A H-bond strategy to develop acid-resistant photoswitchable rhodamine spirolactams for super-resolution single-molecule localization microscopy

Photo-uncaging Triggers on Self-Blinking to Control Single-Molecule Fluorescence Kinetics for Super-resolution Imaging

Super-resolution imaging, especially a single-molecule localization approach, has raised a fluorophore engineering revolution chasing sparse single-molecule dark-bright blinking transforms. Yet, it is a challenge to structurally devise fluorophores manipulating the single-molecule blinking kinetics. In this pursuit, we have developed a triggering strategy by innovatively integrating the photoactivatable nitroso-caging strategy into self-blinking sulfonamide to form a nitroso-caged sulfonamide rhodamine (NOSR). Our fluorophore demonstrated controllable self-blinking events upon phototriggered caging unit release. This exceptional blink kinetics improved the super-resolution imaging integrity on microtubules compared to self-blinking analogues. With the aid of paramount single-molecule fluorescence kinetics, we successfully reconstructed the ring structure of nuclear pores and the axial morphology of mitochondrial outer membranes. We foresee that our synthetic approach of photoactivation and self-blinking would facilitate rhodamine devising for super-resolution imaging.

A Nonlinear Photochromic Reaction Based on Sensitizer-Free Triplet-Triplet Annihilation in a Perylene-Substituted Rhodamine Spirolactam

Nonlinear photochromic reactions that work with weak incoherent light are important for molecular operations with high spatial resolution and multiple photofunctions based on single molecules. However, nonlinear photochromic compounds generally require complex molecular design, restricting accessibility in various fields. Herein, we report nonlinear photochromic properties in a perylene-substituted rhodamine spirolactam derivative (Rh-Pe), which is synthesized from rhodamine B in facile procedures. Direct excitation of Rh-Pe produces the triplet excited state via the charge-transfer (CT) state. The triplet excited state causes triplet-triplet annihilation to bring the generation of the intensely colored ring-open form with nonlinear behavior. Furthermore, green- and red-light-induced photochromism was achieved in Rh-Pe using triplet sensitizers, although Rh-Pe can be directly excited only by ultraviolet and blue light. Our findings are expected to contribute to the development of photofunctional materials showing nonlinear behavior and low-energy light responsivity.

Squaraine Dyes Exhibit Spontaneous Fluorescence Blinking That Enables Live-Cell Nanoscopy

Hampered by their susceptibility to nucleophilic attack and chemical bleaching, electron-deficient squaraine dyes have long been considered unsuitable for biological imaging. This study unveils a surprising twist: in aqueous environments, bleaching is not irreversible but rather a reversible spontaneous quenching process. Leveraging this new discovery, we introduce a novel deep-red squaraine probe tailored for live-cell super-resolution imaging. This probe enables single-molecule localization microscopy (SMLM) under physiological conditions without harmful additives or intense lasers and exhibits spontaneous blinking orchestrated by biological nucleophiles, such as glutathione or hydroxide anion. With a low duty cycle (∼0.1%) and high-emission rate (∼6 × 104 photons/s under 400 W/cm2), the squaraine probe surpasses the benchmark Cy5 dye by 4-fold and Si-rhodamine by a factor of 1.7 times. Live-cell SMLM with the probe reveals intricate structural details of cell membranes, which demonstrates the high potential of squaraine dyes for next-generation super-resolution imaging.

Chemical Approaches to Optimize the Properties of Organic Fluorophores for Imaging and Sensing

Organic fluorophores are indispensable tools in cells, tissue and in vivo imaging, and have enabled much progress in the wide range of biological and biomedical fields. However, many available dyes suffer from insufficient performances, such as short absorption and emission wavelength, low brightness, poor stability, small Stokes shift, and unsuitable permeability, restricting their application in advanced imaging technology and complex imaging. Over the past two decades, many efforts have been made to improve these performances of fluorophores. Starting with the luminescence principle of fluorophores, this review clarifies the mechanisms of the insufficient performance for traditional fluorophores to a certain extent, systematically summarizes the modified approaches of optimizing properties, highlights the typical applications of the improved fluorophores in imaging and sensing, and indicates existing problems and challenges in this area. This progress not only proves the significance of improving fluorophores properties, but also provide a theoretical guidance for the development of high-performance fluorophores.

