Copper Sulfide Perfluorocarbon Nanodroplets as Clinically Relevant Photoacoustic/Ultrasound Imaging Agents

Laser-activated perfluorocarbon nanodroplets for intracerebral delivery and imaging via blood-brain barrier opening and contrast-enhanced imaging

BACKGROUND

Ultrasound and photoacoustic (US/PA) imaging is a promising tool for in vivo visualization and assessment of drug delivery. However, the acoustic properties of the skull limit the practical application of US/PA imaging in the brain. To address the challenges in targeted drug delivery to the brain and transcranial US/PA imaging, we introduce and evaluate an intracerebral delivery and imaging strategy based on the use of laser-activated perfluorocarbon nanodroplets (PFCnDs).

METHODS

Two specialized PFCnDs were developed to facilitate blood‒brain barrier (BBB) opening and contrast-enhanced US/PA imaging. In mice, PFCnDs were delivered to brain tissue via PFCnD-induced BBB opening to the right side of the brain. In vivo, transcranial US/PA imaging was performed to evaluate the utility of PFCnDs for contrast-enhanced imaging through the skull. Ex vivo, volumetric US/PA imaging was used to characterize the spatial distribution of PFCnDs that entered brain tissue. Immunohistochemical analysis was performed to confirm the spatial extent of BBB opening and the accuracy of the imaging results.

RESULTS

In vivo, transcranial US/PA imaging revealed localized photoacoustic (PA) contrast associated with delivered PFCnDs. In addition, contrast-enhanced ultrasound (CEUS) imaging confirmed the presence of nanodroplets within the same area. Ex vivo, volumetric US/PA imaging revealed PA contrast localized to the area of the brain where PFCnD-induced BBB opening had been performed. Immunohistochemical analysis revealed that the spatial distribution of immunoglobulin (IgG) extravasation into the brain closely matched the imaging results.

CONCLUSIONS

Using our intracerebral delivery and imaging strategy, PFCnDs were successfully delivered to a targeted area of the brain, and they enabled contrast-enhanced US/PA imaging through the skull. Ex vivo imaging, and immunohistochemistry confirmed the accuracy and precision of the approach.

Multiplex Ultrasound Imaging of Perfluorocarbon Nanodroplets Enabled by Decomposition of Postvaporization Dynamics

Despite the real-time, nonionizing, and cost-effective nature of ultrasound imaging, there is a dearth of methods to visualize two or more populations of contrast agents simultaneously─a technique known as multiplex imaging. Here, we present a new approach to multiplex ultrasound imaging using perfluorocarbon (PFC) nanodroplets. The nanodroplets, which undergo a liquid-to-gas phase transition in response to an acoustic trigger, act as activatable contrast agents. This work characterized the dynamic responses of two PFC nanodroplets with boiling points of 28 and 56 °C. These characteristic responses were then used to demonstrate that the relative concentrations of the two populations of PFC nanodroplets could be accurately measured in the same imaging volume within an average error of 1.1%. Overall, the findings indicate the potential of this approach for multiplex ultrasound imaging, allowing for the simultaneous visualization of multiple molecular targets simultaneously.

Biodegradable germanium nanoparticles as contrast agents for near-infrared-II photoacoustic imaging

Photoacoustic (PA) imaging using contrast agents with strong near-infrared-II (NIR-II, 1000-1700 nm) absorption enables deep penetration into biological tissue. Besides, biocompatibility and biodegradability are essential for clinical translation. Herein, we developed biocompatible and biodegradable germanium nanoparticles (GeNPs) with high photothermal stability as well as strong and broad absorption for NIR-II PA imaging. We first demonstrate the excellent biocompatibility of the GeNPs through experiments, including the zebrafish embryo survival rates, nude mouse body weight curves, and histological images of the major organs. Then, comprehensive PA imaging demonstrations are presented to showcase the versatile imaging capabilities and excellent biodegradability, including in vitro PA imaging which can bypass blood absorption, in vivo dual-wavelength PA imaging which can clearly distinguish the injected GeNPs from the background blood vessels, in vivo and ex vivo PA imaging with deep penetration, in vivo time-lapse PA imaging of a mouse ear for observing biodegradation, ex vivo time-lapse PA imaging of the major organs of a mouse model for observing the biodistribution after intravenous injection, and notably in vivo dual-modality fluorescence and PA imaging of osteosarcoma tumors. The in vivo biodegradation of GeNPs is observed not only in the normal tissue but also in the tumor, making the GeNPs a promising candidate for clinical NIR-II PA imaging applications.

Real-time monitoring of NIR-triggered drug release from phase-changeable nanodroplets by photoacoustic/ultrasound imaging

Optical-responsive nanodroplets have recently been studied as a new mode of remotely controlled drug delivery. As a class of new emerging smart drug carriers, NIR-absorber-loaded perfluorocarbon nanodroplets can be converted into gas bubbles through laser stimulation, called optical droplet vaporization (ODV), which provides a potential strategy to deliver therapeutic agents to solid tumors on demand. However, there is a lack of suitable technologies to monitor these drug-loaded nanodroplet behaviors in vivo, and control the site and amount of drug released. In this study, ultrasound and photoacoustic imaging technology were applied to directly monitor optical-responsive, drug-loaded nanodroplets within the tissue. We explored the effects of laser energy, repetition rate, and number of pulses on the release profiles of the delivered drug as well as ultrasound and photoacoustic imaging signal-intensity curves. The conducted studies demonstrated that this noninvasive technology helped determine the optimum time point for laser activation on accumulated drug-loaded nanodroplets within tissues, allowing for the potential to effectively treat pathologies while minimizing drug-related toxicities.

Biomedical Photoacoustic Imaging for Molecular Detection and Disease Diagnosis: "Always-On" and "Turn-On" Probes

Photoacoustic (PA) imaging is a nonionizing, noninvasive imaging technique that combines optical and ultrasonic imaging modalities to provide images with excellent contrast, spatial resolution, and penetration depth. Exogenous PA contrast agents are created to increase the sensitivity and specificity of PA imaging and to offer diagnostic information for illnesses. The existing PA contrast agents are categorized into two groups in this review: "always-on" and "turn-on," based on their ability to be triggered by target molecules. The present state of these probes, their merits and limitations, and their future development, is explored.

