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The deployment of small‐molecule fluorescent agents plays an ever‐growing role in medicine and drug development. Herein, we complement the portfolio of powerful fluorophores, reporting the serendipitous discovery and development of a novel class with an imidazo[1,2‐a]pyridinium triflate core, which we term PyrAtes. These fluorophores are synthesized in a single step from readily available materials (>60 examples) and display Stokes shifts as large as 240 nm, while also reaching NIR−I emissions at λmax as long as 720 nm. Computational studies allow the development of a platform for the prediction of λmax and λEm. Furthermore, we demonstrate the compatibility of these novel fluorophores with live cell imaging in HEK293 cells, suggesting PyrAtes as potent intracellular markers. [ABSTRACT FROM AUTHOR]

By synergistically employing four key strategies: (I) introducing tetraphenylethylene groups as the central core unit with aggregation‐induced emission (AIE) properties, (II) optimizing the π‐conjugated length by extending the building block branches, (III) incorporating flexible groups containing ethylenic bonds, and (IV) applying crystal engineering to attain dense stacking mode and highly twisty conformation, we successfully synthesized a series of hydrogen‐bonded organic frameworks (HOFs) exhibiting exceptional one/two‐photon excited fluorescence. Notably, when utilizing the fluorescently superior building block L2, HOF‐LIFM‐7 and HOF‐LIFM‐8 exhibiting high quantum yields (QY) of 82.1 % and 77.1 %, and ultrahigh two‐photon absorption (TPA) cross‐sections of 148959.5 GM and 123901.1 GM were achieved. These materials were successfully employed in one and two‐photon excited lysosome‐targeting cellular imaging. It is believed that this strategy, combining building block optimization and crystal engineering, holds significant potential for guiding the development of outstanding fluorescent HOF materials. [ABSTRACT FROM AUTHOR]

Various fluorogenic probes utilizing tetrazine (Tz) as a fluorescence quencher and bioorthogonal reaction partner have been extensively studied over the past few decades. Herein, we synthesized a series of boron‐dipyrromethene (BODIPY)‐Tz probes using monochromophoric design strategy for bioorthogonal cellular imaging. The BODIPY‐Tz probes exhibited excellent bicyclo[6.1.0]nonyne (BCN)‐selective fluorogenicity with three‐ to four‐digit‐fold enhancements in fluorescence over a wide range of emission wavelengths, including the far‐red region. Furthermore, we demonstrated the applicability of BODIPY‐Tz probes in bioorthogonal fluorescence imaging of cellular organelles without washing steps. We also elucidated the aromatized pyridazine moiety as the origin of BCN‐selective fluorogenic behavior. Additionally, we discovered that the fluorescence of the trans‐cyclooctene (TCO) adducts was quenched in aqueous media via photoinduced electron transfer (PeT) process. Interestingly, we observed a distinctive recovery of the initially quenched fluorescence of BODIPY‐Tz‐TCO upon exposure to hydrophobic media, accompanied by a significant bathochromic shift of its emission wavelength relative to that exhibited by the corresponding BODIPY‐Tz‐BCN. Leveraging this finding, for the first time, we achieved dual‐color bioorthogonal cellular imaging with a single BODIPY‐Tz probe. [ABSTRACT FROM AUTHOR]

Multiplex optical detection in live cells is challenging due to overlapping signals and poor signal‐to‐noise associated with some chemical reporters. To address this, the application of spectral phasor analysis to stimulated Raman scattering (SRS) microscopy for unmixing three bioorthogonal Raman probes within cells is reported. Triplex detection of a metallacarborane using the B−H stretch at 2480–2650 cm−1, together with a bis‐alkyne and deuterated fatty acid can be achieved within the cell‐silent region of the Raman spectrum. When coupled to imaging in the high‐wavenumber region of the cellular Raman spectrum, nine discrete regions of interest can be spectrally unmixed from the hyperspectral SRS dataset, demonstrating a new capability in the toolkit of multiplexed Raman imaging of live cells. [ABSTRACT FROM AUTHOR]

Aryl alcohol‐type or phenolic fluorophores offer diverse opportunities for developing bioimaging agents and fluorescence probes. Due to the inherently acidic hydroxyl functionality, phenolic fluorophores provide pH‐dependent emission signals. Therefore, except for developing pH probes, the pH‐dependent nature of phenolic fluorophores should be considered in bioimaging applications but has been neglected. Here we show that a simple structural remedy converts conventional phenolic fluorophores into pH‐resistant derivatives, which also offer "medium‐resistant" emission properties. The structural modification involves a single‐step introduction of a hydrogen‐bonding acceptor such as morpholine nearby the phenolic hydroxyl group, which also leads to emission bathochromic shift, increased Stokes shift, enhanced photo‐stability and stronger emission for several dyes. The strategy greatly expands the current fluorophores' repertoire for reliable bioimaging applications, as demonstrated here with ratiometric imaging of cells and tissues. [ABSTRACT FROM AUTHOR]

The metabolic labeling of nucleic acids in living cells is highly desirable to track the dynamics of nucleic acid metabolism in real‐time and has the potential to provide novel insights into cellular biology as well as pathogen‐host interactions. Catalyst‐free inverse electron demand Diels–Alder reactions (iEDDA) with nucleosides carrying highly reactive moieties such as axial 2‐trans‐cyclooctene (2TCOa) would be an ideal tool to allow intracellular labeling of DNA. However, cellular kinase phosphorylation of the modified nucleosides is needed after cellular uptake as triphosphates are not membrane permeable. Unfortunately, the narrow substrate window of most endogenous kinases limits the use of highly reactive moieties. Here, we apply our TriPPPro (triphosphate pronucleotide) approach to directly deliver a highly reactive 2TCOa‐modified 2′‐deoxycytidine triphosphate reporter into living cells. We show that this nucleoside triphosphate is metabolically incorporated into de novo synthesized cellular and viral DNA and can be labeled with highly reactive and cell‐permeable fluorescent dye‐tetrazine conjugates via iEDDA to visualize DNA in living cells directly. Thus, we present the first comprehensive method for live‐cell imaging of cellular and viral nucleic acids using a two‐step labeling approach. [ABSTRACT FROM AUTHOR]

