Clinically translatable quantitative molecular photoacoustic imaging with liposome-encapsulated ICG J-aggregates

Stabilising indocyanine green J-aggregate theranostics in biological milieu via liposomal envelopment

Indocyanine green (ICG) J-aggregate (IJA) is a self-assembled ICG with a red-shift absorption band, enabling better tissue penetration than the monomeric ICG. Despite its superior photoacoustic imaging capabilities and heating stability to ICG, IJA suffers from low optical stability in aqueous and biological media, jeopardising their biomedical applications. The present work focused on loading p-IJA into liposomes to enhance their promising therapeutic and imaging applications. To optimise IJA loading into liposomes, we investigated the effect of lipid bilayer composition (lipid melting points, cholesterol, DSPE-PEG2000, and lipid charge) on the encapsulation of pre-formed IJA (p-IJA) into liposomes. Our findings showed the significance of high melting point lipids, high cholesterol, and DSPE-PEG2000 contents for persevering p-IJA following loading into liposomes. Moreover, low percentages (∼5 mol %) of positively charged (DOTAP) or negatively charged (DSPG) lipids could still be incorporated into our liposomes without affecting p-IJA loading. Promisingly, p-IJA-liposomes enhanced p-IJA optical stability in a range of biological media, such as serum proteins, blood and collagen. Finally, lyophilised p-IJA-liposomes for long-term storage were successfully prepared. The present study solely focused on evaluating the enhanced photothermal stability of p-IJA following liposome envelopment. Nevertheless, our lipid-enveloped p-IJA could offer a biodegradable and stable platform for multimodal applications, including photoacoustic imaging, photothermal therapy (PTT), photodynamic (PDT), nanobubble-mediated ablation, and combination therapy with chemotherapeutics agents.

Indocyanine Green Aggregation-Induced Hypotonic Stress to Remodel Aloe Exosome-like Vesicles for Enhanced Tumor Penetration and Phototherapy

As ubiquitous transport nanovesicles in cell biology, plant exosome-like vesicles (PELVs) have enormous potential to deliver drugs safely and effectively. Drug encapsulation and mechanical stability of vesicles are key limitations influencing their delivery efficiency. However, common methods (i.e., ultrasound, electroporation) for drug loading inevitably affect the inherent vesicle characteristics, which influence their stability, leakproof nature, cellular internalization, and tumor penetration. Herein, in order to balance this contradiction, we put forward a strategy to skillfully remodel aloe exosome-like vesicles (AELVs) through indocyanine green (ICG)-induced hypotonic stress during endogenous drug loading. We observe that the rigidity of AELVs is enhanced with the accumulation of long hydrocarbon chain lipids under ICG-induced hypotonic stress. Synchronously, ICG is also loaded into AELVs (ICG/AELVs, IAs), which effectively prevents secondary damage during drug loading. More interestingly, we find that hypotonic stress promotes IA secretion with less intravesicular protein, which is beneficial to enlarge their inner space for more drug loading. The IAs show great storage stability, leakproof, and antidegradation performance. Compared with control AELVs, IAs with higher rigidity are more liable to penetrate into the tumor. IAs further modifying with the AS1411 aptamer (AS1411-IAs, AIAs) exhibit high tumor targeting in vivo. After intravenous administration, the 4T1 tumor is obviously inhibited by AIAs plus NIR irradiation, which effectively improves the survival rate of tumor-bearing mice. Overall, we systematically explore the effects of drug-induced osmotic stress on PELVs during endogenous drug loading and achieve efficient tumor therapy. This work simplifies the process of drug loading in PELVs and enhances their plasticity, which provides a promising perspective for PELV-based drug delivery and clinical application.

Targeted Delivery of Chlorin-e6-Loaded Carbon Nanotube-Based Nanobiocomposite to Cancer Stem Cells for Enhanced Photodynamic Therapy

Background: Globally, colorectal cancer (CRC) is the third-most diagnosed cancer among males and the second-most diagnosed cancer among females. In cancer, stem cells are a subset of neoplastic cells capable of tumorigenesis and exhibit properties like normal stem cells. Moreover, they are resistant to conventional cancer treatments and can repopulate the tumor following treatment. Cancer cells are stimulated to undergo apoptosis by photodynamic therapy (PDT), which involves a light source, a photosensitizer, and reactive oxygen species. Methods: In this study, colon cancer stem cells were isolated from colon cancer cells and characterized using flow cytometry and immunofluorescence techniques. To treat colon cancer stem cells (CCSCs), single-walled carbon nanotubes (SWCNTs) were coupled with hyaluronic acid (HA) and loaded with chlorin-e6 (Ce6). Nanobiocomposite toxicity was assessed using CCSCs with two fluences of 5 J/cm2 and 10 J/cm2. The cellular changes were observed at 24 and 48 h using microscopy, Results: LDH cytotoxicity assay, and cell death induction by annexin propidium iodide assay. An intracellular analysis of reactive oxygen species (ROS) detected oxidative stress within CCSCs. Conclusions: Overall, the results showed that the newly synthesized nanobiocomposite enhanced the ability of PDT to act as a photosensitizer carrier and induced cell death in CCSCs.

Understanding the formulation parameters for engineering indocyanine green J-aggregate lipid nanocapsules and solid lipid nanoparticles as promising photothermal agents

Indocyanine green J-aggregate (IJA) is a promising photothermal (PTT) agent that has recently been utilised in preclinical studies for cancer diagnostics and treatment. The unique properties, such as the red-shift absorption band and longer wavelengths, are behind IJA's superior thermal stability compared to its monomeric ICG. Loading IJA into nanoparticles (NPs) has proven advantageous in enhancing its in vivo targeting of various cancer models. However, the loading of IJA into more complex lipids, such as lipid nanocapsules (LNCs) and solid lipid nanoparticles (SLNs), has not been reported. The present work focuses on investigations of the effect of formulation parameters on pre-formed IJA (p-IJA) stability and the formation of p-IJA-loaded LNCs and SLNs, thus enhancing their theranostic applications. We investigated the effect of the lipid shell of LNCs and the lipid core of SLN on p-IJA stability. Our findings demonstrated the significant role of lipophilic surfactants (Span 85) and a high-melting-point lipid core (sodium stearate) in enhancing the p-IJA ratio and heating capacity following loading into SLNs. More importantly, p-IJA-SLN enhanced the optical stability of p-IJA in a range of biological media, such as serum proteins, blood, and collagen. Furthermore, lyophilised p-IJA-SLNs were successfully obtained after long-term storage. Overall, p-IJA-loaded lipid NPs could provide a promising platform for various applications, including photoacoustic imaging, PTT, photodynamic therapy (PDT), and combination therapy with chemotherapeutics.

