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

A Golgi apparatus-targeted ratiometric fluorescent probe for HOCl and its applications for anti-inflammatory evaluation of Dachengqi Decoction

Verifying the fluctuations of reactive oxidative species in the Golgi apparatus (GA) is crucial to investigate the pathology in inflammation. In this work, we present a fluorescent probe GA-PBC based on the phenothiazine-coumarin chromophore with a benzenesulfonamide unit as the GA target. GA-PBC manifests a red fluorescence peak at 620 nm, while it shifts to 510 nm upon reaction with HOCl, thus facilitating a ratiometric sensing manner. The probe shows high selectivity, superb sensitivity (limit of detection: 85.8 nM), rapid response (within seconds), and predominant accumulation in the GA. Intracellular imaging tests demonstrates the ability of GA-PBC to indicate the concentration changes of HOCl in live cells. Especially, it can be utilized to identify the active ingredients of Dachengqi Decoction (a kind of Traditional Chinese Medicine formula) in inflamed cells using HOCl in the GA as biomarker, suggesting that this probe is potentially useful for the evaluation of anti-oxidation efficacy of natural medicine.

Harnessing machine learning for the rational design of high-performance fluorescent dyes

The design of fluorescent dyes with optimized performance is crucial for advancements in various fields, including bioimaging, diagnostics, and optoelectronics. Traditional approaches to dye design often rely on trial-and-error experimentation, which can be time-consuming and resource-intensive. 42 ML models are tried for each property. One best model is selected for each property. Gradient boosting regressor is best model for the prediction of excitation values while extra trees regressor is best model for the prediction of emission values. A database of 5000 new dyes is generated and analyzed. 30 dyes with higher excitation and emission values are selected. Synthetic accessibility analysis is done for 30 dyes and majority of dyes are easy to synthesized. Our results demonstrate that ML-assisted design can significantly accelerate the discovery process, reduce the need for costly experimental iterations, and lead to the development of dyes with tailored properties for specific applications.

Labeling of oligosaccharides and N-linked glycans by a rhodamine-based fluorescent tag for analysis by capillary electrophoresis with laser-induced fluorescence and mass spectrometry detection

In this work, we present the synthesis and application of fluorescent rhodamine B hydrazide for the derivatization of simple oligosaccharides and complex glycans using a hydrazone formation chemistry approach. The labeling conditions and the experimental setup of CE/LIF were optimized by analyzing oligosaccharide standards. The CE/LIF separations were performed in polybrene-coated capillaries eliminating the need for the purification step after derivatization. The addition of methanol to the background electrolyte significantly increased the LIF detection sensitivity reaching the limits of detection in the attomole range. The resolution of carbohydrate samples was improved by using long (98 cm) capillaries and polymer additives (polybrene). The developed method was applied for CE/LIF and CE-MS analysis of N-linked glycans released from bovine ribonuclease B and the therapeutic monoclonal antibody of trastuzumab.

Fluorogenic Probes for Real-Time Tracking of Bacterial Cell Wall Dynamics with Nanoscopy

The bacterial cell wall, an essential structure for maintaining cell morphology and protecting against environmental hazards, is predominantly composed of peptidoglycan (PG). This intricate macromolecule undergoes dynamic synthesis and remodeling throughout the cell cycle. Despite its importance, monitoring PG dynamics in live cells, particularly with detailed spatial distribution, poses significant challenges. To this end, we present a series of rhodamine-based fluorogenic probes specifically optimized for real-time and super-resolution imaging of PG synthesis. By fine-tuning the self-aggregation of the probes through the incorporation of hydrophobic linkers, we achieved a substantial reduction in background fluorescence and significant fluorogenicity after labeling. These advancements have enabled us to attain wash-free labeling across a diverse array of bacterial species. Our approach facilitates the direct visualization of PG synthesis patterns, enabling the quantification of septal PG (sPG) synthesis rates in living bacterial cells. Furthermore, it allows for simultaneous imaging of cell division machinery in living cells via both two-dimensional (2D) and three-dimensional (3D) STED microscopy. This study provides a powerful toolkit for investigating the architecture and dynamics of the bacterial cell wall, paving new paths for research on PG-related cellular processes.

A near-infrared fluorescence probe for sensing mitochondrial viscosity in cells and mice

Mitochondria play a critical role in providing energy to maintain cellular physiological functions. The viscosity in mitochondria is one of the important indicators of mitochondrial microenvironment. When mitochondrial viscosity increases, it often indicates the occurrence or development of certain diseases. Herein, a series of near-infrared (NIR) fluorescent probes (ZHY-1 ∼ 4) were developed to detect viscosity changes. After screening, we selected ZHY-2 for cellular imaging, since it had the largest fluorescence intensity enhancement (222 times) in response to viscosity compared to the other probes (ZHY-1, ZHY-3, ZHY-4). In addition, ZHY-2 responded to viscosity specifically, and was not affected by pH and other biological species. Also, the probe ZHY-2 had good biocompatibility and mitochondria-targeting ability. It has been applied to measure viscosity changes after stimulation of nystatin and rapamycin. Finally, using probe ZHY-2, we have achieved the real-time fluorescence imaging of viscosity during starvation, as well as in drug-induced liver injury mice.

Rhodamine B-Derived Low-Toxicity Full-Color Carbon Dots with Wide Tunable High-Stable Liquid-State Lasers

Carbon dots (CDs) serve as a novel, non-toxic, cost-effective, and highly-stable solution-processable nanolaser material. However, compared to commonly used commercial laser dyes, CDs exhibit lower photoluminescence quantum yields (PLQYs), radiation transition rates, and gain coefficients. Consequently, this leads to higher laser thresholds that significantly impede the expansion of practical applications for CDs. Therefore, enhancing the gain performance of CDs is crucial in guiding the design of CD gain materials and promoting their practical applications. Herein, Rhodamine B (RhB) is employed as a sole precursor for the synthesis of full-color CDs (FCDs) with vibrant blue, green, yellow, red, and NIR (denoted as B-CDs, G-CDs, Y-CDs, R-CDs, and NIR-CDs) fluorescence through cross-linking, polymerization, and carbonization processes. The photoluminescence (PL) spectra ranged from 434 to 703 nm. Notably, the PLQYs and gain performance of FCDs are improved due to cross-linked enhanced emission (CEE) effects. Green, yellow, red, and NIR laser emission is achieved with lower laser thresholds and exhibited superior laser stabilities than RhB. Furthermore, cytotoxicity tests confirm that FCDs possess significantly lower toxicity than RhB. This study not only validates the applicability of CEE in CDs for developing multicolor gain materials but also advances the practical application of miniaturized lasers based on CDs.

Recent Advances of Nitrobenzoselenadiazole for Imaging and Therapy

The development and practical applications of multifunctional organic fluorophores have garnered significant attention in translational research in recent years. Among the fluorophores, nitrobenzodioxazole (NBD) has been widely used in various fields due to its small size and neutral character, both of which are advantageous for biorelated applications. However, NBD presents some limitations, including (1) suboptimal photophysical properties for in vivo applications and (2) its monofunctional nature, which restricts its use in fluorescence-based bioimaging and sensing. To overcome these challenges, recent research has focused on the development of nitrobenzoselenadiazole (NBSD) derivatives, a selenium analog of NBD. In this review article, we systematically summarize recent advancements in the development of NBSD and highlight examples of its application in translational research as a multifunctional organic fluorophore. We also explore the potential applications of NBSD and present representative case studies, providing valuable context for the ongoing development of new NBSD derivatives in the field of fluorophore-related material science.