Hydroxyl-group functionalized phenanthroline diimides as efficient masking agents for Am(III)/Eu(III) separation under harsh conditions

The separation of Lns(III) from radioactive Ans(III) in high-level liquid waste remains a formidable hydrometallurgical challenge. Water-soluble ligands are believed to be new frontiers in the search of efficient Lns/Ans separation ligands to close the nuclear fuel cycles and dealing with current existing nuclear waste. Currently, the development of hydrophilic ligands far lags behind their lipophilic counterparts due to their complicated synthetic procedures, inferior extraction performances, and acid tolerances. In this paper, we have showed a series of hydroxyl-group functionalized phenanthroline diimides were efficient masking agents for Am(III)/Eu(III) separation under high acidity (˃ 1 M HNO3). Record high SFEu(III)/Am(III) of 162 and 264 were observed for Phen-2DIC2OH and Phen-2DIC4OH in 1.25 M HNO3 which represents the best Eu(III)/Am(III) separation performance at this acidity. UV-vis absorption, NMR and TRLFS titrations were conducted to elucidate the predominant of 1:1 ligand/metal species under extraction conditions. X-ray data of both the ligand and Eu(III) complex together with DFT calculations revealed the superior extraction performances and selectivities. The current reported hydrophilic ligands were easy to prepare and readily to scale-up, acid tolerant and highly efficient, together with their CHON-compatible nature make them promising candidates in the development of advanced separation processes.

Xanthene, cyanine, oxazine and BODIPY: the four pillars of the fluorophore empire for super-resolution bioimaging

In the realm of biological research, the invention of super-resolution microscopy (SRM) has enabled the visualization of ultrafine sub-cellular structures and their functions in live cells at the nano-scale level, beyond the diffraction limit, which has opened up a new window for advanced biomedical studies to unravel the complex unknown details of physiological disorders at the sub-cellular level with unprecedented resolution and clarity. However, most of the SRM techniques are highly reliant on the personalized special photophysical features of the fluorophores. In recent times, there has been an unprecedented surge in the development of robust new fluorophore systems with personalized features for various super-resolution imaging techniques. To date, xanthene, cyanine, oxazine and BODIPY cores have been authoritatively utilized as the basic fluorophore units in most of the small-molecule-based organic fluorescent probe designing strategies for SRM owing to their excellent photophysical characteristics and easy synthetic acquiescence. Since the future of next-generation SRM studies will be decided by the availability of advanced fluorescent probes and these four fluorescent building blocks will play an important role in progressive new fluorophore design, there is an urgent need to review the recent advancements in designing fluorophores for different SRM methods based on these fluorescent dye cores. This review article not only includes a comprehensive discussion about the recent developments in designing fluorescent probes for various SRM techniques based on these four important fluorophore building blocks with special emphasis on their effective integration into live cell super-resolution bio-imaging applications but also critically evaluates the background of each of the fluorescent dye cores to highlight their merits and demerits towards developing newer fluorescent probes for SRM.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Spontaneously Blinking Rhodamine Dyes for Single-Molecule Localization Microscopy

Single-molecule localization microscopy (SMLM) has found extensive applications in various fields of biology and chemistry. As a vital component of SMLM, fluorophores play an essential role in obtaining super-resolution fluorescence images. Recent research on spontaneously blinking fluorophores has greatly simplified the experimental setups and extended the imaging duration of SMLM. To support this crucial development, this review provides a comprehensive overview of the development of spontaneously blinking rhodamines from 2014 to 2023, as well as the key mechanistic aspects of intramolecular spirocyclization reactions. We hope that by offering insightful design guidelines, this review will contribute to accelerating the advancement of super-resolution imaging technologies.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

SIM imaging resolves endocytosis of SARS-CoV-2 spike RBD in living cells

It is urgent to understand the infection mechanism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for the prevention and treatment of COVID-19. The infection of SARS-CoV-2 starts when the receptor-binding domain (RBD) of viral spike protein binds to angiotensin-converting enzyme 2 (ACE2) of the host cell, but the endocytosis details after this binding are not clear. Here, RBD and ACE2 were genetically coded and labeled with organic dyes to track RBD endocytosis in living cells. The photostable dyes enable long-term structured illumination microscopy (SIM) imaging and to quantify RBD-ACE2 binding (RAB) by the intensity ratio of RBD/ACE2 fluorescence. We resolved RAB endocytosis in living cells, including RBD-ACE2 recognition, cofactor-regulated membrane internalization, RAB-bearing vesicle formation and transport, RAB degradation, and downregulation of ACE2. The RAB was found to activate the RBD internalization. After vesicles were transported and matured within cells, RAB was finally degraded after being taken up by lysosomes. This strategy is a promising tool to understand the infection mechanism of SARS-CoV-2.

