Bright Far‐Red/Near‐Infrared Conjugated Polymer Nanoparticles for In Vivo Bioimaging

A highly emissive far‐red/near‐infrared (FR/NIR) fluorescent conjugated polymer (CP), poly[(9,9‐dihexylfluorene)‐co‐2,1,3‐benzothiadiazole‐co‐4,7‐di(thiophen‐2‐yl)‐2,1,3‐benzothiadiazole] (PFBTDBT10) is designed and synthesized via Suzuki polymerization. Formulation of PFBTDBT10 using 1,2‐distearoyl‐sn‐glycero‐3‐phosphoethanolamine‐N‐[methoxy(polyethylene glycol)‐2000] (DSPE‐PEG₂₀₀₀) and DSPE‐PEG₅₀₀₀‐folate as the encapsulation matrix yielded CP‐loaded DSPE‐PEG‐folic acid nanoparticles (CPDP‐FA NPs) with bright FR/NIR fluorescence (27% quantum yield) and a large Stoke's shift of 233 nm in aqueous solution. CPDP‐FA NPs show improved thermal/photostabilities and larger Stoke's shifts as compared to commercially available quantum dots (Qdot 655) and organic dyes such as Alexa Fluor 555 and Rhodamine 6G. In vivo studies of CPDP‐FA NPs on a hepatoma H22 tumor‐bearing mouse model reveal that they could serve as an efficient FR/NIR fluorescent probe for targeted in vivo fluorescence imaging and cancer detection in a high contrast and specific manner. Together with the negligible in vivo toxicity, CPDP‐FA NPs are promising FR/NIR fluorescent probes for future in vivo applications.     

Aptamer‐Based Multicolor Fluorescent Gold Nanoprobes for Multiplex Detection in Homogeneous Solution

The design of a novel multicolor fluorescent gold nanoprobe for homogeneous detection of small‐molecule targets is reported, which combines the specific binding abilities of aptamers with the ultrahigh quenching ability of gold nanoparticles (AuNPs). Dye‐tagged aptamers and their complementary sequence with thiol labels are co‐assembled at the surface of AuNPs. As a proof of concept, it is demonstrated that such a multicolor fluorescent gold nanoprobe can simultaneously detect adenosine, potassium ion, and cocaine with high selectivity. This potentially generic strategy is shown to be promising for rapid screening of small molecular targets.     

Theranostic Upconversion Nanobeacons for Tumor mRNA Ratiometric Fluorescence Detection and Imaging‐Monitored Drug Delivery

Remote optical detection and imaging of specific tumor‐related biomarkers and simultaneous activation of therapy according to the expression level of the biomarkers in tumor site with theranostic probes should be an effective modality for treatment of cancers. Herein, an upconversion nanobeacon (UCNPs‐MB/Dox) is proposed as a new theranostic nanoprobe to ratiometrically detect and visualize the thymidine kinase 1 (TK1) mRNA that can simultaneously trigger the Dox release to activate the chemotherapy accordingly. UCNPs‐MB/Dox is constructed with the conjugation of a TK1 mRNA‐specific molecular beacon (MB) bearing a quencher (BHQ‐1) and an alkene handle modified upconversion nanoparticle (UCNP) through click reaction and subsequently loading with a chemotherapy drug (Dox). With this nanobeacon, quantitative ratiometric upconversion detection of the target with high sensitivity and selectivity as well as the target triggered Dox release in vitro is demonstrated. The sensitive and selective ratiometric detection and imaging of TK1 mRNA under the irradiation of near infrared light (980 nm) and the mRNA‐dependent release of Dox for chemotherapy in the tumor MCF‐7 cells and A549 cells are also shown. This work provides a smart and robust platform for gene‐related tumor theranostics.     

