A Self-Assembled Albumin-Based Nanoprobe for In Vivo Ratiometric Photoacoustic pH Imaging

FeS2-modified MXene nanocomposite platform for efficient PTT/CDT/TDT integration through enhanced GSH consumption

Hypoxic microenvironment and glutathione (GSH) accumulation in tumours limit the efficacy of cytotoxic reactive oxygen species (ROS) anti-tumour therapy. To address this challenge, we increased the consumption of GSH and the production of ROS through a novel nanoplatform with the action of inorganic nanoenzymes. In this study, we prepared mesoporous FeS2 using a simple template method, efficiently loaded AIPH, and assembled Ti3C2/FeS2-AIPH@BSA (TFAB) nanocomposites through self-assembly with BSA and 2D Ti3C2. The constructed TFAB nanotherapeutic platform enhanced chemodynamic therapy (CDT) by generating toxic hydroxyl radicals (˙OH) via FeS2, while consuming GSH to reduce the loss of generated ˙OH via glutathione oxidase-like (GSH-OXD). In addition, TFAB is able to stimulate the decomposition of AIPH under 808 nm laser irradiation to produce oxygen-independent biotoxic alkyl radicals (˙R) for thermodynamic therapy (TDT). In conclusion, TFAB represents an innovative nanoplatform that effectively addresses the limitations of free radical-based treatment strategies. Through the synergistic therapeutic strategy of photothermal therapy (PTT), CDT, and TDT within the tumor microenvironment, TFAB nanoplatforms achieve controlled AIPH release, ROS generation, intracellular GSH consumption, and precise temperature elevation, resulting in enhanced intracellular oxidative stress, significant apoptotic cell death, and notable tumor growth inhibition. This comprehensive treatment strategy shows great promise in the field of tumor therapy.

Manganese Dioxide-Based Nanomaterials for Medical Applications

Manganese dioxide (MnO2) nanomaterials can react with trace hydrogen peroxide (H2O2) to produce paramagnetic manganese (Mn2+) and oxygen (O2), which can be used for magnetic resonance imaging and alleviate the hypoxic environment of tumors, respectively. MnO2 nanomaterials also can oxidize glutathione (GSH) to produce oxidized glutathione (GSSG) to break the balance of intracellular redox reactions. As a consequence of the sensitivity of the tumor microenvironment to MnO2-based nanomaterials, these materials can be used as multifunctional diagnostic and therapeutic platforms for tumor imaging and treatment. Importantly, when MnO2 nanomaterials are implanted along with other therapeutics, synergetic tumor therapy can be achieved. In addition to tumor treatment, MnO2-based nanomaterials display promising prospects for tissue repair, organ protection, and the treatment of other diseases. Herein, we provide a thorough review of recent progress in the use of MnO2-based nanomaterials for biomedical applications, which may be helpful for the design and clinical translation of next-generation MnO2 nanomaterials.

Reproducible Synthesis of Biocompatible Albumin Nanoparticles Designed for Intra-articular Administration of Celecoxib to Treat Osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis, with intra-articular (IA) delivery of therapeutics being the current best option to treat pain and inflammation. However, IA delivery is challenging due to the rapid clearance of therapeutics from the joint and the need for repeated injections. Thus, there is a need for long-acting delivery systems that increase the drug retention time in joints with the capacity to penetrate OA cartilage. As pharmaceutical utility also demands that this is achieved using biocompatible materials that provide colloidal stability, our aim was to develop a nanoparticle (NP) delivery system loaded with the COX-2 inhibitor celecoxib that can meet these criteria. We devised a reproducible and economical method to synthesize the colloidally stable albumin NPs loaded with celecoxib without the use of any of the following conditions: high temperatures at which albumin denaturation occurs, polymer coatings, oils, Class 1/2 solvents, and chemical protein cross-linkers. The spherical NP suspensions were biocompatible, monodisperse with average diameters of 72 nm (ideal for OA cartilage penetration), and they were stable over 6 months at 4 °C. Moreover, the NPs loaded celecoxib at higher levels than those required for the therapeutic response in arthritic joints. For these reasons, they are the first of their kind. Labeled NPs were internalized by primary human articular chondrocytes cultured from the knee joints of OA patients. The NPs reduced the concentration of inflammatory mediator prostaglandin E2 released by the primaries, an indication of retained bioactivity following NP synthesis. Similar results were observed in lipopolysaccharide-stimulated human THP-1 monocytes. The IA administration of these NPs is expected to avoid side-effects associated with oral administration of celecoxib and to maintain a high local concentration in the knee joint over a sustained period. They are now ready for evaluation by IA administration in animal models of OA.

High-Contrast Photoacoustic Imaging of Localized Cysteine in Orthotopic Breast Cancer Enabled by A Totally-Caged Methylene Blue Probe

High-contrast photoacoustic sensing imaging (PASI) was greatly determined by optical absorption changes of the absorbers usually enabled by activatable probes via controllably converting the absorbed electromagnetic energy to ultrasound waves. However, most of current photoacoustic probes still suffer from limited imaging contrast towards specific species because of their small absorption spectral changes in the near infrared (NIR) region. Herein, we developed a methylene blue-based photoacoustic probe with its NIR optical absorption totally caged, which could afford dramatical "OFF-to-ON" absorption transition for high-contrast photoacoustic imaging towards the localized cysteine. The rationally designed methylene blue-based probe for cysteine (MB-Cys) would keep in off state with almost no absorption in NIR region, while upon activated by cysteine through cyclization reaction with acrylates, it would reconstruct the π-conjugation system to release the free methylene blue with strong absorption centered at 665 nm (>130-fold enhancement). The unique responsive behavior could enable the PASI for photoacoustic mapping the cysteine in orthotopic breast cancer in a high-contrast manner. Therefore, this work established an up-to-date strategy to originally eliminate the background photoacoustic signal for PASI to accurately monitor cysteine in vivo.

Recent advances in DNA-based probes for photoacoustic imaging

Photoacoustic imaging(PAI) is a widely developing imaging modality that has seen tremendous evolvement in the last decade. PAI has gained the upper hand in the imaging field as it takes advantage of optical absorption and ultrasound detection that imparts higher resolution, rich contrast and elevated penetration depth. Unlike other imaging techniques, PAI does not use ionising radiation and is a better, cost-effective and healthier alternative to other imaging techniques. It offers greater specificity than conventional ultrasound imaging with the ability to detect haemoglobin, lipids, water and other light-absorbing chromophores. These properties of PAI have led to its extended applications in the biomedical field in the treatment of diseases such as cancer. This paper reviews how DNA probes have been used in PAI, the various techniques by which it has been modified, and their role in the process. We also focus on different nanocomposites containing DNA having PAI and photothermal therapy(PTT) properties for detection, diagnosis and therapy, its constituents and the role of DNA in it.

