Listening for the therapeutic window: Advances in drug delivery utilizing photoacoustic imaging

Shedding light on ultrasound in action: Optical and optoacoustic monitoring of ultrasound brain interventions

Monitoring brain responses to ultrasonic interventions is becoming an important pillar of a growing number of applications employing acoustic waves to actuate and cure the brain. Optical interrogation of living tissues provides a unique means for retrieving functional and molecular information related to brain activity and disease-specific biomarkers. The hybrid optoacoustic imaging methods have further enabled deep-tissue imaging with optical contrast at high spatial and temporal resolution. The marriage between light and sound thus brings together the highly complementary advantages of both modalities toward high precision interrogation, stimulation, and therapy of the brain with strong impact in the fields of ultrasound neuromodulation, gene and drug delivery, or noninvasive treatments of neurological and neurodegenerative disorders. In this review, we elaborate on current advances in optical and optoacoustic monitoring of ultrasound interventions. We describe the main principles and mechanisms underlying each method before diving into the corresponding biomedical applications. We identify areas of improvement as well as promising approaches with clinical translation potential.

Advances in photoacoustic imaging aided by nano contrast agents: special focus on role of lymphatic system imaging for cancer theranostics

Photoacoustic imaging (PAI) is a successful clinical imaging platform for management of cancer and other health conditions that has seen significant progress in the past decade. However, clinical translation of PAI based methods are still under scrutiny as the imaging quality and clinical information derived from PA images are not on par with other imaging methods. Hence, to improve PAI, exogenous contrast agents, in the form of nanomaterials, are being used to achieve better image with less side effects, lower accumulation, and improved target specificity. Nanomedicine has become inevitable in cancer management, as it contributes at every stage from diagnosis to therapy, surgery, and even in the postoperative care and surveillance for recurrence. Nanocontrast agents for PAI have been developed and are being explored for early and improved cancer diagnosis. The systemic stability and target specificity of the nanomaterials to render its theranostic property depends on various influencing factors such as the administration route and physico-chemical responsiveness. The recent focus in PAI is on targeting the lymphatic system and nodes for cancer diagnosis, as they play a vital role in cancer progression and metastasis. This review aims to discuss the clinical advancements of PAI using nanoparticles as exogenous contrast agents for cancer theranostics with emphasis on PAI of lymphatic system for diagnosis, cancer progression, metastasis, PAI guided tumor resection, and finally PAI guided drug delivery.

EGFR Targeted Redox Sensitive Chitosan Nanoparticles of Cabazitaxel: Dual-Targeted Cancer Therapy, Lung Distribution, and Targeting Studies by Photoacoustic and Optical Imaging

In this research, we have modified tocopheryl polyethylene glycol succinate (TPGS) to a redox-sensitive material, denoted as TPGS-SH, and employed the same to develop dual-receptor-targeted nanoparticles of chitosan loaded with cabazitaxel (CZT). The physicochemical properties and morphological characteristics of all nanoparticle formulations were assessed. Dual-receptor targeting redox-sensitive nanoparticles of CZT (F-CTX-CZT-CS-SH-NPs) were developed by a combination of pre- and postconjugation techniques by incorporating synthesized chitosan-folate (F) and TPGS-SH during nanoparticle synthesis and further postconjugated with cetuximab (CTX) for epidermal growth factor receptor (EGFR) targeting. The in vitro release of the drug was seemingly higher in the redox-sensitive buffer media (GSH, 20 mM) compared to that in physiological buffer. However, the extent of cellular uptake of dual-targeted nanoparticles was significantly higher in A549 cells than other control nanoparticles. The IC50 values of F-CTX-CZT-CS-SH-NPs against A549 cells was 0.26 ± 0.12 μg/mL, indicating a 6.3-fold and 60-fold enhancement in cytotoxicity relative to that of dual-receptor targeted, nonredox sensitive nanoparticles and CZT clinical injection, respectively. Furthermore, F-CTX-CZT-CS-SH-NPs demonstrated improved anticancer activity in the benzo(a)pyrene lung cancer model with a higher survival rate. Due to the synergistic combination of enhanced permeability and retention (EPR) effect of small-sized nanoparticles, the innovative and redox sensitive TPGS-SH moiety and the dual folate and EGFR mediated augmented endocytosis have all together significantly enhanced their biodistribution and targeting exclusively to the lung which is evident from their ultrasound/photoacoustic and in vivo imaging system (IVIS) studies.

