"Four-In-One" Design of a Hemicyanine-Based Modular Scaffold for High-Contrast Activatable Molecular Afterglow Imaging

Red-emitting fluorescent probe with excellent water solubility for the in situ monitoring of endogenous H2S in wheat under salt and Al3+ stress

Hydrogen sulfide (H2S) is a pivotal signaling molecule in plants and appropriate levels are essential for normal growth. As such the real-time detection of H2S in plants is required since it enables timely targeted interventions. However, most fluorescent probes for detecting H2S reported to date exhibit fluorescence quenching in aqueous solution thereby significantly constraining their potential for in vivo applications. In response to this challenge, we present a natural flavylium-inspired fluorescent probe with robust water solubility for turn-on detection of H2S in organisms. The probe exhibits a remarkable 28-fold turn-on signal at 619 nm with rapid reaction kinetics (-20 min), coupled with high sensitivity (LOD = 0.37 μM) and exceptional selectivity for H2S. By employing the probe as an imaging agent, we managed to successfully visualize the fluctuations of exogenous and endogenous H2S levels in HeLa cells. More importantly, the probe enabled the facile and precise visualization of H2S in stressed wheat roots, achieving remarkable micron-level resolution through in-situ imaging, thereby confirming the upregulation of H2S in response to aluminum ion and salt stress. Our research provides a novel tool to investigate the response and mitigation mechanisms of H2S in plants under diverse stress conditions, as well as strategies for enhancing crop resilience.

Kinetic Equation Modeling-Guided Luminescence Modulation in Photochemical Afterglow

Photochemical reaction-based afterglow has been widely applied in information storage, biodetection, and bioimaging. It is achieved through a cascade of photophysical processes and chemical reactions. However, comprehensive kinetic study of its complex processes remains limited. In this work, we conducted numerical simulations of the entire afterglow process based on chemical reaction kinetic equations, focusing on key kinetic processes and identifying the rate-determining step. By varying the rate constants of the key steps, we provided theoretical insights into effectively regulating the afterglow intensity and lifetime. Furthermore, we designed and synthesized several derivative molecules for experimental validation, achieving optimization of both intensity and lifetime. Through the integration of chemical kinetic analysis with experimental validation, this study develops an in-depth comprehension of complex kinetic processes and establishes a robust framework for molecular design in photochemical afterglow and related systems.

Sterically Controlled Cyclobutane-Dioxetane Ultrabright Afterglow Nanosystem for Cyclic Therapy of Choroidal Neovascularization in Mice

Afterglow occurring after light excitation ceases offers a safer light source to the laser-activated verteporfin therapy approved by the FDA for choroidal neovascularization (CNV). However, conventional afterglow molecules, especially adamantane-dioxetanes with high steric hindrance, exhibit limited chemiexcitation, restricting electron transfer and diminishing therapeutic effects. Here, we constructed ultrabright afterglow nanosystems by integrating low-hindrance cyclobutane moieties into the dioxetane framework. Among these cyclobutane substituents, the benzyl oxocyclobutane-dioxetane is the brightest afterglow molecule due to its lowest hindrance, showing 35.7 times faster relative chemiexcitation rate and 59 times higher afterglow intensity than adamantane-dioxetane, alongside a three-order-of-magnitude increase in total afterglow emission. Consequently, at the equivalent concentration, the benzyl oxocyclobutane-dioxetane-based nanosystem produces nearly five times more singlet oxygen than free verteporfin. In a CNV mouse model, cyclic treatment with our nanosystem reduced lesion areas by 64.9%, outperforming the 39.3% reduction achieved by free verteporfin counterpart. By eliminating the need for laser activation, this strategy minimizes ocular damage, providing a safe and effective treatment for CNV and other retinal disorders.

A Novel Afterglow Molecular Probe for Monitoring of pH and Viscosity in Infected Wounds with Two-Dimensional Signal

Organic afterglow materials have shown tremendous potential in the field of biomedical imaging. However, reports on small-molecule afterglow probes, particularly those with multitarget detection capabilities, remain limited. Here, we report a novel afterglow molecule probe (Hcy-Br-SO) that effectively responds to changes in pH and viscosity during wound infection, based on a two-dimensional (2D) signal. In this design, the enhancement of molecular afterglow performance was achieved through molecular engineering, and the underlying mechanism of afterglow emission was derived. Additionally, the synergistic enhancement of the afterglow intensity of Hcy-Br-SO by the increase in the pH and viscosity was confirmed. Besides, we observed that viscosity could retard the photoreaction process, thereby extending the duration of afterglow emission. Based on this phenomenon, we transformed the traditional time-dependent characteristics of afterglow into a measurable parameter for monitoring viscosity changes. It is noteworthy that the introduction of the time dimension not only facilitates the separation of signal sources but also explores the application potential of afterglow molecular probes. To the best of our knowledge, this is the first afterglow small-molecule probe that uses 2D signals (intensity and half-life) to monitor binocular targets. Furthermore, the Hcy-Br-SO probe was successfully used to distinguish between normal and infected wounds. This work may be useful to unravel the pathological mechanisms of chronic wounds and provide guidance for intervention.

Recent Advances in Reactive Oxygen Species -Mediated Near-Infrared Organic Long-Persistent Luminescence Imaging

Organic luminophores have found extensive applications in cellular and in vivo fluorescence imaging. However, their efficacy is often hindered by formidable challenges, including a low signal-to-noise ratio (SNR), susceptibility to false-positive signals, limited tissue penetration depth, and autofluorescence arising from non-negligible background interference. The emergence of near-infrared (NIR) afterglow imaging has addressed these problems. Organic afterglow imaging distinguishes by its unique capacity to emit light long after the cessation of external excitation, thereby exhibiting extraordinary persistence in luminescence. The integration of deep tissue penetration with prolonged luminescence in NIR organic long-persistent luminescent materials confers a distinct advantage for in vivo biological imaging, effectively minimizing the confounding effects of autofluorescence while enhancing spatial resolution for imaging in deep tissues, which is favorable for biosensing. In this review, we present a comprehensive summary of recent advancements in reactive oxygen species (ROS)-mediated NIR organic afterglow imaging, positioning this emerging technique as an exceptionally promising approach for in vivo biosensing, biological imaging, imaging-guided surgery, and therapeutic applications. Furthermore, we critically examine the challenges facing this field and propose future avenues for its continued evolution and refinement.

A dark-state-dominated photochemical upconversion afterglow via triplet energy transfer relay

Photochemical afterglow materials have drawn considerable attention due to their attractive luminescent properties and great application potential. Considering the classical photochemical afterglow materials always exhibit poor luminescence, it is urgent to gain fundamental understanding of the main limiting factors. Here, we identified the existence of a dark-state triplet in the photochemical process, and an overwhelming percentage of ~98.5% was revealed for this non-emissive triplet state. Guided by these observations, we proposed to activate an unprecedented triplet energy transfer relay to simultaneously harness the singlet and triplet energy. Consequently, an upconverted afterglow material was constructed with amazing luminescence performance albeit its moderate fluorescence emission property. The generality of this strategy was evidenced by the adaptation to similar emitters with varied emission wavelengths. The optimized afterglow performance enabled time-gated upconversion bioimaging under ultralow-power excitation. This study not only reveals the energy transfer pathways for photochemical afterglow but also paves the way for rational design of bright upconverted materials with ultralong lifetime.