AIE and ICT Synergistic Lysosome-Targeted Ratiometric Fluorescence Sensor for the Detection and Imaging of Th4+ in the Liver of Zebrafish and Mice

The sensitive detection of the radioactive thorium (Th) ion with an oxidation state of +4 (Th4+) is of great significance for environmental protection and life safety. In this study, five fluorescence sensors with regulated donor-acceptor (D-A) interactions were constructed for Th4+ detection based on intramolecular charge transfer and aggregation-induced emission mechanisms. Among the developed sensors, TPE-D bearing electron-deficient π-bridge and weak D-A interactions presented ratiometric fluorescence detection behavior toward Th4+ in aqueous solution due to its aggregation-induced emission characteristics and unique D-A-D structures. Moreover, TPE-D showed excellent selectivity and sensitivity for Th4+ detection, and the detection limit was as low as 8.1 × 10-8 M. The sensing mechanism observation revealed that Th4+ could coordinate with the hydroxyl, imine, and carbonyl groups of TPE-D accompanied by an electron transfer process. In addition, TPE-D could selectively be enriched in the lysosome. Both the detection of Th4+ in the lysosome and liver of mice and zebrafish were realized based on this strategy, and a mobile-assisted detection approach toward Th4+ in actual water samples was also established with high sensitivity. This is the first report for Th4+ detection in organelles and organs, which provides a great significance and reliable strategy for radionuclide toxicology detection and analysis applications.

A dual-functional fluorescent probe for biosystem imaging and food safety monitoring of HSO3- with high selectivity and sensitivity

In the food field, HSO3- is commonly used as a beverage additive, antioxidant, enzyme inhibitor, and preservative to extend shelf life and freshness. However, excessive intake of exogenous HSO3- can lead to abnormal HSO3- concentration levels in the body, causing cardiovascular and respiratory diseases. This highlights the urgent need to develop a rapid and sensitive probe for the quantitative detection of HSO3- in foods and biosystems. In this study, we design and synthesize a novel HSO3- fluorescent probe named DCPD. Bioimaging experiments show that DCPD has good mitochondrial targeting and can be used to imaging the redox process of HSO3-/H2O2 in cells and tissue. In addition, DCPD has been used in detecting HSO3- in foods with satisfactory recoveries (98.62-105.06%), further demonstrating its compatibility and utility. Thus, the DCPD probe offers substantial promise for application in food analysis and the assessment of HSO3- concentrations in biological systems.

Synthesis, fluorescence and theoretical insights into a novel FRET-based dansyl-rhodamine sensor for the in vitro detection of toxic bioaccumulated Hg(II) ions

This work describes the successful design and synthesis of a new fluorescence resonance energy transfer (FRET)-based sensor, denoted as RD1. This sensor incorporates a robust dual-fluorophore design, which combines a rhodamine and a dansyl derivative, functionalized with a thiosemicarbazide group that acts as Hg(II) specific recognition site. A synthetic pathway was developed that allowed the efficient synthesis of RD1 with a remarkable overall yield of 44% over four steps, through microwave-assisted protocols. The influence of ethyl, benzyl and phenyl substituents of isothiocyanate in the preparation of the thiosemicarbazide moiety was studied, revealing a crucial dependence of the nature of the isothiocyanate in the formation of the recognition site. Owing to its characteristic ratiometric detection, RD1 exhibited remarkable robustness to external parameters such as pH and solvent composition. The sensor demonstrated a hybrid two-stage response to Hg(II), with an initial quenching of fluorescence followed by an enhancement of emission through a FRET mechanism, both stages being corroborated by DFT (density functional theory) calculations. In vitro studies demonstrated that RD1 presents excellent cytocompatibility and capacity to permeate cellular membranes and be effectively internalized by L929 cell line. Importantly, RD1 retained its sensory ability in a complex cellular environment, affirming its efficacy as a fluorescent sensor for the in vitro detection of bioaccumulated mercury species. These results suggest the potential of RD1 for the detection of toxic bioaccumulated mercury species, aiding in environmental and biomedical research.

Construction of a novel NIR-emissive rhodamine derivative for monitoring mitochondrial viscosity in ferroptosis

Ferroptosis, an iron-dependent programmed cell death mechanism, is mediated by distinct molecular pathways of lipid peroxidation caused by intracellular iron supplementation and glutathione synthesis inhibition that cause oxidative damage to the cell membrane. Monitoring viscosity changes of mitochondria is essential for a deeper understanding of ferroptosis, as mitochondria will be shrunk with increased membrane density and leading to drastic mitochondrial viscous changes during ferroptosis process. Thus, it is essential to explore novel and efficient fluorescent probes for monitoring viscosity in organisms. In this work, we designed and synthesized a mitochondria-targeting probe TJ-FRP for cellular viscosity measurement via fluorescence imaging method. To obtain this probe, we firstly developed a novel modifiable fluorescent π-extended xanthene dye TJ-FR by replacing the benzoic acid group with a strong electron-withdrawing perfluorobenzoic acid group at the 9-position of xanthene framework. The dye not only presents emission wavelength at 758 nm and a large stokes shift of 142 nm in water, but also the dye is low biotoxic, membrane permeable. By reaction with 4-aminobutyltriphenylphosphonium bromide, TJ-FR was converted to the mitochondria-targeting probe TJ-FRP. TJ-FRP was successfully applied for the imaging of viscosity in living cells. Especially, the probe can be applied for visualizing mitochondrial viscosity changes during various inducers-stimulated ferroptosis process in model cells. These findings suggest that this novel NIR fluorescent probe can serve as a powerful tool to monitor the viscosity in biological samples and may provide new insights for various diseases during ferroptosis.

Coumarin Excimer Nanotube for Long-Time Lysosome Tracking

Lysosome abnormality closely relates to a variety of diseases; thus, its long-time tracking could benefit accurate disease diagnosis. Current long-time lysosome imaging probes are not biocompatible enough, while compatible peptide-based probes are easily degraded by the abundant proteinases in lysosome. Herein, we rationally design a d-amino acid-containing peptide Cys(StBu)-d-Glu-Lys(coumarin)-d-Glu-CBT (Cou-D/L-CBT) which is subjected to intracellular GSH-initiated CBT-Cys click reaction and assembles into nanotubes in acidic lysosome. In vitro experiments showed that, under reduction environment and at pH 4.8, Cou-D/L-CBT assembled into nanotubes with an outer diameter of 156 nm, accompanied by "turn-on" coumarin excimer fluorescence at 550 nm. Cell experiments indicated that while Cou-D/L-CBT provided 29 h of lysosome fluorescence imaging, control probe Cou-L-CBT sustained only 6 h. We expect that our Cou-D/L-CBT could be applied for in vitro sensitive diagnosis of lysosome-related diseases in the clinic in the near future.