Accelerated MINFLUX Nanoscopy, through Spontaneously Fast-Blinking Fluorophores

The introduction of MINFLUX nanoscopy allows single molecules to be localized with one nanometer precision in as little as one millisecond. However, current applications have so far focused on increasing this precision by optimizing photon collection, rather than minimizing the localization time. Concurrently, commonly used fluorescent switches are specifically designed for stochastic methods (e.g., STORM), optimized for a high photon yield and rather long on-times (tens of milliseconds). Here, accelerated MINFLUX nanoscopy with up to a 30-fold gain in localization speed is presented. The improvement is attained by designing spontaneously blinking fluorescent markers with remarkably fast on-times, down to 1-3 ms, matching the iterative localization process used in a MINFLUX microscope. This design utilizes a silicon rhodamine amide core, shifting the spirocyclization equilibrium toward an uncharged closed form at physiological conditions and imparting intact live cell permeability, modified with a fused (benzo)thiophene spirolactam fragment. The best candidate for MINFLUX microscopy (also suitable for STORM imaging) is selected through detailed characterization of the blinking behavior of single fluorophores, bound to different protein tags. Finally, optimization of the localization routines, customized to the fast blinking times, renders a significant speed improvement on a commercial MINFLUX microscope.

Subtle Structural Translation Magically Modulates the Super-Resolution Imaging of Self-Blinking Rhodamines

The evolution of super-resolution imaging techniques is benefited from the ongoing competition for optimal rhodamine fluorophores. Yet, it seems blind to construct the desired rhodamine molecule matching the imaging need without the knowledge on imaging impact of even the minimum structural translation. Herein, we have designed a pair of self-blinking sulforhodamines (STMR and SRhB) with the bare distinction of methyl or ethyl substituents and engineered them with Halo protein ligands. Although the two possess similar spectral properties (λ_ab, λ_fl, ϕ, etc.), they demonstrated unique single-molecule characteristics preferring to individual imaging applications. Experimentally, STMR with high emissive rates was qualified for imaging structures with rapid dynamics (endoplasmic reticulum, and mitochondria), and SRhB with prolonged on-times and photostability was suited for relatively "static" nuclei and microtubules. Using this new knowledge, the mitochondrial morphology during apoptosis and ferroptosis was first super-resolved by STMR. Our study highlights the significance of even the smallest structural modification to the modulation of super-resolution imaging performance and would provide insights for future fluorophore design.

Small-molecule fluorogenic probes for mitochondrial nanoscale imaging

Mitochondria are inextricably linked to the development of diseases and cell metabolism disorders. Super-resolution imaging (SRI) is crucial in enhancing our understanding of mitochondrial ultrafine structures and functions. In addition to high-precision instruments, super-resolution microscopy relies heavily on fluorescent materials with unique photophysical properties. Small-molecule fluorogenic probes (SMFPs) have excellent properties that make them ideal for mitochondrial SRI. This paper summarizes recent advances in the field of SMFPs, with a focus on the chemical and spectroscopic properties required for mitochondrial SRI. Finally, we discuss future challenges in this field, including the design principles of SMFPs and nanoscopic techniques.

Photochemical Mechanisms of Fluorophores Employed in Single-Molecule Localization Microscopy

Decoding cellular processes requires visualization of the spatial distribution and dynamic interactions of biomolecules. It is therefore not surprising that innovations in imaging technologies have facilitated advances in biomedical research. The advent of super-resolution imaging technologies has empowered biomedical researchers with the ability to answer long-standing questions about cellular processes at an entirely new level. Fluorescent probes greatly enhance the specificity and resolution of super-resolution imaging experiments. Here, we introduce key super-resolution imaging technologies, with a brief discussion on single-molecule localization microscopy (SMLM). We evaluate the chemistry and photochemical mechanisms of fluorescent probes employed in SMLM. This Review provides guidance on the identification and adoption of fluorescent probes in single molecule localization microscopy to inspire the design of next-generation fluorescent probes amenable to single-molecule imaging.

