Size-tunable ICG-based contrast agent platform for targeted near-infrared photoacoustic imaging

Size-Controlled Self-Assembly for Bimodal In Vivo Imaging

Contrast agents (CAs) are essential in biomedical imaging to aid in the diagnosis and therapy monitoring of disease. However, they are typically restricted to one imaging modality and have fixed properties such as size, shape, toxicity profile, or photophysical characteristics, which hampers a comprehensive view of biological processes. Herein, rationally designed dye assemblies are introduced as a unique CA platform for simultaneous multimodal and multiscale biomedical imaging. To this end, a series of amphiphilic aza-BODIPY dyes are synthesized with varying hydrophobic domains (C1, C8, C12, and C16) that self-assemble in aqueous media into nanostructures of tunable size (50 nm-1 µm) and photophysical properties. While C1 exhibits oblique-type exciton coupling and negligible emission, C8-C16 bearing longer alkyl chains undergo J-type aggregation with NIR absorption and emission and excellent photoacoustic properties. Given these advantageous features, aza-BODIPY specific, semi-quantitative fluorescence reflectance and photoacoustic imaging both in vitro and in vivo are established. Additionally, in vitro cell viability as well as murine in vivo biodistribution analysis with ex vivo validation showed excellent biocompatibility and a size-dependent biodistribution of nanostructures to different organ beds. These results broaden the scope of aqueous self-assembly to multimodal imaging and highlight its great potential for rationalizing numerous biomedical questions.

Quantitative pharmacodynamics functional evaluation of Chinese medicine Qizhu formula in mice with dynamic near-infrared photoacoustic imaging

Background & Aims

Effective anti-fibrotic drugs and new non-invasive evaluation methods for liver fibrosis (LF) are urgently needed. Our study aimed to evaluate the histological effects of the Qizhu (QZ) formula on LF and to explore a non-invasive Near-infrared photoacoustic imaging (NIR-PAI) kinetic model for liver function detection and pharmacodynamic evaluation.

Methods

C57BL/6 J mice were randomly divided into six groups (n=6). An LF model was induced by CCl4 for 8 weeks, followed by an 8-week treatment period. Histological and serological parameters were assessed, and indocyanine green (ICG) metabolism (maximum peak time [Tmax] and half-life [T1/2]) was monitored by NIR-PAI. Spearman correlation analysis was conducted to evaluate correlations.

Results & Conclusions

Histological and serological results confirmed the anti-fibrotic effects of QZ. NIR-PAI kinetic parameters indicated that QZ shortened the Tmax and T1/2 of ICG. There were good correlations between ICG metabolism and liver histopathology. The non-invasive NIR-PAI kinetic model shows potential in liver function detection and pharmacodynamic evaluation.

Bornite (Cu5FeS4) nanocrystals as an ultrasmall biocompatible NIR-II contrast agent for photoacoustic imaging

In this study, we demonstrate the potential of the bornite crystal structure (Cu5FeS4) of copper iron sulfide as a second near infrared (NIR-II) photoacoustic (PA) contrast agent. Bornite exhibits comparable dose-dependent biocompatibility to copper sulfide nanoparticles in a cell viability study with HepG2 cells, while exhibiting a 10-fold increase in PA amplitude. In comparison to other benchmark contrast agents at similar mass concentrations, bornite demonstrated a 10× increase in PA amplitude compared to indocyanine green (ICG) and a 5× increase compared to gold nanorods (AuNRs). PA signal was detectable with a light pathlength greater than 5 cm in porcine tissue phantoms at bornite concentrations where in vitro cell viability was maintained. In vivo imaging of mice vasculature resulted in a 2× increase in PA amplitude compared to AuNRs. In summary, bornite is a promising NIR-II contrast agent for deep tissue PA imaging.

Photoacoustic polydopamine-indocyanine green (PDA-ICG) nanoprobe for detection of senescent cells

Cellular senescence is considered an important tumour suppression mechanism in response to damage and oncogenic stress in early lesions. However, when senescent cells are not immune-cleared and persist in the tumour microenvironment, they can drive a variety of tumour-promoting activities, including cancer initiation, progression, and metastasis. Additionally, there is compelling evidence demonstrating a direct connection between chemo(radio)therapy-induced senescence and the development of drug resistance and cancer recurrence. Therefore, detection of senescent cells in tissues holds great promise for predicting cancer occurrence earlier, assessing tumour progression, aiding patient stratification and prognosis, and informing about the efficacy of potential senotherapies. However, effective detection of senescent cells is limited by lack of biomarkers and readout strategies suitable for in vivo clinical imaging. To this end, a nanoprobe composed of biocompatible polydopamine (PDA) nanoparticle doped with FDA-approved indocyanine green (ICG) dye, namely PDA-ICG, was designed as a contrast agent for senescence detection using photoacoustic imaging (PAI). In an in vitro model of chemotherapy-induced senescence, PDA-ICG nanoprobe showed an elevated uptake in senescent cells relative to cancer cells. In addition to its improved photostability, 2.5-fold enhancement in photoacoustic signal relative to ICG was observed. Collectively, the results indicate that the PDA-ICG nanoprobe has the potential to be used as a contrast agent for senescence detection of chemotherapy-induced senescence using PAI.

