Self-Assembled Semiconducting Polymer Nanoparticles for Ultrasensitive Near-Infrared Afterglow Imaging of Metastatic Tumors

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.

Molecular Engineering of a Self-Sustaining Modular Afterglow Scaffold for In Vivo Activatable Imaging

Self-sustaining afterglow molecules (SAMs) offer high simplicity, reproducibility, and design flexibility compared to common multicomponent systems. To date, only a few SAMs have been reported. However, these studies mainly focus on probe selection and screening, without providing the guidance for constructing SAMs from the bottom up. Herein, we report the molecular design and tuning of a boron dipyrromethene derivative (BDI), with structural engineering to enhance the singlet oxygen (1O2) reactivity and photosensitivity, aiming to construct SAMs for activatable afterglow imaging. The optimized BDI is customized into water-soluble nanoparticles (i.e., BDI-NPs) aided by an amphiphilic polymer, achieving all-in-one afterglow luminescence with a peak at 780 nm. An activatable afterglow probe (i.e., BDIS-NPs) is fabricated, which can simultaneously activate fluorescence and afterglow signals in the presence of hydrogen disulfide (H2S). Owing to the elimination of autofluorescence and high activation contrast of the afterglow signal, BDIS-NPs enables early monitoring of lipopolysaccharide (LPS)-induced acute lung injury within 15 min and sensitive visualization of H2S accumulation in the brain of schizophrenia mice with a high signal-to-background ratio (SBR), which is not achievable by fluorescence imaging. This study provides an in-depth understanding and design guidelines for SAMs and activatable afterglow imaging.

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.

Controllable Self-Assembly Morphologies of PPV-Based Block Copolymers

Poly(p-phenylenevinylene) (PPV) is a classic semiconducting π-conjugated polymer with outstanding optical and electronic properties, which shows important applications in the fields of optoelectronic, such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect transistors (OFETs). In the working process of the device, the microstate of PPV decides its property. Therefore, it is significant to achieve ordered morphologies based on PPV at micro scale. Due to the long rigid backbone and large area of delocalized electron, PPV has a strong tendency towards ordered aggregation through intermolecular π-π interaction, and "rod-coil" type block copolymer (BCP) based on PPV with a corona chain to improve the solubility is always built for self-assembly in situ solution. However, obtaining regular PPV based micro-/nano-structures in a controllable and uniform form remains challenging. In this review, we summarize the progresses in constructing multi-dimensional regular self-assembly morphologies based on PPV BCPs and exploring the application potential of these delicate functional nanomaterials. The molecular design strategy and growth mechanism can be extended to regulate the aggregation state of functional semiconducting conjugated polymers, which is beneficial to improving their performance in application of microelectronics, optoelectronics, biology and so on.

Near‐Infrared Emission Perovskites for Multifunctional Bioimaging

Bioimaging with remarkable noninvasive nature, ultrahigh resolution and sensitivity allows detection of pathologies of bones, organs, and tissues. Nevertheless, the achievement of more complete information in vivo is challenged by the necessity of multiple photodetectors with diverse response ranges. Herein, a multifunctional bioimaging with Cs2AgInCl6:Yb3+ perovskites via a single InGaAs detector for superior tissue presentation is realized in this work. Co‐incorporation of foreign dopant contributes to alterations of local structural symmetry of the Cs2AgInCl6 host, disruption of parity‐forbidden transitions, and reduction in electron–phonon coupling strength, thereby boosting the near‐infrared (NIR) intensity by 40‐fold of the corresponding perovskites drastically. Moreover, an X‐ray excited NIR light output is 2.83 times that of commercial Bi4Ge3O12 scintillators. Thanks to the efficient NIR emission, the versatile perovskites film endows a multifunctional bioimaging with detailed information of biological tissue in vivo, which fundamentally offers viable avenues for promoting bioimaging technology with integrated access of tissue presentation.

Biodegradable semiconducting polymer nanoparticles for phototheranostics

Semiconducting polymer nanoparticles (SPNs) have been widely applied for phototheranostics. However, the disadvantage of in vivo long-term metabolism greatly suppresses the clinical application of SPNs. To improve the metabolic rate and minimize the long-term toxicity of SPNs, biodegradable semiconducting polymers (BSPs), whose backbones may be degraded under certain conditions, have been designed. This review summarizes recent advances in BSP-constructed nanoparticles (BSPNs) for phototheranostics. BSPs are divided into two categories: conjugated backbone degradable BSPs (CBD-BSPs) and non-conjugated backbone degradable BSPs (NCBD-BSPs), based on the feature of chemical structure. The biological applications, including cancer imaging and combination therapy, of these BSPNs are described. Finally, the conclusion and future perspectives of this field are discussed.

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.

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.

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.

Catalytic NIR chemiluminescence sensor with enhanced persistence and intensity for in vivo imaging

Chemiluminescence (CL) is a self-illumination phenomenon that involves the emission of light from chemical reactions, and it provides favorable spatial and temporal information on biological processes. However, it is still a great challenge to construct effective CL sensors that equip strong CL intensity, long emission wavelength, and persistent luminescence for deep tissue imaging. Here, we report a liposome encapsulated polymer dots (Pdots)-based system using catalytic CL substrates (L-012) as energy donor and fluorescent polymers and dyes (NIR 695) as energy acceptors for efficient Near-infrared (NIR) CL in vivo imaging. Thanks to the modulation of paired donor and acceptor distance and the slow diffusion of biomarker by liposome, the Pdots show a NIR emission wavelength (λ em, max = 720 nm), long CL duration (>24 h), and a high chemiluminescence resonance energy transfer efficiency (46.5 %). Furthermore, the liposome encapsulated Pdots possess excellent biocompatibility, sensitive response to H2O2, and persistent whole-body NIR CL imaging in the drug-induced inflammation and the peritoneal metastatic tumor mouse model. In a word, this NIR-II CL nanoplatform with long-lasting emission and high spatial-temporal resolution will be a concise strategy in deep tissue imaging and clinical diagnostics.