Activatable Probes for Ratiometric Imaging of Endogenous Biomarkers In Vivo

Dynamic variations in the concentration and abnormal distribution of endogenous biomarkers are strongly associated with multiple physiological and pathological states. Therefore, it is crucial to design imaging systems capable of real-time detection of dynamic changes in biomarkers for the accurate diagnosis and effective treatment of diseases. Recently, ratiometric imaging has emerged as a widely used technique for sensing and imaging of biomarkers due to its advantage of circumventing the limitations inherent to conventional intensity-dependent signal readout methods while also providing built-in self-calibration for signal correction. Here, the recent progress of ratiometric probes and their applications in sensing and imaging of biomarkers are outlined. Ratiometric probes are classified according to their imaging mechanisms, and ratiometric photoacoustic imaging, ratiometric optical imaging including photoluminescence imaging and self-luminescence imaging, ratiometric magnetic resonance imaging, and dual-modal ratiometric imaging are discussed. The applications of ratiometric probes in the sensing and imaging of biomarkers such as pH, reactive oxygen species (ROS), reactive nitrogen species (RNS), glutathione (GSH), gas molecules, enzymes, metal ions, and hypoxia are discussed in detail. Additionally, this Review presents an overview of challenges faced in this field along with future research directions.

Molecular imaging of tumour-associated pathological biomarkers with smart nanoprobe: From "Seeing" to "Measuring"

Although the extraordinary progress has been made in molecular biology, the prevention of cancer remains arduous. Most solid tumours exhibit both spatial and temporal heterogeneity, which is difficult to be mimicked in vitro. Additionally, the complex biochemical and immune features of tumour microenvironment significantly affect the tumour development. Molecular imaging aims at the exploitation of tumour-associated molecules as specific targets of customized molecular probe, thereby generating image contrast of tumour markers, and offering opportunities to non-invasively evaluate the pathological characteristics of tumours in vivo. Particularly, there are no "standard markers" as control in clinical imaging diagnosis of individuals, so the tumour pathological characteristics-responsive nanoprobe-based quantitative molecular imaging, which is able to visualize and determine the accurate content values of heterogeneous distribution of pathological molecules in solid tumours, can provide criteria for cancer diagnosis. In this context, a variety of "smart" quantitative molecular imaging nanoprobes have been designed, in order to provide feasible approaches to quantitatively visualize the tumour-associated pathological molecules in vivo. This review summarizes the recent achievements in the designs of these nanoprobes, and highlights the state-of-the-art technologies in quantitative imaging of tumour-associated pathological molecules.

NIR-dye bridged human serum albumin reassemblies for effective photothermal therapy of tumor

Human serum albumin (HSA) based drug delivery platforms that feature desirable biocompatibility and pharmacokinetic property are rapidly developed for tumor-targeted drug delivery. Even though various HSA-based platforms have been established, it is still of great significance to develop more efficient preparation technology to broaden the therapeutic applications of HSA-based nano-carriers. Here we report a bridging strategy that unfastens HSA to polypeptide chains and subsequently crosslinks these chains by a bridge-like molecule (BPY-Mal2) to afford the HSA reassemblies formulation (BPY@HSA) with enhanced loading capacity, endowing the BPY@HSA with uniformed size, high photothermal efficacy, and favorable therapeutic features. Both in vitro and in vivo studies demonstrate that the BPY@HSA presents higher delivery efficacy and more prominent photothermal therapeutic performance than that of the conventionally prepared formulation. The feasibility in preparation, stability, high photothermal conversion efficacy, and biocompatibility of BPY@HSA may facilitate it as an efficient photothermal agents (PTAs) for tumor photothermal therapy (PTT). This work provides a facile strategy to enhance the loading capacity of HSA-based crosslinking platforms in order to improve delivery efficacy and therapeutic effect.

Biomimetic biomineralization nanoplatform-mediated differentiation therapy and phototherapy for cancer stem cell inhibition and antitumor immunity activation

Growing evidence suggests that the presence of cancer stem cells (CSCs) is a major challenge in current tumor treatments, especially the transition from non-CSCs to differentiation of CSCs for evading conventional therapies and driving metastasis. Here we propose a therapeutic strategy of synergistic differentiation therapy and phototherapy to induce differentiation of CSCs into mature tumor cells by differentiation inducers and synergistic elimination of them and normal cancer cells through phototherapy. In this work, we synthesized a biomimetic nanoplatform loaded with IR-780 and all-trans retinoic acid (ATRA) via biomineralization. This method can integrate aluminum ions into small-sized protein carriers to form nanoclusters, which undergo responsive degradation under acidic conditions and facilitate deep tumor penetration. With the help of CSC differentiation induced by ATRA, IR-780 inhibited the self-renewal of CSCs and cancer progression by generating hyperthermia and reactive oxygen species in a synergistic manner. Furthermore, ATRA can boost immunogenic cell death induced by phototherapy, thereby strongly causing a systemic anti-tumor immune response and efficiently eliminating CSCs and tumor cells. Taken together, this dual strategy represents a new paradigm of targeted eradication of CSCs and tumors by inducing CSC differentiation, improving photothermal therapy/photodynamic therapy and enhancing antitumor immunity.

Construction of pH-Sensitive Nanovaccines Encapsulating Tumor Cell Lysates and Immune Adjuvants for Breast Cancer Therapy

The current immunotherapy strategies for triple negative breast cancer (TNBC) are greatly limited due to the immunosuppressive tumor microenvironment (TME). Immunization with cancer vaccines composed of tumor cell lysates (TCL) can induce an effective antitumor immune response. However, this approach also has the disadvantages of inefficient antigen delivery to the tumor tissues and the limited immune response elicited by single-antigen vaccines. To overcome these limitations, a pH-sensitive nanocalcium carbonate (CaCO3 ) carrier loaded with TCL and immune adjuvant CpG (CpG oligodeoxynucleotide 1826) is herein constructed for TNBC immunotherapy. This tailor-made nanovaccine, termed CaCO3 @TCL/CpG, not only neutralizes the acidic TME through the consumption of lactate by CaCO3 , which increases the proportion of the M1/M2 macrophages and promotes infiltration of effector immune cells but also activates the dendritic cells in the tumor tissues and recruits cytotoxic T cells to further kill the tumor cells. In vivo fluorescence imaging study shows that the pegylated nanovaccine could stay longer in the blood circulation and extravasate preferentially into tumor site. Besides, the nanovaccine exhibits high cytotoxicity in 4T1 cells and significantly inhibits tumor growth of tumor-bearing mice. Overall, this pH-sensitive nanovaccine is a promising nanoplatform for enhanced immunotherapy of TNBC.