Review on Photoacoustic Monitoring after Drug Delivery: From Label-Free Biomarkers to Pharmacokinetics Agents

Photoacoustic imaging (PAI) is an emerging noninvasive and label-free method for capturing the vasculature, hemodynamics, and physiological responses following drug delivery. PAI combines the advantages of optical and acoustic imaging to provide high-resolution images with multiparametric information. In recent decades, PAI's abilities have been used to determine reactivity after the administration of various drugs. This study investigates photoacoustic imaging as a label-free method of monitoring drug delivery responses by observing changes in the vascular system and oxygen saturation levels across various biological tissues. In addition, we discuss photoacoustic studies that monitor the biodistribution and pharmacokinetics of exogenous contrast agents, offering contrast-enhanced imaging of diseased regions. Finally, we demonstrate the crucial role of photoacoustic imaging in understanding drug delivery mechanisms and treatment processes.

Tailoring Indocyanine Green J-Aggregates for Imaging, Cancer Phototherapy, and Drug Delivery: A Review

Indocyanine green J-aggregates (ICG-Jagg) have emerged as a significant subject of interest in biomedical applications due to their unique optical properties, tunable size, and excellent biocompatibility. This comprehensive review aims to provide an in-depth exploration of ICG-Jagg, with a focus on elucidating the diverse facets of their preparation and the factors that influence the preparation process. Additionally, the review discusses their applications in biomedical diagnostics, such as imaging and contrast agents, as well as their utilization in drug delivery and various phototherapeutic interventions.

A Facile Approach to Producing Liposomal J-Aggregates of Indocyanine Green with Diagnostic and Therapeutic Potential

Liposomal J-Aggregates of Indocyanine Green (L-JA) can serve as a biocompatible and biodegradable nanoparticle for photoacoustic imaging and photothermal therapy. When compared to monomeric IcG, L-JA are characterized by longer circulation, improved photostability, elevated absorption at longer wavelengths, and increased photoacoustic signal generation. However, the documented methods for production of L-JA vary widely. We developed an approach to efficiently form IcG J-aggregates (IcG-JA) directly in liposomes at elevated temperatures. Aggregating within fully formed liposomes ensures particle uniformity and allows for control of J-aggregate size. L-JA have unique properties compared to IcG. L-JA provide significant contrast enhancement in photoacoustic images for up to 24 hours after injection, while IcG and unencapsulated IcG-JA are cleared within an hour. L-JA allow for more accurate photoacoustic-based sO2 estimation and particle tracking compared to IcG. Furthermore, photothermal heating of L-JA with an 852nm laser is demonstrated to be more effective at lower laser powers than conventional 808nm lasers for the first time. The presented technique offers an avenue for formulating a multi-faceted contrast agent for photoacoustic imaging and photothermal therapy that offers significant advantages over other conventional agents.

Repurposing indocyanine green: exploring the potential of an old drug in modern medicine

The repurposing of existing drugs, referred to as theranostics, has made profound impacts on precision medicine. Indocyanine green (ICG), a well-established and clinical dye, has continued to be a star agent, described as a multifunctional molecule with concurrent photo- or sono-sensitiveness capabilities and co-delivery accessibility, showing remarkable potential in the area of unimodal or multimodal imaging-guided therapy of various diseases, leading to the extensive consideration of immediate clinical translations. In this review, we strive to bring the understanding of repurposing performance assessment for ICG into practice by clarifying the relationships between its features and applicability. Specifically, we address the obstacles encountered in the process of developing an ICG repurposing strategy, as well as the noteworthy advancements made in the field of ICG repurposing. We also go into detail about the structure-function correlations of drugs containing ICG and how different structural groups significantly affect the physicochemical properties.