In vivo photoacoustic image-guided tumor photothermal therapy and real-time temperature monitoring using a core-shell polypyrrole@CuS nanohybrid

Near-infrared (NIR) laser triggered theranostic platforms are increasingly used in clinical nanomedicine applications. In this work, a core-shell composite consisting of polypyrrole (PPy) coated copper sulfide (CuS) nanospheres with high photothermal efficiency and good photostability has been fabricated via a facile interfacial polymerization. The PPy@CuS nanohybrid had a hydrodynamic diameter of 58.5 nm with a CuS core and PPy shell and exhibited strong optical absorption and photon-to-heat conversion in the NIR region, leading to a sufficient photohyperthermic effect under irradiation with a 808 nm continuous wave laser. In vivo studies showed that the Ppy@CuS nanohybrids produced significant photoacoustic signals and exhibited remarkable photothermal therapeutic efficacy. Furthermore, the core-shell composites exhibited improved temperature elevation and photostability. The temperature-induced changes can be detected and monitored using photoacoustic imaging, thus allowing the control of the thermal dose while minimizing photothermal damage to surrounding healthy tissues. In summary, this study demonstrates that this novel platform could potentially be used for photoacoustic image-guided photothermal therapy and real-time temperature monitoring in cancer theranostics.

Focused Acoustic Vortex-Regulated Composite Nanodroplets Combined with Checkpoint Blockade for High-Performance Tumor Synergistic Therapy

The combination of checkpoint blockade with focused ultrasound (FUS) physical therapy can enhance antitumor immune response by improving the precision and efficiency of immunotherapy. However, one of the major disadvantages of conventional FUS treatment is the small lesion size, which prolongs treatment duration. We constructed a focused acoustic vortex (FAV) system with a hollow cylindrical focal region, which exhibited a larger focal region compared to conventional FUS of the same frequency. We developed an all-in-one synergistic therapy against metastatic breast cancer based on integrated FAV double combination sequence-regulated phase-transformation nanodroplets (CPDA@PFH) with checkpoint blockade immunotherapy. A single treatment with FAV + CPDA@PFH resulted in 2.25-fold higher inhibition of tumor growth compared to that with FUS + CPDA@PFH. In addition, FAV-regulated CPDA@PFH combined with ICB induced a systemic immune response that not only inhibited the growth of primary (98.41% inhibition rate) and distal (80.71%) 4T1 tumors but also reduced the progression of lung metastasis. In addition, the synergistic therapy achieved long-term immune memory that effectively prevented tumor growth and improved the survival time of mice. The long-term survival rate of 4T1 tumor-bearing mice treated with FAV + CPDA@PFH + Anti-PD-L1 was 57.14% on day 60 after treatment. Our study is a proof-of-concept of cascade-amplified synergistic tumor therapeutics based on ultrasonic-hyperthermia, cavitation, sonodynamic therapy (SDT), and checkpoint blockade immunotherapy through FAV-regulated CPDA@PFH phase-transformation nanodroplets.

Copper sulfide nanostructures: synthesis and biological applications

Over the past few years, considerable attention has been paid to biomedical applications of copper sulfide nanostructures owing to their enhanced physiochemical and pharmacokinetics characteristics in comparison to gold, silver, and carbon nanomaterials. The small-sized Cu x S y nanoparticles have the advantage to absorb efficiently in the near-infrared region (NIR) above 700 nm and the absorption can be tuned by altering their stoichiometries. Moreover, their easy removal through the kidneys overpowers the issue of toxicity caused by many inorganic substances. The low cost and selectivity further add to the advantages of Cu x S y nanostructures as electrode materials in comparison to relatively expensive materials such as silver and gold nanoparticles. This review is mainly focused on the synthesis and biomedical applications of Cu x S y nanostructures. The first part summarizes the various synthetic routes used to produce Cu x S y nanostructures with varying morphologies, while the second part targets the recent progress made in the application of small-sized Cu x S y nanostructures as biosensors, and their analysis and uses in the cure of cancer. Photoacoustic imaging and other cancer treatment applications are discussed. Research on Cu x S y nanostructures will continue to increase over the next few decades, and great opportunities lie ahead for potential biomedical applications of Cu x S y nanostructures.

Phase-shift nanodroplets as an emerging sonoresponsive nanomaterial for imaging and drug delivery applications

Nanodroplets - emerging phase-changing sonoresponsive materials - have attracted substantial attention in biomedical applications for both tumour imaging and therapeutic purposes due to their unique response to ultrasound. As ultrasound is applied at different frequencies and powers, nanodroplets have been shown to cavitate by the process of acoustic droplet vapourisation (ADV), causing the development of mechanical forces which promote sonoporation through cellular membranes. This allows drugs to be delivered efficiently into deeper tissues where tumours are located. Recent reviews on nanodroplets are mostly focused on the mechanism of cavitation and their applications in biomedical fields. However, the chemistry of the nanodroplet components has not been discussed or reviewed yet. In this review, the commonly used materials and preparation methods of nanodroplets are summarised. More importantly, this review provides examples of variable chemistry components in nanodroplets which link them to their efficiency as ultrasound-multimodal imaging agents to image and monitor drug delivery. Finally, the drawbacks of current research, future development, and future direction of nanodroplets are discussed.

Copper-induced tumor cell death mechanisms and antitumor theragnostic applications of copper complexes

Recent studies found that unbalanced copper homeostasis affect tumor growth, causing irreversible damage. Copper can induce multiple forms of cell death, including apoptosis and autophagy, through various mechanisms, including reactive oxygen species accumulation, proteasome inhibition, and antiangiogenesis. Hence, copper in vivo has attracted tremendous attention and is in the research spotlight in the field of tumor treatment. This review first highlights three typical forms of copper's antitumor mechanisms. Then, the development of diverse biomaterials and nanotechnology allowing copper to be fabricated into diverse structures to realize its theragnostic action is discussed. Novel copper complexes and their clinical applications are subsequently described.