Cyclometalated Iridium(III) Schiff Base Complexes for Chemiluminogenic Bioprobes

Chemiluminogenic bioimaging has emerged as a promising paradigm due to its independence from light excitation, thereby circumventing challenges related to light penetration depth and background autofluorescence. However, the availability of effective chemiluminophores remains limited, which substantially impedes their bio-applications. Herein, we discovered for the first time that cyclometalated iridium(III) Schiff base complexes can unexpectedly generate chemiluminescence. Notably, the chemiluminescence reaction was rapid, with a half-life of only 0.86 s, significantly faster than previously reported examples. Unlike conventional chemiluminescent scaffolds, the distinguishing feature of the chemiluminogenic iridium(III) complex is its unique intramolecular imine-to-amide conversion upon reaction with reactive oxygen species (ROS). Intriguingly, the chemiluminogenicity of these complexes is not influenced by the cyclometalating ligands but is closely associated with the Schiff base ligand, allowing for tuning of the emission colors via altering the cyclometalating ligands. Additionally, we formulated one of the Schiff base complexes (1) as water-soluble chemiluminogenic nanoparticles (CLNPs) and successfully employed them as activatable chemiluminescence bioprobes for precise and rapid imaging of hypochlorite-related biological events both in vitro and in vivo. We believe that this significant finding of the development of chemiluminogenic Schiff base complexes will greatly facilitate the designing of innovative chemiluminophores for theranostic applications.

"All-in-One" Photochemical Afterglow Nanoplatform Based on Perovskite Quantum Dots

Photochemical reaction-based afterglow materials offer a promising solution to the tissue autofluorescence issues associated with real-time excitation in traditional fluorescence probes. Conventional photochemical afterglow systems typically consist of three components: a photosensitizer, an energy cache unit (ECU), and an emitter. However, their physical separation leads to inefficient energy transfer. We present a strategy for constructing an "all-in-one" afterglow nanoplatform (AGNP) based on perovskite quantum dots (PQDs) to enhance the energy transfer efficiency by minimizing physical separation. Modified with 1-pyrenecarboxylic acid (PCA), CsPbBr3 PQDs can serve as a photosensitizer, emitter, and ECU-phenylacetic acid (ECU-COOH) host simultaneously. The afterglow intensity of the AGNP shows a remarkable 30-fold enhancement compared with the separated ECU afterglow system, attributed to the decreased energy transfer distance. The AGNP also exhibits great versatility, enabling tunable afterglow emission across the visible region. The AGNP is further adopted for in vivo afterglow imaging with a signal-to-noise ratio of 41. This work provides an idea for constructing "all-in-one" afterglow systems and demonstrates their potential for background-free bioimaging.

Chemical Energy Lights Up Europium-Based Ultra-bright Afterglow for Bioanalysis Application

Photochemical afterglow materials are gaining great attention for the property to continuously emit light after the excitation source is removed. However, their limited luminescence quantum yield (QY) and brightness hinder the use in biological applications. In this study, we introduce a novel photochemical afterglow system that combines a newly designed photoenergy cache unit (PCU) with an emitter through coordination covalent bonds. The PCU boasts a dark state to significantly emit photons only through chemiexcitation in the process of photochemical reactions, facilitating direct energy transfer to the emitter and resulting in bright afterglow. The related mechanisms further guided us to achieve the highest reported afterglow luminescence quantum yield of 27.5 %. The system can be encapsulated and dispersed in aqueous solutions for in vivo bioimaging in living mice under mild and simple conditions (low concentration, low excitation power, short excitation time, short exposure time), and also for in vitro diagnostic through lateral flow immunoassay, enabling the highly sensitive detection of the inflammatory biomarker serum amyloid A (SAA) and demonstrating excellent correlation with clinical test results. This study offers new insights into enhancing luminescence QY and brightness of afterglow, highlighting the potential of such systems for further biomedical applications.

Crystallization-Induced Emission Enhancement or Quenching? Elucidating the Mechanism behind Using Single-Molecule-Based Versatile Crystals

It is challenging to predict optical properties of fluorescent dyes, especially in the crystalline state, owing to the uncertainty in conformation, packing, and coupling. Herein, we elucidate the decisive role of molecular conformation and molecular packing in the fluorescence emissions of some crystalline materials based on experimental results and theoretical calculations. Two homologous fluorophores (Ph-MP and Ph-HP) were synthesized, and they both exhibited interesting crystallization-induced emission enhancement and quenching. Although the homologues show almost the same fluorescence behavior in the solid state, on-off emission of their crystals depends upon different factors. Emission of the Ph-MP crystals is governed by the twisted intramolecular charge transfer effect, while emission of the Ph-HP crystals relied on π-π stacking. Based on this understanding, application of single-molecule-based versatile crystals in information encryption was demonstrated. It is believed that the evidence and unveiled mechanism for the effect of crystallization on emission will contribute to development in high-performance luminescent materials.

Ultrabright difuranfluoreno-dithiophen polymers for enhanced afterglow imaging of atherosclerotic plaques

Cardiovascular diseases, including stroke driven by atherosclerosis, remain a leading global health concern. Current diagnostic imaging modalities such as magnetic resonance imaging fail to characterize oxidative stress within atherosclerotic plaques. Here, we introduce difuranfluoreno-dithiophen-based polymers designed for afterglow imaging, offering ultrabright luminescence, ultralow-power excitation (0.087 milliwatts per square centimeter), and ultrashort acquisition times (0.01 seconds). Through a molecular engineering strategy, we have optimized polymers for enhanced reactive oxygen species (ROS) generation capability, ROS capturing capability, and fluorescence quantum yield, resulting in an increase in afterglow intensity (~130-fold) compared to commonly used 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene polymer (MEHPPV). Additionally, we have developed ratiometric afterglow nanoparticles doped with oxidative stress-responsive molecules, enabling imaging of oxidative stress markers in atherosclerotic plaque. This approach provides a tool for cardiovascular imaging and diagnostics, which is conducive to the auxiliary diagnosis and risk stratification of atherosclerosis.

Reversible redox 19F magnetic resonance imaging nanoprobes for monitoring the redox state in vivo

Redox processes are indispensable for physiology, and dysregulated redox balance is critical in various metabolic diseases. The development of imaging diagnosis tools for real-time monitoring of the redox state in vivo is of great importance yet highly challenging. Here, we designed trifluoromethyl (-CF3) grafted selenide polymer nanoprobes for reversible redox sensing in vivo. Based on the reversible shift of the 19F-nuclear magnetic resonance (NMR) peak between oxidation and reduction states of the nanoprobes exposed to different redox species, the 19F-magnetic resonance imaging (MRI) signal ratio of S Ox/(S Ox + S Red) was successfully applied to monitor the redox state in a tumor. These nanoprobes demonstrated good biocompatibility and great potential for exploring physiological and pathological redox processes in deep tissues. We envision that this work will enable the rational design of 19F-MRI nanoprobes with excellent redox response for the real-time monitoring of the redox state at the lesion location.

pH-Activatable NIR Hemicyanine for Mitochondria-Targeted Cancer Phototheranostics

Photodynamic therapy (PDT) has garnered significant attention for cancer treatment due to its noninvasive nature, reduced drug resistance, and spatiotemporal controllability. However, traditional photosensitizers (PSs) face limitations such as severe systemic phototoxicity and shallow tissue penetration, which hinder the widespread clinical application of PDT. Capitalizing on the strong near-infrared (NIR) absorption and ease of structural modification of hemicyanine, we have designed a pH-activatable NIR hemicyanine PS (LET-15). It is specifically activated in the acid tumor microenvironment, subsequently targeting mitochondria and generating cytotoxic singlet oxygen under 660 nm laser irradiation, which selectively destroys tumor tissues while minimizing damage to healthy tissues. Additionally, it offers activatable fluorescence (FL) imaging with a high signal-to-noise ratio, enabling FL imaging-assisted tumor photoeradication. This study provides valuable guidance for designing tumor-specifically activated NIR PSs for precision PDT.