pH-Responsive Drug Delivery and Imaging Study of Hybrid Mesoporous Silica Nanoparticles

A system of pH-responsive and imaging nanocarriers was developed using mesoporous silica nanoparticles (MSNs), in which gadolinium (Gd) was doped through in situ doping (Gd₂O₃@MSN). Sodium alginate (SA) was attached to the surfaces of the amino groups of MSNs (NH₂-Gd₂O₃@MSN) through the electrostatic adsorption between the amino groups and the carboxyl groups with the formation of hybrid SA-Gd₂O₃@MSN nanoparticles (NPs). The SA-coated NPs were spherical or near-spherical in shape with an average size of nearly 83.2 ± 8.7 nm. The in vitro drug release experiments of a model rhodamine B (RhB) cargo were performed at different pH values. The result confirmed the pH-responsiveness of the nanocarriers. The results of the cytotoxicity studies indicated that the SA-Gd₂O₃@MSN NPs were not cytotoxic by themselves. The results of the in vivo safety evaluation and the hemolysis assay confirmed that the system is highly biocompatible. It is noteworthy that the T1 contrast of the system was significantly enhanced by the Gd, as indicated by the result of the MR imaging. This study confirms that the synthesized hybrid nanosystem is promising for pH-responsive drug delivery and MR imaging for cancer diagnosis and treatment.

Design and Synthesis of RhodIndolizine Dyes with Improved Stability and Shortwave Infrared Emission up to 1250 nm

The design of shortwave infrared (SWIR) emissive small molecules with good stability in water remains an important challenge for fluorescence biological imaging applications. A series of four SWIR emissive rhodindolizine (RI) dyes were rationally designed and synthesized to probe the effects of nonconjugated substituents, conjugated donor groups, and nanoencapsulation in a water-soluble polymer on the stability and optical properties of the dyes. Steric protecting groups were added at the site of a significant LUMO presence to probe the effects on stability. Indolizine donor groups with added dimethylaniline groups were added to reduce the electrophilicity of the dyes toward nucleophiles such as water. All of the dyes were found to absorb (920-1096 nm peak values) and emit (1082-1256 nm peak values) within the SWIR region. Among xanthene-based emissive dyes, emission values >1200 nm are exceptional with 1256 nm peak emission being a longer emission than the recent record setting VIX-4 xanthene-based dye. Half-lives were improved from ∼5 to >24 h through the incorporation of either steric-based core protection groups or donors with increased donation strength. Importantly, the nanoencapsulation of the dyes in a water-soluble surfactant (Triton-X) allows for the use of these dyes in biological imaging applications.

Comparison of rhodamine 6G, rhodamine B and rhodamine 101 spirolactam based fluorescent probes: A case of pH detection

Ring-opening reaction of rhodamine spirolactam has been widely applied to construct fluorescent probes. The fluorescence properties of the probe were finely tuned for specific purpose through changing the rhodamine fluorophore. However, the influence on response range and kinetic parameters of the probe during the change has been seldom discussed. Herein, we took pH detection as an example and constructed spirolactam based probes (RLH A-C) with Rhodamine 6G, Rhodamine B and Rhodamine 101. The pK_a values and observed rate constant k_obs of RLH A-C were determined and found to negatively correlated with the calculated Gibbs free energy differences ΔG_C-O and ΔG_TS respectively. The potential applications of RLH A-C in imaging acidic microenvironment were also investigated in cells. We expect the comparison of rhodamine fluorophores will facilitate the quantitative optimization of rhodamine spirolactam based fluorescent probes.

A Critical Review on Organic Small Fluorescent Probes for Monitoring Carbon Monoxide in Biology

Endogenous carbon monoxide (CO) is an important intracellular gas messenger that is intimately involved in many physiological and pathological processes. The abnormal concentration of CO in living organisms can cause many diseases. Therefore, it is of great significance to monitor CO in biological samples. Fluorescent probe technology provides an effective and convenient method for CO monitoring, with the advantages of high selectivity and sensitivity, fast response time and in situ fluorescence imaging in biological tissues, which is favored by the majority of researchers. In this paper, the research progress of CO fluorescent probes since 2018 is reviewed, and the design, detection mechanism and biological application of the related fluorescent probes are summarized. And the relationship between the structure and performance of the probes is discussed. Furthermore, the development trend and application prospect of CO fluorescent probes are prospected.