Biological Utility of Fluorinated Compounds: from Materials Design to Molecular Imaging, Therapeutics and Environmental Remediation

The applications of fluorinated molecules in bioengineering and nanotechnology are expanding rapidly with the controlled introduction of fluorine being broadly studied due to the unique properties of C-F bonds. This review will focus on the design and utility of C-F containing materials in imaging, therapeutics, and environmental applications with a central theme being the importance of controlling fluorine-fluorine interactions and understanding how such interactions impact biological behavior. Low natural abundance of fluorine is shown to provide sensitivity and background advantages for imaging and detection of a variety of diseases with ¹⁹F magnetic resonance imaging, ¹⁸F positron emission tomography and ultrasound discussed as illustrative examples. The presence of C-F bonds can also be used to tailor membrane permeability and pharmacokinetic properties of drugs and delivery agents for enhanced cell uptake and therapeutics. A key message of this review is that while the promise of C-F containing materials is significant, a subset of highly fluorinated compounds such as per- and polyfluoroalkyl substances (PFAS), have been identified as posing a potential risk to human health. The unique properties of the C-F bond and the significant potential for fluorine-fluorine interactions in PFAS structures necessitate the development of new strategies for facile and efficient environmental removal and remediation. Recent progress in the development of fluorine-containing compounds as molecular imaging and therapeutic agents will be reviewed and their design features contrasted with environmental and health risks for PFAS systems. Finally, present challenges and future directions in the exploitation of the biological aspects of fluorinated systems will be described.

Effects of shell-integrated Sudan Black dye on the acoustic activity and ultrasound imaging properties of lipid-shelled nanoscale ultrasound contrast agents

SIGNIFICANCE

An effective contrast agent for concurrent multimodal photoacoustic (PA) and ultrasound (US) imaging must have both high optical absorption and high echogenicity. Integrating a highly absorbing dye into the lipid shell of gas core nanobubbles (NBs) adds PA contrast to existing US contrast agents but may impact agent ultrasonic response.

AIM

We report on the development and ultrasonic characterization of lipid-shell stabilized C3F8 NBs with integrated Sudan Black (SB) B dye in the shell as dual-modal PA-US contrast agents.

APPROACH

Perfluoropropane NBs stabilized with a lipid shell including increasing concentrations of SB B dye were formulated by amalgamation (SBNBs). Physical properties of SBNBs were characterized using resonant mass measurement, transmission electron microscopy and pendant drop tensiometry. Concentrated bubble solutions were imaged for 8 min to assess signal decay. Diluted bubble solutions were stimulated by a focused transducer to determine the response of individual NBs to long cycle (30 cycle) US. For assessment of simultaneous multimodal contrast, bulk populations of SBNBs were imaged using a PA and US imaging platform.

RESULTS

We produced high agent yield (∼1011) with a mean diameter of ∼200 to 300 nm depending on SB loading. A 40% decrease in bubble yield was measured for solutions with 0.3 and 0.4  mg  /  ml SB. The addition of SB to the shell did not substantially affect NB size despite an increase in surface tension by up to 8  mN  /  m. The bubble decay rate increased after prolonged exposure (8 min) by dyed bubbles in comparison to their undyed counterparts (2.5-fold). SB in bubble shells increased gas exchange across the shell for long cycle US. PA imaging of these agents showed an increase in power (up to 10 dB) with increasing dye.

CONCLUSIONS

We added PA contrast function to NBs. The addition of SB increased gas exchange across the NB shell. This has important implications in their use as multimodal agents.

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.

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.

Broad Chiroptical Activity from Ultraviolet to Short-Wave Infrared by Chirality Transfer from Molecular to Micrometer Scale

Chiral nanomaterials provide a rich platform for versatile applications. Tuning the wavelength of polarization rotation maxima in the broad range including short-wave infrared (SWIR) is a promising candidate for infrared neural stimulation, imaging, and nanothermometry. However, the majority of previously developed chiral nanomaterials reveal the optical activity in a relatively shorter wavelength range (ultraviolet-visible, UV-vis), not in SWIR. Here, we demonstrate a versatile method to synthesize chiral copper sulfides using cysteine, as the stabilizer, and transferring the chirality from molecular- to the microscale through self-assembly. The assembled structures show broad chiroptical activity in the UV-vis-NIR-SWIR region (200-2500 nm). Importantly, we can tune the chiroptical activity by simply changing the reaction conditions. This approach can be extended to materials platforms for developing next-generation optical devices, metamaterials, telecommunications, and asymmetric catalysts.

Multimodal Contrast Agents for Optoacoustic Brain Imaging in Small Animals

Optoacoustic (photoacoustic) imaging has demonstrated versatile applications in biomedical research, visualizing the disease pathophysiology and monitoring the treatment effect in an animal model, as well as toward applications in the clinical setting. Given the complex disease mechanism, multimodal imaging provides important etiological insights with different molecular, structural, and functional readouts in vivo. Various multimodal optoacoustic molecular imaging approaches have been applied in preclinical brain imaging studies, including optoacoustic/fluorescence imaging, optoacoustic imaging/magnetic resonance imaging (MRI), optoacoustic imaging/MRI/Raman, optoacoustic imaging/positron emission tomography, and optoacoustic/computed tomography. There is a rapid development in molecular imaging contrast agents employing a multimodal imaging strategy for pathological targets involved in brain diseases. Many chemical dyes for optoacoustic imaging have fluorescence properties and have been applied in hybrid optoacoustic/fluorescence imaging. Nanoparticles are widely used as hybrid contrast agents for their capability to incorporate different imaging components, tunable spectrum, and photostability. In this review, we summarize contrast agents including chemical dyes and nanoparticles applied in multimodal optoacoustic brain imaging integrated with other modalities in small animals, and provide outlook for further research.

Ultrasound and Photoacoustic Imaging of Laser-Activated Phase-Change Perfluorocarbon Nanodroplets

Laser-activated perfluorocarbon nanodroplets (PFCnDs) are emerging phase-change contrast agents that showed promising potential in ultrasound and photoacoustic (US/PA) imaging. Unlike monophase gaseous microbubbles, PFCnDs shift their state from liquid to gas via optical activation and can provide high US/PA contrast on demand. Depending on the choice of perfluorocarbon core, the vaporization and condensation dynamics of the PFCnDs are controllable. Therefore, these configurable properties of activation and deactivation of PFCnDs are employed to enable various imaging approaches, including contrast-enhanced imaging and super-resolution imaging. In addition, synchronous application of both acoustic and optical pulses showed a promising outcome vaporizing PFCnDs with lower activation thresholds. Furthermore, due to their sub-micrometer size, PFCnDs can be used for molecular imaging of extravascular tissue. PFCnDs can also be an effective therapeutic tool. As PFCnDs can carry therapeutic drugs or other particles, they can be used for drug delivery, as well as photothermal and photodynamic therapies. Blood barrier opening for neurological applications was recently demonstrated with optically-triggered PFCnDs. This paper specifically focuses on the activation and deactivation properties of laser-activated PFCnDs and associated US/PA imaging approaches, and briefly discusses their theranostic potential and future directions.