Phosphorescent probes often show sensitive response toward analytes at a specific wavelength. However, oxygen quenching usually occurs at the same wavelength and thus hinders the accurate detection of analytes. In this study, we have developed dual‐emissive iridium(III) complexes that exhibit phosphorescence responses to copper(II) ions at a wavelength distinct from that where oxygen quenching occurs. The complexes displayed colorimetric phosphorescence response in aqueous solutions under different copper(II) and oxygen conditions. In cellular imaging, variation in oxygen concentration over a large range from 5 % to 80 % can modulate the intensity and lifetime of green phosphorescence without affecting the response of red phosphorescence toward intracellular copper(II) ions. [ABSTRACT FROM AUTHOR]

The low oxygen dependence of type I photosensitizers (PSs) has made them a popular choice for treating solid tumors. However, the drawbacks of poor water solubility, short emission wavelength, poor stability, and inability to distinguish cancer cells from normal cells limit the application of most type I PSs in clinical therapy. Thereby, developing novel type I PSs for overcoming these problems is an urgent but challenging task. Herein, by utilizing the distinctive structural characteristics of anion‐π+ interactions, a highly water‐soluble type I PS (DPBC‐Br) with aggregation‐induced emission (AIE) characteristic and near‐infrared (NIR) emission is fabricated for the first time. DPBC‐Br displays remarkable water solubility (7.3 mM) and outstanding photobleaching resistance, enabling efficient and precise differentiation between tumor cells and normal cells in a wash‐free and long‐term tracking manner via NIR‐I imaging. Additionally, the superior type I reactive oxygen species (ROS) produced by DPBC‐Br provide both specific killing of cancer cells in vitro and inhibition of tumor growth in vivo, with negligible systemic toxicity. This study rationally constructs a highly water‐soluble type I PS, which has higher reliability and controllability compared with conventional nanoparticle formulating procedures, offering great potential for clinical cancer treatment. [ABSTRACT FROM AUTHOR]

Synthetic catalytic DNA circuits have been recognized as a promising signal amplification toolbox for sensitive intracellular imaging, yet their selectivity and efficiency are always constrained by uncontrolled off‐site signal leakage and inefficient on‐site circuitry activation. Thus, the endogenously controllable on‐site exposure/activation of DNA circuits is highly desirable for achieving the selective imaging of live cells. Herein, an endogenously activated DNAzyme strategy was facilely integrated with a catalytic DNA circuit for guiding the selective and efficient microRNA imaging in vivo. To prevent the off‐site activation, the circuitry constitute was initially caged without sensing functions, which could be selectively liberated by DNAzyme amplifier to guarantee the high‐contrast microRNA imaging in target cells. This intelligent on‐site modulation strategy can tremendously expand these molecularly engineered circuits in biological systems. [ABSTRACT FROM AUTHOR]

NETosis, the peculiar type of neutrophil death, plays important roles in pro‐tumorigenic functions and inhibits cancer immunotherapy. Non‐invasive real‐time imaging is thus imperative for prognosis of cancer immunotherapy yet remains challenging. Herein, we report a Tandem‐locked NETosis Reporter 1 (TNR1) that activates fluorescence signals only in the presence of both neutrophil elastase (NE) and cathepsin G (CTSG) for the specific imaging of NETosis. In the aspect of molecular design, the sequence of biomarker‐specific tandem peptide blocks can largely affect the detection specificity towards NETosis. In live cell imaging, the tandem‐locked design allows TNR1 to differentiate NETosis from neutrophil activation, while single‐locked reporters fail to do so. The near‐infrared signals from activated TNR1 in tumor from living mice were consistent with the intratumoral NETosis levels from histological results. Moreover, the near‐infrared signals from activated TNR1 negatively correlated with tumor inhibition effect after immunotherapy, thereby providing prognosis for cancer immunotherapy. Thus, our study not only demonstrates the first sensitive optical reporter for noninvasive monitoring of NETosis levels and evaluation of cancer immunotherapeutic efficacy in tumor‐bearing living mice, but also proposes a generic approach for tandem‐locked probe design. [ABSTRACT FROM AUTHOR]

Probes allowing high‐contrast discrimination of cancer cells and effective retention are powerful tools for the early diagnosis and treatment of cancer. However, conventional small‐molecule probes often show limited performance in both aspects. Herein, we report an ingenious molecular engineering strategy for tuning the cellular uptake and retention of rhodamine dyes. Introduction of polar aminoethyl leads to the increased brightness and reduced cellular uptake of dyes, and this change can be reversed by amino acetylation. Moreover, these modifications allow cancer cells to take up more dyes than normal cells (16‐fold) through active transport. Specifically, we further improve the signal contrast (56‐fold) between cancer and normal cells by constructing activatable probes and confirm that the released fluorophore can remain in cancer cells with extended time, enabling long‐term and specific tumor imaging. [ABSTRACT FROM AUTHOR]

Here we report on a label‐free electrochemiluminescence (ECL) microscopy using exceptionally low concentrations of the [Ru(bpy)3]2+ luminophore. This work addresses the central point of the minimal concentration of the ECL luminophore required to image single entities. We demonstrate the possibility to record ECL images of cells and mitochondria at concentrations down to nM and pM. This is 7 orders of magnitude lower than classically‐used concentrations and corresponds to a few hundreds of luminophores diffusing around the biological entities. Yet, it produces remarkably sharp negative optical contrast ECL images, as demonstrated by structural similarity index metric analyses and supported by predictions of the ECL image covering time. Finally, we show that the reported approach is a simple, fast, and highly sensitive method, which opens new avenues for ultrasensitive ECL imaging and ECL reactivity at the single molecule level. [ABSTRACT FROM AUTHOR]