Amplifying Persistent Luminescence in Heavily Doped Nanopearls for Bioimaging and Solar-to-Chemical Synthesis

Lanthanides are widely codoped in persistent luminescence phosphors (PLPs) to elevate defect concentration and enhance luminescence efficiency. However, the deleterious cross-relaxation between activators and lanthanides inevitably quenches persistent luminescence, particularly in heavily doped phosphors. Herein, we report a core-shell engineering strategy to minimize the unwanted cross-relaxation but retain the charge trapping capacity of heavily doped persistent luminescence phosphors by confining the activators and lanthanides in the core and shell, respectively. As a proof of concept, we prepared a series of codoped ZnGa2O4:Cr, Ln (CD-Ln, Ln = Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) and core-shell structured ZnGa2O4:Cr@ZnGa2O4:Ln (CS-Ln) nanoparticles. First-principles investigations suggested that lanthanide doping elevated the electron trap concentration for enhancing persistent luminescence, but energy transfer (ET) from Cr3+ to Ln3+ ions quenched the persistent luminescence. The spatial separation of Cr3+ and Ln3+ ions in the core-shell structured CS-Ln nanoparticles suppressed the ET from Cr3+ to Ln3+. Due to the efficient suppression of deleterious ET, the optimal doping concentration of Ln in CS-Ln was elevated 50 times compared to CD-Ln. Moreover, the persistent luminescence intensity of CS-5%Ln was up to 60 times that of the original ZnGa2O4:Cr. The CS-5%Ln displayed significantly improved signal-to-noise ratios in bioimaging. Further, the CS-Ln was interfaced with the lycopene-producing bacteria Rhodopseudomonas palustris for solar-to-chemical synthesis, and the lycopene productivity was increased by 190%. This work provides a reliable solution to fulfill the potential of lanthanides in enhancing persistent luminescence and can further promote the applications of persistent luminescence phosphors in biomedicine and solar-to-chemical synthesis.

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.

HClO-Activated Near-Infrared Chemiluminescent Probes with a Malononitrile Group for In-Vivo Imaging

Chemiluminescence (CL) imaging has emerged as a powerful approach to molecular imaging that allows exceptional sensitivity with virtually no background interference because of its unique capacity to emit photons without an external excitation source. Despite its high potential, the application of this nascent technique faces challenges because the current chemiluminescent agents have limited reactive sites, require complex synthesis, are insufficiently bright, and lack near-infrared emission. Herein, a series of HClO-activated chemiluminescent probes that exhibit robust near-infrared emission are studied. Specifically engineered to respond to HClO, a known biomarker of acute inflammation, these probes achieve high-contrast in vivo imaging by eliminating the need for constant external excitation. Comprehensive experimental and theoretical investigations demonstrate that the CL of the probes depends on the reactivity of the vinylene bonds, following a concerted decomposition of the oxidized chemiluminescent molecule. The application of these chemiluminescent nanoparticles in vivo facilitates high-contrast imaging of acute inflammation, providing real-time, high-contrast visualization of inflammatory conditions. This advancement signifies a leap forward for chemiluminescent nanoplatforms in biomedical imaging and expands the available methodologies in this field.

Activatable Molecular Probes With Clinical Promise for NIR-II Fluorescent Imaging

The second near-infrared window (NIR-II) fluorescence imaging has been widely adopted in basic scientific research and preclinical applications due to its exceptional spatiotemporal resolution and deep tissue penetration. Among the various fluorescent agents, organic small-molecule fluorophores are considered the most promising candidates for clinical translation, owing to their well-defined chemical structures, tunable optical properties, and excellent biocompatibility. However, many currently available NIR-II fluorophores exhibit an "always-on" fluorescence signal, which leads to background noise and compromises diagnostic accuracy during disease detection. Developing NIR-II activatable organic small-molecule fluorescent probes (AOSFPs) for accurately reporting pathological changes is key to advancing NIR-II fluorescence imaging toward clinical application. This review summarizes the rational design strategies for NIR-II AOSFPs based on four core structures (cyanine, hemicyanine, xanthene, and BODIPY). These NIR-II AOSFPs hold substantial potential for clinical translation. Furthermore, the recent advances in NIR-II AOSFPs for NIR-II bioimaging are comprehensively reviewed, offering clear guidance and direction for their further development. Finally, the prospective efforts to advance NIR-II AOSFPs for clinical applications are outlined.

Highly Photoreactive Semiconducting Polymers with Cascade Intramolecular Singlet Oxygen and Energy Transfer for Cancer-Specific Afterglow Theranostics

Afterglow luminescence provides ultrasensitive optical detection by minimizing tissue autofluorescence and increasing the signal-to-noise ratio. However, due to the lack of suitable unimolecular afterglow scaffolds, current afterglow agents are nanocomposites containing multiple components with limited afterglow performance and have rarely been applied for cancer theranostics. Herein, we report the synthesis of a series of oxathiine-containing donor-acceptor block semiconducting polymers (PDCDs) and the observation of their high photoreactivity and strong near-infrared (NIR) afterglow luminescence. We reveal that PDCDs absorb NIR light to undergo a photodynamic process to generate singlet oxygen (1O2), which intramolecularly transfers to and efficiently reacts with the oxathiine block to form the afterglow oxathiine intermediates due to the low Gibbs free energy changes required for this photoreaction. Following intramolecular afterglow energy transfer from the oxathiine donor block to the acceptor block, NIR afterglow emission is produced from PDCDs. Owing to the efficient cascade intramolecular photochemical process, PDCD-based nanoparticles achieve a higher brightness and longer NIR emission compared to most reported afterglow agents, even after ultrashort photoirradiation for only 3 s. Furthermore, the cascade photochemical process within PDCD can be inhibited after bioconjugation with a quencher-linked peptide. This allows the construction of a cancer-activatable afterglow theranostic probe (CATP) that only switches on the afterglow signal and photodynamic function in the presence of a cancer-overexpressed enzyme. Thereby, CATP represents the first afterglow phototheranostic probe that permits cancer-specific detection and photodynamic cancer therapy under preclinical settings. In summary, this study provides a molecular guideline to develop afterglow probes from photoreactive polymers.

Tetraphenylethylene-Derived Tetracarboxylate Featuring AIE Properties for Dual Ion Sensing and Mechanochromic Self-Erasable Writing

The integration of multiple functions within a single fluorescent molecule provides a promising platform for developing versatile, efficient, and cost-effective materials with enhanced performance across diverse applications. In this study, we introduce TPEC, an aggregation-induced emission (AIE) molecule derived from tetraphenylethylene-based tetracarboxylate, which demonstrates multifunctional capabilities, including metal ion sensing and self-erasable writing. TPEC exhibits amphiphilicity in water, self-assembling into single-layer nanosheets with robust blue fluorescence. Notably, the aqueous solution of TPEC displays a fluorescence colorimetric response to Al3+ ions and fluorescence quenching in the presence of Fe3+ ions. Additionally, TPEC powders undergo fluorescence colorimetric changes under mechanical stimulation, enabling self-erasable writing on prepared paper. This study presents a straightforward strategy for the development of multifunctional luminescent materials based on the self-assembly of a single-component fluorophore.

