Preparation Of Lanthanide Complex Composite Particles With Stable Luminescence In Aqueous Solution

With the development of life science,the analysis of unknown biomarkers and identification of pathogenicity markers have raised higher requirements for the large-scale screening of biomolecules.The high throughput analysis and highly sensitive detection of the above analytes can be realized by the suspension array technology based on the fluorescence-encoded microspheres.How to obtain fluorescence-encoded materials with better fluorescence properties is the key probelm in the development of the suspension array technology.As efficient optical conversion molecular devices,lanthanide complexes have many excellent optical properties,such as long emission lifetimes,high luminescence intensity,large Stokes’shifts,and well-defined narrow emission peaks.They possess a great potential to replace the traditional encoding materials such as fluorescent molecules and quantum dots.However,a significant obstacle to their application arised from their limited luminescent stability and intensity in the physiological systems,owing to the sensitivity of coordination bonds-based lanthanide complexes to the aqueous environment.Organic ligands with the ability of polydentate chelation have attracted extensive attention in recent years,and the progress of the latest research is expected to achieve the high-efficiency sensitization of lanthanide ions and the stability of lanthanide complexes in water.Meanwhile,the host-guest composite system is the main construction strategy of the fluorescent encoded materials in the current field.As carrier materials,the micro/nano-scale microporous and mesoporous materials with large specific surface areas and pore volumes are very helpful to achieve highloading amounts of lanthanide complexes and a significant increase of luminescence for the encoded materials.In this paper,the lanthanide complexes with stable luminescence in aqueous solution were first obtained,based on the proper selection of organic ligands.Subsequently,the luminescent encoded materials based on lanthanide complexes were obtained with stably strong photoluminescence in salt-containing physiological solvent system by using different routes.The main contents are as follows:（1）Screening of organic ligands for lanthanide complex.Complexes were synthesized withβ-diketones,aromatic carboxylic acids and pyridine heterocyclic compounds as organic ligands of Eu³⁺and Tb³⁺.Then,by characterizations and comparison of luminescent properties,the tridentate pyridine-tetrazolate（H₂pytz）ligands,which can sensitize Eu³⁺and Tb³⁺simultaneously,were selected for the following investigations.The anionic complexes（Ln（pytz）₃）have high luminescent intensity,as well as high luminescence stability with no obvious decline in deionized water for 60 min.（2）Preparation of mesoporous composite luminescent nanoparticles through the guest-loading method.Mesoporous silica nanoparticles（MSN）were prepared by a templated synthesis route,and the ionic liquid with the ability to bind lanthanide complexes was grafted onto the surface of the as-prepared MSN.Subsequently,a large amount of lanthanide complexes were stably loaded into MSN by the anion exchange between complexes and the anions of the ionic liquid.The results showed that the carrier materials with large surface areas and pore volumes can effectively increase the loading capacity of the guest lanthanide complexes.The obtained MSN-IMI-Tb（pytz）₃particles possess narrow full-width half-maximum（FWHM,13 nm）,large absorption cross-section（2.7×10^-1212 cm²）,and long luminescence lifetimes（2.1 ms）in PBS buffer,which are far superior to the traditional encoding materials such as quantum dots and organic fluorescent dyes.Furthermore,the photoluminescence intensity of MSN-IMI-Tb（pytz）₃ nanoparticles maintained 70%of its initial value when monitored for 60 min in PBS buffer.Although the luminescence stability of MSN-IMI-Tb（pytz）₃particles is higher than that of pure lanthanide complexes in PBS,it is still difficult to meet the requirements of fluorescent-encoded materials in the suspension array technology.（3）Preparation of microporous composite luminescent nanoparticles through an insitu encapsulation method.In this work,luminescence materials with higher photo-stability in aqueous media were the goal of material developments.The lanthanide complexes were encapsulated into zeolitic imidazolate framework-8（ZIF-8）nanoparticles insitu during the ZIF-8 frameworks formation,through the electrostatic attraction andπ-πstacking interactions.The ZIF-8 hosts(Ln complex@ZIF-8,Ln=Tb³⁺and Eu³⁺)were selectively plugged by the aforementioned ionic liquid stopper at the pore entrances located at the exterior surface of the ZIF-8 hosts.The obtained Ln complex@ZIF-8@stopper particles possesse a large absorption cross-section(10^-12 cm²),high quantum efficiencies（23.2%and 8.48%,respectively）and long luminescence lifetimes（1.9 and 3.0 ms,respectively）in PBS buffer.Simultaneously,the photoluminescence intensity of Ln complex@ZIF-8@stopper maintained 95%of its initial value after monitored for 8 h in PBS buffer.Compared with MSN-IMI-Tb（pytz）₃,Ln complex@ZIF-8@stopper particles have higher quantum yields and more stable luminescence intensity in PBS buffer.Therefore,by employing red/green emission Eu/Tb complexes as encoding elements,single and double-color encoded system were obtained by altering the ratio and amount of complexes in the synthesis.In summary,the luminescence stability of lanthanide complexes in aqueous media was solved,and the lanthanide complex composite particles with stable luminescence were obtained.It is possible to enhance the luminescence performance of fluorescent-encoded microspheres in suspended array detection technology.Encoded materials with the aforementioned propertiesare expected to provide new concepts approaches for the development of encoding materials in the suspension array technology.