Amplified ATP imaging in inflammatory cells is highly desirable. However, the spatial selectivity of current amplification methods is limited, that is, signal amplification is performed systemically and not in a disease site‐specific manner. Here we present a versatile strategy, termed enzymatically triggerable, aptamer‐based signal amplification (ETA‐SA), that enables inflammatory cell‐specific imaging of ATP through spatially‐resolved signal amplification. The ETA‐SA leverages a translocated enzyme in inflammatory cells to activate DNA aptamer probes and further drive cascade reactions through the consumption of hairpin fuels, which, however, exerts no ATP response activity in normal cells, leading to a significantly improved sensitivity and spatial specificity for the inflammation‐specific ATP imaging in vivo. Benefiting from the improved spatial selectivity, enhanced signal‐to‐background ratios were achieved for ATP imaging during acute hepatitis. [ABSTRACT FROM AUTHOR]

Fluorescent probes are attractive in diagnosis and sensing. However, most reported fluorophores can only detect one or few analytes/parameters, notably limiting their applications. Here we have designed three phenanthridine‐based fluorophores (i.e. B1, F1, and T1 with 1D, 2D, and 3D molecular configuration, respectively) capable of monitoring various microenvironments. In rigidifying media, all fluorophores show bathochromic emissions but with different wavelength and intensity changes. Under compression, F1 shows a bathochromic emission of over 163 nm, which results in organic fluorophore‐based full‐color piezochromism. Moreover, both B1 and F1 exhibit an aggregation‐caused quenching (ACQ) behavior, while T1 is an aggregation‐induced emission (AIE) fluorophore. Further, F1 and T1 selectively concentrate in cell nucleus, whereas B1 mainly stains the cytoplasm in live cell imaging. This work provides a general design strategy of versatile fluorophores for microenvironmental monitoring. [ABSTRACT FROM AUTHOR]

MicroRNA (miRNA) imaging in disease sites is vital to elucidate their role in cancer progression. However, limited tumor specificity remains a major barrier for traditional amplification approaches due to associated background signal leakage. Here, we report a generalizable approach via the combination of enzymatically triggered catalytic hairpin assembly with lipid nanoparticles (LNPs)‐based delivery strategy for tumor‐specific activation of signal amplification and therefore sensitive miRNA imaging. The signal amplification is established via engineering of traditional catalytic hairpin assembly with enzymatically activated motifs to achieve triggable miRNA imaging in cancer cells. Furthermore, by the introduction of LNPs to combat biological barriers, we demonstrate that the system enables amplified miRNA imaging in vivo with reduced off‐tumor signal, leading to enhanced tumor‐to‐background contrast compared with traditional methods. This approach that relies on specific triggers and controlled delivery to distinguish miRNA in cancer cells from normal cells should be useful in tumor diagnosis. [ABSTRACT FROM AUTHOR]

The insulin‐like growth factor‐1 receptor (IGF‐1R) is a receptor tyrosine kinase (RTK) that plays critical roles in cancer. Microarray, computational, thermodynamic, and cellular imaging studies reveal that activation of IGF‐1R by its cognate ligand IGF1 is inhibited by shorter, soluble heparan sulfate (HS) sequences (e.g., HS06), whereas longer polymeric chains do not inhibit the RTK, a phenomenon directly opposed to the traditional relationship known for GAG‐protein systems. The inhibition arises from smaller oligosaccharides binding in a unique pocket in the IGF‐1R ectodomain, which competes with the natural cognate ligand IGF1. This work presents a highly interesting observation on preferential and competing inhibition of IGF‐1R by smaller sequences, whereas polysaccharides are devoid of this function. These insights will be of major value to glycobiologists and anti‐cancer drug discoverers. [ABSTRACT FROM AUTHOR]

Lack of appropriate tools for visualizing cell membrane molecules at the nanoscale in a non‐invasive and label‐free fashion limits our understanding of many vital cellular processes. Here, we use tip‐enhanced Raman spectroscopy (TERS) to visualize the molecular distribution in pancreatic cancer cell (BxPC‐3) membranes in ambient conditions without labelling, with a spatial resolution down to ca. 2.5 nm. TERS imaging reveals segregation of phenylalanine‐, histidine‐, phosphatidylcholine‐, protein‐, and cholesterol‐rich BxPC‐3 cell membrane domains at the nm length‐scale. TERS imaging also showed a cell membrane region where cholesterol is mixed with protein. Interestingly, the higher resolution TERS imaging revealed that the molecular domains observed on the BxPC‐3 cell membrane are not chemically "pure" but also contain other biomolecules. These results demonstrate the potential of TERS for non‐destructive and label‐free imaging of cell membranes with nanoscale resolution. [ABSTRACT FROM AUTHOR]

We report here the development of clickable and highly near‐infrared (NIR) fluorescent lanthanide (Ln) complexes for bioorthogonal labeling of biomolecules. These azide‐ or alkyne‐functionalized Ln complexes are hydrophilic and fluorogenic, exhibiting a strong increase of NIR fluorescence upon conjugation with biomolecules. Metabolic labeling of biomolecules with azide or alkyne, followed by click labeling with the Ln complexes, enables NIR fluorescence (NIRF) imaging of DNA, RNA, proteins, and glycans in cells. Furthermore, multicolor imaging is performed by combining click‐labeling with the Ln complexes and immunostaining. In addition, the Ln complexes is compatible with click‐expansion microscopy (click‐ExM), which enables high‐resolution NIRF imaging of cellular glycoproteins. Finally, the Ln complexes can be used for time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS) imaging, thus achieving the first example of dual‐modal imaging combining NIRF and SIMS microscopies. [ABSTRACT FROM AUTHOR]