Cascade targeting tumor mitochondria with CuS nanoparticles for enhanced photothermal therapy in the second near-infrared window

Photothermal therapy, assisted by local heat generation using photothermal nanoparticles (NPs), is an emerging strategy to treat tumors noninvasively. To improve treatment outcomes and to alleviate potential side effects on normal tissue cells, utilizing the optically transparent second near-infrared (NIR-II) window and actively targeting tumors are critical. Considering that mitochondria are heat sensitive and play an important role in the up-regulation of metabolic activity in tumor cells, herein we report a cascade targeting scheme that enables active photothermal ablation of tumor mitochondria. First, NIR-II absorbing CuS NPs were surface modified with the mitochondria targeting moiety (3-carboxypropyl) triphenylphosphonium bromide (TPP) and then shielded with CD44 targeting hyaluronic acid, which will only expose TPP upon reaching the tumor sites. This allowed over 90% CuS NP enrichment at tumor mitochondria, and as a result, significantly improved tumor cell photothermal ablation was observed at the cellular level. An in vivo study demonstrated enhanced tumor uptake and improved tumor growth suppression by using these cascade targeting CuS NPs as NIR-II photothermal agents.

Recent Progresses in Organic-Inorganic Nano Technological Platforms for Cancer Therapeutics

Nanotechnology offers promising tools in interdisciplinary research areas and getting an upsurge of interest in cancer therapeutics. Organic nanomaterials and inorganic nanomaterials bring revolutionary advancement in cancer eradication process. Oncology is achieving new heights under nano technological platform by expediting chemotherapy, radiotherapy, photo thermodynamic therapy, bio imaging and gene therapy. Various nanovectors have been developed for targeted therapy which acts as "Nano-bullets" for tumor cells selectively. Recently combinational therapies are catching more attention due to their enhanced effect leading towards the use of combined organicinorganic nano platforms. The current review covers organic, inorganic and their hybrid nanomaterials for various therapeutic action. The technological aspect of this review emphasizes on the use of inorganic-organic hybrids and combinational therapies for better results and also explores the future opportunities in this field.

Near-Infrared Responsive Phase-Shifted Nanoparticles for Magnetically Targeted MR/US Imaging and Photothermal Therapy of Cancer

Accurate diagnosis, providing guidance for early treatment, can greatly improve the survival rate of cancer patients. However, there are still some difficulties with the existing diagnostic technology and early treatment methods. Here, near-infrared responsive phase-shifted nanoparticles (NRPNs) have been designed for magnetically targeted MR/US imaging and photothermal therapy of tumors. In this study, we fabricated a multifunctional polymer nanoparticle encapsulating indocyanine green (ICG), magnetic Fe₃O₄ nanoparticles and perfluoropentane (PFP). Under laser irradiation, the NRPNs, which trigger a phase-shifted expansion effect due to the quick conversion from light to heat by ICG and Fe₃O₄, can be used for ultrasound (US) imaging. At the same time, such nanoparticles can kill cancer cells via photothermal therapy (PTT). As a kind of negative enhancement agent, magnetic Fe₃O₄ nanoparticles in NRPNs showed high spatial resolution in MR imaging. Moreover, with the help of the magnetic field, the NRPNs nanoparticles showed high cellular uptake and high tumor accumulation, indicating their magnetic targeting property without biosafety concerns. Therefore, we present a strategy for magnetically targeted MR/US imaging guided photothermal therapy for the accurate diagnosis and efficient treatment of tumors.

The Coppery Age: Copper (Cu)-Involved Nanotheranostics

As an essential trace element in the human body, transitional metal copper (Cu) ions are the bioactive components within the body featuring dedicated biological effects such as promoting angiogenesis and influencing lipid/glucose metabolism. The recent substantial advances of nanotechnology and nanomedicine promote the emerging of distinctive Cu-involved biomaterial nanoplatforms with intriguing theranostic performances in biomedicine, which are originated from the biological effects of Cu species and the physiochemical attributes of Cu-composed nanoparticles. Based on the very-recent significant progresses of Cu-involved nanotheranostics, this work highlights and discusses the principles, progresses, and prospects on the elaborate design and rational construction of Cu-composed functional nanoplatforms for a diverse array of biomedical applications, including photonic nanomedicine, catalytic nanotherapeutics, antibacteria, accelerated tissue regeneration, and bioimaging. The engineering of Cu-based nanocomposites for synergistic nanotherapeutics is also exemplified, followed by revealing their intrinsic biological effects and biosafety for revolutionizing their clinical translation. Finally, the underlying critical concerns, unresolved hurdles, and future prospects on their clinical uses are analyzed and an outlook is provided. By entering the "Copper Age," these Cu-involved nanotherapeutic modalities are expected to find more broad biomedical applications in preclinical and clinical phases, despite the current research and developments still being in infancy.

A stimulated liquid-gas phase transition nanoprobe dedicated to enhance the microwave thermoacoustic imaging contrast of breast tumors

Microwave-induced thermoacoustic imaging (MTAI), combining the advantages of the high contrast of microwave imaging and the high resolution of ultrasonic imaging, is a potential candidate for breast tumor detection. MTAI probes have been used to extend thermoacoustic imaging to molecular imaging. However, due to the high content of water molecules in tissues, the thermoelastic expansion-based probes used in conventional MTAI are not capable of adequate enhancement. Herein, an MTAI nanoprobe for amplification of thermoacoustic (TA) signals by the stimulated liquid-gas phase transition mechanism has been developed, providing significantly higher signal amplitude than that from the conventional mechanism of thermoelastic expansion. The nanoprobe consists of liquid perfluorohexane (PFH) and tungsten disulfide (WS2) nanoparticles rich in defect electric dipoles. When irradiated with pulsed microwaves, the defect electric dipoles in WS2 were repeatedly polarized by gigahertz. This results in localized transient heating and an acoustic shockwave, which destroys the van der Waals forces between PFH molecules. Ultimately, liquid PFH droplets undergo a liquid-gas phase transition, generating dramatically enhanced TA signals. The practical feasibility was tested in vitro and in a breast tumor animal model. The results show that the proposed nanoprobe can greatly improve the contrast of tumor imaging. It will be a new generation probe for MTAI.