Real-time monitoring of ONOO⁻ in cerebral ischemia-reperfusion injury mouse models using a hydrazine-based NIR fluorescent probe

Accurate and selective techniques for visualizing endogenous peroxynitrite (ONOO-) in cerebral ischemia-reperfusion injury (CIRI) models are essential for understanding its complex pathological processes. Here, we introduced a longwave fluorescent probe TJO for detecting ONOO- rapidly and sensitively, with a low detection limit of 91 nM. Furthermore, TJO exhibits excellent fluorescence imaging capabilities, enabling detailed visualization of ONOO⁻ in CIRI mice model. This highlights its potential for real-time monitoring of ONOO⁻-related pathological conditions.

Hypochlorous Acid-Activatable NIR Fluorescence/Photoacoustic Dual-Modal Probe with High Signal-to-Background Ratios for Imaging of Liver Injury and Plasma Diagnosis of Sepsis

Hypochlorous acid can be employed as a biomarker for blood infection (such as sepsis) and tissue damage (such as drug-induced liver injury, DILI), and the diagnosis of tissue damage or blood infection can be achieved through the detection of hypochlorous acid in relevant biological samples. Considering the complex environment and the diverse interferences in living organisms and blood plasma, developing new detection methods for HClO with high signal-to-background ratios is particularly important, and it can improve the accuracy of detection and quality of imaging based on a higher contrast, which makes the detection of HClO clearer and more accurate. Here, based on the advantages of the NIR fluorescence/photoacoustic dual-modal probe, we reported a hypochlorous acid-activatable NIR fluorescence/photoacoustic dual-modal probe (NIRF-PA-HClO) based on the spirolactam ring-opening strategy in this paper. NIRF-PA-HClO showed excellent NIRF/PA dual-modal responses with high SBRs for HClO in solution, cells, and mice. Moreover, NIRF-PA-HClO was successfully applied for high-contrast imaging of DILI. Finally, NIRF-PA-HClO was employed for the blood plasma diagnosis of sepsis with satisfactory results. In summary, the above results proved that NIRF-PA-HClO would be a potentially useful tool for the study of physiological and pathological roles of HClO, the investigation of the pathology and therapeutic mechanisms of hepatotoxicity, and the diagnosis of blood infection. Also, the development of NIRF-PA-HClO provides new design mentality for constructing other analyte-activatable NIRF/PA dual-modal probes with high SBRs.

Advancements in fluorescent labeling in assessing the probiotic adhesion capacity - A review

Adhesion capacity of probiotics is closely related to their intestinal-protective effects. The conventional techniques used to evaluate probiotic adhesion capacity have limitations in terms of imaging resolution and quantitative analysis. Fluorescent labelling technology has shown immense potential in recent years owing to its high specificity and sensitivity for resolving probiotic adhesion mechanisms. Although there are still problems with the fluorescence signal intensity and hysteresis effect, this technology has significantly advanced the accurate detection and evaluation of probiotic adhesion capacity. This review examines the critical role of probiotic adhesion and its detection methods, with a special focus on the application of fluorescent-labeling technology. Our objective was to identify more accurate and efficient approaches for evaluating the adhesion capacity of probiotic bacteria while promoting in-depth research into the underlying mechanisms that govern probiotic adhesion.

Xanthene-based NIR organic phototheranostics agents: design strategies and biomedical applications

Fluorescence imaging and phototherapy in the near-infrared window (NIR, 650-1700 nm) have attracted great attention for biomedical applications due to their minimal invasiveness, ultra-low photon scattering and high spatial-temporal precision. Among NIR emitting/absorbing organic dyes, xanthene derivatives with controllable molecular structures and optical properties, excellent fluorescence quantum yields, high molar absorption coefficients and remarkable chemical stability have been extensively studied and explored in the field of biological theranostics. The present study was aimed at providing a comprehensive summary of the progress in the development and design strategies of xanthene derivative fluorophores for advanced biological phototheranostics. This study elucidated several representative controllable strategies, including electronic programming strategies, extension of conjugated backbones, and strategic establishment of activatable fluorophores, which enhance the NIR fluorescence of xanthene backbones. Subsequently, the development of xanthene nanoplatforms based on NIR fluorescence for biological applications was detailed. Overall, this work outlines future efforts and directions for improving NIR xanthene derivatives to meet evolving clinical needs. It is anticipated that this contribution could provide a viable reference for the strategic design of organic NIR fluorophores, thereby enhancing their potential clinical practice in future.

Glycosylated and rhodamine-conjugated tetraphenylethylene: a type I and II reactive oxygen species generator for photodynamic therapy

A lactosylated and AIE-active multifunctional photosensitizer (Lac-TR) was synthesized. Lac-TR can self-assemble into fluorescent nanoparticles (Lac-TRs) to achieve fluorescence self-reporting during photodynamic therapy and induce pyroptosis under both normoxia and hypoxia to kill HepG2 cells.

Paper and Pencil Design of Color-Pure Organic Emitters: The Curious Case of Xanthene Dyes

The quest for color-pure emitters for multicolor bioimaging as well as for ultrahigh definition organic light-emitting diodes demands facile design concepts to avoid tedious synthetic or computational trial-and-error procedures. We have recently presented a simple recipe to construct color-pure blue emitters, which combines basic resonance structure and frontier molecular orbital treatments; this recipe applies to multiresonant type emitters and allows to enlarge the chemical space toward novel structural motifs. In the current work, we show that such fundamental considerations further apply to the structurally entirely different family of xanthene dyes. Opposite to the related polymethine dye family with small bond length alternation (BLA) in the ground and in the excited state (S0, S1), however, xanthene dyes display large BLA in S0 and in S1, so that the overall change in BLA, ΔBL, is small. This gives equally rise to color-pure emission; the underlying reasons for this curious behavior are carved out in the current study. This generalization of the recipe in fact constitutes the desired "paper and pencil" design strategy, spanning now the whole visible range.

Precision Molecular Engineering of Compact Near-Infrared Fluorophores

Organic fluorophores with near-infrared (NIR) emission and reduced molecular size are crucial for advancing bioimaging and biosensing technologies. Traditional methods, such as conjugation expansion and heteroatom engineering, often fail to reduce fluorophore size without sacrificing NIR emission properties. Addressing this challenge, our study utilized quantum chemical calculations and structure-property relationship analysis to establish an iterative design approach and enable precision engineering for compact, single-benzene-based NIR fluorophores. These newly developed fluorophores exhibit emissions up to 759 nm and maintain molecular weights as low as 192 g/mol, approximately 50% of that of Cy7. Additionally, they display unique environmental sensitivity─nonemissive in aqueous solutions but highly emissive in lipid environments. This property significantly enhances their utility in wash-free imaging of live cells. Our findings mark a substantial breakthrough in fluorophore engineering, paving the way for more efficient and adaptable imaging methodologies.

Determining the Recruiting Rate of Spontaneously Blinking Rhodamines by Density Functional Calculations

A recruiting rate (krc) of 0.1-5 s-1 has been proposed as the criterion for super-resolution spontaneously blinking rhodamines. Accurate prediction of the recruiting rate (krc) of rhodamines is very important for developing spontaneously blinking rhodamines. However, as far as we know, there is no reliable theoretical method to predict the krc. Herein, we meticulously investigated the effect of intermolecular hydrogen bonds on the spirocyclization reactions of rhodamines. Moreover, a theoretical descriptor (ΔEC-T) was proposed to reliably assess the krc. ΔEC-T quantified the ring-opening energy barrier of spirocyclization reactions. A robust linear correlation was established between theoretical ΔEC-T values and experimentally krc values. Based on this correlation, we designed and screened five spontaneously blinking sulfonamide rhodamine dyes with optimized krc values. We expected that these findings could enable the targeted design of spontaneously blinking rhodamines.