Environment‐responsive in situ synthesis of molecular fluorescent dyes is challenging. Herein, we develop a photoextension strategy to make trimethine cyanines with decent conversion efficiency (up to 81 %) using 1‐butyl 2,3,3‐trimethyl 3H‐indole derivatives as the sole precursors, and demonstrate a free radical mechanism. In the inducer‐extension stage, free radicals and reactive oxygen species (ROS) were able to mediate similar reactions with no assistance of light. We explored a Mito‐extension strategy to in situ synthesize trimethine cyanines in the living cells. The cellular ROS‐dependence provided a foundation for preferential cyanine expression in cancer cells. Finally, we applied an iodized precursor as an intrinsic ROS‐activated theranostic agent that integrated mitochondria‐targeted cyanine synthesis, cell imaging and phototherapy. [ABSTRACT FROM AUTHOR]

Self‐labeling protein tags can introduce advanced molecular motifs to specific cellular proteins. Here we introduce the third‐generation covalent TMP‐tag (TMP‐tag3) and showcase its comparison with HaloTag and SNAP‐tag. TMP‐tag3 is based on a proximity‐induced covalent Michael addition between an engineered Cys of E. coli dihydrofolate reductase (eDHFR) and optimized trimethoprim (TMP)–acrylamide conjugates with minimal linkers. Compared to previous versions, the TMP‐tag3 features an enhanced permeability when conjugated to fluorogenic spirocyclic rhodamines. As a small protein, the 18‐kD eDHFR is advantageous in tagging selected mitochondrial proteins which are less compatible with bulkier HaloTag fusions. The proximal N−C termini of eDHFR also enable facile insertion into various protein loops. TMP‐tag3, HaloTag, and SNAP‐tag are orthogonal to each other, collectively forming a toolbox for multiplexed live‐cell imaging of cellular proteins under fluorescence nanoscopy. [ABSTRACT FROM AUTHOR]

Real‐time optical imaging of immune cells can contribute to understanding their pathophysiological roles, which still remains challenging. Current sensitive chemiluminophores have issues of short half‐lives and low brightness, limiting their ability for in vivo longitudinal monitoring of immunological processes. To tackle these issues, we report benzoazole‐phenoxyl‐dioxetane (BAPD)‐based chemiluminophores with intramolecular hydrogen bonding for in vivo imaging of neutrophils. Compared with the classical counterpart, chemiluminescence half‐lives and brightness of BAPDs in the aqueous solution are increased by ∼ 33‐ and 8.2‐fold, respectively. Based on the BAPD scaffold, a neutrophil elastase‐responsive chemiluminescent probe is developed for real‐time imaging of neutrophils in peritonitis and psoriasis mouse models. Our study provides an intramolecular hydrogen bonding molecular design for improving the performance of chemiluminophores in advanced imaging applications. [ABSTRACT FROM AUTHOR]

Non‐conjugated fluorescent polymers have attracted great attention due to their excellent biocompatibility and environmental friendliness. However, it remains a huge challenge to obtain a polymer with high fluorescence quantum yield (QY) and multicolor emission simultaneously. Herein, we reported three kinds of nonaromatic hyperbranched polyborates (P1–P3) with multicolor emission, surprisingly, P2 also exhibits an unanticipated high QY (54.1 %). The natural bond orbital (NBO) analysis and density functional theory (DFT) calculation results revealed that the synergistic effect of rigid BO3 planar and flexible carbon chain, as well as the through‐space dative bond in supramolecular aggregate, were the key factors contributing to the ultrahigh QY of P2. Moreover, the applications of P2 in Fe3+ ions detection and cell imaging were also investigated. This work provides a new perspective for designing non‐conjugated fluorescent polymers with both high QY and multicolor emission. [ABSTRACT FROM AUTHOR]

Perylene diimides (PDIs), a well‐studied class of organic dyes, have a strong tendency to self‐aggregate in water, thus greatly restricting their phototheranostic applications. Herein, we report a water‐soluble PDI cyclophane "Gemini Box" (GBox‐14+), consisting of a central PDI chromophore enclosed by double‐sided cationic molecular straps. Owing to the effective spatial isolation, the chromophore self‐aggregation can be completely eliminated, even in a concentrated aqueous solution up to 2 mM. To our knowledge, GBox‐14+ represents an interesting example of a fluorescent PDI cyclophane in water, capable of being employed for lysosome‐targetable live‐cell imaging. More importantly, the highly concentrated aqueous solution of PDI radical anion can be significantly stabilized by GBox‐14+ to exhibit an excellent near‐infrared photothermal effect, which was further exploited for efficient and selective antibacterial applications. This work provides a new access to water‐soluble non‐aggregated organic dyes and promotes their potential biomedical applications. [ABSTRACT FROM AUTHOR]

In photoswitches that undergo fluorescence switching upon ultraviolet irradiation, photoluminescence and photoisomerization often occur simultaneously, leading to unstable fluorescence properties. Here, we successfully demonstrated reversible solid‐state triple fluorescence switching through "Pump–Trigger" multiphoton manipulation. A novel fluorescence photoswitch, BOSA‐SP, achieved green, yellow, and red fluorescence under excitation by pump light and isomerization induced by trigger light. The energy ranges of photoexcitation and photoisomerization did not overlap, enabling appropriate selection of the multiphoton light for "pump" and "trigger" photoswitching, respectively. Additionally, the large free volume of the spiropyran (SP) moiety in the solid state promoted reversible photoisomerization. Switching between "pump" and "trigger" light is useful for three‐color tunable switching cell imaging, which can be exploited in programmable fluorescence switching. Furthermore, we exploited reversible dual‐fluorescence switching in a single molecular system to successfully achieve two‐color super‐resolution imaging. [ABSTRACT FROM AUTHOR]