Photoacoustic based evaluation of viscoelastic properties of Gram-negative and Gram-positive bacterial colonies

Mechanical properties of bacterial colonies are crucial considering both addressing their pathogenic effects and exploring their potential applications. Viscoelasticity is a key mechanical property with major impacts on the cell shapes and functions, which reflects the information about the cell envelope constituents. Hereby, we have proposed the application of photoacoustic viscoelasticity (PAVE) for studying the rheological properties of bacterial colonies. In this regard, we employed an intensity-modulated laser beam as the excitation source followed by the phase delay measurement between the generated PA signal and the reference for the characterization of colonies of two different types of Gram-positive and Gram-negative bacteria. The results of our study show that the colony of Staphylococcus aureus as Gram-positive bacteria has a significantly higher viscoelasticity ratio compared to that value for Acinetobacter baumannii as Gram-negative bacteria (77% difference). This may be due to the differing cell envelope structure between the two species, but we cannot rule out effects of biofilm formation in the colonies. Furthermore, a lumped model has been provided for the mechanical properties of bacterial colonies.

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.

Supramolecular Loading of DNA Hydrogels with Dye-Drug Conjugates for Real-Time Photoacoustic Monitoring of Chemotherapy

A longstanding problem with conventional cancer therapy is the nonspecific distribution of chemotherapeutics. Monitoring drug release in vivo via noninvasive bioimaging can thus have value, but it is difficult to distinguish loaded from released drug in live tissue. Here, this work describes an injectable supramolecular hydrogel that allows slow and trackable release of doxorubicin (Dox) via photoacoustic (PA) tomography. Dox is covalently linked with photoacoustic methylene blue (MB) to monitor Dox before, during, and after release from the hydrogel carrier. The conjugate (MB-Dox) possesses an IC50 of 161.4 × 10-9  m against human ovarian carcinoma (SKOV3) cells and loads into a DNA-clad hydrogel with 91.3% loading efficiency due to MB-Dox's inherent intramolecular affinity to DNA. The hydrogel is biodegradable by nuclease digestion, which causes gradual release of MB-Dox. This release rate is tunable based on the wt% of the hydrogel. This hydrogel maintains distinct PA contrast on the order of days when injected in vivo and demonstrates activatable PA spectral shifts   during hydrogel degradation. The released and loaded payload can be imaged relative to live tissue via PA and ultrasound signal being overlaid in real-time. The hydrogel slowed the rate of the murine intraperitoneal tumor growth 72.2% more than free Dox.

The sound of drug delivery: Optoacoustic imaging in pharmacology

Optoacoustic (photoacoustic) imaging offers unique opportunities for visualizing biological function in vivo by achieving high-resolution images of optical contrast much deeper than any other optical technique. The method detects ultrasound waves that are generated inside tissue by thermo-elastic expansion, i.e., the conversion of light absorption by tissue structures to ultrasound when the tissue is illuminated by the light of varying intensity. Listening instead of looking to light offers the major advantage of image formation with a resolution that obeys ultrasonic diffraction and not photon diffusion laws. While the technique has been widely used to explore contrast from endogenous photo-absorbing molecules, such as hemoglobin or melanin, the use of exogenous agents can extend applications to a larger range of biological and possible clinical applications, such as image-guided surgery, disease monitoring, and the evaluation of drug delivery, biodistribution, and kinetics. This review summarizes recent developments in optoacoustic agents, and highlights new functions visualized and potent pharmacology applications enabled with the use of external contrast agents.

Low Intensity Focused Ultrasound Ignited “Deep-Penetration Nanobomb” (DPNB) for Tetramodal Imaging Guided Hypoxia-Tolerant Sonodynamic Therapy Against Hypoxic Tumors

Background

Sonodynamic therapy (SDT) has been regarded as a novel therapeutic modality for killing tumors. However, the hypoxic tumor microenvironment, especially deep-seated tumors distant from blood vessels, severely restricts therapeutic efficacy due to the oxygen-dependent manner of SDT.

Methods

Herein, we report a novel ultrasonic cavitation effect-based therapeutic modality that is able to facilitate the hypoxia-tolerant SDT for inducing hypoxic tumor death. A tLyP-1 functionalized liposomes is fabricated, composed of hematoporphyrin monomethyl ether gadolinium as the sonosentizer and perfluoropentane (PFP) as the acoustic environment regulator. Moreover, the tLyP-1 functioned liposomes could achieve active tumor homing and effective deep-penetrating into hypoxic tumors. Upon low intensity focused ultrasound (LIFU) irradiation, the acoustic droplet vaporization effect of PFP induced fast liquid-to-gas transition and quick bubbles explosion to generate hydroxyl radicals, efficiently promoting cell death in both normoxic and hypoxic microenvironment (acting as deep-penetration nanobomb, DPNB).

