Non-invasive multimodal functional imaging of the intestine with frozen micellar naphthalocyanines

Potential applications for photoacoustic imaging using functional nanoparticles: A comprehensive overview

This paper presents a comprehensive overview of the potential applications for Photo-Acoustic (PA) imaging employing functional nanoparticles. The exploration begins with an introduction to nanotechnology and nanomaterials, highlighting the advancements in these fields and their crucial role in shaping the future. A detailed discussion of the various types of nanomaterials and their functional properties sets the stage for a thorough examination of the fundamentals of the PA effect. This includes a thorough chronological review of advancements, experimental methodologies, and the intricacies of the source and detection of PA signals. The utilization of amplitude and frequency modulation, design of PA cells, pressure sensor-based signal detection, and quantification methods are explored in-depth, along with additional mechanisms induced by PA signals. The paper then delves into the versatile applications of photoacoustic imaging facilitated by functional nanomaterials. It investigates the influence of nanomaterial shape, size variation, and the role of composition, alloys, and hybrid materials in harnessing the potential of PA imaging. The paper culminates with an insightful discussion on the future scope of this field, focusing specifically on the potential applications of photoacoustic (PA) effect in the domain of biomedical imaging and nanomedicine. Finally, by providing the comprehensive overview, the current work provides a valuable resource underscoring the transformative potential of PA imaging technique in biomedical research and clinical practice.

Erythrocyte Membrane Camouflaged Nanotheranostics for Optical Molecular Imaging-Escorted Self-Oxygenation Photodynamic Therapy

Hypoxic tumor microenvironment (TME) hampers the application of oxygen (O2)-dependent photodynamic therapy (PDT) in solid tumors. To address this problem, a biomimetic nanotheranostics (named MMCC@EM) is developed for optical molecular imaging-escorted self-oxygenation PDT. MMCC@EM is synthesized by encapsulating chlorin e6 (Ce6) and catalase (CAT) in metal-organic framework (MOF) nanoparticles with erythrocyte membrane (EM) camouflage. Based on the biomimetic properties of EM, MMCC@EM efficiently accumulates in tumor tissues. The enriched MMCC@EM achieves TME-activatable drug release, thereby releasing CAT and Ce6, and this process can be monitored through fluorescence (FL) imaging. In addition, endogenous hydrogen peroxide (H2O2) will be decomposed by CAT to produce O2, which can be reflected by the measurement of intratumoral oxygen concentration using photoacoustic (PA) imaging. Such self-oxygenation nanotheranostics effectively mitigate tumor hypoxia and improve the generation of singlet oxygen (1O2). The 1O2 disrupts mitochondrial function and triggers caspase-3-mediated cellular apoptosis. Furthermore, MMCC@EM triggers immunogenic cell death (ICD) effect, leading to an increased infiltration of cytotoxic T lymphocytes (CTLs) into tumor tissues. As a result, MMCC@EM exhibits good therapeutic effects in 4T1-tumor bearing mice under the navigation of FL/PA duplex imaging.

Engineering Cyanine- and Hemicyanine-Based Probes for Optical Imaging of Kidney Diseases

Molecular optical probes play pivotal roles in in vivo imaging of biomarkers associated to kidney diseases. Relying on structural tunability and high fluorescence quantum yields, versatile optical probes have been constructed on cyanine or hemicyanine-based scaffold in recent years. This review summaries the recent progress on the development of optical probes for imaging of kidney diseases, particularly through near-infrared fluorescence, chemiluminescence and photoacoustic imaging modalities. The chemical design and sensing mechanisms are discussed along with applications in the detection of renal cell carcinoma and acute kidney injury. This progress provides insights and directions for the development of next generation kidney-targeted probes and for pushing their further applications in preclinical and clinical research.

Recent advances in corneal neovascularization imaging

Corneal neovascularization (CoNV) is a vision-threatening ocular disease commonly secondary to infectious, inflammatory, and traumatic etiologies. Slit lamp photography, in vivo confocal microscopy, angiography, and optical coherence tomography angiography (OCTA) are the primary diagnostic tools utilized in clinical practice to evaluate the vasculature of the ocular surface. However, there is currently a dearth of comprehensive literature that reviews the advancements in imaging technology for CoNV administration. Initially designed for retinal vascular imaging, OCTA has now been expanded to the anterior segment and has shown promising potential for imaging the conjunctiva, cornea, and iris. This expansion allows for the quantitative monitoring of the structural and functional changes associated with CoNV. In this review, we emphasize the impact of algorithm optimization in anterior segment-optical coherence tomography angiography (AS-OCTA) on the diagnostic efficacy of CoNV. Through the analysis of existing literature, animal model assessments are further reported to investigate its pathological mechanism and exhibit remarkable therapeutic interventions. In conclusion, AS-OCTA holds broad prospects and extensive potential for clinical diagnostics and research applications in CoNV.

Multimodal optoacoustic imaging: methods and contrast materials

Optoacoustic (OA) imaging offers powerful capabilities for interrogating biological tissues with rich optical absorption contrast while maintaining high spatial resolution for deep tissue observations. The spectrally distinct absorption of visible and near-infrared photons by endogenous tissue chromophores facilitates extraction of diverse anatomic, functional, molecular, and metabolic information from living tissues across various scales, from organelles and cells to whole organs and organisms. The primarily blood-related contrast and limited penetration depth of OA imaging have fostered the development of multimodal approaches to fully exploit the unique advantages and complementarity of the method. We review the recent hybridization efforts, including multimodal combinations of OA with ultrasound, fluorescence, optical coherence tomography, Raman scattering microscopy and magnetic resonance imaging as well as ionizing methods, such as X-ray computed tomography, single-photon-emission computed tomography and positron emission tomography. Considering that most molecules absorb light across a broad range of the electromagnetic spectrum, the OA interrogations can be extended to a large number of exogenously administered small molecules, particulate agents, and genetically encoded labels. This unique property further makes contrast moieties used in other imaging modalities amenable for OA sensing.