Simultaneous imaging of multiple microRNAs (miRNAs) in individual living cells is challenging due to the lack of spectrally distinct encoded fluorophores and non‐cytotoxic methods. We describe a multiplexed error‐robust combinatorial fluorescent label‐encoding method, termed fluorophores encoded error‐corrected labels (FluoELs), enabling multiplexed miRNA imaging in living cells with error‐correcting capability. The FluoELs comprise proportional dual fluorophores for encoding and a constant quantitative single fluorophore for error‐corrected quantification. Both are embedded in 260 nm core–shell silica nanoparticles modified with molecular beacon detection probes. The FluoELs are low cytotoxic and could accurately quantify and spatially resolve nine breast‐cancer‐related miRNAs and evaluate their coordination. The FluoELs enabled a single‐cell analysis platform to evaluate miRNA expression profiles and the molecular mechanisms underlying miRNA‐associated diseases. [ABSTRACT FROM AUTHOR]

Lowly expressed analyte in complex cytoplasmic milieu necessitates the development of non‐enzymatic autocatalytic DNA circuits with high amplification and anti‐interference performance. Herein, we engineered a versatile and robust stimuli‐responsive autocatalytic hybridization assembly (AHA) circuit for high‐performance in vivo bioanalysis. Under a moderately confined condition, the initiator motivated the autonomous and cooperative cross‐activation of cascade hybridization reaction and catalytic DNA assembly for generating an exponentially amplified readout without the parasite steric hindrance and random diffusion side effects. The AHA circuit was systematically investigated by a series of experimental studies and theoretical simulations. The successively guaranteed target recognition and synergistically accelerated signal‐amplification enabled the sensitive and selective detection of analyte, and realized the robust miRNA imaging in living cells and mice. This autocatalytic DNA circuit could substantially expand the toolbox for accurate diagnosis and programmable therapeutics. [ABSTRACT FROM AUTHOR]

We report a photodynamic therapy driven by electrochemiluminescence (ECL). The luminescence generated by Ru(bpy)32+ and co‐reactant tripropylamine (TPA) pair acts as both optical readout for ECL imaging, and light source for the excitation of photosensitizer to produce reactive oxygen species (ROS) in photodynamic therapy (PDT) system. The ECL‐driven PDT (ECL‐PDT) relies on the effective energy transfer from ECL emission to photosensitizer chlorin e6 (Ce6), which sensitizes the surrounding O2 into ROS. The dynamic process of gradual morphological changes, the variation of cell‐matrix adhesions, as well as the increase of cell membrane permeability in the process of ECL‐PDT were monitored under ECL microscopy (ECLM) with good spatiotemporal resolution. Combining real‐time imaging with ECL‐PDT, this new strategy provides not only new insights into dynamic cellular processes, but also promising potential of ECL in clinical applications. [ABSTRACT FROM AUTHOR]

Inside living cells, regulation of catalytic activity of artificial enzymes remains challenging due to issues such as biocompatibility, efficiency, and stability of the catalyst, by which the practical applications of artificial enzymes have been severely hindered. Here, an artificial enzyme, PTT‐SGH, with responsiveness to reactive oxygen species (ROS), was obtained by introducing a catalytic histidine residue to pentaerythritol tetra(3‐mercaptopropionate) (PTT). The artificial enzyme formed large aggregates in cells via the intracellular ROS‐mediated oxidation of thiol groups. The process was significantly facilitated in tumor cells because of the higher ROS concentration in the tumor microenvironment. The catalytic activity of this artificial enzyme was intensively enhanced through deprotonation of cross‐linked PTT‐SGH, which showed typical esterase activities. Selective fluorescence imaging of tumor cells was achieved using the artificial enzyme to trigger the cleavage of the ester bond of the caged fluorophore inside living cells. [ABSTRACT FROM AUTHOR]

The cell membrane is a dynamic and heterogeneous structure composed of distinct sub‐compartments. Within these compartments, preferential interactions occur among various lipids and proteins. Currently, it is still challenging to image these short‐lived membrane complexes, especially in living cells. In this work, we present a DNA‐based probe, termed "DNA Zipper", which allows the membrane order and pattern of transient interactions to be imaged in living cells using standard fluorescence microscopes. By fine‐tuning the length and binding affinity of DNA duplex, these probes can precisely extend the duration of membrane lipid interactions via dynamic DNA hybridization. The correlation between membrane order and the activation of T‐cell receptor signaling has also been studied. These programmable DNA probes function after a brief cell incubation, which can be easily adapted to study lipid interactions and membrane order during different membrane signaling events. [ABSTRACT FROM AUTHOR]

Methods for the site‐selective labeling of long, native RNAs are needed for studying mRNA biology and future therapies. Current approaches involve engineering RNA sequences, which may alter folding, or are limited to specific sequences or bases. Here, we describe a versatile strategy for mRNA conjugation via a novel DNA‐tiling approach. The method, TRAIL, exploits a pool of "protector" oligodeoxynucleotides to hybridize and block the mRNA, combined with an "inducer" DNA that extrudes a reactive RNA loop for acylation at a predetermined site. Using TRAIL, an azido‐acylimidazole reagent was employed for labeling and controlling RNA for multiple applications in vitro and in cells, including analysis of RNA‐binding proteins, imaging mRNA in cells, and analysis and control of translation. The TRAIL approach offers an efficient and accessible way to label and manipulate RNAs of virtually any length or origin without altering native sequence. [ABSTRACT FROM AUTHOR]

