Xiaolei Cai

Bioorthogonal Turn‐On Probe Based on Aggregation‐Induced Emission Characteristics for Cancer Cell Imaging and Ablation

Bioorthogonal turn-on probes have been widely utilized in visualizing various biological processes. Most of the currently available bioorthogonal turn-on probes are blue or green emissive fluorophores with azide or tetrazine as functional groups. Herein, we present an alternative strategy of designing bioorthogonal turn-on probes based on red-emissive fluorogens with aggregation-induced emission characteristics (AIEgens). The probe is water soluble and non-fluorescent due to the dissipation of energy through free molecular motion of the AIEgen, but the fluorescence is immediately turned on upon click reaction with azide-functionalized glycans on cancer cell surface. The fluorescence turn-on is ascribed to the restriction of molecular motion of AIEgen, which populates the radiative decay channel. Moreover, the AIEgen can generate reactive oxygen species (ROS) upon visible light (λ=400-700 nm) irradiation, demonstrating its dual role as an imaging and phototherapeutic agent.

Biocompatible Green and Red Fluorescent Organic Dots with Remarkably Large Two-Photon Action Cross Sections for Targeted Cellular Imaging and Real-Time Intravital Blood Vascular Visualization.

Fluorescent organic dots are emerging as promising bioimaging reagents because of their high brightness, good photostability, excellent biocompatibility, and facile surface functionalization. Organic dots with large two-photon absorption (TPA) cross sections are highly desired for two-photon fluorescence microscopy. In this work, we report two biocompatible and photostable organic dots fabricated by encapsulating tetraphenylethene derivatives within DSPE-PEG matrix. The two organic dots show absorption maxima at 425 and 483 nm and emit green and red fluorescence at 560 and 645 nm, with high fluorescence quantum yields of 64% and 22%, respectively. Both organic dots exhibit excellent TPA property in the range of 800-960 nm, affording upon excitation at 820 nm remarkably large TPA cross sections of 1.2×10(6) and 2.5×10(6) GM on the basis of dot concentration. The bare fluorophores and their organic dots are biocompatible and have been used to stain living cells for one- and two-photon fluorescence bioimagings. The cRGD-modified organic dots can selectively target integrin αvβ3 overexpressing breast cancer cells for targeted imaging. The organic dots are also applied for real-time two-photon fluorescence in vivo visualization of the blood vasculature of mouse ear, providing the spatiotemporal information about the whole blood vascular network. These results demonstrate that the present fluorescent organic dots are promising candidates for living cell and tissue imaging.

A fluorescent light-up probe based on AIE and ESIPT processes for β-galactosidase activity detection and visualization in living cells

A novel fluorescent probe SA-βGal is reported here with light-up response to β-galactosidase. SA-βGal possesses the β-galactopyranoside group to react with β-galactosidase and releases the fluorescent salicylaldehyde azine with both aggregation induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. The linear fluorescent response enables the in vitro quantification of β-galactosidase activity in a range of 0-0.1 U mL-1 with a detection limit of 0.014 U mL-1. The probe exhibits significant advantages, such as no self-quenching at high concentrations, a large Stokes shift (190 nm) and high specificity to β-galactosidase with an excellent light-up ratio of 820 fold. Moreover, thanks to its good retention in living cells, the application of SA-βGal for the imaging of cellular β-galactosidase was also achieved with high contrast.

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 × 104 m-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.

Biocompatible Red Fluorescent Organic Nanoparticles with Tunable Size and Aggregation-Induced Emission for Evaluation of Blood–Brain Barrier Damage

Detection of damage to the blood-brain barrier (BBB) is important for the diagnosis of brain diseases and therapeutic drug evaluation. The widely used probe, Evans blue, suffers from low specificity and high toxicity in vivo. It is shown that organic nanoparticles with tuneable size, good biocompatibility, and aggregation-induced emission characteristics offer high detection specificity to detect BBB damage via a photothrombotic ischemia rat model.

Encapsulated Conjugated Oligomer Nanoparticles for Real-Time Photoacoustic Sentinel Lymph Node Imaging and Targeted Photothermal Therapy.

Noninvasive and nonionizing imaging of sentinel lymph nodes (SLN) is highly desirable for the detection of breast cancer metastasis through sentinel lymph node biopsy. Photoacoustic (PA) imaging is an emerging imaging technique that can serve as a suitable approach for SLN imaging. Herein, novel conjugated oligomer based nanoparticles (NPs) with strong NIR absorption, good biocompatibility, excellent PA contrast, and good photothermal conversion efficiency are reported. Real-time PA imaging of SLN reveals high resolution of the NPs via injection from the left forepaw pad. In addition, the surface functionalized NPs can target breast cancer cells and kill them efficiently and specifically through photothermal therapy upon 808 nm laser irradiation. This work shows great potential of the nanoparticle PA contrast agent to serve as a multifunctional probe for photothermal therapy at SLNs to achieve the inhibition of cancer cell metastasis in the near future.