Nitrile-aminothiol bioorthogonal near-infrared fluorogenic probes for ultrasensitive in vivo imaging

Bioorthogonal chemistry-mediated self-assembly holds great promise for dynamic molecular imaging in living organisms. However, existing approaches are limited to nanoaggregates with 'always-on' signals, suffering from high signal-to-background ratio (SBR) and compromised detection sensitivity. Herein we report a nitrile-aminothiol (NAT) bioorthogonal fluorogenic probe (CyNAP-SS-FK) for ultrasensitive diagnosis of orthotopic hepatocellular carcinoma. This probe comprises a nitrile-substituted hemicyanine scaffold with a cysteine tail dually locked with biomarker-responsive moieties. Upon dual cleavage by tumor-specific cathepsin B and biothiols, the 1,2-aminothiol residue is exposed and spontaneously reacts with nitrile group for in situ intramolecular macrocyclization, enabling near-infrared fluorescence (NIRF) turn-on as well as self-assembly. In living male mice, such 'cleavage-click-assembly' regimen allows for real-time and ultrasensitive detection of small cancerous lesions (~2 mm in diameter) with improved SBR (~5) and extended detection window (~36 h), outperforming conventional clinical assays. This study not only presents NAT click reaction-based fluorogenic probes but also highlights a generic dual-locked design of these probes.

Design strategies and applications of cyanine dyes in phototherapy

Cyanine dyes have been widely used in phototherapy in recent years due to their excellent optical properties and diverse modifiable structures. This review provides detailed descriptions of the basic structures of various cyanines and their derivatives as well as their optical properties. It summarizes the strategies for constructing cyanine dyes for phototherapy and discusses their structure-effect relationship. Furthermore, a comprehensive classification and summary of the applications of cyanine dyes in phototherapy are presented. Importantly, this review also addresses both the advances made in this field as well as the challenges that need to be overcome. We hope that these profound insights into phototherapy using cyanine dyes will facilitate the design of future systems for clinical applications based on these compounds.

Shortening the early diagnostic window of Hg2+-induced liver injury with a H2O2-activated fluorescence/afterglow imaging assay

Mercury ions (Hg2+) and mercury derivatives are a serious threat to ecosystems and human health due to their toxicity, and their toxicological effects are associated with a burst of reactive oxygen species (ROS) due to the oxidative stress. Endogenous hydrogen peroxide (H2O2), a featured ROS in vivo, plays an irreplaceable role in a significant number of pathological processes. However, the exact bioeffect role that H2O2 plays in Hg2+-induced oxidative stress in a specific disease has not been well answered. In particular, optical imaging probes for H2O2 endowed with afterglow emission properties are very rare. Here, the first fluorescence/afterglow probe (FA-H2O2) for accurate and specific detection of H2O2 in cells, zebrafish, and mice under Hg2+-induced oxidative stress is reported. Moreover, FA-H2O2 in its afterglow emission enables efficient monitoring of endogenous H2O2 with a higher signal-to-noise ratio (SNR) in comparison to its fluorescence signals. More importantly, by virtue of the merits of afterglow emission that can eliminate autofluorescence, thus for the first time, shortening the diagnostic window of Hg2+-induced liver injury with FA-H2O2 via noninvasive afterglow emission tracking of H2O2 is achieved, which definitely provides a new opportunity and promising tool for early diagnosis of Hg2+-induced liver injury.

A multifunctional "three-in-one" fluorescent theranostic system for hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (HIRI) is the main cause of postoperative liver dysfunction and liver failure. Traditional separation of HIRI diagnosis and therapy confers several disadvantages, including the inability to visualize the therapeutic and asynchronous action. However, developing a versatile material with integrated diagnosis and treatment for HIRI remains a great challenge. Given that hypochlorous acid (HOCl) plays a crucial oxidative role in HIRI, we developed a single-component multifunctional fluorescent theranostic platform (MB-Gly) with a "three-in-one" molecular design incorporating a near-infrared fluorophore methylene blue, glycine and a HOCl-response unit, which could not only provide real-time visualization of HIRI but also boost targeted drug delivery. Using MB-Gly, we were able to achieve real-time and dynamic monitoring of HOCl during HIRI in hepatocytes and mouse livers and reduce the liver damage in hepatocytes and mice. RNA sequencing illustrated the therapeutic role of MB-Gly associated with changes in gene expression related to apoptosis, oxidative stress, metabolism and inflammation. To the best of our knowledge, this is the first multifunctional fluorescent theranostic system for HIRI reported to date. Our smart "three-in-one" approach shines light on the etiology and pathogenesis of HIRI, providing profound insights into the development of potential therapeutic targets.

Recent progress in small-molecule fluorescent probes for the detection of superoxide anion, nitric oxide, and peroxynitrite anion in biological systems

Superoxide anion (O2˙-), nitric oxide (NO), and peroxynitrite anion (ONOO-) play essential roles in physiological and pathological processes, which are related to various symptoms and diseases. There is a growing need to develop reliable techniques for effectively monitoring the changes in these three reactive species across different molecular events. Currently, small-molecule fluorescent probes have been demonstrated to be reliable imaging tools for the optical detection and biological analysis of reactive species in biological systems due to their high spatiotemporal resolution and in situ capabilities. In consideration of the distinct features of these three reactive species, abundant fluorescent probes have been developed to meet various requirements. In this context, we systematically summarized the latest progress (2020-2023) in organic fluorescent probes for monitoring O2˙-, NO, and ONOO- in living systems. Furthermore, the working principles and biological applications of representative fluorescent probes were illustrated. Moreover, we highlighted the current challenges and future trends of fluorescent probes, offering general insights into future research.

PEGylated BODIPY Photosensitizer for Type I Dominant Photodynamic Therapy and Afterglow Imaging

Type I photodynamic therapy (PDT) exhibits outstanding therapeutic effects in hypoxic environments in tumors, but the design of type I photosensitizers (PSs), especially those with simple structures but dramatic properties, remains a challenge. Herein, we report a design strategy for developing type I PSs in one molecule with afterglow luminescence. As a proof concept, a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) PS (BIP) bearing water-soluble poly(ethylene glycol) (mPEG550) chains is synthesized, and BIP can self-assemble into nanoparticles (BIPNs). Interestingly, BIPNs exhibit an O2•--triggered afterglow luminescence, which is scarce, especially for BODIPY derivatives. BIPNs demonstrate outstanding type I dominant PDT at an ultralow dose under both hypoxic and normoxic environments, which can significantly inhibit tumor growth under irradiation. This work highlights a high-performance PS with afterglow luminescence and excellent PDT effects, underscoring the significant potential of versatile PSs in clinical tumor theranostics.