Many bioconjugation strategies for DNA oligonucleotides and antibodies suffer limitations, such as site‐specificity, stoichiometry and hydrolytic instability of the conjugates, which makes them unsuitable for biological applications. Here, we report a new platform for the preparation of DNA‐antibody bioconjugates with a simple benzoylacrylic acid pentafluorophenyl ester reagent. Benzoylacrylic‐labelled oligonucleotides prepared with this reagent can be site‐specifically conjugated to a range of proteins and antibodies through accessible cysteine residues. The homogeneity of the prepared DNA‐antibody bioconjugates was confirmed by a new LC‐MS protocol and the bioconjugate probes were used in fluorescence or super‐resolution microscopy cell imaging experiments. This work demonstrates the versatility and robustness of our bioconjugation protocol that gives site‐specific, well‐defined and plasma‐stable DNA‐antibody bioconjugates for biological applications. [ABSTRACT FROM AUTHOR]

Although super‐resolution imaging offers an opportunity to visualize cellular structures and organelles at the nanoscale level, cellular heterogeneity and unpredictability still pose a significant challenge in the dynamic imaging of live cells. It is thus vital to develop better‐performing and more photostable probes for long‐term super‐resolution imaging. Herein, we report a probe, LD‐FG, for imaging lipid droplet (LD) dynamics using structured illumination microscopy (SIM). LD‐FG allows wash‐free imaging of LDs, owing to a hydrogen‐bond sensitive fluorogenic response. The replacement of photobleached LD‐FG by intact probe molecules outside the LDs ensures the long‐time stability of the fluorescence imaging. With this buffering fluorogenic probe, fast and unpredictable dynamic processes of LDs can be visualized. Using this probe, two LD coalescence modes were discovered. The dynamic imaging also allowed us to propose a new model of LD maturation during adipocyte differentiation, i.e. a fast LD coalescence followed by a slow ripening step. The excellent performance of LD‐FG makes the buffer strategy an effective method for designing fluorescent probes for cell dynamic imaging. [ABSTRACT FROM AUTHOR]

Guanosine tetra‐ and pentaphosphate, (p)ppGpp, are important alarmone nucleotides that regulate bacterial survival in stressful environment. A direct detection of (p)ppGpp in living cells is critical for our understanding of the mechanism of bacterial stringent response. However, it is still challenging to image cellular (p)ppGpp. Here, we report RNA‐based fluorescent sensors for the live‐cell imaging of (p)ppGpp. Our sensors are engineered by conjugating a recently identified (p)ppGpp‐specific riboswitch with a fluorogenic RNA aptamer, Broccoli. These sensors can be genetically encoded and enable direct monitoring of cellular (p)ppGpp accumulation. Unprecedented information on cell‐to‐cell variation and cellular dynamics of (p)ppGpp levels is now obtained under different nutritional conditions. These RNA‐based sensors can be broadly adapted to study bacterial stringent response. [ABSTRACT FROM AUTHOR]

N6‐methyladenosine (m6A) modification—the most prevalent mammalian RNA internal modification—plays key regulatory roles in mRNA metabolism. Current approaches for m6A modified RNA analysis limit at bulk‐population level, resulting in a loss of spatiotemporal and cell‐to‐cell variability information. Here we proposed a m6A‐specific in situ hybridization mediated proximity ligation assay (m6AISH‐PLA) for cellular imaging of m6A RNA, allowing to identify m6A modification at specific location in RNAs and image m6A RNA with single‐cell and single‐molecule resolution. Using m6AISH‐PLA, we investigated the m6A level and subcellular location of HSP70 RNA103‐m6A in response to heat shock stress, and found an increased m6A modified ratio and an increased distribution ratio in cytoplasm under heat shock. m6AISH‐PLA can serve in the study of m6A RNA in single cells for deciphering epitranscriptomic mechanisms and assisting clinical diagnosis. [ABSTRACT FROM AUTHOR]

DNA nanotechnology provides powerful tools for developing cancer theranostics. Here we introduce the autonomous surface‐nucleolin‐guided HCR that leads to the polymerization of G‐quadruplex polymer chains, in which the ZnII‐protoporphyrin IX is intercalated. We demonstrate that MDA‐MB‐231 (Triple Negative Breast Cancer cells, TNBC) with overexpressed surface nucleolin were able to induce HCR leading to the formation of the ZnIIPPIX‐loaded G‐quadruplex polymer chains, while the M10 epithelial breast cells served as control. The ZnIIPPIX‐loaded nanowires allow the selective imaging of TNBC, and their permeation into the TNBC leads to selective cytotoxicity and guided photodynamic therapy toward the cancer cells due to structural perturbation of the membranes. The aptamer‐guided HCR‐generated G‐quadruplex polymer chains may serve as a versatile tool to target TNBC featuring poor prognosis and high pathological risk of recurrence, thus offering a promising theranostic platform. [ABSTRACT FROM AUTHOR]

Fluorescent chemosensors are powerful imaging tools in the fields of life sciences and engineering. Based on the principle of supramolecular chemistry, indicator displacement assay (IDA) provides an alternative approach for constructing and optimizing chemosensors, which has the advantages of simplicity, tunability, and modularity. However, the application of IDA in bioimaging continues to face a series of challenges, including interfering signals, background noise, and inconsistent spatial location. Accordingly, we herein report a supramolecular bioimaging strategy of Förster resonance energy transfer (FRET)‐assisted IDA by employing macrocyclic amphiphiles as the operating platform. By merging FRET with IDA, the limitations of IDA in bioimaging were addressed. As a proof of concept, the study achieved mitochondria‐targeted imaging of adenosine triphosphate in live cells with signal amplification. This study opens a non‐covalent avenue for bioimaging with advancements in tunability, generality, and simplicity, apart from the covalent approach. [ABSTRACT FROM AUTHOR]

