Near-Infrared Spontaneously Blinking Fluorophores for Live Cell Super-Resolution Imaging with Minimized Phototoxicity.

Single-molecule localization microscopy (SMLM) requires high-intensity laser irradiation, typically exceeding kW/cm2, to yield a sufficient photon count. However, this intense visible light exposure incurs substantial cellular toxicity, hindering its use in living cells. Here, we developed a class of near-infrared (NIR) spontaneously blinking fluorophores for SMLM. These NIR fluorophores are a combination of rhodamine spirolactams and merocyanine derivatives, where the rhodamine spirolactam component converts between a bright and dark state based on pH-dependent spirocyclization and merocyanine derivatives shift the excitation wavelength into the infrared. Single-molecule characterizations demonstrated their potential for SMLM. At a moderate power density of 3.93 kW/cm2, these probes exhibit duty cycle as low as 0.18% and an emission rate as high as 26,700 photons/s. Phototoxicity assessment under single-molecule imaging conditions reveals that NIR illumination (721 nm) minimizes harm to living cells. Employing these NIR fluorophores, we successfully captured time-lapse super-resolution tracking of mitochondria at a Fourier ring correlation (FRC) resolution of 69.4 nm and reconstructed the ultrastructures of endoplasmic reticulum (ER) in living cells.

A Universal Photoactivatable Tag Attached to Fluorophores Enables Their Use for Single-Molecule Imaging.

Single molecule localization microscopy based on photoactivation is a powerful tool for investigating the ultrastructure of cells. We developed a general strategy for photoactivatable fluorophores, using 2,3-dihydro-1,4-oxathiine group (SO) as a tag to attach to various skeletal structures, including coumarin, BODIPY, rhodamine, and cyanine. The conjugation of SO resulted in a significant loss of fluorescence due to photoinduced electron transfer (PeT). Under the irradiation of excitation light, singlet oxygen generated by the fluorophores converted the SO moiety into its ester derivative, terminated the PeT process, and restored the fluorescence. Single molecule localization imaging was achieved using a dual functional illuminating beam in the visible, acting as both the activating and the exciting source. We successfully applied these photoactivatable probes for time-lapse super-resolution tracking in living cells and super-resolution imaging of microtubule structures in neurons.

Glutathione-Responsive Chemodynamic Therapy of Manganese(III/IV) Cluster Nanoparticles Enhanced by Electrochemical Stimulation via Oxidative Stress Pathway.

Escalating the level of reactive oxygen species (ROS) in a tumor microenvironment is one of the effective strategies to improve the efficacy of anticancer therapy. In this work, manganese cluster nanoparticles (Mn12) encapsulated with heparin (Mn12-heparin) were developed as a chemodynamic therapeutic agent for cancer treatment by raising ROS levels in tumor cells via cascade reactions. The manganese cluster is a cluster of mixed valence (III/IV) with acetate as the ligand. The cluster is readily subject to reduction by glutathione (GSH) to release Mn(II), which reacts with H2O2 to generate hydroxyl radicals via a Fenton-like pathway. The generation of hydroxyl radicals could be enhanced by the stimulation of an external alternative electric field during which GSH acts as an electron mediator to enhance the release of Mn(II) from the cluster. The relatively high levels of both H2O2 and GSH and the acidic environment in tumor cells strengthen its specificity when the manganese cluster system is employed to suppress or eliminate tumors. Both in vitro and in vivo results suggest that, in addition to the cytotoxicity imposed by the raised ROS level due to the presence of Mn(II) species, the depletion of endogenous GSH leads indirectly to the inhibition of glutathione peroxidase 4 (GPX4), consequently raising the lipid peroxidation (LPO) level to cause ferroptosis. The apoptosis and ferroptosis jointly render the manganese-based agent potent efficacy with tumor-targeting specificity in antitumor treatment under electric stimulation.

Tumor Microenvironment-Activated Nanoparticles Loaded with an Iron-Carbonyl Complex for Chemodynamic Immunotherapy of Lung Metastasis of Melanoma In Vivo.