A Tumor-Activatable Liposomal Nanoprobe for Selective Visualization of Metastatic Lymph Nodes

The precise identification of sentinel lymph nodes (SLNs) during surgery and assessment of their benign status is crucial for accurate tumor staging and optimal treatment strategizing. Currently, a deficiency exists in non-invasive in vivo diagnostic techniques that can accurately pinpoint SLNs during surgery while simultaneously evaluating their benign status. Here, a tumor-activatable liposomal nanoprobe (nTAL) is developed, remotely loaded with clinically approved photosensitizer, methyl aminolevulinate (MAL), to noninvasively visualize the tumor metastasis lymph nodes (LNs) with precision. Benefited from the highly efficient LNs draining of nanosized liposome and tumor cell-specific transformation of the non-fluorescent MAL to fluorescent protoporphyrin IX (PPIX), nTAL succeeded in targeting the SLNs and differentiated the metastatic from the benign ones with a positive correlation between PPIX generation and tumor cell infiltration in LNs. Moreover, the nTAL technology is capable of probing the early metastatic stage with a primary tumor size of 50 mm3. This study provides a new strategy for intraoperative visualization of real-time sentinel node dissection.

NIR afterglow nanosystem for photodynamic therapy

Within the milieu of immune dysfunction, reactive oxygen species (ROS) play a pivotal role in inducing immunogenic cell death (ICD), countering the dysregulated tumor microenvironment. However, the administration of ROS at indiscriminate dosages may provoke deleterious immune responses. Therefore, precise regulation of ROS production is crucial to achieve efficacious therapeutic outcomes. We engineered an innovative afterglow nanosystem which is capable of real-time monitoring of ROS levels. Our findings reveal that Ru/CYQ@CPPO exhibits a markedly enhanced and prolonged afterglow luminescence, coupled with superior singlet oxygen (O2) generation, compared to the commercially available indocyanine green (ICG). In vitro studies demonstrated that Ru/CYQ@CPPO exhibits remarkable efficacy in photodynamic therapy (PDT) under irradiation at a wavelength of 450 nm. Furthermore, a significant correlation (R 2 = 0.987) was observed between the intensity of afterglow luminescence and the rate of cancer cell inhibition.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

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.

Afterglow Performance of Phenylenevinylene-Based Semiconducting Polymer Nanoparticles Doped with Photosensitizers Containing Electron-Withdrawing Groups

It is usually believed that doping with photosensitizers capable of generating singlet oxygen (1O2) plays a pivotal role in enhancing the afterglow performance of semiconducting polymer nanoparticles (SPNs). However, the effect of doping photosensitizer bearing electron-withdrawing groups has not been reported. Here we report the effect of doping with six photosensitizers possessing different electron-withdrawing groups on the afterglow performance of SPNs using poly[(9,9-di(2-ethylhexyl)-9H-fluo-rene-2,7-vinylene)-co-(1-methoxy-4-(2-ethylhexyloxy)-2,5-phenylenevinylene)] (PF-MEHPPV) as substrate. It was found that the afterglow performance of SPNs was significantly influenced by doping with photosensitizers bearing electron-withdrawing groups. For the doped photosensitizers with strong electron-withdrawing groups, the stronger the electron-withdrawing ability of the group, the worse of the afterglow performance of the SPN regardless of the 1O2 generation ability of the photosensitizer. When the doped photosensitizer exhibited weak or none electron-withdrawing effect, the 1O2 generation ability of the photosensitizer played a dominant role on the afterglow performance of the SPNs. This work deepens the understanding of the design and synthesis of SPNs with different afterglow properties.

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.

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

Modular Synthesis of Semiconducting Graft Copolymers to Achieve "Clickable" Fluorescent Nanoparticles with Long Circulation and Specific Cancer Targeting

Semiconducting polymer nanoparticles (SPNs) are explored for applications in cancer theranostics because of their high absorption coefficients, photostability, and biocompatibility. However, SPNs are susceptible to aggregation and protein fouling in physiological conditions, which can be detrimental for in vivo applications. Here, a method for achieving colloidally stable and low-fouling SPNs is described by grafting poly(ethylene glycol) (PEG) onto the backbone of the fluorescent semiconducting polymer, poly(9,9'-dioctylfluorene-5-fluoro-2,1,3-benzothiadiazole), in a simple one-step substitution reaction, postpolymerization. Further, by utilizing azide-functionalized PEG, anti-human epidermal growth factor receptor 2 (HER2) antibodies, antibody fragments, or affibodies are site-specifically "clicked" onto the SPN surface, which allows the functionalized SPNs to specifically target HER2-positive cancer cells. In vivo, the PEGylated SPNs are found to have excellent circulation efficiencies in zebrafish embryos for up to seven days postinjection. SPNs functionalized with affibodies are then shown to be able to target HER2 expressing cancer cells in a zebrafish xenograft model. The covalent PEGylated SPN system described herein shows great potential for cancer theranostics.