Visualizing plant salt stress with a NaCl-responsive fluorescent probe

Salt stress is an adverse environmental condition that harms plant growth and development. The development of salt stress probes is critical for tracking the growth dynamics of plants, molecular breeding or screening of growth regulators. The sodium chloride (NaCl)-responsive fluorescent probe Aza-CyBz is designed based on the tenet that NaCl induces formation of ordered aggregates, and the sensitive fluorescence response can enable the visualization of plant salt stress in root tip tissues and live plants. Herein, we describe a detailed three-step route for synthesis of Aza-CyBz and applications to monitoring salt stress in Arabidopsis thaliana. The procedures for operating fluorescence imaging under various stresses are also listed to eliminate interference from the oxidative mechanism of salt stress. Compared with conventional invasive approaches such as inductively coupled plasma emission spectrometry and flame photometer, our protocol can real-time monitor salt stress experienced by plants, which demands simple pretreatment procedure and staining technique. Due to near infrared fluorescence, this method provides direct visual observation of salt stress at both tissue and live plant levels, which is superior to conventional noninvasive approaches. The preparation of probe Aza-CyBz takes ~2 d, and the imaging experiments for assessing salt stress experienced by plants, including the preparation of stressed plant samples takes ~9-11 d for root tip tissues and ~23 d for live plants. Notably, acquisition and analysis visual images of salt stress in plants can be completed within 2 h and they require only a basic knowledge of spectroscopy and chemistry.

Molecular Trojan Based on Membrane-Mimicking Conjugated Electrolyte for Stimuli-Responsive Drug Release

Enhancing payload encapsulation stability while enabling controlled drug release are both critical objectives in drug delivery systems but are challenging to reconcile. This study introduces a zwitterionic conjugated electrolyte (CE) molecule named Zwit, which acts as a molecular Trojan by mimicking the lipid bilayers. When integrated into liposome membranes, Zwit rigidifies the bilayer structure likely due to its hydrophobic interactions providing structural support, thus inhibiting drug leakage. Upon 808 nm laser excitation, Zwit rapidly accelerates DOX release from liposome core, likely due to light-triggered conformational changes or photothermal effects that compromise membrane permeability. These findings demonstrate Zwit's ability to overcome the challenge of simultaneously preventing premature payload leakage and enabling stimuli-responsive drug release with a single component. Additionally, Zwit exhibits excellent biocompatibility with membranes, outperforming its quaternary ammonium counterpart and commonly used dye indocyanine green (ICG). By harnessing its NIR-II emission, Zwit enables durable in vivo biodistribution tracking of nanocarriers, whereas ICG suffers from significant dye leakage. In subcutaneous tumor models, the synergistic effects of chemotherapy and thermotherapy facilitated by this light-triggered system induced a potent antitumor immune response, further enhancing anticancer efficacy. This work underscores the potential of membrane-mimicking CEs as multifunctional tools in advanced drug delivery systems.

Activatable Molecular Probes With Clinical Promise for NIR-II Fluorescent Imaging

The second near-infrared window (NIR-II) fluorescence imaging has been widely adopted in basic scientific research and preclinical applications due to its exceptional spatiotemporal resolution and deep tissue penetration. Among the various fluorescent agents, organic small-molecule fluorophores are considered the most promising candidates for clinical translation, owing to their well-defined chemical structures, tunable optical properties, and excellent biocompatibility. However, many currently available NIR-II fluorophores exhibit an "always-on" fluorescence signal, which leads to background noise and compromises diagnostic accuracy during disease detection. Developing NIR-II activatable organic small-molecule fluorescent probes (AOSFPs) for accurately reporting pathological changes is key to advancing NIR-II fluorescence imaging toward clinical application. This review summarizes the rational design strategies for NIR-II AOSFPs based on four core structures (cyanine, hemicyanine, xanthene, and BODIPY). These NIR-II AOSFPs hold substantial potential for clinical translation. Furthermore, the recent advances in NIR-II AOSFPs for NIR-II bioimaging are comprehensively reviewed, offering clear guidance and direction for their further development. Finally, the prospective efforts to advance NIR-II AOSFPs for clinical applications are outlined.

High-Throughput Microfluidic Production of Ultrasmall Lecithin Nanoliposomes for High-Efficacy Transdermal Delivery and Skin-Aging Treatment

BACKGROUND

Liposome particles with smaller sizes could increase transdermal drug delivery efficacy for enhanced skin penetration. While microfluidic methods have enabled controlled liposome synthesis, achieving efficient production of ultrasmall nanoliposomes (NLPUS) with a size smaller than 40 nm yet remains an unmet challenge.

METHODS

In this study, we employed a helical-blade-strengthened co-flow focusing (HBSCF) device to efficiently synthesize NLPUS, which demonstrated superior skin permeation and retention.

RESULTS

Liposome formulation primarily contains unsaturated lecithin, which endows an unprecedented capacity to NLPUS to scavenge reactive oxygen species (ROS). Moreover, NLPUS can effectively encapsulate a broad spectrum of anti-aging agents, including coenzyme Q10 (CoQ10), while preserving its physical properties. In a photoaged skin model, topical application of CoQ10-loaded NLPUS (CoQ10@NLPUS) inhibited ultraviolet B (UVB)-induced matrix metalloproteinase-1 (MMP-1) production, and promoted collagen type I (Col-I) synthesis in skin cells, thereby effectively rejuvenating the photoaged skin.

CONCLUSIONS

This study presents a straightforward and efficient method for the production of NLPUS, thereby offering a promising platform for transdermal delivery of diverse therapeutic agents.

Recent Advances in Indocyanine Green-Based Probes for Second Near-Infrared Fluorescence Imaging and Therapy

Fluorescence imaging, a highly sensitive molecular imaging modality, is being increasingly integrated into clinical practice. Imaging within the second near-infrared biological window (NIR-II; 1,000 to 1,700 nm), also referred to as shortwave infrared, has received substantial attention because of its markedly reduced autofluorescence, deeper tissue penetration, and enhanced spatiotemporal resolution as compared to traditional near-infrared (NIR) imaging. Indocyanine green (ICG), a US Food and Drug Administration-approved NIR fluorophore, has long been used in clinical applications, including blood vessel angiography, vascular perfusion monitoring, and tumor detection. Recent advancements in NIR-II imaging technology have revitalized interest in ICG, revealing its extended tail fluorescence beyond 1,000 nm and reaffirming its potential as a clinically translatable NIR-II fluorophore for in vivo imaging and theranostic applications for diagnosing various diseases. This review emphasizes the notable advances in the use of ICG and its derivatives for NIR-II imaging and image-guided therapy from both fundamental and clinical perspectives. We also provide a concise conclusion and discuss the challenges and future opportunities with NIR-II imaging using clinically approved fluorophores.

