@NaYF₄:Yb³⁺,Er³⁺@Na Lu F₄@Na Er F₄:Tm³⁺@Na Lu F₄ nanoparticles were prepared by layer-by-layer coating.The effects of ion doping method and concentration in the luminescent layer,the thickness of the isolation layer and the relative position of the luminescent layer in the particles on the fluorescence performance of the core/multishell nanoparticles were adjusted during the shell coating process,and the blue/green/red orthogonal fluorescence signals were successfully obtained under 808 nm/980 nm/1532nm excitation.Based on the inner filter effect,the multiplexed detection performance of the designed core/multishell nanoparticles was verified by simultaneous detection of the MO/Rh B/MB concentration in aqueous solution.The detection limits were calculated to be～0.1μg/m L,respectively,which confirmed the multiple detection performance of the designed core/multishell nanopartlcies.In addition,by depositing the multiplexed UC detection layer and superhydrophobic Si O₂ layer successively on the substrate,a reproducible and self-cleaning sensor was developed to achieve highly sensitive multiplexed detection of a single analytical droplet（≈10μL）.Based on orthogonal emission upconversion nanoparticles,a dual-channel nanoprobe for H₂S and CO was further constructed and applied to monitor the concentration of endogenous H₂S and CO in cells.In order to obtain orthogonal upconversion emission with high color purity under high power density excitation,the effects of doping position of activators and thickness of luminescence layer of core/multishell nanoparticles were investigated.The optimal nano-structure were determined as NaYF₄:Yb³⁺,Er³⁺@NaYF₄:Yb³⁺,Nd³⁺@Na Lu F₄@NaYF₄:Yb³⁺,Tm³⁺@Na Lu F₄,in which the optimal thicknesses of NaYF₄:Yb³⁺,Tm³⁺luminescent layer was 6 nm.Subsequently,the specific recognition fluorophores of H₂S and CO were coupled to the surface of nanoparticles using DNA as the medium.The fluorescence sensing results in aqueous solution showed that the designed dual-mode nanoprobe exhibited linear relationships with the concentration of H₂S and CO,and the detection limits were determined to be 10.3 n M and 6.8 n M.In addition,the intracellular sensing results indicated that the probe has good biocompatibility,and the fluorescence intensity was also dependent with the concentration of H₂S and CO,and the as-designed dual-channel nanoprobe was successfully applied to monitor the changes of endogenous H₂S and CO concentration in cardiomyocytes during ischemia/reperfusion injury.