Förster resonance energy transfer (FRET)-based small-molecule sensors and imaging agents

Cysteine-assisted synthesis of copper nanoclusters for construction of FRET-based ratiometric sensor for visual detection of alkaline phosphatase

Abnormal alkaline phosphatase (ALP) levels in the human body are closely associated with various diseases, particularly hepatobiliary diseases and bone diseases. Herein, we constructed a ratiometric sensor based on Förster resonance energy transfer (FRET) using strongly photoluminescent copper nanoclusters (Cu NCs) for the detection of ALP with high sensitivity and specificity. The cysteine-stabilized Cu NCs (Cys-Cu NCs) were synthesized through a ligand-exchange reaction and core-size etching focusing, which displayed bright photoluminescence (PL) with a quantum yield (QY) of 10.5 %. Multispectral characterization indicated that zwitterionic cysteine ligands without obvious steric hindrance could significantly enhance intra/inter-ligand-involved charge transfer, leading to a significant increase in fluorescence emission (∼14 folds) compared to precursor Cu NCs. A FRET-based ratiometric sensor for ALP detection was constructed by combining Cys-Cu NCs with a Cu2+-assisted oxidation reaction of o-phenylenediamine (OPD) to generate fluorescent 2,3-diaminophenazine (DAP). The strong coordination interaction between the ALP substrate and Cu2+ significantly affected the FRET process between Cys-Cu NCs and DAP, thereby altering the fluorescence ratio. Based on the specific response of ALP to its substrate, the ratiometric sensors showed good linear relationship within the range of 0.1-50 U/L, with a detection limit (LOD) of 0.075 U/L. Furthermore, the FRET-based ratiometric sensor was integrated with a polymer hydrogel to fabricate a portable hydrogel sensor for simple and visual detection of ALP.

Reconnecting the roots of hydrogen sulfide (H2S) with medicinal chemistry: Lessons accomplished and challenges so far

Previously known for its unpleasant odour and mortality in elevated concentrations, hydrogen sulfide (H2S) is currently considered a complex molecule having significant physiological advantages. After nitric oxide (NO) and carbon monoxide (CO), H2S is regarded as the third endogenous gasotransmitter, performing many biological functions in the human body. The essential functions include but are not limited to regulating inflammation, maintaining the redox potential, cellular signalling, and metabolic processes. Moreover, an imbalance in its expression or dysfunction of its precursors and associated enzymes in its biosynthesis leads to multiple pathological conditions, including cancer, diabetes, neurodegenerative disorders, COVID-19, etc. Nonetheless, its upregulation is also reported to dysregulate normal physiological conditions and precipitate different diseases and cancer, thus acting as a "Double-edged sword." Despite this, H2S is still being widely explored for its therapeutic potential in various disease states. The present review is put forth to focus on hydrogen sulfide's dichotomous properties, emphasising its critical functions and therapeutic applications. This compilation provides a state-of-the-art analysis of the broad application of H2S donors in developing therapeutic interventions, release mechanisms, and their use in numerous diseases and disorders. Furthermore, various analytical techniques for detecting and quantifying the H2S release in biological samples via the hybrid donors are also discussed. We herein expect that an in-depth comprehension of the multiple activities of H2S can aid in discovering novel therapeutic interventions critical for holistic disease management measures in the future.

Nanomaterial-enhanced fluorescence sensors for dopamine neurotransmitters: a photophysical perspective

Neurotransmitters are critical in regulating mood, motivation, reward, and various bodily functions. These are necessary elements for cognitive and physical processes. In addition, neurotransmitters play a crucial role in the electrochemical signaling molecules that are crucial for regulating the proper functioning of the brain. Dysfunction of neurotransmitters is associated with several mental disorders. Consequently, detecting and monitoring neurotransmitters are of utmost importance for neurological diagnosis and treatment. Biosensors play a crucial role in detecting and monitoring neurotransmitters like dopamine (DA). This review examines the fundamental nanomaterials and mechanisms utilized in fluorescent-based DA biosensors, with an emphasis on fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) mechanisms. Carbon dots, gold nanoparticles, quantum dots, graphene, and carbon nanotubes have been widely utilized for FRET- and PET-based DA sensing fluorescent probes, demonstrating high sensitivity and specificity. Beyond these conventional mechanisms, innovative fluorescence strategies such as aggregation-induced emission (AIE), turn-on fluorescent probes, and ratiometric fluorescence approaches have further enhanced dopamine detection. Additionally, advanced fluorescent-based nanomaterials like gold nanoclusters, metal-organic frameworks (MOFs), polymer nanocomposites, and liposome-based sensors have expanded the capabilities of fluorescence biosensing. Various fluorescence spectroscopy and microscopy techniques are discussed. Additionally, this review explores emerging technologies and future advancements in fluorescence-based dopamine sensing, highlighting the role of nanomaterial functionalization in enhancing diagnostic accuracy and real-world applicability.

Measurements of Local pH Gradients for Electrocatalysts in the Oxygen Evolution Reaction by Electrochemiluminescence

An accurate understanding of the mechanism of the oxygen evolution reaction (OER) is crucial for catalyst design in the hydrogen energy industry. Despite significant advancements in microscopic pH detection, selective, sensitive, speedy, and reliable detection of local pH gradients near the catalysts during the OER remains elusive. Here, we pioneer an electrochemiluminescence (ECL) method for local pH detection during the OER. For this purpose, a new class of ECL emitters based on ECL resonance energy transfer was theoretically predicted and facilely synthesized by grafting functional fluorescent dyes onto noble 2D carbon nitride. By positioning one of the as-prepared ECL emitters with pH-responsibility neighboring the OER catalysts, local pH gradient generation near the catalysts could be qualitatively measured in real-time with a subsecond resolution. It provided details of the reaction mechanism of the OER and unveiled the catalyst degrading pathway caused by proton accumulation. Besides, the average proton generation rate on the catalyst was also extractable from the local pH measurement as a quantitative descriptor of the OER reaction rate. Owing to the high designability of the grafting method, this study opens up new strategies for studying reaction mechanisms and detecting intermediates.

Internal energy recycling in FAPbI3/MXene for enhanced photocatalytic H2 evolution

Carrier recombination is a significant impediment to efficient charge separation, thereby severely limiting the performance of photocatalytic systems. In this study, we feature an innovative internal energy cycling mechanism through the non-radiative fluorescence resonance energy transfer (FRET) between perovskite and MXene, to exploit the energy released by carrier recombination for enhancing H2 evolution rate. Consequently, a rapid H2 evolution rate of 2394 µmol g-1 h-1 under 1.5 AM simulated sunlight, from the composite of FAPbI3/MXene/Pt, was acquired, which is more than one order of magnitude higher than that of FAPbI3/Pt (64 µmol g-1 h-1). The innovative approach of FRET induced internal energy cycling will open up opportunities to design other novel heterogeneous catalytic materials and promote their application potential in various catalytic fields.

Black phosphorus nanocomposites with near-infrared chemiluminescence and their application in reactive oxygen species imaging

Black phosphorus (BP) has many excellent physical and chemical properties, including high photothermal conversion efficiency, and high biocompatibility, leading to its wide applications in biomedicine. Abnormal proliferation of reactive oxygen species is one of the features of many diseases such as inflammation and tumor. It is important for the visual monitoring of reactive oxygen species. Herein, we developed fluorescent dyes RhB and Cy5.5 co-conjugated BP nanocomposites (BP-Lu-RhB-Cy5.5) for the imaging of abnormal ROS sites by using the PEGylated BP/luminol nanosheets as the substrate. In BP-Lu-RhB-Cy5.5, luminol will be oxidized by ROS to an excited state, which then releases photons. Chemiluminescence migration to the near-infrared region through intramolecular Chemiluminescence Resonance Energy Transfer (CRET) and Fluorescence Resonance Energy Transfer (FRET) effects, enabling deep in vivo tissue imaging. The detection limit of BP-Lu-RhB-Cy5.5 for hydrogen peroxide reached 6.1 × 10-10 M, and a penetration depth of 7 mm was achieved in in vitro experiments. Moreover, we validated the efficacy of the BP-Lu-RhB-Cy5.5 in vivo imaging using subcutaneous inflammation and tumor model. Chemiluminescence excludes the interference of additional excitation light and ensures the signal-to-noise ratio. The black phosphorus nanosheets as carriers ensure the biosafety of the whole material. This work demonstrated the feasibility of utilizing BP-Lu-RhB-Cy5.5 for monitoring and therapy, providing an avenue for the development of multifunctional biomedical materials.