Tumor Microenvironment Activatable Nanoprodrug System for In Situ Fluorescence Imaging and Therapy of Liver Cancer

The development of new imaging and treatment nanoprodrug systems is highly demanded for diagnosis and therapy of liver cancer, a severe disease characterized by a high recurrence rate. Currently, available small molecule drugs are not possible for cancer diagnosis because of the fast diffusion of imaging agents and low efficacy in treatment due to poor water solubility and significant toxic side effects. In this study, we report the development of a tumor microenvironment activatable nanoprodrug system for the diagnosis and treatment of liver cancer. This nanoprodrug system can accumulate in the tumor site and be selectively activated by an excess of hydrogen peroxide (H2O2) in the tumor microenvironment, releasing near-infrared solid-state organic fluorescent probe (HPQCY-1) and phenylboronic acid-modified camptothecin (CPT) prodrug. Both HPQCY-1 and CPT prodrugs can be further activated in tumor sites for achieving more precise in situ near-infrared (NIR) fluorescence imaging and treatment while reducing the toxic effects of drugs on normal tissues. Additionally, the incorporation of hydrophilic multivalent chitosan as a carrier effectively improved the water solubility of the system. This research thus provides a practical new approach for the diagnosis and treatment of liver cancer.

Nanomaterials for light-mediated therapeutics in deep tissue

Light-mediated therapeutics, including photodynamic therapy, photothermal therapy and light-triggered drug delivery, have been widely studied due to their high specificity and effective therapy. However, conventional light-mediated therapies usually depend on the activation of light-sensitive molecules with UV or visible light, which have poor penetration in biological tissues. Over the past decade, efforts have been made to engineer nanosystems that can generate luminescence through excitation with near-infrared (NIR) light, ultrasound or X-ray. Certain nanosystems can even carry out light-mediated therapy through chemiluminescence, eliminating the need for external activation. Compared to UV or visible light, these 4 excitation modes penetrate more deeply into biological tissues, triggering light-mediated therapy in deeper tissues. In this review, we systematically report the design and mechanisms of different luminescent nanosystems excited by the 4 excitation sources, methods to enhance the generated luminescence, and recent applications of such nanosystems in deep tissue light-mediated therapeutics.

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.

Design of donor-acceptor conjugated polymers based on diketopyrrolopyrrole for NIR-II multifunctional imaging

Diketopyrrolopyrrole (DPP) is an excellent photosensitizer and photothermal agent with the advantages of good planarity, strong electron affinity, high electron mobility, easy purification, easy structural modification and high molar absorption coefficient. It is regarded as one of the ideal choices for the design and synthesis of efficient organic photovoltaic materials. Therefore, two kinds of donor-acceptor (D-A) conjugated polymers were designed and synthesized with DPP as the acceptor, and their optical properties and applications in the near-infrared region were studied. The quantum yield (QY) of PBDT-DPP is 0.46%, and the highest temperature reached within 10 minutes after irradiation with a 660 nm laser is 60 °C. Another polymer, EDOT-DPP, has a QY of 0.48%, and its semiconductor polymer nanoparticle aqueous solution can reach 60 °C within 12 minutes under laser irradiation, achieving photothermal treatment of nude mice tumors. Both polymer NPs have good biocompatibility and promising applications in bioimaging and photothermal therapy.

A Highly Bright Near-Infrared Afterglow Luminophore for Activatable Ultrasensitive In Vivo Imaging

Afterglow luminescence imaging probes, with long-lived emission after cessation of light excitation, have drawn increasing attention in biomedical imaging field owing to their elimination of autofluorescence. However, current afterglow agents always suffer from an unsatisfactory signal intensity and complex systems consisting of multiple ingredients. To address these issues, this study reports a near-infrared (NIR) afterglow luminophore (TPP-DO) by chemical conjugation of an afterglow substrate and a photosensitizer acting as both an afterglow initiator and an energy relay unit into a single molecule, resulting in an intramolecular energy transfer process to improve the afterglow brightness. The constructed TPP-DO NPs emit a strong NIR afterglow luminescence with a signal intensity of up to 108  p/s/cm2 /sr at a low concentration of 10 μM and a low irradiation power density of 0.05 W/cm2 , which is almost two orders of magnitude higher than most existing organic afterglow probes. The highly bright NIR afterglow luminescence with minimized background from TPP-DO NPs allows a deep tissue penetration depth ability. Moreover, we develop a GSH-activatable afterglow probe (Q-TPP-DO NPs) for ultrasensitive detection of subcutaneous tumor with the smallest tumor volume of 0.048 mm3 , demonstrating the high potential for early diagnosis and imaging-guided surgical resection of tumors.