Biodegradable lipid bilayer-assisted indocyanine green J- aggregates for photothermal therapy: Formulation, in vitro toxicity and in vivo clearance

Indocyanine green (ICG) J-aggregates (IJA) are a unique form of aggregation that exhibits superior properties to monomeric ICG. Despite their higher photoacoustic (PA) signals for imaging and heating stability during photothermal therapy (PTT), they exhibit low stability under a biological milieu. Our group previously proposed a simple procedure for in-situ preparation of IJA into liposomes, accelerating their formation and optical properties. To comprehend their potential applications, we systematically investigated the effect of the lipid bilayer composition on ICG J-aggregation and stability. Moreover, their in vitro compatibility and photothermal toxicity in monolayers and cancer spheroids, besides their in vivo biodistribution and clearance were evaluated. Our findings revealed the importance of high cholesterol and PEG-lipid content and low charged lipids (∼ 5 mol %) in liposomes to promote a high IJA/ICG ratio and, thus, high heating stability. More importantly, IJA-liposomes revealed high biocompatibility in monolayer and cancer spheroids with efficient photothermal toxicity. Finally, IJA-liposomes were cleared from the body without toxicity. Interestingly, IJA-liposomes mainly showed lower affinity to the liver than monomeric ICG, resulting in higher renal clearance. Overall, our biodegradable IJA-liposomes could be an excellent alternative to gold-based agents suitable for PA imaging and cancer PTT.

Molecular Engineering of Ultrabright Biomimetic NanoGhost for Site-Selective Tumor Imaging and Biodistribution

Optically active ultrabright imaging agents are shown to delineate tumor location with deep tissue visualization in pre noclinical tumor models. NanoGhosts (NGs) particles are reconstructed from the cell membrane and integrated with organic fluorophores to attain ultra-brightness for solid tumor imaging. Moreover, the integration of amphiphilic and lipophilic molecules reveals structural characteristics of NGs (≈70 nm), which also alter their brightness. Upon intravenous administration (10 mg kg-1 single dose), these ultrabright NGs (778 MESF) enable the high-resolution of tumor site and real-time tracking of vital organs with high-contrast fluorescence signals. Engineered biomimetic NGs demonstrates better resolution and tissue penetration as compared to the clinically approved indocyanine green (ICG). High precision in tumor detection (0.5 h) and strong tumor retention (24 h which is further up to 30th day) without affecting healthy tissues ensure the future scope of NGs in early-stage cancer imaging. These findings suggest that these NGs mimic the biological characteristics of native cells, enabling them to evade immune clearance and target the solid tumor naturally.

Quantitative photoacoustic spectral transformations in theranostic solid lipid nanoparticles labelled with increasing concentrations of a photoacoustic NIR BODIPY

Solid lipid nanoparticles (SLNs) have shown great capabilities for drug delivery and are therefore attractive theranostic candidates when labelled with an imaging contrast agent. This work aims to create the first SLNs labelled for photoacoustic (PA) imaging by encapsulating a specially designed and near-infrared absorbing BODIPY dye (BY-aniline-Palm) into SLNs of dexamethasone palmitate. A one-pot formulation protocol enabled us to replace the prodrug with the BY-aniline-Palm label in various proportions up to 100%. Increasing the dye content resulted in complex but gradual transformations of the SLNs in terms of optical absorption and PA spectra, and the formation of aggregates at high concentration. A comprehensive and quantitative PA spectrometric study revealed a photoacoustic generation efficiency (PGE) that was spectrally varying and notably greater than 1. A joint spectral decomposition of the absorption and PA spectra into the sum of three Gaussian functions displayed a per-band evolution of the PGE when the concentration of BY-aniline-Palm varied and showed an interplay between the bands with a constant spectrum area. Finally, a novel quantitative PA spectroscopic approach, involving measurements at three different ambient temperatures, demonstrated that the remarkable PGE values arose from a significant thermo-elastic expansion of the SLNs during PA signal generation independently of the absorption band. This study highlights that labeled SLNs are promising agents for PA imaging and also unveils complex transformations that can occur in such nanosystems with a dye prone to aggregation.

Photoresponsive prodrug-based liposomes for controllable release of the anticancer drug chlorambucil

The on-demand delivery and release of chemotherapeutic drugs have attracted great attention, among which photoresponsive prodrug systems have shown specific advantages for effective cancer treatment due to their spatiotemporal control, non-invasive nature and easy operation. Unlike the traditional strategy of physical encapsulation of drugs in liposomes, we herein report a biomimetic and photoresponsive drug delivery system (DDS) based on a lipid prodrug liposomal formulation (LNC), which combines the features of the prodrug and nanomedicines, and can realize photocontrollable release of anticancer drugs. The lipid prodrug comprises three functional moieties: a single-arm phospholipid (Lyso PC), an o-nitrobenzyl alcohol (NB) and chlorambucil (CBL). Before irradiation, LNC formed liposomal assemblies in water with an average size of about 200 nm, and upon light irradiation, the efficient photocleavage reaction of NB facilitated the disintegration of liposomal assemblies and the release of drug CBL. Photolysis analysis showed that LNC exhibited accurate and controllable drug release in response to UV 365 nm irradiation. Cell viability assays showed that LNC liposomes demonstrated very low cytotoxicity in the dark and high cellular toxicity upon light irradiation, with toxicity even higher than free CBL. Our results suggest that our photoresponsive lipid prodrug represents a promising strategy to construct controlled DDS for cancer therapy.

