Preparation Of Squaraine Nanoparticles For Optical Imaging Photothermal Therapy

Fluorescent imaging in the second near-infrared window（NIR-II,1000-1700 nm）is a novel imaging technology in recent years,which allows precise diagnosis in deep tissue penetration and a high signal-to-background ratio due to its intrinsic advantages of minimal tissues light scattering and negligible autofluorescence.However,most of the organic NIR-II molecules are inherently hydrophobic,leading to unavoidable molecular aggregation and severe fluorescence quenching when loaded into hydrophilic polymer matrices,which further limit their application in clinical usage.Besides,current available photoacoustic imaging（PAI）guided photothermal therapy（PTT）theranostic nanoagents can not achieve the best effect due to the poor active-target,immensely decreasing the photoacoustic-photothermal anti-cancer effect.In this paper,a squaraine small molecules was synthesized.In view of the above problems,we first control the aggregation state of squaraine to improve the NIR-II fluorescence intensity of squaraine nanoparticles.Secondly,we introduced functional sugar polymer to amphiphilic copolymer to enhanced the active-target ability of squaraine nanoparticels in vivo,realizing high efficient photoacoustic imaging and photothermal therapy to MCF-7 tumor.The specific contents of this paper are as follows:（1）Preparation of squaraine nanoparticles,and how the aggregation state（J-or H-）effect the NIR-II fluorescence intensity and the imaging quality:First,condensation of squaric acid（electron acceptor）with two equivalents of bispyrrole（electron donor）afforded the target SQP.The normalized UV-vis-NIR absorption spectra and fluorescence spectra of SQP displayed a strong absorption and emission,the absorption band was at 766 nm with a high mass extinction coefficient of 126 L/（g·cm）,suggesting the admirable photophysical properties of SQP.Then,an amphiphilic copolymer（PEG-b-PPG-b-PEG,F-127）was introduced to prepare water-soluble SQP nanoparticles by a co-precipitation method.By changing the self-assembly process,we prepared two kind of squarine nanoparticles,one is J-aggregate nanoparticles SQP-NPs_（J）and the other one is H-aggregate nanoparticles SQP-NPs_（H）.The NIR-II emission intensity of the SQP-NPs_（J）was 4.8-fold higher than that of the SQP-NPs_（H）at the same concentration.After applying the two NPs in in vitro and in vivo NIR-II fluorescence imaging,the brighter signal on MCF-7 cells and the sharper image quality of healthy mice proved the superiority of the SQP-NPs_（J）.Last,a MCF-7 tumor bearing mouse was treated with SQP-NPs_（J）,proving SQP-NPs_（J）successfully accumulated into tumor and identified the blood vessels of the tumor with respect to the surrounding background tissue.（2）Fructose polymer coated squaraine nanoparticles for breast tumor targeted photoacoustic imaging&photothermal therapy:Atom transfer radical polymerization was used to prepared amphiphilic fructose copolymer Poly（3-O-MAFru）-b-PPG-b-Poly（3-O-MAFru）（hereinafter referred to as PPG-2Pfru）.Calculating form ¹H-NMR and GPC,one fructose polymer has 28 repeating fructose monomer at each side of PPG.After self-assembly process of SQP and fructose polymer in water,the SQP-PFRU-NPs was obtained with high density of fructose on the surface of NPs.The fructose not only brings perfect water solubility and biocompatibility to nanoparticles,but also leads to specific targeting ability to triple-negative breast tumor.SQP-PFRU-NPs have good stability and great near infrared absorption ability（the absorption range from 600 nm to 950 nm）.With the irradiation of 810 nm laser,SQP-PFRU-NPs simultaneously realize photoacoustic signal and photothermal effect,and its photothermal conversion efficiency is 36%.Above all,by setting up the control trial,fructose polymer coated squaraine nanoparticles have proven to enhance the accumulation of NPs into MCF-7cells and tumor and can greatly strengthen the effect of photoacoustic&photothermal theranostic to MCF-7 cells and tumor.