An Indocyanine Green-Based Nanoprobe for In Vivo Detection of Cellular Senescence

There is an urgent need to improve conventional cancer-treatments by preventing detrimental side effects, cancer recurrence and metastases. Recent studies have shown that presence of senescent cells in tissues treated with chemo- or radiotherapy can be used to predict the effectiveness of cancer treatment. However, although the accumulation of senescent cells is one of the hallmarks of cancer, surprisingly little progress has been made in development of strategies for their detection in vivo. To address a lack of detection tools, we developed a biocompatible, injectable organic nanoprobe (NanoJagg), which is selectively taken up by senescent cells and accumulates in the lysosomes. The NanoJagg probe is obtained by self-assembly of indocyanine green (ICG) dimers using a scalable manufacturing process and characterized by a unique spectral signature suitable for both photoacoustic tomography (PAT) and fluorescence imaging. In vitro, ex vivo and in vivo studies all indicate that NanoJaggs are a clinically translatable probe for detection of senescence and their PAT signal makes them suitable for longitudinal monitoring of the senescence burden in solid tumors after chemotherapy or radiotherapy.

Ultrasound generation in water via quasi-periodically snapping polymeric core-shell micro-bead excited with radiowaves

This work reports the results of a theoretical and numerical study showing the occurrence of stochastically resonating bistable dynamic in polymeric micro-bead of sub-micrometric size with stiff core and soft shell. The system, submerged in water, is excited with a pulsed laser working in the Mega-Hertz frequency range and tuned to match both an optical and acoustic resonance of the system. The laser interacts with the carbon nanotubes embedded in the shell of the polymeric micro-bead generating heat. The concurrent action of the generated heat with the standing acoustic oscillations, gives rise to a stochastically resonating bistable system. The system in fact is forced to switch between two states (identifiable with the creation and organized disruption of a quasi-hexagonal tessellation) via a snap-through-buckling mechanism. This phenomenon results in the unprecedented generation of pressure oscillations. These results open the way to develop a new type of core-shell micro-transducers for radioacoustic imaging applications able to work in the Mega-Hertz frequency range. From a more general thermodynamic perspective, the reported mechanism shows a remarkable periodicity and energy conversion efficiency.

Platelet membrane-coated bio-nanoparticles of indocyanine green/elamipretide for NIR diagnosis and antioxidant therapy in acute kidney injury

Acute kidney injury (AKI) is a prevalent condition in critically ill patients that is often associated with significant morbidity and mortality. As the lack of effective early diagnosis methods often delays AKI treatment, there is currently no definitive clinical intervention available. In this study, we aimed to address these challenges by developing a nano-system called Platelet membranes-ICG-SS31-PLGA (PISP), which was designed to selectively target to the kidney site, taking advantage of the natural tendency of platelets to accumulate at sites of vascular injury. This approach allowed for the accumulation of PISP within the kidney as the disease progresses. By incorporating ICG, the in vivo distribution of PISP can be observed for NIR diagnosis of AKI. This non-invasive imaging technique holds great promise for early detection and monitoring of AKI. Furthermore, Elamipretide (SS31) acts as a mitochondria-targeted antioxidant that protects against mitochondrial damage and reduces oxidative stress, inflammation, and apoptosis. The combination of diagnostic and therapeutic capabilities within a single nano-system makes the PISP approach a valuable tool for addressing AKI. This intervention helps to prevent the deterioration of AKI and promotes the recovery. STATEMENT OF SIGNIFICANCE.

Visualization of photothermal therapy by semiconducting polymer dots mediated photoacoustic detection in NIR II

Visualization of photothermal therapy mediated by photothermal transduction agents (PTAs) is important to promote individual treatment of patients with low side effects. Photoacoustic detection has emerged as a promising noninvasive method for the visualization of PTAs distribution but still has limitations in temperature measurement, including poor measurement accuracy and low tissue penetration depth. In this study, we developed biocompatible semiconducting polymer dots (SPD) for in situ coupling of photothermal and photoacoustic detection in the near-infrared II window. SPD has dual photostability under pulsed laser and continuous-wave laser irradiation with a photothermal conversion efficiency of 42.77%. Meanwhile, a strong correlation between the photoacoustic signal and the actual temperature of SPD can be observed. The standard deviation of SPD-mediated photoacoustic thermometry can reach 0.13 °C when the penetration depth of gelatin phantom is 9.49 mm. Preliminary experimental results in vivo show that SPD-mediated photoacoustic signal has a high signal-to-noise ratio, as well as good performance in temperature response and tumor enrichment. Such a study not only offers a new nanomaterial for the visualization of photothermal therapy but will also promote the theranostic platform for clinical applications.