Oxygen Self-Supplied Perfluorocarbon-Modified Micelles for Enhanced Cancer Photodynamic Therapy and Ferroptosis

Photodynamic therapy (PDT) and ferroptosis show significant potential in tumor treatment. However, their therapeutic efficacy is often hindered by the oxygen-deficient tumor microenvironment and the challenges associated with efficient intracellular drug delivery into tumor cells. Toward this end, this work synthesized perfluorocarbon (PFC)-modified Pluronic F127 (PFC-F127), and then exploits it as a carrier for codelivery of photosensitizer Chlorin e6 (Ce6) and the ferroptosis promoter sorafenib (Sor), yielding an oxygen self-supplying nanoplatform denoted as Ce6-Sor@PFC-F127. The PFCs on the surface of the micelle play a crucial role in efficiently solubilizing and delivering oxygen as well as increasing the hydrophobicity of the micelle surface, giving rise to enhanced endocytosis by cancer cells. The incorporation of an oxygen-carrying moiety into the micelles enhances the therapeutic impact of PDT and ferroptosis, leading to amplified endocytosis and cytotoxicity of tumor cells. Hypotonic saline technology was developed to enhance the cargo encapsulation efficiency. Notably, in a murine tumor model, Ce6-Sor@PFC-F127 effectively inhibited tumor growth through the combined use of oxygen-enhanced PDT and ferroptosis. Taken together, this work underscores the promising potential of Ce6-Sor@PFC-F127 as a multifunctional therapeutic nanoplatform for the codelivery of multiple cargos such as oxygen, photosensitizers, and ferroptosis inducers.

An Activatable Dual Polymer Nanosystem for Photoimmunotherapy and Metabolic Modulation of Deep-Seated Tumors

Nanomedicine in combination with immunotherapy has shown great potential in the cancer treatment, but phototherapeutic nanomaterials that specifically activate the immunopharmacological effects in deep tumors have rarely been developed due to limited laser penetration depth and tumor immune microenvironment. Herein, this work reports a newly synthesized semiconducting polymer (SP) grafted with imiquimod R837 and indoxmid encapsulated micelle (SPRIN-micelle) with strong absorption in the second near infrared window (NIR-II) that can relieve tumor immunosuppression and enhance the photothermal immunotherapy and catabolic modulation on tumors. Immune agonists (Imiquimod R837) and immunometabolic modulators (indoxmid) are covalently attached to NIR-II SP sensors via a glutathione (GSH) responsive self-immolation linker and then loaded into Pluronic F127 (F127) micelles by a temperature-sensitive critical micelle concentration (CMC)-switching method. Using this method, photothermal effect of SPRIN-micelles in deep-seated tumors can be activated, leading to effective tumor ablation and immunogenic cell death (ICD). Meanwhile, imiquimod and indoxmid are tracelessly released in response to the tumor microenvironment, resulting in dendritic cell (DC) maturation by imiquimod R837 and inhibition of both indoleamine 2,3-dioxygenase (IDO) activity and Treg cell expression by indoxmid. Ultimately, cytotoxic T-lymphocyte infiltration and tumor metastasis inhibition in deep solid tumors (9 mm) are achieved. In summary, this work demonstrates a new strategy for the combination of photothermal immunotherapy and metabolic modulation by developing a dual functional polymer system including activable SP and temperature-sensitive F127 for the treatment of deep solid tumors.

Light on Alzheimer's disease: from basic insights to preclinical studies

Alzheimer's disease (AD), referring to a gradual deterioration in cognitive function, including memory loss and impaired thinking skills, has emerged as a substantial worldwide challenge with profound social and economic implications. As the prevalence of AD continues to rise and the population ages, there is an imperative demand for innovative imaging techniques to help improve our understanding of these complex conditions. Photoacoustic (PA) imaging forms a hybrid imaging modality by integrating the high-contrast of optical imaging and deep-penetration of ultrasound imaging. PA imaging enables the visualization and characterization of tissue structures and multifunctional information at high resolution and, has demonstrated promising preliminary results in the study and diagnosis of AD. This review endeavors to offer a thorough overview of the current applications and potential of PA imaging on AD diagnosis and treatment. Firstly, the structural, functional, molecular parameter changes associated with AD-related brain imaging captured by PA imaging will be summarized, shaping the diagnostic standpoint of this review. Then, the therapeutic methods aimed at AD is discussed further. Lastly, the potential solutions and clinical applications to expand the extent of PA imaging into deeper AD scenarios is proposed. While certain aspects might not be fully covered, this mini-review provides valuable insights into AD diagnosis and treatment through the utilization of innovative tissue photothermal effects. We hope that it will spark further exploration in this field, fostering improved and earlier theranostics for AD.

Hybrid ultrasound and photoacoustic contrast agent designs combining metal phthalocyanines and PBCA microbubbles

Photoacoustic (PA) imaging is an emerging diagnostic technology that combines the penetration depth of ultrasound (US) imaging and the contrast resolution of optical imaging. Although PA imaging can visualize several endogenous chromophores to obtain clinically-relevant information, multiple applications require the administration of external contrast agents. Metal phthalocyanines have strong PA properties and chemical stability, but their extreme hydrophobicity requires their encapsulation in delivery systems for biomedical applications. Hence, we developed hybrid US/PA contrast agents by encapsulating metal phthalocyanines in poly(butyl cyanoacrylate) microbubbles (PBCA MB), which display acoustic response and ability to efficiently load hydrophobic drugs. Six different metal chromophores were loaded in PBCA MB, showing greater encapsulation efficiency with higher chromophore hydrophobicity. Notably, while the US response of the MB was unaffected by the loading of the chromophores, the PA characteristics varied greatly. Among the different formulations, MB loaded with zinc and cobalt naphthalocyanines showed the strongest PA contrast, as a result of high encapsulation efficiencies and tunable optical properties. The strong US and PA contrast signals of the formulations were preserved in biological environment, as demonstrated by in vitro imaging in serum and whole blood, and ex vivo imaging in deceased mice. Taken together, these findings highlight the advantages of combining highly hydrophobic PA contrast agents and polymeric MB for the development of contrast agents for hybrid US/PA imaging, where different types of information (structural, functional, or potentially molecular) can be acquired by combining both imaging modalities.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

Rectal delivery of 89Zr-labeled infliximab-loaded nanoparticles enables PET imaging-guided localized therapy of inflammatory bowel disease

