Afterglow Imaging Research Articles

Recent Development of Organic Afterglow Probes for Diagnosis and Treatment of Cancer

Afterglow imaging plays a crucial role in the cancer treatment field. In contrast to inorganic afterglow imaging agents, organic afterglow imaging agents possess easily modifiable structures and exhibit excellent biocompatibility, thereby presenting significant prospects for application in tumor diagnosis and management. In this review, we summarize the design principles and applications of afterglow probes in tumor imaging and therapy. Finally, we discuss the future challenges and prospects of organic afterglow probes in cancer diagnosis and therapy.

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.

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.

Persistent luminescent nanoparticles with enhanced afterglow through polydopamine modification for separation-free and visual detection of iron ions in water

Fluorescence analysis is one of the most popular methods in metal ions detection, but the background interference is an unavoidable obstacle in the fluorescence analysis of complex samples. In this work, a persistent luminescence nanoprobe was designed to detect iron ions in real samples by avoiding background interference. First, the Sr4Al14O25:Eu2+, Dy3+ persistent luminescent nanoparticles (PLNPs) were prepared by solid-state reaction protocols and polydopamine (PDA) encapsulation. After modification, these PLNPs@PDA showed better afterglow performance. More importantly, the PLNPs@PDA are highly selective toward iron ions, and could serve as an afterglow “turn off” nanoprobe for selective detection of iron ions through a dynamic quenching mechanism, with a detection limit of 2.86 μM. To further realize rapid and on-site detection, a test strip based on PLNPs@PDA was prepared and applied, which also showed good detection performance in real water samples. Compared with other detection methods, this afterglow imaging detection does not depend on expensive instruments, and can effectively shield the interference of background fluorescence from complex water samples, which has a good application prospects in the actual water sample. This work opens a new avenue for developing afterglow probe for the detection of metal ion in water samples without background interference.

Single-Atom Iridium Nanozyme-Based Persistent Luminescence Nanoparticles for Multimodal Imaging-Guided Combination Tumor Therapy.

Persistent luminescence nanoparticles (PLNPs) can achieve autofluorescence-free afterglow imaging, while near-infrared (NIR) emission realizes deep tissue imaging. Nanozymes integrate the merits of nanomaterials and enzyme-mimicking activities with simple preparation. Here PLNPs are prepared of Zn1.2Ga1.6Ge0.2O4:Cr0.0075 with NIR emission at 700 nm. The PLNPs are then incubated with IrCl3 solution, and the nanoparticles are collected and annealed at 750 °C to obtain iridium@PLNPs. Iridium is observed on the PLNPs at the atomic level as a single-atom nanozyme with peroxidase-like catalytic activity, photothermal conversion, and computed tomography (CT) contrast capability. After coating with exosome membrane (EM), the Ir@PLNPs@EM composite exhibits long-lasting NIR luminescence, peroxidase-like catalytic activity, photothermal conversion, and CT contrast capability, with the targeting capability and biocompatibility from EM. Thus, NIR afterglow/photothermal/CT trimodal imaging-guided photothermal-chemodynamic combination therapy is realized as validated with the in vitro and in vivo inhibition of tumor growth, while toxicity and side effects are avoided as drug-free treatment. This work offers a promising avenue for advanced single-atom nanozyme@PLNPs to promote the development of nanozymes and PLNPs for clinical applications.

Enabling robust near-infrared afterglow polymers through cascade energy transfer

Near-infrared afterglow materials, which can significantly reduce background fluorescence and improve penetration in living organisms, are vital for precision imaging. However, the practicability of near-infrared afterglow materials has been hindered by their short lifetime and low luminescence quantum efficiency. Herein, we propose an effective strategy for doping water-soluble afterglow polymer host materials with fluorescent dyes, leveraging the step-by-step Förster energy transfer principle to realize near-infrared afterglow. Benefiting from the ultralong lifetime of 4.2 s and high quantum efficiency of 20.1 % for the blue host PAMCz as well as efficient cascade energy transfer efficiency of 83.3 %, the developed NIR afterglow exhibits luminescence peaked at 750 nm, a lifetime of 1.4 s, and a quantum efficiency of 17.1 %. A successful demonstration of near-infrared afterglow biological imaging with a penetration depth of 3.4 mm and signal-to-background ratio of 48.3, has been established. These advancements expand the scope of near-infrared afterglow materials by combining an ultralong lifetime with high quantum efficiency, providing a roadmap for designing robust near-infrared materials.