A flexible optoacoustic blood 'stethoscope' for noninvasive multiparametric cardiovascular monitoring

Quantitative and multiparametric blood analysis is of great clinical importance in cardiovascular disease diagnosis. Although there are various methods to extract blood information, they often require invasive procedures, lack continuity, involve bulky instruments, or have complicated testing procedures. Flexible sensors can realize on-skin assessment of several vital signals, but generally exhibit limited function to monitor blood characteristics. Here, we report a flexible optoacoustic blood 'stethoscope' for noninvasive, multiparametric, and continuous cardiovascular monitoring, without requiring complicated procedures. The optoacoustic blood 'stethoscope' features the light delivery elements to illuminate blood and the piezoelectric acoustic elements to capture light-induced acoustic waves. We show that the optoacoustic blood 'stethoscope' can adhere to the skin for continuous and non-invasive in-situ monitoring of multiple cardiovascular biomarkers, including hypoxia, intravascular exogenous agent concentration decay, and hemodynamics, which can be further visualized with a tailored 3D algorithm. Demonstrations on both in-vivo animal trials and human subjects highlight the optoacoustic blood 'stethoscope''s potential for cardiovascular disease diagnosis and prediction.

Cathepsin K-Activated Probe for Fluoro-Photoacoustic Imaging of Early Osteolytic Metastasis

Precise detection of early osteolytic metastases is crucial for their treatment but remains challenging in the clinic because of the limited sensitivity and specificity of traditional imaging techniques. Although fluorescence imaging offers attractive features for the diagnosis of osteolytic metastases, it is hampered by limited penetration depth. To address this issue, a fluoro-photoacoustic dual-modality imaging probe comprising a near-infrared dye caged by a cathepsin K (CTSK)-cleavable peptide sequence on one side and functionalized with osteophilic alendronate through a polyethylene glycol linker on the other side is reported. Through systematic in vitro and in vivo experiments, it is demonstrated that in response to CTSK, the probe generated both near-infrared fluorescent and photoacoustic signals from bone metastatic regions, thus offering a potential strategy for detecting deep-seated early osteolytic metastases.

A targeted activatable NIR-II nanoprobe for positive visualization of anastomotic thrombosis and sensitive identification of fresh fibrinolytic thrombus

Anastomotic thrombosis prevalently causes anastomosis failure, accompanied with ischemia and necrosis, the early diagnosis of which is restricted by inherent shortcomings of traditional imaging techniques in clinic and lack of appropriate prodromal biomarkers for thrombosis initiation. Herein, a fresh thrombus-specific molecular event, protein disulfide isomerase (PDI) is innovatively chosen as the activating factor, and a thrombosis targeting and PDI-responsive turn-on near infrared II (NIR-II) fluorescence nanoprobe is firstly developed. The supramolecular complex-based nanoprobe IR806-PDA@BSA-CREKA is fabricated by assembling NIR-II emitting cyanine derivative IR806-PDA with bovine serum albumin (BSA), which could ameliorate the stability and pharmacokinetics of the nanoprobe, addressing the contradiction in the balance of brightness and biocompatibility. The NIR-II-off nanoprobe exhibits robust turn-on NIR-II fluorescence upon PDI-specific activation, in vitro and in vivo. Of note, the constructed nanoprobe demonstrates superior photophysical stability, efficient fibrin targeting peptide-derived thrombosis binding and a maximum signal-to-background ratio (SBR) of 9.30 for anastomotic thrombosis in NIR-II fluorescent imaging. In conclusion, the exploited strategy enables positive visualized diagnosis for anastomotic thrombosis and dynamic monitoring for thrombolysis of fresh fibrinolytic thrombus, potentially contributes a novel strategy for guiding the therapeutic selection between thrombolysis and thrombectomy for thrombosis treatment in clinic.

Albumin-based formononetin nanomedicines for lung injury and fibrosis therapy via blocking macrophage pyroptosis

Pulmonary fibrosis that occurs following lung injury is a progressive and fatal disease since continual damage to lung tissue triggers the dysregulated inflammation response and accompanying abnormal healing process. Pyroptosis of alveolar macrophages has been found to play an essential role in the deterioration of lung injury and fibrosis. However, the lack of inhibitors against this inflammatory cell death in macrophages and the dense stroma pose major barriers to lung injury and fibrosis treatment. Herein, we developed an albumin-based nanoformulation to realize active delivery of formononetin (FMN) to improve the treatment of lung injury and fibrosis. The obtained nanoparticle, FMN@BSA NPs, could efficiently accumulate at the impaired lesion benefiting from the leaky vasculatures and the affinity between albumin and the overexpressed SPARC protein. Through blocking the NLRP3 inflammasome-involved pyroptosis process of macrophages, FMN@BSA NPs remarkably improved lung function and prolonged animal survival in the bleomycin (BLM)-induced lung injury and fibrosis model without noticeable side effects. Meanwhile, we proved FMN as a pyroptosis inhibitor and the corresponding lipid metabolism-related mechanisms through multi-omics analysis. This study first employed an albumin-based nanoparticle to deliver the pyroptosis inhibitor to the impaired lung tissue actively, providing a promising strategy for lung injury and fibrosis treatment.

The CD47-SIRPα axis is a promising target for cancer immunotherapies

Cluster of differentiation 47(CD47) is a transmembrane protein that is ubiquitously found on the surface of many cells in the body and uniquely overexpressed by both solid and hematologic malignant cells. CD47 interacts with signal-regulatory protein α (SIRPα), to trigger a "don't eat me" signal and thereby achieve cancer immune escape by inhibiting macrophage-mediated phagocytosis. Thus, blocking the CD47-SIRPα phagocytosis checkpoint, for release of the innate immune system, is a current research focus. Indeed, targeting the CD47-SIRPα axis as a cancer immunotherapy has shown promising efficacies in pre-clinical outcomes. Here, we first reviewed the origin, structure, and function of the CD47-SIRPα axis. Then, we reviewed its role as a target for cancer immunotherapies, as well as the factors regulating CD47-SIRPα axis-based immunotherapies. We specifically focused on the mechanism and progress of CD47-SIRPα axis-based immunotherapies and their combination with other treatment strategies. Finally, we discussed the challenges and directions for future research and identified potential CD47-SIRPα axis-based therapies that are suitable for clinical application.

