An in cellulo-activated multicolor cell labeling approach used to image dying cell clearance.

Dying cell clearance is critical for myriad biological processes such as tissue homeostasis. We herein report an enzyme-activated fluorescence cell labeling approach and its use for multicolor imaging of dying cell clearance. Diacetylated 4-hydroxymandelic acid (DHA)-conjugated dyes give rise to reactive quinone methides upon deacetylation in live cells, which in turn covalently labels cellular proteins.

On the use of abiotic sialic acids to attenuate cell inflammation.

Sialic acid (Sia) residues on cell surface are critical for myriad cellular events such as immunity and inflammation. We herein reported the use of abiotic Sia to raise the thresholds of inflammatory cell responses. Identified from a panel of structurally diversified Sia analogs via a cell inflammation assay, Sia-2, with N-butyryl moiety at C-5, markedly lowered LPS-stimulated NF-κB activity in macrophages.

Senescence-associated sialidase revealed by an activatable fluorescence-on labeling probe.

We report senescence imaging with a fluorescence-quenched self-immolative sialoside probe (Sia-RQ) which gives a reactive quinone methide to allow in situ fluorescence labeling of sialidases upon desialylation. Dramatic upregulation of lysosome-associated sialidase was uncovered in cell senescence with Sia-RQ, suggesting the use of sialidase as a new biomarker for senescence.

Bifunctional Super-resolution Imaging Probe with Acidity-Independent Lysosome-Retention Mechanism.

Spatiotemporal imaging is of enormous use to explore organelle biology, necessitating organelle-tracing techniques reliable in varied cell stress. We herein reported lysosomal imaging using rhodamine-X-integrated sialic acid (SA), which is stably maintained in lysosomes irrespective of lysosomal pH changes. Exhibiting bright fluorescence and superior photostability, SA enables 120 h continual tracking of fusion/fission of lysosomes and mitochondrion-lysosome interaction in mitophagy.

Bioorthogonal Conjugation Directed by a Sugar-Sorting Pathway for Continual Tracking of Stressed Organelles.

Selective and continuous tracking of dynamic organelles is crucial for modern biology. We herein report a ship-in-a-bottle strategy for tagging lysosomes by a strain-promoted azide-alkyne cycloaddition to couple a pH sensor (RC) with mannose-6-carboxylate (M6C) actively transported into lysosomes through cell sorting. In contrast to classical acidotropic sensors, which are prone to dissipate from lysosomes, M6C-RC formed in situ is stably trapped in lysosomes without resort to lysosomal acidity and exhibits "always-on" blue fluorescence to pinpoint lysosomes and red-to-blue fluorescence ratios indicative of the lysosomal pH value.

Organelle-Directed Staudinger Reaction Enabling Fluorescence-on Resolution of Mitochondrial Electropotentials via a Self-Immolative Charge Reversal Probe.

Organelles often feature parameters pertinent to functions and yet responsive to biochemical stress. The electropotential across the mitochondrial membrane (ΔΨm) is a crucial mediator of cell fates. Herein we report a bioorthogonal reaction enabled fluorescence-on probing of ΔΨm alterations featuring anionic fluorescein-triphenylphosphonium diad (F-TPP), which is released via intramitochondria Staudinger reaction triggered self-immolation of o-azidomethylbenzoylated F-TPP.

Imaging Lysosomal pH Alteration in Stressed Cells with a Sensitive Ratiometric Fluorescence Sensor.

The organelle-specific pH is crucial for cell homeostasis. Aberrant pH of lysosomes has been manifested in myriad diseases. To probe lysosome responses to cell stress, we herein report the detection of lysosomal pH changes with a dual colored probe (CM-ROX), featuring a coumarin domain with "always-on" blue fluorescence and a rhodamine-lactam domain activatable to lysosomal acidity to give red fluorescence.

Defining Cancer Cell Bioenergetic Profiles Using a Dual Organelle-Oriented Chemosensor Responsive to pH Values and Electropotential Changes.

Cell fate is largely shaped by combined activity of different types of organelles, which often feature functionally critical parameters that succumb to pathological inducers. We herein report the analysis of cell bioenergetic profiles with a dual organelle-oriented chemosensor (RC-AMI), partitioning in mitochondria to give blue fluorescence and in lysosomes to give red fluorescence. Responsive to lysosomal pH and mitochondrial transmembrane potential (ΔΨ), two parameters crucial to cell bioenergetics, RC-AMI enables dual colored reporting of lysosomal acidity and ΔΨ, revealing upregulated ΔΨ and imbalance dramatically shifted favoring ΔΨ over lysosomal acidity in cancer cells whereas the tendency is reversed in starved cells.

Responsive hetero-organelle partition conferred fluorogenic sensing of mitochondrial depolarization.

Malfunctioning organelles are often difficult to probe with classical organelle-homing sensors owing to disruption of physiological organelle-probe affinity. We herein report the use of a responsive hetero-organelle partition and signal activable probe (RC-TPP) for detecting mitochondrial depolarization, a pathologically relevant event featuring loss of the electrical potentials across the mitochondrial membrane (Δ). Partitioned in mitochondria to give blue fluorescence, RC-TPP relocates into lysosomes upon mitochondrial depolarization and exhibits red fluorescence triggered by lysosomal acidity, enabling determination of autophagy relevant mitochondrial depolarization and the chronological sequence of mitochondrial depolarization and lysosomal neutralization in distinct cell death signalling pathways.

Centrifugation aided highly sensitive detection of nitrite with a dye-silica conjugate featuring cleavable linkages.

Rhodamine-silica nanocomposite bridged by a cleavable linker was used for highly sensitive nitrite detection via analyte triggered release of rhodamine from silica particles. Centrifugal removal of pristine nanoconjugate from the assay medium effectively decreased background signals in the supernatant whereas rhodamine unleashed from silica platform is retained in the supernatant, enabling facile detection of nitrite with an assay limit of 50 nM which is 400 folds lower than legislated maximum contaminant levels of nitrite in drinking water. Assays based on small molecular chemosensors are often compromised by their intrinsic fluorescence signals and low aqueous compatibility.

Chromo-fluorogenic detection of aldehydes with a rhodamine based sensor featuring an intramolecular deoxylactam.

A chromogenic and fluorogenic detection of aldehydes was achieved via analyte triggered opening of the deoxylactam of N-(rhodamine B)-deoxylactam-ethylenediamine (dRB-EDA). The utility of the sensor was demonstrated by fluorescent labeling of aldehyde-displaying sialoproteins on cell surfaces.

Visual and fluorogenic detection of a nerve agent simulant via a Lossen rearrangement of rhodamine-hydroxamate.

A visual and fluorogenic detection method for a nerve agent simulant was developed based on a Lossen rearrangement of rhodamine-hydroxamate, in the presence of diethyl chlorophosphate, under alkaline conditions.