Light/X-ray/ultrasound activated delayed photon emission of organic molecular probes for optical imaging: mechanisms, design strategies, and biomedical applications

Conventional optical imaging, particularly fluorescence imaging, often encounters significant background noise due to tissue autofluorescence under real-time light excitation. To address this issue, a novel optical imaging strategy that captures optical signals after light excitation has been developed. This approach relies on molecular probes designed to store photoenergy and release it gradually as photons, resulting in delayed photon emission that minimizes background noise during signal acquisition. These molecular probes undergo various photophysical processes to facilitate delayed photon emission, including (1) charge separation and recombination, (2) generation, stabilization, and conversion of the triplet excitons, and (3) generation and decomposition of chemical traps. Another challenge in optical imaging is the limited tissue penetration depth of light, which severely restricts the efficiency of energy delivery, leading to a reduced penetration depth for delayed photon emission. In contrast, X-ray and ultrasound serve as deep-tissue energy sources that facilitate the conversion of high-energy photons or mechanical waves into the potential energy of excitons or the chemical energy of intermediates. This review highlights recent advancements in organic molecular probes designed for delayed photon emission using various energy sources. We discuss distinct mechanisms, and molecular design strategies, and offer insights into the future development of organic molecular probes for enhanced delayed photon emission.

Reactive oxygen species-mediated organic long-persistent luminophores light up biomedicine: from two-component separated nano-systems to integrated uni-luminophores

Organic luminophores have been widely utilized in cells and in vivo fluorescence imaging but face extreme challenges, including a low signal-to-noise ratio (SNR) and even false signals, due to non-negligible background signals derived from real-time excitation lasers. To overcome these challenges, in the last decade, functionalized organic long-persistent luminophores have gained much attention. Such luminophores could not only overcome the biological toxicity of inorganic long-persistent luminescent materials (metabolic toxicity and leakage risk of inorganic heavy metals), but also continue to emit long-persistent luminescence after removing the excitation source, thus effectively improving imaging quality. More importantly, organic long-persistent luminophores have good structure tailorability for the construction of activable probes, which is favorable for biosensing. Recently, the development of reactive oxygen species (ROS)-mediated long-persistent (ROSLP) luminophores (especially organic small-molecule ROSLP luminophores) is still in the rising stage. Notably, ROSLP luminophores for in vivo imaging have experienced from two-component separated nano-systems to integrated uni-luminophores, which obtained gradually better designability and biocompatibility. In this review, we summarize the progress and challenges of organic long-persistent luminophores, focusing on their development history, long-persistent luminescence working mechanisms, and biomedical applications. We hope that these insights will help scientists further develop functionalized organic long-persistent luminophores for the biomedical field.

Microenvironment-Activatable Probe for Precise NIR-II Monitoring and Synergistic Immunotherapy in Rheumatoid Arthritis

Rheumatoid arthritis (RA) represents an insidious autoimmune inflammatory disorder that severely lowers the life quality by progressively destructing joint functions and eventually causing permanent disability, posing a serious public health problem. Here, an advanced theranostic probe is introduced that integrates activatable second near-infrared (NIR-II) fluorescence imaging for precise RA diagnosis with multi-pronged RA treatments. A novel molecular probe comprising a long-wavelength aggregation-induced emission unit and a manganese carbonyl cage motif is synthesized, which enables NIR-II fluorescence activation and concurrently releasing therapeutic carbon monoxide (CO) gas in inflamed joint microenvironment. This molecular probe self-assembles into a biocompatible nanoprobe, which is subsequently conjugated with anti-IL-6R antibody to afford active-targeting ability of RA. The nanoprobe exhibits significant turn-on NIR-II fluorescence signal at the RA lesion, enabling highly sensitive RA diagnosis and real-time therapeutic monitoring. The combination of ROS scavenging, on-demand CO gas release, and IL-6 signaling blockade results in potent therapeutic effect and synergistic immunomodulation impact, significantly alleviating the RA symptoms and preventing joint destruction. This research introduces a novel paradigm for the development of high-performance, activatable theranostic strategies to facilitate precise detection and enhanced treatment of RA-related diseases.

Dissecting Exciton Dynamics in pH-Activatable Long-Wavelength Photosensitizers for Traceable Photodynamic Therapy

Tumor-specific activatable long-wavelength (LW) photosensitizers (PSs) show promise in overcoming the limitations of traditional photodynamic therapy (PDT), such as systemic phototoxicity and shallow tissue penetration. However, their insufficient LW light absorption and low singlet oxygen quantum yield (Φ 1O2) usually require high laser power density to produce thermal energy and synergistically enhance PDT. The strong photothermal radiation causing acute pain significantly reduces patient compliance and hinders the broader clinical application of LW PDT. Through the exciton dynamics dissection strategy, we have developed a series of pH-activatable cyanine-based LW PSs (LET-R, R = H, Cl, Br, I), among which the activated LET-I exhibits strong light absorption at 808 nm and a remarkable 3.2-fold enhancement in Φ 1O2 compared to indocyanine green. Transient spectroscopic analysis and theoretical calculations confirmed its significantly promoted intersystem crossing and simultaneously enhanced LW fluorescence emission characteristics. These features enable the activatable fluorescence and photoacoustic dual-modal imaging-escorted complete photodynamic eradication of tumors by the folic acid (FA)-modified LET-I probe (LET-I-FA), under the ultralow 808 nm laser power density (0.2 W cm-2) for irradiation, without the need for photothermal energy synergy. This research presents a novel strategy of dissecting exciton dynamics to screen activatable LW PSs for traceable PDT.

Ultrarobust stable ABTS radical cation prepared using Spore@Cu-TMA biocomposites for antioxidant capacity assay

Herein, spore@Cu-trimesic acid (TMA) biocomposites were prepared by self-assembling Cu-based metal-organic framework on the surface of Bacillus velezensis spores. The laccase-like activity of spore@Cu-TMA biocomposites was enhanced by 14.9 times compared with that of pure spores due to the reaction of Cu2+ ions with laccase on the spore surface and the microporous structure of Cu-TMA shell promoting material transport and increasing substrate accessibility. Spore@Cu-TMA rapidly oxidized and transformed 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) into ABTS●+ without using H2O2. Under optimum conditions, the ABTS●+ could be stored for 21 days at 4 °C and 7 days at 37 °C without the addition of any stabilizers, allowing for the large-scale preparation and long-term storage of ABTS●+. The ultrarobust stable ABTS●+ obtained with the use of Cu-TMA could effectively reduce the "back reaction" by preventing the leaching of the metabolites released by the spores. On the basis of these findings, a rapid, low-cost, and eco-friendly colorimetric platform was successfully developed for the detection of antioxidant capacity. Determination of antioxidant capacity for several antioxidants such as caffeic acid, glutathione, and Trolox revealed their corresponding limits of detection at 4.83, 8.89, and 7.39 nM, respectively, with linear ranges of 0.01-130, 0.01-140, and 0.01-180 μM, respectively. This study provides a facile way to prepare ultrarobust stable ABTS●+ and presents a potential application of spore@Cu-TMA biocomposites in food detection and bioanalysis.

Two spirobifluene-based turn-on fluorescent probes for highly selective detection of Cysteine and the applications in cells two-photon fluorescence imaging

Two spirobifluene-based fluorescent probes SPF1 and SPF2, were designed and synthesized. The probes displayed "turn-on" fluorescence response for Cysteine. One of the challenges in developing a Cysteine probe is to secure high selectivity. SPF1/SPF2 can discriminate Cysteine from GSH as well as Hcy, and showed high substrate selectivity. The detection limit of SPF1 is 36 nM, which is excellent comparing with other optical sensors for Cysteine. The sensing mechanism of SPF1/SPF2 was verified by experimental data and theoretical calculations. There was a good linear relationship between the fluorescence intensity of SPF1/SPF2 and the concentration of Cysteine. The MTT tests indicated that SPF1/SPF2 had low cytotoxicity and good biocompatibility. Theoretical calculations demonstrated that SPF1, SPF2, and their related reaction products with Cysteine exhibited good two-photon absorption properties. Finally, SPF1/SPF2 had been successfully applied to the imaging of Cysteine in living cells under two-photon excitation.