Dual fluorescent hollow silica nanofibers for in situ pH monitoring using an optical fiber

This study reports a sensitive and robust pH sensor based on dual fluorescent doped hollow silica nanofibers (hSNFs) for in situ and real-time pH monitoring. Fluorescein isothiocyanate (FITC) and tris(2,2'-bipyridyl)dichlororuthenium(ii) hexahydrate (Ru(BPY)3) were chosen as a pH sensitive dye and reference dye, respectively. hSNFs were synthesized using a two-step method in a reverse micelle system and were shown to have an average length of 6.20 μm and average diameter of 410 nm. The peak intensity ratio of FITC/Ru(BPY)3 was used to calibrate to solution pH changes. An optical-fiber-based fluorescence detection system was developed that enabled feasible and highly efficient near-field fluorescence detection. The developed system enables fully automated fluorescence detection, where components including the light source, detector, and data acquisition unit are all controlled by a computer. The results show that the developed pH sensor works in a linear range of pH 4.0-9.0 with a fast response time of less than 10 s and minimal sample volume of 50 μL, and can be stored under dark conditions for one month without failure. In addition, the as-prepared hSNF-based pH sensors also have excellent long-term durability. Experimental results from ratiometric sensing confirm the high feasibility, accuracy, stability and simplicity of the dual fluorescent hSNF sensors for the detection of pH in real samples.

A Biocompatible Probe for the Detection of Neutrophil Elastase Free from the Interference of Structural Changes and Its Application to Ratiometric Photoacoustic Imaging In Vivo

Neutrophil elastase (NE) plays a key role in chronic inflammation and acute responses to infection and injury. Effective disease interventions thus call for precise identification of NE to aid the clinical treatment of such diseases. However, the detection process suffers from the interference of structural changes of NE. Herein, we introduce a molecular probe with high biocompatibility to overcome the interference, which was achieved by combining theoretical calculations and experimental studies, that permits highly specific and sensitive detection of NE in cells and in vivo. The upregulated NE accumulation was specifically measured in inflammation by ratiometric photoacoustic and near-infrared fluorescence imaging, providing a new method for developing more specific fluorogenic probes for other enzymes.

An autocatalytically-activatable hydrogen peroxide photoacoustic sensor for in situ visualization precise diagnosis and drug intervention tracing in diabetes syndrome

In situ visualization for the diagnosis of diabetic syndrome and visual monitoring the response to drug treatment is a challenge. Herein, we designed and prepared an autocatalytically-activatable hydrogen peroxide photoacoustic (PA) sensor. We first prepared the FeMoO_x nanoparticle with catalase activity, then combined it to 2,2'-azino-bis(3-ethylbenzothi-azoline-6-sulfonic acid) (ABTS) and distearoylphos-phoethanola-mine-polyethylene-glycol (DSPE-PEG) to construct a autocatalytically-activatable PA sensor (FeMoO_x@ABTS@DSPE-PEG). In its presence, ABTS can be converted into oxidized ABTS·⁺ by H₂O₂. ABTS·⁺ exhibits strong light absorption in the near-infrared region, and can serve as an ideal contrast agent for PA imaging. H₂O₂ as a biomarker of oxidative stress response is closely related to the occurrence and development of diabetes mellitus and its complications. Therefore, FeMoO_x@ABTS@DSPE-PEG was used as a PA sensor of H₂O₂ for visual monitoring of the progression of diabetes-induced liver injury and metformin-mediated treatment of diabetes. The autocatalytically-activatable PA sensor developed in this study provides a promising platform for in situ visual diagnosis of diabetes and its syndrome and monitoring the response to therapy.

Recent Advances in Contrast-Enhanced Photoacoustic Imaging: Overcoming the Physical and Practical Challenges

For decades now, photoacoustic imaging (PAI) has been investigated to realize its potential as a niche biomedical imaging modality. Despite its highly desirable optical contrast and ultrasonic spatiotemporal resolution, PAI is challenged by such physical limitations as a low signal-to-noise ratio (SNR), diminished image contrast due to strong optical attenuation, and a lower-bound on spatial resolution in deep tissue. In addition, contrast-enhanced PAI has faced practical limitations such as insufficient cell-specific targeting due to low delivery efficiency and difficulties in developing clinically translatable agents. Identifying these limitations is essential to the continuing expansion of the field, and substantial advances in developing contrast-enhancing agents, complemented by high-performance image acquisition systems, have synergistically dealt with the challenges of conventional PAI. This review covers the past four years of research on pushing the physical and practical challenges of PAI in terms of SNR/contrast, spatial resolution, targeted delivery, and clinical application. Promising strategies for dealing with each challenge are reviewed in detail, and future research directions for next generation contrast-enhanced PAI are discussed.

Albumin-Consolidated AIEgens for Boosting Glioma and Cerebrovascular NIR-II Fluorescence Imaging

The application of an exogenous polymer matrix to construct aggregation-induced emission (AIE) nanoprobes promotes the utility of AIE luminogens (AIEgens) in diagnosing brain diseases. However, the limited fluorescence (FL) and low active-targeting abilities of AIE-based nanoprobes impede their imaging application. Here, we employed endogenous albumin as an effective matrix to encapsulate AIEgens to enhance FL quantum yield (QY) and active-targeting ability. The albumin-consolidated strategy effectively inhibited the intramolecular vibration of AIEgens and enhanced endocytosis mediated by the gp60 receptor. The QYs of three kinds of albumin-based AIE nanoprobes with FL emissions ranging from the visible (400-650 nm) to the second near-infrared (NIR-II, 1000-1700 nm) region was at least 10% higher, and the tumor-targeting efficiency was ∼25% higher, compared with those of nanoprobes constructed by the exogenous polymer. Albumin-based AIE nanoprobes have achieved active-targeting NIR-II imaging of brain tumors and cerebrovascular imaging with a high signal-to-background ratio (SBR, ∼90) and high resolution (∼70 μm) in mouse models. Therefore, the albumin-based AIE nanoprobes will enable FL imaging-guided surgery of brain tumors and cerebral ischemia, which will improve surgical efficacy to prevent recurrence and side effects.

