Studies On The Design Of The Fluorescence Sensors Based On Coordination Assembly And Its Bioimaging Application

Bioimaging is an important technology for monitoring the morphology of biological tissues and biological processes at the molecular level and even the entire human body,visually detecting biological molecules,identifying metal ions,and characterizing life activities.In recent years,scientists have focused their research on studying molecular biology,imaging methods,and designing and synthesizing new molecular sensors.Among many biological imaging technologies,fluorescence assays have become one of the most advanced technologies for studying biological systems due to their rapid execution,non-destructive,highly sensitive,suitable for high-throughput screening applications,and can provide true information about positioning and quantification.Therefore,the rational design of fluorescent sensors with different chemical material compositions and different functions is of great significance for the accurate study of biological phenomena.In this thesis,a series of fluorescent sensors have been developed based on peptide biomolecules and rare earth complexes for the detection of metal ions,biothiols,temperature,hypochlorous acid,etc.and biological targeted imaging.The dissertation is mainly divided into following eight chapters:Chapter 1:Briefly discusses the basic classification,design principles and research progress of fluorescence sensors;focuses on the research status and progress of peptide-based fluorescence sensors and rare earth-based fluorescence sensors.Chapter 2:Herein,a novel fluorescence chemosensor DP（Dansyl-Leu-Leu-Cys-Acp-Asp-OH）based on biomolecular peptide has been designed and synthesized,which can be used in the detection of intracellular and environmental Ag⁺and H₂S.The DP exhibited high selectivity and sensitivity,excellent cell permeation,biodegradability,good water solubility,and p H insensitivity over a biologically relevant range,with detection limits of 61.7 n M and 74.0 n M for Ag⁺and H₂S,respectively.This work can inspire the design of multi-functional fluorescence sensor based on beacon peptides by modifying lateral and terminal groups for imaging applications in physiological and pathological events.Chapter 3:Herein,we utilized the native chemical ligation（NCL）reaction mechanism to develop a F?rster resonance energy transfer（FRET）strategy for designing a cell penetration peptide TAT-modified ratiometric two-photon biothiols probe（TAT-probe）.The TAT-probe can not only rapidly enter into mitochondria assisted by TAT peptide,but also simultaneously detect biothiols and sequentially distinguish GSH.When the TAT-probe was excited with 404/820 nm wavelength light,it showed a change in the ratio of fluorescence after adding biothiols,including a quenched red fluorescence intensity(λ_em=585 nm)and an enhanced signal in green fluorescence intensity(λ_em=520 nm).Excitingly,the TAT-probe excited at 545 nm could display a red fluorescence(λ_em=585 nm)towards GSH and a quenched signal towards Hcy or Cys.This specific fluorescence response indicated the TAT-probe could effectively detect biothiols and differentiate GSH from Cys/Hcy in mitochondria.This work pioneered a new approach to design and synthesize biothiol-probes based on peptides and NCL reaction mechanism.Chapter 4:Here,we assembled up-conversion nanoparticles Na YF₄,Yb/Er@Na YF₄（UCNPs）and Mn Fe₂O₄（MF）into multi-functional nanohybrid through direct coordination using polyacrylic acid（PAA）as the surficial bridging linker.Afterwards,the photosensitizer molecules Rose Bengal（RB）and PEG-COOH were covalently grafted onto the nanohybrid.UCNPs effectively stimulated RB by means of fluorescence resonance energy transfer effect to convert O₂ to ¹O₂.Meanwhile,MF NPs worked as a Fenton catalyst to continuously generate O₂ by decomposing H₂O₂ in the H₂O₂ over-expression tumor micro-environment.Thus,a comprehensive therapeutic system was successfully constructed,which can efficiently perform photodynamic therapy（PDT）of hypoxic tumor under the excitation of 980 nm laser.This work explored a new method for the assembly of nanohybrid using heterogeneous nanomaterials by coordination with bridging ligands between NPs and provided a versatile PDT candidate for hypoxic tumor.Chapter 5:Here,we propose a new strategy to obtain Eu³⁺-complex nanoparticles（Eu-NPs）with self-assembly induced luminescence（SAIL）characteristics without encapsulation or hybridization.Compared with previous assembly-induced fluorescence or phosphorescence emission,the SAIL phenomena of increased luminescence intensity and lifetime in aqueous solution are due to the combined effect of self-assembly confining the molecular motion and shielding the water quenching.As a proof of concept,we also show that this system can be further applied in bioimaging of temperature and HCl O sensing.The SAIL activity of the RE system proposed here offers a further step forward on the roadmap for the development of RE light conversion and their integration in bioimaging and therapy applications.Chapter 6:In this part,we designed and synthesized a novel Eu³⁺/Tb³⁺supramolecular assembly hybrids（Eu/Tb-SAH）with the excellent characteristics of water dispersion stability,biocompatibility and luminous properties.As anthrax spore biomarker,2,6-pyridinedicarboxylic acid（DPA）can coordinate with Tb³⁺and sensitize Tb³⁺,resulting in a proportional change of fluorescence intensity and lifetime on the ms timescales,thereby realizing rapid and sensitive detection of DPA in water media.To confirm our prediction,accurate and selective detection of DPA was achieved with Eu/Tb-SAH as a nanoprobe through steady-state ratiometric fluorescence and time-resolved technology,of which the low detection limits are 27.3 n M and 1.06 n M,respectively.This work paves a new way to fabricate luminescent RE nanomaterials and provides new ideas for the design of rationmatic lifetime imaging biosensors biosensors in the meantime.Chapter 7:Herein,AIE luminogens（AIEgens）-based Tb³⁺complex（TPE-Tb）was designed and synthesized for the first time,which can self-assemble into novel TPE-Tb nanoparticles to be used as ratiometric fluorescent probe for sensitive and rapid detection of anthrax spore biomarker in aqueous solution or actual spores.The results indicated that the limit of detection（LOD）of this ratiometric fluorescent probe was as low as 0.187 n M and 1.64×10⁴spores/m L in water solution or actual spore samples,respectively.This work explored a new method for the combination of AIEgens-based materials and RE complexes by coordination mode and provided a versatile nanoprobe candidate for anthrax biomarker detection.Chapter 8:Summary and prospect of the work of this paper.