Amphiphilic hemicyanine molecular probes crossing the blood-brain barrier for intracranial optical imaging of glioblastoma

Intracranial optical imaging of glioblastoma (GBM) is challenging due to the scarcity of effective probes with blood-brain barrier (BBB) permeability and sufficient imaging depth. Herein, we describe a rational strategy for designing optical probes crossing the BBB based on an electron donor-π-acceptor system to adjust the lipid/water partition coefficient and molecular weight of probes. The amphiphilic hemicyanine dye (namely, IVTPO), which exhibits remarkable optical properties and effective BBB permeability, is chosen as an efficient fluorescence/photoacoustic probe for in vivo real-time imaging of orthotopic GBM with high resolution through the intact skull. Abnormal leakage of IVTPO adjacent to the developing tumor is unambiguously observed at an early stage of tumor development prior to impairment of BBB integrity, as assessed by commercial Evans blue (EB). Compared with EB, IVTPO demonstrates enhanced optical imaging capability and improved tumor-targeting efficacy. These results offer encouraging insights into medical diagnosis of intracranial GBM.

A lysosome-targeting rhodamine fluorescent probe for Cu2+ detection and its applications in test kits and zebrafish imaging

Tracing copper ions levels in the environment and subcellular microenvironment is crucial due to the key role copper ions play in physiological and pathological processes. Herein, a novel naphthalimide-fused rhodamine probe Rh-Naph-Cu was prepared through modification with phenylhydrazine to produce a closed and non-fluorescent spirolactam. Based on the copper-induced spirolactam ring-opening and hydrolysis process, Rh-Naph-Cu can be employed as a fluorescence off-on probe for copper ions with high selectivity, high sensitivity (limit of detection: 33.0 nM), broad pH-response range (pH: 5.0-10.0), and color change visible with the naked eye. Rh-Nap-Cu could be made into test strips for the in-situ chromogenic detection of Cu2+. Significantly, Rh-Naph-Cu can be utilized for the detection of copper ions in living HeLa cells and zebrafish, and exhibits excellent lysosomal-targeting ability with high Pearson's correlation coefficient (PCC) of 0.96.

Mitochondria-targeted fluorescent probes based on coumarin-hemicyanine for viscosity changes and their applications in cells and mice

As an important parameter of the cellular microenvironment, the changes in mitochondrial viscosity are closely related to various life activities. Therefore, the development of fluorescent probes for test the changes of mitochondrial viscosity has great significance. In this study, we developed two fluorescent probes for the detection of the mitochondrial viscosity changes. The probes exhibited different fluorescence intensities at different viscosity based on the twisted intramolecular charge transfer process. The characteristics of high anti-interference performance, wide pH applicability, low cytotoxicity and excellent mitochondrial targeting performance made the probes successfully used to distinguish normal cells from cancer cells, achieving visualization of viscosity changes. Furthermore, probes P1 and P2 can also be used as early diagnosis of tumors in mice and reveal the pathology of tumor development. The probes could be serve as a promising viscosity detection tool for discriminating normal cells and cancer cells in biology-related research.

A near-infrared fluorescent molecular rotor for viscosity detection in biosystem and fluid beverages

Viscosity is closely associated with physiological and pathological processes, as well as food quality. Herein, a novel fluorescent molecular rotor, BMCY-V, was presented and applied for detection of viscosity. BMCY-V contained a benzoindole unit as electron donor and a malononitrile group as acceptor. In low-viscous solvents, the rotor can freely rotate, leading to dissipation of excited-state energy. In high-viscous media, however, the free rotation of the rotor is severely restricted, thus reducing non-radiative transition and resulting in significantly enhanced fluorescence intensity. BMCY-V is extremely sensitive to viscosity, showing about 3968 times increase of fluorescence intensity at 728 nm from water to 95 % glycerol. Due to the excellent photophysical property such as near-infrared emission, BMCY-V was successfully used to visualize viscosity in live cells and in liver tissues. In addition, BMCY-V can also evaluate the thickening effect of various thickeners and visualize the changes of viscosity during deterioration of fluid drinks.

Photon-Driven Dye Induction Pyroptosis: An Emerging Anti-Tumor Immunotherapy Paradigm

Photoimmunotherapy represents a novel and promising modality in anti-tumor immunotherapy, offering new hope in the realm of cancer treatment due to its distinctive mechanism and substantial therapeutic efficacy. This innovative approach synergistically integrates photon technology with immunological principles, utilizing photon energy to activate the body's immune response. Photon-driven pyroptosis, a pivotal element of photoimmunotherapy, has significantly revitalized the advancement of this discipline. To support this critical progress, this minireview offers an exhaustive examination of the organic dyes presently employed for photon-driven pyroptosis, alongside an analysis of the prevailing challenges and opportunities in dye molecule design. It is our aspiration that this minireview will contribute to the acceleration of developments in photon-driven pyroptosis dye and the broader field of photoimmunotherapy.

General (hetero)polyaryl amine synthesis via multicomponent cycloaromatization of amines

(Hetero)polyaryl amines are extensively prevalent in pharmaceuticals, fine chemicals, and materials but the intricate and varied nature of their structures severely restricts their synthesis. Here, we present a selective multicomponent cycloaromatization of structurally and functionally diverse amine substrates for the general and modular synthesis of (hetero)polyaryl amines through copper(I)-catalysis. This strategy directly constructs a remarkable range of amino group-functionalized (hetero)polyaryl frameworks (194 examples), including naphthalene, binaphthalene, phenanthren, benzothiophene, dibenzothiophene, benzofuran, dibenzofuran, quinoline, isoquinoline, quinazoline, and others, which are challenging or impossible to obtain using alternative methods. Copper(III)-acetylide species are involved in driving the exclusive 7-endo-dig cyclization, suppressing many side-reactions that are susceptible to occur. Due to the easy introduction of various functional units into heteropolyarylamines, multiple functionalized fluorescent dyes can be arbitrarily synthesized, which can serve as effective fluorescent probes for monitoring the pathological processes (e.g. chemotherapy-induced cell apoptosis) and studying the related disease mechanisms.

Tailoring near-infrared amyloid-β probes with high-affinity and low background based on CN and amphipathic regulatory strategies and in vivo imaging of AD mice

Amyloid-β (Aβ) species (Aβ fibrils and Aβ plaques), as one of the typical pathological markers of Alzheimer's disease (AD), plays a crucial role in AD diagnosis. Currently, some near-infrared I (NIR I) Aβ probes have been reported in AD diagnosis. However, they still face challenges such as strong background interference and the lack of effective probe design. In this study, we propose molecular design strategy that incorporates CN group and amphiphilic modulation to synthesize a series of amphiphilic NIR I Aβ probes, surpassing the commercial probe ThT and ThS. Theoretical calculations indicate that these probes exhibit stronger interaction with amino acid residues in the cavities of Aβ. Notably, the probes containing CN group display the ability of binding two distinct sites of Aβ, which dramatically enhanced the affinity to Aβ species. Furthermore, these probes exhibit minimal fluorescence in aqueous solution and offer ultra-high signal-to-noise ratio (SNR) for in vitro labeling, even in wash-free samples. Finally, the optimal probe DM-V2CN-PYC3 was utilized for in vivo imaging of AD mice, demonstrating its rapid penetration through the blood-brain barrier and labelling to Aβ species. Moreover, it enabled long-term monitoring for a duration of 120 min. These results highlight the enhanced affinity and superior performance of the designed NIR I Aβ probe for AD diagnosis. The molecular design strategy of CN and amphiphilic modulation presents a promising avenue for the development Aβ probes with low background in vivo/in vitro imaging for Aβ species.