Temporal dynamics of fluorescence and photoacoustic signals of a Cetuximab-IRDye800 conjugate in EGFR-overexpressing tumors

Molecular fluorescence-guided surgery has shown promise for tumor margin delineation but is limited by its depth profiling capability. Interestingly, most fluorophores, either clinically approved or in clinical trials, can also be used as photoacoustic contrast agents, yet their use is limited due to the low light fluence permitted for clinical use and the limited sensitivity of current photoacoustic imaging systems. There is therefore an urgent unmet need to establish methods for enhancing contrast in molecular targeted PA imaging which could potentially complement and overcome limitations in molecular fluorescence guided therapies. In this study, we compare the photoacoustic (PA) and fluorescence imaging capabilities of a cetuximab-IRDye800 conjugate in a subcutaneous tumor xenograft model. We demonstrate that while the fluorescence signal increases steadily over time after administration of cetuximab-IRDye800, PA signal peaks early (~2 fold higher at 6-hour as compared to pre-injection controls) and then decreases (~1.3 fold higher at 24-hour as compared to pre-injection controls). This pattern aligns with previous findings using other antibody-conjugated PA contrast agents. Mechanistically, we demonstrate that the formation of H-aggregates upon antibody conjugation enhances PA contrast of the IRDye800. The disruption of these H-aggregates, as the antibody-dye conjugate is degraded post receptor-mediated endocytosis, decreases PA signal intensity. The timeframe of maximum PA signal and decrease thereafter is consistent with the time frame of receptor-mediated endocytosis of cetuximab-IRDye800. Our data suggests that tumor cell surface binding results in peak PA signal while lysosomal localization and degradation results in a significant drop in PA signal. Our study sheds light on the distinct temporal dynamics of PA and fluorescence signals of Cetuximab-IRDye800 conjugate and we propose that optimizing IRDye800 conjugation to antibodies can further enhance PA signal intensity when timed to precisely to capture IRDye800 in an H-aggregate form.

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.

Facilely Achieving Near-Infrared-II J-Aggregates through Molecular Bending on a Donor-Acceptor Fluorophore for High-Performance Tumor Phototheranostics

Constructing J-aggregated organic dyes represents a promising strategy for obtaining biomedical second near-infrared (NIR-II) emissive materials, as they exhibit red-shifted spectroscopic properties upon assembly into nanoparticles (NPs) in aqueous environments. However, currently available NIR-II J-aggregates primarily rely on specific molecular backbones with intricate design strategies and are susceptible to fluorescence quenching during assembly. A facile approach for constructing bright NIR-II J-aggregates using prevalent donor-acceptor (D-A) molecules is still lacking. In this study, we present a facile method that transforms D-A molecules into J-aggregates by simply bending the molecule through introducing a methyl group, enabling high-performance NIR-II phototheranostics. The TAA-BT-CN molecule exhibits hypsochromic-shift absorption upon forming H-aggregated NPs, while the designed mTAA-BT-CN with a bent structure demonstrates a bathochromic shift of over 100 nm in absorption upon forming J-aggregated NPs, leading to much enhanced NIR-II emission beyond 1100 nm. With respect to its H-aggregated counterpart with the aggregation-caused quenching (ACQ) phenomenon, the J-aggregated mTAA-BT-CN NPs exhibit a 7-fold increase in NIR-II fluorescence owing to their aggregation-induced emission (AIE) property as well as efficient generation of heat and reactive oxygen species under 808 nm light excitation. Finally, the mTAA-BT-CN NPs are employed for whole-body blood vessel imaging using NIR-II technology as well as imaging-guided tumor phototherapies. This study will facilitate the flourishing advancement of J-aggregates based on prevalent D-A-type molecules.

Emissive Lipid Nanoparticles as Biophotonic Contrast Agent for Site-Selective Solid Tumor Imaging in Pre-Clinical Models

Small organic dye-based fluorescent agents are highly potent in solid tumor imaging but face challenges such as poor photostability, nonspecific distribution, low circulation, and weak tumor binding. Nanocarriers overcome these issues with better physicochemical and biological performance, particularly in cancer imaging. Among the various nanosized carriers, lipid formulations are clinically approved but yet to be designed as bright nanocontrast agents for solid tumor diagnosis without affecting surrounding tissues. Herein, indocyanine green (ICG) encapsulated targetable lipid nanoparticles (698 ICG/LNPs) as safe contrast agents (∼200 nm) have been developed and tested for solid tumor imaging and biodistribution. Our findings reveal that nanoprecipitation produces ICG-LNPs with a unique assembly, which contributes to their high brightness with improved quantum yield (3.5%) in aqueous media. The bright, optically stable (30 days) biophotonic agents demonstrate rapid accumulation (within 1 h) and prolonged retention (for up to 168 h) at the primary tumor site, with better signal intensity following a one-time dose administration (17.7 × 109 LNP per dose). Incorporated folic acid (735 folic acid/LNPs) helps in selective tumor binding and the specific biodistribution of intravenously injected nanoparticles without affecting healthy tissues. Designed targetable ICG-LNP (634 MESF) demonstrates high-contrast fluorescence and resolution from the tumor area as compared to the targetable ICG-liposomal nanoparticles (532 MESF). Various in vitro and in vivo findings reveal that the cancer diagnostic efficacy elicited by designed bright lipid nanoparticles are comparable to reported clinically accepted imaging agents. Thus, such LNPs hold translational potential for cancer diagnosis at an early stage.

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.

Indocyanine green J-aggregate (IJA) theranostics: Challenges and opportunities

Indocyanine green is an FDA-approved fluorescent imaging dye used for determining cardiac output, hepatic function, liver blood flow, and retinal perfusion. It has been investigated preclinically in photoacoustic imaging and photothermal therapy (PTT); however, ICG photodegradation limits its biomedical applications. An aggregated form of ICG, known as J-aggregate (IJA), exhibits superior photoacoustic signals and thermal stability than the monomeric ICG. Nevertheless, IJA still suffers from low stability in the biological milieu, and short in vivo blood circulation. To address these limitations, a range of nanocarriers have been developed to enhance IJA stability and performance. This review focuses on IJA potentials and limitations, besides the recent development of IJA-loaded nanocarriers, particularly for cancer imaging and therapy.

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.

"Rigid-Flexible" Dual-Ferrocene Chimeric Nanonetwork for Simultaneous Tumor-Targeted Tracing and Photothermal/Photodynamic Therapy

There is an urgent need to develop phototherapeutic agents with imaging capabilities to assess the treatment process and efficacy in real-time during cancer phototherapy for precision cancer therapy. The safe near-infrared (NIR) fluorescent dyes have garnered significant attention and are desirable for theranostics agents. However, until now, achieving excellent photostability and fluorescence (FL) imaging capability in aggregation-caused quenching (ACQ) dyes remains a big challenge. Here, for the only FDA-approved NIR dye, indocyanine green (ICG), we developed a dual-ferrocene (Fc) chimeric nanonetwork ICG@HFFC based on the rigid-flexible strategy through one-step self-assembly, which uses rigid Fc-modified hyaluronic acid (HA) copolymer (HA-Fc) and flexible octadecylamine (ODA) bonded Fc (Fc-C18) as the delivery system. HA-Fc reserved the ability of HA to target the CD44 receptor of the tumor cell surface, and the dual-Fc region provided a rigid space for securely binding ICG through metal-ligand interaction and π-π conjugation, ensuring excellent photostability. Additionally, the alkyl chain provided flexible confinement for the remaining ICG through hydrophobic forces, preserving its FL. Thereby, a balance is achieved between outstanding photostability and FL imaging capability. In vitro studies showed improved photobleaching resistance, enhanced FL stability, and increased singlet oxygen (1O2) production efficiency in ICG@HFFC. Further in vivo results display that ICG@HFFC had good tumor tracing ability and significant tumor inhibition which also exhibited good biocompatibility.. Therefore, ICG@HFFC provides an encouraging strategy to realize simultaneous enhanced tumor tracing and photothermal/photodynamic therapy (PTT/PDT) and offers a novel approach to address the limitations of ACQ dyes.

