Time-lapse imaging of cell death in cell culture and whole living organisms using turn-on deep-red fluorescent probes

Structure-activity relationships of aniline-based squaraines for distinguishable staining and bright two-photon fluorescence bioimaging in plant cells

An organelle-selective vision provides insights into the physiological response of plants and crops to environmental stresses in sustainable agriculture ecosystems. Biological applications often require two-photon excited fluorophores with low phototoxicity, high brightness, deep penetration, and tuneable cell entry. We obtained three aniline-based squaraines (SQs) tuned from hydrophobic to hydrophilic characteristics by modifying terminal pendant groups and substituents, and investigated their steady-state absorption and far-red-emitting fluorescence properties. The SQs exhibited two-photon absorption (2PA) ranging from 750 to 870 nm within the first biological spectral window; their structure-property relationships, corresponding to the 2PA cross sections (δ2PA), and structure differences were demonstrated. The maximum δ2PA value was ∼1220 GM at 800 nm for hydrophilic SQ3. Distinct biological staining efficiency and selective SQ bioimaging were evaluated utilizing the onion epidermal cell model. Contrary to the hydrophobic SQ1 results in the onion epidermal cell wall, amphiphilic SQ2 tagged the vacuole and nucleus and SQ3 tagged the vacuole. Distinguishable staining profiles in the roots and leaves were achieved. We believe that this study is the first to demonstrate distinct visualisation efficiency induced by the structure differences of two-photon excited SQs. Our results can help establish the versatile roles of novel near-infrared-emitting SQs in biological applications.

Guidelines for Regulated Cell Death Assays: A Systematic Summary, A Categorical Comparison, A Prospective

Over the past few years, the field of regulated cell death continues to expand and novel mechanisms that orchestrate multiple regulated cell death pathways are being unveiled. Meanwhile, researchers are focused on targeting these regulated pathways which are closely associated with various diseases for diagnosis, treatment, and prognosis. However, the complexity of the mechanisms and the difficulties of distinguishing among various regulated types of cell death make it harder to carry out the work and delay its progression. Here, we provide a systematic guideline for the fundamental detection and distinction of the major regulated cell death pathways following morphological, biochemical, and functional perspectives. Moreover, a comprehensive evaluation of different assay methods is critically reviewed, helping researchers to make a reliable selection from among the cell death assays. Also, we highlight the recent events that have demonstrated some novel regulated cell death processes, including newly reported biomarkers (e.g., non-coding RNA, exosomes, and proteins) and detection techniques.

Supramolecular Loading of a Broad Spectrum of Molecular Guests In Hyperbranched Polytriazole Nanoparticles with Cores Containing Multiple Functional Groups

This study evaluated the supramolecular properties of a new family of water-soluble hyperbranched polytriazoles that have a unimolecular micelle structure. Two new, structurally related hyperbranched polymers (HBPa and HBPn), with the same size (D_h = 11 nm) and core-shell architecture, were prepared and found to act as nanoscale hosts for a broad spectrum of molecular guests. The globular-shaped hyperbranched polymers were synthesized by a straightforward one-pot polymerization method that permits easy synthetic control of the multiple functional groups within the core. Surrounding the core is a shell of polyethylene glycol chains that promotes solubility in pH 7.4 buffer solution and inhibits self-aggregation of the nanoparticles. The core of HBPa, containing a mixture of anionic carboxylate groups and 1,2,3-triazole rings, could be loaded with cationic hydrophilic (i.e., propidium iodide) or partially hydrophobic (i.e., Hoechst 33342) dyes or drugs, including a binary dye/drug pair (i.e., indocyanine green/mitoxantrone). The core of HBPn, containing a mixture of uncharged 2-pentanone chains and 1,2,3-triazole rings, could be loaded with uncharged and very hydrophobic dyes (i.e., Nile Red) or drugs. Improved aqueous solubility of camptothecin was achieved 10-fold from 8.4 to 75 ng/mL. Additionally, cell toxicity studies showed that HBPn was able to release the camptothecin drug inside A549 cancer cells resulting in increased cell death. Taken together, the results suggest that this new family of water-soluble hyperbranched polytriazoles could be broadly useful as nanocarriers for various applications in therapy, imaging, or a combination of the two (theranostics).

Detection of cell-surface phosphatidylserine using the fluorogenic probe P-IID

The fluorogenic probe P-IID enables the detection of cell-surface phosphatidylserine (PS) using both fluorescence imaging and flow cytometry. Here we provide a detailed protocol for the use of P-IID for the qualitative detection of externalized PS in apoptotic cells using confocal microscopy, including the real-time imaging of apoptosis upon drug treatment. We also provide a detailed method for the quantitative analysis of cell death by flow cytometry, using P-IID in conjunction with the nuclear stain propidium iodide. P-IID is superior to commonly used Annexin-V fluorophore conjugates for PS detection as it provides a "turn-on" fluorescence response, displays rapid binding kinetics and can be used at low temperature (4°C), without washing and in the absence of Ca²⁺ ions.

Extended conjugation in stilbenoid squaraines

Squaraines, two-fold condensation products in 1,3-position of squaric acid, represent dyes or pigments of high actuality. After their first boom in electrophotography diverse applications are presently studied in a wide area of research, which reaches from electrooptical materials to biosensors and compounds used in photodynamic therapy. Absorption and/or emission ranges in the NIR are mandatory for many of these techniques. The present article deals with stilbenoid squaraines, which feature an extended conjugation in their biradicaloid D-π-A-π-D structure. Due to the charge-transfer character of the excitation, boundaries are set for the optimal length of the conjugation. The absorption maxima of the stilbenoid squaraines and their aggregates are lying in chloroform as a solvent between 600 and 1000 nm. In the solid state panchromatic absorptions can be observed, which reach far into the NIR region. The facile preparation of squaraines bearing stilbene building blocks in one or two of their arms and moreover the easy access to dyes with multiple squaraine units fixed to stilbenoid scaffolds promise a wide palette of further applications in materials science.

A fluorogenic BODIPY molecular rotor as an apoptosis marker

Based on a BODIPY molecular rotor, we designed a probe that lights up its green fluorescence in apoptotic cells and distinguishes between early and late apoptosis.