Functional nucleic acid-based fluorescence imaging for tumor microenvironment monitoring: A review

BACKGROUND

The tumor microenvironment (TME) refers to the complex ecological system surrounding tumor cells, which is intimately associated with regulating tumor cell growth, invasive behavior, and metastatic capacity. Hence, in situ imaging of related bioactivity with resolution in the TME is critical for early cancer detection and accurate diagnosis. In recent years, fluorescence imaging technology has become a widely used tool in TME research due to its non-invasive nature, high spatiotemporal resolution, and capability for real-time monitoring. Among these advancements, signal probes designed based on functional nucleic acids (FNAs) provide a promising and innovative toolkit for targeted imaging analysis of the TME.

RESULTS

This review provides a comprehensive discussion on the construction of FNA-based biosensors and their advancements in TME monitoring. In this review, we initially provide a systematic summary of the current targeting strategies of FNA-based biosensors for visual monitoring of the TME, focusing on targeting cell surface and extracellular matrix components. Subsequently, we further explore the application of FNA-based biosensors in monitoring the TME. These biosensors have successfully achieved the monitoring of key parameters, bioactive molecules and other tumor markers in the tumor microenvironment due to their excellent molecular recognition ability and high sensitivity. Finally, we discuss some of the challenges currently faced in the field. In response to these challenges, we propose potential research directions and look forward to the future development prospects of this field.

SIGNIFICANCE

Unlike previous reviews of biosensors based on FNAs for imaging tumor markers in the TME, this work is the first to review how such biosensors can be anchored in the TME. With continued efforts and advancements, we believe an increasing number of FNA-based fluorescence imaging probes will be utilized for TME imaging. This progress will significantly enhance our understanding of disease pathogenesis and progression, thereby offering substantial potential in biosensing and imaging analysis.

A novel idiotypic-based noncompetitive immunoassay based on the dissociation of immunocomplex for detection atrazine in vegetables

Atrazine is a selective systemic herbicide of the chlorotriazine class that is commonly used for controlling annual broadleaf and grassy weeds. However, its residue can harm the environment and human health. We have therefore developed a novel idiotypic-based noncompetitive immunoassay for the detection of atrazine by exploiting the distinctive recognition properties of anti-idiotypic antibodies. This method utilizes atrazine as a "key" to specifically dissociation the "lock" of an anti-idiotypic antibody and detection antibody immunocomplex, thereby enabling both qualitative and quantitative analysis of atrazine. Following all necessary optimizations, this method was capable exhibiting a limit of detection (LOD) of 0.52 ng/mL with R2 = 0.990, and a linear range of 1.76 to 2604.61 ng/mL. This immunoassay offered its potential towards detection of atrazine in water and 10 kinds of vegetable samples with a recovery ranging from 70.76 to 119.28 %. The idiotypic-based noncompetitive immunoassay provides a well suitable method for low-molecular-weight contaminants immunoassay.

Orthogonal Site-Specific Dual Bioconjugation of Aryl and Alkyl Thiols

We introduce aryl thiols as nucleophiles for site-specific protein and antibody bioconjugation, which allows the orthogonal labeling of native cysteines for double modification strategies. In a high-yielding synthesis, we introduce aromatic thiol substituents in two amino acids (4-SH-L-Phe and 3-SH-L-Tyr), which can be site-specifically incorporated into the C-terminus of a protein using the enzyme tubulin tyrosine ligase (TTL, Tub-tag labeling). In particular, we found that 3-SH-L-tyrosine shows excellent water solubility and incorporation rates, similar to previously described Tyr-derivatives. 2D NMR experiments revealed a pKa value of 5.5 for the aryl thiol modality of 3-SH-L-tyrosine, which matches the pH-dependent reactivity profile toward thiol-selective ethynyl-triazolyl-phosphinate (ETP) electrophiles. Most importantly, we found that the addition of glutathione had no significant effect on the reaction between ETPs and the aryl thiol at pH 7.0 and below, supporting orthogonal reactivity between the aryl and alkyl thiols. We utilized these findings to develop an orthogonal thiol-selective dual bioconjugation protocol for proteins, featuring TTL-ligation to site-specifically incorporate the arylthiol-containing amino acid derivative, followed by aryl thiolate functionalization at pH 5.5 and subsequent conjugation of cysteines at pH 8.3. This dual bioconjugation strategy was used to generate a highly fluorescent photostabilized nanobody and a fully functionalized antibody-drug conjugate carrying two different cytotoxic payloads, which displays potent cytotoxicity toward cells carrying the target antigen in addition to a strong bystander effect.

Metal-Free Elemental Selenium Quantum Dots: A Novel and Robust Fluorescent Nanoprobe for Cell Imaging and the Sensitive Detection of Cr(VI)

In this paper, we present a simple solvothermal method to synthesize highly fluorescent metal-free elemental selenium quantum dots (SeQDs) using cost-effective bulk selenium powder. The SeQDs exhibit a small and uniform size, excellent aqueous dispersibility, a high photoluminescence quantum yield (PLQY) of 19.3% with stable fluorescence, and scalable production with a 7.2% yield. Owing to the inner filter effect (IFE), these SeQDs function as a highly effective nanoprobe for Cr(VI) detection, exhibiting exceptional sensitivity (detection limit: 145 nM) and selectivity over a wide linear range (5-105 μM), along with rapid response kinetics. Moreover, SeQDs show low cytotoxicity and efficient cellular uptake, enabling cell imaging and intracellular Cr(VI) monitoring. Significant fluorescence quenching in Cr(VI)-exposed cells confirms the potential of SeQDs as a viable fluorescent nanoprobe for Cr(VI) detection in complex cellular environments. This work thus not only establishes a simple method for the preparation of fluorescent SeQDs but also develops a promising fluorescent nanoprobe for cell imaging and Cr(VI) sensing.

RAS/RAF/MEK/MAPK signaling pathway as a therapeutic target in breast cancer: Emphasis on a novel carrier for tamoxifen and digestion behaviors

Objective

This research attempted to increase the bioactivity and solubility and reduce the side effects of Tamoxifen (TMX) by using the cellulose nanocrystals (CNCs) extracted from walnut shells as a carrier and studied the interaction behavior of CNCs-TMX with hemoglobin.

Materials and Methods

The synthesized CNCs and CNCs-TMX were analyzed through the usage of XRD, FTIR, TEM, SEM, and multi-spectroscopic techniques. A real-time PCR assay was also conducted to further unravel the underlying mechanism of CNCs- TMX.

Results

Our synthesized products including CNCs and CNCs- TMX had spherical morphologies in small sizes of 17.42 nm and 56.38 nm, respectively. The changes in FTIR spectrum signified the induced alterations in the samples functional group during the steps of preparation, while the crystallinity index of CNCs was 71.35%. Fluorescence spectroscopy confirmed the quencher functionality of CNCs-TMX along with the dominance of static quenching mechanism. Also, synchronous fluorescence displayed its binding to Hb in the vicinity of Tryptophanresidue. FRET was applied to calculate the interaction energy transfer of 0.18 nm. Next to achieving satisfactory results from oxygen-hemoglobin dissociation studies, the presence of CNCs-TMX caused a reduction in hemoglobin affinity for oxygen.

