Cooperative Blinking from Dye Ensemble Activated by Energy Transfer for Super-resolution Cellular Imaging

Multicolor Photoacoustic Volumetric Imaging of Subcellular Structures

Photoacoustic imaging (PAI) has been widely used in multiscale and multicontrast imaging of biological structures and functions. Optical resolution photoacoustic microscopy (OR-PAM), an emerging submodality of PAI, features high lateral resolution and rich optical contrast, indicating great potential in visualizing cellular and subcellular structures. However, three-dimensional (3D) imaging of subcellular structures using OR-PAM has remained a challenge due to the limited axial resolution. In this study, we propose a multicolor 3D photoacoustic microscopy with high lateral/axial resolutions of 0.42/2 and 0.5/2.5 μm at 532 and 780 nm excitation, respectively. Owing to the significantly increased axial resolution, we could visualize the volumetric subcellular structures of melanoma cells using intrinsic contrast. In addition, we carried out multicolor imaging of labeled microtubules/clathrin-coated pits (CCP) and microtubules/mitochondria, respectively, with one scanning by using two different excitation wavelengths. The internal connections between different subcellular structures are revealed by quantitatively comparing the spatial distributions of microtubules/CCP and microtubules/mitochondria in a single cell. Current results suggest that the proposed OR-PAM may serve as an efficient tool for subcellular and cytophysiological studies.

Recent Advances in the Development and Applications of Conjugated Polymer dots

Conjugated polymer dots or semiconducting polymer nanoparticles (Pdots) are nanoparticles prepared based on organic polymers. Pdots have the advantages of lower cost, simple preparation process, good biocompatibility, excellent stability, easy...

A pH-Responsive Nanoplatform Based on Fluorescent Conjugated Polymer Dots for Imaging-Guided Multitherapeutics Delivery and Combination Cancer Therapy

For cancer treatment, nanocarriers were designed with cationic lipids and polymers to improve the cytosolic delivery efficiency of siRNA. Though the positively charged nanocarriers showed great potential for RNA therapy, it was inevitable to generate the potential cytotoxicity. We constructed a pH-responsive nanoplatform, which co-carried siRNA and anticancer drug (hydroxycamptothecine, HCPT), to integrate gene therapy and chemotherapy for combination cancer therapy. The fluorescent conjugated polymer nanoparticles (CPNPs) modified with cell-penetrating peptides were employed as cores to carry siRNA molecules (siRNA-CPNPs) and track the biodistribution of nanotherapeutics by virtue of fluorescence. Calcium phosphate (CaP) nanocoatings were deposited on the surface of siRNA-CPNPs, followed by loading with HCPT and aptamers targeting cancer cells to obtain a targeted and tumor acid-responsive biocompatible nanoplatform. After the uptake of cancer cells, the CaP nanocoatings were decomposed in the acidic endo/lysosomes to release HCPT, and the siRNA-CPNPs were exposed to facilitate the siRNA endo/lysosome escape and cytoplasm delivery. Results obtained from both in vitro and in vivo studies in tumor inhibition expressed that the combined therapy exhibited a better therapeutic efficacy than any monotherapy.

A Continuous Add-On Probe Reveals the Nonlinear Enlargement of Mitochondria in Light-Activated Oncosis

Oncosis, depending on DNA damage and mitochondrial swelling, is an important approach for treating cancer and other diseases. However, little is known about the behavior of mitochondria during oncosis, due to the lack of probes for in situ visual illumination of the mitochondrial membrane and mtDNA. Herein, a mitochondrial lipid and mtDNA dual-labeled probe, MitoMN, and a continuous add-on assay, are designed to image the dynamic process of mitochondria in conditions that are unobservable with current mitochondrial probes. Meanwhile, the MitoMN can induce oncosis in a light-activated manner, which results in the enlargement of mitochondria and the death of cancer cells. Using structured illumination microscopy (SIM), MitoMN-stained mitochondria with a dual-color response reveals, for the first time, how swelled mitochondria interacts and fuses with each other for a nonlinear enlargement to accelerate oncosis into an irreversible stage. With this sign of irreversible oncosis revealed by MitoMN, oncosis can be segregated into three stages, including before oncosis, initial oncosis, and accelerated oncosis.

Second near-infrared photoactivatable biocompatible polymer nanoparticles for effective in vitro and in vivo cancer theranostics

Photoacoustic imaging (PAI)-guided photothermal therapy (PTT) has drawn considerable attention due to the deeper tissue penetration and higher maximum permissible exposure. However, current phototheranostic agents are greatly restricted by weak absorption in the second near-infrared (NIR-II, 1000-1700 nm) window, long-term toxicity, and poor photostability. In this report, novel organic NIR-II conjugated polymer nanoparticles (CPNs) based on narrow bandgap donor-acceptor BDT-TBZ polymers were developed for effective cancer PAI and PTT. Characterization data confirmed the high photothermal conversion efficiency, good photostability, excellent PAI performance, and superior biocompatibility of as-obtained CPNs. In addition, in vitro and in vivo tests demonstrated the efficient PTT effect of CPNs in ablating cancer cells and inhibiting tumor growth under 1064 nm laser irradiation. More importantly, the CPNs exhibited rapid clearance capability through the biliary pathway and negligible systematic toxicity. Thus, this work provides a novel organic theranostic nanoplatform for NIR-II PAI-guided PTT, which advances the future clinical translation of biocompatible and metabolizable conjugated nanomaterials in cancer diagnosis and therapy.