Real-Time Specific Light-Up Sensing of Transferrin Receptor: Image-Guided Photodynamic Ablation of Cancer Cells through Controlled Cytomembrane Disintegration

Transferrin receptor (TfR) represents a unique target for specific imaging of cancer cells and targeted delivery of therapeutic reagents. Detection and qualification of TfR is thus of great importance for cancer diagnosis and therapy. In this contribution, a light-up probe TPETH-2T7 was developed by conjugating a red-emissive photosensitizer with aggregation-induced emission (AIE) characteristics to a TfR-targeting peptide T7. The probe is almost nonemissive by itself, but it gives turn-on fluorescence in the presence of TfR with a detection limit of 0.45 μg/mL. Cellular experiments show that the probe specifically binds to TfR-overexpressed cancer cells. Real-time imaging results reveal that the probe stains the MDA-MB-231 cell membrane in 30 min, which is followed by probe internalization. Experiments on image-guided photodynamic cancer ablation show that the therapeutic performance is better when TPETH-2T7 is localized on the cell membrane as compared to that being internalized into cells. Confocal laser scanning microscopy (CLSM) study reveals that cytomembrane disintegration allows quick ablation of MDA-MB-231 cells.

Organic molecules with propeller structures for efficient photoacoustic imaging and photothermal ablation of cancer cells

Photoacoustic (PA) imaging has recently attracted great attention due to its noninvasive and nonionizing properties and high penetration depth. This technique is particularly attractive for sentinel lymph node (SLN) imaging, which is highly desirable during sentinel lymph node biopsy for the detection of breast cancer metastasis. In this work, we report the design and synthesis of BTPETTQ with a propeller structure and a donor–acceptor–donor configuration, which exhibits strong NIR absorption, extremely weak fluorescence and a high PA signal in solution as molecular species. After being encapsulated into a polymeric matrix, BTPETTQ nanoparticles (NPs) also show excellent PA signal output, which is superior to the widely used gold nanorods based on the same mass and is also better than that from the NPs based on the core molecule of TTQ without tetraphenylethene modification. High-resolution PA imaging of SLN is achieved after injection of BTPETTQ NPs into the left paw of rats. The good photothermal conversion efficiency (40%) of BTPETTQ NPs also ensures their good performance in photothermal therapy, which is validated by the effective killing of HeLa cells upon 808 nm laser irradiation. This work demonstrates the great potential of compounds with propeller structures for PA imaging and photothermal therapy applications.

A reusable and naked-eye molecular probe with aggregation-induced emission (AIE) characteristics for hydrazine detection

We report a fluorogenic probe for naked-eye sensing of hydrazine in solution and in the gaseous phase. The probe based on tetraphenylethylene (TPE) with aggregation-induced emission (AIE) characteristics shows OFF-ON fluorescence as observed by thin-layer chromatography (TLC) upon treatment with hydrazine. Specifically, the fluorescence of the probe was quenched due to the attached N[double bond, length as m-dash]N group, which can be reduced to -NH-NH- in the presence of hydrazine to turn on the fluorescence. The reduced intermediate can be easily oxidized in air to regenerate the original probe for recyclable usage. Both fluorometric and colorimetric readings were achieved by TLC with high sensitivity and excellent selectivity. This study thus represents a simple example of a reusable and naked-eye molecular probe for monitoring environmental hazards. Finally, the probe has also been applied to detect hydrazine in live cells.

Organic Nanoparticles with Aggregation-Induced Emission for Bone Marrow Stromal Cell Tracking in a Rat PTI Model.

Stem-cell based therapy is an emerging therapeutic approach for ischemic stroke treatment. Bone marrow stromal cells (BMSCs) are in common use as a cell source for stem cell therapy and show promising therapeutic outcomes for stroke treatment. One challenge is to develop a reliable tracking strategy to monitor the fate of BMSCs and assess their therapeutic effects in order to improve the success rate of such treatment. Herein, TPEEP, a fluorogen with aggregation-induced emission characteristics and near-infrared emission are designed and synthesized and further fabricated into organic nanoparticles (NPs). The obtained NPs show high fluorescence quantum yield, low cytotoxicity with good physical and photostability, which display excellent tracking performance of BMSCs in vitro and in vivo. Using a rat photothrombotic ischemia model as an example, the NP-labeled BMSCs are able to migrate to the stroke lesion site to yield bright red fluorescence. Immunofluorescence staining shows that the NP labeling does not affect the normal function of BMSCs, proving their good biocompatibility in vivo. These merits make TPEEP NP a potential cell tracker to evaluate the fate of BMSCs in cell therapy.