Supramolecular engineering cascade regulates NIR-II J-aggregates to improve photodynamic therapy

Rational design of small organic molecule-based NIR-II photosensitizers (PSs) with high singlet oxygen quantum yield in aqueous solution for deep tissue imaging and cancer therapy still presents challenges. Herein, we devised a general synthesis strategy to obtain six NIR-II region PSs with tunable aggregation states by adjusting the steric effect, and all PSs possess longer NIR absorption/emission wavelengths with tails extending beyond 1200 nm. Notably, ATX-6 possessed a singlet oxygen quantum yield of 38.2% and exhibited concentration-dependent J-aggregation properties upon self-assembly in an aqueous solution. What's more, supramolecular engineering with DSPE-PEG2000 further enhanced its degree of J-aggregation, which was attributed to the dimer-excited reduction of the energy levels of the single-linear/triple-linear states and the facilitation of intersystem crossover processes. In addition, ATX-6 NPs showed superior photodynamic therapy effects and great potential in high-contrast in vivo bioimaging of the NIR-II region. These results provide valuable insights for achieving the diagnostic and therapeutic integration of tumors.

Remote Control of Energy Transformation-Based Cancer Imaging and Therapy

Cancer treatment requires precise tumor-specific targeting at specific sites that allows for high-resolution diagnostic imaging and long-term patient-tailorable cancer therapy; while, minimizing side effects largely arising from non-targetability. This can be realized by harnessing exogenous remote stimuli, such as tissue-penetrative ultrasound, magnetic field, light, and radiation, that enable local activation for cancer imaging and therapy in deep tumors. A myriad of nanomedicines can be efficiently activated when the energy of such remote stimuli can be transformed into another type of energy. This review discusses the remote control of energy transformation for targetable, efficient, and long-term cancer imaging and therapy. Such ultrasonic, magnetic, photonic, radiative, and radioactive energy can be transformed into mechanical, thermal, chemical, and radiative energy to enable a variety of cancer imaging and treatment modalities. The current review article describes multimodal energy transformation where a serial cascade or multiple types of energy transformation occur. This review includes not only mechanical, chemical, hyperthermia, and radiation therapy but also emerging thermoelectric, pyroelectric, and piezoelectric therapies for cancer treatment. It also illustrates ultrasound, magnetic resonance, fluorescence, computed tomography, photoluminescence, and photoacoustic imaging-guided cancer therapies. It highlights afterglow imaging that can eliminate autofluorescence for sustained signal emission after the excitation.

Heavy-atom-free BODIPY dendrimer: utilizing the spin-vibronic coupling mechanism for two-photon photodynamic therapy in zebrafish

In this study, the heavy-atom-free BODIPY dendrimer TM4-BDP was synthesized for near-infrared photodynamic therapy, and was composed of a triphenylamine-BODIPY dimer and four 1-(2-morpholinoethyl)-1H-indole-3-ethenyl groups. The TM4-BDP could achieve near-infrared photodynamic therapy through two different photosensitive pathways, which include one-photon excitation at 660 nm and two-photon excitation at 1000 nm. In the one-photon excitation pathway, the TM4-BDP could generate singlet oxygen and superoxide radicals under 660 nm illumination. In addition, the one-photon PDT experiment in human nasopharyngeal carcinoma (CNE-2) cells also indicated that the TM4-BDP could specifically accumulate in lysosomes and show great cell phototoxicity with an IC50 of 22.1 μM. In the two-photon excitation pathway, the two-photon absorption cross-section at 1030 nm of TM4-BDP was determined to be 383 GM, which means that it could generate reactive oxygen species (ROS) under 1000 nm femtosecond laser excitation. Moreover, the two-photon PDT experiment in zebrafish also indicated the TM4-BDP could be used for two-photon fluorescence imaging and two-photon induced ROS generation in biological environments. Furthermore, in terms of the ROS generation mechanism, the TM4-BDP employed a novel spin-vibronic coupling intersystem crossing (SV-ISC) process for the mechanism of ROS generation and the femtosecond transient absorption spectra indicated that this novel SV-ISC mechanism was closely related to its charge transfer state lifetime. These above experiments of TM4-BDP demonstrate that the dendrimer design is an effective strategy for constructing heavy-atom-free BODIPY photosensitizers in the near-infrared region and lay the foundation for two-photon photodynamic therapy in future clinical trials.

Leveraging Long-Distance Singlet-Oxygen Transfer for Bienzyme-Locked Afterglow Imaging of Intratumoral Granule Enzymes

Dual-locked activatable optical probes, leveraging the orthogonal effects of two biomarkers, hold great promise for the specific imaging of biological processes. However, their design approaches are limited to a short-distance energy or charge transfer mechanism, while the signal readout relies on fluorescence, which inevitably suffers from tissue autofluorescence. Herein, we report a long-distance singlet oxygen transfer approach to develop a bienzyme-locked activatable afterglow probe (BAAP) that emits long-lasting self-luminescence without real-time light excitation for the dynamic imaging of an intratumoral granule enzyme. Composed of an immuno-biomarker-activatable singlet oxygen (1O2) donor and a cancer-biomarker-activatable 1O2 acceptor, BAAP is initially nonafterglow. Only in the presence of both immune and cancer biomarkers can 1O2 be generated by the activated donor and subsequently diffuse toward the activated acceptor, resulting in bright near-infrared afterglow with a high signal-to-background ratio and specificity toward an intratumoral granule enzyme. Thus, BAAP allows for real-time tracking of tumor-infiltrating cytotoxic T lymphocytes, enabling the evaluation of cancer immunotherapy and the differentiation of tumor from local inflammation with superb sensitivity and specificity, which are unachievable by single-locked probes. Thus, this study not only presents the first dual-locked afterglow probe but also proposes a new design way toward dual-locked probes via reactive oxygen species transfer processes.

Ratiometric Afterglow Luminescent Imaging of Matrix Metalloproteinase-2 Activity via an Energy Diversion Process

Ratiometric afterglow luminescent (AGL) probes are attractive for in vivo imaging due to their high sensitivity and signal self-calibration function. However, there are currently few ratiometric AGL probes available for imaging enzymatic activity in living organisms. Here, we present an energy diversion (ED) strategy that enables the design of an enzyme-activated ratiometric AGL probe (RAG-RGD) for in vivo afterglow imaging. The ED process provides RAG-RGD with a radiative transition for an 'always on' 520-nm AGL signal (AGL520) and a cascade three-step energy transfer (ET) process for an 'off-on' 710-nm AGL signal (AGL710) in response to a specific enzyme. Using matrix metalloproteinase-2 (MMP-2) as an example, RAG-RGD shows a significant ~11-fold increase in AGL710/AGL520 toward MMP-2. This can sensitively detect U87MG brain tumors through ratiometric afterglow imaging of MMP-2 activity, with a high signal-to-background ratio and deep imaging depth. Furthermore, by utilizing the self-calibration effect of ratiometric imaging, RAG-RGD demonstrated a strong negative correlation between the AGL710/AGL520 value and the size of orthotopic U87MG tumor, enabling accurate monitoring of orthotopic glioma growth in vivo. This ED process may be applied for the design of other enzyme-activated ratiometric afterglow probes for sensitive afterglow imaging.