Structural basis for ring-opening fluorescence by the RhoBAST RNA aptamer

Tagging RNAs with fluorogenic aptamers has enabled imaging of transcripts in living cells, thereby revealing novel aspects of RNA metabolism and dynamics. While a diverse set of fluorogenic aptamers has been developed, a new generation of aptamers are beginning to exploit the ring-opening of spirocyclic rhodamine dyes to achieve robust performance in live mammalian cells. These fluorophores have two chemical states: a colorless, cell-permeable spirocyclic state and a fluorescent zwitterionic state. Recently, the developed dye SpyRho555 almost exclusively adopts the closed state in solution and becomes fluorescent in complex with the RhoBAST aptamer. To understand the basis for RhoBAST-SpyRho555 fluorogenicity, we have determined crystal structures of RhoBAST in complex with 5-carboxytetramethylrhodamine and a SpyRho555 analogue, MaP555. RhoBAST is organized by a perfect four-way junction that positions two loops to form the dye-binding pocket. The core of the ligand resides between a tri-adenine floor and a single guanine base, largely driven by π-stacking interactions. Importantly, the unpaired guanine interacts with the 3-position group of MaP555 to stabilize the open conformation, supported by mutagenesis data, and may play an active role in promoting the open conformation of the dye.

Monitoring Endoplasmic Reticulum Peroxynitrite Fluctuations in Primary Tendon-Derived Stem Cells and Insights into Tendinopathy

Tendinopathy is one of the most prevalent musculoskeletal disorders, significantly affecting the quality of life of patients. Treatment outcomes can be improved with an early diagnosis and timely targeted interventions. Increasing evidence indicates that ROS and endoplasmic reticulum (ER) stress play key roles in modulating the differentiation processes of tendon-derived stem cells (TDSCs), thereby contributing to the initiation and progression of tendinopathy. However, the relationship between ONOO- and the differentiation process, as well as the various stages of tendinopathy, remains unexplored. Herein, we developed two highly specific and sensitive fluorescent probes (Rod-Cl and Rod-Br) for detecting ONOO- in the ER. Rod-Br can detect basal levels of ONOO- in the ER of TDSCs and measure ONOO- levels in primary TDSCs stimulated by interleukin-1β over various durations, allowing for comparisons between chondrogenic and osteogenic differentiation and ER stress levels. Additionally, we examined ONOO- variations in different stages of tendinopathy and treatment rat models in vivo and discussed the potential mechanisms. This research provides a robust tool for analyzing ONOO- dynamics in the tenogenic and osteogenic differentiation of TDSCs, offering new insights into the pathophysiology and treatment of tendinopathy.

Illuminating cisplatin-induced ferroptosis in non-small-cell lung cancer with biothiol-activatable fluorescent/photoacoustic bimodal probes

Ferroptosis modulation represents a pioneering therapeutic approach for non-small-cell lung cancer (NSCLC), where precise monitoring and regulation of ferroptosis levels are pivotal for achieving optimal therapeutic outcomes. Cisplatin (Cis), a widely used chemotherapy drug for NSCLC, demonstrates remarkable therapeutic efficacy, potentially through its ability to induce ferroptosis and synergize with other treatments. However, in vivo studies of ferroptosis face challenges due to the scarcity of validated biomarkers and the absence of reliable tools for real-time visualization. Biothiols emerge as suitable biomarkers for ferroptosis, as their concentrations decrease significantly during this process. To address these challenges, fluorescence/photoacoustic (PA) bimodal imaging offers a promising solution by providing more accurate in vivo information on ferroptosis. Therefore, the development of methods to detect biothiols using fluorescence/PA bimodal imaging is highly desirable for visualizing ferroptosis in NSCLC. In this study, we designed and constructed two activatable near-infrared (NIR) fluorescent/PA bimodal imaging probes specifically for visualizing ferroptosis by monitoring the fluctuations in biothiol levels. These probes exhibited excellent bimodal response performance in solution, cells, and tumors. Furthermore, they were successfully applied for real-time monitoring of biothiol changes during the ferroptosis process in NSCLC cells and tumors. Importantly, our findings revealed that the combined use of erastin and cisplatin exacerbates the consumption of biothiols, suggesting an enhancement of ferroptosis in NSCLC. This work not only provides powerful tools for monitoring in vivo ferroptosis but also facilitates the study of ferroptosis mechanisms and holds the potential to further advance the treatment of NSCLC.

Biomimetic Metallacage Nanoparticles with Aggregation-Induced Emission for NIR-II Fluorescence Imaging-Guided Synergistic Immuno-Phototherapy of Tumors

The integration of theranostics, which combines diagnostics with therapeutics, has markedly improved the early detection of diseases, precise medication management, and assessment of treatment outcomes. In the realm of oncology, organoplatinum-based supramolecular coordination complexes (SCCs) that can coload therapeutic agents and imaging molecules have emerged as promising candidates for multimodal theranostics of tumors. To address the challenges of tumor-targeted delivery and multimodal theranostics for SCCs, this study employs a cell membrane cloaking strategy to fabricate biomimetic metallacage nanoparticles (MCNPs) with multimodal imaging capabilities and homologous targeting capabilities. Specifically, a photosensitizer molecule (BTTP) containing AIE-active groups was assembled into a metallacage of C-BTTP through Pt-N coordination. This process endows the metallacage with strong NIR-II fluorescence in the aggregated state and significantly superior ROS generation compared to that of the precursor ligand. After being encapsulated with F127, the MCNPs were further cloaked with U87 cancer cell membranes, creating biomimetic MCNPs that achieve tumor-targeting capabilities. Verified by in vitro and in vivo experiments, MCNPs enable multimodal imaging and initiate immunotherapy under photothermal and photodynamic stimulation, leading to synergistic antitumor effects. Furthermore, the evaluation of immunogenic cell death and dendritic cell maturation rate in U87 tumor-bearing mice confirmed the mechanism of photothermal and photodynamic synergistic immunotherapy. This study provides an innovative strategy for enhancing the tumor-targeting and therapeutic efficiency of SCCs, offering a versatile strategy for efficient and minimally invasive theranostics of tumors. The development of such biomimetic nanoparticles represents a significant advancement in the field of nanomedicine, potentially transforming cancer treatment through personalized and targeted therapies.

Mechanochemical Synthesis of Molecular Chemoreceptors

The design of environmentally friendly methods for synthesizing molecular receptors is an expanding area within applied organic chemistry. This work systematically summarizes advances in the mechanochemical synthesis of molecular chemoreceptors. It discusses key achievements related to the synthesis of chemoreceptors containing azine, Schiff base, thiosemicarbazone, hydrazone, rhodamine 6G, imide, or amide moieties. Additionally, it highlights the application potential of mechanochemically synthesized molecular chemoreceptors in the recognition of ions and small molecules, along with a discussion of the mechanisms of detection processes.