Nanosized Phase-Changeable "Sonocyte" for Promoting Ultrasound Assessment

Despite the ability of microbubble contrast agents to improve ultrasound diagnostic performance, their application potential is limited due to low stability, fast clearance, and poor tissue permeation. This study presents a promising nanosized phase-changeable erythrocyte (Sonocyte), composed of liposomal dodecafluoropentane coated with multilayered red blood cell membranes (RBCm), for improving ultrasound assessments. Sonocyte is the first RBCm-functionalized ultrasound contrast agent with uniform nanosized morphology, and exhibits good stability, systemic circulation, target-tissue accumulation, and even ultrasound-responsive phase transition, thereby satisfying the inherent requirement of ultrasound imaging. It is identified that Sonocyte displays similar sensitivity as microbubble SonoVue, a clinical ultrasound contrast agent, for effectively detecting normal parenchyma and hepatic necrosis. Importantly, compared with SonoVue lacking of ability to detect tumors, Sonocyte can identify tumors with high sensitivity and specificity due to superior tumor accumulation and penetration. Therefore, Sonocyte exhibits superior capabilities over SonoVue, endowing with a great clinical application potential.

A HMCuS@MnO2 nanocomplex responsive to multiple tumor environmental clues for photoacoustic/fluorescence/magnetic resonance trimodal imaging-guided and enhanced photothermal/photodynamic therapy

Hollow mesoporous copper sulfide nanoparticles (HMCuS NPs) are advantageous for loading small-molecule therapeutic drugs coupled with photothermal ablation for synergistic tumor therapy. However, treatment efficacy mediated by HMCuS NPs is not always satisfactory owing to their insensitivity toward the tumor microenvironment (TME), and unpredictable drug leakage may also result in deleterious systemic toxicity. Here, a novel HMCuS@MnO₂-based core-shell nanoplatform was developed as a highly efficient TME modulator, which could alleviate tumor hypoxia, deplete the level of intracellular glutathione (GSH) and trigger the dissolution of Mn²⁺. Moreover, MnO₂, in situ grown on the surface of HMCuS, may act as a gatekeeper by forming a stimulus-responsive plug within the mesoporous structure, which effectively prevented the premature release of encapsulated photosensitizer chlorin e6 (Ce6) and was responsive to the acidic TME for demand-based drug release. Under the condition of 660/808 nm dual-wavelength laser irradiation, hyperthermia-mediated photothermal therapy (PTT) and reactive oxygen species (ROS)-mediated photodynamic therapy (PDT) can be triggered for tumor eradication, which were further enhanced upon the modification of the TME. In the meantime, splendid photoacoustic (PA)/fluorescence (FL)/magnetic resonance (MR) imaging properties of HMCuS@MnO₂/Ce6 (CMC) NPs could enable the realization of more precise, reliable and on-demand combination therapy. In a word, this study illustrated a promising approach to strengthen the efficacy of HMCuS-based nanotherapeutics, which would definitely promote the further exploitation of smarter nanoplatforms for synergistic disease management.

From Light to Sound: Photoacoustic and Ultrasound Imaging in Fundamental Research of Alzheimer's Disease

Alzheimer's disease (AD) causes severe cognitive dysfunction and has long been studied for the underlining physiological and pathological mechanisms. Several biomedical imaging modalities have been applied, including MRI, PET, and high-resolution optical microscopy, for research purposes. However, there is still a strong need for imaging tools that can provide high spatiotemporal resolutions with relatively deep penetration to enhance our understanding of AD pathology and monitor treatment progress in fundamental research. Photoacoustic (PA) imaging and ultrasound (US) imaging can potentially address these unmet needs in AD research. PA imaging provides functional information with endogenous and/or exogenous contrast, while US imaging provides structural information. Recent studies have demonstrated the ability to monitor physiological parameters in small-animal brains with PA and US imaging as well as the feasibility of using US imaging as a therapeutic tool for AD. This concise review aims to introduce recent advances in AD research using PA and US imaging, provide the fundamentals, and discuss the potentials and challenges for future advances.

Carbon Nitride Hollow Theranostic Nanoregulators Executing Laser-Activatable Water Splitting for Enhanced Ultrasound/Fluorescence Imaging and Cooperative Phototherapy

The limited efficacy of "smart" nanotheranostic agents in eradicating tumors calls for the development of highly desirable nanoagents with diagnostics and therapeutics. Herein, to surmount these challenges, we constructed an intelligent nanoregulator by coating a mesoporous carbon nitride (C₃N₄) layer on a core-shell nitrogen-doped graphene quantum dot (N-GQD)@hollow mesoporous silica nanosphere (HMSN) and decorated it with a P-PEG-RGD polymer, to achieve active-targeting delivery (designated as R-NCNP). Upon irradiation, the resultant R-NCNP nanoregulators exhibit significant catalytic breakdown of water molecules, causing a sustainable elevation of oxygen level owing to the C₃N₄ shell, which facilitates tumor oxygenation and relieves tumor hypoxia. The generated oxygen bubbles serve as an echogenic source, triggering tissue impedance mismatch, thereby enhancing the generation of an echogenicity signal, making them laser-activatable ultrasound imaging agents. In addition, the encapsulated photosensitizers and C₃N₄-layered photosensitizer are simultaneously activated to maximize the yield of ROS, actualizing a triple-photosensitizer hybrid nanosystem exploited for enhanced PDT. Intriguingly, the N-GQDs endow the R-NCNP nanoregulator with a photothermal effect for hyperthemia, making it exhibit considerable photothermal outcomes and infrared thermal imaging (IRT). Importantly, further analysis reveals that the polymer-modified R-NCNPs actively target specific tumor tissues and display a triple-modal US/IRT/FL imaging-assisted cooperative PTT/PDT for real-time monitoring of tumor ablation and therapeutic evaluation. The rational synergy of triple-model PDT and efficient PTT in the designed nanoregulator confers excellent anticancer effects, as evidenced by in vitro and in vivo assays, which might explore more possibilities in personalized cancer treatment.