Functionalized [2.2]Paracyclophanedienes as Monomers for Poly(p-phenylenevinylene)s

Poly(p-phenylenevinylene)s (PPVs) featuring complex side-chains, to date, have only been synthesized by nonliving polymerization methods which have no control over PPV molecular weights, dispersities, or end groups. [2.2]Paracyclophane-1,9-diene (pCpd) has gained attention as a monomer for its ability to be ring-opened to PPV in a living fashion. pCpd, an organic cyclic scaffold with planar chirality, has seen minimal structural diversity due to the harsh reaction conditions required to afford the highly strained compound. Herein, we introduce a general method to overcome this by targeting the synthesis of a monohydroxy-pCpd via mono-demethylation of a dialkoxy-pCpd. The monohydroxy-pCpd can then be functionalized easily, which we demonstrate using three distinct side-chains with four moieties commonly incorporated in conjugated polymers: an alkyl bromide, an oligo(ethylene glycol) chain, an enantiomerically pure side-chain, and a Boc-protected amine. These monofunctionalized-pCpds were investigated as monomers in the ring-opening metathesis polymerization (ROMP) to afford functionalized PPVs in a living manner. The functional-group-containing PPVs are synthesized with full control over their end groups, repeat units, and dispersities. The feasibility of post-polymerization modifications to incorporate any desired moiety to PPV fabricated by this method was demonstrated using an azide-alkyne click reaction. All synthesized PPVs were soluble in organic solvents and display the same fluorescent emission, indicating their conjugated backbones are unaltered.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Iron-chelated semiconducting oligomer nanoparticles for NIR-II fluorescence imaging-guided enhanced chemodynamic/photothermal combination therapy

Chemodynamic therapy (CDT) has attracted increasing attention owing to its high tumor specificity and low number of side effects. However, the low absolute concentration of reactive oxygen species (ROS) within tumor cells restricts the CDT efficacy. Herein, we use dihydroartemisinin (DHA) to enhance the CDT efficacy and combine photothermal therapy (PTT) to further improve the anticancer effect. To achieve such a goal, an iron-containing semiconducting oligomer nanoparticle (DHA@FePSOD) is prepared by loading DHA into a Fe3+-chelated NIR-II fluorescent semiconducting oligomer (FePSOD). The Fe3+ ion within DHA@FePSOD can be reduced to the Fe2+ ion by glutathione (GSH) and subsequently catalyze the decomposition of hydrogen peroxide (H2O2) into the highly toxic hydroxyl radical (˙OH) for CDT. The loaded DHA may be further reduced by Fe2+ and generate a DHA radical to enhance the CDT efficacy. In addition, DHA@FePSOD shows a good photothermal effect and intense NIR-II fluorescence signal under 808 nm laser irradiation. Both in vitro and in vivo studies prove the better anticancer effect of DHA@FePSOD than FePSOD, which is attributed to the loaded DHA. Furthermore, DHA@FePSOD can effectively accumulate into a tumor and delineate the tumor via NIR-II fluorescence imaging. This study thus provides an efficient approach for developing a NIR-II fluorescence imaging-guided enhanced chemodynamic/photothermal combination therapeutic nanoplatform.

Afterglow/Photothermal Bifunctional Polymeric Nanoparticles for Precise Postbreast-Conserving Surgery Adjuvant Therapy and Early Recurrence Theranostic

Adjuvant whole-breast radiotherapy is essential for breast cancer patients who adopted breast-conserving surgery (BCS) to reduce the risk of local recurrences, which however suffer from large-area and highly destructive ionizing radiation-induced adverse events. To tackle this issue, an afterglow/photothermal bifunctional polymeric nanoparticle (APPN) is developed that utilizes nonionizing light for precise afterglow imaging-guided post-BCS adjuvant second near-infrared (NIR-II) photothermal therapy. APPN consists of a tumor cell targeting afterglow agent, which is doped with a NIR dye as an afterglow initiator and a NIR-II light-absorbing semiconducting polymer as a photothermal transducer. Such a design realizes precise afterglow imaging-guided NIR-II photothermal ablation of minimal residual breast tumor foci after BCS, thus achieving complete inhibition of local recurrences. Moreover, APPN enables early diagnosis and treatment of local recurrence after BCS. This study thus provides a nonionizing modality for precision post-BCS adjuvant therapy and early recurrence theranostic.

Near-infrared absorbing semiconducting polymer nanomedicines for cancer therapy

As a new type of organic optical nanomaterials, semiconducting polymer nanoparticles (SPNs) have the advantages of good optical characteristics and photostability, low toxicity concerns, and relatively simple preparation processes. Particularly, near-infrared (NIR) absorbing SPNs have shown a great promise in biomedicine. In addition to acting as nanoprobes for molecular imaging, these SPNs can produce local heat and reactive oxygen species with the stimulation of NIR light, allowing photothermal therapy (PTT) and photodynamic therapy (PDT), respectively. Herein, we summarize the recent development of SPN-based nanomedicines for cancer therapy. The rational designs of SPNs for enhanced PTT, PDT, or combinational PTT/PDT to achieve effective ablation of tumor tissues are highlighted. Via loading/conjugating SPNs with other therapeutic elements (such as chemotherapeutic drugs and immunotherapeutic agents), phototherapy-combined chemotherapy or immunotherapy can be realized, which is then discussed. In especial, the constructions of SPN-based nanomedicines for NIR photoactivatable chemotherapy and immunotherapy are introduced with representative examples. Finally, we discuss the current challenges and key concerns of SPNs for their biomedical applications and give an outlook for their future clinical translation. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Conjugated Polymer Nanoparticles for Tumor Theranostics

Water-dispersible conjugated polymer nanoparticles (CPNs) have demonstrated great capabilities in biological applications, such as in vitro cell/subcellular imaging and biosensing, or in vivo tissue imaging and disease treatment. In this review, we summarized the recent advances of CPNs used for tumor imaging and treatment during the past five years. CPNs with different structures, which have been applied to in vivo solid tumor imaging (fluorescence, photoacoustic, and dual-modal) and treatment (phototherapy, drug carriers, and synergistic therapy), are discussed in detail. We also demonstrated the potential of CPNs as cancer theranostic nanoplatforms. Finally, we discussed current challenges and outlooks in this field.