An estrogen receptor β-targeted near-infrared probe for theranostic imaging of prostate cancer

Estrogen receptor β (ERβ) is aberrantly expressed in castration-resistant prostate cancer (CRPC). Therefore, a diagnostic and therapeutic ERβ probe not only helps to reveal the complex role of ERβ in prostate cancer (PCa), but also promotes ERβ-targeted PCa therapy. Herein, we reported a novel ERβ-targeted near-infrared fluorescent probe D3 with both imaging and therapeutic functions, which had the advantages of high ERβ selectivity, good optical performance, and strong anti-interference ability. In addition, it displayed excellent antiproliferative activity in CRPC cells. Finally, D3 was also successfully applied to the in vivo imaging of ERβ in the prostate cancer mouse model. Thus, this ERβ-targeted near-infrared fluorescent probe can be used as a potential tool for the study of ERβ-targeted diagnostic and therapeutic PCa.

Water-Soluble Fluorescent Sensors for Quantification of Trace Cisplatin in Body Fluids from Clinical Cancer Patients

Accurate quantification of cisplatin (cDDP) in body fluids (blood, urine, and ascites) is crucial in monitoring therapeutic processes, assessing drug metabolism, and optimizing treatment schedules for cancer patients. Nonetheless, due to the inherent fluorescence and complexity of the body fluid matrix, along with the low cDDP concentrations in these fluids during treatment, using fluorescent sensors for fluid detection remains a subject of ongoing research. Herein, a series of water-soluble cDDP-activatable fluorescent sensors was rationally constructed by introducing thioether groups to the xanthene skeleton based on the chalcogenophilicity of platinum. These sensors exhibit excellent sensitivity and certain anti-interference capabilities for sensing cDDP in living cells, rat tissues, and zebrafish. Especially, with a simplified sample pretreatment procedure, for the first time, Rh3 and Rh4 have enabled quantitative detection of cDDP levels in diversiform body fluids from clinical ovarian and bladder cancer patients. These results are highly consistent with those obtained by ICP-MS detection. This work paves the way for utilizing fluorescent sensors in clinical body fluid analysis, thus potentially revolutionizing the monitoring methods of cDDP in clinic settings.

A benzofuran-[b]-fused BODIPY trimer enabled by dual TBET and PET mechanisms for high-performance two-photon fluorescence imaging

A benzofuran-[b]-fused BODIPY trimer has been efficiently synthesized, featuring a unique structural design that harmoniously integrates TBET (through bond energy transfer) and PET (photo-induced electron transfer) mechanisms. This trimer boasts exceptional optical properties, including a large pseudo-Stokes shift of 100 nm, an impressive fluorescence quantum yield (ΦFL = 0.931), an outstandingly high extinction coefficient (182 100 M-1 cm-1), a remarkable FEF (fluorescence enhancement factors, 22.4-fold) values as well as exhibiting AIE (aggregation-induced emission) activity, and has been successfully utilized in two-photon fluorescence imaging of live-cell lipid droplets.

Efficient green synthesis of biocompatible MPN fluorescent microspheres via hydrophobic-force-driven strategy for enhanced immunochromatographic assays

The unique fluorescence properties of aggregation-induced emission (AIE) fluorescent microspheres (FMs) make them ideal signal markers. Traditional synthesis methods are complex, labor-intensive, and hazardous, leading to AIEFMs that lack biocompatibility and require further modification for immunoprobe preparation. This study introduces a novel hydrophobic force-driven method for rapid synthesis of highly biocompatible FMs (H-FMs), demonstrating their benefits in immunochromatographic assay (ICA) applications. The metal-polyphenol network (MPN) shell around the AIEgen core structure of H-FMs is quickly and safely formed by depositing MPN onto AIEgen nano-aggregates, achieving high dye utilization, affordability, and design flexibility, while producing H-FMs with fluorescence across 300-800 nm. The excellent biocompatibility of H-FMs eliminates the need for additional modifications, allowing antibodies to be coupled swiftly (within 10 min) with a high coupling efficiency of 93.4 %. The resulting immunoprobes exhibit strong target recognition and 90.6 % fluorescence retention over 30 days. These features support their application in double antibody sandwich and competitive ICA formats, with detection limits of 9.62 × 10² CFU/mL for E. coli O157:H7 and 0.0081 ng/mL for AFM1. This study provides new insights into designing fluorescent probes for safety monitoring of hazardous materials in the environment.

Investigating the photophysical properties of rhodamines using a spectroscopic single-molecule fluorescence method

The photophysical properties of rhodamine molecules play a critical role in their performance across various applications. The spectroscopic single-molecule fluorescence (sSMF) technique overcomes the limitations of conventional SMF by distinguishing individual fluorophores based on their emission spectra. This enables precise measurement and direct comparison of photophysical properties among distinct molecules under identical conditions, without requiring separation of molecules. In this study, using a custom sSMF instrument, we successfully identified individual rhodamine B molecules and their various N-dealkylated intermediates, allowing for simultaneous investigation of their photophysical properties. Notably, we observed that rhodamine B undergoing a single dealkylation step exhibited a striking enhancement in photostability compared to its fully intact counterparts and those undergoing two dealkylation steps. This enhancement persisted across various buffer conditions, including different pH levels and the presence or absence of an oxygen scavenger system (OSS). Despite these differences in photostability, time-dependent density functional theory (TD-DFT) calculations revealed that all these rhodamine molecules examined shared a similar energy gap (∼0.6 eV) between their first excited singlet and triplet states.

Click-ready iridium(iii) complexes as versatile bioimaging probes for bioorthogonal metabolic labeling

Herein, we report the synthesis, photophysical characterization and validation of iridium(iii)-polypyridine complexes functionalized for click chemistry and bioorthogonal chemistry, as well as their versatile applications as probes in bioimaging studies exploiting metabolic labeling. The designed dyes are conjugated to chemical reporters in a specific manner within cells by CuAAC ligation and display attractive photophysical properties in the UV-visible range. They are indeed highly photostable and emit in the far-red to near-IR region with long lifetimes and large Stokes shifts. We demonstrate that they can be efficiently used to monitor nascent intracellular sialylated glycoconjugates in bioorthogonal MOE studies with a varied panel of optical and non-optical techniques, namely conventional UV-vis laser scanning confocal microscopy (for routine purposes), UV-vis time-resolved luminescence imaging (for specificity and facilitated multiplexing with nano-environment sensitivity), synchrotron radiation based X-ray fluorescence nanoimaging (for high resolution, elemental mapping and quantification in situ) and inductively coupled plasma mass spectrometry (for routine quantification on cell populations with high statistical confidence). The synthesized Ir(iii) complexes were utilized in single labeling experiments, as well as in dual click-labeling experiments utilizing two distinct monosaccharide reporters relevant to the same metabolic pathway.

