Study On NIR-Ⅱ Fluorescence Imaging And Photothermal Therapy Of Squarayl Conjugated Polymer

Compared with the traditional near-infrared fluorescence imaging(600-900 nm),the second near-infrared fluorescence imaging(1000-1700 nm)has the advantages of small light scattering and weak biological autofluorescence,which can obtain high signal-to-noise ratio imaging in deeper biological tissues.In addition,NIR-Ⅱ fluorescence imaging has a micron-level high resolution(20 microns),which can achieve accurate diagnosis at the lesion site.Therefore,exploring of NIR-Ⅱ materials has attracted widespread attention in the imaging of tumors and other diseases.To present,NIR-Ⅱ fluorescent materials are mainly nanoparticles coated by co-precipitation method,and water-soluble NIR-Ⅱ still needs more development.In this paper,a new type of squaraine molecule with emission wavelength in the near-infrared region was synthesized and co-precipitated with an amphiphilic block copolymer to obtain squaraine nanoparticles with good biocompatibility.Furthermore,we introduced azide into the squaraine molecule,and connected the water-soluble oligomer(POEGMA)to the squaraine molecule through a click chemistry reaction.As a result,a new type of water-soluble squaric acid nanoparticles(SQ-POEGMA)with low toxicity and excellent photothermal effect in the organism was prepared.The specific research content is as follows:(1)Preparation of squaric acid nanoparticles: Squaric acid small molecule(SQ1)with absorption and emission in near infrared region was synthesized by condensation of 2,7-bis [2-(1-methylpyrrole)vinyl]-9,9 ’-dibromohexylfluorene as electron donor and squaric acid as electron acceptor.The reaction feed ratio is 2.1:1.Subsequently,it was co-precipitated with the amphiphilic block copolymer F-127 to prepare squaraine nanoparticles(SQ NP)dispersed in water,with the maximum emission peak at 1064 nm.Experiments show that SQ NP not only has good photophysical properties,photostability and biocompatibility,but also has good photothermal properties,with a photothermal conversion efficiency of 38%,and has potential applications in photothermal therapy.(2)Preparation of water-soluble squaric acid NIR-Ⅱ diagnostic and therapeutic agent:The introduction of azide on the basis of small molecules of squaraine,and the use of click chemistry to link oligomers(POEGMA)to obtain near-infrared two-region fluorescent materials(SQ-POEGMA)with side chains modified with water-soluble polymers.The tissue penetration depth of SQ-POEGMA reaches 4 mm,which effectively realizes the NIR-Ⅱ fluorescence imaging of tumor-bearing mice.SQ-POEGMA has a good photothermal effect,with a photothermal conversion efficiency of 33%,so it is used for photothermal treatment of tumors.The results showed that SQ-POEGMA can accumulate well in the tumor site,and the long-term tumor suppression effect can be achieved through photothermal treatment.In addition,SQ-POEGMA has low biological toxicity in the organism,and is an excellent photothermal treatment agent.