Designing Sub‐2 nm Organosilica Nanohybrids for Far‐Field Super‐Resolution Imaging

Zirconium Oxide Doped Organosilica Nanodots as Light- and Charge-Management Cathode Interlayer for Highly Efficient and Stable Inverted Organic Solar Cells

In this work, it is reported that zirconium oxide (ZrO2) doped organosilica nanodots (OSiNDs: ZrO2) with light- and charge-management properties serve as efficient cathode interlayers for high-efficiency inverted organic solar cells (i-OSCs). ZrO2 doping effectively improves the light harvesting of the active layer, the physical contact between the active layer, as well as the electron collection property by habiting charge recombination loss. Consequently, all devices utilizing the OSiNDs: ZrO2 cathode interlayer exhibit enhanced power conversion efficiency (PCE). Specifically, i-OSCs based on PM6:Y6 and PM6:BTP-eC9 achieve remarkable PCEs of 17.16% and 18.43%, respectively. Furthermore, the PCE of device based on PM6:Y6 maintains over 97.2% of its original value following AM 1.5G illumination (including UV light) at 100 mW cm-2 for 600 min.

Monodispersed and Monofunctionalized DNA-Caged Au Nano-Clusters with Enhanced Optical Properties for STED Imaging

The performance of Stimulated Emission Depletion (STED) microscopy depends critically on the fluorescent probe. Ultrasmall Au nanoclusters (Au NCs) exhibit large Stokes shift, and good stimulated emission response, which are potentially useful for STED imaging. However, Au NCs are polydispersed in size, sensitive to the surrounding environment, and difficult to control surface functional group stoichiometry, which results in reduced density and high heterogeneity in the labeling of biological structures. Here, this limitation is overcome by developing a method to encapsulate ultrasmall Au NCs with DNA cages, which yielded monodispersed, and monofunctionalized Au NCs that are long-term stable. Moreover, the DNA-caging also greatly improved the fluorescence quantum yield and photostability of Au NCs. In STED imaging, the DNA-caged Au NCs yielded ≈40 nm spatial resolution and are able to resolve microtubule line shapes with good labeling density and homogeneity. In contrast, without caging, the Au NCs-DNA conjugates only achieved ≈55 nm resolution and yielded spotted, poorly resolved microtubule structures, due to the presence of aggregates. Overall, a method is developed to achieve precise surface functionalization and greatly improve the monodispersity, stability, as well as optical properties of Au NCs, providing a promising class of fluorescent probes for STED imaging.

Surface-Engineered Gold Nanoclusters for Stimulated Emission Depletion and Correlated Light and Electron Microscopy Imaging

Stimulated emission depletion (STED) nanoscopy is an emerging super-resolution imaging platform for the study of the cellular structure. Developing suitable fluorescent probes of small size, good photostability, and easy functionalization is still in demand. Herein, we introduce a new type of surface-engineered gold nanoclusters (Au NCs) that are ultrasmall (1.7 nm) and ultrabright (QY = 60%) for STED bioimaging. A rigid shell formed by l-arginine (l-Arg) and 6-aza-2-thiothymine (ATT) on the Au NC surface enables not only its strong fluorescence in aqueous solution but also its easy chemical modification for specific biomolecule labeling. Au NCs show remarkable performance as STED nanoprobes, including high depletion efficiency, good photobleaching resistance, and low saturation intensity. Super-resolution imaging has been achieved with these Au NCs, and targeted nanoscopic imaging of cellular tubulin has been demonstrated. Moreover, the circular structure of lysosomes in live cells has been revealed. As a Au NC is also an ideal probe for electron microscopy, dual imaging of Aβ₄₂ aggregates with the single labeling probe of Au NCs has been realized in correlative light and electron microscopy (CLEM). This work reports, for the first time, the application of Au NCs as a novel probe in STED and CLEM imaging. With their excellent properties, Au NCs show promising potential for nanoscale bioimaging.

Cd-free InP/ZnSeS quantum dots for ultrahigh-resolution imaging of stimulated emission depletion

Stimulated emission depletion (STED) nanoscopy is a promising super-resolution imaging technique for microstructure imaging; however, the performance of super-resolution techniques critically depends on the properties of the fluorophores (photostable fluorophores) used. In this study, a suitable probe for improving the resolution of STED nanoscopy was investigated. Quantum dots (QDs) typically exhibit good photobleaching resistance characteristics. In comparison with CdSe@ZnS QDs and CsPbBr₃ QDs, Cd-free InP/ZnSeS QDs have a smaller size and exhibit an improved photobleaching resistance. Through imaging using InP/ZnSeS QDs, we achieved an ultrahigh resolution of 26.1 nm. Furthermore, we achieved a 31 nm resolution in cell experiments involving InP/ZnSeS QDs. These results indicate that Cd-free InP/ZnSeS QDs have significant potential for application in fluorescent probes for STED nanoscopy.