Conclusion

Our findings pointed out the remarkable potential of TMX-loaded CNCs, derived from walnut shell, in suppressing the proliferation, migration, and invasion of breast cancer cells by quelling the RAS/RAF/MEK/MAPK signaling pathways. The gathered data approved the promising applicability of the obtained CNCs from walnut shell in the delivery system of anti-cancer drugs throughout pharmaceutical applications.

Ultrabright and ultrafast afterglow imaging in vivo via nanoparticles made of trianthracene derivatives

Low sensitivity, photobleaching, high-power excitation and long acquisition times constrain the utility of afterglow luminescence. Here we report the design and imaging performance of nanoparticles made of electron-rich trianthracene derivatives that, on excitation by room light at ultralow power (58 μW cm-2), emit afterglow luminescence at ~500 times those of commonly used organic afterglow nanoparticles. The nanoparticles' ultrabright afterglow allowed for deep-tissue imaging (up to 6 cm), for ultrafast afterglow imaging (at short acquisition times down to 0.01 s) of naturally behaving mice with negligible photobleaching, even after re-excitation for over 15 cycles, and for the accurate visualization of subcutaneous and orthotopic tumours and of plaque in carotid arteries. We also show that an afterglow nanoparticle that is activated only in the presence of granzyme B allowed for the tracking of granzyme-B activity in the context of therapeutic monitoring. The high sensitivity and negligible photobleaching of the organic afterglow nanoparticles offer advantages for real-time in vivo monitoring of physiopathological processes.

Advances in Fluorescence-based Probes for Abiotic Stress Detection in Plants

Abiotic stress poses significant challenges to the ecological environment and global food security. Early and accurate diagnosis of abiotic stress is essential for modern agriculture. Recently, fluorescence sensing technology has emerged as a valuable tool for monitoring abiotic stress due to its ease of use and capability for spatiotemporal visualization. These probes specifically bind to abiotic stress biomarkers, facilitating the detection of stress responses and advancing related biological research. However, there is a lack of comprehensive reviews on fluorescence probe for abiotic stress, which limits progress in this area. This review outlines the biological markers of abiotic stress, discusses the types and design principles of fluorescence probe, and reviews research on detecting plant responses to such stress. Its goal is to inspire the rational design of fluorescence probe for plant bioimaging, promote early diagnosis of abiotic stress, and enhance the understanding of plant defense mechanisms at the molecular level, ultimately providing a scientific basis for stress management in agriculture.

Reversible excited state electron transfer in an acceptor-acceptor hetero dyad

In this manuscript, we create a new hetero dyad consisting of two electron acceptors with nearly isoenergetic HOMO and LUMO levels, namely perylene diimide (PDI) and aza dioxa triangulenium (ADOTA). This dyad system displays an unusual and reversible excited state electron transfer process. Upon excitation, the dyad shows complete energy transfer from the locally excited PDI to the ADOTA moiety in ∼1 ps, followed by photoinduced electron transfer (PET), forming oxidized PDI and reduced ADOTA. While this PET process is fast (k PET≈ 150 ps), the reversibility establishes an equilibrium between fluorescent locally excited ADOTA and the dark charge shifted PET state. We investigate the formation of and decay from this unusual reversible excited state electron transfer system by fs transient absorption and time-resolved fluorescence spectroscopy in different solvent mixtures because the solvent modulates the deactivation rate of the PET state. Electrochemistry confirms that both the local HOMOs and LUMOs of PDI and ADOTA are nearly isoenergetic but can be shifted by solvent polarity, which elucidates the reason for the unusual reversible electron transfer process and its sensitivity to the solvent. We further investigate near degeneracy of the LUMOs through spectroscopy of the chemically reduced dyad. We find that there is an equilibrium between the reduction of the cationic ADOTA to a neutral dyad, which is favored in DCM. However, in DMF, we find reduction of the PDI leads to formation of the zwitterionic dyad.

Fluorescent probes in autoimmune disease research: current status and future prospects

Autoimmune diseases (AD) present substantial challenges for early diagnosis and precise treatment due to their intricate pathogenesis and varied clinical manifestations. While existing diagnostic methods and treatment strategies have advanced, their sensitivity, specificity, and real-time applicability in clinical settings continue to exhibit significant limitations. In recent years, fluorescent probes have emerged as highly sensitive and specific biological imaging tools, demonstrating substantial potential in AD research.This review examines the response mechanisms and historical evolution of various types of fluorescent probes, systematically summarizing the latest research advancements in their application to autoimmune diseases. It highlights key applications in biomarker detection, dynamic monitoring of immune cell functions, and assessment of drug treatment efficacy. Furthermore, this article analyzes the technical challenges currently encountered in probe development and proposes potential directions for future research. With ongoing advancements in materials science, nanotechnology, and bioengineering, fluorescent probes are anticipated to achieve higher sensitivity and enhanced functional integration, thereby facilitating early detection, dynamic monitoring, and innovative treatment strategies for autoimmune diseases. Overall, fluorescent probes possess substantial scientific significance and application value in both research and clinical settings related to autoimmune diseases, signaling a new era of personalized and precision medicine.

Activatable Photosensitizers: From Fundamental Principles to Advanced Designs

Photodynamic therapy (PDT) is a promising treatment that uses light to excite photosensitizers in target tissue, producing reactive oxygen species and localized cell death. It is recognized as a minimally invasive, clinically approved cancer therapy with additional preclinical applications in arthritis, atherosclerosis, and infection control. A hallmark of ideal PDT is delivering disease-specific cytotoxicity while sparing healthy tissue. However, conventional photosensitizers often suffer from non-specific photoactivation, causing off-target toxicity. Activatable photosensitizers (aPS) have emerged as more precise alternatives, offering controlled activation. Unlike traditional photosensitizers, they remain inert and photoinactive during circulation and off-target accumulation, minimizing collateral damage. These photosensitizers are designed to "turn on" in response to disease-specific biostimuli, enhancing therapeutic selectivity and reducing off-target effects. This review explores the principles of aPS, including quenching mechanisms stemming from activatable fluorescent probes and applied to activatable photosensitizers (RET, PeT, ICT, ACQ, AIE), as well as pathological biostimuli (pH, enzymes, redox conditions, cellular internalization), and bioresponsive constructs enabling quenching and activation. We also provide a critical assessment of unresolved challenges in aPS development, including limitations in targeting precision, selectivity under real-world conditions, and potential solutions to persistent issues (dual-lock, targeting moieties, biorthogonal chemistry and artificial receptors). Additionally, it provides an in-depth discussion of essential research design considerations needed to develop translationally relevant aPS with improved therapeutic outcomes and specificity.

Imidazo-phenanthroline based ratiometric optical sensing platform for cyanide and fluoride ions

The severe toxicity and widespread distribution of fluoride (F-) and cyanide (CN-) ions in various environmental matrices highlight the urgent need for their efficient and reliable detection methods. In this study, we present a fluorogenic imidazo-phenanthroline based probe (L) for selective detection of F- and CN- in semi-aqueous medium. Probe L exhibits a pronounced ratiometric fluorescence response upon interaction with these anions, driven by hydrogen bonding interaction involving the N-H group of the imidazole moiety. Notably, L enables clear discrimination of CN- from other anions through a distinct color change, with an impressive detection limit in the nanomolar (nM) range. To enhance its practical applicability, paper-based sensing strips embedded with L were developed, effectively detecting CN- and F- under UV light illumination. The probe's exceptional sensitivity and selectivity could be attributed to the strong acidity of the N-H proton, facilitating efficient hydrogen bonding interactions followed by deprotonation. The binding mechanism was thoroughly investigated using Job's plot, NMR, and DFT analyses. Additionally, L demonstrated versatility in environmental and biological applications, successfully detecting cyanide and fluoride ions in soil samples and identifying F- in live MCF-7 cell lines via blue fluorescence channel imaging.