Inflammatory bowel diseases (IBDs) like Crohn's disease and ulcerative colitis involve chronic gastrointestinal inflammation. The pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) drives IBD pathogenesis. Anti-TNF-α therapies using monoclonal antibodies (mAbs) like infliximab (INF) help treat IBD but have limitations. We developed inflammation-targeting polyphenol-poloxamer nanoparticles loaded with the anti-inflammatory mAb INF (INF@PPNP) as a novel IBD therapy. Characterization showed that INF@PPNP had favorable stability and purity. Radiolabeling INF@PPNP with 89Zr enabled tracking localization with positron emission tomography (PET) imaging. Rectal administration of 89Zr-INF@PPNP led to colon delivery with remarkably reduced systemic exposure versus intravenous INF revealed by non-invasive PET imaging. 89Zr-INF@PPNP retention at inflamed foci indicated prolonged INF@PPNP action. INF@PPNP rectally achieved similar anti-inflammatory effects as intravenously injected INF, demonstrating the high therapeutic potential. Our findings support the use of nanoparticle-based rectal administration for localized drug delivery, prolonging drug activity and minimizing systemic exposure, ultimately offering an effective approach for treating IBD.

Achieving safe and high-performance gastrointestinal tract spectral CT imaging with small-molecule lanthanide complex

BACKGROUND

Non-intrusive imaging of gastrointestinal (GI) tract using computed tomography (CT) contrast agents is of the most significant issues in the diagnosis and treatment of GI diseases. Moreover, spectral CT, which can generate monochromatic images to display the X-ray attenuation characteristics of contrast agents, provides a better imaging sensitivity for diagnose inflammatory bowel disease (IBD) than convention CT imaging.

METHODS

Herein, a convenient and one-pot synthesis method is provided for the fabrication of small-molecule lanthanide complex Holmium-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (Ho-DOTA) as a biosafe and high-performance spectral CT contrast agent for GI imaging with IBD. In vivo CT imaging was administered with both healthy mice and colitis mice induced by dextran sodium sulfate.

RESULTS

We found that Ho-DOTA accumulated in inflammation sites of large intestines and produced high CT contrast compared with healthy mice. Both in vitro and in vivo experimental results also showed that Ho-DOTA provided much more diagnostic sensitivity and accuracy due to the excellent X-ray attenuation characteristics of Ho-DOTA compared with clinical iodinate agent. Furthermore, the proposed contrast media could be timely excreted from the body via the urinary and digestive system, keeping away from the potential side effects due to long-term retention in vivo.

CONCLUSION

Accordingly, Ho-DOTA with excellent biocompatibility can be useful as a potential high-performance spectral CT contrast agent for further clinical imaging of gastrointestinal tract and diagnosis of intestinal system diseases.

A Transformable Mucoadhesive Microgel Network for Noninvasive Multimodal Imaging And Radioprotection of a Large Area of the Gastrointestinal Tract

The lack of noninvasive imaging and modulation of a large area of the gastrointestinal (GI) tract constrain the diagnosis and treatment of many GI-related diseases. Recent advances use novel mucoadhesive materials to coat a part of the GI tract and then modulate its functions. High mucoadhesion is the key factor of the partial coating, but also the limitation for not spreading and covering the lower GI tract. Here, a bismuth-pectin organic-inorganic hybrid complex is screened and engineered into a transformable microgel network (Bi-GLUE) with high flowability and mucoadhesion, such that it can quickly transit through and coat a large area of the GI tract. In murine and porcine models, Bi-GLUE delivers contrast agents to achieve real-time, large-area GI-tract imaging under X-ray or magnetic resonance  modalities and to facilitate the non-invasive diagnosis of familial adenomatous polyposis. Moreover, Bi-GLUE, like an intracorporal radiation shield, decreases the radiotoxicity in a whole-abdomen irradiation rat model. This transformable microgel network offers a new direction that can modulate a large area of the GI tract and may have broad applications for GI-related conditions.

H2O2 Self-Supply and Glutathione Depletion Engineering Nanoassemblies for NIR-II Photoacoustic Imaging of Tumor Tissues and Photothermal-Enhanced Gas Starvation-Primed Chemodynamic Therapy

The development of tumor microenvironment (TME)-activated nanoassemblies which can produce a photoacoustic (PA) signal and enhance the H2O2 level is critical to achieve accurate diagnosis and highly efficient chemodynamic therapy (CDT). In this study, we developed nanoassemblies consisting of oxygen vacancy titanium dioxide (TiO2-x) surface-constructed copper, sulfur-doped mesoporous organosilica and glucose oxidase (TiO2-x@Cu,S-MONs@GOx, hereafter TMG). We found that highly abundant glutathione (GSH) in the TME nanoassemblies can reduce tetrasulfide bonds and Cu2+ to sulfur ions and Cu+ in the TMG nanoassemblies, respectively, causing the breakage of the tetrasulfide bond and the mesoporous structure collapse, releasing Cu+ ions and TiO2-x nanoparticles, and producing hydrogen sulfide gas, thereby achieving synergistic multimodal tumor treatment through TME-activated NIR-II PA imaging and photothermal-enhanced gas starvation-primed CDT. Therefore, the TMG nanoassemblies form a smart nanoplatform that can serve as an excellent tumor diagnosis-treatment agent by playing an important role in imaging-guided precision diagnosis of cancer and efficient targeting treatment.

Barium sulfate and pigment admixture for photoacoustic and x-ray contrast imaging of the gut

Significance

X-ray imaging is frequently used for gastrointestinal imaging. Photoacoustic imaging (PAI) of the gastrointestinal tract is an emerging approach that has been demonstrated for preclinical imaging of small animals. A contrast agent active in both modalities could be useful for imaging applications.

Aim

We aimed to develop a dual-modality contrast agent comprising an admixture of barium sulfate with pigments that absorb light in the second near-infrared region (NIR-II), for preclinical imaging with both x-ray and PAI modalities.

Approach

Eleven different NIR-II dyes were evaluated after admixture with a 40% w/v barium sulfate mixture. The resulting NIR-II absorption in the soluble fraction and in the total mixture was characterized. Proof-of-principle imaging studies in mice were carried out.