Ultra-long Near-infrared Repeatable Photochemical Afterglow Mediated by Reversible Storage of Singlet Oxygen for Information Encryption

Photochemical afterglow systems have drawn considerable attention in recent years due to their regulable photophysical properties and charming application potential. However, conventional photochemical afterglow suffered from its unrepeatability due to the consumption of energy cache units as afterglow photons are emitted. Here we report a novel strategy to realize repeatable photochemical afterglow (RPA) through the reversible storage of ¹ O₂ by 2-pyridones. Near-infrared afterglow with a lifetime over 10 s is achieved, and its initial intensity shows no significant reduction over 50 excitation cycles. A detailed mechanism study was conducted and confirmed the RPA is realized through the singlet oxygen-sensitized fluorescence emission. Furthermore, the generality of this strategy is demonstrated and tunable afterglow lifetimes and colors are achieved by rational design. The developed RPA is further applied for attacker-misleading information encryption, presenting a repeatable-readout.

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

Afterglow luminescence (long persistent luminescence) holds great potential for nonbackground molecular imaging. However, current afterglow probes are mainly nanoparticles, and afterglow imaging systems based on organic small molecules are still lacking and have rarely been reported. Moreover, the lack of reactive sites and a universal molecular scaffold makes it difficult to design activatable afterglow probes. To address these issues, this study reports a novel kind of hemicyanine-based molecule scaffolds with stimuli-responsive afterglow luminescence, which is dependent on an intramolecular cascade photoreaction between ¹O₂ and the afterglow molecule to store the photoenergy for delayed luminescence after light cessation. As a proof of concept, three modular activatable molecular afterglow probes (MAPs) with a "four-in-one" molecular design by integrating a stimuli-responsive unit, ¹O₂-generating unit, ¹O₂-capturing unit, and luminescent unit into one probe are customized for quantification and imaging of targets including pH, superoxide anions, and aminopeptidase. Notably, MAPs show higher sensitivity in afterglow imaging than in fluorescence imaging because the responsive unit simultaneously controls the initiation of fluorescence (S₁ to S₀) and ¹O₂ generation (S₁ to T₁). Finally, MAPs are applied for high-contrast afterglow imaging of drug-induced hepatotoxicity, which is poorly evaluated in clinics and drug discovery. By reporting the sequential occurrence of oxidative stress and upregulation of aminopeptidase, such activatable afterglow probes allow noninvasive imaging of hepatotoxicity earlier than the serological and histology manifestation, indicating their promise for early diagnosis of hepatotoxicity.

Recent advances of CREKA peptide-based nanoplatforms in biomedical applications

Nanomedicine technology is a rapidly developing field of research and application that uses nanoparticles as a platform to facilitate the diagnosis and treatment of diseases. Nanoparticles loaded with drugs and imaging contrast agents have already been used in clinically, but they are essentially passive delivery carriers. To make nanoparticles smarter, an important function is the ability to actively locate target tissues. It enables nanoparticles to accumulate in target tissues at higher concentrations, thereby improving therapeutic efficacy and reducing side effects. Among the different ligands, the CREKA peptide (Cys-Arg-Glu-Lys-Ala) is a desirable targeting ligand and has a good targeting ability for overexpressed fibrin in different models, such as cancers, myocardial ischemia-reperfusion, and atherosclerosis. In this review, the characteristic of the CREKA peptide and the latest reports regarding the application of CREKA-based nanoplatforms in different biological tissues are described. In addition, the existing problems and future application perspectives of CREKA-based nanoplatforms are also addressed.

Nanoparticles in the diagnosis and treatment of cancer metastases: Current and future perspectives

Metastasis accounts for greater than 90% of cancer-related deaths. Despite recent advancements in conventional chemotherapy, immunotherapy, targeted therapy, and their rational combinations, metastatic cancers remain essentially untreatable. The distinct obstacles to treat metastases include their small size, high multiplicity, redundancy, therapeutic resistance, and dissemination to multiple organs. Recent advancements in nanotechnology provide the numerous applications in the diagnosis and prophylaxis of metastatic diseases, including the small particle size to penetrate cell membrane and blood vessels and their capacity to transport complex molecular 'cargo' particles to various metastatic regions such as bones, brain, liver, lungs, and lymph nodes. Indeed, nanoparticles (NPs) have demonstrated a significant ability to target specific cells within these organs. In this regard, the purpose of this review is to summarize the present state of nanotechnology in terms of its application in the diagnosis and treatment of metastatic cancer. We intensively reviewed applications of NPs in fluorescent imaging, PET scanning, MRI, and photoacoustic imaging to detect metastasis in various cancer models. The use of targeted NPs for cancer ablation in conjunction with chemotherapy, photothermal treatment, immuno therapy, and combination therapy is thoroughly discussed. The current review also highlights the research opportunities and challenges of leveraging engineering technologies with cancer cell biology and pharmacology to fabricate nanoscience-based tools for treating metastases.