In this work, a nanoplatform (FeCORM NPs) loaded with an iron-carbonyl complex was constructed. By exploiting chemodynamic therapy (CDT) and immunogenic cell death (ICD)-induced immunotherapy (IMT), the nanoparticles exhibited excellent efficacy against lung metastasis of melanoma in vivo. The iron-carbonyl compound of the nanomaterials could be initiated by both glutathione (GSH) and hydrogen peroxide (H2O2) to release CO and generate ferrous iron through ligand exchange and oxidative destruction pathways. The released CO caused mitochondria damage, whereas the generated ferrous iron led to oxidative stress via the Fenton reaction. On the other hand, the nanomaterials induced ICD-based IMT, which worked jointly with CDT to exhibit excellent effects against lung metastasis of melanoma through a mouse model. This work demonstrated how a nanoplatform, simple and stable but showing excellent efficacy against tumors, could be built using simple building blocks via a self-assembling approach. Importantly, the system took advantage of relatively high levels of GSH and H2O2 in tumors to initiate the therapeutic effects, which rendered the nanoplatform with a capability to differentiate normal cells from tumor cells. In principle, the system has great potential for future clinical applications, not only in the treatment of lung metastasis of melanoma but also in suppressing other types of tumors.

Hollow Bimetallic Complex Nanoparticles for Trimodality Imaging and Photodynamic Therapy In Vivo.

Hollow nanoparticles have received an enormous amount of attention in the field of nanomedicine. Herein, water-soluble hollow bimetallic complex nanoparticles, holmium(III)/iridium(III) bimetallic complex nanoparticles (Ir-Ho HNPs), were fabricated via a coordination assembly. Owing to the special metal-to-ligand charge transfer (MLCT) and the heavy-atom effect of Ir(III) in an iridium complex, Ir-Ho HNPs exhibited an intense phosphorescence and the generation of singlet oxygen (1O2). With the long electron relaxation time and high magnetic moment of Ho(III), Ir-Ho HNPs presented a high longitudinal relaxivity (r2) value (160.0 mM-1 s-1at 7.0 T). Their unique hollow structure resulted in their strong and stable ultrasound signal in an aqueous solution. As a proof of concept, Ir-Ho HNPs have been developed for the phosphorescence imaging and photodynamic therapy for living cells, ultrasound imaging, and high-field magnetic resonance imaging in vivo. Our work opened up an avenue for novel application of an iridium complex in cancer theranostics.

Ir-Ho bimetallic complex-mediated low-dose radiotherapy/radiodynamic therapy in vivo.

We report a bimetallic complex [Ir4Ho2(pq)8(H2dcbpy)4(OAc)2] (denoted as Ir4Ho2, pq = 2-phenylquinoline, H2dcppy = 2,2'-bipyridine-3,3'-dicarboxylic acid) and its application for radiotherapy/radiodynamic therapy (RT/RDT). In a tumor xenograft mouse model, Ir4Ho2 exerted a tumor-suppressive effect through efficient low-dose RT/RDT.

Flower-like MoS2 decorated with Cu2O nanoparticles for non-enzymatic amperometric sensing of glucose.

In this study, a novel nanohybrid consisting of flower-like MoS2 decorated with Cu2O nanoparticles has been successfully synthesized for non-enzymatic amperometric sensing of glucose. Structural characterizations revealed that Cu2O nanoparticles were highly dispersed on MoS2 nanosheets. Electrochemical performances were investigated by cyclic voltammetry (CV) and chronoamperometry. Compared to single Cu2O component, the-synthesized Cu2O/MoS2 nanohybrid showed superior electrocatalysis to the oxidation of glucose. The fabricated non-enzymatic amperometric glucose sensor exhibited a wide linear range from 0.01 to 4.0mM with a low detection limit of 1.0µM (S/N =3) and a high sensitivity of 3108.87µAmM-1cm-2. Meanwhile, the non-enzymatic sensor also possesses satisfactory stability, good reproducibility and high selectivity to interfering components of uric acid, dopamine and ascorbic acid. The excellent analytical performances are resulted from the synergistic effect provided by the Cu2O nanoparticals and MoS2 nanosheets.