Results

Pigments that produced more uniform suspensions were assessed further for photoacoustic contrast signal at a wavelength of 1064 nm that corresponds to the output of the Nd:YAG laser used. Phantom imaging studies demonstrated that the pigment-barium sulfate mixture generated imaging contrast in both x-ray and PAI modalities. The optimal pigment selected for further study was a cyanine tetrafluoroborate salt. Ex-vivo and whole-body mouse imaging demonstrated that photoacoustic and x-ray contrast signals co-localized in the intestines for both imaging modalities.

Conclusion

These data demonstrate that commercially-available NIR-II pigments can simply be admixed with barium sulfate to generate a dual-modality contrast agent appropriate for small animal gastrointestinal imaging.

Automated Laser-Fiber Coupling Module for Optical-Resolution Photoacoustic Microscopy

Photoacoustic imaging has emerged as a promising biomedical imaging technique that enables visualization of the optical absorption characteristics of biological tissues in vivo. Among the different photoacoustic imaging system configurations, optical-resolution photoacoustic microscopy stands out by providing high spatial resolution using a tightly focused laser beam, which is typically transmitted through optical fibers. Achieving high-quality images depends significantly on optical fluence, which is directly proportional to the signal-to-noise ratio. Hence, optimizing the laser-fiber coupling is critical. Conventional coupling systems require manual adjustment of the optical path to direct the laser beam into the fiber, which is a repetitive and time-consuming process. In this study, we propose an automated laser-fiber coupling module that optimizes laser delivery and minimizes the need for manual intervention. By incorporating a motor-mounted mirror holder and proportional derivative control, we successfully achieved efficient and robust laser delivery. The performance of the proposed system was evaluated using a leaf-skeleton phantom in vitro and a human finger in vivo, resulting in high-quality photoacoustic images. This innovation has the potential to significantly enhance the quality and efficiency of optical-resolution photoacoustic microscopy.

Phthalocyanine-Blue Nanoparticles for the Direct Visualization of Tumors with White Light Illumination

The current standard of care for colon cancer surveillance relies heavily on white light endoscopy (WLE). However, dysplastic lesions that are not visible to the naked eye are often missed when conventional WLE equipment is used. Although dye-based chromoendoscopy shows promise, current dyes cannot delineate tumor tissues from surrounding healthy tissues accurately. The goal of the present study was to screen various phthalocyanine (PC) dye-loaded micelles for their ability to improve the direct visualization of tumor tissues under white light following intravenous administration. Zinc PC (tetra-tert-butyl)-loaded micelles were identified as the optimal formulation. Their accumulation within syngeneic breast tumors led the tumors to turn dark blue in color, making them clearly visible to the naked eye. These micelles were similarly able to turn spontaneous colorectal adenomas in Apc+/Min mice a dark blue color for easy identification and could enable clinicians to more effectively detect and remove colonic polyps.

Imaging of Gastrointestinal Tract Ailments

Gastrointestinal (GI) disorders comprise a diverse range of conditions that can significantly reduce the quality of life and can even be life-threatening in serious cases. The development of accurate and rapid detection approaches is of essential importance for early diagnosis and timely management of GI diseases. This review mainly focuses on the imaging of several representative gastrointestinal ailments, such as inflammatory bowel disease, tumors, appendicitis, Meckel's diverticulum, and others. Various imaging modalities commonly used for the gastrointestinal tract, including magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT), and photoacoustic tomography (PAT) and multimodal imaging with mode overlap are summarized. These achievements in single and multimodal imaging provide useful guidance for improved diagnosis, staging, and treatment of the corresponding gastrointestinal diseases. The review evaluates the strengths and weaknesses of different imaging techniques and summarizes the development of imaging techniques used for diagnosing gastrointestinal ailments.

Platinum Drug-Incorporating Polymeric Nanosystems for Precise Cancer Therapy

Platinum (Pt) drugs are widely used in clinic for cancer therapy, but their therapeutic outcomes are significantly compromised by severe side effects and acquired drug resistance. With the emerging immunotherapy and imaging-guided cancer therapy, precise delivery and release of Pt drugs have drawn great attention these days. The targeting delivery of Pt drugs can greatly increase the accumulation at tumor sites, which ultimately enhances antitumor efficacy. Further, with the combination of Pt drugs and other theranostic agents into one nanosystem, it not only possesses excellent synergistic efficacy but also achieves real-time monitoring. In this review, after the introduction of Pt drugs and their characteristics, the recent progress of polymeric nanosystems for efficient delivery of Pt drugs is summarized with an emphasis on multi-modal synergistic therapy and imaging-guided Pt-based cancer treatment. In the end, the conclusions and future perspectives of Pt-encapsulated nanosystems are given.

Review on ultrasound-guided photoacoustic imaging for complementary analyses of biological systems in vivo

Photoacoustic imaging has been developed as a new biomedical molecular imaging modality. Due to its similarity to conventional ultrasound imaging in terms of signal detection and image generation, dual-modal photoacoustic and ultrasound imaging has been applied to visualize physiological and morphological information in biological systems in vivo. By complementing each other, dual-modal photoacoustic and ultrasound imaging showed synergistic advances in photoacoustic imaging with the guidance of ultrasound images. In this review, we introduce our recent progresses in dual-modal photoacoustic and ultrasound imaging systems at various scales of study, from preclinical small animals to clinical humans. A summary of the works reveals various strategies for combining the structural information of ultrasound images with the molecular information of photoacoustic images.

Pluronic F127 coating performance on PLGA nanoparticles: Enhanced flocculation and instability

Nanoparticles (NPs) can be incorporated into hydrogels to obtain multifunctional hybrid systems to meet the delivery needs of different drugs. However, the stability of NPs in hydrogels is rarely revealed. In this article, we tried to explore the underlying mechanism of an interesting phenomenon that poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PNPs) could flocculate and deposit in Pluronic F127 (F127) hydrogels at 4 °C. The results showed that this flocculation was relevant to the type of emulsifier formulated in PNPs, the particle materials and the F127 concentration, but independent of PLGA polymer end groups. Exactly, PNPs containing polyvinyl alcohol (PVA) as the emulsifier flocculated in F127 solution with a concentration above 15 %. The flocculated PNPs possessed increased particle size, decreased zeta potential, reduced hydrophobicity and an obvious coating layer, and these characteristics could be restored almost to the original state after two washes of flocculated PNPs with water. Moreover, the flocculation had no impact on the long-term size stability and drug-loading capacity of PNPs, and F127-treated PNPs showed improved cellular uptake than untreated PNPs. These results provide the evidence that adsorption of high concentrations of F127 on the surface of PNPs/PVA may lead to flocculation, and the flocculation is reversible by simply washing the flocs with water. To the best of our knowledge, this is the first study to scientifically explore the stability of PNPs in F127 hydrogels, providing theoretical and experimental support for the rational design and further development of nanoparticle-hydrogel composite.