Gadolinium-Coated Mesoporous Silica Nanoparticle for Magnetic Resonance Imaging

Magnetic resonance molecular imaging can provide anatomic, functional and molecular information. However, because of the intrinsically low sensitivity of magnetic resonance imaging (MRI), high-performance MRI contrast agents are required to generate powerful image information for image diagnosis. Herein, we describe a novel T₁ contrast agent with magnetic-imaging properties facilitated by the gadolinium oxide (Gd₂O₃) doping of mesoporous silica nanoparticles (MSN). The size, morphology, composition, MRI relaxivity (r₁), surface area and pore size of these nanoparticles were evaluated following their conjugation with Gd₂O₃ to produce Gd₂O₃@MSN. This unique structure led to a significant enhancement in T₁ contrast with longitudinal relaxivity (r₁) as high as 51.85 ± 1.38 mM⁻¹s⁻¹. Gd₂O₃@MSN has a larger T₁ relaxivity than commercial gadolinium diethylene triamine pentaacetate (Gd-DTPA), likely due to the geometrical confinement effect of silica nanoparticles. These results suggest that we could successfully prepare a novel high-performance T₁ contrast agent, which may be a potential candidate for in-vivo MRI.

A Self-locked β-Cyclodextrin-rhodamine B Spirolactam with Photoswitching Properties

Supramolecular organization and self-assembly are the pillars of functionality of many nanosystems. The covalent conjugate (6-spirolactam rhodamine B-6-monodeoxy)-β-cyclodextrin (Rho-βCD) is assembled as a self-included, rigid nanostructure, identical in the crystal and in aqueous solution, as revealed by detailed X-ray and NMR analyses. Rho-βCD self-assembly is the result of an interesting reaction pathway, which partially de-aggregates Rho and disturbs the zwitterion↔spirolactone equilibrium. Rho-βCD is stable at pH 4.6, but displays controllable photoswitching between the colored, fluorescent, zwitterionic and the colorless, non-fluorescent closed structures, during several iterative cycles. After an initial drop in absorbance, the on-off process continues without further changes under our irradiation conditions, a consequence of the specific self-locked arrangement of Rho in the cavity. Rho-βCD exemplifies a water soluble photoresponsive nanosystem with improved photostability suggesting promising applications in super resolution bioimaging.

Stabilizing the framework of SAPO-34 zeolite toward long-term methanol-to-olefins conversion

As a commercial MTO catalyst, SAPO-34 zeolite exhibits excellent recyclability probably due to its intrinsic good hydrothermal stability. However, the structural dynamic changes of SAPO-34 catalyst induced by hydrocarbon pool (HP) species and the water formed during the MTO conversion as well as its long-term stability after continuous regenerations are rarely investigated and poorly understood. Herein, the dynamic changes of SAPO-34 framework during the MTO conversion were identified by 1D ²⁷Al, ³¹P MAS NMR, and 2D ³¹P-²⁷Al HETCOR NMR spectroscopy. The breakage of T-O-T bonds in SAPO-34 catalyst during long-term continuous regenerations in the MTO conversion could be efficiently suppressed by pre-coking. The combination of catalyst pre-coking and water co-feeding is established to be an efficient strategy to promote the catalytic efficiency and long-term stability of SAPO-34 catalysts in the commercial MTO processes, also sheds light on the development of other high stable zeolite catalyst in the commercial catalysis.

Stability of zeolite catalysts is a highly desirable property for commercial methanol to olefins conversion but extremely challenging to achieve. Here, the authors combine the catalyst pre-coking and water co-feeding to develop an efficient strategy to enhance the long-term stability of SAPO-34 catalyst.

