Conjugated Polymer-based NIR-Ⅱ Fluorescence/photothermal Diagnostic Agent In Tumor Bioimaging And Therapy Applications

The second near-infrared fluorescence imaging(NIR-Ⅱ,1000-1700 nm)has aroused great interests of researchers due to its advantages of high penetration depth,low background noise and strong contrast,greatly improving the quality of fluorescence imaging.NIR-Ⅱ fluorescent probes with NIR absorption properties can be acted as an integrated diagnosis and treatment nano-platform that integrates NIR-Ⅱ fluorescence imaging and photothermal therapy(PTT).PTT,converting light energy from thermal materials into heat,is a non-invasive strategy for ablation of tumors.However,the poor solubility and the obvious aggregation-induced quenching(ACQ)effect of NIR-Ⅱ fluorescent probes lead to low NIR-Ⅱ fluorescence signal,which limits its further application in imaging.In this paper,a conjugated polymer(TTQ-2TC)with simple preparation and excellent solubility was synthesized for NIR-Ⅱ fluorescence imaging-guided NIR-Ⅱ PTT.In addition,the absorption and emission properties of conjugated polymers are adjusted by adopting the strategy of adjusting the electron withdrawing density and the flexible side chains of alkyl groups.And then NIRII fluorescence probe(TTQ-2TC-4T)with superior photophysical performances was selected for NIR-Ⅱ fluorescence imaging.Finally,NIR-Ⅱ fluorescent molecules based on different receptors and conjugated polymers with absorption in NIR-Ⅱ were assembled by nanoprecipitation method,and the molecular pairs(TTQ-W and IGT-DPP molecule pair)were chosen as an activatable probe.The specific contents of this paper are as follows:(1)Conjugated polymer(TTQ-2TC)with superior solubility for NIR-Ⅱ fluorescence imaging guided NIR-Ⅱ PTT: In this chapter,6,7-bis(4-(hexyloxy)phenyl)-4,9-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline(TTQ)as electron acceptor and dithiophene(2TC)as an electron donor synthesized the conjugated polymer(TTQ-2TC).The introduction of 2TC greatly improved the solubility of TTQ-2TC in organic solvents.After that,water-soluble nanoparticles(TTQ-2TC NPs)were prepared using nanoprecipitation method.TTQ-2TC NPs have good dispersibility in water,excellent biocompatibility,and superior light stability.In addition,the photothermal conversion efficiency of TTQ-2TC NPs reached to 34.9% by in vitro photothermal experiment with the 1064 nm laser irradiation and exhibited superior PTT effect.The signal-to-background ratio(SBR)of blood vessels of the brain and hind limbs,measured by the NIR-Ⅱ fluorescence imaging of blood vessels under the 808 nm laser irradiation,was calculated to be 8 and 9,respectively,which suggested that TTQ-2TC NPs exhibited high-resolution fluorescence imaging capabilities.Finally,through the in vivo NIR-Ⅱ fluorescence imaging of tumors,it was found that the fluorescence intensity of tumor sites reached the maximum at 12 h post injection,and TTQ-2TC NPs realized the NIR-Ⅱ fluorescence imaging-guided NIR-Ⅱ PTT.(2)The strategy of adjusting acceptor densities to enhance fluorescence emission of conjugated polymer and the NIR-Ⅱ fluorescence imaging application.First,a series of D-A type conjugated polymers(TTQ-n T,n = 1,2,3,and 4)based on acceptor TTQ were prepared by introducing thiophene(T)donor with different lengths through the Stille polymerization.Secondly,thiophene with a long alkyl chain was introduced to prepare a series of novel conjugated polymers(TTQ-2TC-n T,n = 1,2,3,and 4)with the superior absorption ability at 1064 nm.Finally,TTQ-2TC-4T with excellent photophysical behaviors was selected for the NIR-Ⅱ fluorescence imaging.In order to further explore the in vivo imaging effect of TTQ-2TC-4T,it was coated with an amphiphilic polymer(Pluronic F-127)to prepare nanoparticles(TTQ-2TC-4T NPs),which displayed good dispersibility in water and excellent biocompatibility.The absorption and fluorescence emission peak of TTQ-2TC-4T NPs are located at 855 and 1059 nm,respectively.And its penetration depth reached to 6 mm.Finally,the high-resolution vascular imaging photos of the head,abdomen,and hind limbs can be obtained,and their corresponding SBR is 3.4,4.5,and 4.8,respectively.In summary,TTQ-2TC-4T NPs have potential application prospects for the high-resolution NIR-Ⅱ fluorescence imaging in vivo.(3)The preliminary study of the activated NIR-Ⅱ fluorescence organic probe: the conjugated polymer with the NIR-Ⅱ absorption(TTQ-4T,IGT-DPP),acting as a quencher,quenched the fluorescence of NIR-Ⅱ fluorescent molecules(TTQ-W,TTDT-W,and TT-4T)to prepare the activated NIR-Ⅱ fluorescent probes.Firstly,NIR-Ⅱ molecules with different receptors and conjugated polymers with NIR-Ⅱ absorption were coated via F-127 to obtain the water-soluble nanoparticles,and the nanoparticles obtained by F-127 separately encapsulating different fluorescent molecules acted as the control groups.Finally,through the quantitative analysis of fluorescence spectrum(PL),the molecular pairs(TTQ-W and IGT-DPP molecular pairs)can better produce the FERT effect,and its quenching multiple was up to 4.58.More importantly,the activated probe can also achieve the NIRII photothermal effect under 1064 nm laser irradiation,which is expected to be used for NIR-Ⅱ PTT of tumors.