Cavitation-on-a-Chip Enabled Size-Specific Liposomal Drugs for Selective Pharmacokinetics and Pharmacodynamics

The size of liposomal drugs has been demonstrated to strongly correlate with their pharmacokinetics and pharmacodynamics. While the microfluidic method successfully achieves the production of liposomes with well-controlled sizes across various buffer/lipid flow rate ratio (FRR) settings, any adjustments to the FRR inevitably influence the concentration, encapsulation efficiency (EE), and stability of liposomal drugs. Here we describe a controllable cavitation-on-a-chip (CCC) strategy that facilitates the precise regulation of liposomal drug size at any desired FRR. The CCC-enabled size-specific liposomes exhibited striking differences in uptake and biodistribution behaviors, thereby demonstrating distinct antitumor efficacy in both tumor-bearing animal and melanoma patient-derived organoid (PDO) models. Intriguingly, as the liposome size decreased to approximately 80 nm, the preferential accumulation of liposomal drugs in the liver transitioned to a predominant enrichment in the kidneys. These findings underscore the considerable potential of our CCC approach in influencing the pharmacokinetics and pharmacodynamics of liposomal nanomedicines.

Expanded ROS Generation and Hypoxia Reversal: Excipient-free Self-assembled Nanotheranostics for Enhanced Cancer Photodynamic Immunotherapy

The efficacy of photodynamic therapy (PDT)-related cancer therapies is significantly restricted by two irreconcilable obstacles, i.e., low reactive oxygen species (ROS) generation capability and hypoxia which constrains the immune response. Herein, this work develops a self-assembled clinical photosensitizer indocyanine green (ICG) and the HSP90 inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) nanoparticles (ISDN) without any excipient. This work discovers that the hydrophobic interaction forces between ICG and 17-DMAG promote the photostability of ICG and its intersystem crossing (ISC) process, thereby improving the ROS quantum yield from 0.112 to 0.46. Augmented ROS generation enhances PDT efficacy and further enhances immunogenic cell death (ICD) effects. 17-DMAG inhibits the HSP90/hypoxia-inducible factor 1α (HIF-1α) axis to dramatically reverse the immunosuppressive tumor microenvironment caused by PDT-aggravated hypoxia. In a mouse model of pancreatic cancer, ISDN markedly improve cytotoxic T lymphocyte infiltration and MHC I and MHC II activation, demonstrating the superior ICD effects in situ tumor and the powerful systematic antitumor immunity generation, eventually achieving vigorous antitumor and recurrence resistance. This study proposes an unsophisticated and versatile strategy to significantly improve PDT efficacy for enhancing systemic antitumor immunity and potentially extending it to multiple cancers.

Supramolecular dye nanoassemblies for advanced diagnostics and therapies

Dyes have conventionally been used in medicine for staining cells, tissues, and organelles. Since these compounds are also known as photosensitizers (PSs) which exhibit photoresponsivity upon photon illumination, there is a high desire towards formulating these molecules into nanoparticles (NPs) to achieve improved delivery efficiency and enhanced stability for novel imaging and therapeutic applications. Furthermore, it has been shown that some of the photophysical properties of these molecules can be altered upon NP formation thereby playing a major role in the outcome of their application. In this review, we primarily focus on introducing dye categories, their formulation strategies and how these strategies affect their photophysical properties in the context of photothermal and non-photothermal applications. More specifically, the most recent progress showing the potential of dye supramolecular assemblies in modalities such as photoacoustic and fluorescence imaging, photothermal and photodynamic therapies as well as their employment in photoablation as a novel modality will be outlined. Aside from their photophysical activity, we delve shortly into the emerging application of dyes as drug stabilizing agents where these molecules are used together with aggregator molecules to form stable nanoparticles.

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.

An Indocyanine Green-Based Nanocluster for Imaging Orthodox Endometriosis Lesions with Negative Contrast

Indocyanine green (ICG), as the sole near-infrared dye FDA-approved, is limited in biomedical applications because of its poor photostability, lack of targeting, and rapid removal in vivo. Herein, we presented a nanoformulation of poly-l-lysine-indocyanine green-hyaluronic acid (PIH) and demonstrated that it can image orthodox endometriosis (EM) lesions with a negative contrast. The PIH nanocluster, with an average diameter of approximately 200 nm, exhibited improved fluorescence photostability and antioxidant ability compared to free ICG. In the in vivo imaging, EM lesions were visualized, featuring apparent voids and clear boundaries. After colocalizing with the green fluorescent protein, we concluded that the contrast provided by PIH peaked at 4 h postinjection and was observable for at least 8 h. The negative contrast, clear boundaries, and enhanced observable time might be due to the low permeation of PIH to lesions and the enhanced retention on the surfaces of lesions. Thus, our findings suggest an ICG-based nanoprobe with the potential to diagnose abdominal diseases.

Natural-product-based, carrier-free, noncovalent nanoparticles for tumor chemo-photodynamic combination therapy

Cancer, with its diversity, heterogeneity, and complexity, is a significant contributor to global morbidity, disability, and mortality, highlighting the necessity for transformative treatment approaches. Photodynamic therapy (PDT) has aroused continuous interest as a viable alternative to conventional cancer treatments that encounter drug resistance. Nanotechnology has brought new advances in medicine and has shown great potential in drug delivery and cancer treatment. For precise and efficient therapeutic utilization of such a tumor therapeutic approach with high spatiotemporal selectivity and minimal invasiveness, the carrier-free noncovalent nanoparticles (NPs) based on chemo-photodynamic combination therapy is essential. Utilizing natural products as the foundation for nanodrug development offers unparalleled advantages, including exceptional pharmacological activity, easy functionalization/modification, and well biocompatibility. The natural-product-based, carrier-free, noncovalent NPs revealed excellent synergistic anticancer activity in comparison with free photosensitizers and free bioactive natural products, representing an alternative and favorable combination therapeutic avenue to improve therapeutic efficacy. Herein, a comprehensive summary of current strategies and representative application examples of carrier-free noncovalent NPs in the past decade based on natural products (such as paclitaxel, 10-hydroxycamptothecin, doxorubicin, etoposide, combretastatin A4, epigallocatechin gallate, and curcumin) for tumor chemo-photodynamic combination therapy. We highlight the insightful design and synthesis of the smart carrier-free NPs that aim to enhance PDT efficacy. Meanwhile, we discuss the future challenges and potential opportunities associated with these NPs to provide new enlightenment, spur innovative ideas, and facilitate PDT-mediated clinical transformation.

