The Preparation Of Fluorescent Probes Based On Mesoporous Silica-Coated Conjugated Polymers For In Vivo NIR-Ⅱ Imaging

Compared with conventional imaging techniques in both the visible region(400-700 nm)and first near infrared window(NIR-I,700-900 nm),bio-imaging in the second near-infrared window(NIR-Ⅱ,1000-1700 nm)has been expanded in recent years,which can further reduced scattering,absorption and tissue autofluorescence,thus providing higher spatial resolution and deeper tissue penetration depth.All these features allow NIR-Ⅱ biological imaging a very promising technique in the diagnosis and treatment of diseases.At present,NIR-Ⅱ fluorescent agents can be divided into peak emission materials and off-peak emission materials,peak emission materials refer to materials with emission peaks located in the NIR-Ⅱ region,and off-peak emission materials refer to emission peaks and are not located at NIR-Ⅱ area,but there is a high intensity fluorescent tailing in this area.As a very important class of developed NIR-II fluorescers,conjugated polymers have a series of advantages such as high fluorescence intensity,long luminescence time,structural diversity and good photochemical stability.However,its inherent hydrophobic properties,as well as the low fluorescence intensity in water,have greatly limited its clinical use.In this paper,in order to solve these problems,a core/shell structure of mesoporous silica-coated conjugated polymer nanoparticles were designed and synthesized,and their ability to deliver drugs and in vivo fluorescence imaging in the second near-infrared window were further studied.In addition,the NIR-Ⅱ fluorescence properties of conjugated polymer Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]dithiophene)-alt-4,7(2,1,3-benzothiadia zole)](PCPDTBT)with NIR-Ⅱ emission tails were also investigated.The specific research content of this paper is mainly divided into the following two aspects:(1)Preparation and NIR-Ⅱ fluorescence imaging of/chemotherapy integrated therapeutic agent:A one-pot method was presented for the preparation of CP@mSiO2-PEG nanoparticles consist of a NIR-Ⅱ conjugated polymer core(PDFT),a mesoporous silica(mSiO2)interlayer,and an outermost layer formed by PEG chains.The highly grafted PEG chain not only provides good water solubility to the nanoparticle,but also enables efficient passive targeting to solid tumors.CP@mSiO2-PEG has a uniform spherical structure with uniform pores distributed on the surface and good monodispersity.The average particle diameter of the nanoparticles is about 30-40 nm,and the size of the nanoparticles can be appropriately adjusted by changing the amount of the polymer added.The fluorescence spectra of CP@mSiO2-PEG aqueous solution shows an emission peak around 1022 nm under 808 nm laser excitation.Compared with the DSPE-PEG coating method,it was proved that the silylation modification can improve the fluorescence emission intensity of the nanoparticles in aqueous solution.The BET specific surface area of the nanoparticles was 503.97 m2/g and the average pore width(4V/A)of BJH adsorption was 2.49 nm.Through in vitro drug loading and release test,the results show that the nanoparticles have a high drug loading capacity(10%)and can achieve pH response release.Moreover,the ability of nanoparticle drug delivery was demonstrated at the cellular level by MTT and confocal experiments.In vivo NIR-Ⅱ fluorescence imaging experiments show that CP@mSiO2-PEG can achieve high-contrast fluorescence imaging of mouse blood vessels and tumors,clearly showing blood vessels as small as 0.21 mm in diameter,and the tumor site has a high signal-to-noise ratio(maximum Up to 4.14±0.1),it is possible to clearly distinguish tumor tissue from normal tissue(2)The conjugated polymer PCPDTBT has a strong NIR-Ⅱ emission tail.In order to study the fluorescence properties of PCPDTBT in the NIR-Ⅱ region,the CP@mSiO2-PEG nanoparticles with polymer PCPDTBT as the core were synthesized by the above silanization modification method The nanoparticles are similar in morphology to the nanoparticles prepared in the previous subject,and the particle size is also distributed between 30-40 nm.The nanoparticles have two emission peaks in the near-infrared region measured by fluorescence spectroscopy,and the emission peak at 917 nm has a long emission tails reaching past 1400 nm.Compared to the NIR-I dye ICG with NIR-II fluorescent tailing,the CP@mSiO2-PEG nanoparticles with the polymer PCPDTBT as the core have better NIR-Ⅱ luminescence properties with a quantum yield of up to 4.1%,and higher photo-stability.It is obtained that the NIR-Ⅱ imaging is significantly better than the NIR-Ⅰ imaging by comparing the in vivo imaging of nanoparticles in the NIR-Ⅰ and NIR-Ⅱ regions of the tumor model.NIR-Ⅱ imaging clearly shows a significant number of vessel veins,and also clearly show the contour and size of the tumor,and the boundary is clear,but for NIR-Ⅰ imaging,the tumor edge is blurred.These phenomena demonstrate the ability and superiority of the nanoparticles to image in the second near-infrared window,which means that the nanoparticles is a powerful substitute for NIR-Ⅱ fluorescent agents,and has broad prospects in guiding surgical resection,early diagnosis of tumors and in vivo long-term monitoring of tumors.