Acoustic-Based Theranostic Probes Activated by Tumor Microenvironment for Accurate Tumor Diagnosis and Assisted Tumor Therapy

Acoustic-based imaging techniques, including ultrasonography and photoacoustic imaging, are powerful noninvasive approaches for tumor imaging owing to sound transmission facilitation, deep tissue penetration, and high spatiotemporal resolution. Usually, imaging modes were classified into "always-on" mode and "activatable" mode. Conventional "always-on" acoustic-based probes often have difficulty distinguishing lesion regions of interest from surrounding healthy tissues due to poor target-to-background signal ratios. As compared, activatable probes have attracted attention with improved sensitivity, which can boost or amplify imaging signals only in response to specific biomolecular recognition or interactions. The tumor microenvironment (TME) exhibits abnormal physiological conditions that can be used to identify tumor sections from normal tissues. Various types of organic dyes and biomaterials can react with TME, leading to obvious changes in their optical properties. The TME also affects the self-assembly or aggregation state of nanoparticles, which can be used to design activatable imaging probes. Moreover, acoustic-based imaging probes and therapeutic agents can be coencapsulated into one nanocarrier to develop nanotheranostic probes, achieving tumor imaging and cooperative therapy. Satisfactorily, ultrasound waves not only accelerate the release of encapsulated therapeutic agents but also activate therapeutic agents to exert or enhance their therapeutic performance. Meanwhile, various photoacoustic probes can convert photon energy into heat under irradiation, achieving photoacoustic imaging and cooperative photothermal therapy. In this review, we focus on the recently developed TME-triggered ultrasound and photoacoustic theranostic probes for precise tumor imaging and targeted tumor therapy.

Synergic Thermo- and pH-Sensitive Hybrid Microgels Loaded with Fluorescent Dyes and Ultrasmall Gold Nanoparticles for Photoacoustic Imaging and Photothermal Therapy

Smart microgels (μGels) made of polymeric particles doped with inorganic nanoparticles have emerged recently as promising multifunctional materials for nanomedicine applications. However, the synthesis of these hybrid materials is still a challenging task with the necessity to control several features, such as particle sizes and doping levels, in order to tailor their final properties in relation to the targeted application. We report herein an innovative modular strategy to achieve the rational design of well-defined and densely filled hybrid particles. It is based on the assembly of the different building blocks, i.e., μGels, dyes, and small gold nanoparticles (<4 nm), and the tuning of nanoparticle loading within the polymer matrix through successive incubation steps. The characterization of the final hybrid networks using UV-vis absorption, fluorescence, transmission electron microscopy, dynamic light scattering, and small-angle X-ray scattering revealed that they uniquely combine the properties of hydrogel particles, including high loading capacity and stimuli-responsive behavior, the photoluminescent properties of dyes (rhodamine 6G, methylene blue and cyanine 7.5), and the features of gold nanoparticle assembly. Interestingly, in response to pH and temperature stimuli, the smart hybrid μGels can shrink, leading to the aggregation of the gold nanoparticles trapped inside the polymer matrix. This stimuli-responsive behavior results in plasmon band broadening and red shift toward the near-infrared region (NIR), opening promising prospects in biomedical science. Particularly, the potential of these smart hybrid nanoplatforms for photoactivated hyperthermia, photoacoustic imaging, cellular internalization, intracellular imaging, and photothermal therapy was assessed, demonstrating well controlled multimodal opportunities for theranostics.

Development of nanocubosomes co-loaded with dual anticancer agents curcumin and temozolomide for effective Colon cancer therapy

Current research aimed to develop nanocubosomes co-loaded with dual anticancer drugs curcumin and temozolomide for effective colon cancer therapy. Drugs co-loaded nanocubosomal dispersion was prepared by modified emulsification method using glyceryl monooleate (GMO), pluronic F127 and bovine serum albumin (BSA) as a lipid phase, surfactant, and stabilizer, respectively. The resulting nanocubosomes were characterized by measuring hydrodynamic particle size, particle size distribution (PSD), drug loading capacity (DL), encapsulation efficiency (EE), colloidal stability and drug release profile. We also physiochemically characterized the nanocubosomes by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and x-rays diffraction (XRD) for their morphology, polymer drug interaction and its nature, respectively. Further, the in-vitro cell-uptake, mechanism of cell-uptake, in-vitro anti-tumor efficacy and apoptosis level were evaluated using HCT-116 colon cancer cells. The prepared nanocubosomes exhibited a small hydrodynamic particle size (PS of 150 ± 10 nm in diameter) with nearly cubic shape and appropriate polydispersity index (PDI), enhanced drug loading capacity (LC of 6.82 ± 2.03% (Cur) and 9.65 ± 1.53% (TMZ), high entrapment efficiency (EE of 67.43 ± 2.16% (Cur) and 75.55 ± 3.25% (TMZ), pH-triggered drug release profile and higher colloidal stability in various physiological medium. Moreover, the nanocubosomes showed higher cellular uptake, in-vitro cytotoxicity and apoptosis compared to free drugs, curcumin and temozolomide, most likely because its small particle size. In addition, BSA-stabilized nanocubosomes were actively taken by aggressive colon cancer cells that over-expressed the albumin receptors and utilized BSA as nutrient source for their growth. In short, this study provides a new and simple strategy to improve the efficacy and simultaneously overawed the adaptive treatment tolerance in colon cancer.

Dual-targeting nanozyme for tumor activatable photo-chemodynamic theranostics

Abstract

Tumor phototheranostics holds a great promise on account of its high spatiotemporal resolution, tumor-specificity, and noninvasiveness. However, physical limitation of light penetration and “always on” properties of conventional photothermal-conversion agents usually cause difficulty in accurate diagnosis and completely elimination of tumor. Meanwhile, nanozymes mediated Fenton reactions can well utilize the tumor microenvironment (TME) to generate hydroxyl radicals for chemodynamic therapy (CDT), but limited by the concentration of H₂O₂ in TME and the delivery efficiency of nanozymes. To overcome these problems, a dual-targeting nanozyme (FTRNPs) is developed for tumor-specific in situ theranostics, based upon the assembling of ultrasmall Fe₃O₄ nanoparticles, 3,3’,5,5’-tetrameth-ylbenzidine (TMB) and the RGD peptide. The FTRNPs after H₂O₂ treatment exhibits superior photothermal stability and high photothermal conversion efficiency (η = 50.9%). FTRNPs shows extraordinary accumulation and retention in the tumor site by biological/physical dual-targeting, which is 3.54-fold higher than that without active targeting. Cascade-dual-response to TME for nanozymes mediated Fenton reactions and TMB oxidation further improves the accuracy of both photoacoustic imaging and photothermal therapy (PTT). The tumor inhibition rate of photo-chemodynamic therapy is ~ 97.76%, which is ~ 4-fold higher than that of PTT or CDT only. Thus, the combination of CDT and PTT to construct “turn on” nanoplatform is of great significance to overcome their respective limitations. Considering its optimized “all-in-one” performance, this new nanoplatform is expected to provide an advanced theranostic strategy for the future treatment of cancers.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01662-9.