Microneedle-mediated nanomedicine to enhance therapeutic and diagnostic efficacy

Nanomedicine has been extensively explored for therapeutic and diagnostic applications in recent years, owing to its numerous advantages such as controlled release, targeted delivery, and efficient protection of encapsulated agents. Integration of microneedle technologies with nanomedicine has the potential to address current limitations in nanomedicine for drug delivery including relatively low therapeutic efficacy and poor patient compliance and enable theragnostic uses. In this Review, we first summarize representative types of nanomedicine and describe their broad applications. We then outline the current challenges faced by nanomedicine, with a focus on issues related to physical barriers, biological barriers, and patient compliance. Next, we provide an overview of microneedle systems, including their definition, manufacturing strategies, drug release mechanisms, and current advantages and challenges. We also discuss the use of microneedle-mediated nanomedicine systems for therapeutic and diagnostic applications. Finally, we provide a perspective on the current status and future prospects for microneedle-mediated nanomedicine for biomedical applications.

Dialysis-functionalized microfluidic platform for in situ formation of purified liposomes

Continuous-flow microfluidic devices have been extensively used for producing liposomes due to their high controllability and efficient synthesis processes. However, traditional methods for liposome purification, such as dialysis, gel chromatography, and ultrafiltration, are incompatible with microfluidic devices, which would dramatically restrict the efficiency of liposome synthesis. In this study, we developed a dialysis-functionalized microfluidic platform (DFMP) for in situ formation of purified drug-loaded liposomes. The device was successfully fabricated by using a high-resolution projection micro stereolithography (PμSL) 3D printer. The integrated DFMP consists of a microfluidic mixing unit, a microfluidic dialysis unit, and a dialysis membrane, enabling the liposome preparation and purification in one device. The purified ICG-loaded liposomes prepared by DFMP had a smaller size (264.01±5.34 nm to 173.93±10.71 nm) and a higher encapsulation efficiency (EE) (43.53±0.07% to 46.07±0.67%). In vivo photoacoustic (PA) imaging experiment demonstrated that ICG-loaded liposomes purified with microfluidic dialysis exhibited a stronger penetration and accumulation (2-3 folds) in tumor sites. This work provides a new strategy for one-step production of purified drug-loaded liposomes.

Cancer cell membrane-coated nanoparticles: a promising anti-tumor bionic platform

Nanoparticle (NP) drug delivery systems have shown promise in tumor therapy. However, limitations such as susceptibility to immune clearance and poor targeting in a complex intercellular environment still exist. Recently, cancer cell membrane-encapsulated nanoparticles (CCM-NPs) constructed using biomimetic nanotechnology have been developed to overcome these problems. Proteins on the membrane surface of cancer cells can provide a wide range of activities for CCM-NPs, including immune escape and homologous cell recognition properties. Meanwhile, the surface of the cancer cell membrane exhibits obvious antigen enrichment, so that CCM-NPs can transmit tumor-specific antigen, activate a downstream immune response, and produce an effective anti-tumor effect. In this review, we first provided an overview of the functions of cancer cell membranes and summarized the preparation techniques and characterization methods of CCM-NPs. Then, we focused on the application of CCM-NPs in tumor therapy. In addition, we summarized the functional modifications of cancer cell membranes and compiled the patent applications related to CCM-NPs in recent years. Finally, we proposed the future challenges and directions of this technology in order to provide guidance for researchers in this field.

Tuning Shortwave-Infrared J-aggregates of Aromatic Ring-Fused Aza-BODIPYs by Peripheral Substituents for Combined Photothermal and Photodynamic Therapies at Ultralow Laser Power

Achieving photothermal therapy (PTT) at ultralow laser power density is crucial for minimizing photo-damage and allowing for higher maximum permissible skin exposure. However, this requires photothermal agents to possess not just superior photothermal conversion efficiency (PCE), but also exceptional near-infrared (NIR) absorptivity. J-aggregates, exhibit a significant redshift and narrower absorption peak with a higher extinction coefficient. Nevertheless, achieving predictable J-aggregates through molecular design remains a challenge. In this study, we successfully induced desirable J-aggregation (λabs max : 968 nm, ϵ: 2.96×105  M-1  cm-1 , λem max : 972 nm, ΦFL : 6.2 %) by tuning electrostatic interactions between π-conjugated molecular planes through manipulating molecular surface electrostatic potential of aromatic ring-fused aza-BODIPY dyes. Notably, by controlling the preparation method for encapsulating dyes into F-127 polymer, we were able to selectively generate H-/J-aggregates, respectively. Furthermore, the J-aggregates exhibited two controllable morphologies: nanospheres and nanowires. Importantly, the shortwave-infrared J-aggregated nanoparticles with impressive PCE of 72.9 % effectively destroyed cancer cells and mice-tumors at an ultralow power density of 0.27 W cm-2 (915 nm). This phototherapeutic nano-platform, which generates predictable J-aggregation behavior, and can controllably form J-/H-aggregates and selectable J-aggregate morphology, is a valuable paradigm for developing photothermal agents for tumor-treatment at ultralow laser power density.

Integrating Fluorescence and Magnetic Resonance Imaging in Biocompatible Scaffold for Real-Time Bone Repair Monitoring and Assessment

In situ monitoring of bone tissue regeneration progression is critical for the development of bone tissue engineering scaffold. However, engineered scaffolds that can stimulate osteogenic progress and allow for non-invasive monitoring of in vivo bone regeneration simultaneously are rarely reported. Based on a hard-and-soft integration strategy, a multifunctional scaffold composed of 3D printed microfilaments and a hydrogel network containing simvastatin (SV), indocyanine green-loaded superamphiphiles, and aminated ultrasmall superparamagnetic iron oxide nanoparticles (USPIO-NH2 ) is fabricated. Both in vitro and in vivo results demonstrate that the as-prepared scaffold significantly promotes osteogenesis through controlled SV release. The biocomposite scaffold exhibits alkaline phosphatase-responsive near-infrared II fluorescence imaging. Meanwhile, USPIO-NH2 within the co-crosslinked nanocomposite network enables the visualization of scaffold degradation by magnetic resonance imaging. Therefore, the biocomposite scaffold enables or facilitates non-invasive in situ monitoring of neo-bone formation and scaffold degradation processes following osteogenic stimulation, offering a promising strategy to develop theranostic scaffolds for tissue engineering.