Potential of a CO2-Responsive supramolecular drug-carrier system as a safer and more effective treatment for cancer

We combined carbon dioxide (CO2)-responsive cytosine-containing rhodamine 6G (Cy-R6G) as a hydrophobic anticancer agent with hydrogen-bonded cytosine-functionalized polyethylene glycol (Cy-PEG) as a hydrophilic supramolecular carrier to construct a CO2-responsive drug delivery system, with the aim of enhancing the responsiveness of the system to the tumor microenvironment and thus the overall effectiveness of anticancer therapy. Due to self-complementary hydrogen bonding interactions between cytosine units, Cy-R6G and Cy-PEG co-assemble in water to form spherical-like nanogels, with Cy-R6G effectively encapsulated within the nanogels. The nanogels exhibit several distinctive physical features, such as widely tunable nanogel size and drug loading capacity for Cy-R6G, intriguing fluorescence properties, high co-assembled structural stability in normal aqueous environments, enhanced anti-hemolytic characteristics, sensitive dual CO2/pH-responsive behavior, and precise and easily controllable CO2-induced release of Cy-R6G. Cytotoxicity assays clearly indicated that, due to the presence of cytosine receptors on the surface of cancer cells, Cy-R6G-loaded nanogels exert selective cytotoxicity against cancer cells in pristine culture medium, but do not affect the viability of normal cells. Surprisingly, in CO2-rich culture medium, Cy-R6G-loaded nanogels exhibit a further significant enhancement in cytotoxicity against cancer cells, and remain non-cytotoxic to normal cells. More importantly, a series of in vitro experiments demonstrated that compared to pristine culture medium, CO2-rich culture medium promotes more rapid selective internalization of Cy-R6G-loaded nanogels into cancer cells through cytosine-mediated macropinocytosis and thus accelerates the induction of apoptosis. Therefore, this newly developed system provides novel avenues for the development of highly effective CO2-responsive drug delivery systems with potent anticancer capabilities.

A nano-biosensing platform based on CuS-BSA for label-free fluorescence detection of Escherichia coli

Bacterial contamination is a serious issue for public health and food safety. In this work, a simple and label-free fluorescence detection nanoplatform for Escherichia coli (E. coli) was established on the basis of the competitive relationship for the reduction of Cu2+ in CuS-BSA between E. coli and O-phenylenediamine (OPD). OPD could be directly oxidized by Cu2+ to produce 2,3-diaminophenazine (ox OPD) with fluorescence properties. When OPD was introduced into an aqueous solution containing CuS-BSA and E. coli, the oxidation of OPD was inhibited owing to the reduction of Cu2+ to Cu+/Cu0 by NADH-2 dehydrogenase in the bacterial copper homeostasis mechanism, thus decreasing the fluorescence response signal of the system. Meanwhile, our strategy exhibited a satisfactory performance with a broad linear response to E. coli ranging from 12 to 1.2 × 107 CFU mL-1, and the limit of detection was 9 CFU mL-1. The practicability of the developed fluorescence biosensing platform in real samples was evaluated by successful determination of E. coli in drinking water and orange juice. These findings provide a new sensing strategy for analyzing other foodborne bacteria and ensuring food safety assessment.

Chitosan-naphthalimide probes for dual channel recognition of HClO and H2S in cells and their application in photodynamic therapy

The combination of bio-imaging with photodynamic therapy (PDT) to accomplish theranostics is promising in cancer treatment. Three chitosan-naphthalimide probes were studied in this work. 4-(5-Bromothiophen-2-yl)-1,8-naphthalic anhydride was first synthesized, and then reacted with chitosan to obtain the macromolecules (CS-N-Br). The recognition group thiomorpholine or its derivatives were introduced into CS-N-Br to obtain nano-probes (CS-N-ML, CS-N-BSZ, CS-N-FSQ) eventually. The studies revealed that CS-N-ML and CS-N-FSQ exhibit high selectivity and can specifically recognize HClO and H2S. CS-N-ML and CS-N-FSQ can perform exogenous and endogenous confocal imaging of HClO and H2S in cells also. CS-N-ML's ability to target lysosomes positions indicated it could act as a lysosome-specific probe. It was discovered that the probes generate superoxide anions (O2•-) via a Type I mechanism. This discovery endows the probes with high photosensitizing activity even under hypoxic conditions. There is a positive correlation between the extent of the conjugated system and the photosensitivity of the probes, indicating that an enhanced conjugation leads to increased photosensitivity. Upon light irradiation, the probes generate ROS within HeLa cells. These results suggested that these probes can achieve theranostics for diseases associated with abnormal levels of HClO and H2S.

Blood-Brain Barrier-Penetrative Fluorescent Anticancer Agents Triggering Paraptosis and Ferroptosis for Glioblastoma Therapy

Currently used drugs for glioblastoma (GBM) treatments are ineffective, primarily due to the significant challenges posed by strong drug resistance, poor blood-brain barrier (BBB) permeability, and the lack of tumor specificity. Here, we report two cationic fluorescent anticancer agents (TriPEX-ClO4 and TriPEX-PF6) capable of BBB penetration for efficient GBM therapy via paraptosis and ferroptosis induction. These aggregation-induced emission (AIE)-active agents specifically target mitochondria, effectively triggering ATF4/JNK/Alix-regulated paraptosis and GPX4-mediated ferroptosis. Specifically, they rapidly induce substantial mitochondria-derived vacuolation, accompanied by reactive oxygen species generation, decreased mitochondrial membrane potential, and intracellular Ca2+ overload, thereby disrupting metabolisms and inducing nonapoptotic cell death. In vivo imaging revealed that TriPEX-ClO4 and TriPEX-PF6 successfully traversed the BBB to target orthotopic glioma and initiated effective synergistic therapy postintravenous injection. Our AIE drugs emerged as the pioneering paraptosis inducers against drug-resistant GBM, significantly extending survival up to 40 days compared to Temozolomide (20 days) in drug-resistant GBM-bearing mice. These compelling results open up new venues for the development of fluorescent anticancer drugs and innovative treatments for brain diseases.

A highly sensitive ratiometric fluorescence probe for sensing and imaging sulfite in food samples and living cells

In this work, a ratiometric and chromogenic fluorescent probe 1 was synthesized for the detection of SO32-. The probe 1 at PBS (10 mM, pH = 7.4) presented a marked emission band at 661 nm. Upon addition of SO32- ions, a highly emissive adduct with a marked fluorescence at 471 nm were obtained through a Michael addition. The probe 1 displayed a noticeable fluorescence ratiometric response with a large shift (190 nm) in emission wavelength. The probe can quantitatively detect SO32- with high specificity, fast response (within 130 s) as well as low detection limit (13 nM), and a large Stokes shift (139 nm). Fluorescence imaging of HeLa cells indicated that 1 could be used for monitoring the intrinsically generated intracellular SO32- in living cells by ratiometric fluorescence imaging. Furthermore, 1 could be application in real water and sugar samples with high sensitivity and good recoveries.

Turn-On Fluorescence Probe for Cancer-Related γ-Glutamyltranspeptidase Detection

The design and development of fluorescent materials for detecting cancer-related enzymes are crucial for cancer diagnosis and treatment. Herein, we present a substituted rhodamine derivative for the chromogenic and fluorogenic detection of the cancer-relevant enzyme γ-glutamyltranspeptidase (GGT). Initially, the probe is non-chromic and non-emissive due to its spirolactam form, which hinders extensive electronic delocalization over broader pathway. However, selective enzymatic cleavage of the side-coupled group triggers spirolactam ring opening, resulting in electronic flow across the rhodamine skeleton, and reduces the band gap for low-energy electronic transitions. This transformation turns the reaction mixture from colorless to intense pink, with prominent UV and fluorescence bands. The sensor's selectivity was tested against various human enzymes, including urease, alkaline phosphatase, acetylcholinesterase, tyrosinase, and cyclooxygenase, and showed no response. Absorption and fluorescence titration analyses of the probe upon incremental addition of GGT into the probe solution revealed a consistent increase in both absorption and emission spectra, along with intensified pink coloration. The cellular toxicity of the receptor was evaluated using the MTT assay, and bioimaging analysis was performed on BHK-21 cells, which produced bright red fluorescence, demonstrating the probe's excellent cell penetration and digestion capabilities for intracellular analytical detection. Molecular docking results supported the fact that probe-4 made stable interactions with the GGT active site residues.