Disulfide-Reduction-Triggered Spontaneous Photoblinking Cy5 Probe for Nanoscopic Imaging of Mitochondrial Dynamics in Live Cells

Mitochondria are highly dynamic organelles with interconnected tubule structures that are sensitive to environmental stress and light illumination. Super-resolution optical imaging of mitochondrial dynamics is of significance for understanding such biological events. Direct stochastic optical reconstruction microscopy has the advantages of a high spatial resolution, low phototoxicity in live-cell imaging, and the capacity to incorporate smart fluorescent probes. However, dSTORM imaging in live cells is challenging because of the requirement for an imaging buffer and a low temporal resolution. In this work, we achieved dSTORM imaging of mitochondrial dynamics in live cells with a disulfide-substituted Cy5 probe without using any toxic imaging buffer. Under the illumination of very low laser power, the probe exhibited spontaneous photoblinking triggered by disulfide-bond reduction in mitochondria of live cells. The obtained thiol attacked nearby carbon to form a six-membered ring and the reversible opening/closing of the ring produced spontaneous photoblinking behavior. With this new STORM strategy, we achieved observation of mitochondrial dynamics for more than 3 min, which provides a promising tool for further studies of mitochondria with an ultrafine structure.

Directed transforming of coke to active intermediates in methanol-to-olefins catalyst to boost light olefins selectivity

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks (coal, natural gas, biomass, CO₂, etc.), is hindered by rapid catalyst deactivation due to coke deposition. Common practice to recover catalyst activity, i.e. removing coke via air combustion or steam gasification, unavoidably eliminates the active hydrocarbon pool species (HCPs) favoring light olefins formation. Density functional theory calculations and structured illumination microscopy reveal that naphthalenic cations, active HCPs enhancing ethylene production, are highly stable within SAPO-34 zeolites at high temperature. Here, we demonstrate a strategy of directly transforming coke to naphthalenic species in SAPO-34 zeolites via steam cracking. Fluidized bed reactor-regenerator pilot experiments show that an unexpectedly high light olefins selectivity of 85% is achieved in MTO reaction with 88% valuable CO and H₂ and negligible CO₂ as byproducts from regeneration under industrial-alike continuous operations. This strategy significantly boosts the economics and sustainability of MTO process.

Methanol-to-olefins is hindered by rapid catalyst deactivation due to coke deposition. Here the authors demonstrate an approach of directly transforming coke to active intermediates to simultaneously recover catalyst activity and boost light olefins selectivity.

Recent Progress in Small Spirocyclic, Xanthene-Based Fluorescent Probes

The use of fluorescent probes in a multitude of applications is still an expanding field. This review covers the recent progress made in small molecular, spirocyclic xanthene-based probes containing different heteroatoms (e.g., oxygen, silicon, carbon) in position 10'. After a short introduction, we will focus on applications like the interaction of probes with enzymes and targeted labeling of organelles and proteins, detection of small molecules, as well as their use in therapeutics or diagnostics and super-resolution microscopy. Furthermore, the last part will summarize recent advances in the synthesis and understanding of their structure-behavior relationship including novel computational approaches.

Molecular Origins of Heteroatom Engineering on the Emission Wavelength Tuning, Quantum Yield Variations and Fluorogenicity of NBD-like SCOTfluors

Molecular engineering of fluorophore scaffolds, especially heteroatom replacement, is a promising method to yield novel fluorophores with tailored properties for various applications. Yet, molecular origins of the distinct fluorescent properties in newly developed SCOTfluors, i. e., varied emission wavelengths, distinct quantum yields, and fluorogenicity, remain elusive. Such understanding, however, is critical for the rational molecular engineering of high-performance fluorophores. Herein, we employed quantum chemical calculations to understand the structure-property relationships of nitrobenzoxadiazole (NBD)-like SCOTfluors. Our findings are important not only for the rational deployment of SCOTfluors, but also for the effective modifications of other fluorophore scaffolds, for satisfying the increasingly diversified requirements of bioimaging and biosensing applications.

Organocatalytic Synthesis of α-Triphenylmethylamines from Diarylketimines and Phenols

A formal Betti reaction between variously substituted phenols and benzophenone-derived imines to afford α-triphenylmethylamines is reported. The key to the success of this transformation is the in situ generation of the reactive benzophenone iminium species under organocatalytic conditions. Different phenols reacted smoothly, enabling the synthesis of an array of α-triphenylmethylamines, which are highly valued structural motifs in bioactive molecules and chemical sensors.