Nanoparticles with ultrasound-induced afterglow luminescence for tumour-specific theranostics

Molecular imaging via afterglow luminescence minimizes tissue autofluorescence and increases the signal-to-noise ratio. However, the induction of afterglow requires the prior irradiation of light, which is attenuated by scattering and absorption in tissue. Here we report the development of organic nanoparticles producing ultrasound-induced afterglow, and their proof-of-concept application in cancer immunotheranostics. The 'sonoafterglow' nanoparticles comprise a sonosensitizer acting as an initiator to produce singlet oxygen and subsequently activate a substrate for the emission of afterglow luminescence, which is brighter and detectable at larger tissue depths (4 cm) than previously reported light-induced afterglow. We formulated sonoafterglow nanoparticles containing a singlet-oxygen-cleavable prodrug for the immune-response modifier imiquimod that specifically turn on in the presence of the inflammation biomarker peroxynitrite, which is overproduced by tumour-associated M1-like macrophages. Systemic delivery of the nanoparticles allowed for sonoafterglow-guided treatment of mice bearing subcutaneous breast cancer tumours. The high sensitivity and depth of molecular sonoafterglow imaging may offer advantages for the real-time in vivo monitoring of physiopathological processes.

Semiconducting Polymer Dots for Point-of-Care Biosensing and In Vivo Bioimaging: A Concise Review

In recent years, semiconducting polymer dots (Pdots) have attracted much attention due to their excellent photophysical properties and applicability, such as large absorption cross section, high brightness, tunable fluorescence emission, excellent photostability, good biocompatibility, facile modification and regulation. Therefore, Pdots have been widely used in various types of sensing and imaging in biological medicine. More importantly, the recent development of Pdots for point-of-care biosensing and in vivo imaging has emerged as a promising class of optical diagnostic technologies for clinical applications. In this review, we briefly outline strategies for the preparation and modification of Pdots and summarize the recent progress in the development of Pdots-based optical probes for analytical detection and biomedical imaging. Finally, challenges and future developments of Pdots for biomedical applications are given.

Organic persistent luminescence imaging for biomedical applications

Persistent luminescence is a unique visual phenomenon that occurs after cessation of excitation light irradiation or following oxidization of luminescent molecules. The energy stored within the molecule is released in a delayed manner, resulting in luminescence that can be maintained for seconds, minutes, hours, or even days. Organic persistent luminescence materials (OPLMs) are highly robust and their facile modification and assembly into biocompatible nanostructures makes them attractive tools for in vivo bioimaging, whilst offering an alternative to conventional fluorescence imaging materials for biomedical applications. In this review, we give attention to the existing limitations of each class of OPLM-based molecular bioimaging probes based on their luminescence mechanisms, and how recent research progress has driven efforts to circumvent their shortcomings. We discuss the multifunctionality-focused design strategies, and the broad biological application prospects of these molecular probes. Furthermore, we provide insights into the next generation of OPLMs being developed for bioimaging techniques.

Recyclable Endogenous H2 S Activation of Self-Assembled Nanoprobe with Controllable Biodegradation for Synergistically Enhanced Colon Cancer-Specific Therapy

Excessive production of hydrogen sulfide (H₂ S) plays a crucial role in the progress of colon cancer. Construction of tumor-specific H₂ S-activated smart nanoplatform with controllable biodegradation is of great significance for precise and sustainable treatment of colon cancer. Herein, an endogenous H₂ S triggered Co-doped polyoxometalate (POM-Co) cluster with self-adjustable size, controlled biodegradation, and sustainable cyclic depletion of H₂ S/glutathione (GSH) is designed for synergistic enhanced tumor-specific photothermal and chemodynamic therapy. The designed POM-Co nanocluster holds H₂ S responsive "turn-on" photothermal property in colon cancer via self-assembling to form large-sized POM-CoS, enhancing the accumulation at tumor sites. Furthermore, the formed POM-CoS can gradually biodegrade, resulting in release of Co²⁺ and Mo⁶⁺ for Co(II)-catalyzed •OH production and Russell mechanism-enabled ¹ O₂ generation with GSH consumption, respectively. More importantly, the degraded POM-CoS is reactivated by endogenous H₂ S for recyclable and sustainable consumption of H₂ S and GSH, resulting in tumor-specific photothermal/chemodynamic continuous therapy. Therefore, this study provides an opportunity of designing tumor microenvironment-driven nanoprobes with controllable biodegradation for precise and sustainable anti-tumor therapy.

The Role of Optical Imaging in Translational Nanomedicine

Nanomedicines have been a major research focus in the past two decades and are increasingly emerging in a broad range of clinical applications. However, a proper understanding of their biodistribution is required to further progress the field of nanomedicine. For this, imaging methods to monitor the delivery and therapeutic efficacy of nanoparticles are urgently needed. At present, optical imaging is the most common method used to study the biodistribution of nanomaterials, where the unique properties of nanomaterials and advances in optical imaging can jointly result in novel methods for optimal monitoring of nanomaterials in preclinical animal models. This review article aims to give an introduction to nanomedicines and their translational impact to highlight the potential of optical imaging to study the biodistribution of nanoparticles and to monitor the delivery and therapeutic efficacy at the preclinical level. After introducing both domains, the review focuses on different techniques that can be used to overcome some intrinsic limitations of optical imaging and how this can specifically benefit nanoparticle studies. Finally, we point out some important key features of nanoparticles that currently hinder their full potential in the clinic and how the advances in optical imaging can help to provide us with the information needed to further boost the clinical translation and expand the field of nanomedicines.

