Syntheses And Biological Imaging Performance Of D-A-D Type NIR-? Fluorescence Probes

As a non-invasive biological imaging modality,fluorescence imaging has several featured advantages,such as high imaging resolution and sensitivity,readily available fluorescence probes,and less expensive instruments,etc.,and has been widely used in biological imaging research.Comparing to the fluorescence imaging in the traditional near-infrared(NIR-I)optical window(750-900 nm),the imaging in the second near-infrared(NIR-II)optical window(1000-1700 nm)exhibits significantly higher spatial resolution,deeper imaging depth and lower autofluorescence,and thus have better application potentials in disease diagnosis especially tumor diagnosis and image-guided tumor excision.The imaging probes with proper emission wavelength and high quantum yield(QY)are prerequisite for high quality fluorescence imaging.When compared with the inorganic NIR-II fluorophores,such as carbon nanotubes,quantum dots,and rare-earth nanoparticles,the organic counterparts possess better biosafety,designable structures,widely tunable optical properties,and thus exhibit higher application potentials in biological imaging.So far,although many types of organic NIR-II fluorophores have been developed,it is still a big challenge to design a NIR-II fluorophore with desirable photophysical properties and useful for labeling biofunctional molecules.In view of this,we studied systematically the synthesis and properties optimization of small molecule NIR-II fluorophores in this thesis.The contents are shown briefly as follows.(1)The fluorophore bearing a single reactive group is indispensable for specifically labeling biofunctional molecules and nanomaterials.However,up to now,this type of fluorophores is still lacking.We synthesized a donor-acceptor-donor(D-A-D)type NIR-II fluorophore bearing an amino group and used it to label covalently cylindrical polymer brushes.It was demonstrated that the dense PEG side chains in the labeled brushes were greatly favorable for their QY in aqueous medium by preventing the fluorophores from?-?stacking and shielding them from the interactions with water.After injected intravenously into tumor-bearing mice,the labeled brushes provided high-resolution fluorescence imaging and showed high tumor accumulation,exhibiting great application potentials in tumor detection.(2)The fluorescence probes with high QY make it possible to attain high imaging quality under short exposure time.With this in mind,we synthesized the NIR-II organic fluorophores bearing amino,tert-butyloxycarbonyl-protected amino and phenylazo groups,respectively,and studied the group effects on their emission properties and QYs via theoretical and experimental approaches.We demonstrated that the phenylazo group could substantially enhance the QY of the NIR-II fluorophore.The QY of the NIR-II fluorophore bearing phenylazo groups is among the highest of the organic NIR-II fluorophores reported so far.For biological applications,the phenylazo-containing fluorophore was encapsulated in polystyrene-co-poly(ethylene glycol)micelles.Thanks to the high QY of the micelles,the mice injected intravenously with the micelles could be imaged clearly by the NIR-II imaging system with exposure time as short as 10 ms,which makes it possible for the micelles to be used in monitoring dynamic biological processes,such as cardiac cycle and heart rate.The fluorophore-loaded micelles accumulated significantly in tumors after tail-vein injection and exhibited great application potentials in tumor detection.(3)NIR-II fluorescence imaging has the advantages of high sensitivity and fast real-time imaging,but the imaging depth is relatively shallow.Magnetic resonance imaging(MRI)is an imaging modality without imaging depth limit and can provide the structural information of a living body,but the imaging speed is slow.Therefore,the NIR-II/MR dual-modal imaging can combine the advantages of the two imaging technologies and make up the shortcoming of the other,providing much more useful medical information.We synthesized the third generation(G3)poly(L-lysine)(PLL)dendron with defect-free chemical structure by a solid-phase synthesis strategy.Using the PLL dendron as a carrier,we conjugated a NIR-II fluorophore and three-valent gadolinium ions(Gd³⁺)chelated by DTPA to the focal and periphery of the dendron,affording the PLL dendron-based NIR-II/MRI dual modal probe.The PLL dendron endowed the probe with good biocompatibility and biodegradability,and well-defined structure.The probe exhibited outstanding imaging contrast in both fluorescence and MR imaging.Comparing to the commercial MRI contrast agent Magnevist,the dendron-based probe could significantly improve the tumor imaging contrast and prolong tumor contrast imaging duration,and thus is very promising in tumor diagnosis.