Black Mesoporous Silicon as a Contrast Agent for LED-Based 3D Photoacoustic Tomography

Mesoporous silicon (PSi) nanoparticles have been widely studied in different biomedical imaging modalities due to their several beneficial material properties. However, they have not been found to be suitable for photoacoustic imaging due to their poor photothermal conversion performance. In the present study, biodegradable black mesoporous silicon (BPSi) nanoparticles with strong light absorbance were developed as superior image contrast agents for photoacoustic tomography (PAT), which was realized with a light-emitting diode (LED) instead of the commonly used laser. LED-based PAT offers the advantages of low cost, compactness, good mobility, and easy operation as compared to the traditional laser-based PAT modality. Nevertheless, the poor imaging sensitivity of the LED-PAT systems has been the main barrier to prevent their wide biomedical application because the LED light has low optical energy. The present study demonstrated that the imaging sensitivity of the LED-PAT system was significantly enhanced with the PEGylated BPSi (PEG-BPSi) nanoparticles. The PEG-BPSi nanoparticles were clearly detectable with a low concentration of 0.05 mg/mL in vitro and with an LED radiation energy of 5.2 μJ. The required concentration of the PEG-BPSi nanoparticles was 10 times lesser than that of the reference gold nanoparticles to reach the corresponding level of the imaging contrast. The ex vivo studies demonstrated that the submillimeter BPSi nanoparticle-based absorbers were distinguishable in chicken breast tissues. The strong contrast provided by the BPSi particles indicated that these particles can be utilized as novel contrast agents in PAT, especially in LED-based systems with low light intensity.

Ultra-Early Diagnosis of Acute Myocardial Infarction in Rats Using Ultrasound Imaging of Hollow Double-Layer Silica Nanospheres

Timely diagnosis of acute myocardial infarction (AMI) strongly impacts the survival rate of patients. The authors report the development of a two-shell hollow silica contrast agent useful for ultrasound (US) imaging, which is able to provide ultra-early diagnosis of AMI. To target the characterization of fast blood flow and high blood pressure in the heart, two shells of hollow silica are adopted with opposite polarities, which assemble based on amino and perfluorodecyl silanes. The external amino silane facilitates the attachment of disease-targeted groups, while the internal perfluorodecyl silane provides great US imaging contrast. The material also possesses superior water dispersity, controllable morphology, low toxicity, and biodegradability both in vitro and in vivo, thus promoting its applications in the ultra-early diagnosis of AMI in rats, and is particularly useful for delineation of myocardial necrosis sites.

Ultrasound-Responsive Conversion of Microbubbles to Nanoparticles to Enable Background-Free in Vivo Photoacoustic Imaging

Photoacoustic (PA) imaging based on the photon-to-ultrasound conversion allows the imaging of optical absorbers in deep tissues with high spatial resolution. However, the inherent optical absorbance of biomolecules (e.g., hemoglobin, melanin, etc.) would show up as tissue background signals to interfere with signals from the contrast agent during in vivo PA imaging, limiting the imaging sensitivity. Herein, an ultrasound (US)-responsive PA imaging probe based on microbubbles (MBs) containing gold nanoparticles (Au NPs) is designed for in vivo "background-free" PA imaging. The obtained Au@lip MBs with separated Au NPs decorated within the lipid shell of MBs show low PA signals under near-infrared (NIR) excitation. Interestingly, under exposure to US pulses, those Au@lip MBs would burst to form nanoscale aggregates of Au@lip NPs, which exhibit significantly enhanced NIR PA signals due to their red-shifted surface plasmon resonance. Therefore, by subtracting the PA image captured pre-US burst from that captured post-US burst, the tissue background PA signals could be deducted to enable background-free PA imaging with high sensitivities as demonstrated by multiple ex vivo and in vivo experiments. This work presents a simple yet effective strategy to deduct background signals during PA imaging, which is promising for accurate PA detection of targets in tissues with a strong background.

Gas-Mediated Cancer Bioimaging and Therapy

Gas-involving cancer theranostics have attracted considerable attention in recent years due to their high therapeutic efficacy and biosafety. We have reviewed the recent significant advances in the development of stimuli-responsive gas releasing molecules (GRMs) and gas nanogenerators for cancer bioimaging, targeted and controlled gas therapy, and gas-sensitized synergistic therapy. We have focused on gases with known anticancer effects, such as oxygen (O₂), carbon monoxide (CO), nitric oxide (NO), hydrogen sulfide (H₂S), hydrogen (H₂), sulfur dioxide (SO₂), carbon dioxide (CO₂), and heavy gases that act via the gas-generating process. The GRMs and gas nanogenerators for each gas have been described in terms of the stimulation method, followed by their applications in ultrasound and multimodal imaging, and finally their primary and synergistic actions with other cancer therapeutic modalities. The current challenges and future possibilities of gas therapy and imaging vis-à-vis clinical translation have also been discussed.

A Dual-Model Imaging Theragnostic System Based on Mesoporous Silica Nanoparticles for Enhanced Cancer Phototherapy

Mesoporous silica nanoparticles (MSNs) show great promise to be exploited as versatile multifunctional nanocarriers for effective cancer diagnosis and treatment. In this work, perfluorohexane (PFH)-encapsulated MSNs with indocyanine green (ICG)-polydopamine (PDA) layer and poly(ethylene glycol)-folic acid coating (designated as MSNs-PFH@PDA-ICG-PEG-FA) are successfully fabricated to achieve tumor ultrasonic (US)/near-infrared fluorescence (NIRF) imaging as well as photothermal therapy (PTT)/photodynamic therapy (PDT). MSNs-PFH@PDA-ICG-PEG-FA exhibits good monodispersity with high ICG loading, significantly enhances ICG photostability, and greatly improves cellular uptake. Upon single 808 nm NIR irradiation, the nanocarrier not only efficiently generates hyperthermia to realize PTT, but also produces reactive oxygen species (ROS) for effective PDT. Meanwhile, NIR irradiation can trigger PFH to undergo vaporization and provide a super-resolution US image. Thus, the PTT/PDT combination therapy can be dually guided by PFH-induced US imaging and ICG-induced NIRF imaging. In vivo antitumor studies demonstrate that PTT/PDT from MSNs-PFH@PDA-ICG-PEG-FA significantly inhibits tumor growth and achieves a cure rate of 60% (three out of five mice are completely cured). Hence, the multifunctional MSNs appear to be a promising theragnostic nanoplatform for multimodal cancer imaging and therapy.