A biomineral-inspired approach of synthesizing colloidal persistent phosphors as a multicolor, intravital light source

Many in vivo biological techniques, such as fluorescence imaging, photodynamic therapy, and optogenetics, require light delivery into biological tissues. The limited tissue penetration of visible light discourages the use of external light sources and calls for the development of light sources that can be delivered in vivo. A promising material for internal light delivery is persistent phosphors; however, there is a scarcity of materials with strong persistent luminescence of visible light in a stable colloid to facilitate systemic delivery in vivo. Here, we used a bioinspired demineralization (BID) strategy to synthesize stable colloidal solutions of solid-state phosphors in the range of 470 to 650 nm and diameters down to 20 nm. The exceptional brightness of BID-produced colloids enables their utility as multicolor luminescent tags in vivo with favorable biocompatibility. Because of their stable dispersion in water, BID-produced nanophosphors can be delivered systemically, acting as an intravascular colloidal light source to internally excite genetically encoded fluorescent reporters within the mouse brain.

Enzyme-mediated intratumoral self-assembly of nanotheranostics for enhanced imaging and tumor therapy

Enzyme-mediated intratumoral self-assembled (EMISA) nanotheranostics represent a new class of smart agents for combined imaging and therapy of cancer. Cancer cells overexpress various enzymes that are essential for high metabolism, fast proliferation, and tissue invasion and metastasis. By conjugating small molecules that contain an enzyme-specific cleavage site to appropriate chemical linkers, it is possible to induce self-assembly of nanostructures in tumor cells having the target enzyme. This approach of injecting small theranostic molecules that eventually become larger nanotheranostics in situ avoids some of the major limitations that are encountered when injecting larger, pre-assembled nanotheranostics. The advantage of EMISA nanotheranostics include the avoidance of nonspecific uptake and rapid clearance by phagocytic cells, increased cellular accumulation, reduced drug efflux and prolonged cellular exposure time, all of which lead to an amplified imaging signal and therapeutic efficacy. We review here the different approaches that can be used for preparing EMISA-based organic, inorganic, or organic/inorganic hybrid nanotheranostics based on noncovalent interactions and/or covalent bonding. Imaging examples are shown for fluorescence imaging, nuclear imaging, photoacoustic imaging, Raman imaging, computed tomography imaging, bioluminescent imaging, and magnetic resonance imaging. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures.

Activatable Persistent Luminescence from Porphyrin Derivatives and Supramolecular Probes with Imaging-Modality Transformable Characteristics for Improved Biological Applications

Persistent luminescence without excitation light and tissue autofluorescence interference holds great promise for biological applications, but is limited by available materials with long-wavelength emission and excellent clinical potential. Here, we report that porphyrin derivatives can emit near-infrared persistent luminescence over 60 min after cessation of excitation light or on interaction with peroxynitrite. A plausible mechanism of the successive oxidation of vinylene bonds was demonstrated. A supramolecular probe with a β-sheet structure was constructed to enhance the tumor targeting ability and the photoacoustic and persistent luminescence signals. Such probes featuring light-triggered function transformation from photoacoustic imaging to persistent luminescence imaging permit advanced image-guided cancer surgery. Furthermore, peroxynitrite-activated persistent luminescence of the supramolecular probe also enables rapid and precise screening of immunogenic cell death drugs.

Multifunction-Harnessed Afterglow Nanosensor for Molecular Imaging of Acute Kidney Injury In Vivo

Afterglow is superior to other optical modalities for biomedical applications in that it can exclude the autofluorescence background. Nevertheless, afterglow has rarely been applied to the high-contrast "off-to-on" activatable sensing scheme because the complicated afterglow systems hamper the additional inclusion of sensory functions while preserving the afterglow luminescence. Herein, a simple formulation of a multifunctional components-incorporated afterglow nanosensor (MANS) is developed for the superoxide-responsive activatable afterglow imaging of cisplatin-induced kidney injury. A multifunctional iridium complex (Ir-OTf) is designed to recover its photoactivities (phosphorescence and the ability of singlet oxygen-generating afterglow initiator) upon exposure to superoxide. To construct the nanoscopic afterglow detection system (MANS), Ir-OTf is incorporated with another multifunctional molecule (rubrene) in the polymeric micellar nanoparticle, where rubrene also plays dual roles as an afterglow substrate and a luminophore. The multiple functions covered by Ir-OTf and rubrene renders the composition of MANS quite simple, which exhibits superoxide-responsive "off-to-on" activatable afterglow luminescence for periods longer than 11 min after the termination of pre-excitation. Finally, MANS is successfully applied to the molecular imaging of cisplatin-induced kidney injury with activatable afterglow signals responsive to pathologically overproduced superoxide in a mouse model without autofluorescence background.

NIR-II imaging-guided diagnosis and evaluation of the therapeutic effect on acute alcoholic liver injury via a nanoprobe

Acute alcoholic liver injury (AALI) is hard to diagnose on account of no obvious clinical symptoms, and thereby it easily develops into serious liver diseases and threatens people's health. However, traditional methods for detecting AALI are far from satisfactory due to the low sensitivity, invasiveness and non-visualization, and the development of new techniques is in urgent demand. Near-infrared (NIR)-II fluorescence imaging has been widely studied in biochemistry and biomedicine. As the blood flow velocity of the liver is closely related to the progression of AALI, herein, a NIR-II fluorescent nanoprobe, NTPB-NPs, was applied to diagnose AALI by monitoring the fluorescence intensity changes in the liver caused by the variations of the blood flow velocity. More importantly, when medication was applied to alleviate the liver injury of AALI mice, NTPB-NPs could also track the therapeutic effect in situ. In this study, the relationship between hepatic vascular velocity and the progression of AALI was confirmed with NTPB-NPs via NIR-II imaging. To the best of our knowledge, this is the first time that a NIR-II fluorescence imaging technique has been used to diagnose AALI mice and evaluate the therapeutic effect on AALI mice. This study may also provide a potential NIR-II imaging agent for clinical research to improve the management of liver injury related diseases.