Water‐Dispersible,pH‐Stable and Highly‐Luminescent Organic Dye Nanoparticles with Amplified Emissions for In Vitro and In Vivo Bioimaging

A new strategy is presented for using doped small‐molecule organic nanoparticles (NPs) to achieve high‐performance fluorescent probes with strong brightness, large Stokes shifts and tunable emissions for in vitro and in vivo imaging. The host organic NPs are used not only as carriers to encapsulate different doped dyes, but also as fluorescence resonance energy transfer donors to couple with the doped dyes (as acceptors) to achieve multicolor luminescence with amplified emissions (AE). The resulting optimum green emitting NPs show high brightness with quantum yield (QY) of up to 45% and AE of 12 times; and the red emitting NPs show QY of 14% and AE of 10 times. These highly‐luminescent doped NPs can be further surface modified with poly(maleic anhydride‐alt‐1‐octadecene)‐polyethylene glycol (C18PMH‐PEG), endowing them with excellent water dispersibility and robust stability in various bio‐environments covering wide pH values from 2 to 10. In this study, cytotoxicity studies and folic acid targeted cellular imaging of these multicolor probes are carried out to demonstrate their potential for in vitro imaging. On this basis, applications of the NP probes in in vivo and ex vivo imaging are also investigated. Intense fluorescent signals of the doped NPs are distinctly, selectively and spatially resolved in tumor sites with high sensitivity, due to the preferential accumulation of the NPs in tumor sites through the passive enhanced permeability and retention effect. The results clearly indicate that these doped NPs are promising fluorescent probes for biomedical applications.     

Prolonged Dye Release from Mesoporous Silica‐Based Imaging Probes Facilitates Long‐Term Optical Tracking of Cell Populations In Vivo

Nanomedicine is gaining ground worldwide in therapy and diagnostics. Novel nanoscopic imaging probes serve as imaging tools for studying dynamic biological processes in vitro and in vivo. To allow detectability in the physiological environment, the nanostructure‐based probes need to be either inherently detectable by biomedical imaging techniques, or serve as carriers for existing imaging agents. In this study, the potential of mesoporous silica nanoparticles carrying commercially available fluorochromes as self‐regenerating cell labels for long‐term cellular tracking is investigated. The particle surface is organically modified for enhanced cellular uptake, the fluorescence intensity of labeled cells is followed over time both in vitro and in vivo. The particles are not exocytosed and particles which escaped cells due to cell injury or death are degraded and no labeling of nontargeted cell populations are observed. The labeling efficiency is significantly improved as compared to that of quantum dots of similar emission wavelength. Labeled human breast cancer cells are xenotransplanted in nude mice, and the fluorescent cells can be detected in vivo for a period of 1 month. Moreover, ex vivo analysis reveals fluorescently labeled metastatic colonies in lymph node and rib, highlighting the capability of the developed probes for tracking of metastasis.     

Fluorescence Quenching Nanoprobes Dedicated to In Vivo Photoacoustic Imaging and High‐Efficient Tumor Therapy in Deep‐Seated Tissue

Photoacoustic imaging (PAI) and photoacoustic (PA) therapy have promising applications for treating tumors. It is known that the utilization of high‐absorption‐coefficient probes can selectively enhance the PAI target contrast and PA tumor therapy efficiency in deep‐seated tissue. Here, the design of a probe with the highest availability of optical‐thermo conversion by using graphene oxide (GO) and dyes via π–π stacking interactions is reported. The GO serves as a base material for loading dyes and quenching dye fluorescence via fluorescence resonance energy transfer (FRET), with the one purpose of maximum of PA efficiency. Experiments verify that the designed fluorescence quenching nanoprobes can produce stronger PA signals than the sum of the separate signals generated in the dye and the GO. Potential applications of the fluorescence quenching nanoprobes are demonstrated, dedicating to enhance PA contrast of targets in deep‐seated tissues and tumors in living mice. PA therapy efficiency both in vitro and in vivo by using the fluorescence quenching nanoprobes is found to be higher than with the commonly used PA therapy agents. Taken together, quenching dye fluorescence via FRET will provide a valid means for developing high‐efficiency PA probes. Fluorescence quenching nanoprobes are likely to become a promising candidate for deep‐seated tumor imaging and therapy.     