Diverse Fluorescent Probe Concepts for Detection and Monitoring of Reactive Oxygen Species

World-wide research on reactive oxygen species (ROS) continues to reveal new information about the role and impact of ROS on human health and disease. ROS are generated in live cells as a byproduct of aerobic metabolism. Physiological concentrations of cellular ROS are important for signaling and homeostasis, but excessive generation of ROS causes apoptotic and necrotic cell death and various health disorders. Fluorescence technology is a powerful tool to detect, monitor, and image cellular ROS. The present review provides an overview of diverse organic dye-based fluorescent probe concepts that involve modifications of traditional fluorescent dyes utilizing basic principles of dye chemistry and photophysics. Fluorescence responses of the probes and their specificity towards ROS are discussed through analyses of their photophysical and photochemical parameters. We also provide an outlook on future directions of ROS-responsive fluorescent dyes, which could enable the design and development of advanced probes for gaining deeper insights into redox biology.

Boosting FRET Efficiency of Chromophores with Aggregation-Caused Quenching by a Crystallization-Induced Precise Co-assembly Strategy

Förster resonance energy transfer (FRET) plays a critical role in organic optoelectronic materials. However, developing facile and effective strategies to achieve high-efficiency energy harvesting of chromophores with aggregation-caused quenching (ACQ) remains an appealing yet challenging task, that has not yet been explored. Herein, a subtly strategy, crystallization-induced precise co-assembly (CIPCA) involving a molecular "lightening agent," to effectively improve FRET efficiency of ACQ chromophores is developed. Bis(phenylethynyl)anthracene (BPA) and bis(phenylethynyl)naphthacene (BPN) with significant ACQ effect are chosen as representative FRET donor and acceptor, respectively, and weakly-fluorescent octafluoronaphthalene (OFN) acted as the "lightening agent." Thanks to precise co-assembly with OFN, the PLQY of solid BPA is enhanced by 107%, and the BPN powder can be unprecedentedly lighted. More importantly, through such powerful CIPCA, the monotonous and weak emission for BPA@BPN can be remarkably regulated to colorful and much brighter ones with FRET efficiency improvement of as high as 180-270%. An in-depth understanding of FRET regulation is elucidated through a precise correlation of the supramolecular structures and properties. Such achievements allow to successfully fabricate distinct multi-stimuli-responsive fluorescent patterns and highly-emissive colorful flowers with high flexibility. This research provides an efficient strategy to improve the FRET efficiency of ACQ pairs.

Zinc(II) organic framework based bifunctional biomarker sensor for efficient detection of urinary 5-Hydroxyindoleacetic acid and serum 3-Nitrotyrosine

Monitoring biomarker levels in body fluids is of great importance in clinical diagnosis. Herein, a robust 3D ZnMOF, {[Zn2(BTPB)0.5(bib)1.5(μ2-OH)]·2H2O}n, was fabricated based on the ligands of 1,4-bis(2,4,6-tricarboxylpyrid-5-yl)benzene (H6BTPB) and 1,4-bis(imidazol-1-yl)benzene (bib). On the basis of its stable architecture and intrinsic luminescence, ZnMOF demonstrated remarkable potential as a bifunctional luminescent sensor for selective and sensitive detecting the biomarkers of 3-nitrotyrosine (3-NT) and 5-hydroxyindoleacetic acid (5-HIAA) in water and body fluids by employing distinct "turn-off" and "turn-on" responses. Additionally, the inherent sensing mechanism was further assessed from the viewpoints of spectral overlap and photo-induced electron transfer. This work manifested MOFs-based luminescent sensors are developing into an effective method for detecting biomarkers in body fluids with perfect practicality and compatibility.

A novel Ln3+/Al3+ metallacrown multifunctional material for latent fingerprint detection, luminescent thermometers and luminescent sensors

Lanthanide luminescent complexes are active and thriving in various research fields due to their unique optical properties, while optical materials across a wide spectral range and with multiple functions in one were rarely reported. In this work, a new class of Ln3+/Al3+ metallacrowns (MCs) were constructed with excellent luminescence properties in both the visible and near-infrared regions, and the elaborate luminescence modulation can be achieved by doping with different Ln3+ ions. Strikingly, the powder of LnMC was developed as a luminescent nanomaterial for the detection of latent fingerprints (LFPs), and even the third level details of fingerprints can be clearly recognized, which provides a reference for the identification of fingerprints in the field of criminal investigation. More importantly, TbMC and Tb0.1Sm0.9MC can be successfully used as luminescent thermometers with sensitivities of 2.51% °C-1 and 2.33% °C-1, respectively, higher than most reported values. Meanwhile, TbMC was developed as a luminescent probe for Fe3+ and 2,6-pyridinedicarboxylic acid (DPA) with low limits of detection (LOD) of 0.51 μM and 4.26 μM, respectively, representing the first example of MC with luminescence sensing. Also of note is that SmMC, Tb0.1Sm0.9MC and TbMC can be functionalized as luminescent inks and films due to their clear recognizable colours in the visible range, suggesting a new strategy for high-level anti-counterfeiting. In short, the LnMC luminescent material has wide application prospects in many fields, especially rare for multifunctional applications of small-molecule complexes with non-metal-organic frameworks.

Novel supramolecular artificial light-harvesting systems based on AIE-active macrocycles for efficient white-light photocatalysis in water

Constructing supramolecular artificial light-harvesting systems (ALHSs) based on the Förster resonance energy transfer (FRET) mechanism provides an optimal platform for understanding natural photosynthesis and simulating natural light-harvesting systems. In the present work, rigid macrocycle K-1 with a nonplanar conformation and aggregation-induced emission (AIE) properties was selected as an energy donor in ALHSs, while the non-cyclic AIEgen K-2 was used for a comparative study. In aqueous solution, an efficient one-step energy-transfer process was established between blue-emitting K-1 and an acceptor (namely PBTB) with orange fluorescence to afford a high energy-transfer efficiency (Φ ET) of up to 82.6%. Notably, bright white light emission can be readily realized. Moreover, the triad FRET system was fabricated through energy transfer from the AIEgens to PBTB, then further transferring the captured energy to the final red-emitting acceptor (namely as Z1), achieving an efficient two-step sequential energy transfer. When the ratio of K-1/PBTB/Z1 assemblies reached 1000 : 40 : 14, the optimal Φ ET was 66.4%. More importantly, it was found that the ALHS based on macrocycle K-1 showed much higher photocatalytic activity for the cross-dehydrogenative coupling (CDC) reaction. Therefore, the flexibility of this novel supramolecular strategy renders the macrocyclic AIEgen a promising candidate to construct efficient ALHSs for photocatalysis.

Ratiometric Detection of Carboxylesterase In Vitro and In Vivo via a BODIPY-Styryl Platform

Hepatocellular carcinoma (HCC) is a highly aggressive liver malignancy and the main form of liver cancer. Early diagnosis and treatment of HCC can effectively reduce mortality. Carboxylesterase (CE) is abundantly present in liver tissue, which shows promise as an innovative diagnostic biomarker for HCC. Herein, we designed and synthesized a novel fluorescent probe BDPPh-CES, based on a boron dipyrromethenes (BODIPY)-styryl framework, for the ratiometric detection of CE. Upon interaction with CEs, the probe demonstrates a characteristic fluorescence emission red shift, completing the reaction within 30 min. Notably, BDPPh-CES maintains specificity against acetylcholinesterase (AChE) and various biological species, while exhibiting robust performance across physiological pH conditions. Comprehensive mechanistic investigations, combining high-resolution mass spectrometry (HRMS) analysis, density functional theory (DFT) computational studies, and molecular docking simulations, provided insights into the binding and sensing mechanisms. The high sensitivity and low cytotoxicity facilitated real-time ratiometric imaging of CEs at the cellular level, successfully distinguishing elevated CE expression in Hepa 1-6 hepatic cancer cells over AML 12 normal hepatocytes. Further validation through in vivo experiments confirmed the liver-specific accumulation and efficient CE detection capabilities. This research presents an innovative approach for ratiometric CE monitoring, with potential implications for the early detection and therapeutic management of CE-associated disorders such as HCC.