Antibody-Conjugated Polymersomes with Encapsulated Indocyanine Green J-Aggregates and High Near-Infrared Absorption for Molecular Photoacoustic Cancer Imaging

Imaging plays a critical role in all stages of cancer care from early detection to diagnosis, prognosis, and therapy monitoring. Recently, photoacoustic imaging (PAI) has started to emerge into the clinical realm due to its high sensitivity and ability to penetrate tissues up to several centimeters deep. Herein, we encapsulated indocyanine green J (ICGJ) aggregate, one of the only FDA-approved organic exogenous contrast agents that absorbs in the near-infrared range, at high loadings up to ∼40% w/w within biodegradable polymersomes (ICGJ-Ps) composed of poly(lactide-co-glycolide-b-polyethylene glycol) (PLGA-b-PEG). The small Ps hydrodynamic diameter of 80 nm is advantageous for in vivo applications, while directional conjugation with epidermal growth factor receptor (EGFR) targeting cetuximab antibodies renders molecular specificity. Even when exposed to serum, the ∼11 nm-thick membrane of the Ps prevents dissociation of the encapsulated ICGJ for at least 48 h with a high ratio of ICGJ to monomeric ICG absorbances (i.e., I895/I780 ratio) of approximately 5.0 that enables generation of a strong NIR photoacoustic (PA) signal. The PA signal of polymersome-labeled breast cancer cells is proportional to the level of cellular EGFR expression, indicating the feasibility of molecular PAI with antibody-conjugated ICGJ-Ps. Furthermore, the labeled cells were successfully detected with PAI in highly turbid tissue-mimicking phantoms up to a depth of 5 mm with the PA signal proportional to the amount of cells. These data show the potential of molecular PAI with ICGJ-Ps for clinical applications such as tumor margin detection, evaluation of lymph nodes for the presence of micrometastasis, and laparoscopic imaging procedures.

Indocyanine-Green-Loaded Liposomes for Photodynamic and Photothermal Therapies: Inducing Apoptosis and Ferroptosis in Cancer Cells with Implications beyond Oral Cancer

Oral cancer represents a global health burden, necessitating novel therapeutic strategies. Photodynamic and photothermal therapies using indocyanine green (ICG) have shown promise due to their distinctive near-infrared (NIR) light absorption characteristics and FDA-approved safety profiles. This study develops ICG-loaded liposomes (Lipo-ICGs) to further explore their potential in oral cancer treatments. We synthesized and characterized the Lipo-ICGs, conducted in vitro cell culture experiments to assess cellular uptake and photodynamic/photothermal effects, and performed in vivo animal studies to evaluate their therapeutic efficacy. Quantitative cell apoptosis and gene expression variation were further characterized using flow cytometry and RNA sequencing, respectively. Lipo-ICGs demonstrated a uniform molecular weight distribution among particles. The in vitro studies showed a successful internalization of Lipo-ICGs into the cells and a significant photodynamic treatment effect. The in vivo studies confirmed the efficient delivery of Lipo-ICGs to tumor sites and successful tumor growth inhibition following photodynamic therapy. Moreover, light exposure induced a time-sensitive photothermal effect, facilitating the further release of ICG, and enhancing the treatment efficacy. RNA sequencing data showed significant changes in gene expression patterns upon Lipo-ICG treatment, suggesting the activation of apoptosis and ferroptosis pathways. The findings demonstrate the potential of Lipo-ICGs as a therapeutic tool for oral cancer management, potentially extending to other cancer types.

Indocyanine Green-Loaded Liposomes-Assisted Photoacoustic Computed Tomography for Evaluating In Vivo Tumor Penetration of Liposomal Nanocarriers

Liposomes possess the potential to enhance drug solubility, prolong the duration of circulation, and augment drug accumulation at the tumor site through passive and active targeting strategies. However, there is a lack of studies examining the in vivo tumor penetration capabilities of liposomes of varying sizes, which hampers the development of drug delivery systems utilizing liposomal nanocarriers. Here, we present an indocyanine green (ICG)-loaded liposomes-assisted photoacoustic computed tomography (PACT) for directly evaluating the tumor penetration ability of liposomal nanocarriers in vivo. Through the utilization of microfluidic mixing combined with extrusion techniques, we successfully prepare liposomes encapsulating ICG in both large (192.6 ± 8.0 nm) and small (61.9 ± 0.6 nm) sizes. Subsequently, we designed a dual-wavelength PACT system to directly monitor the in vivo tumor penetration of large- and small-size ICG-encapsulated liposomes. In vivo PACT experiments indicate that ICG-loaded liposomes of smaller size exhibit enhanced penetration capability within tumor tissues. Our work presents a valuable approach to directly assess the penetration ability of liposomal nanocarriers in vivo, thereby facilitating the advancement of drug delivery systems with enhanced tumor penetration and therapeutic efficacy.

Near-infrared light activatable niosomes loaded with indocyanine green and plasmonic gold nanorods for theranostic applications

Light-mediated theranostic platforms involve the use of agents (small molecules/nanomaterials), which can absorb light to produce either heat or reactive chemical species (RCS) and emit fluorescence. Such platforms are advantageous in the field of personalized medicine, as they provide enhanced diagnostic capabilities, improved therapeutic efficiencies, and can also simultaneously monitor the treatment outcomes using imaging modalities. Specifically, agents absorbing near-infrared (NIR) light can provide minimal scattering, low autofluorescence, superior spatio-temporal resolution, and deeper tissue penetration depths. Gold nanorods (GNR) and indocyanine green (ICG) are two agents known to absorb light in the NIR region. GNR can provide tunable plasmonic properties, while ICG is an FDA-approved NIR fluorophore. However, the use of ICG and GNR suffers from various limitations, such as photobleaching, non-specificity, toxicity, and aggregation in solution. To overcome these limitations, herein, we report on NIR light-activatable niosomes loaded with GNR and ICG for cancer theranostic applications. Both agents were encapsulated into non-ionic surfactant-based biocompatible niosomes to form ICG-GNR@Nio with superior loading efficiencies and enhanced properties. ICG-GNR@Nio offers excellent storage stability, photostability, elevated temperature rise and generation of reactive oxygen species (ROS) upon 1064 nm laser irradiation. Subsequently, the enhanced phototherapeutic capabilities mediated by ICG-GNR@Nio were validated in the in vitro cellular experiments. Overall, ICG-GNR@Nio-based theranostic platforms can provide a significant benchmark in the improved diagnosis and therapeutic capabilities for biomedical clinicians to tackle various diseases.