A zero-background fluorescent probe for sensing and imaging of glutathione via the "covalent-assembly" approach

Developing selective and sensitive fluorescent probes for the detection of glutathione (GSH) concentration and intracellular distribution is of great significance for early diagnosis and treatment of diseases such as liver injury and cancer since GSH plays irreplaceable roles in regulating intracellular redox homeostasis. Herein, we present a new fluorescent probe that can be specifically activated by GSH through the conjugate addition and hydrolysis induced covalent-assembly approach for achieving zero-background interference fluorescence off-on sensing. Besides, the probe exhibited prominent selectivity and sensitivity, a low detection limit and cytotoxicity, thus successfully realizing specific real-time monitoring and tracking of GSH levels in living cells. As a consequence, this work might provide a potentially promising candidate for validating the function of GSH in various physiological and pathological processes, which is beneficial for early diagnosis and therapeutics of related diseases.

The Influence of Thickness and Spectral Properties of Green Color-Emitting Polymer Thin Films on Their Implementation in Wearable PLED Applications

A systematic investigation of optical, electrochemical, photophysical, and electrooptical properties of printable green color-emitting polymer (poly(9,9-dioctylfluorene-alt-bithiophene)) (F8T2) and spiro-copolymer (SPG-01T) was conducted to explore their potentiality as an emissive layer for wearable polymer light-emitting diode (PLED) applications. We compared the two photoactive polymers in terms of their spectral characteristics and color purity, as these are the most critical factors for wearable lighting sources and optical sensors. Low-cost, solution-based methods and facile architecture were applied to produce rigid and flexible light-emitting devices with high luminance efficiencies. Emission bandwidths, color coordinates, operational characteristics, and luminance were also derived to evaluate the device's stability. The tuning of emission's spectral features by layer thickness variation was realized and was correlated with the interplay between H-aggregates and J-aggregates formations for both conjugated polymers. Finally, we applied the functional green light-emitting PLED devices based on the two studied materials for the detection of Rhodamine 6G. It was determined that the optical detection of the R6G photoluminescence is heavily influenced by the emission spectrum characteristics of the PLED and changes in the thickness of the active layer.

Accelerated Computer-Aided Screening of Optical Materials: Investigating the Potential of Δ-SCF Methods to Predict Emission Maxima of Large Dye Molecules

Accurate simulation of electronic excited states of large chromophores is often difficult due to the computationally expensive nature of existing methods. Common approximations such as fragmentation methods that are routinely applied to ground-state calculations of large molecules are not easily applicable to excited states due to the delocalized nature of electronic excitations in most practical chromophores. Thus, special techniques specific to excited states are needed. Δ-SCF methods are one such approximation that treats excited states in a manner analogous to that for ground-state calculations, accelerating the simulation of excited states. In this work, we employed the popular initial maximum overlap method (IMOM) to avoid the variational collapse of the electronic excited state orbitals to the ground state. We demonstrate that it is possible to obtain emission energies from the first singlet (S1) excited state of many thousands of dye molecules without any external intervention. Spin correction was found to be necessary to obtain accurate excitation and emission energies. Using thousands of dye-like chromophores and various solvents (12,318 combinations), we show that the spin-corrected initial maximum overlap method accurately predicts emission maxima with a mean absolute error of only 0.27 eV. We further improved the predictive accuracy using linear fit-based corrections from individual dye classes to achieve an impressive performance of 0.17 eV. Additionally, we demonstrate that IMOM spin density can be used to identify the dye class of chromophores, enabling improved prediction accuracy for complex dye molecules, such as dyads (chromophores containing moieties from two different dye classes). Finally, the convergence behavior of IMOM excited state SCF calculations is analyzed briefly to identify the chemical space, where IMOM is more likely to fail.

Applications of Lightsheet Fluorescence Microscopy by High Numerical Aperture Detection Lens

This Review explores the evolution, improvements, and recent applications of Light Sheet Fluorescence Microscopy (LSFM) in biological research using a high numerical aperture detection objective (lens) for imaging subcellular structures. The Review begins with an overview of the development of LSFM, tracing its evolution from its inception to its current state and emphasizing key milestones and technological advancements over the years. Subsequently, we will discuss various improvements of LSFM techniques, covering advancements in hardware such as illumination strategies, optical designs, and sample preparation methods that have enhanced imaging capabilities and resolution. The advancements in data acquisition and processing are also included, which provides a brief overview of the recent development of artificial intelligence. Fluorescence probes that were commonly used in LSFM will be highlighted, together with some insights regarding the selection of potential probe candidates for future LSFM development. Furthermore, we also discuss recent advances in the application of LSFM with a focus on high numerical aperture detection objectives for various biological studies. For sample preparation techniques, there are discussions regarding fluorescence probe selection, tissue clearing protocols, and some insights into expansion microscopy. Integrated setups such as adaptive optics, single objective modification, and microfluidics will also be some of the key discussion points in this Review. We hope that this comprehensive Review will provide a holistic perspective on the historical development, technical enhancements, and cutting-edge applications of LSFM, showcasing its pivotal role and future potential in advancing biological research.

Heavy-atom-free triplet benzothiophene-fused BODIPY derivatives for lipid droplet-specific biomaging and photodynamic therapy

The twist fusion of a benzothiophene group and the introduction of a 4-methyloxystyryl donor group to the BODIPY core resulted in large spin-orbit coupling values and smaller singlet-triplet energy gaps for the novel infrared absorbed photosensitizers named BSBDP. They show a high reactive oxygen species efficiency exceeding 69% and a fluorescence quantum yield of 23% and are successfully applied in imaging-guided photodynamic therapy in vitro and in vivo.

Activatable Heavy-Atom-Free Photosensitizer with Large Stokes Shift and a NIR-II Emission Harnessing Rhodamine Ring-Opening Strategy

Activatable photosensitizers (PSs) generating 1O2 only under specific conditions can minimize concomitant injury to normal tissues. Heavy-atom-free PSs hold the merits of low dark toxicity, long triplet-state lifetimes, good photostability, and relatively low cost. PSs with emission in the second near-infrared (NIR-II) window are highly valuable for deep-tissue, high-contrast imaging. Herein, we have designed and synthesized a series of heavy-atom-free PSs by a one-step reaction between an easily accessible rhodamine derivative and commercially available thiophene aldehydes. One of the as-prepared PSs, 2b-3T, exhibits emission maxima at 810 nm and tails to the NIR-II region at 1140 nm, together with large Stokes shift (178 nm). Importantly, the newly developed PSs, featuring functional carboxylic acid groups, present promising opportunities as versatile platforms for creating activatable PSs. To validate our concept, we developed Cu2+/pH-activatable PSs using the spirocyclization mechanism of rhodamine. Ultimately, we showcased the effectiveness of these innovative PSs in photodynamic therapy through in vitro experiments.