We synthesized the first multifunctionalized phosphoinositide polyphosphate derivatives featuring a photo‐removable protecting group ("cage"), a photo‐crosslinkable diazirine group, and a terminal alkyne group useful for click chemistry. We demonstrate that the lipid derivatives readily enter cells. After photo‐crosslinking, cell fixation and fluorescent tagging via click chemistry, we determined the intracellular location of the lipid derivatives before and after uncaging of the lipids. We find that there is rapid trafficking of PI(3,4)P2 and PI(3,4,5)P3 derivatives to the plasma membrane, opening the intriguing possibility that there is active transport of these lipids involved. We employed the photo‐crosslinking and click chemistry functions to analyze the proteome of PI(3,4,5)P3‐binding proteins. From the latter, we validated by RNAi that the putative lipid binding proteins ATP11A and MPP6 are involved in the transport of PI(3,4,5)P3 to the plasma membrane. [ABSTRACT FROM AUTHOR]

Photoactivated trimerization of 2,3,3‐trimethyl‐3H‐indole derivatives created near infrared fluorophore Cy5. The synthetic method is air‐tolerant, photosensitizer free, metal free, and condensation agent free. Living cells make Cy5 on a time scale of minutes under white light irradiation at a low power intensity, with the monomer as the only exogenous agent. The new method is promising to find applications in cell studies for in situ spatiotemporally controlled fluorescence imaging in living cells. [ABSTRACT FROM AUTHOR]

Despite increasing awareness of the biological impacts of long‐chain fatty acyl‐CoA esters (LCACoAs), our knowledge about the subcellular distribution and regulatory functions of these acyl‐CoA molecules is limited by a lack of methods for detecting LCACoAs in living cells. Here, we report development of a genetically encoded fluorescent sensor that enables ratiometric quantification of LCACoAs in living cells and subcellular compartments. We demonstrate how this FadR‐cpYFP fusion "LACSer sensor" undergoes LCACoA‐induced conformational changes reflected in easily detectable fluorescence responses, and show proof‐of‐concept for real‐time monitoring of LCACoAs in human cells. Subsequently, we applied LACSer in scientific studies investigating how disruption of ACSL enzymes differentially reduces cytosolic and mitochondrial LCACoA levels, and show how genetic disruption of an acyl‐CoA binding protein (ACBP) alters mitochondrial accumulation of LCACoAs. [ABSTRACT FROM AUTHOR]

Cell junctions are protein structures located at specific cell membrane domains that determine key processes in multicellular development. Here we report spatially selective imaging of cell junctions by electrochemiluminescence (ECL) microscopy. By regulating the concentrations of luminophore and/or co‐reactant, the thickness of ECL layer can be controlled to match with the spatial location of different cell junctions. At a low concentration of luminophore, ECL generation is confined to the electrode surface, thus revealing only cell–matrix adhesions at the bottom of cells. While at a high concentration of luminophore, the ECL layer can be remarkably extended by decreasing the co‐reactant concentration, thus allowing the sequential imaging of cell–matrix and cell–cell junctions at the bottom and near the apical surface of cells, respectively. This strategy not only provides new insights into the ECL mechanisms but also promises wide applications of ECL microscopy in bioimaging. [ABSTRACT FROM AUTHOR]

Ultrabright fluorescent nanoparticles (NPs) hold great promise for demanding bioimaging applications. Recently, extremely bright molecular crystals of cationic fluorophores were obtained by hierarchical coassembly with cyanostar anion‐receptor complexes. These small‐molecule ionic isolation lattices (SMILES) ensure spatial and electronic isolation to prohibit aggregation quenching of dyes. We report a simple, one‐step supramolecular approach to formulate SMILES materials into NPs. Rhodamine‐based SMILES NPs stabilized by glycol amphiphiles show high fluorescence quantum yield (30 %) and brightness per volume (5000 M−1 cm−1/nm3) with 400 dye molecules packed into 16‐nm particles, corresponding to a particle absorption coefficient of 4×107 M−1 cm−1. UV excitation of the cyanostar component leads to higher brightness (>6000 M−1 cm−1/ nm3) by energy transfer to rhodamine emitters. Coated NPs stain cells and are thus promising for bioimaging. [ABSTRACT FROM AUTHOR]

A range of unprocessed, reducing sugar substrates (mono‐, di‐, and trisaccharides) is shown to take part in a straightforward four‐step synthetic route to water‐soluble, uncharged BODIPY derivatives with unimpaired chiral integrity and high fluorescence efficiency. A wide compatibility with several postfunctionalizations is demonstrated, thus suggesting a universal utility of the multifunctional glycoconjugates, which we call GlycoBODIPYs. Knoevenagel condensations are able to promote a red‐shift in the spectra, thereby furnishing strongly fluorescent red and far‐red glycoconjugates of high hydrophilicity. The synthetic outcome was studied by X‐ray crystallography and by comprehensive photophysical investigations in several solvent systems. Furthermore, cell experiments illustrate efficient cell uptake and demonstrate differential cell targeting as a function of the integrated chiral information. [ABSTRACT FROM AUTHOR]

Sucrose is the main saccharide used for long‐distance transport in plants and plays an essential role in energy metabolism; however, there are no analogues for real‐time imaging in live cells. We have optimised a synthetic approach to prepare sucrose analogues including very small (≈50 Da or less) Raman tags in the fructose moiety. Spectroscopic analysis identified the alkyne‐tagged compound 6 as a sucrose analogue recognised by endogenous transporters in live cells and with higher Raman intensity than other sucrose derivatives. Herein, we demonstrate the application of compound 6 as the first optical probe to visualise real‐time uptake and intracellular localisation of sucrose in live plant cells using Raman microscopy. [ABSTRACT FROM AUTHOR]