Systematic study of synthesizing various heteroatom-substituted rhodamines from diaryl ether analogues

The dye rhodamine, as the most popular scaffold to construct fluorescent labels and probes, has been explored extensively on its structure-fluorescence relationships. Particularly, the replacement of the oxygen atom in the 10th position with heteroatoms obtained various new rhodamines with improved photophysical properties, such as brightness, photostability, red-shifted emission and fluorogenicity. However, the applications of heteroatom-substituted rhodamines have been hindered by difficult synthetic routes. Herein, we explored the condensation strategy of diaryl ether analogues and o-tolualdehyde to synthesize various heteroatom-substituted rhodamines. We found that the electron property and steric effect in the rhodamine 10th position determined the synthetic yield. It's concluded that this condensation method was more suitable for the synthesis of heteroatom-substituted rhodamines with small or electron-donating groups like rhodamine, S-rhodamine and Si-rhodamine. We hope these results will benefit the design and synthesis of heteroatom-substituted rhodamines.

Multiple Factors Regulate the Spirocyclization Equilibrium of Si-Rhodamines

Si-rhodamine has been extensively used in super-resolution fluorescence imaging in recent years. Its equilibrium between ring-closed nonfluorescent spirolactones and ring-opened fluorescent zwitterions endows Si-rhodamine with excellent fluorogenicity, membrane permeability, and photostability. In this paper, the equilibrium of Si-rhodamine between lactones and zwitterions was revealed to be greatly affected by various environmental factors, including molecular aggregation, solvent polarity, pH, metal ions, irradiation, and temperature. These environmental sensitivities make Si-rhodamine useful as a hydrochromic material, a fluorescent sensor array for metal ions or solvents, and a photoactivatable switch. Importantly, these results indicate that using Si-rhodamine as a fluorogenic probe or a blinking fluorophore in single-molecule localization super-resolution microscopy requires caution on possible false signals caused by its environmental sensitivity.

Imaging spatiotemporal evolution of molecules and active sites in zeolite catalyst during methanol-to-olefins reaction

Direct visualization of spatiotemporal evolution of molecules and active sites during chemical transformation in individual catalyst crystal will accelerate the intuitive understanding of heterogeneous catalysis. So far, widespread imaging techniques can only provide limited information either with large probe molecules or in model catalyst of large size, which are beyond the interests of industrial catalysis. Herein, we demonstrate a feasible deep data approach via synergy of multiscale reaction-diffusion simulation and super-resolution structured illumination microscopy to  illustrate the dynamical evolution of spatiotemporal distributions of gas molecules, carbonaceous species and acid sites in SAPO-34 zeolite crystals of several micrometers that are typically used in industrial methanol-to-olefins process. The profound insights into the inadequate utilization of activated acid sites and rapid deactivation are unveiled. The notable elucidation of molecular reaction-diffusion process  at the scale of single catalyst crystal via this approach opens an interesting method for mechanism study in materials synthesis and catalysis.

Visualizing semipermeability of the cell membrane using a pH-responsive ratiometric AIEgen

In clinical chemotherapy, some basic drugs cannot enter the hydrophobic cell membrane because of ionization in the acidic tumor microenvironment, a phenomenon known as ion trapping. In this study, we developed a method to visualize this ion trapping phenomenon by utilizing a pH-responsive ratiometric AIEgen, dihydro berberine (dhBBR). By observing the intracellular fluorescence of dhBBR, we found that non-ionized dhBBR can enter cells more easily than ionized forms, which is in accordance with the concept of ion trapping. In addition, dhBBR shows superior anti-photobleaching ability to Curcumin thanks to its AIE properties. These results suggest that dhBBR can serve as a bioprobe for ion trapping.

A General Descriptor ΔE Enables the Quantitative Development of Luminescent Materials Based on Photoinduced Electron Transfer

Photoinduced electron transfer (PET) is one of the most important mechanisms for developing fluorescent probes and biosensors. Quantitative prediction of the quantum yields of these probes and sensors is crucial to accelerate the rational development of novel PET-based functional materials. Herein, we developed a general descriptor (ΔE) for predicting the quantum yield of PET probes, with a threshold value of ∼0.6 eV. When ΔE < ∼0.6 eV, the quantum yield is low (mostly <2%) due to the substantial activation of PET in polar environments; when ΔE > ∼0.6 eV, the quantum yield is high because of the inhibition of PET. This simple yet effective descriptor is applicable to a wide range of fluorophores, such as BODIPY, fluorescein, rhodamine, and Si-rhodamine. This ΔE descriptor enables us not only to establish new applications for existing PET probes but also to quantitatively design novel PET-based fluorophores for wash-free bioimaging and AIEgen development.

