High-Efficiency Cell-Penetrating Helical Poly(phenyl isocyanide) Chains Modified Cellular Tracer and Nanovectors with Thiol Ratiometric Fluorescence Imaging Performance

In order to precisely tail the endocytosis process and determine the internal location of drug carriers in cells, fluorescent tracers with high sensitivity and versatility are one of the most powerful tools. Nevertheless, conventional single fluorescent probes always suffered from the interference of background fluorescence or the lack of long-time monitoring capability, resulting in the low resolution and efficiency. To overcome this drawback, nanocarriers capable of multicolor fluorogenic and ratiometric properties became an urgently needed solution. In this contribution, starting from pentafluorophenyl ester (PFP)- and tetraphenylethene (TPE)-functionalized phenyl isocyanide (PI) monomers as well as L-hydrophilic (HP) PI monomers, a type of well-defined amphiphilic block copolymer, P(PFPPI-co-TPEPI-co-HPPI)-b-HPPPI, with controlled molecular weights and tunable compositions was prepared through sequential living copolymerization with phenylethynyl Pd(II) complex as a single catalyst in one pot. Disulfide bonds were then introduced by the exchange reaction between PFP units and cystamine (Cys; a degradable cross-linker). The resultant P(CysPI-co-TPEPI-co-HPPI)-b-HPPPI copolymers showed a time-dependent disruption in the conditions mimicking the intracellular reducing environment and an aggregation-caused quenching (ACQ) optical behavior that they were emissive when single chain dispersed but became nonfluorescent if the polymer chains were aggregated. Thanks to such a unique optical phenomenon, nanocarriers capable of fluorescence ratiometric property could be constructed after incorporating another solvatochromic dye, Nile red (NR), in water. This new class of core cross-linked NR@P(CysPI-co-TPEPI-co-HPPI)-b-HPPPI micelles not only exhibited excellent fluorescence ratiometric cell imaging ability but also possessed rapid cell membrane permeability due to the PEGylated single left-handed helical PPI corona and exposed the real-time disintegration of nanocarriers in front of us. Fatal and irreversible damage to cancer cells could be achieved by the high-efficiency delivery of chemotherapeutic agents. We speculate that these newly developed fluorescent integrated nanocarriers can potentially be utilized as a promising approach to cancer diagnosis and therapy.