In Situ Generation of Red-to-NIR Emissive Radical Cations in the Stomach for Gastrointestinal Imaging

Red-to-near-infrared (NIR) fluorescent probes, with advantages such as high spatiotemporal resolution and in situ sensing abilities, are highly attractive for diagnosis of gastrointestinal diseases and targeted drug development. However, conventional red-to-NIR fluorophores with electron closed-shell structures require tedious synthetic procedures for preparation, and it is difficult to further decorate them with sensing groups. In this study, a series of easily prepared pyrroles with simple structures that can quickly be transformed into red-to-NIR emissive radical cations in acidic buffer solution and in vivo stomachs is developed. The in-situ-generated red-to-NIR emissive pyrrole radical cations in the stomach have excellent biocompatibility and stability and can be used not only for intravital gastrointestinal imaging with high spatiotemporal resolution, but also for dynamic monitoring of the gastric emptying process and assessment of anti-gastric-acid therapy. The acidity-induced generation of pyrrole radical cations is believed to provide a facile strategy for developing red-to-NIR fluorophores and studying gastrointestinal diseases.

Radiolabeled nanomaterial for cancer diagnostics and therapeutics: principles and concepts

In the last three decades, radiopharmaceuticals have proven their effectiveness for cancer diagnosis and therapy. In parallel, the advances in nanotechnology have fueled a plethora of applications in biology and medicine. A convergence of these disciplines has emerged more recently with the advent of nanotechnology-aided radiopharmaceuticals. Capitalizing on the unique physical and functional properties of nanoparticles, radiolabeled nanomaterials or nano-radiopharmaceuticals have the potential to enhance imaging and therapy of human diseases. This article provides an overview of various radionuclides used in diagnostic, therapeutic, and theranostic applications, radionuclide production through different techniques, conventional radionuclide delivery systems, and advancements in the delivery systems for nanomaterials. The review also provides insights into fundamental concepts necessary to improve currently available radionuclide agents and formulate new nano-radiopharmaceuticals.

In situ synthesized nanozyme for photoacoustic-imaging-guided photothermal therapy and tumor hypoxia relief

Nanozymes have attracted extensive research interest due to their ideal enzymatic catalytic performance; however, uncontrollable activities and nonspecific accumulation limit their further clinical application. To overcome these obstacles, we proposed in situ synthesized nanozyme, and realized the concept through an intelligent nanosystem (ISSzyme) based on Prussian blue (PB) precursor. PB nanozyme was synthesized at the tumor sites through the interaction of ISSzyme with glutathione, which was demonstrated by comparing with conventional PB nanozyme. ISSzyme is capable of tumor-specific photoacoustic imaging (PAI) and photothermal therapy (PTT), reducing the false-positive signals of PAI and the treatment side effects of PTT. ISSzyme has catalase-like activities, resulting in tumor hypoxia relief and metastasis inhibition. More importantly, the in situ synthesized PB nanozyme has the favorable property of minimal liver accumulation. Considering the above advantages, ISSzyme is expected to shed light on the design of the next-generation artificial enzymes, with many new biomedical applications.

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.

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.

High current short pulse driver using a high power diode laser for optoacoustic biomedical imaging techniques

Optoacoustic biomedical imaging combines the high spatial resolution of the ultrasound imaging with the specificity of the optical absorption spectroscopy techniques. It is being used in various scenarios such as anatomical, functional and molecular imaging. Typically light sources for this imaging technique is based on solid state lasers since they can produce high energy short optical pulses. However, they are bulky, expensive and the imaging speed is limited because their low pulse repetition rate. High power diode lasers (HPDLs) are a promising alternative for imaging small volume absorbers as they are compact, affordable and allow high repetition rates. However, HPDLs provide relative low peak optical power compared to solid state lasers. Therefore, imaging systems based on diode lasers require much longer pulse duration resulting in lower in-depth resolution and optoacoustic conversion efficiency. HPDLs need dedicated fast electronics to generate short optical pulses. In this work, we have designed, built and test a pulsed diode laser driver based on RF power MOSFETs, specifically considering the optimization of the current pulse in order to maximize the optical peak power, achieving current pulses of more than 900 A with a duration of 50 ns. We have studied the operation of a low cost HPDL out of the manufacturers datasheet ratings without noticeable degradation at high current (> 250 A) and short pulse duration (< 60 ns). We have obtained an optical peak power of 750 W and a energy per pulse of 31.2 µJ at 40 ns optical pulse duration. The optoacoustic images obtained in this operation regime shown a clear enhancement respect to the ones obtained in standard operation of the HPDL.

Penetration and translocation of functional inorganic nanomaterials into biological barriers

With excellent physicochemical properties, inorganic nanomaterials (INMs) have exhibited a series of attractive applications in biomedical fields. Biological barriers prevent successful delivery of nanomedicine in living systems that limits the development of nanomedicine especially for sufficient delivery of drugs and effective therapy. Numerous researches have focused on overcoming these biological barriers and homogeneity of organisms to enhance therapeutic efficacy, however, most of these strategies fail to resolve these challenges. In this review, we present the latest progress about how INMs interact with biological barriers and penetrate these barriers. We also summarize that both native structure and components of biological barriers and physicochemical properties of INMs contributed to the penetration capacity. Knowledge about the relationship between INMs structure and penetration capacity will guide the design and application of functional and efficient nanomedicine in the future.