Ultrabright Renal-Clearable Cyanine-Protein Nanoprobes for High-Quality NIR-II Angiography and Lymphography

The renal-clearable aspect of imaging agent with minimum toxicity issues and side effects is essential for clinical translation, yet clinical near-infrared-I/II (NIR-I/II) fluorophores with timely renal-clearance pathways are very limited. Herein, we rationally develop the cyanine-protein composite strategy through covalent bonding of β-lactoglobulin (β-LG) and chloride-cyanine dye to produce a brilliant and stable NIR-I/II fluorophore (e.g., β-LG@IR-780). The β-LG acts as a protecting shell with small molecular weight (18.4 kDa) and ultrasmall size (&lt;5 nm), thus endowing the β-LG@IR-780 with excellent biocompatibility and renal excretion. Our β-LG@IR-780 probe enables noninvasive and precise NIR-II visualization of the physiological and pathological conditions of the vascular and lymphatic drainage system, facilitating intraoperative imaging-guided surgery and postoperative noninvasive monitoring. The minimum accumulation of our probes in the main organs improves the overall biosafety. This study provides a facile methodology for new-generation NIR-II fluorophores and largely improves the brightness and pharmacokinetics of small molecular dyes.

Nanomedicines Targeting Metabolism in the Tumor Microenvironment

Cancer cells reprogram their metabolism to meet their growing demand for bioenergy and biosynthesis. The metabolic profile of cancer cells usually includes dysregulation of main nutritional metabolic pathways and the production of metabolites, which leads to a tumor microenvironment (TME) having the characteristics of acidity, hypoxic, and/or nutrient depletion. Therapies targeting metabolism have become an active and revolutionary research topic for anti-cancer drug development. The differential metabolic vulnerabilities between tumor cells and other cells within TME provide nanotechnology a therapeutic window of anti-cancer. In this review, we present the metabolic characteristics of intrinsic cancer cells and TME and summarize representative strategies of nanoparticles in metabolism-regulating anti-cancer therapy. Then, we put forward the challenges and opportunities of using nanoparticles in this emerging field.

An Activatable Polymeric Nanoprobe for Fluorescence and Photoacoustic Imaging of Tumor-Associated Neutrophils in Cancer Immunotherapy

Imaging to evaluate tumor-associated neutrophils (TANs) is imperative for cancer immunotherapy but remains challenging. We herein report an activatable semiconducting polymer nanoprobe (SPCy) for near-infrared fluorescence (NIRF) and photoacoustic (PA) imaging of neutrophil elastase (NE), a biomarker of TANs. SPCy comprises a semiconducting polymer conjugated with a hemicyanine (hemi-Cy) dye caged by a NE-cleavable peptide as the side chain. After systemic administration, SPCy passively targets the tumor and reacts with NE to "uncage" the hemi-Cy, leading to enhanced NIRF and PA signals of the hemi-Cy but unchanged signals of the SP. Such NE-activated ratiometric NIRF and enhanced PA signals of SPCy correlate with the intratumoral population of TANs. Thus, this study not only presents the first TAN-specific PA probe, but also provides a general molecular design strategy for PA imaging of other immune-related biomarkers to facilitate screening of cancer immunotherapeutics.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

Novel Glutathione Activated Smart Probe for Photoacoustic Imaging, Photothermal Therapy, and Safe Postsurgery Treatment

Preventing tumor recurrence is the most important target for cancer treatment. However, the current effective and advanced technology relies on the use of near-infrared region (NIR), and the equipment of NIR-I and NIR-II fluorescence imaging technique-based fluorescent-guided surgery is expensive and complicated to operate. Here, we report a safe and effective strategy of an organic-inorganic hybrid gold nanoparticle-based novel smart probe (Au@PDA-ss-PEGm NPs) which is appropriate for photoacoustic imaging (PAI) and plasmonic photothermal therapy (PPTT) of tumors in vivo. After intravenous injection, the probe would be transported to the tumor to penetrate the cellular membrane. Then the disulfide bond on the probe surface would be broken with the help of a high concentration of glutathione in the tumor cell. The remaining Au@PDA NPs would aggregate to form plasmonic nanoclusters and exhibit a notable plasmon coupling enhanced photothermal (PCEPT) effect. Besides, the results further proved its good biosafety and pharmacokinetic characteristics in vivo and, more important, a short time exposure under 808 nm laser after surgical removal of the tumor, which would be effective to prevent tumor recurrence and bring dawn to the high-efficiency treatment of tumors.

Biomedical polymers: synthesis, properties, and applications

Biomedical polymers have been extensively developed for promising applications in a lot of biomedical fields, such as therapeutic medicine delivery, disease detection and diagnosis, biosensing, regenerative medicine, and disease treatment. In this review, we summarize the most recent advances in the synthesis and application of biomedical polymers, and discuss the comprehensive understanding of their property-function relationship for corresponding biomedical applications. In particular, a few burgeoning bioactive polymers, such as peptide/biomembrane/microorganism/cell-based biomedical polymers, are also introduced and highlighted as the emerging biomaterials for cancer precision therapy. Furthermore, the foreseeable challenges and outlook of the development of more efficient, healthier and safer biomedical polymers are discussed. We wish this systemic and comprehensive review on highlighting frontier progress of biomedical polymers could inspire and promote new breakthrough in fundamental research and clinical translation.

Advancements in cell membrane camouflaged nanoparticles: A bioinspired platform for cancer therapy

The idea of employing natural cell membranes as a coating medium for nanoparticles (NPs) endows man-made vectors with natural capabilities and benefits. In addition to retaining the physicochemical characteristics of the NPs, the biomimetic NPs also have the functionality of source cell membranes. It has emerged as a promising approach to enhancing the properties of NPs for drug delivery, immune evasion, imaging, cancer-targeting, and phototherapy sensitivity. Several studies have been reported with a multitude of approaches to reengineering the surface of NPs using biological membranes. Owing to their low immunogenicity and intriguing biomimetic properties, cell-membrane-based biohybrid delivery systems have recently gained a lot of interest as therapeutic delivery systems. This review summarises different kinds of biomimetic NPs reported so far, their fabrication aspects, and their application in the biomedical field. Finally, it briefs on the latest advances available in this biohybrid concept.

