Andong Shao

Far‐Red and Near‐IR AIE‐Active Fluorescent Organic Nanoprobes with Enhanced Tumor‐Targeting Efficacy: Shape‐Specific Effects

The rational design of high-performance fluorescent materials for cancer targeting in vivo is still challenging. A unique molecular design strategy is presented that involves tailoring aggregation-induced emission (AIE)-active organic molecules to realize preferable far-red and NIR fluorescence, well-controlled morphology (from rod-like to spherical), and also tumor-targeted bioimaging. The shape-tailored organic quinoline-malononitrile (QM) nanoprobes are biocompatible and highly desirable for cell-tracking applications. Impressively, the spherical shape of QM-5 nanoaggregates exhibits excellent tumor-targeted bioimaging performance after intravenously injection into mice, but not the rod-like aggregates of QM-2.

Insight into aggregation-induced emission characteristics of red-emissive quinoline-malononitrile by cell tracking and real-time trypsin detection

Water-soluble, long wavelength fluorescent aggregation-induced emission (AIE)-active materials are in great demand for high contrast biosensing and bioimaging. The substitution position effects of the sulfonate group on the basis of two quinoline-malononitrile (QM) derivatives (EDS and EDPS) provide insight into efficient modulation in the hydrophilicity, emitting color, and specific AIE characteristics. EDS shows a unique AIE behaviour in aqueous solution, but EDPS does not. The abnormal non-fluorescence aggregation for EDS in pure water is capsule-like with loose packing characteristics, but still has enough cavities or free volume to consume the radiative energy, resulting in nearly no fluorescence. When binding with the protein BSA, the sulfonate unit as a conformation function group (CFG) plays a vital role in altering its initial loose ensemble into tightly compact aggregation with light-up AIE characteristics. By cell tracking, dynamic light scattering (DLS) and transmission electron microscopy (TEM), the key role of sulfonate groups in the conformation alteration has been well demonstrated for the first time. Moreover, EDS is successfully exploited in a label-free real time AIE fluorescent assay for trypsin detection and inhibitor screening. The hydrophilic sulfonate group from the different substitution position in the AIE-active QM building blocks provides an effective way to tailor the intermolecular aggregation associated with molecular stacking, especially for in situ cell tracking and real-time trypsin detection.

Morphology‐Tailoring of a Red AIEgen from Microsized Rods to Nanospheres for Tumor‐Targeted Bioimaging

Efficient morphology modulation of a red AIEgen from pristine microsized rods to nanospheres is achieved via encapsula ting QM-2 (quinolinemalononitrile-2) into hybrid micelles. This novel reagent shows great potential in tumor-targeted bioimaging because of its monodispersion in aqueous systems, the uniform diameter of ≈30 nm, enhanced fluorescence brightness with a large Stokes shift of 190 nm, and strongly increased biocompatibility and photostability.

Long wavelength AIEgen of quinoline-malononitrile

The development of novel building blocks as long wavelength aggregation-induced emission (AIE)-active fluorophores/chromophores is in high demand for high performance luminescent and optical bioimaging agents. In this Highlight, we summarize some recent advances in the area of red to near-infrared (NIR) fluorescent AIE-active organic materials derived from our established building block of quinoline-malononitrile (QM), focusing on the AIE mechanism, water-soluble and shape-specific effects, use as hybridized dye-doped prodrug, as well as the facile scale-up and fast preparation for AIE-active nanoparticles through flash nanoprecipitation.

A novel colorimetric and ratiometric NIR fluorescent sensor for glutathione based on dicyanomethylene-4 H -pyran in living cells

Glutathione (GSH) plays a critical role in maintaining oxidation-reduction homeostasis in biological systems. Considering the detection of GSH by fluorescence sensors is limited by either the short wavelength emission or the poor photostability, a highly stable colorimetric and ratiometric NIR fluorescent sensor (DCM-S) for GSH detection has been constructed on the basis of dicyanomethylene-4H-pyran (DCM) chromophore. The specific disulfide bond is incorporated via a carbamate linker as the GSH responsive group, which simultaneously blue-shifts and quenches the fluorescence. Upon addition of GSH, DCM-S exhibits outstanding colorimetric (from yellow to red) and ratiometric fluorescent response with the 6-fold enhancement of NIR fluorescence at 665 nm in quantum yield. More importantly, the GSH-treated DCM-S (DCM-NH2 actually) possesses 20-fold longer fluorescence half-life period as well as much better photostability than the FDA-approved ICG. Finally, the ratiometric detection of GSH is also successfully operated in the living cell imaging, exhibiting NIR fluorescence and large Stokes shift (215 nm) with nearly no background fluorescence interference. As a consequence, DCM-S can be utilized as colorimetric and ratiometric NIR fluorescent sensor for GSH, with a great potential in the development of GSH-induced drug delivery system.

