Preparation of AIE Polymer Dots (Pdots) Based on Poly(N-vinyl-2-pyrrolidone)-Eu(III) Complex and Dual-color Live Cell Imaging
Preparation of AIE Polymer Dots (Pdots) Based on Poly(N-vinyl-2-pyrrolidone)-Eu(III) Complex and Dual-color Live Cell Imaging
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基于聚(N-乙烯基-2-吡咯烷酮)-Eu(III)络合物和双色活细胞成像的AIE聚合物点(Pdots)的制备
DOI：
10.6023/a19090349
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发表时间：
2019-12-15
影响因子：
2.5
通讯作者：
Lei Ziqiang
中科院分区：
文献类型：
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作者：
Guan Xiaolin;Li Zhifei;Lei Ziqiang
近年来，聚合物量子点（Pdots）因其优异的光学性能、多样的结构、易于表面修饰和良好的生物相容性而成为一种优良的有机荧光纳米粒子。因此，它们在生物成像、传感和检测、药物输送和治疗诊断等方面具有重要的应用潜力。然而，由于聚集引起的猝灭（ACQ）效应，具有大共轭结构的半导体Pdot的荧光猝灭限制了其在聚集态生物成像中的应用。通过在Pdot中引入聚集诱导发射（AIE）活性分子，可以消除Pdot的ACQ现象。本文以四苯乙烯（TPE）和聚（N-乙烯基-2-吡咯烷酮）-Eu（III）配合物（PVP-Eu（III））为原料，构建了一种具有蓝色荧光发射的响应型AIE活性Pdot。首先，以4，4 '-偶氮二（4-氰基戊酸）为引发剂，合成了四臂TPE衍生物引发剂（TPE-tetraAZO），并以此为引发剂成功合成了具有多刺激响应性的两亲性聚合物四苯乙烯接枝聚（N-乙烯基-2-吡咯烷酮）（TPE-tetraPVP）。最后，通过TPE-tetraPVP与稀土元素Eu（III）的配位反应，得到了具有AIE特性和双重荧光的TPE-tetraPVP-Eu（III）配合物。两亲性四臂星星聚合物TPE-tetraPVP-Eu（III）通过自组装过程形成了由疏水性AlEgens TPE核和亲水性PVP壳组成的Pdot。用透射电子显微镜（TEM）研究了Pdot的形貌和粒径。结果表明，Pdots的粒径在20 nm左右，呈规则的球形。荧光实验结果表明，TPE-tetraPVP-Eu（III）Pdot在360和395 nm激发下，分别具有中心波长为435 nm（蓝光）和615 nm（红光）的两个发射带，波长差为180 nm。其中，蓝色发光表现出典型的AIE性质。此外，TPE-tetraPVP-Eu（III）在水溶液中的低临界溶解温度（LCST）约为37 V，这接近于正常体温。在10 ~ 60 V的温度范围内，TPE-tetraPVP-Eu（III）Pdot的光致发光（PL）强度随温度的升高先降低后升高。有趣的是，Pdots的荧光响应可能是由PVP的相转移引起的。此外，Pdots在不同pH值下的荧光强度也不同，因此，TPE-tetraPVP-Eu（III）Pdots有望成为一种多功能的智能荧光传感器。细胞成像结果表明，Pdot在HeLa、HepG 2和A549细胞中具有较好的细胞摄取能力和较低的细胞毒性。并且，通过简单地调节激发波长，可以容易地在三个电池中实现光开关双发射。因此，非偶联Pdot是一种理想的双色活细胞成像探针。
In recent years, polymer dots (Pdots) have been developed as an excellent organic fluorescent nanoparticles due to its excellent optical properties, diverse structures, easy surface modification and good biocompatibility. So, they have important application potential in biological imaging, sensing and detection, drug delivery and therapeutic diagnosis. However, the fluorescence quenching of semiconducting Pdots with large conjugated structure due to aggregation-caused quenching (ACQ) effect limits its applications for bioimaging in aggregated states. The ACQ phenomenon of Pdots could been eliminated by introducing aggregation-induced emission (AIE)-active molecules in Pdots. In this paper, a kind of responsive AIE-active Pdots, which were composed of tetraphenylethylene (TPE) with blue fluorescent light emission and poly(N-vinyl-2-pyrrolidone)-Eu(III) complex (PVP-Eu(III)) with red fluorescent light emission, were constructed. Firstly, a TPE derivative initiator (TPE-tetraAZO) containing four arms was synthesized by using 4,4'-azobis-(4-cyanovaleric acid) to modify TPE, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly(N-vinyl-2-pyrrolidone) (TPE-tetraPVP) was then successfully synthesized by using TPE-tetraAZO as initiator. Finally, the complex TPE-tetraPVP-Eu(III) with AIE characteristic and dual fluorescence was obtained through the coordination between TPE-tetraPVP and rare earth element Eu(III). The amphiphilic 4-arm star polymer TPE-tetraPVP-Eu(III) formed Pdots consisted of hydrophobic AlEgens TPE core and hydrophilic PVP shell by a self-assembling process. The morphology and particle size of Pdots were investigated by transmission electron microscope (TEM). Results showed that Pdots was a relatively uniform diameter around 20 nm and exhibited regular sphere morphology. The results of fluorescence experiments showed that TPE-tetraPVP-Eu(III) Pdots had two emission bands centered at about 435 (blue) and 615 nm (red) with a wavelength difference of 180 nm, which were obtained under optimum excitation at 360 and 395 nm, respectively. Among them, the blue emission showed typical AIE property. Moreover, the lower critical solution temperature (LCST) of TPE-tetraPVP-Eu(III) in aqueous solution was about 37 V, which was close to normal body temperature. Meanwhile, at different temperatures from 10 to 60 V, photoluminescence (PL) intensities of TPE-tetraPVP-Eu(III) Pdots firstly decreased with increasing temperature from 10 to 36 V, and then increased with increasing temperature from 37 to 60 V . It was interesting that the fluorescent response of Pdots could be caused by the phase transfer of PVP. Besides, the PL intensity of Pdots in aqueous solution changed at different pH. Therefore, TPE-tetraPVP-Eu(III) Pdots might be used as multi-functional and smart fluorescent sensors. Furthermore, the results of cellular imaging indicated the efficient cellular uptake and low cytotoxicity of Pdots in HeLa, HepG2 and A549 cells. And, the photoswitchable dual-emission could be easily realized in three cells by simply tuning the excitation wavelength. Thus, the non-conjugated Pdots is an ideal dual-color live cell imaging probe.