Imaging-guided companion diagnostics in radiotherapy by monitoring APE1 activity with afterglow and MRI imaging

Companion diagnostics using biomarkers have gained prominence in guiding radiotherapy. However, biopsy-based techniques fail to account for real-time variations in target response and tumor heterogeneity. Herein, we design an activated afterglow/MRI probe as a companion diagnostics tool for dynamically assessing biomarker apurinic/apyrimidinic endonuclease 1(APE1) during radiotherapy in vivo. We employ ultrabright afterglow nanoparticles and ultrasmall FeMnOx nanoparticles as dual contrast agents, significantly broadening signal change range and enhancing the sensitivity of APE1 imaging (limit of detection: 0.0092 U/mL in afterglow imaging and 0.16 U/mL in MRI). We devise longitudinally and transversely subtraction-enhanced imaging (L&T-SEI) strategy to markedly enhance MRI contrast and signal-to-noise ratio between tumor and normal tissue of living female mice. The combined afterglow and MRI facilitate both anatomical and functional imaging of APE1 activity. This probe enables correlation of afterglow and MRI signals with APE1 expression, radiation dosage, intratumor ROS, and DNA damage, enabling early prediction of radiotherapy outcomes (as early as 3 h), significantly preceding tumor size reduction (6 days). By monitoring APE1 levels, this probe allows for early and sensitive detection of liver organ injury, outperforming histopathological analysis. Furthermore, MRI evaluates APE1 expression in radiation-induced abscopal effects provides insights into underlying mechanisms, and supports the development of treatment protocols.

Multifunctional Thermally Activated Delayed Fluorescence Carbon Dots for Temperature‐Responsive Sensor, Information Encryption, and Organelle Imaging

Abstract Thermally activated delay fluorescence (TADF) has great potential for information encryption, temperature detection, and bioimaging due to its long‐lived luminescence, temperature‐sensitive and high signal‐to‐noise ratio. However, it is still a challenge to establish TADF in aqueous environments. In this study, the composite with TADF (M‐FNCDs) is prepared using fluorine‐nitrogen co‐doped carbon dots (FNCDs) and melamine. It is worth mentioning that the M‐FNCDs show stable TADF under long‐wavelength excitation (470 nm) in aqueous environments. Moreover, the M‐FNCDs has distinctive temperature‐responsive properties and exhibit good linear relationships in the temperature range of 77–370 K. Simultaneously, M‐FNCDs suspension as the ink is utilized to realize information encryption/decryption due to their afterglow cannot be quenched in an aqueous solution. More importantly, M‐FNCDs with biocompatibility can target the mitochondria and lysosomes of living cells, and for the first time achieve the high signal‐to‐noise ratio and low background signal afterglow imaging of organelles. This work proposes a new strategy to prepare the stable TADF in aqueous solutions under long‐wavelength excitation and extend the TADF material potential applications in the future.

Chemiluminescent Afterglow Material for Enhanced Tumor Diagnosis and Photodynamic Therapy

AbstractAfterglow materials offer great advantages for imaging, including ultra‐long luminescent lifetimes for sustained signal after excitation, high signal‐to‐noise ratios due to minimal tissue autofluorescence interference, and the ability to achieve deep tissue penetration with near‐infrared (NIR) afterglow. AIEgens, known for their potent singlet oxygen (¹O₂) generation during photodynamic therapy (PDT), further enhance the approach. Here is the first report on how to integrate AIEgens with chemiluminescent agents for constructing NIR afterglow materials, enabling chemiluminescence resonance energy transfer (CRET)‐mediated activation of AIEgens for targeted PDT. DCL/TBQ nanoparticles (NPs) exemplify this promising theranostic design. These NPs exhibit high selectivity and sensitivity toward ONOO−, a biomarker associated with tumors, with a low limit of detection (46.1 nm). Additionally, DCL/TBQ NPs boast impressive deep tissue penetration (2 cm) and a remarkable 120‐fold improvement in signal‐to‐noise ratio for tumor afterglow imaging. Most importantly, significant tumor growth inhibition capabilities are demonstrated. This approach holds immense potential for the development of next‐generation theranostic agents, enabling simultaneous tumor diagnosis and treatment with improved accuracy and efficacy.

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

AbstractRatiometric 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.

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.

Edible Long-Afterglow Photoluminescent Materials for Bioimaging.

Confining luminophores into modified hydrophilic matrices or polymers is a straightforward and widely used approach for afterglow bioimaging. However, the afterglow quantum yield and lifetime of the related material remain unsatisfactory, severely limiting the using effect especially for deep-tissue time-resolved imaging. This fact largely stems from the dilemma between material biocompatibility and the quenching effect of water environment. Herein an in situ metathesis promoted doping strategy is presented, namely, mixing ≈10-3 weight ratio of organic-emitter multicarboxylates with inorganic salt reactants, followed by metathesis reactions to prepare a series of hydrophilic but water-insoluble organic-inorganic doping afterglow materials. This strategy leads to the formation of edible long-afterglow photoluminescent materials with superior biocompatibility and excellent bioimaging effect. The phosphorescence quantum yield of the materials can reach dozens of percent (the highest case: 66.24%), together with the photoluminescent lifetime lasting for coupes of seconds. Specifically, a long-afterglow barium meal formed by coronene salt emitter and BaSO4 matrix is applied into animal experiments by gavage, and bright stomach afterglow imaging is observed by instruments or mobile phone after ceasing the photoexcitation with deep tissue penetration. This strategy allows a flexible dosage of the materials during bioimaging, facilitating the development of real-time probing and theranostic technology.

