Combining array tomography with electron tomography provides insights into leakiness of the blood-brain barrier in mouse cortex.

Like other volume electron microscopy approaches, automated tape-collecting ultramicrotomy (ATUM) enables imaging of serial sections deposited on thick plastic tapes by scanning electron microscopy (SEM). ATUM is unique in enabling hierarchical imaging and thus efficient screening for target structures, as needed for correlative light and electron microscopy. However, SEM of sections on tape can only access the section surface, thereby limiting the axial resolution to the typical size of cellular vesicles with an order of magnitude lower than the acquired xy resolution.

Push-Pull Fluorescent Dyes with Trifluoroacetyl Acceptor for High-Fidelity Sensing of Polarity and Heterogeneity of Lipid Droplets.

Imaging and sensing of lipid droplets (LDs) attracted significant attention due to growing evidence for their important role in cell life. Solvatochromic dyes are promising tools to probe LDs' local polarity, but this analysis is biased by their non-negligible emission from intracellular membranes and capacity to emit from both the apolar core and polar interface of LDs. Here, we developed two push-pull solvatochromic dyes based on naphthalene and fluorene cores bearing an exceptionally strong electron acceptor, the trifluoroacetyl group.

Direct Zeptomole Detection of RNA Biomarkers by Ultrabright Fluorescent Nanoparticles on Magnetic Beads.

Nucleic acids are important biomarkers in cancer and viral diseases. However, their ultralow concentration in biological/clinical samples makes direct target detection challenging, because it leads to slow hybridization kinetics with the probe and its insufficient signal-to-noise ratio. Therefore, RNA target detection is done by molecular (target) amplification, notably by RT-PCR, which is a tedious multistep method that includes nucleic acid extraction and reverse transcription.

Supramolecular Heterodimer Peptides Assembly for Nanoparticles Functionalization.

Nanoparticle (NP) surface functionalization with proteins, including monoclonal antibodies (mAbs), mAb fragments, and various peptides, has emerged as a promising strategy to enhance tumor targeting specificity and immune cell interaction. However, these methods often rely on complex chemistry and suffer from batch-dependent outcomes, primarily due to limited control over the protein orientation and quantity on NP surfaces. To address these challenges, a novel approach based on the supramolecular assembly of two peptides is presented to create a heterotetramer displaying VHs on NP surfaces.

Fluorescent Probes Based on Charge and Proton Transfer for Probing Biomolecular Environment.

Fluorescent probes for sensing fundamental properties of biomolecular environment, such as polarity and hydration, help to study assembly of lipids into biomembranes, sensing interactions of biomolecules and imaging physiological state of the cells. Here, we summarize major efforts in the development of probes based on two photophysical mechanisms: (i) an excited-state intramolecular charge transfer (ICT), which is represented by fluorescent solvatochromic dyes that shift their emission band maximum as a function of environment polarity and hydration; (ii) excited-state intramolecular proton transfer (ESIPT), with particular focus on 5-membered cyclic systems, represented by 3-hydroxyflavones, because they exhibit dual emission sensitive to the environment. For both ICT and ESIPT dyes, the design of the probes and their biological applications are summarized.

Mixing versus Polymer Chemistry in the Synthesis of Loaded Polymer Nanoparticles through Nanoprecipitation.

Polymer nanoparticles (NPs) loaded with drugs and contrast agents have become key tools in the advancement of nanomedicine, requiring robust technologies for their synthesis. Nanoprecipitation is a particularly interesting technique for the assembly of loaded polymer NPs, which is well-known to proceed under kinetic control, with a strong influence of the assembly conditions. On the other hand, the nature of the used polymer also influences the outcome of nanoprecipitation.

Characterizing Counterion-Dependent Aggregation of Rhodamine B by Classical Molecular Dynamics Simulations.

The aggregation in a solution of charged dyes such as Rhodamine B (RB) is significantly affected by the type of counterion, which can determine the self-assembled structure that in turn modulates the optical properties. RB aggregation can be boosted by hydrophobic and bulky fluorinated tetraphenylborate counterions, such as F5TPB, with the formation of nanoparticles whose fluorescence quantum yield (FQY) is affected by the degree of fluorination. Here, we developed a classical force field (FF) based on the standard generalized Amber parameters that allows modeling the self-assembling process of RB/F5TPB systems in water, consistent with experimental evidence.

Brightness of fluorescent organic nanomaterials.

Brightness is a fundamental property of fluorescent nanomaterials reflecting their capacity to absorb and emit light. In sensing materials, brightness is crucial for high-sensitivity (bio)molecular detection, while in optical bioimaging it ensures high spatial and temporal resolution. Fluorescent organic nanoparticles (NPs) are particularly attractive because of their superior brightness compared to organic dyes.

Long-Range Energy Transfer between Dye-Loaded Nanoparticles: Observation and Amplified Detection of Nucleic Acids.

Förster resonance energy transfer (FRET) is essential in optical materials for light-harvesting, photovoltaics, and biosensing, but its operating range is fundamentally limited by the Förster radius of ≈5 nm. In this work, FRET between fluorescent organic nanoparticles (NPs) is studied in order to break this limit. The donor and acceptor NPs are built from charged hydrophobic polymers loaded with cationic dyes and bulky hydrophobic counterions.

Tuning Directed Photooxidation-Induced Conversion of Pyrrole-Based Styryl Coumarin Dual-Color Photoconverters.

Invited for the cover of this issue is the group of Mayeul Collot at the University of Strasbourg (CNRS). The image depicts the effect of simple chemical tuning on coumarin dyes to tune and improve the DPIC photoconversion mechanism. Read the full text of the article at 10.