Near-infrared dye IRDye800CW-NHS coupled to Trastuzumab for near-infrared II fluorescence imaging in tumor xenograft models of HER-2-positive breast cancer

Near-infrared II fluorescent probes targeting tumors for diagnostic purposes have received much attention in recent years. In this study, a fluorescent probe for the NIR-II was constructed by using IRDye800CW-NHS fluorescent dye with Trastuzumab, which was investigated for its ability to target HER-2-positive breast cancer in xenograft mice models. This probe was compared with Trastuzumab-ICG which was synthesized using a similar structure, ICG-NHS. The results demonstrated that the IRDye800CW-NHS had significantly stronger fluorescence in the NIR-I and NIR-II than ICG-NHS in the aqueous phase. And the different metabolic modes of IRDye800CW-NHS and ICG-NHS were revealed in bioimaging experiments. IRDye800CW-NHS was mainly metabolised by the kidneys, while ICG-NHS was mainly metabolised by the liver. After coupling with Trastuzumab, Trastuzumab-800CW (TMR = 5.35 ± 0.39) not only had a stronger tumor targeting ability than Trastuzumab-ICG (TMR = 4.42 ± 0.10) based on the calculated maximum tumor muscle ratio (TMR), but also had a comparatively lower hepatic uptake and faster metabolism. Histopathology analysis proved that both fluorescent probes were non-toxic to various organ tissues. These results reveal the excellent optical properties of IRDye800CW-NHS, and the great potential of coupling with antibodies to develop fluorescent probes that will hopefully be applied to intraoperative breast cancer navigation in humans.

NIR-II Nanoprobes: A Review of Components-Based Approaches to Next-Generation Bioimaging Probes

Fluorescence and photoacoustic imaging techniques offer valuable insights into cell- and tissue-level processes. However, these optical imaging modalities are limited by scattering and absorption in tissue, resulting in the low-depth penetration of imaging. Contrast-enhanced imaging in the near-infrared window improves imaging penetration by taking advantage of reduced autofluorescence and scattering effects. Current contrast agents for fluorescence and photoacoustic imaging face several limitations from photostability and targeting specificity, highlighting the need for a novel imaging probe development. This review covers a broad range of near-infrared fluorescent and photoacoustic contrast agents, including organic dyes, polymers, and metallic nanostructures, focusing on their optical properties and applications in cellular and animal imaging. Similarly, we explore encapsulation and functionalization technologies toward building targeted, nanoscale imaging probes. Bioimaging applications such as angiography, tumor imaging, and the tracking of specific cell types are discussed. This review sheds light on recent advancements in fluorescent and photoacoustic nanoprobes in the near-infrared window. It serves as a valuable resource for researchers working in fields of biomedical imaging and nanotechnology, facilitating the development of innovative nanoprobes for improved diagnostic approaches in preclinical healthcare.

Miniature Probe for Optomechanical Focus-Adjustable Optical-Resolution Photoacoustic Endoscopy

Photoacoustic microscopy (PAM) is a promising imaging modality because it is able to reveal optical absorption contrast in high resolution on the order of a micrometer. It can be applied in an endoscopic approach by implementing PAM into a miniature probe, termed photoacoustic endoscopy (PAE). Here we develop a miniature focus-adjustable PAE (FA-PAE) probe characterized by both high resolution (in micrometers) and large depth of focus (DOF) via a novel optomechanical design for focus adjustment. To realize high resolution and large DOF in a miniature probe, a 2-mm plano-convex lens is specially adopted, and the mechanical translation of a single-mode fiber is meticulously designed to allow the use of multi-focus image fusion (MIF) for extended DOF. Compared with existing PAE probes, our FA-PAE probe achieves high resolution of [Formula: see text] within unprecedentedly large DOF of 3.2 mm, more than 27 times the DOF of the probe without performing focus adjustment for MIF. The superior performance is first demonstrated by imaging both phantoms and animals including mice and zebrafish in vivo by linear scanning. Further, in vivo endoscopic imaging of a rat's rectum by rotary scanning of the probe is conducted to showcase the capability of adjustable focus. Our work opens new perspectives for PAE biomedical applications.

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

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

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

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

Recent Advances in Photoacoustic Agents for Theranostic Applications

Photoacoustic agents are widely used in various theranostic applications. By evaluating the biodistribution obtained from photoacoustic images, the effectiveness of theranostic agents in terms of their delivery efficiency and treatment responses can be analyzed. Through this study, we evaluate and summarize the recent advances in photoacoustic-guided phototherapy, particularly in photothermal and photodynamic therapy. This overview can guide the future directions for theranostic development. Because of the recent applications of photoacoustic imaging in clinical trials, theranostic agents with photoacoustic monitoring have the potential to be translated into the clinical world.