Developing substrate-based small molecule fluorescent probes for super-resolution fluorescent imaging of various membrane transporters

Super-resolution imaging technology has been a powerful tool for revealing fine biological structures and functions. Its high-quality imaging always needs highly accurate labeling. Here, by exploiting the high specificity and affinity of natural substrates to transporters, we developed one set of substrate-based small molecule fluorescent probes for labeling membrane transporters. A glucose-based probe (Glu-probe) and tyrosine-based probe (Tyr-probe) were synthesized as two examples. Confocal imaging showed that the Glu-probe could label glucose transporters on live cells by being stuck into the binding site. Compared with antibody-probe labeling, the labeling advantages of the Glu-probe were revealed. High specificity of the Glu-probe or Tyr-probe was examined by a colocalization experiment and glucose replacement or amino acid (AA) blocking. The synthetic probes were also tested on imaging HeLa cells to confirm their wide labeling application. Additionally, we found that membrane transporters were mostly in the clustered state on cellular membranes, changing their assembly pattern to regulate the transport effectiveness. These results suggest that the substrate-based probes can serve as valuable tools for investigating the spatial information of membrane transporters.

In vivo real-time tracking of tumor-specific biocatalysis in cascade nanotheranostics enables synergistic cancer treatment

Glucose oxidase (GOD)-based synergistic cancer therapy has aroused great research interest in the context of cancer treatment due to the inherent biocompatibility and biodegradability. However, this emerging therapeutic system still lacks a strategy to predict and regulate the in vivo biocatalytic behavior of GOD in real time to minimize the side effects on normal tissues. Herein, we developed a tumor-specific cascade nanotheranostic system (BNG) that combines GOD-catalyzed oxidative stress and dual-channel fluorescent sensing, significantly improving the synergistic therapeutic efficacy with real-time feedback information. The nanotheranostic system remains completely silent in the blood circulatory system and selectively releases GOD enzymes in the tumor site, with enhanced near-infrared (NIR) fluorescence at 825 nm. Subsequently, GOD catalyzes H2O2 production, triggering cascade reactions with NIR fluorescence at 650 nm as an optical output, along with GSH depletion, enabling synergistic cancer treatment. The designed nanotheranostic system, integrated with tumor-activated cascade reactions and triggering a dual-channel output at each step, represents an insightful paradigm for precise cooperative cancer therapy.

In vivo ratiometric tracking of endogenous β-galactosidase activity using an activatable near-infrared fluorescent probe

Herein, we developed a dual-channel and light-up near-infrared fluorescent probe for ratiometric sensing of β-galactosidase (β-gal) activity. The well-designed probe, which shows ratiometric optical response with a significant red-shift (from 575 nm to 730 nm), was successfully applied to detect endogenous β-gal activity in SKOV-3 cells and tumor-bearing mice.

Quaternary Piperazine-Substituted Rhodamines with Enhanced Brightness for Super-Resolution Imaging

Insufficient brightness of fluorophores poses a major bottleneck for the advancement of super-resolution microscopes. Despite being widely used, many rhodamine dyes exhibit sub-optimal brightness due to the formation of twisted intramolecular charge transfer (TICT) upon photoexcitation. Herein, we have developed a new class of quaternary piperazine-substituted rhodamines with outstanding quantum yields (Φ = 0.93) and superior brightness (ε × Φ = 8.1 × 10⁴ L·mol^-1·cm^-1), by utilizing the electronic inductive effect to prevent TICT. We have also successfully deployed these rhodamines in the super-resolution imaging of the microtubules of fixed cells and of the cell membrane and lysosomes of live cells. Finally, we demonstrated that this strategy was generalizable to other families of fluorophores, resulting in substantially increased quantum yields.

A new mitochondrion targetable fluorescent probe for carbon monoxide-specific detection and live cell imaging

A new mitochondrion targetable molecular probe for carbon monoxide (CO)-specific detection based on palladium-free mediated opening of spirolactam was designed. The turn-on red fluorescence caused by CO enables a safe and powerful method for unravelling the function of CO in biological systems to be established.