Click and shift: the effect of triazole on solvatochromic dyes

Solvatochromic dyes are prime candidates for exploring complex polarity-dependent biological processes. The design of novel dyes for these applications typically presents long synthetic routines. Herein, we report a concise synthesis of azido-functionalised push-pull fluorenes, belonging to the most potent groups of fluorosolvatochromic compounds. These fluorenes can be attached to multiple alkynes via the highly versatile copper-catalysed azide-alkyne cycloaddition (CuAAC). Our study focuses on the beneficial effect of the triazole, formed by CuAAC, comparing the simple push-pull fluorene FR1 with the novel model compound FR1TP. While the triazole in FR1TP is not conjugated to the π-system of the dye, the heterocycle surprisingly produces a bathochromic emission shift of around 50 nm. This effect, caused by triazole-induced LUMO stabilisation, was also observed for two other model compounds: FR2TP and FR1TM. All compounds display photophysical properties that are highly desired for in vivo imaging dyes, including remarkable two-photon absorption properties. The experimental results are supported by theoretical calculations. We anticipate that our findings will enable synthesis of new high-performance fluorosolvatochromic dyes for diverse applications.

Efficient multilayer near-infrared micro-bottle laser pumped by a 532 nm nanosecond laser

This paper explores the development and optimization of organic near-infrared micro-cavity lasers for biophotonic applications. Four micro-bottle laser configurations inclouding single-layer, two-layer, and three-layer structures were designed and fabricated using Nile-Blue (NB) and Rhodamine B (RhB) laser dyes doped in SU-8 polymer as laser-active materials. While NB achieves lasing near 750 nm, its absorption of common pump sources such as Nd: YAG lasers at 532 nm is limited. Therefore, Forster resonance energy transfer (FRET) between RhB and NB was employed to enhance NB's lasing efficiency under 532 nm excitation. Experimental and simulation results demonstrate that multilayer designs, particularly the three-layer configuration, outperform others, achieving higher emission intensity, improved stability, and reduced lasing thresholds. The inclusion of RhB optimizes pump absorption and enables efficient energy transfer, facilitating stable Near-IR lasing at 720-750 nm. These findings highlight the potential of multilayer micro-cavity lasers for compact, efficient, and stable organic laser systems in biophotonic and sensing applications.

Engineering DNA Nanodevices with Multi-site Recognition and Multi-signal Output for Accurate Intracellular LncRNA Imaging

Dynamic DNA nanodevices, known for their high programmability and controllability, are pivotal in intracellular biomarker imaging. However, these nanodevices often suffer from inadequate detection sensitivity and specificity due to limited cellular loading capacity and low signal feedback. Herein, we engineered an integrated multi-site recognition and multi-signal output of four-leaf clover dynamic DNA nanodevice (MEMORY) that enables sensitive and accurate intracellular long noncoding RNA (lncRNA) imaging. MEMORY features one fluorophore (FAM)-modified cross-shaped structure as spatial-confinement scaffolds loaded with four identical quenchers (BHQ1)-modified recognition probes (RPs), ensuring a low background signal initially. In the presence of target lncRNA, the multiple recognition sites of MEMORY facilitate hybridization with the target to selectively release the RPs, exposing the toehold region and outputting the green fluorescence (FAM) signal. Furthermore, the exposed toehold region can trigger efficient and rapid hybridization chain reaction (HCR) amplification, outputting the red fluorescence (Cy5) signal. MEMORY's multiple recognition sites increase the likelihood of target collisions, enhancing reaction efficiency, while its multi-signal output provides sequential feedback through FAM and Cy5, boosting overall signal intensity. With the lncRNA metastasis-related lung adenocarcinoma transcript 1 (MALAT1) as a detection model, MEMORY offers a linear detection range from 1 pM to 100 nM, with a limit of detection of 0.29 pM. We demonstrated that MEMORY can differentiate between normal and tumor cells based on intracellular MALAT1 imaging. This integrated DNA nanodevice will offer valuable tools for sensitive and accurate imaging of intracellular biomarkers.

Novel förster resonance energy transfer (FRET)-based ratiometric fluorescent probe for detection of cyanides by nucleophilic substitution of aromatic hydrogen (SNArH)

The development of novel fluorescent probes for real-time detection of cyanides (CN-) in environmental and biological systems has become a significant focus in chemical sensing. Particularly, ratiometric fluorescence sensing offers a unique method for precise and quantitative detection of cyanides, even under complex conditions. We report herein the design of a new ratiometric fluorescent probe for cyanides based on modulation of Förster resonance energy transfer (FRET) coupled with novel cyanide-induced nucleophilic substitution of aromatic hydrogen (SNArH). The target probe (R1) is developed by introducing coumarin fluorophores as FRET donors into a 3-nitro-naphthalimide acceptor, which is easily synthesized and exhibits a colorimetric change from colorless to faint yellow and a significant ratiometric fluorescence shift (Δλ = 114 nm) upon cyanide binding. A clear ratiometric signal at I582/I468 was obtained, with a limit of detection of 5.69 μM. The sensing mechanism was confirmed through 1H NMR titration and LC-MS analysis. Additionally, R1-loaded strips were easily prepared, serving as a portable device for detecting CN- with visible color changes. The probe R1 has been successfully utilized for real-time monitoring of cyanide in food materials and water samples. Importantly, fluorescence bioimaging studies in HeLa cells were conducted, demonstrating the probe's capability for ratiometric detection of exogenous CN- in living systems.

Novel Bioorthogonal Theranostic Scaffold Enables on-Target Drug Release and Real Time Monitoring In Vivo

Bioorthogonal chemistry-based prodrug strategy features spatiotemporally controlled release of therapeutic agent and/or imaging probe. However, the integration of diagnosis and therapy into a single molecule paired with a single bioorthogonal trigger remains a challenge. In this study, we devised a novel bioorthogonal theranostic scaffold amenable to the conjugation of various targeting agent and click-to-release reaction with the bioorthogonal prodrug to enable targeted drug liberation with concomitant fluorescence emission. Such one-stone-three-birds scaffold consists of a new fluorophore phenanthrodioxine (PDO) linked with a fluorescence masking group, tetrazine (Tz) which serves as a dual switch for the activation of fluorophore and drug. Further installation of a warhead of phenylboronic acid (PBA) ensures the targeted accumulation of the resultant PBA-PDO-Tz conjugate in tumor cells, thereby achieving on-demand activation of trans-cyclooctene-caged anticancer drug Doxorubicin with real-time monitoring and on-target cytotoxicity in live cells and an A549 xenograft mouse model. The targeted single trigger-dual response scaffold holds promise for precise theranostics applications in vivo.

A mononuclear iron(II) complex constructed using a complementary ligand pair exhibits intrinsic luminescence-spin-crossover coupling

Molecular materials that exhibit synergistic coupling between luminescence and spin-crossover (SCO) behaviors hold significant promise for applications in molecular sensors and memory devices. However, the rational design and underlying coupling mechanisms remain substantial challenges in this field. In this study, we utilized a luminescent complementary ligand pair as an intramolecular luminophore to construct a new Fe-based SCO complex, namely [FeL1L2](BF4)2·H2O (1-Fe, L1 is a 2,2':6',2''-terpyridine (TPY) derivative ligand and L2 is 2,6-di-1H-pyrazol-1-yl-4-pyridinecarboxylic acid), and two isomorphic analogs (2-Co, [CoL1L2](BF4)2·H2O and 3-Zn, [ZnL1L2](BF4)2·H2O). Magnetic studies reveal that 1-Fe exhibits thermally induced SCO within the temperature range of 150-350 K. Variable-temperature fluorescence emission spectral analysis of the three complexes confirmed the occurrence of SCO-luminescence coupling in 1-Fe. Furthermore, variable-temperature UV-vis absorption spectra and time-dependent density functional theory (TD-DFT) calculations elucidate the intramolecular luminescence emission behavior, highlighting the critical role of charge transfer processes between the L1 ligand and FeII ions with different spin states. Our research presents a novel construction strategy for synthesizing synergistic SCO-luminescent materials and contributes to the understanding of the mechanisms underlying SCO-luminescence coupling.