Synthesis of Liquid Gallium@Reduced Graphene Oxide Core-Shell Nanoparticles with Enhanced Photoacoustic and Photothermal Performance

This report presents nanoparticles composed of a liquid gallium core with a reduced graphene oxide (RGO) shell (Ga@RGO) of tunable thickness. The particles are produced by a simple, one-pot nanoprobe sonication method. The high near-infrared absorption of RGO results in a photothermal energy conversion of light to heat of 42.4%. This efficient photothermal conversion, combined with the large intrinsic thermal expansion coefficient of liquid gallium, allows the particles to be used for photoacoustic imaging, that is, conversion of light into vibrations that are useful for imaging. The Ga@RGO results in fivefold and twofold enhancement in photoacoustic signals compared with bare gallium nanoparticles and gold nanorods (a commonly used photoacoustic contrast agent), respectively. A theoretical model further reveals the intrinsic factors that affect the photothermal and photoacoustic performance of Ga@RGO. These core-shell Ga@RGO nanoparticles not only can serve as photoacoustic imaging contrast agents but also pave a new way to rationally design liquid metal-based nanomaterials with specific multi-functionality for biomedical applications.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

Human-Body-Temperature Triggerable Phase Transition of W-VO2@PEG Nanoprobes with Strong and Switchable NIR-II Absorption for Deep and Contrast-Enhanced Photoacoustic Imaging

The immense potential of temperature-responsive nanomaterials for use as contrast agents has propelled much recent research and development in the field of photoacoustic (PA) imaging, while the exorbitant transition temperature exceeding the human-tolerable range and the low reversibility of the reported temperature-sensitive nanosystems are still two severe issues that hinder effective imaging and long-term monitoring in practical applications. Herein, we propose a high-performing thermoresponsive polyethylene glycol-coated tungsten-doped vanadium dioxide (W-VO₂@PEG) nanoprobe (NP) with strong and switchable optical absorption in the near-infrared-II (NIR-II) biowindow (1000-1700 nm) near human-body temperature, to achieve deep and contrast-enhanced PA imaging. Our study shows that the PA signal amplitude of W-VO₂@PEG NPs at 1064 nm increases up to 260% when the temperature increases from 35 °C to 45 °C, with a signal fluctuation of less than 10% after 10 temperature cycles, therefore enabling great potential of "off-to-on" dynamic contrast-enhanced imaging capability in deep-seated tissues. Experiments on tissue-mimicking phantoms and in vitro chicken breast showed that, by levering the prepared W-VO₂@PEG NPs and dynamically modulating the temperature field with an external NIR optical stimulus, contrast-enhanced PA images of the target can be obtained with an imaging depth up to 1.5 cm. Furthermore, in vivo potential of the prepared thermoresponsive NPs for the detection and identification of deep-seated tumors by directly comparing to conventional "always on" NPs has been demonstrated. Our work will offer feasible guidance for the development of smart temperature-activatable PA NPs with improved imaging depth and imaging contrast.

Recent Advance in Biological Responsive Nanomaterials for Biosensing and Molecular Imaging Application

In recent decades, as a subclass of biomaterials, biologically sensitive nanoparticles have attracted increased scientific interest. Many of the demands for physiologically responsive nanomaterials in applications involving the human body cannot be met by conventional technologies. Due to the field's importance, considerable effort has been expended, and biologically responsive nanomaterials have achieved remarkable success thus far. This review summarizes the recent advancements in biologically responsive nanomaterials and their applications in biosensing and molecular imaging. The nanomaterials change their structure or increase the chemical reaction ratio in response to specific bio-relevant stimuli (such as pH, redox potentials, enzyme kinds, and concentrations) in order to improve the signal for biologically responsive diagnosis. We use various case studies to illustrate the existing issues and provide a clear sense of direction in this area. Furthermore, the limitations and prospects of these nanomaterials for diagnosis are also discussed.

Engineering Molecular Probes for In Vivo Near-Infrared Fluorescence/Photoacoustic Duplex Imaging of Human Neutrophil Elastase

Early detection of human neutrophil elastase (HNE), the potential biomarker of lung cancer, is crucial for the accurate diagnosis and evaluation of lung cancer. Currently, little progress of HNE-activated probes has been made for in vivo imaging. Herein, assisted by probe-active pocket match engineering, we synthesized a series of near-infrared fluorescence (NIRF) and photoacoustic (PA) duplex imaging probes by conjugating diverse fluorinated amide chains onto hemi-cyanine. Finally, we identified that probe 2 (denoted as LET-8), with the pentafluoroethyl group, is a superior probe to detect HNE with the best selectivity as well as good response ability and thus successfully realized NIRF/PA duplex imaging of HNE activity both in vitro and in vivo.

Targeted contrast agents and activatable probes for photoacoustic imaging of cancer

Photoacoustic (PA) imaging has emerged as a powerful technique for the high resolution visualization of biological processes within deep tissue. Through the development and application of exogenous targeted contrast agents and activatable probes that can respond to a given cancer biomarker, researchers can image molecular events in vivo during cancer progression. This information can provide valuable details that can facilitate cancer diagnosis and therapy monitoring. In this tutorial review, we provide a step-by-step guide to select a cancer biomarker and subsequent approaches to design imaging agents for in vivo use. We envision this information will be a useful summary to those in the field, new members to the community, and graduate students taking advanced imaging coursework. We also highlight notable examples from the recent literature, with emphasis on the molecular designs and their in vivo PA imaging performance. To conclude, we provide our outlook and future perspective in this exciting field.

Acoustics at the nanoscale (nanoacoustics): A comprehensive literature review.: Part II: Nanoacoustics for biomedical imaging and therapy

In the past decade, acoustics at the nanoscale (i.e., nanoacoustics) has evolved rapidly with continuous and substantial expansion of capabilities and refinement of techniques. Motivated by research innovations in the last decade, for the first time, recent advancements of acoustics-associated nanomaterials/nanostructures and nanodevices for different applications are outlined in this comprehensive review, which is written in two parts. As part II of this two-part review, this paper concentrates on nanoacoustics in biomedical imaging and therapy applications, including molecular ultrasound imaging, photoacoustic imaging, ultrasound-mediated drug delivery and therapy, and photoacoustic drug delivery and therapy. Firstly, the recent developments of nanosized ultrasound and photoacoustic contrast agents as well as their various imaging applications are examined. Secondly, different types of nanomaterials/nanostructures as nanocarriers for ultrasound and photoacoustic therapies are discussed. Finally, a discussion of challenges and future research directions are provided for nanoacoustics in medical imaging and therapy.