Intraperitoneal administration for sustained photoacoustic contrast agent imaging

Photoacoustic (PA) imaging at 1064 nm in the second near-infrared (NIR-II) has attracted recent attention. We recently reported a surfactant-based formulation of a NIR-II dye (BIBDAH) for NIR-II PA contrast. Here, we investigated BIBDAH as a NIR-II PA contrast agent for longitudinal preclinical PA imaging. When administered to mice by the conventional intravenous (I.V.) route, BIBDAH was rapidly cleared from circulation, as indicated by a decrease in NIR-II absorption in sampled plasma. Conversely, when mice were injected with BIBDAH by the intraperitoneal (I.P.) route, peak NIR-II absorption levels in plasma were lower initially, but there was a sustained dye presence that resulted in a more consistent concentration of dye in plasma over 2 days. Increasing the I.P. injection dose and volume resulted in increased NIR-II area under the curve (AUC) in serum. Bimodal PA and ultrasound imaging reflected these results, showing a rapid decrease in PA signal in blood with I.V. administration, but permitting sustained imaging with I.P. administration. These results show that I.P. administration can be considered as an administration route in preclinical animal studies for improved longitudinal observation with more consistent contrast signal intensity.

Design and application of organic contrast agents for molecular imaging in the second near infrared (NIR-II) window

Optical imaging in the second near-infrared (NIR-II) window has attracted interest in recent years because of the merits of reduced light scattering, minimal autofluorescence from biological tissues and deeper penetration depth in this wavelength range. In this review, we summarize NIR-II organic contrast agents reported in the past decade for photoacoustic and fluorescence imaging including members of the cyanine family, D-A-D structure dyes, phthalocyanines and semiconducting polymers. Improved imaging contrast and higher resolution could be favorably achieved by rational design of NIR-II fluorophores by tuning their properties including molar extinction coefficient, fluorescence quantum yield, emission wavelength and others. A wide variety of applications using NIR-II dyes has been realized including imaging of tumors, lymphatics, brains, intestines and others. Emerging applications such as targeted imaging and activable imaging with improved resolution and sensitivity have been demonstrated by innovative chemical modification of NIR-II dyes. Looking forward, rational design of improved NIR-II dyes for advanced bioimaging is likely to remain an area of interest for next-generation potential approaches to disease diagnosis.

Food-Grade Activated Charcoal for Contrast-Enhanced Photoacoustic Imaging of Aspiration: A Phantom Study

Aspiration pneumonia has the highest attributable mortality of all medical complications post-stroke, or in individuals with progressive neurological diseases. For optimum health outcomes for individuals with dysphagia, a non-invasive and convenient method for objectively detecting aspiration is needed. This study introduces a potential new aspiration screening method based on photoacoustic imaging (PAI), a medical imaging technology that measures the optical contrast of tissue rather than mechanical or elastic properties. In this preliminary study, a tissue-mimicking neck phantom was designed to test the performance of PAI for aspiration screening with a charcoal solution as a contrast agent. A 1064 nm wavelength light source was illuminated on the anterior of the neck phantom to induce the photoacoustic effect. The resulting photoacoustic signal of the charcoal contrast in the mock trachea was detected by a linear transducer array with a 2.25 MHz central ultrasound frequency. The phantom results showed that charcoal solution at 10 mg/ml exhibited strong photoacoustic signals when flowing into the phantom trachea. By overlaying the photoacoustic signals of the charcoal contrast on top of the ultrasound image, we were able to simultaneously visualize the movement of food contrast and a cross-section of tissue structures during mock swallowing. Moreover, we confirmed the ability to detect the flow of charcoal contrast at a small bolus volume of ~ 7 μl through the phantom, suggesting high sensitivity to detect small aspiration events. The study suggests that PAI holds promise to be developed as an aspiration detection tool with charcoal powder as a contrast agent.

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.

Ce doped polyaniline nanoparticles for absorption and photoacoustic imaging response to GSH in vitro and in vivo

Glutathione (GSH) is an important biological thiol in cells, which is involved in many physiological processes in the organism and regulates pathological processes of cells. Rapid and accurate monitoring of GSH in vitro and in vivo is quite needed in investigating important biochemical events. In this contribution, innovative cerium (Ce) doped polyaniline (Ce–Fe@PANI NPs) were prepared via Fe(III) induced oxidization polymerization method. Upon addition of GSH, the absorption of Ce–Fe@PANI NPs red shifted from the visible to the NIR region, confirming the excellent absorption response to GSH. Moreover, Ce–Fe@PANI NPs exhibited excellent photoacoustic (PA) imaging enhancement in tube and shifted the PA intensity peak from 680 nm to 820 nm upon addition of GSH. In vitro and in vivo experiment verified that Ce–Fe@PANI NPs can monitor GSH in deep tissues via PA imaging technology. Collectively, this research provides Ce–Fe@PANI NPs would serve as a powerful nanoplatform to realize PA imaging detection of GSH in vitro and in vivo.

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Ce doped polyaniline nanoparticles (Ce–Fe@PANI NPs) with NIR absorption were prepared.

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Ce–Fe@PANI NPs demonstrated absorption response to GSH.

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Ce–Fe@PANI NPs had excellent PA enhancement and shifted the PA intensity peak from 680 nm to 820 nm upon addition of GSH.

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Ce–Fe@PANI NPs can monitor GSH in deep tissues via PA imaging technology in vivo.

Manganese Coordination Micelles That Activate Stimulator of Interferon Genes and Capture In Situ Tumor Antigens for Cancer Metalloimmunotherapy

Cancer immunotherapy holds great promise but is generally limited by insufficient induction of anticancer immune responses. Here, a metal micellar nanovaccine is developed by the self-assembly of manganese (Mn), a stimulator of interferon genes (STING) agonist (ABZI) and naphthalocyanine (ONc) coordinated nanoparticles (ONc-Mn-A) in maleimide-modified Pluronic F127 (malF127) micelles. Owing to synergy between Mn and ABZI, the nanovaccine, termed ONc-Mn-A-malF127, elevates levels of interferon-β (IFNβ) by 324- and 8-fold in vivo, compared to use of Mn or ABZI alone. As such, the activation of the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-STING pathway induces sufficient dendritic cell (DC) maturation, eventually resulting in the death of CD8⁺ T cell-sensitive tumors and CD8⁺ T cell-resistant tumors by simultaneously promoting cytotoxic CD8⁺ T cells and NK cells, respectively. Furthermore, with ONc used as a Mn chelator and an efficient photosensitizer, photoinduced immunogenic cell death (ICD) of tumor cells releases damage-associated molecular patterns (DAMPs) and neoantigens from dying primary tumor cells upon laser irradiation, which are captured in situ by malF127 in tumor cells and then transported to DCs. After laser treatment, in addition to the photothermal therapy, immune responses characterized by the level of IFNβ are further elevated by another 4-fold. In murine cancer models, ICD-based metalloimmunotherapy using the ONc-Mn-A-malF127 nanovaccine in a single dose by intravenous injection achieved eradication of primary and distant tumors. Taken together, ONc-Mn-A-malF127 offers a nanoplatform to enhance anticancer efficacy by metalloimmunotherapy and photoinduced ICD based immunotherapy with strong abscopal effect.