Results

The loading of PFP is proved to significantly enhance the therapeutic efficacy of hypoxic tumors. In particular, these DPNB can also act as ultrasound, photoacoustic, magnetic resonance, and near-infrared fluorescence tetramodal imaging agents for guiding the therapeutic process.

Conclusion

This study is the first report involving that liquid-to-gas transition based SDT has the potential to combat hypoxic tumors.

Unveiling the improved targeting migration of mesenchymal stem cells with CXC chemokine receptor 3-modification using intravital NIR-II photoacoustic imaging

Background

Therapy with genetically modified mesenchymal stem cells (MSCs) has clinical translation promise. Optimizing the targeting migratory ability of MSCs relies on accurate imaging of the distribution and extravasation kinetics of MSCs, and the corresponding imaging results could be used to predict therapeutic outcomes and guide the optimization of the treatment program. Among the different imaging modalities, second near-infrared (NIR-II) optical-resolution photoacoustic microscopy (OR-PAM) has merits, including a fine resolution, a deep penetration, a high sensitivity, and a large signal-to-background ratio. It would be an ideal candidate for precise monitoring of MSCs, although it has not been tested for this purpose so far.

Results

Penetrating peptide-decorated conjugated polymer nanoparticles (TAT-CPNPs) with strong NIR-II absorbance were used to label chemokine-receptor genetically modified MSCs, which were subsequently evaluated under intravital NIR-II OR-PAM regarding their targeting migratory ability. Based on the upregulation of chemokine (C-X-C motif) ligand 10 in the inflamed ears of contact hypersensitivity mice, MSCs with overexpression of corresponding receptor, chemokine (C-X-C motif) receptor 3 (Cxcr3) were successfully generated (MSC^Cxcr3). TAT-CPNPs labeling enabled NIR-II photoacoustic imaging to discern MSC^Cxcr3 covered by 1.2 cm of chicken breast tissue. Longitudinal OR-PAM imaging revealed enhanced inflammation-targeting migration of MSC^Cxcr3 over time attributed to Cxcr3 gene modification, which was further validated by histological analysis.

Conclusions

TAT-CPNPs-assisted NIR-II PA imaging is promising for monitoring distribution and extravasation kinetics of MSCs, which would greatly facilitate optimizing MSC-based therapy.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01513-7.

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.

Biomedical polymers: synthesis, properties, and applications

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

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

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

Photomedicine based on heme-derived compounds

Photoimaging and phototherapy have become major platforms for the diagnosis and treatment of various health complications. These applications require a photosensitizer (PS) that is capable of absorbing light from a source and converting it into other energy forms for detection and therapy. While synthetic inorganic materials such as quantum dots and gold nanorods have been widely explored for their medical diagnosis and photodynamic (PDT) and photothermal (PTT) therapy capabilities, translation of these technologies has lagged, primarily owing to potential cytotoxicity and immunogenicity issues. Of the various photoreactive molecules, the naturally occurring endogenous compound heme, a constituent of red blood cells, and its derivatives, porphyrin, biliverdin and bilirubin, have shown immense potential as noteworthy candidates for clinically translatable photoreactive agents, as evidenced by previous reports. While porphyrin-based photomedicines have attracted significant attention and are well documented, research on photomedicines based on two other heme-derived compounds, biliverdin and bilirubin, has been relatively lacking. In this review, we summarize the unique photoproperties of heme-derived compounds and outline recent efforts to use them in biomedical imaging and phototherapy applications.

Photoacoustic monitoring of angiogenesis predicts response to therapy in healing wounds

Chronic wounds are a major health problem that cause the medical infrastructure billions of dollars every year. Chronic wounds are often difficult to heal and cause significant discomfort. Although wound specialists have numerous therapeutic modalities at their disposal, tools that could three dimensional-map wound bed physiology and guide therapy do not exist. Visual cues are the current standard but are limited to surface assessment; clinicians rely on experience to predict response to therapy. Photoacoustic (PA) ultrasound (US) is a non-invasive, hybrid imaging modality that can solve these major limitations. PA relies on the contrast generated by haemoglobin in blood which allows it to map local angiogenesis, tissue perfusion and oxygen saturation-all critical parameters for wound healing. This work evaluates the use of PA-US to monitor angiogenesis and stratify patients responding versus not-responding to therapy. We imaged 19 patients with 22 wounds once a week for at least 3 weeks. Our findings suggest that PA imaging directly visualises angiogenesis. Patients responding to therapy showed clear signs of angiogenesis and an increased rate of PA increase (p = 0.002). These responders had a significant and negative correlation between PA intensity and wound size. Hypertension was correlated to impaired angiogenesis in non-responsive patients. The rate of PA increase and hence the rate of angiogenesis was able to predict healing times within 30 days from the start of monitoring (power = 88%, alpha = 0.05). This early response detection system could help inform management and treatment strategies while improving outcomes and reducing costs.