Expansion Microscopy with Multifunctional Polymer Dots

Expansion microscopy (ExM) provides nanoscale resolution on conventional microscopes via physically enlarging specimens with swellable polyelectrolyte gels. However, challenges involving fluorophore degradation and dilution during sample expansion have yet to be overcome. Herein, sequential cellular targeting, gel anchoring, and high-fidelity fluorescence reported using multifunctional polymer dots (Pdots) designed for ExM applications are demonstrated. The impressive brightness of the Pdots facilitates multicolor ExM, thereby enabling visualization of a variety of subcellular structures and neuron synapses. The average fluorescence intensities of Pdots in ExM range from ≈3 to 6 times higher than those achieved using commercially available Alexa dyes. Moreover, the fluorescence brightness and optical fluctuation are significantly improved by a surfactant-containing expansion buffer, which enables further resolution enhancement via super-resolution optical fluctuation imaging (SOFI). The combination of ExM and SOFI allows subcellular structures of ≈30 nm to be resolved by conventional microscopes. These results highlight the immense potential of multifunctional Pdots for ExM-enhanced super-resolution imaging.

Engineering fluorescent semiconducting polymer nanoparticles for biological applications and beyond

We summarize the recent advances in engineering approaches to obtain functionalized semiconducting polymer nanoparticles (SPNs) for biological applications. The challenges and outlook of fabricating functionalized SPNs are also provided.

Core Size does not Affect Blinking Behavior of Dye-Doped Ag@SiO2 Core-Shell Nanoparticles for Super-Resolution Microscopy

Dye-doped nanoparticles have been investigated as bright, luminescent labels for super-resolution microscopy via localization methods. One key factor in super-resolution is the size of the luminescent label, which in some cases results in a frame shift between the label target and the label itself. Ag@SiO₂ core–shell nanoparticles, doped with organic fluorophores, have shown promise as super-resolution labels. One key aspect of these nanoparticles is that they blink under certain conditions, allowing super-resolution localization with a single excitation source in aqueous solution. In this work, we investigated the effects of both the Ag core and the silica (SiO₂) shell on the self-blinking properties of these nanoparticles. Both core size and shell thickness were manipulated by altering the reaction time to determine core and shell effects on photoblinking. Size and shell thickness were investigated individually under both dry and hydrated conditions and were then doped with a 1 mM solution of Rhodamine 110 for analysis. We observed that the cores themselves are weakly luminescent and are responsible for the blinking observed in the fully-synthesized metal-enhanced fluorescence nanoparticles. There was no statistically significant difference in photoblinking behavior—both intensity and duty cycle—with decreasing core size. This observation was used to synthesize smaller nanoparticles ranging from approximately 93 nm to 110 nm as measured using dynamic light scattering. The blinking particles were localized via super-resolution microscopy and show single particle self-blinking behavior. As the core size did not impact blinking performance or intensity, the nanoparticles can instead be tuned for optimal size without sacrificing luminescence properties.

Dye-doped nanoparticles have been investigated as bright, luminescent labels for super-resolution microscopy via localization methods.

Donor-Acceptor-Type Conjugated Polymer-Based Multicolored Drug Carriers with Tunable Aggregation-Induced Emission Behavior for Self-Illuminating Cancer Therapy

Nowadays, multicolored drug carriers have exhibited high significance in designing self-illuminating drug delivery systems to adapt different experimental conditions. In this study, we developed an efficient strategy for self-illuminating antitumor therapy using multicolored aggregation-induced emission (AIE)-active drug carriers by tuning electron donor moieties in donor-acceptor (D-A) structures. Three amphipathic conjugated polymers, P1 to P3, were successfully synthesized using an AIE-active tetraphenylethylene (TPE) moiety and donor-acceptor (D-A)-type electronic structure. Interestingly, the fluorescence behavior of P1 to P3 could be tuned between aggregation-caused quenching and AIE by changing the electron donor moiety. Their fluorescence color in aqueous solution could be easily adjusted from yellow to red by choosing stronger electron donors. After the anticancer drug paclitaxel was loaded, two AIE-active polymers, P1 and P2, could be engineered into polymer dots (Pdots) and applied in self-illuminating cancer therapy. The Pdots could not only reveal their location by a yellow- or red-colored fluorescence signal but also exhibit almost two times in vivo antitumor efficacy, high biocompatibility, and obvious tumor-targeting behavior compared to the commercially available anticancer drug Taxol. Furthermore, P2dots exhibited similar in vivo antitumor efficacy and biocompatibility compared to nonemission Abraxane, a commercially available drug delivery system. This work demonstrates the significant application of a D-A-type structure in the design of self-illuminating drug delivery systems.