Live cell imaging of lysosome positioning and motility is critical to studying lysosome status and function for pharmacological interventions. To create a super stable lysosomal probe for long‐term live cell imaging, we have designed and synthesized an aromatic‐peptide‐conjugated cyclometalated iridium(III) complex that emits light via π–π stacking oriented self‐assembly in water at extremely low concentration. Through endocytic trafficking, self‐assemblies are transformed from nanoparticles into sturdily packed networks that are stabilized in lysosomal acidic environment. Upon short time/low dose treatment of the iridium complex at passage 0, live cell lysosomal tracking is applicable beyond the 14th passage of cells with high labelling rate and a mild decline in luminescence intensity. The illuminated lysosomes are trackable using super‐resolution imaging to study their response to cellular processes. [ABSTRACT FROM AUTHOR]

Super‐resolution optical fluctuation imaging (SOFI) is a super‐resolution microscopy technique that overcomes the diffraction limit by analyzing intensity fluctuations of statistically independent emitters in a time series of images. The final images are background‐free and show confocality and enhanced spatial resolution (super‐resolution). Fluorophore photobleaching, however, is a key limitation for recording long time series of images that will allow for the calculation of higher order SOFI results with correspondingly increased resolution. Here, we demonstrate that photobleaching can be circumvented by using fluorophore labels that reversibly and transiently bind to a target, and which are being replenished from a buffer which serves as a reservoir. Using fluorophore‐labeled short DNA oligonucleotides, we labeled cellular structures with target‐specific antibodies that contain complementary DNA sequences and record the fluctuation events caused by transient emitter binding. We show that this concept bypasses extensive photobleaching and facilitates two‐color imaging of cellular structures with SOFI. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells are immune cells that can kill certain types of cancer cells. Adoptive transfer of NK cells represents a promising immunotherapy for malignant tumours; however, there is a lack of methods to validate anti‐tumour activity of NK cells in vivo. Herein, we report a new chemiluminescent probe to image in situ the granzyme B‐mediated killing activity of NK cells against cancer cells. We have optimised a granzyme B‐specific construct using an activatable phenoxydioxetane reporter so that enzymatic cleavage of the probe results in bright chemiluminescence. The probe shows high selectivity for active granzyme B over other proteases and higher signal‐to‐noise ratios than commercial fluorophores. Finally, we demonstrate that the probe can detect NK cell activity in mouse models, being the first chemiluminescent probe for in vivo imaging of NK cell activity in live tumours. [ABSTRACT FROM AUTHOR]

Protein lipoylation is a post‐translational modification of emerging importance in both prokaryotes and eukaryotes. However, labeling and large‐scale profiling of protein lipoylation remain challenging. Here, we report the development of iLCL (iodoacetamide‐assisted lipoate‐cyclooctyne ligation), a chemoselective reaction that enables chemical tagging of protein lipoylation. We demonstrate that the cyclic disulfide of lipoamide but not linear disulfides can selectively react with iodoacetamide to produce sulfenic acid, which can be conjugated with cyclooctyne probes. iLCL enables tagging of lipoylated proteins for gel‐based detection and cellular imaging. Furthermore, we apply iLCL for proteomic profiling of lipoylated proteins in both bacteria and mammalian cells. In addition to all of the eight known lipoylated proteins, we identified seven candidates for novel lipoylated proteins. The iLCL strategy should facilitate uncovering the biological function of protein lipoylation. [ABSTRACT FROM AUTHOR]

Spatial positioning and proximity of relevant biomolecules such as DNA epigenetic marks are fundamental to a deeper understanding of life. However, it remains poorly explored and technically challenging. Here we report the pairwise proximity‐differentiated visualization of single‐cell 5‐formylcytosine (5fC) and 5‐hydroxymethylcytosine (5hmC). These two marks on chromatin in fixed cells are successively labeled and crosslinked with their DNA primer probes via click chemistry. Based on a pairwise proximity‐differentiated mechanism, proximal 5fC/5hmC sites and residual 5fC or 5hmC sites are encoded with respective circularized barcodes. These barcodes are simultaneously amplified for multiplexed single‐molecule imaging. We thus demonstrate the differentiated visualization of 5fC or 5hmC spatial positioning and their pairwise proximity in single cells. Such multi‐level subcellular information may provide insights into regulation functions and mechanisms of chromatin modifications, and the spatial proximity can expose the potential crosstalk or interaction between their reader proteins. [ABSTRACT FROM AUTHOR]

In the article "Inside Back Cover: Ultrafluorogenic Monochromophore-Type BODIPY-Tetrazine Series for Dual-Color Bioorthogonal Imaging with a Single Probe," the authors discuss the development of a series of fluorogenic BODIPY-Tz probes for dual-color bioorthogonal imaging. The probes demonstrated selective fluorescence enhancement in various wavelengths, including the far-red region, and allowed for dual-color bioorthogonal cellular imaging using a single probe. The authors also discovered the origin of the probes' selective behavior and observed a unique fluorescence recovery in hydrophobic media. This research opens up exciting possibilities for bioorthogonal imaging with improved efficiency and simplicity. [Extracted from the article]

In a research article published in Angewandte Chemie International Edition, Rachel C. Evans et al. demonstrate the use of ultra-small nanoparticle probes for anti-Stokes fluorescence lifetime imaging in living cells. These probes are based on triplet-triplet annihilation upconversion (TTA-UC) chromophores encapsulated in an organic-inorganic ureasil host. The researchers found that the nanoparticles can be used to map local oxygen diffusion across the subcellular structure, as indicated by fluctuations in the upconversion lifetime in stained cells. The study provides valuable insights into the potential applications of these nanoparticles in imaging techniques. [Extracted from the article]