Magneto-optical nanosystems for tumor multimodal imaging and therapy in-vivo

Multimodal imaging, which combines the strengths of two or more imaging modalities to provide complementary anatomical and molecular information, has emerged as a robust technology for enhancing diagnostic sensitivity and accuracy, as well as improving treatment monitoring. Moreover, the application of multimodal imaging in guiding precision tumor treatment can prevent under- or over-treatment, thereby maximizing the benefits for tumor patients. In recent years, several intriguing magneto-optical nanosystems with both magnetic and optical properties have been developed, leading to significant breakthroughs in the field of multimodal imaging and image-guided tumor therapy. These advancements pave the way for precise tumor medicine. This review summarizes various types of magneto-optical nanosystems developed recently and describes their applications as probes for multimodal imaging and agents for image-guided therapeutic interventions. Finally, future research and development prospects of magneto-optical nanosystems are discussed along with an outlook on their further applications in the biomedical field.

Multiple photofluorochromic luminogens via catalyst-free alkene oxidative cleavage photoreaction for dynamic 4D codes encryption

Controllable photofluorochromic systems with high contrast and multicolor in both solutions and solid states are ideal candidates for the development of dynamic artificial intelligence. However, it is still challenging to realize multiple photochromism within one single molecule, not to mention good controllability. Herein, we report an aggregation-induced emission luminogen TPE-2MO2NT that undergoes oxidation cleavage upon light irradiation and is accompanied by tunable multicolor emission from orange to blue with time-dependence. The photocleavage mechanism revealed that the self-generation of reactive oxidants driving the catalyst-free oxidative cleavage process. A comprehensive analysis of TPE-2MO2NT and other comparative molecules demonstrates that the TPE-2MO2NT molecular scaffold can be easily modified and extended. Further, the multicolor microenvironmental controllability of TPE-2MO2NT photoreaction within polymer matrices enables the fabrication of dynamic fluorescence images and 4D information codes, providing strategies for advanced controllable information encryption.

Lysosomal-targeted fluorescent probe based pH regulating reactivity for tracking cysteine dynamics under oxidative stress

The ability to detect and visualize cellular events and associated biological analytes is essential for the understanding of their physiological and pathological functions. Cysteine (Cys) plays a crucial role in biological systems and lysosomal homeostasis. This puts forward higher requirements on the performance of the probe. Herein, we rationally designed a coumarin-based probe for the reversible, specific, sensitive, and rapid detection of Cys based on pH regulating reactivity. The obtained probe (ECMA) introduces a morpholine moiety to target lysosomes, and α,β-unsaturated-ketone with an electron-withdrawing CN group served as a reversible reaction site for Cys. Importantly, ECMA was successfully applied to the real-time monitoring of Cys dynamics in living cells. Furthermore, cell imaging clearly revealed that exogenous Cys could induce the up-regulation of lysosomal ROS, which provided a powerful tool for investigating the relationship between oxidative stress and lysosomal Cys.

Lanthanide Inorganic Nanoparticles Enhance Semiconducting Polymer Nanoparticles Afterglow Luminescence for In Vivo Afterglow/Magnetic Resonance Imaging

Dual/multimodal imaging strategies are increasingly recognized for their potential to provide comprehensive diagnostic insights in cancer imaging by harnessing complementary data. This study presents an innovative probe that capitalizes on the synergistic benefits of afterglow luminescence and magnetic resonance imaging (MRI), effectively eliminating autofluorescence interference and delivering a superior signal-to-noise ratio. Additionally, it facilitates deep tissue penetration and enables noninvasive imaging. Despite the advantages, only a limited number of probes have demonstrated the capability to simultaneously enhance afterglow luminescence and achieve high-resolution MRI and afterglow imaging. Herein, we introduce a cutting-edge imaging platform based on semiconducting polymer nanoparticles (PFODBT) integrated with NaYF4@NaGdF4 (Y@Gd@PFO-SPNs), which can directly amplify afterglow luminescence and generate MRI and afterglow signals in tumor tissues. The proposed mechanism involves lanthanide nanoparticles producing singlet oxygen (1O2) upon white light irradiation, which subsequently oxidizes PFODBT, thereby intensifying afterglow luminescence. This innovative platform paves the way for the development of high signal-to-background ratio imaging modalities, promising noninvasive diagnostics for cancer.

Recent Advances of Aminopeptidases-Responsive Small-Molecular Probes for Bioimaging

Aminopeptidases, enzymes with critical roles in human body, are emerging as vital biomarkers for metabolic processes and diseases. Aberrant aminopeptidase levels are often associated with diseases, particularly cancer. Small-molecule probes, such as fluorescent, fluorescent/photoacoustics, bioluminescent, and chemiluminescent probes, are essential tools in the study of aminopeptidases-related diseases. The fluorescent probes provide real-time insights into protein activities, offering high sensitivity in specific locations, and precise spatiotemporal results. Additionally, photoacoustic probes offer signals that are able to penetrate deeper tissues. Bioluminescent and chemiluminescent probes can enhance in vivo imaging abilities by reducing the background. This comprehensive review is focused on small-molecule probes that respond to four key aminopeptidases: aminopeptidase N, leucine aminopeptidase, Pyroglutamate aminopeptidase 1, and Prolyl Aminopeptidase, and their utilization in imaging tumors and afflicted regions. In this review, the design strategy of small-molecule probes, the variety of designs from previous studies, and the opportunities of future bioimaging applications are discussed, serving as a roadmap for future research, sparking innovations in aminopeptidase-responsive probe development, and enhancing our understanding of these enzymes in disease diagnostics and treatment.

Single-Component Photochemical Afterglow Near-Infrared Luminescent Nano-Photosensitizers: Bioimaging and Photodynamic Therapy

Long afterglow luminescence-guided photodynamic therapy (PDT) performs advantages of noninvasiveness, spatiotemporal controllability, and higher signal to noise ratio. Photochemical afterglow (PCA) system emitting afterglow in an aqueous environment is highly suitable for biomedical applications, but still faces the challenges of poor tissue penetration depth and responsive sensitivity. In this work, two novel compounds, Iso-TPA and ABEI-TPA, are designed and synthesized to integrate the PCA system as a single component by coupling near-infrared (NIR) photosensitizers with singlet oxygen cache units, respectively. Both compounds emit NIR afterglow based on photochemical reaction. ABEI-TPA exhibits higher photoluminescence quantum efficiency with nonconjugated linkage, while Iso-TPA with conjugated linkage possesses better reactive oxygen species generation efficiency to achieve stronger PCA and effective PDT, which is ascribed to stronger intramolecular charge transfer effect of Iso-TPA. Iso-TPA nanoparticles can achieve effective long-lasting NIR afterglow in vivo bioimaging up to 120 s with higher imaging resolution and outstanding PDT efficacy of tumor, exhibiting promising potential on bioimaging and therapy.

A near-IR ratiometric fluorescent probe for the precise tracking of senescence: a multidimensional sensing assay of biomarkers in cell senescence pathways

Senescence is a complex physiological process that can be induced by a range of factors, and cellular damage caused by reactive oxygen species (ROS) is one of the major triggers. In order to learn and solve age-related diseases, tracking strategies through biomarkers, including senescence-associated β-galactosidase (SA-β-gal), with high sensitivity and accuracy, have been considered as a promising solution. However, endogenous β-gal accumulation is not only associated with senescence but also with other physiological processes. Therefore, additional assays are needed to define cellular senescence further. In this work, a fancy fluorescent probe SA-HCy-1 for accurately monitoring senescence is developed, with SA-β-gal and HClO as targets under high lysosomal pH conditions (pH > 6.0) specifically, on account of the role β-gal commonly played as an ovarian cancer biomarker. Therefore, precise tracking of cellular senescence could be achieved in view of these three dimensions, with response in dual fluorescence channels providing a ratiometric sensing pattern. This elaborate strategy has been verified to be suitable for biological applications by skin photo-aging evaluation and cellular passage tracing, displaying a significantly improved sensitivity compared with the commercial X-gal kit measurement.