Excellent Persistent Near-Infrared Room Temperature Phosphorescence from Highly Efficient Host-Guest Systems.

Organic near-infrared (NIR) room temperature phosphorescence (RTP) materials become a hot topic in bioimaging and biosensing for the large penetration depth and high signal-to-background ratio (SBR). However, it is challenging to achieve persistent NIR phosphorescence for severe nonradiative transitions by energy-gap law. Herein, a universal system with persistent NIR RTP is built by visible (host) and NIR phosphorescence (guest) materials, which can efficiently suppress the nonradiative transitions by rigid environment of crystalline host materials with good matching, and further promote phosphorescence emission by the additional phosphorescence resonance energy transfer (≈100%) between them. The persistent NIR phosphorescence with ten-folds enhancement of RTP lifetimes, compared to those of guest luminogens, can be achieved by modulation of aggregated structures of host-guest systems. This work provides a convenient way to largely prolong the phosphorescence lifetimes of various NIR luminogens, promoting their application in afterglow imaging with deeper penetration and higher SBRs.

An upconverted afterglow color conversion strategy for in-situ activated persistent luminescent imaging of medical implants

Upconverted afterglow imaging presents a promising avenue for long-term auto-fluorescence-free imaging applications without the necessity of expensive time-resolved equipment. In this research, inspired by LED design, we devised a straightforward ternary upconverted afterglow conversion (UAC) strategy that amalgamates upconversion NaYbF4: Tm0.005 (UP), afterglow ZnS:Cu,Co (AP), and color conversion CaAlSiN3:Eu phosphors (CP). This fusion resulted in a UAC composite that displays a deep-red to near-infrared (NIR) afterglow with a peak at 663 nm, following a brief activation period by 980 nm light. Importantly, an enhancement of 116 times was realized by using the UAC strategy when comparing with a typical single phase afterglow phosphor, Zn3Ga2SnO8:Cr,Yb,Er. The NIR-rechargeable afterglow sustained for a minimum of 100 min after a mere 3 s of NIR wireless charging process and is chemically stable. This makes it highly suitable for long-term luminescence imaging applications. To demonstrate its potential, we employed our ternary UAC phosphor to image medical plastic prostheses through pig skin in vitro and simulated a plastic surgery on a mouse model in vivo. Such luminescent information could prove invaluable for planning future surgical interventions, such as prosthesis replacement, removal, or necessary debris cleaning.

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.

Mitochondria-targeting near-infrared fluorescence/afterglow sensing assay for the rapid detection of HClO and its application in the early detection of Alzheimer's disease

Hypochloric acid (HClO) in living organisms is generated by the catalysis of myeloperoxidase (MPO). As an inflammatory signaling molecule, it can lead to neuronal cell death in the process of neuroinflammation, which is closely related to the etiology of Alzheimer’s disease (AD). Therefore, it is of great significance to develop effective tools for the localization of HClO in the early pathological process of AD. Therefore, a near-infrared (NIR) fluorescent probe HCy-1 targeting mitochondria for brain HClO detection was developed in this work. The reaction time between HCy-1 and HClO is short (within in 10 minutes), and the rapid detection of hypochlorous acid can be realized by naked eyes. HCy-1 also shows high selectivity and sensitivity to HClO with a detection limit of 34.5 nM, and the fluorescence intensity of HCy-1 at 715 nm is increased over 38 times after the incubation of HClO. HCy-1 can be used to detect both exogenous and endogenous HClO in PC-12 nerve cells and RAW 264.7 cells, and it can also be used for oxidative stress imaging analysis in AD cell model. For in vivo experiments, HCy-1 showed a strong ability to penetrate the blood-brain barrier, and the fluctuation of HClO could be detected in AD mice. More importantly, the special structure of hemicyanine was used to perform afterglow imaging under in vitro light irradiation, which proved that HCy-1 could detect the early onset of AD in a lower background.

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.

Regulating Triplet Excitons of Organic Luminophores for Promoted Bioimaging.

Afterglow materials with organic room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF) exhibit significant potential in biological imaging due to their long lifetime. By utilizing time-resolved technology, interference from biological tissue fluorescence can be mitigated, enabling high signal-- to-background ratio imaging. Despite the continued emergence of individual reports on RTP or TADF in recent years, comprehensive reviews addressing these two materials are rare. Therefore, this review aims to provide a comprehensive overview of several typical molecular designs for organic RTP and TADF materials. It also explores the primary methods through which triplet excitons resist quenching by water and oxygen. Furthermore, we analyze the principal challenges faced by afterglow materials and discuss key directions for future research with the hope of inspiring developments in afterglow imaging.

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.