Water-Processed Organic Solar Cell with Efficiency Exceeding 11

Water processing is an ideal strategy for the ecofriendly fabrication of organic photovoltaics (OPVs) and exhibits a strong market-driven demand. Here, we report a state-of-the-art active material, namely PM6:BTP-eC9, for the synthesis of water-borne nanoparticle (NP) dispersion towards ecofriendly OPV fabrication. The surfactant-stripping technique, combined with a poloxamer, facilitates purification and eliminates excess surfactant in water-dispersed organic semiconducting NPs. The introduction of 1,8-diiodooctane (DIO) for the synthesis of surfactant-stripped NP (ssNP) further promotes a percolated microstructure of the polymer and NFA in each ssNP, yielding water-processed OPVs with a record efficiency of over 11%. The use of an additive during water-borne ssNP synthesis is a promising strategy for morphology optimization in NP OPVs. It is believed that the findings in this work will engender more research interest and effort relating to water-processing in preparation of the industrial production of OPVs.

A Self-Assembly ICG Nanoparticle Potentiating Targeted Photothermal and Photodynamic Therapy in NSCLC

In nonsmall cell lung cancers (NSCLC), near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) has proven to be an efficient approach for locating pulmonary nodules and pulmonary sentinel lymph nodes. However, due to a lack of tumor selectivity, ICG's use as a photosensitizer for photothermal therapy (PTT) and photodynamic therapy (PDT) is restricted. In the current study, we aimed to develop a type of high-performance NIR nanoparticle formulated with ICG to enhance its targeted efficacy and tumor specificity on NSCLC. An ICG-osimertinib nanoparticle (ICG-Osi) was self-assembled through π-π stacking, with a size of 276 nm and a surface charge of -7.4 mV. The NIR visibility and epidermal growth factor receptor (EGFR) targetability of the ICG-Osi was confirmed by its binding efficiency to EGFR-expressing NSCLC cells in vitro and in vivo, regardless of EGFR mutation status. The targeted effect was further confirmed in mouse xenograft models and showed an extended tumor retention time (>96 h). We demonstrated a significantly enhanced hyperthermia effect and a retained reactive oxygen species (ROS) generating ability of ICG-Osi, resulting in a 2-fold higher cell death rate than ICG alone. The ICG-Osi down-regulated GPX4 and p62 expression while up-regulating caspase-3 and beclin1 expression in NSCLC cells, indicating a complex network of cell death-related proteins. Considering the merits of simple assembly, EGFR binding efficacy, improved hyperthermia effect, and efficient cancer cell suppression, the ICG-Osi exhibits great potential for clinical application in EGFR-expressing NSCLC therapy.

Contrast Agents for Photoacoustic Imaging: A Review Focusing on the Wavelength Range

Photoacoustic imaging using endogenous chromophores as a contrast has been widely applied in biomedical studies owing to its functional imaging capability at the molecular level. Various exogenous contrast agents have also been investigated for use in contrast-enhanced imaging and functional analyses. This review focuses on contrast agents, particularly in the wavelength range, for use in photoacoustic imaging. The basic principles of photoacoustic imaging regarding light absorption and acoustic release are introduced, and the optical characteristics of tissues are summarized according to the wavelength region. Various types of contrast agents, including organic dyes, semiconducting polymeric nanoparticles, gold nanoparticles, and other inorganic nanoparticles, are explored in terms of their light absorption range in the near-infrared region. An overview of the contrast-enhancing capacity and other functional characteristics of each agent is provided to help researchers gain insights into the development of contrast agents in photoacoustic imaging.

Fast Fourier Transform-weighted Photoacoustic Imaging by In Vivo Magnetic Alignment of Hybrid Nanorods

Photoacoustic (PA) imaging uses photon-phonon conversion for high-resolution tomography of biological tissues and functions. Exogenous contrast agents are often added to improve the image quality, but the interference from endogenous molecules diminishes the imaging sensitivity and specificity. We report a background-free PA imaging technique based on the active modulation of PA signals via magnetic alignment of Fe₃O₄@Au hybrid nanorods. Switching the field direction creates enhanced and deactivated PA imaging modalities, enabling a simple pixel subtraction to effectively minimize background noises. Under an alternating magnetic field, the nanorods exhibit PA signals of coherently periodic changes that can be converted into a sharp peak in a frequency domain via the fast Fourier transform. Automatic pixel-wise screening of nanorod signals performed using a computational algorithm across a time-sequence set of PA images regenerates a background-free PA image with significantly improved contrast, specificity, and fidelity.

State of the Art in Carbon Nanomaterials for Photoacoustic Imaging

Photoacoustic imaging using energy conversion from light to ultrasound waves has been developed as a powerful tool to investigate in vivo phenomena due to their complex characteristics. In photoacoustic imaging, endogenous chromophores such as oxygenated hemoglobin, deoxygenated hemoglobin, melanin, and lipid provide useful biomedical information at the molecular level. However, these intrinsic absorbers show strong absorbance only in visible or infrared optical windows and have limited light transmission, making them difficult to apply for clinical translation. Therefore, the development of novel exogenous contrast agents capable of increasing imaging depth while ensuring strong light absorption is required. We report here the application of carbon nanomaterials that exhibit unique physical, mechanical, and electrochemical properties as imaging probes in photoacoustic imaging. Classified into specific structures, carbon nanomaterials are synthesized with different substances according to the imaging purposes to modulate the absorption spectra and highly enhance photoacoustic signals. In addition, functional drugs can be loaded into the carbon nanomaterials composite, and effective in vivo monitoring and photothermal therapy can be performed with cell-specific targeting. Diverse applied cases suggest the high potential of carbon nanomaterial-based photoacoustic imaging in in vivo monitoring for clinical research.

