Preparation Of Amphiphilic Centipede-like Copolymer PASP-Na-DDA-PEG And Synthesis Of Targeted Nanoprob

Semiconductor QDs are a new class of fluorescent labeling agents and haverecently been used for a broad range of biological applications. This broad interest isdriven by their unique optical and electronic properties such as size tunable lightemission, superior signal brightness, resistance to photobleaching, and simultaneousexcitation of multiple fluorescence colors. Thus, these QDs show promise asfluorescent probes for cell labeling and tracking. However, hydrophobic QDsprepared in organic phase make them insoluble in physiological solution, which to alarge extent limits their application in bioengineering. In this paper, we synthesis anovel class of amphiphilic centipede-like copolymer PASP-Na-DDA-PEG, totransfer hydrophobic octadecylamine–coated CdSe/ZnS QDs into hydrophiphilicones via surface modification.As we all know, aspartic acid is a kind of natural amino acid. The amphiphiliccopolymer we prepare is derivated from aspartic acid. Polymer itself can degradeinto non-toxic molecules that do no harm to environment.The amphiphilic comb copolymer PASP-Na-DDA was synthesized by thermalcondensation of aspartic acid (ASP) and aminolysis by dodecylamine (DDA),followed by hydrolysis of the remaining succinimide units in the copolymerbackbone. We synthesized a series of amphiphilic comb copolymer with differentDDA grafting level. The ratio of hydrophiphilic and hydrophobic chain werecontrolled by the regants. Then we studied the effect of grafting level on micellarbehavior in water solution. CMC, hydrodynamic diameter and micellar morphologywere determined. Considering all the factors above, we supposed the optimum polymer used for QDs modification was the one with DDA grafting level of40%.Experiments demonstrated comb-shape copolymer could be used to prepare denseand small nanoparticles.As is well known, PEG is widely used in bioengineering system because it issoluble and biocompatible. So we consider to graft PEG into the comb copolymer, toprepare amphiphilic centipede-like copolymer PASP-Na-DDA-PEG. We found theproperties of QDs nanocomposites, including particle size, optical propertie andmorphology, were affected by PEG chain density of the polymer coating. ComparedHD and PL spectra of QDs nanocomposites, with different PEG grafting level from0~60%. Results indicated that when PEG grafting level was40%, QDsnanocomposites showed the smallest size (105nm), and simultaneously exhibitedsuperior fluorescent properties among all the nanocomposites. These shell/corespherical structural nanoparticles were well dispersed in water, and did not formlarge aggregates. Apparently, polymer with PEG chain density of40%was theoptimum surface coating for QDs. The optical properties of QDs before and afterencapsulation were identical. The QDs nanocomposites in aqueous solutionpresented the same peak shape of absorption as initial QDs in chloroform), whichindicated that this transfer process didn’t destroy the structure of QDs nanocrystal.Finally, we studied the high-quality QDs nanocomposites, with VEGF antibodybinding to, served as a probe for tumor cell targeting and tracking. Anti-VEGF canspecificly recognize VEGF receptor which can be overexpressed by liver cancercells. Then we used the luminescence preporty of QDs to determine the location oftumor. This could improve the precision and sensitivity of cancer detection. PEGchain in the polymer coating limited nonspecific binding of QDs-anti-VEGF andcells and permitted cell receptors to access the antibody on the particle surface withhigh efficiency. PEG could effectively reduce the toxicity of QDs-anti-VEGFnanoprobe, which was demonatrated by Cytotoxicity Test.