Biotinylated Fluorescent Polymeric Nanoparticles for Enhanced Immunostaining.

The performance of fluorescence immunostaining is physically limited by the brightness of organic dyes, whereas fluorescence labeling with multiple dyes per antibody can lead to dye self-quenching. The present work reports a methodology of antibody labeling by biotinylated zwitterionic dye-loaded polymeric nanoparticles (NPs). A rationally designed hydrophobic polymer, poly(ethyl methacrylate) bearing charged, zwitterionic and biotin groups (PEMA-ZI-biotin), enables preparation of small (14 nm) and bright fluorescent biotinylated NPs loaded with large quantities of cationic rhodamine dye with bulky hydrophobic counterion (fluorinated tetraphenylborate).

Tuning Directed Photooxidation-Induced Conversion of Pyrrole-Based Styryl Coumarin Dual-Color Photoconverters.

Dual-emissive photoconvertible fluorophores (DPCFs) are powerful tools to unambiguously track labeled cells in bioimaging. We recently introduced a new rational mechanism called directed photooxidation-induced conversion (DPIC) enabling efficient DPCFs to be obtained by conjugating a coumarin to aromatic singlet-oxygen reactive moieties (ASORMs). Pyrrole was found to be a suitable ASORM as it provided a high hypsochromic shift along with a fast and efficient conversion.

Study of surfactant cross-linking by click chemistry on a model water/oil interface.

In this study, we explored how chemical reactions of amphiphile compounds can be characterized and followed-up on model interfaces. A custom-made surfactant containing three alkyne sites was first adsorbed and characterized at a water/oil interface. These amphiphiles then underwent interfacial crosslinking by click chemistry upon the addition of a second reactive agent.

Controlled Release and Capture of Aldehydes by Dynamic Imine Chemistry in Nanoemulsions: From Delivery to Detoxification.

Current biomedical applications of nanocarriers are focused on drug delivery, where encapsulated cargo is released in the target tissues under the control of external stimuli. Here, we propose a very different approach, where the active toxic molecules are removed from biological tissues by the nanocarrier. It is based on the drug-sponge concept, where specific molecules are captured by the lipid nanoemulsion (NE) droplets due to dynamic covalent chemistry inside their oil core.

Intracellular accumulation and immunological response of NIR-II polymeric nanoparticles.

Polymeric nanoparticles (NPs) are extremely promising for theranostic applications. However, their interest depends largely on their interactions with immune system, including the capacity to activate inflammation after their capture by macrophages. In the present study, we generated monodisperse poly(ethyl methacrylate) (PEMA) NPs loaded with hydrophobic photoluminescent gold nanoclusters (Au NCs) emitting in the NIR-II optical windows and studied their interaction in vitro with J774.

Dual-Color Photoconvertible Fluorescent Probes Based on Directed Photooxidation Induced Conversion for Bioimaging.

We herein present a new concept to produce dual-color photoconvertible probes based on a mechanism called Directed Photooxidation Induced Conversion (DPIC). As a support of this mechanism, styryl-coumarins (SCs) bearing Aromatic Singlet Oxygen Reactive Moieties (ASORMs) like furan and pyrrole have been synthesized. SCs are bright fluorophores, which undergo a hypsochromic conversion upon visible light irradiation due to directed photooxidation of the ASORM that leads to the disruption of conjugation.

Fluorogenic Dimers as Bright Switchable Probes for Enhanced Super-Resolution Imaging of Cell Membranes.

Super-resolution fluorescence imaging based on single-molecule localization microscopy (SMLM) enables visualizing cellular structures with nanometric precision. However, its spatial and temporal resolution largely relies on the brightness of ON/OFF switchable fluorescent dyes. Moreover, in cell plasma membranes, the single-molecule localization is hampered by the fast lateral diffusion of membrane probes.

Pathogenic variants of sphingomyelin synthase SMS2 disrupt lipid landscapes in the secretory pathway.

Sphingomyelin is a dominant sphingolipid in mammalian cells. Its production in the Golgi traps cholesterol synthesized in the ER to promote formation of a sphingomyelin/sterol gradient along the secretory pathway. This gradient marks a fundamental transition in physical membrane properties that help specify organelle identify and function.

Engineering Novel 3D Models to Recreate High-Grade Osteosarcoma and its Immune and Extracellular Matrix Microenvironment.

Osteosarcoma (OS) is the most common primary bone cancer, where the overall 5-year surviving rate is below 20% in resistant forms. Accelerating cures for those poor outcome patients remains a challenge. Nevertheless, several studies of agents targeting abnormal cancerous pathways have yielded disappointing results when translated into clinic because of the lack of accurate OS preclinical modeling.

In Vivo Imaging Evaluation of Fluorescence Intensity at Tail Emission of Near-Infrared-I (NIR-I) Fluorophores in a Porcine Model.

Over the last decade fluorescence-guided surgery has been primarily focused on the NIR-I window. However, the NIR-I window has constraints, such as limited penetration and scattering. Consequently, exploring the performance of NIR-I dyes at longer wavelengths (i.

Assembly of Fluorescent Polymer Nanoparticles Using Different Microfluidic Mixers.

Nanoprecipitation is a facile and efficient approach to the assembly of loaded polymer nanoparticles (NPs) for applications in bioimaging and targeted drug delivery. Their successful use in clinics requires reproducible and scalable synthesis, for which microfluidics appears as an attractive technique. However, in the case of nanoprecipitation, particle formation depends strongly on mixing.