Listening to drug delivery and responses via photoacoustic imaging

Administrating pharmaceutic agents efficiently to achieve the therapeutic effect is the aim of all drug delivery techniques. Recent drug delivery systems aim to deliver high doses of drugs to disease sites accurately while maximizing therapeutic effects and minimizing potential side effects. Key approaches apply image guidance techniques for the quantification of drug biodistribution and pharmacokinetic parameters during drug delivery. This review highlights recent research on image-guided drug delivery systems based on photoacoustic imaging, which has been attracting attention for its non-invasiveness, non-ionizing radiation, and real-time imaging functions. Photoacoustic imaging based on the photothermal conversion efficiency of agents can be easily combined with various phototherapeutics, making them highly suitable for drug delivery therapy platforms. Here, we summarize and compare the characteristics of various types of photoacoustic imaging systems, focus on contrast-enhanced photoacoustic imaging and controlled release of therapeutics in drug delivery systems for synergistic therapies.

High Spatial and Temporal Resolution NIR-IIb Gastrointestinal Imaging in Mice

Conventional biomedical imaging modalities, including endoscopy, X-rays, and magnetic resonance, are invasive and insufficient in spatial and temporal resolutions for gastrointestinal (GI) tract imaging to guide prognosis and therapy. Here we report a noninvasive method based on lanthanide-doped nanocrystals with ∼1530 nm fluorescence in the near-infrared-IIb window (NIR-IIb, 1500-1700 nm). The rational design of nanocrystals have led to an absolute quantum yield (QY) up to 48.6%. Further benefiting from the minimized scattering through the NIR-IIb window, we enhanced the spatial resolution to ∼1 mm in GI tract imaging, which is ∼3 times higher compared with the near-infrared-IIa (NIR-IIa, 1000-1500 nm) method. The approach also realized a high temporal resolution of 8 frames per second; thus the moment of mice intestinal peristalsis can be captured. Furthermore, with a light-sheet imaging system, we demonstrated a three-dimensional (3D) imaging on the GI tract. Moreover, we successfully translated these advances to diagnose inflammatory bowel disease.

Photoacoustic imaging systems based on clinical ultrasound platform

Photoacoustic imaging has drawn a significant amount of attention due to its unique capacity for functional, metabolic, and molecular imaging, which is achieved by the combination of optical excitation and acoustic detection. With both strengths of light and ultrasound, photoacoustic images can provide strong optical contrast at high ultrasound resolution in deep tissue. As photoacoustic imaging can be used to visualize complementary information to ultrasound imaging using the same data acquisition process, several studies have been conducted on combining photoacoustic imaging with existing clinical ultrasound systems. This review highlights our development of a photoacoustic/ultrasound dual-modal imaging system, various features and functionalities implemented for clinical translation, and preclinical/clinical studies performed by using the systems.

In vivo three-dimensional multispectral photoacoustic imaging of dual enzyme-driven cyclic cascade reaction for tumor catalytic therapy

Non-invasive visualization of dynamic molecular events in real-time via molecular imaging may enable the monitoring of cascade catalytic reactions in living systems, however effective imaging modalities and a robust catalytic reaction system are lacking. Here we utilize three-dimensional (3D) multispectral photoacoustic (PA) molecular imaging to monitor in vivo cascade catalytic therapy based on a dual enzyme-driven cyclic reaction platform. The system consists of a two-dimensional (2D) Pd-based nanozyme conjugated with glucose oxidase (GOx). The combination of nanozyme and GOx can induce the PA signal variation of endogenous molecules. Combined with the PA response of the nanozyme, we can simultaneously map the 3D PA signals of dynamic endogenous and exogenous molecules associated with the catalytic process, thus providing a real-time non-invasive visualization. We can also treat tumors under the navigation of the PA imaging. Therefore, our study demonstrates the imaging-guided potential of 3D multispectral PA imaging in feedback-looped cascade catalytic therapy.

Segmentation and Quantitative Analysis of Photoacoustic Imaging: A Review

Photoacoustic imaging is an emerging biomedical imaging technique that combines optical contrast and ultrasound resolution to create unprecedented light absorption contrast in deep tissue. Thanks to its fusional imaging advantages, photoacoustic imaging can provide multiple structural and functional insights into biological tissues such as blood vasculatures and tumors and monitor the kinetic movements of hemoglobin and lipids. To better visualize and analyze the regions of interest, segmentation and quantitative analyses were used to extract several biological factors, such as the intensity level changes, diameter, and tortuosity of the tissues. Over the past 10 years, classical segmentation methods and advances in deep learning approaches have been utilized in research investigations. In this review, we provide a comprehensive review of segmentation and quantitative methods that have been developed to process photoacoustic imaging in preclinical and clinical experiments. We focus on the parametric reliability of quantitative analysis for semantic and instance-level segmentation. We also introduce the similarities and alternatives of deep learning models in qualitative measurements using classical segmentation methods for photoacoustic imaging.

Surfactant-Stripped Semiconducting Polymer Micelles for Tumor Theranostics and Deep Tissue Imaging in the NIR-II Window

Photoacoustic imaging (PA) in the second near infrared (NIR-II) window presents key advantages for deep tissue imaging owing to reduced light scattering and low background signal from biological structures. Here, a thiadiazoloquinoxaline-based semiconducting polymer (SP) with strong absorption in the NIR-II region is reported. After encapsulation of SP in Pluronic F127 (F127) followed by removal of excess surfactant, a dual functional polymer system named surfactant-stripped semiconductor polymeric micelles (SSS-micelles) are generated with water solubility, storage stability, and high photothermal conversion efficiency, permitting tumor theranostics in a mouse model. SSS-micelles have a wideband absorption in the NIR-II window, allowing for the PA imaging at both 1064 and 1300 nm wavelengths. The PA signal of the SSS-micelles can be detected through 6.5 cm of chicken breast tissue in vitro. In mice or rats, SSS-micelles can be visualized in bladder and intestine overlaid 5 cm (signal to noise ratio, SNR ≈ 17 dB) and 5.8 cm (SNR over 10 dB) chicken breast tissue, respectively. This work demonstrates the SSS-micelles as a nanoplatform for deep tissue theranostics.