Preparation Of Neutral Luminescent Radical Nanoparticles And Application In Fluorescence Imaging

Fluorescence imaging technology has been attracting sustained attention given that it bears a series of advantages,such as noninvasiveness,high sensitivity,and good-spatiotemporal resolution.Over the past few dacades,a plenty of fluorescent nanoparticles,including quantum dots,metallic particles,and organic small molecules encapsulated with polymer,have thus been synthesized and studied in the past few decades.As one of the most mature materials,organic small molecules encapsulated with polymer have good biocompatibility and small size that are ideal for intracellular target labeling and have advantages of good photostability and easy surface functionalization.Compared with conventional organic dyes mentioned above,there is a kind of brand new molecule:neutral luminescent radicals which is commonly used as emitters in the application of organic light-emitting diodes(OLEDs)because of the doublet emission(D₁?D₀).Since there exists no inhibition in the transition of doublet excitons,the doublet excitons utilization rate of electroluminescence can reach 100%,which fundamentally avoid triplet excitons utilization rate.This achievement has attracted widespread attention.With its unique open shell structure,it has made lots of improvements in many field,such as sound,light,electricity,magnetism,fluorescence probe and even biological field.Although neutral luminescent radicals integrate many interesting properties,their application in fluorescence imaging has been rarely reported.Most of the neutral luminescent radicals are slightly dissolved in water and show very weak even no luminescence in polar solvents due to their charge transfer excitation properties.Even though the amphiphilic polymers are used to self-assembled during the nanoprecipitation to form nanoparticle to avoid poor solubility in water,the aggregation quenching of radicals is very serious in the aggregation state.Thus their use in fluorescence imaging are seriously hindered.In addition,with further development of fluorescence imaging,the development of new and efficient near-infrared light-emitting materials are needed desperately.Because noise signals such as autofluorescence will be generated during the fluorescence imaging of animals and their tissues in the range of visible light,the imaging results would be seriously disturbed.Based on the fact that animals and their tissues rarely produce auto-fluorescence in the near-infrared region(NIR),the NIR(700-1700 nm)is also called biologically transparent window.Centered at above problems,we carried out the following work in this paper.1.A novel derivative of tris(2,4,6-trichlorotriphenyl)methyl radical,TTM-Cz-Br(charge transfer state),was synthesized via conjugation of an electron-withdrawing TTM radical moiety and an electron-3-bromo-9H-carbazole(3-Br-Cz)group given a donor–acceptor radical(D-A·).A universal amphiphilic block copolymer,1,2-distearoyl-snglycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)(DSPE-PEG₂₀₀₀),was selected to encapsulate the hydrophobic radical and its precursor at a premium proportion to enhance biocompatibility and stability of the radical nanoparticals(NPs)as well as ensure the optical properties in large polar solvent via nanoprecipitation following the reported technique.The obtained radical NPs showed good stability under physiological conditions.The sizes of radical NPs kept high stability.The results of cell imaging experiments showed that the radical nanoparticles successfully was internalizd in the cell,distributed in the cytoplasm and emitted bright red emission.MTT methods showed that the radical NPs had low cytotoxicity and good biocompatibility.2.TTM-TPA,a triphenylmethyl radical derivative with near-infrared emission,was selected to prepare radical NPs as its core.At the same time,a certain proportion of its precursor(HTTM-TPA)was doped into the nanoparticles to avoid radical aggregation concentration quenching.We tested the photophysical properties and physiological stability of radical nanoparticles.3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)experiment showed the good biocompatibility of radical NPs.Confocal laser scanning microscope experiments show that the radical NPs can be successfully internalized into HCT116 cells and dispersed in the cytoplasm,and near infrared emission can be observed.The above experimental results prove that radical nanoparticles(TTM-TPA)with near infrared emission is expected to be used in vivo in the future,showing a greater application prospect.