"Zero" Intrinsic Fluorescence Sensing-Platforms Enable Ultrasensitive Whole Blood Diagnosis and In Vivo Imaging

Abnormal physiological processes and diseases can lead to content or activity fluctuations of biocomponents in organelles and whole blood. However, precise monitoring of these abnormalities remains extremely challenging due to the insufficient sensitivity and accuracy of available fluorescence probes, which can be attributed to the background fluorescence arising from two sources, 1) biocomponent autofluorescence (BCAF) and 2) probe intrinsic fluorescence (PIF). To overcome these obstacles, we have re-engineered far-red to NIR II rhodol derivatives that possess weak BCAF interference. And a series of "zero" PIF sensing-platforms were created by systematically regulating the open-loop/spirocyclic forms. Leveraging these advancements, we devised various ultra-sensitive NIR indicators, achieving substantial fluorescence boosts (190 to 1300-fold). Among these indicators, 8-LAP demonstrated accurate tracking and quantifying of leucine aminopeptidase (LAP) in whole blood at various stages of tumor metastasis. Furthermore, coupling 8-LAP with an endoplasmic reticulum-targeting element enabled the detection of ERAP1 activity in HCT116 cells with p53 abnormalities. This delicate design of eliminating PIF provides insights into enhancing the sensitivity and accuracy of existing fluorescence probes toward the detection and imaging of biocomponents in abnormal physiological processes and diseases.

Synergetic Pyroptosis with Apoptosis Improving Phototherapy of Mitochondria-Targeted Cyanines with Superior Photostability

Pyroptosis has been reported to improve the antitumor effect by evoking a more intense immune response and a therapeutic effect. For phototherapy, several photosensitizers have been found to initiate pyroptosis. However, the effect of pyroptosis associated with apoptosis in enhancing the antitumor therapy needs sufficient characterization, especially under long-term treatment. As a NIR photosensitizer, heptamethine cyanines have been discovered for anticancer phototherapy for deep tissue penetration and inherent tumor-targeted capability. However, they are not quite stable for long-term performance. To investigate the effect of pyroptosis along with apoptosis on the anticancer immune responses and phototherapy, here, we chemically modulate the cyanine IR780 to regulate hydrophobicity, stability, and intracellular targeting. Two photosensitizers, T780T-TPP and T780T-TPP-C12, were finally optimized and showed excellent photostability with high photothermal conversion efficiency. Although the cellular uptake of the two molecules was both mediated by OATP transporters, T780T-TPP induced tumor cell death via pyroptosis and apoptosis and accumulated in tumor accumulation, while T780T-TPP-C12 was prone to accumulate in the liver. Ultimately, via one injection-multiple irradiation treatment protocol, T780T-TPP displayed a significant antitumor effect, even against the growth of large tumors (200 mm3).

Acidity-activatable upconversion afterglow luminescence cocktail nanoparticles for ultrasensitive in vivo imaging

Activatable afterglow luminescence nanoprobes enabling switched "off-on" signals in response to biomarkers have recently emerged to achieve reduced unspecific signals and improved imaging fidelity. However, such nanoprobes always use a biomarker-interrupted energy transfer to obtain an activatable signal, which necessitates a strict distance requisition between a donor and an acceptor moiety (<10 nm) and hence induces low efficiency and non-feasibility. Herein, we report organic upconversion afterglow luminescence cocktail nanoparticles (ALCNs) that instead utilize acidity-manipulated singlet oxygen (1O2) transfer between a donor and an acceptor moiety with enlarged distance and thus possess more efficiency and flexibility to achieve an activatable afterglow signal. After in vitro validation of acidity-activated afterglow luminescence, ALCNs achieve in vivo imaging of 4T1-xenograft subcutaneous tumors in female mice and orthotopic liver tumors in male mice with a high signal-to-noise ratio (SNR). As a representative targeting trial, Bio-ALCNs with biotin modification prove the enhanced targeting ability, sensitivity, and specificity for pulmonary metastasis and subcutaneous tumor imaging via systemic administration of nanoparticles in female mice, which also implies the potential broad utility of ALCNs for tumor imaging with diverse design flexibility. Therefore, this study provides an innovative and general approach for activatable afterglow imaging with better imaging performance than fluorescence imaging.

Molecularly generated light and its biomedical applications

Molecularly generated light, referred to here as "molecular light", mainly includes bioluminescence, chemiluminescence, and Cerenkov luminescence. Molecular light possesses unique dual features of being both a molecule and a source of light. Its molecular nature enables it to be delivered as molecules to regions deep within the body, overcoming the limitations of natural sunlight and physically generated light sources like lasers and LEDs. Simultaneously, its light properties make it valuable for applications such as imaging, photodynamic therapy, photo-oxidative therapy, and photobiomodulation. In this review article, we provide an updated overview of the diverse applications of molecular light and discuss the strengths and weaknesses of molecular light across various domains. Lastly, we present forward-looking perspectives on the potential of molecular light in the realms of molecular imaging, photobiological mechanisms, therapeutic applications, and photobiomodulation. While some of these perspectives may be considered bold and contentious, our intent is to inspire further innovations in the field of molecular light applications.

Bifunctional Tumor-Targeted Bioprobe for Phototheranosis

Background: Near-infrared (NIR) phototheranostics provide promising noninvasive imaging and treatment for head and neck squamous cell carcinoma (HNSCC), capitalizing on its adjacency to skin or mucosal surfaces. Activated by laser irradiation, targeted NIR fluorophores can selectively eradicate cancer cells, harnessing the power of synergistic photodynamic therapy and photothermal therapy. However, there is a paucity of NIR bioprobes showing tumor-specific targeting and effective phototheranosis without hurting surrounding healthy tissues. Methods: We engineered a tumor-specific bifunctional NIR bioprobe designed to precisely target HNSCC and induce phototheranosis using bioconjugation of a cyclic arginine-glycine-aspartic acid (cRGD) motif and zwitterionic polymethine NIR fluorophore. The cytotoxic effects of cRGD-ZW800-PEG were measured by assessing heat and reactive oxygen species (ROS) generation upon an 808-nm laser irradiation. We then determined the in vivo efficacy of cRGD-ZW800-PEG in the FaDu xenograft mouse model of HNSCC, as well as its biodistribution and clearance, using a customized portable NIR imaging system. Results: Real-time NIR imaging revealed that intravenously administered cRGD-ZW800-PEG targeted tumors rapidly within 4 h postintravenous injection in tumor-bearing mice. Upon laser irradiation, cRGD-ZW800-PEG produced ROS and heat simultaneously and exhibited synergistic photothermal and photodynamic effects on the tumoral tissue without affecting the neighboring healthy tissues. Importantly, all unbound bioprobes were cleared through renal excretion. Conclusions: By harnessing phototheranosis in combination with tailored tumor selectivity, our targeted bioprobe ushers in a promising paradigm in cancer treatment. It promises safer and more efficacious therapeutic avenues against cancer, marking a substantial advancement in the field.