A Porphyrin‐Based Conjugated Polymer for Highly Efficient In Vitro and In Vivo Photothermal Therapy

Conjugated polymers have been increasingly studied for photothermal therapy (PTT) because of their merits including large absorption coefficient, facile tuning of exciton energy dissipation through nonradiative decay, and good therapeutic efficacy. The high photothermal conversion efficiency (PCE) is the key to realize efficient PTT. Herein, a donor–acceptor (D–A) structured porphyrin‐containing conjugated polymer (PorCP) is reported for efficient PTT in vitro and in vivo. The D–A structure introduces intramolecular charge transfer along the backbone, resulting in redshifted Q band, broadened absorption, and increased extinction coefficient as compared to the state‐of‐art porphyrin‐based photothermal reagent. Through nanoencapsulation, the dense packing of a large number of PorCP molecules in a single nanoparticle (NP) leads to favorable nonradiative decay, good photostability, and high extinction coefficient of 4.23 × 10⁴m ^?1 cm^?1 at 800 nm based on porphyrin molar concentration and the highest PCE of 63.8% among conjugated polymer NPs. With the aid of coloaded fluorescent conjugated polymer, the cellular uptake and distribution of the PorCP in vitro can be clearly visualized, which also shows effective photothermal tumor ablation in vitro and in vivo. This research indicates a new design route of conjugated polymer‐based photothermal therapeutic materials for potential personalized theranostic nanomedicine.     

Upconversion Luminescence Resonance Energy Transfer (LRET)‐Based Biosensor for Rapid and Ultrasensitive Detection of Avian Influenza Virus H7 Subtype

Avian influenza viruses (AIV) with good adaptation and various mutations have threatened both human and animals’ health. The H7 subtypes have the potential to cause pandemic threats to human health due to the highly pathogenic characteristics. Therefore, it is quite urgent to develop a novel biosensor for rapid and sensitive detection of H7 subtypes. In this work, a biosensor based on luminescence resonance energy transfer (LRET) from BaGdF₅:Yb/Er upconversion nanoparticles (UCNPs) to gold nanoparticles (AuNPs) has been developed for rapid and sensitive H7 subtypes detection. The amino modified capture oligonucleotide probes are covalently linked to poly(ethylenimine) (PEI) modified BaGdF₅:Yb/Er UCNPs. The thiol modified oligonucleotides with H7 hemagglutinin gene sequence are conjugated to surfaces of AuNPs. The hybridization process between complementary strands of H7 Hemagglutinin gene and its probe brings the energy donor and acceptor into close proximity, leading to the quenching of fluorescence of UCNPs. A linear response is obtained ranging from 10 pm to 10 nm and the limit of detection (LOD) is around 7 pm with detection time around 2 hours. This biosensor is expected to be a valuable diagnostic tool for rapid and sensitive detection of AIV.     

High‐Performance Upconversion Nanoprobes for Multimodal MR Imaging of Acute Ischemic Stroke

Multimodal magnetic resonance (MR) imaging, including MR angiography (MRA) and MR perfusion (MRP), plays a critical role in the diagnosis and surveillance of acute ischemic stroke. However, these techniques are hindered by the low T₁ relaxivity, short circulation time, and high leakage rate from vessels of clinical Magnevist. To address these problems, nontoxic polyethylene glycol (PEG)ylated upconversion nanoprobes (PEG‐UCNPs) are synthesized and first adopted for excellent MRA and MRP imaging, featuring high diagnostic sensitivity toward acute ischemic stroke in high‐resolution imaging. The investigations show that the agent possesses superior advantages over clinical Magnevist, such as much higher relaxivity, longer circulation time, and lower leakage rate, which guarantee much better imaging efficiency. Remarkably, an extremely small dosage (5 mg Gd kg^?1) of PEG‐UCNPs provides high‐resolution MRA imaging with the vascular system delineated much clearer than the Magnevist with clinical dosage as high as 108 mg Gd kg^?1. On the other hand, the long circulation time of PEG‐UCNPs enables the surveillance of the progression of ischemic stroke using MRA or MRP. Once translated, these PEG‐UCNPs are expected to be a promising candidate for substituting the clinical Magnevist in MRA and MRP, which will significantly lengthen the imaging time window and improve the overall diagnostic efficiency.