Biodegradable and Excretable 2D W1.33 C i-MXene with Vacancy Ordering for Theory-Oriented Cancer Nanotheranostics in Near-Infrared Biowindow

MXenes, a new class of two-dimensional (2D) nanomaterials, have shown enormous potential for biological applications. Notably, the development of 2D MXenes in nanomedicine is still in its infancy. Herein, a distinct W1.33 C i-MXene with multiple theranostic functionalities, fast biodegradation, and satisfactory biocompatibility is explored. By designing a parent bulk laminate in-plane ordered (W2/3 Y1/3 )2 AlC ceramic and optionally etching aluminum (Al) and yttrium (Y) elements, 2D W1.33 C i-MXene nanosheets with ordered divacancies are efficiently fabricated. Especially, theoretical simulations reveal that W1.33 C i-MXene possesses a strong predominance of near-infrared (NIR) absorbance. The constructed ultrathin W1.33 C nanosheets feature excellent photothermal-conversion effectiveness (32.5% at NIR I and 49.3% at NIR II) with desirable biocompatibility and fast degradation in normal tissue rather than in tumor tissue. Importantly, the multimodal-imaging properties and photothermal-ablation performance of W1.33 C-BSA nanosheets are systematically revealed and demonstrated both in vitro and in vivo. The underlying mechanism and regulation factors for the W1.33 C-BSA nanosheets-induced hyperthermia ablation are also revealed by transcriptome and proteome sequencing. This work offers a paradigm that i-MXenes achieve the tailoring biomedical applications through composition and structure design on the atomic scale.

Photoactivatable Biomedical Materials Based on Luminogens with Aggregation-Induced Emission (AIE) Characteristics

Fluorescence probes with aggregation-induced emission (AIE) property are fascinating and vital in biological fields due to their bright fluorescence in the solid state. In contrast, traditional AIE materials are obscured by the off-target effects and lack of spatial and temporal control. Photoactivatable materials with AIE characteristics, whose physicochemical behaviors can be remotely activated by light, provide great potential in biochemical information acquisition with high spatial and temporal resolution. By using AIE-featured photoactivatable fluorescence probes, accurate analysis of the targets of interest is possible. For example, where, when, and to what extent a process is started or stopped by manipulating the non-invasive light accurately. Thus, many researchers are enthusiastic about developing AIE-featured photoactivatable materials and mainly focus on developing novel molecules by rational molecular structure design, and exploring advanced applications by appropriate molecular functionalization. In this review, the recent achievements of photoactivatable materials with AIE characteristics from the aspects involving inherent mechanism of photoactivity, molecular design strategy, and the corresponding applications in biological fields, are summarized. The biological applications are highlighted and discussed, including photoactivatable bioimaging, diagnosis, and photo-controlled therapy. Finally, the challenges and prospects of the AIE-featured photoactivatable materials are also outlined and discussed.

Morphology-dependent resonance enhanced nonlinear photoacoustic effect in nanoparticle suspension: a temporal-spatial model

The morphology-dependent resonances (MDRs) hotspot, ubiquity formed between the pairs of nanoparticles in close vicinity, has garnered considerable recent attention. By extending this phenomenon to pulse-laser irradiated nanoparticle suspension, we demonstrate that such collective optical/thermal enhancement can give rise to the nonlinear photoacoustic (PA) generation. In this study, a temporal-spatial analytical expression is derived to quantitatively describe the nonlinear PA signal generation from nanoparticles, incorporating the Grüneisen increase at the microscopic individual particle level and MRDs enhancement at the macroscopic suspension level. The dependence of PA nonlinearity on the critical contributors, including the laser pulse width, the particle size, and the statistical interparticle spacing, is quantitatively discussed. The theory is well validated with the finite element method (FEM) and experimentally proved with semiconducting polymer nanoparticles (SPN) suspension. This work may pave a new direction towards effective MDR based nonlinear PA contract agent design.

Ultrahigh Sensitive and Tumor-Specific Photoacoustography in NIR-II Region: Optical Writing and Redox-Responsive Graphic Fixing by AgBr@PLGA Nanocrystals

The highly up-regulated glutathione (GSH) concentration in the tumor microenvironment is generally identified to be an effective endogenous characteristic of cancerous tissues. Herein, an ultrahigh-sensitive and tumor-specific photoacoustography technique in the near-infrared (NIR-II) region based on optical writing and redox-responsive chromogenic graphic fixing is developed by introducing a self-synthesized photosensitive silver bromide modified with poly lactic-co-glycolic acid (AgBr@PLGA) nanocrystals. After they are optically triggered by external light, the NIR-transparent AgBr@PLGA nanocrystals can be reduced by the tumor-abundant GSH into strongly absorbing silver nanoparticles, significantly boosting the "turn-on" photoacoustic (PA) signal in the NIR-II region; therefore, the tumor area can be graphically fixed and developed in the photoacoustography. Experiments on both in vitro phantoms and in vivo mouse models demonstrate that the tumor area is specifically identified by the photoacoustography with the background signals effectively suppressed by dynamically modulating the exposure time. The tumor-specific photoacoustography technique prefigures great potential for high-precision cancer diagnosis and treatment monitoring.

Bioresponsive nanomedicines based on dynamic covalent bonds

Trends in the development of modern medicine necessitate the efficient delivery of therapeutics to achieve the desired treatment outcomes through precise spatiotemporal accumulation of therapeutics at the disease site. Bioresponsive nanomedicine is a promising platform for this purpose. Dynamic covalent bonds (DCBs) have attracted much attention in studies of the fabrication of bioresponsive nanomedicines with an abundance of combinations of therapeutic modules and carrier function units. DCB-based nanomedicines could be designed to maintain biological friendly synthesis and site-specific release for optimal therapeutic effects, allowing the complex to retain an integrated structure before accumulating at the disease site, but disassembling into individual active components without compromising function in the targeted organs or tissues. In this review, we focus on responsive nanomedicines containing dynamic chemical bonds that can be cleaved by various specific stimuli, enabling achievement of targeted drug release for optimal therapy in various diseases.