Tuning the ultrasonic and photoacoustic response of polydopamine-stabilized perfluorocarbon contrast agents

Contrast-enhanced ultrasound (CEUS) offers the exciting prospect of retaining the ease of ultrasound imaging while enhancing imaging clarity, diagnostic specificity, and theranostic capability. To advance the capabilities of CEUS, the synthesis and understanding of new ultrasound contrast agents (UCAs) is a necessity. Many UCAs are nano- or micro-scale materials composed of a perfluorocarbon (PFC) and stabilizer that synergistically induce an ultrasound response that is both information-rich and easily differentiated from natural tissue. In this work, we probe the extent to which CEUS is modulated through variation in a PFC stabilized with fluorine-modified polydopamine nanoparticles (PDA NPs). The high level of synthetic tunability in this system allows us to study signal as a function of particle aggregation and PFC volatility in a systematic manner. Separation of aggregated and non-aggregated nanoparticles lead to a fundamentally different signal response, and for this system, PFC volatility has little effect on CEUS intensity despite a range of over 50 °C in boiling point. To further explore the imaging tunability and multimodality, Fe3+-chelation was employed to generate an enhanced photoacoustic (PA) signal in addition to the US signal. In vitro and in vivo results demonstrate that PFC-loaded PDA NPs show stronger PA signal than the non-PFC ones, indicating that the PA signal can be used for in situ differentiation between PFC-loading levels. In sum, these data evince the rich role synthetic chemistry can play in guiding new directions of development for UCAs.

Toward optimization of blood brain barrier opening induced by laser-activated perfluorocarbon nanodroplets

The blood brain barrier (BBB), a component of the brain's natural defense system, is often a roadblock for the monitoring and treatment of neurological disorders. Recently, we introduced a technique to open the blood brain barrier through the use of laser-activated perfluorohexane nanodroplets (PFHnDs), a phase-change nanoagent that undergoes repeated vaporization and recondensation when excited by a pulsed laser. Laser-activated PFHnDs were shown to enable noninvasive and localized opening of the BBB, allowing extravasation of various sized agents into the brain tissue. In this current work, the laser-activated PFHnD-induced BBB opening is further explored. In particular, laser fluence and the number of laser pulses used for the PFHnD-induced BBB opening are examined and evaluated both qualitatively and quantitatively to determine the effect of these parameters on BBB opening. The results of these studies show trends between increased laser fluence and an increased BBB opening as well as between an increased number of laser pulses and an increased BBB opening, however, with limitations on the extent of the BBB opening after a certain number of pulses. Overall, the results of these studies serve as a guideline to choosing suitable laser parameters for safe and effective BBB opening.

Lipid Shell Composition Plays a Critical Role in the Stable Size Reduction of Perfluorocarbon Nanodroplets

Perfluorocarbon nanodroplets (PFCnDs) are phase-change contrast agents that have the potential to enable extravascular contrast-enhanced ultrasound and photoacoustic (US/PA) imaging. Producing consistently small, monodisperse PFCnDs remains a challenge without resorting to technically challenging methods. We investigated the impact of variable shell composition on PFCnD size and US/PA image properties. Our results suggest that increasing the molar percentage of PEGylated lipid reduces the size and size variance of PFCnDs. Furthermore, our imaging studies revealed that nanodroplets with more PEGylated lipids produce increased US/PA signal compared with those with the standard formulation. Finally, we highlight the ability of this approach to facilitate US/PA imaging in a murine model of breast cancer. These data indicate that, through a facile synthesis process, it is possible to produce monodisperse, small-sized PFCnDs. Novel in their simplicity, these methods may promote the use of PFCnDs among a broader user base to study a variety of extravascular phenomena.

Color-coded perfluorocarbon nanodroplets for multiplexed ultrasound and Photoacoustic imaging

Laser-activated perfluorocarbon nanodroplets are an emerging class of phase change, dual-contrast agents that can be utilized in ultrasound and photoacoustic imaging. Through the ability to differentiate subpopulations of nanodroplets via laser activation at different wavelengths of near-infrared light, optically-triggered color-coded perfluorocarbon nanodroplets present themselves as an attractive tool for multiplexed ultrasound and photoacoustic imaging. In particular, laser-activated droplets can be used to provide quantitative spatiotemporal information regarding distinct biological targets, allowing for their potential use in a wide range of diagnos tic and therapeutic applications. In the work presented, laser-activated color-coded perfluorocarbon nanodroplets are synthesized to selectively respond to laser irradiation at corresponding wavelengths. The dynamic ultrasound and photoacoustic signals produced by laser-activated perfluorocarbon nanodroplets are evaluated in situ prior to implementation in a murine model. In vivo, these particles are used to distinguish unique particle trafficking mechanisms and are shown to provide ultrasound and photoacoustic contrast for up to 72 hours within lymphatics. Overall, the conducted studies show that laser-activated color-coded perfluorocarbon nanodroplets are a promising agent for multiplexed ultrasound and photoacoustic imaging.

Copper sulfide: An emerging adaptable nanoplatform in cancer theranostics

Copper sulfide nanoparticles (CuS NPs), emerging nanoplatforms with dual diagnostic and therapeutic applications, are being actively investigated in this era of "war on cancer" owing to their versatility and adaptability. This article discusses the pros and cons of using CuS NPs in diagnostics, therapeutics, and theranostics. The first section introduces CuS NPs and discusses the features that render them more advantageous than other established nanoplatforms in cancer management. Subsequent sections include specific in vitro and in vivo results of different studies showing the potential of CuS NPs as nanoplatforms. Methods used for visualization (photoacoustic imaging and magnetic resonance imaging) of CuS NPs and treatment (phototherapy and combinatorial therapy) have also been discussed. Furthermore, the challenges and opportunities associated with using CuS NPs have been elucidated. Further investigations on CuS NPs are required to translate it for clinical applications.

Metabolizable Semiconducting Polymer Nanoparticles for Second Near-Infrared Photoacoustic Imaging

Photoacoustic (PA) imaging in the second near-infrared (NIR-II) window (1000-1700 nm) holds great promise for deep-tissue diagnosis due to the reduced light scattering and minimized tissue absorption; however, exploration of such a noninvasive imaging technique is greatly constrained by the lack of biodegradable NIR-II absorbing agents. Herein, the first series of metabolizable NIR-II PA agents are reported based on semiconducting polymer nanoparticles (SPNs). Such completely organic nanoagents consist of π-conjugated yet oxidizable optical polymer as PA generator and hydrolyzable amphiphilic polymer as particle matrix to provide water solubility. The obtained SPNs are readily degraded by myeloperoxidase and lipase abundant in phagocytes, transforming from nonfluorescent nanoparticles (30 nm) into NIR fluorescent ultrasmall metabolites (≈1 nm). As such, these nanoagents can be effectively cleared out via both hepatobiliary and renal excretions after systematic administration, leaving no toxicity to living mice. Particularly these nanoagents possess high photothermal conversion efficiencies and emit bright PA signals at 1064 nm, enabling sensitive NIR-II PA imaging of both subcutaneous tumor and deep brain vasculature through intact skull in living animals at a low systematic dosage. This study thus provides a generalized molecular design toward organic metabolizable semiconducting materials for biophotonic applications in NIR-II window.