Polymeric agents for activatable fluorescence, self-luminescence and photoacoustic imaging

Numerous polymeric agents have been widely applied in biology and medicine by virtue of the facile chemical modification, feasible nano-engineering approaches and fine-tuned pharmacokinetics. To endow polymeric imaging agents with ability to monitor and measure subtle molecular or cellular alterations at diseased sites, activatable polymeric probes that can elicit signal changes in response to biomolecular interactions or the analytes of interest have to be developed. Herein, this review aims to provide a systemic interpretation and summarization of the design methodology and imaging utility of recently emerged activatable polymeric probes. An introduction of activatable probes allowing for precise imaging and classification of polymeric imaging agents is reported first. Then, we give a detailed discussion of the contemporary design approaches toward activatable polymeric probes in diverse imaging modes for the detection of various stimuli and their imaging applications. Finally, current challenges and future advances are discussed and highlighted.

Ratiometric afterglow luminescent nanoplatform enables reliable quantification and molecular imaging

Afterglow luminescence is an internal luminescence pathway that occurs after photo-excitation, holds great promise for non-background molecular imaging in vivo, but suffer from poor quantitative ability owing to luminescent attenuation over time. Moreover, the inert structure and insufficient reactive sites of current afterglow materials make it hard to design activatable afterglow probes for specific detection. Here, we report a ratiometric afterglow luminescent nanoplatform to customize various activatable afterglow probes for reliable quantification and molecular imaging of specific analytes, such as NO, ONOO⁻ or pH. Notably, these afterglow probes can not only address the attenuation of afterglow intensity and eliminate the interference of factors (e.g., laser power, irradiation time, and exposure time), but also significantly improve the imaging reliability in vivo and signal-to-background ratios (~1200-fold), both of which enable more reliable quantitative analysis in biological systems. Moreover, as a proof-of-concept, we successfully design an NO-responsive ratiometric afterglow nanoprobe, RAN1. This nanoprobe can monitor the fluctuations of intratumoral NO, as a biomarker of macrophage polarization, making it possible to real-time dynamically evaluate the degree cancer immunotherapy, which provides a reliable parameter to predict the immunotherapeutic effect.

Afterglow luminescence is promising for non-background molecular imaging in vivo. Here the authors report a ratiometric afterglow luminescent nanoplatform to generate activatable afterglow probes for quantification of specific analytes including NO.

Near-Infrared Afterglow Luminescence of Chlorin Nanoparticles for Ultrasensitive In Vivo Imaging

Afterglow imaging holds great potential for ultrasensitive biomedical imaging. As it detects photons after the cessation of real-time light excitation, autofluorescence can therefore be effectively eliminated. However, afterglow imaging is still in its infant stage due to the lack of afterglow agents with satisfactory lifetime, biocompatibility, and high luminescence brightness, particularly afterglow in the near-infrared region for in vivo applications. To address these issues, this study for the first time reports chlorin nanoparticles (Ch-NPs) emitting afterglow luminescence peaking at 680 nm with a half-life of up to 1.5 h, which is almost 1 order of magnitude longer than those of other reported organic afterglow probes. In-depth experimental and theoretical studies revealed that the brightness of the afterglow luminescence is strongly correlated with the singlet oxygen (¹O₂) capacity and the oxidizability of the chlorins. Benefitting from the ultralong half-life and the minimized imaging background, small metastatic tumor foci of 3 mm³ were successfully resected under the guidance of the afterglow luminescence generated upon a single shot of activation prior to the injection, which was impossible for conventional near-infrared fluorescence imaging due to tissue autofluorescence.

Enhancing Penetration Ability of Semiconducting Polymer Nanoparticles for Sonodynamic Therapy of Large Solid Tumor

Sonodynamic therapy (SDT) holds growing promise in deep-seated or large solid tumor treatment owing to its high tissue penetration depth ability; however, its therapeutic efficacy is often compromised due to the hypopermeable and hypoxic characteristics in the tumor milieu. Herein, a semiconducting polymer nanoparticle (SPNC) that synergistically enhances tumor penetration and alleviates tumor hypoxia is reported for sonodynamic therapy of large solid tumors. SPNC comprises a semiconducting polymer nanoparticle core as a sonodynamic converter coated with a poly (ethylene glycol) corona. An oxygen-modulating enzyme, catalase, is efficiently conjugated to the surface of nanoparticles via the coupling reaction. Superior to its counterpart SPNCs (SPNC2 (84 nm) and SPNC3 (134 nm)), SPNC with the smallest size (SPNC1 (35 nm)) can efficiently penetrate throughout the tumor interstitium to alleviate whole tumor hypoxia in a large solid tumor model. Upon ultrasound (US) irradiation, SPNC1 can remotely generate sufficient singlet oxygen to eradicate tumor cells at a deep-tissue depth. Such a single treatment of SPNC1-medicated sonodynamic therapy effectively inhibits tumor growth in a large solid tumor mouse model. Therefore, this study provides a generalized strategy to synergistically overcome both poor penetration and hypoxia of large tumors for enhanced cancer treatment.