Solvent-Free Artificial Light-Harvesting System in a Fluid Donor with Highly Efficient Förster Resonance Energy Transfer

Multi-step Förster resonance energy transfer (FRET) plays a vital role in photosynthesis. While the energy transfer efficiency (ΦET) of a naturally occurring system can reach 95%, that of most artificial light-harvesting systems (ALHSs) is still limited. Herein, we propose a strategy to construct highly efficient ALHSs using a blue-emitting, supercooled ionic compound of naphthalimide (NPI) as the donor, a green-emitting BODIPY derivate as a relay acceptor, and a commercially available, red-emitting dye [rhodamine B (RhB)] as the final acceptor. The broad emission of the fluid donor can overlap simultaneously with the absorption of BODIPY and RhB, enabling the occurrence of a sequential FRET from NPI to BODIPY to RhB as well as a parallel FRET directly from NPI to RhB. These two complementary energy transfer routes lead to an overall ΦET up to 97.4%, which is the champion among all of the reported ALHSs and is also higher than that found in plants and photosynthetic bacteria. This strategy is universal, and ΦET of the system could be further improved by optimizing the structures of the fluid donor and relay acceptor.

Enhancement of sensitivity for moxifloxacin spectrofluorimetric analysis through photoinduced electron transfer inhibition. Green assessment with application to pharmaceutical eye drops

A green, simple, rapid, selective, and highly sensitive fluorimetric protocol has been established for quantitative analysis of the antibacterial drug moxifloxacin in its pure form and pharmaceutical dosage form. Owing to photoinduced electron transfer, moxifloxacin exhibits low native fluorescence in neutral media. Based on that, the developed fluorimetric protocol depends on inhibiting the photoinduced electron transfer effect of the nitrogen atom presented on the pyrrolidine ring in moxifloxacin by suitable adjusting of pH of the medium surrounding it, leading to its protonation. It is simply achieved by using 0.5 M acetic acid. This protonation enhances the native fluorescence of moxifloxacin, turning it into a stronger one. This fluorescence was measured at 498 nm after excitation at 295 nm with a linearity range from 10 to 60 ng mL-1 and a high correlation coefficient value of 0.9998. The fluorimetric approach could be applied for moxifloxacin detection with a limit of 0.89 ng mL-1 and a quantification limit of 2.69 ng mL-1. The developed method has been validated according to ICH guidelines, indicating high accuracy and excellent precision. Furthermore, the developed fluorimetric protocol was applied successfully for moxifloxacin analysis in pharmaceutical eye drops. As a result, the proposed protocol could be easily applied for quality control of moxifloxacin in different laboratories all over the world.

Recent advances and design strategies for organic afterglow agents to enhance autofluorescence-free imaging performance

Long-lasting afterglow luminescence imaging that detects photons slowly being released from chemical defects has emerged, eliminating the need for real-time photoexcitation and enabling autofluorescence-free in vivo imaging with high signal-to-background ratios (SBRs). Organic afterglow nano-systems are notable for their tunability and design versatility. However, challenges such as unsatisfactory afterglow intensity, short emission wavelengths, limited activatable strategies, and shallow tissue penetration depth hinder their widespread biomedical applications and clinical translation. Such contradiction between promising prospects and insufficient properties has spurred researchers' efforts to improve afterglow performance. In this review, we briefly outline the general composition and mechanisms of organic afterglow luminescence, with a focus on design strategies and an in-depth understanding of the structure-property relationship to advance afterglow luminescence imaging. Furthermore, pending issues and future perspectives are discussed.

Amidine-functionalized aggregation-induced emission luminogen and a 3D-printed digital sensor platform for ultrafast and visual detection of heparin

BACKGROUND

Heparin is a widely used anticoagulant in clinic. However, improper dosing can increase the risk of thromboembolic events, potentially leading to life-threatening complications. Clinic monitoring of heparin is very important for its use safety. Rapid and accurate point-of-care testing can significantly reduce the risk of thrombotic events. The detection of heparin using fluorescent probes has emerged as a significant area of research, driven by the need for rapid, sensitive, and selective methods for monitoring this crucial anticoagulant in clinical settings. However, the absence of convenient and user-friendly heparin testing methods continues to pose a challenge.

RESULTS

In this work, a tetraphenylethylene derivatives with four amidine active groups (TPE-4+) was prepared. TPE-4+ has obvious aggregation-induced emission (AIE) effect on the heparin with a 127-fold enhancement occurring within just 3 s. The molecular docking simulation showed that TPE-4+ was closely embedded in the heparin by the electrostatic force between four amidine of TPE-4+ and sulfate ester group of heparin, restricted intramolecular motion of TPE-4+, and causing obvious AIE features. The fluorescence intensity of TPE-4+ was line with the concentration of heparin in the range of 0-2.0 U/mL with a lowest detection limit of 0.0038 U/mL. The possible interference in the serum samples had no influence on the determination of heparin. Using 3D printing technology, a compact, portable digital sensor platform for straightforward monitoring of heparin levels was fabricated.

SIGNIFICANCE

The proposed innovative platform provides a powerful tool to make portable and real-time monitoring of heparin possible, and thereby contributing to achieve point-of-care testing and decrease the risk of thrombotic events. This novel method of combining the probe with the sensing platform simplifies the detection process and enhances patient care by providing more accurate diagnostic capabilities.

Enhanced Emission in Polyelectrolyte Assemblies for the Development of Artificial Light-Harvesting Systems and Color-Tunable LED Device

Artificial light-harvesting systems (LHSs) are of growing interest for their potential in energy capture and conversion, but achieving efficient fluorescence in aqueous environments remains challenging. In this study, a novel tetraphenylethylene (TPE) derivative, TPEN, is synthesized and co-assembled with poly(sodium 4-styrenesulfonate) (PSS) to enhance its fluorescence via electrostatic interactions. The resulting PSS⊃TPEN network significantly increased blue emission, which is further harnessed by an energy-matched dye, 4,7-di(2-thienyl)benzo[2,1,3]thiadiazole (DBT), to produce an efficient LHS with yellow emission. Moreover, this system is successfully applied to develop color-tunable light-emitting diode (LED) devices. The findings demonstrate a cost-effective and environmentally friendly approach to designing tunable luminescent materials, with promising potential for future advancements in energy-efficient lighting technologies.

Molecular Probe for Specific Recognition of TKX-50: 'Luminescence-ON' Response and its Integration to a Smart Device for Surveillance

In response to the growing concerns about the unauthorized use of advanced secondary explosives such as TKX-50 against non-combatant targets, there is an urgent need for effective detection methods or techniques to ensure efficient security screening, homeland security, and public safety. Herein, a new polymeric receptor (IV) derived from functionalized tetraphenylethylene moiety (TPE) and 1,3,5-tris(4-aminophenyl)benzene (TAPB)  moieties for the efficient detection of TKX-50 through a 'switch ON' luminescence response upon specific binding to the explosive, is reported. The observed 'luminescence ON' response is rationalized based on a charge transfer complex formation between TKX-50 and the polymeric receptor IV (Ka = 1.7 × 104 m-1). This is validated by the steady and excited-state luminescence studies, along with detailed computational studies. The authors' presumptions are further validated with adequate control studies using an appropriate monomeric derivative (III) of TPE. Moreover, this 'luminescence ON' response can be integrated into a smart and user-friendly Internet of Things (IoT)-based prototype device. This device can effectively convert optical responses into digital output to develop an optical device for real-time detection of TKX-50 in solution. This lightweight, portable device is ideally suited for remote surveillance and monitoring of TKX-50; such examples are rare in contemporary literature.