Optothermal properties of plasmonic inorganic nanoparticles for photoacoustic applications

Plasmonic systems are becoming a favourable alternative to dye molecules in the generation of photoacoustic signals for spectroscopy and imaging. In particular, inorganic nanoparticles are appealing because of their versatility. In fact, as the shape, size and chemical composition of nanoparticles are directly correlated with their plasmonic properties, the excitation wavelength can be tuned to their plasmon resonance by adjusting such traits. This feature enables an extensive spectral range to be covered. In addition, surface chemical modifications can be performed to provide the nanoparticles with designed functionalities, e.g., selective affinity for specific macromolecules. The efficiency of the conversion of absorbed photon energy into heat, which is the physical basis of the photoacoustic signal, can be accurately determined by photoacoustic methods. This review contrasts studies that evaluate photoconversion in various kinds of nanomaterials by different methods, with the objective of facilitating the researchers' choice of suitable plasmonic nanoparticles for photoacoustic applications.

Engineering of magnetic nanoparticles as magnetic particle imaging tracers

Magnetic particle imaging (MPI) has recently emerged as a promising non-invasive imaging technique because of its signal linearly propotional to the tracer mass, ability to generate positive contrast, low tissue background, unlimited tissue penetration depth, and lack of ionizing radiation. The sensitivity and resolution of MPI are highly dependent on the properties of magnetic nanoparticles (MNPs), and extensive research efforts have been focused on the design and synthesis of tracers. This review examines parameters that dictate the performance of MNPs, including size, shape, composition, surface property, crystallinity, the surrounding environment, and aggregation state to provide guidance for engineering MPI tracers with better performance. Finally, we discuss applications of MPI imaging and its challenges and perspectives in clinical translation.

Gold Nanorod-Melanin Hybrids for Enhanced and Prolonged Photoacoustic Imaging in the Near-Infrared-II Window

Photoacoustic (PA) imaging holds great promise as a noninvasive imaging modality. Gold nanorods (GNRs) with absorption in the second near-infrared (NIR-II) window have emerged as excellent PA probes because of their tunable optical absorption, surface modifiability, and low toxicity. However, pristine GNRs often undergo shape transition upon laser illumination due to thermodynamic instability, leading to a reduced PA signal after a few seconds of imaging. Here, we report monodisperse GNR-melanin nanohybrids where a tunable polydopamine (PDA) coating was conformally coated on GNRs. GNR@PDAs showed a threefold higher PA signal than pristine GNRs due to the increased optical absorption, cross-sectional area, and thermal confinement. More importantly, the PA signal of GNR@PDAs only decreased by 29% during the 5 min of laser illumination in the NIR-II window, while significant attenuation (77%) was observed for GNRs. The GNR@PDAs maintained 87% of its original PA signal in vivo even after 10 min of laser illumination. This PDA-enabled strategy affords a rational design for robust PA imaging probes and provides more opportunities for other types of photomediated biomedicines, such as photothermal and photodynamic regimens.

Gold nanoparticles to enhance ophthalmic imaging

The use of gold nanoparticles as diagnostic tools is burgeoning, especially in the cancer community with a focus on theranostic applications to both cancer diagnosis and treatment. Gold nanoparticles have also demonstrated great potential for use in diagnostic and therapeutic approaches in ophthalmology. Although many ophthalmic imaging modalities are available, there is still a considerable unmet need, in particular for ophthalmic molecular imaging for the early detection of eye disease before morphological changes are more grossly visible. An understanding of how gold nanoparticles are leveraged in other fields could inform new ways they could be utilized in ophthalmology. In this paper, we review current ophthalmic imaging techniques and then identify optical coherence tomography (OCT) and photoacoustic imaging (PAI) as the most promising technologies amenable to the use of gold nanoparticles for molecular imaging. Within this context, the development of gold nanoparticles as OCT and PAI contrast agents are reviewed, with the most recent developments described in detail.