Fabrication of mesoporous silica nanoparticles hybridised with fluorescent AIE-active quinoline-malononitrile for drug delivery and bioimaging

A novel type of fluorescent mesoporous silica nanoparticle (FMSN) has been successfully synthesised by hybridising mesoporous silica nanospheres with an aggregation-induced emission luminogen, a quinoline-malononitrile derivative. The FMSNs with uniform morphology show excellent AIE-active luminescence and good biocompatibility. Transmission electron microscopy (TEM) demonstrates that the well-ordered mesoporous structure in FMSNs is beneficial for drug delivery. When loaded with doxorubicin (DOX), DOX@FMSNs demonstrate pH-dependent release character and high cytotoxicity towards MCF-7 cancer cells. These FMSNs are expected to be promising multifunctional candidates as both bioimaging agents and drug carriers in cancer therapy.

cNGR-based synergistic-targeted NIR fluorescent probe for tracing and bioimaging of pancreatic ductal adenocarcinoma

Identification of fluorescent biomarkers with peptide ligand-directed receptors for diagnosis or theranostic of pancreatic ductal adenocarcinoma (PDAC) is still challenging. As potential prognostic/predictive bioimaging targets, both aminopeptidase N (APN, known as CD13) and Caveolin-1 are found as upregulation on the cell membrane surface of PDAC, in which APN is the principal receptor of the cyclic peptide cNGR (Asn-Gly-Arg, NGR) and Caveolin-1 can synergistically mediate endocytosis in this receptor-targeted process. Herein, we conjugate cNGR to dicyanomethylene-4H-pyran (DCM) chromophore to develop a synergistic-targeted near-infrared (NIR) fluorescent probe DCM-cNGR with strongly intrinsic NIR fluorescence, stable optical performance, low cytotoxicity, and rapid accumulation in PANC-1 cells with the synergistic overexpressed APN receptor-targeted and Caveolin-1-mediated endocytosis. As demonstrated, DCM-cNGR can realize noninvasive NIR imaging for targeting PANC-1 tumor in vivo after intravenous injection into PANC-1 xenograft tumor of nude mice, making a great promise to improve the precision diagnosis and therapy of pancreatic cancer with real time tracing and bioimaging of PDAC in vitro and in vivo.

Peptide Receptor-Targeted Fluorescent Probe: Visualization and Discrimination between Chronic and Acute Ulcerative Colitis

The inflammatory activity of ulcerative colitis plays an important role in the medical treatment. However, accurate and real-time monitoring of the colitis activity with noninvasive bioimaging method is still challenging, especially in distinguishing between chronic and acute colitis. As a good receptor, the oligopeptide transporter (PepT1) is overexpressed in the colonic epithelial cells of chronic ulcerative colitis, which can deliver tripeptide KPV (Lys-Pro-Val, the C-terminal sequence of α-MSH) into cytosol in the intestine. Herein, we report a PepT1 peptide receptor-targeted fluorescent probe, dicyanomethylene-4H-pyran (DCM)-KPV, with the strategy of conjugating the KPV into the DCM chromophore. The diagnostic fluorescent probe bestows a specific receptor-targeted interaction with PepT1 through the KPV moiety, possessing several beneficial characteristics, such as efficient long emission, low photobleaching, negligible cytotoxicity, and high cytocompatibility in living cells. We build the overexpressed PepT1 on the cytomembrane of ulcerative colitis model Caco-2 cell as the efficient receptor to accumulate the targeted tripeptide KPV in the cytoplasm and nucleus. With the co-localization of DCM-KPV and the DNA-specific fluorophore, DAPI, the specifically long emission from chromophore DCM and efficient receptor-targeted peptide KPV, the fluorescent probe of DCM-KPV makes a breakthrough to the direct noninvasive observation of the accumulation in colon inflammation regions via intestinal mucosa, even successfully distinguishing the chronic, acute ulcerative colitis and normal groups. Compared with the traditional unenhanced magnetic resonance imaging and hematoxylin and eosin (H&E) staining, we make full use of exploiting the specific target-receptor interaction between the tripeptide unit, KPV, and the oligopeptide transporter, PepT1, for sensing selectivity. The desirable diagnostic ability of DCM-KPV can guarantee the real-time tracking and visualization of the role of intracellular KPV on ulcerative colitis, which provides an alternative to replace the time-consuming and tissue sampling-invasive H&E staining diagnosis.

CHAPTER 5:Bioimaging Nanomaterials Based on Near Infrared Organic Dyes

Organic fluorescent dyes active in the near infrared (NIR) region have attracted ongoing attention because of their diverse applications in biomedicine, materials, and related fields. The advantages include minimal interfering absorption and fluorescence from biological samples, inexpensive laser diode excitation, reduced scattering, and enhanced tissue penetration depth. Great efforts have been made in the design, synthesis, and application of organic NIR fluorophores. So far, several classes of NIR dyes, including bay-substituted perylene or naphthalene bisimides, cyanine dyes, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives, 1,4-diketo-3,6-diphenylpyrrole[3,4-c]pyrrole (DPP) derivatives, and porphyrin analogues, have been developed and intensively researched. However, most organic NIR fluorophores, which commonly have a large conjugation system, suffer from low stability. Although structural modification of existing fluorophores could enhance stability to some extent, attention has increasingly been focused on the fabrication of NIR dye-based nanomaterials with better stability and performance than free dyes. Various kinds of nanoparticles based on different substrates that encapsulate or dope NIR dyes (and therapeutic agents), some of which are surface modified by functional groups, have been derived for biological application. Moreover, fluorophores with very bright fluorescence in the aggregated form, also known as aggregation-induced emission (AIE) derivatives, have recently become a brand new research field. AIE derivatives with NIR fluorescence have exhibited excellent performance in in vivo bioimaging. This chapter focuses on recent progress in this area, including major NIR organic chromophores, luminescent principles, and construction methods, as well as applications in biomedicine and challenges.