Reversible fluorescence/photochromic switching of repeated-response cellulose-based hydrogels for information encryption

The rapid development of anti-counterfeiting technology has brought new challenges to the repeatability and stability of reversible fluorescence/photochromic switching hydrogels. To address this issue, a series of chemical cross-linked cellulose-based intelligent responsive hydrogels were synthesized by free-radical graft copolymerization in a hydrothermal process. This strategy allows for the creation of a chemical cross-linked three-dimensional structure that anchors photochromic ammonium molybdate and fluorescent carbon dots together, resulting in enhanced stability and mechanical properties. Especially, the tensile and compressive strength of hydrogel reached a maximum value of 280 kPa and 560 kPa, respectively, which far exceeds that of some reported hydrogels. The resultant hydrogels exhibited desired reversible fluorescence/photochromic switching, reversible printing and erasing of patterns, and information encryption/decryption. Notably, the change of photochromism from yellow to green can be realized, and the self-fading process can be shortened to 25 min at 60 °C instead of 6 h at room temperature. More importantly, the fluorescence quenching phenomenon of the hydrogel occurs gradually after 2 min of continuous irradiation, and it can be recovered by selective treatment with ethanol. Overall, this study provides a simple strategy for the preparation of environmentally friendly reversible fluorescence/photochromic switching cellulose-based hydrogels for information encryption.

The Rapid Transport of Excitons in Organic Crystals Can Be Regulated by the Molecular Packing Form

Long-range exciton transport is crucial for optoelectronic devices based on organic semiconductors, but the method for increasing and regulating the exciton transport rate in organic semiconductors is still underexplored. Here we have achieved rapid-transporting excitons in organic crystals assembled of difluoroboron β-diketonate (BCZ) and found that the exciton transport rate of BCZ crystals can be regulated by the molecular packing form. Using transient absorption microscopy, we find that the BCZ-Y crystal in which BCZ molecules experience uniform head-to-tail antiparallel molecular packing has anisotropic long-range exciton transport. The exciton diffusion constants along the fast and slow axes are 2.0 and 0.9 cm2/s, respectively. By contrast, there is no obvious exciton transport in BCZ-R crystals, in which BCZ molecules form tightly stacked dimers. Theoretical calculations prove that energy transfer in BCZ-Y is much faster than that in BCZ-R because of the different molecular arrangements.

Hydrazone fluorescent sensors for the monitoring of toxic metals involved in human health from 2014-2024

Hydrazone-based fluorescent sensors have been instrumental for the detection of toxic metals over the past decade due to their ease of synthesis and unique properties. This review summaries the diverse range of sensors reported for toxic metals (Al3+, Fe3+, Cu2+, Zn2+ and Hg2+) highlighting the key role this class of sensors will play in the foreseeable future.

Frontiers in fluorescence imaging: tools for the in situ sensing of disease biomarkers

Fluorescence imaging has been recognized as a powerful tool for the real-time detection and specific imaging of biomarkers within living systems, which is crucial for early diagnosis and treatment evaluation of major diseases. Over the years, significant advancements in this field have been achieved, particularly with the development of novel fluorescent probes and advanced imaging technologies such as NIR-II imaging, super-resolution imaging, and 3D imaging. These technologies have enabled deeper tissue penetration, higher image contrast, and more accurate detection of disease-related biomarkers. Despite these advancements, challenges such as improving probe specificity, enhancing imaging depth and resolution, and optimizing signal-to-noise ratios still remain. The emergence of artificial intelligence (AI) has injected new vitality into the designs and performances of fluorescent probes, offering new tools for more precise disease diagnosis. This review will not only discuss chemical modifications of classic fluorophores and in situ visualization of various biomarkers including metal ions, reactive species, and enzymes, but also share some breakthroughs in AI-driven fluorescence imaging, aiming to provide a comprehensive understanding of these advancements. Future prospects of fluorescence imaging for biomarkers including the potential impact of AI in this rapidly evolving field are also highlighted.

Smartphone-assisted detection of trace methyl orange in water by ratiometric nanosensors based on down/up-conversion luminescence

A ratiometric nanosensor was developed for detecting methyl orange (MO) based on down/up-conversion luminescence achieved by a triplet-triplet annihilation upconversion luminescence (TTA-UCL) system. The probe, utilizing sensitizer and annihilator fluorophores encapsulated in nanomicelles, demonstrated high sensitivity and selectivity for MO detection. The energy transfer from UCL to MO endowed the sensor with responsive capabilities. The unaffected triplet-triplet energy transfer process maintained the phosphorescence signal constant, serving as a reference to construct the ratiometric sensor along with the UCL signal. Additionally, a smartphone-assisted colorimetric detection method was also developed based on the ratiometric sensor, enabling rapid and convenient detection of MO without the need for a spectrometer. The performance of the nanosensor in real water samples confirmed its potential for practical environmental applications.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

Molecular mechanism of enhancing antitumor activity through the interaction between monosaccharides and human serum albumin

This study investigated the molecular mechanisms of the interactions between three antitumor active monosaccharides and human serum albumin (HSA) using spectroscopic and electrochemical analyses, supplemented by molecular docking simulations. The antitumor efficacy of these monosaccharides can be significantly enhanced by covalent drug coupling, while HSA, with its long half-life and low immunogenicity, provides new opportunities for the development of advanced antitumor drug delivery systems. The results showed that these monosaccharides effectively burst the fluorescence of HSA. Thermodynamic analysis revealed that Fucose undergoes a spontaneous, exothermic process that decreases entropy, while the binding of Mannose and Galactose is entropy-driven. Notably, the addition of these three monosaccharides slightly compacts the structure of HSA, stabilizing its transport and delivery in vivo, with the binding strength categorized as Fucose > Mannose > Galactose. These variations in binding constants explain the differences in efficacy and potential side effects in antitumor therapy. Further studies have shown that the interaction between monosaccharides and HSA improves drug stability and targeting, thereby enhancing antitumor activity. An in-depth study of these interactions may provide new insights into the design and optimization of antitumor drugs and the further development of novel antitumor therapies.

Visualization of Subcellular mTOR Complex 1 Activity with a FRET-Based Sensor (TORCAR)

The mechanistic target of rapamycin complex 1 (mTORC1) is a nutrient-sensing complex that integrates inputs from several pathways to promote cell growth and proliferation. mTORC1 localizes to many cellular compartments, including the nucleus, lysosomes, and plasma membrane. However, little is known about the spatial regulation of mTORC1 and the specific functions of mTORC1 at these locations. To address these questions, we previously developed a Förster resonance energy transfer (FRET)-based mTORC1 activity reporter (TORCAR) to visualize the dynamic changes in mTORC1 activity within live cells. Here, we describe a detailed protocol for using subcellularly targeted TORCAR constructs to investigate subcellular mTORC1 activities via live-cell fluorescence microscopy.

High-Throughput Approaches to Engineer Fluorescent Nanosensors

Optical sensors are powerful tools to identify and image (biological) molecules. Because of their optoelectronic properties, nanomaterials are often used as building blocks. To transduce the chemical interaction with the analyte into an optical signal, the interplay between surface chemistry and nanomaterial photophysics has to be optimized. Understanding these aspects promises major opportunities for tailored sensors with optimal performance. However, this requires methods to create and explore the many chemical permutations. Indeed, many current approaches are limited in throughput. This affects the chemical design space that can be studied, the application of machine learning approaches as well as fundamental mechanistic understanding. Here, an overview of selection-limited and synthesis-limited approaches is provided to create and identify molecular nanosensors. Bottlenecks are discussed and opportunities of non-classical recognition strategies are highlighted such as corona phase molecular recognition as well as the requirements for high throughput and scalability. Fluorescent carbon nanotubes are powerful building blocks for sensors and their huge chemical design space makes them an ideal platform for high throughput approaches. Therefore, they are the focus of this article, but the insights are transferable to any nanosensor system. Overall, this perspective aims to provide a fresh perspective to overcome current challenges in the nanosensor field.