Development of Acoustically Active Nanocones Using the Host-Guest Interaction as a New Histotripsy Agent

Histotripsy is a noninvasive and nonthermal ultrasound ablation technique, which mechanically ablates the tissues using very short, focused, high-pressured ultrasound pulses to generate dense cavitating bubble cloud. Histotripsy requires large negative pressures (≥28 MPa) to generate cavitation in the target tissue, guided by real-time ultrasound imaging guidance. The high cavitation threshold and reliance on real-time image guidance are potential limitations of histotripsy, particularly for the treatment of multifocal or metastatic cancers. To address these potential limitations, we have recently developed nanoparticle-mediated histotripsy (NMH) where perfluorocarbon (PFC)-filled nanodroplets (NDs) with the size of ∼200 nm were used as cavitation nuclei for histotripsy, as they are able to significantly lower the cavitation threshold. However, although NDs were shown to be an effective histotripsy agent, they pose several issues. Their generation requires multistep synthesis, they lack long-term stability, and determination of PFC concentration in the treatment dose is not possible. In this study, PFC-filled nanocones (NCs) were developed as a new generation of histotripsy agents to address the mentioned limitations of NDs. The developed NCs represent an inclusion complex of methylated β-cyclodextrin as a water-soluble analog of β-cyclodextrin and perfluorohexane (PFH) as more effective PFC derivatives for histotripsy. Results showed that NCs are easy to produce, biocompatible, have a size <50 nm, and have a quantitative complexation that allows us to directly calculate the PFH amount in the used NC dose. Results further demonstrated that NCs embedded into tissue-mimicking phantoms generated histotripsy cavitation "bubble clouds" at a significantly lower transducer amplitude compared to control phantoms, demonstrating the ability of NCs to function as effective histotripsy agents for NMH.

Perfluoroheptane-Loaded Hollow Gold Nanoshells Reduce Nanobubble Threshold Flux

The threshold flux for nanobubble formation and liposome rupture is reduced by 50-60% by adding a liquid mixture of tetradecanol and perfluoroheptane to the interior cavity of 40 nm diameter hollow gold nanoshells (HGN), and allowing the tetradecanol to solidify to hold the perfluoroheptane in place. On absorption of picosecond pulses of near-infrared light, the perfluoroheptane vaporizes to initiate cavitation-like nanobubbles as the HGN temperature increases. The lower spinodal temperature and heat capacity of perfluoroheptane relative to water causes the threshold flux for nanobubble formation to decrease. The perfluoroheptane-containing HGN can be linked via thiol-PEG-lipid tethers to carboxyfluorescein-containing liposomes and shows a similar decreased flux necessary for liposome contents release.

Photoacoustic Imaging: Contrast Agents and Their Biomedical Applications

Photoacoustic (PA) imaging as a fast-developing imaging technique has great potential in biomedical and clinical applications. It is a noninvasive imaging modality that depends on the light-absorption coefficient of the imaged tissue and the injected PA-imaging contrast agents. Furthermore, PA imaging provides superb contrast, super spatial resolution, and high penetrability and sensitivity to tissue functional characteristics by detecting the acoustic wave to construct PA images. In recent years, a series of PA-imaging contrast agents are developed to improve the PA-imaging performance in biomedical applications. Here, recent progress of PA contrast agents and their biomedical applications are outlined. PA contrast agents are classified according to their components and function, and gold nanocrystals, gold-nanocrystal assembly, transition-metal chalcogenides/MXene-based nanomaterials, carbon-based nanomaterials, other inorganic imaging agents, small organic molecules, semiconducting polymer nanoparticles, and nonlinear PA-imaging contrast agents are discussed. The applications of PA contrast agents as biosensors (in the sensing of metal ions, pH, enzymes, temperature, hypoxia, reactive oxygen species, and reactive nitrogen species) and in bioimaging (lymph nodes, vasculature, tumors, and brain tissue) are discussed in detail. Finally, an outlook on the future research and investigation of PA-imaging contrast agents and their significance in biomedical research is presented.

The application of small organic π-conjugated discotic derivatives in photoacoustic imaging and photothermal conversion

Near-infrared absorbing dyes are catching people's attention as they are committed to find materials with greater photoacoustic (PA) and photothermal (PT) effect. In this study, a new series of organic π-conjugated discotic derivatives synthesized via [2 + 2] click chemistry were introduced. The PA intensity and PT conversion effect of the derivatives were monitored. It was found that the π-conjugated discotic derivatives had a proper absorption peak and PA intensity by introducing the click regents. Furthermore, the PA intensity remained relatively high, while B12 molecules were embedded in hydrophobic phospholipid bilayer of liposomes (B12⊂L). The application in biological therapy for tumors become possible as the toxicity of B12⊂L was low. What's more, when B12 molecules embedded in poly (N-isopropylacrylamide)-block-poly (2-nitrobenzyl methacrylate) (PNIPAM-b-PNBM) thermosensitive micelles were irradiated by laser, the molecules could take the place of direct temperature stimulus. This work affords us a way to solve the problem in which direct temperature stimulus is inapplicable.

Cerasome-based gold-nanoshell encapsulating L-menthol for ultrasound contrast imaging and photothermal therapy of cancer

Various nanoformulations of perfluorocarbon have been developed thus far, to achieve ultrasound imaging of tumors and tumor-targeted therapy. However, their application has been greatly limited by their short sonographic duration and large size distribution. A novel theranostic agent was constructed based on gold nanoshell cerasome-encapsulated L-menthol (GNC-LM). Owing to the sustained and controllable generation of L-menthol bubbles under near-infrared laser irradiation, GNC-LM showed good performance in contrast enhancement of ultrasound imaging in vivo. GNC-LM could be imaged for 30 min, which is much longer than the imaging time of SonoVue (commercially used microbubbles). Moreover, photothermal therapy (PTT) based on the light-to-heat conversion of the nanosystem effectively ablated the tumor. Our study demonstrated the promising potential of the obtained GNC-LM to serve as a therapeutic nanoprobe for ultrasound contrast imaging and PTT of tumors.