Artificial Nanotargeted Cells with Stable Photothermal Performance for Multimodal Imaging-Guided Tumor-Specific Therapy

Organic-inorganic hybrid materials have drawn increasing attention as photothermal agents in tumor therapy due to the advantages of green synthesis, high loading efficiency of hydrophobic drugs, facile incorporation of theranostic iron, and excellent photothermal efficiency without inert components or additives. Herein, we proposed a strategy for biomimetic engineering-mediated enhancement of photothermal performance in the tumor microenvironment (TME). This strategy is based on the specific characteristics of organic-inorganic hybrid materials and endows these materials with homologous targeting ability and photothermal stability in the TME. The hybrid materials perform the functions of cancer cells to target homolytic tumors (acting as "artificial nanotargeted cells (ANTC)"). Inspired by the pH-dependent disassembly behaviors of tannic acid (TA) and ferric ion (Fe^III) and subsequent attenuation of photothermal performance, cancer cell membranes were self-deposited onto the surfaces of protoporphyrin-encapsulated TA and Fe^III nanoparticles to achieve ANTC with TME-stable photothermal performance and tumor-specific phototherapy. The resulting ANTC can be used as contrast agents for concurrent photoacoustic imaging, magnetic resonance imaging, and photothermal imaging to guide the treatment. Importantly, the high loading efficiency of protoporphyrin enables the initiation of photodynamic therapy to enhance photothermal therapeutic efficiency, providing antitumor function with minimal side effects.

Engineering Plasmonic Nanoparticles for Enhanced Photoacoustic Imaging

Photoacoustic (PA) imaging is an emerging imaging modality whereby pulsed laser illumination generates pressure transients that are detectable using conventional ultrasound. Plasmonic nanoparticles such as gold nanorods and nanostars are often used as PA contrast agents. The thermoelastic expansion model best describes the PA response from plasmonic nanoparticles: Light absorption causes a small increase in temperature leading to thermoelastic expansion. The conversion of optical energy into pressure waves (po) is dependent on several features: (i) the absorption coefficient (μa), (ii) the thermal expansion coefficient (β), (iii) specific heat capacity (Cp) of the absorbing material, (iv) speed of sound in the medium (c), and (v) the illumination fluence (F). Controlling the geometry, composition, coatings, and solvents around plasmonic nanostructures can help tune these variables to generate the optimum PA signal. The thermoelastic expansion model is not limited to plasmonic structures and holds true for all absorbing molecules. Here, we focus on ways to engineer these variables to enhance the PA response from plasmonic nanoparticles.

TME-activatable theranostic nanoplatform with ATP burning capability for tumor sensitization and synergistic therapy

Adenosine triphosphate (ATP), as a key substance for regulating tumor progression in the tumor microenvironemnt (TME), is an emerging target for tumor theranostics. Herein, we report a minimalist but versatile nanoplatform with simultaneously TME-responsive drug release, TME-enhanced imaging, ATP-depletion sensitized chemotherapy and photothermal therapy for intelligent tumor theranostics.

Methods: The Fe³⁺ and tannic acid (TA) coordination were self-deposited on doxorubicin (Dox) in a facile method to prepare Dox-encapsulated nanoparticles (DFTNPs).

Results: When irradiated by a near infrared laser, the DFTNPs could elevate the temperature in the tumor region efficiently. Subsequently, the Dox could be released by the disassembly of Fe³⁺/TA in the TME to initiate chemotherapy. Particularly, the smart nanoagent not only enabled ATP-depletion and enhanced the therapeutic effect of chemotherapy, but also acted as photothermal transduction agent for photothermal therapy. Moreover, the nanoagent also acted as T₁-weighted MR imaging,photoacoustic imaging and photothermal imaging contrast agent. The mice treated by DFTNPs plus laser showed a complete tumor eradication in 14d observation.

Conclusion: This as-prepared versatile nanoplatform offers new insights toward the application of smart nanoagents for improved tumor theranostics.