Coassembly of Dual-Modulated AIE-ESIPT Photosensitizers and UCNPs for Enhanced NIR-Excited Photodynamic Therapy

Aggregation-induced emission (AIE) photosensitizers are promising for photodynamic therapy, yet their short excitation wavelengths present a limitation. In this study, we develop a series of organic photosensitizers with dual modulation capabilities based on excited-state intramolecular proton transfer (ESIPT) and AIE. Notably, we synthesize near-infrared (NIR)-excited photosensitive nanoparticles through a coassembly strategy utilizing upconversion nanoparticles (UCNPs) and amphiphilic polymers. The spectroscopic analysis and theoretical calculations elucidate the significant impact of additional or π-spacer groups on the conformational change and the energy barrier of the ESIPT process. An efficient Förster resonance energy transfer between the photosensitizer and UCNPs is achieved through the coassembly strategy. Both in vitro and in vivo experiments demonstrate the antitumor efficacy of these nanoparticles under NIR excitation. This work not only introduces a novel approach for simultaneously modulating AIE properties and the ESIPT process but also provides a robust solution for overcoming the excitation wavelength limitations of many organic photosensitizers.

Whispering gallery mode optical resonators for biological and chemical detection: current practices, future perspectives, and challenges

Sensors are important for a wide variety of applications include medical diagnostics and environmental monitoring. Due to their long photon confinement times, whispering gallery mode (WGM) sensors are among the most sensitive sensors currently in existence. We briefly discuss what are WGM sensors, the principles of WGM sensing, and the history of the field, beginning with Mie theory. We discuss recent work in the field on using these WGM resonators as sensors, focusing particularly on biological and chemical sensing applications. We discuss how sensorgrams are acquired and fundamental measurement limits. In addition, we discuss how to interpret binding curves and extract physical parameters such as binding affinity constants. We discuss the controversy surrounding single-molecule detection and discuss hybrid WGM nanoparticle sensors. In addition, we place these sensors in context with others sensing technologies both labeled and label-free. Finally, we discuss what we believe are the most promising applications for these devices, outline remaining challenges, and provide an outlook for the future.

Networked Multicomponent Ensemble as AND Gate with FRET Output

A networked supramolecular logic AND gate system is accomplished using precise chemical communication within a multicomponent ensemble via metal ion-driven self-sorting processes. The cybernetic AND gate is composed of a copper(I)-loaded nanoswitch, an aza-crown ether and a rhodamine receptor. The modus operandi of the AND gate, from state (0,0), was induced with stoichiometric amounts of two inputs (IN-1=Hg2+, IN-2=Li+) generating copper(I) ions as output only in state (1,1). Generation of state (1,1) from state (0,0) involves selective Cu+ ion translocation from the nanoswitch to the aza-crown ether in the first step (IN-1) and then from the aza-crown ether to the rhodamine receptor in the second step (IN-2). The released copper(I) output acts as a messenger that binds to the rhodamine receptor, triggering it's spiro-lactam ring opening, which leads to a diagnostic FRET emission from the copper(I)-loaded rhodamine scaffold accompanied by a remarkable fluorescence and colour change from pale yellow to pink.

Unveiling the Ultrafast Excitation Energy Transfer in Tetraarylpyrrolo[3,2-b]pyrrole-BODIPY Dyads

We have synthesized two dyads (dyad 1 and 2) comprising of tetraarylpyrrolo[3,2-b]pyrrole (TAPP) and BODIPY. In dyad 1, two BODIPYs are directly connected with TAPP moiety whereas in dyad 2, BODIPYs are connected through phenylethynyl linkers. TAPP is a blue energy donor which is easy to synthesize and functionalize as compared to other well-known blue energy donors like pyrene, perylene etc. This is the first report of using TAPP as an energy donor in BODIPY based dyad molecules. Complete quenching of TAPP fluorescence in the dyads suggests fast energy transfer from TAPP to BODIPY unit (ETE~99.9 %). Ultrafast fluorescence and transient absorption spectroscopic studies of dyad 1 showed TAPP to BODIPY energy transfer in 125 fs (kET=8.0×1012 s-1) which is one of the fastest energy transfer events in BODIPY based dyad reported so far. Whereas, in dyad 2, energy transfer is almost four times slower (480 fs, kET=2.1×1012 s-1). These results were rationalized by theoretical Förster formulations. This study shows that suitably matched optical properties of TAPP and BODIPY dyes along with their easy syntheses will be the key to develop highly efficient energy transfer systems in future for multiple applications.

Visible-Light-Driven Solid-State Fluorescent Photoswitches for High-Level Information Encryption

Developing visible-light-driven fluorescent photoswitches in the solid state remains an enormous challenge in smart materials. Such photoswitches are obtained from salicylaldimines through excited-state intramolecular proton transfer (ESIPT) and subsequent cis-trans isomerization strategies. By incorporating a bulky naphthalimide fluorophore into a Schiff base, three photoswitches achieve dual-mode changes (both in color and fluorescence) in the solid state. In particular, the optimal one generates triple fluorescence changing from green, to yellow and finally to orange upon visible-light irradiation. This switching process is fully reversible and can be repeated at least 10 times without obvious attenuation, suggesting its good photo-fatigue resistance. Mechanism studies reveal that the naphthalimide group not only enables the tuning of multicolor with an additional emission, but also induces a folded structure, reducing molecular stacking and facilitating ESIPT and cis-trans isomerization. As such, photopatterning, ternary encoding and transient information recording and erasing are successfully developed. The present study provides a reliable strategy for visible-light-driven fluorescent photoswitches, showing implications for advanced information encryption materials.

Unlocking cell surface enzymes: A review of chemical strategies for detecting enzymatic activity

BACKGROUND

Cell surface enzymes are important proteins that play essential roles in controlling a wide variety of biological processes, such as cell-cell adhesion, recognition and communication. Dysregulation of enzyme-catalyzed processes is known to contribute to numerous diseases, including cancer, cardiovascular diseases and neurodegenerative disease. From the perspective of drug discovery and development, there is a growing interest in detecting the cell surface enzyme activity, propelled by the arising need for innovative diagnostic and therapeutic approaches to address various health conditions.

RESULTS

In this review, we focus on advances in chemical strategies for the detection of cell surface enzyme activity. Firstly, this comprehensive review delves into the diverse landscape of cell surface enzymes, detailing their structural features and diverse biological functions. Various enzyme families on the cell surface are examined in depth, elucidating their roles in cellular homeostasis and signaling cascades. Subsequently, various biosensors, including electrochemical biosensors, optical biosensors and dual-mode biosensors, used for detecting the cell surface enzyme activity are described. Exemplars are provided to illustrate the mechanisms, limit of detection and prospective applications of these different biosensors. Furthermore, this review unravels the intricate interplay between cell surface enzymes and cellular physiology, contributing to the development of novel diagnostic and therapeutic strategies for various diseases. In the end, the review provides insights into the ongoing challenges and future prospects associated with the detection of cell surface enzyme activity.

SIGNIFICANCE

Detecting cell surface enzyme activity holds pivotal significance in biomedical research, offering valuable insights into cellular physiology and disease pathology. Understanding enzyme activity aids in elucidating signaling pathways, drug interactions and disease mechanisms. This knowledge informs the development of diagnostic tools and therapeutic interventions targeting various ailments, from cancer to neurodegenerative disease. Additionally, it contributes to the advancement of drug screening and personalized medicine approaches.