Responsive Carbonized Polymer Dots for Optical Super-resolution and Fluorescence Lifetime Imaging of Nucleic Acids in Living Cells

The rapid development of advanced optical imaging methods including stimulated emission depletion (STED) and fluorescence lifetime imaging microscopy (FLIM) has provided powerful tools for real-time observation of submicrometer biotargets to achieve unprecedented spatial and temporal resolutions. However, the practical imaging qualities are often limited by the performance of fluorescent probes, leading to unsatisfactory results. In particular, long-term imaging of nucleic acids in living cells with STED and FLIM remained desirable yet challenging due to the lack of competent probes combining targeting specificity, biocompatibility, low power requirement, and photostability. In this work, we rationally designed and synthesized a nanosized carbonized polymer dot (CPD) material, CPDs-3, with highly efficient and photostable emission for the super-resolution and fluorescence lifetime imaging of nucleic acids in living cells. The as-fabricated nanoprobe showed responsive emission properties upon binding with nucleic acids, providing an excellent signal-to-noise ratio in both spatial and temporal dimensions. Moreover, the characteristic saturation intensity value of CPDs-3 was as low as 0.68 mW (0.23 MW/cm²), allowing the direct observation of chromatin structures with subdiffraction resolution (90 nm) at very low excitation (<1 μW) and depletion power (<5 mW). Owing to its low toxicity, high photonic efficiency, and outstanding photostability, CPDs-3 was capable of performing long-term imaging both with STED and FLIM setups, demonstrating great potential for the dynamic study of nucleic acid functionalities in the long run.

Shedding New Lights Into STED Microscopy: Emerging Nanoprobes for Imaging

First reported in 1994, stimulated emission depletion (STED) microscopy has long been regarded as a powerful tool for real-time superresolved bioimaging . However, high STED light power (10^1∼3 MW/cm²) is often required to achieve significant resolution improvement, which inevitably introduces phototoxicity and severe photobleaching, damaging the imaging quality, especially for long-term cases. Recently, the employment of nanoprobes (quantum dots, upconversion nanoparticles, carbon dots, polymer dots, AIE dots, etc.) in STED imaging has brought opportunities to overcoming such long-existing issues. These nanomaterials designed for STED imaging show not only lower STED power requirements but also more efficient photoluminescence (PL) and enhanced photostability than organic molecular probes. Herein, we review the recent progress in the development of nanoprobes for STED imaging, to highlight their potential in improving the long-term imaging quality of STED microscopy and broadening its application scope. We also discuss the pros and cons for specific classes of nanoprobes for STED bioimaging in detail to provide practical references for biological researchers seeking suitable imaging kits, promoting the development of relative research field.

Improving the image quality in STED nanoscopy using frequency spectrum modulation

Since stimulated emission depletion (STED) nanoscopy was invented in 1994, this technique has been widely used in the fields of biomedicine and materials science. According to the imaging principle of STED technology, increasing the power of the depletion laser within a certain threshold can improve the resolution. However, it will cause not only severe photo-damage to the samples and photo-bleaching to the fluorophores but also serious background noise, leading to the degeneration of the quality of STED images. Here we propose a new processing method based on frequency spectrum modulation to improve the quality of STED images, abbreviated as FM-STED. We have demonstrated the performance of FM-STED in improving the signal-to-noise ratio and the resolution using fluorescent beads and biological cells as samples.

Super-resolution Microscopy for Biological Imaging

Studying the ultra-fine structures and functions of the subcellular organelles and exploring the dynamic biological events in depth are the key issues in contemporary biological research. Fluorescence bio-imaging has been used to study cell biology for decades. However, the structures and functions of the subcellular organelles which fall under the diffraction limit are still not explored fully at a nanoscale level. Several super-resolution microscopy (SRM) techniques have been devised over the years which can be utilized to overcome diffraction limit. These techniques have opened a new window in biological research. However, SRM methods are highly vulnerable to the lack of appropriate fluorophores and other sophisticated technical considerations. Therefore, this chapter briefly summarizes the basic principles of various SRM methods which have been frequently utilized in biological imaging. The chapter not only gives an overview of the technical advantages and drawbacks about using different SRM techniques for bio-imaging applications but also briefly articulates the nitty-gritties of selecting a proper fluorescent probe for a specific SRM experiment with biological samples.

Facile Synthesis, Enhanced Photostability, and Long-term Cellular Imaging of Bright Red Luminescent Organosilica Nanoparticles

We herein demonstrate a facile approach for the preparation of red luminescent organosilica nanoparticles (OSi NPs) via the addition reaction of indocyanine green (ICG) and (3-aminopropyl)trimethoxysilane (APTMS). Photoluminescent quantum yield (PLQY) of the resulting OSi NPs was tunable by simply changing the molar ratio of ICG and APTMS used in the reactions. Under the optimized molar ratio of ICG and APTMS, that is, 1:4, PLQY of the red luminescent OSi NPs was as high as 32%. The resulting OSi NPs presented greatly enhanced photostability, attributing to the promoted decay rate of the excited state and thus suppressed the generation of the reactive oxygen species in the OSi NPs. The integrated superiorities of high PLQY, enhanced photostability, low toxicity, and excellent biocompatibility endow the red luminescent OSi NPs extremely promising for long-term cellular imaging.