Iodide-doped precious metal nanoparticles: measuring oxidative stress in vivo via photoacoustic imaging

Accumulation of reactive oxygen and nitrogen species (RONS) can induce cell damage and even cell death. RONS are short-lived species, which makes direct, precise, and real-time measurement difficult. Biologically-relevant RONS levels are in the nM-μM scale; hence, there is a need for highly sensitive RONS probes. We previously used hybrid gold-core silver-shell nanoparticles with mM sensitivity to H2O2. These particles reported the presence of RONS via spectral shifts which could easily be quantified via photoacoustic imaging. Here, we used halide doping to tune the electrochemical properties of these materials to better match the oxidation potential of RONS. This work describes the synthesis, characterization, and application of these AgI-coated gold nanorods (AgI/AuNR). The I : Ag molar ratio, pH, and initial Ag shell thickness were optimized for good RONS detection limits. Halide doping lowers the reduction potential of Ag from to resulting in a 1000-fold increase in H2O2 and 100 000-fold increase in ONOO- sensitivity. The AgI/AuNR system also etches 45-times faster than undoped Ag/AuNR. The AgI/AuNR easily reported the endogenously produced RONS in established cells lines as well as murine models.

Assessing the range of enzymatic and oxidative tunability for biosensor design

Development of multi-functional materials and biosensors that can achieve an in situ response designed by the user is a current need in the biomaterials field, especially in complex biological environments, such as inflammation, where multiple enzymatic and oxidative signals are present. In the past decade, there has been extensive research and development of materials chemistries for detecting and monitoring enzymatic activity, as well as for releasing therapeutic and diagnostic agents in regions undergoing oxidative stress. However, there has been limited development of materials in the context of enzymatic and oxidative triggers together, despite their closely tied and overlapping mechanisms. With research focusing on enzymatically and oxidatively triggered materials separately, these systems may be inadequate in monitoring the complexity of inflammatory environments, thus limiting in vivo translatability and diagnostic accuracy. The intention of this review is to highlight a variety of enzymatically and oxidatively triggered materials chemistries to draw attention to the range of synthetic tunability available for the construction of novel biosensors with a spectrum of programmed responses. We focus our discussion on several types of macromolecular sensors, generally classified by the causative material response driving ultimate signal detection. This includes sensing based on degradative processes, conformational changes, supramolecular assembly/disassembly, and nanomaterial interactions, among others. We see each of these classes providing valuable tools toward coalescing current gaps in the biosensing field regarding specificity, selectivity, sensitivity, and flexibility in application. Additionally, by considering the materials chemistry of enzymatically and oxidatively triggered biomaterials in tandem, we hope to encourage synthesis of new biosensors that capitalize on their synergistic roles and overlapping mechanisms in inflammatory environments for applications in disease diagnosis and monitoring.

Evoking Photothermy by Capturing Intramolecular Bond Stretching Vibration-Induced Dark-State Energy

Development of highly effective approaches to desirable photothermal conversion agents is particularly valuable. Herein, we report a concept, namely, bond stretching vibration-induced photothermy, that serves as a mechanism to construct advanced photothermal conversion agents. As a proof-of-concept, two compounds (DCP-TPA and DCP-PTPA) with donor-acceptor (D-A) structures were synthesized. The bond stretching vibration of the pyrazine-containing unit in these molecules is vigorous and insensitive to the external environmental restraint, which efficiently transforms the absorbed photons to dark-state heat energy. The nanoparticles (NPs) of DCP-TPA and DCP-PTPA show rather high photothermal conversion efficiency (52% and 59%) and stronger photoacoustic (PA) signal than commercial methylene blue and reported high-performance semiconducting polymer nanoparticles. The DCP-PTPA NPs perform better than DCP-TPA NPs in terms of photothermal conversion, PA signal production, and in vivo PA tumor imaging because of the increased bond stretching vibration in the former molecule.

H2S-activatable near-infrared afterglow luminescent probes for sensitive molecular imaging in vivo

Afterglow luminescent probes with high signal-to-background ratio show promise for in vivo imaging; however, such probes that can be selectively delivered into target sites and switch on afterglow luminescence remain limited. We optimize an organic electrochromic material and integrate it into near-infrared (NIR) photosensitizer (silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) containing nanoparticles, developing an H2S-activatable NIR afterglow probe (F12+-ANP). F12+-ANP displays a fast reaction rate (1563 ± 141 M-1 s-1) and large afterglow turn-on ratio (~122-fold) toward H2S, enabling high-sensitivity and -specificity measurement of H2S concentration in bloods from healthy persons, hepatic or colorectal cancer patients. We further construct a hepatic-tumor-targeting and H2S-activatable afterglow probe (F12+-ANP-Gal) for noninvasive, real-time imaging of tiny subcutaneous HepG2 tumors (<3 mm in diameter) and orthotopic liver tumors in mice. Strikingly, F12+-ANP-Gal accurately delineates tumor margins in excised hepatic cancer specimens, which may facilitate intraoperative guidance of hepatic cancer surgery.