Electron-Withdrawing Substituents Allow Boosted NIR-II Fluorescence in J-Type Aggregates for Bioimaging and Information Encryption

Developing molecular fluorophores with enhanced fluorescence in aggregate state for the second near-infrared (NIR-II) imaging is highly desirable but remains a tremendous challenge due to the lack of reliable design guidelines. Herein, we report an aromatic substituent strategy to construct highly bright NIR-II J-aggregates. Introduction of electron-withdrawing substituents at 3,5-aryl and meso positions of classic boron dipyrromethene (BODIPY) skeleton can promote slip-stacked J-type arrangement and further boost NIR-II fluorescence of J-aggregates via increased electrostatic repulsion and intermolecular hydrogen bond interaction. Notably, NOBDP-NO2 with three nitro groups (-NO2 ) shows intense NIR-II fluorescence at 1065 nm and high absolute quantum yield of 3.21 % in solid state, which can be successfully applied in bioimaging, high-level encoding encryption, and information storage. Moreover, guided by this electron-withdrawing substituent strategy, other skeletons (thieno-fused BODIPY, aza-BODIPY, and heptamethine cyanine) modified with -NO2 are converted into J-type aggregates with enhanced NIR-II fluorescence, showing great potential to convert aggregation caused emission quenching (ACQ) dyes into brilliant J-aggregates. This study provides a universal method for construction of strong NIR-II emissive J-aggregates by rationally manipulating molecular packing and establishing relationships among molecular structures, intermolecular interactions, and fluorescence properties.

Near-infrared-II photoacoustic imaging and photo-triggered synergistic treatment of thrombosis via fibrin-specific homopolymer nanoparticles

The formation of an occlusive thrombus in the blood vessel is the main culprit for numerous life-threatening cardiovascular diseases that represent the leading cause of morbidity and mortality worldwide. Herein, we develop a polymer nanoplatform that integrates long-wavelength second near-infrared (NIR-II) photoacoustic imaging-based thrombosis detection and antithrombotic activity. We design and synthesize a semiconducting homopolymer with strong absorption in the NIR-II region and molecular motion that boosts photothermal conversion and photoacoustic signal. We dope the homopolymer with a thermosensitive nitric oxide donor to formulate a nanoplatform, on which a fibrin-specific ligand is functionalized to ensure selective thrombus targeting. We show that with strong NIR-II light harvesting capability, bright photoacoustic signal and active thrombus accumulation ability, the NIR-II photoacoustic nanoprobes are able to sensitively and selectively delineate thrombi. We find that the nanoplatform also displays rapid and efficient blood clot removal activity with nearly complete blood flow restoration in both carotid thrombosis models and low extremity arterial thrombosis models under NIR-II light trigger by integrating a thrombus-localized photothermal effect and on-demand nitric oxide release. This nanoplatform offers a versatile approach for the diagnosis and treatment of life-threatening diseases caused by various thrombotic disorders.

Enhanced stability and photothermal efficiency of Indocyanine Green J-aggregates by nanoformulation with Calix[4]arene for photothermal therapy of cancers

Photothermal therapy (PTT) is a method of growing attention, owing to its controllable process, high efficiency and minimal side effect. Indocyanine Green (ICG) is as Food and Drug Administration (FDA) approved agent that stands on the frontline of further developments of PTT toward clinics. However, the applicability of ICG-mediated PTT is limited by the rapid in vivo clearance and photo-degradation of ICG. To improve those parameters, nanosized ICG-loaded nanoparticles (ICG-J/CX) were fabricated in this study by co-assembly of anionic ICG J-aggregates (ICG-J) with cationic tetraguanidinium calix[4]arene (CX). This very simple approach produces ICG-J/CX with a well-defined nanometer range size and a close to neutral charge. The nanoparticles demonstrate high photothermal conversion efficiency (PCE) and dramatically improved photostability, as compared with ICG. The in vitro cellular uptake and cytotoxicity studies further demonstrated that the ICG-J/CX nanoparticles enhance uptake and photothermal efficiency in comparison with ICG or non-formulated ICG-J, overall demonstrating that ICG-J/CX mediated photothermal therapy have significant potential for attaining cancer treatment.

Assembly of fluorophore J-aggregates with nanospacer onto mesoporous nanoparticles for enhanced photoacoustic imaging

Many fluorophores, such as indocyanine green (ICG), have poor photostability and low photothermal efficiency hindering their wide application in photoacoustic (PA) tomography. In the present study, a supramolecular assembly approach was used to develop the hybrid nanoparticles (Hy NPs) of ICG and porous silicon (PSi) as a novel contrast agent for PA tomography. ICG was assembled on the PSi NPs to form J-aggregates within 30 min. The Hy NPs presented a red-shifted absorption, improved photothermal stability, and enhanced PA performance. Furthermore, 1-dodecene (DOC) was assembled into the NPs as a 'nanospacer', which enhanced non-radiative decay for increased thermal release. Compared to the Hy NPs, adding DOC into the Hy NPs (DOC-Hy) increased the PA signal by 83%. Finally, the DOC-Hy was detectable in PA tomography at 1.5 cm depth in tissue phantom even though its concentration was as low as 6.25 µg/mL, indicating the potential for deep tissue PA imaging.

Photo-Induced Electron Transfer-Triggered Structure Deformation Promoting Near-Infrared Photothermal Conversion for Tumor Therapy

Photothermal therapy (PTT) is a promising approach to cancer treatment. Heptamethine cyanine (Cy7) is an attractive photothermal reagent because of its large molar absorption coefficient, good biocompatibility, and absorption of near-infrared irradiation. However, the photothermal conversion efficiency (PCE) of Cy7 is limited without ingenious excitation-state regulation. In this study, the photothermal conversion ability of Cy7 is efficiently enhanced based on photo-induced electron transfer (PET)-triggered structural deformation. Three Cy7 derivatives, whose Cl is replaced by carbazole, phenoxazine, and phenothiazine at the meso-position (CZ-Cy7, PXZ-Cy7, and PTZ-Cy7), are presented as examples to demonstrate the regulation of the energy release of the excited states. Because the phenothiazine moiety exhibits an obvious PET-induced structural deformation in the excited state, which quenches the fluorescence and inhibits intersystem crossing of S1 →T1 , PTZ-Cy7 exhibits a PCE as high as 77.5%. As a control, only PET occurs in PXZ-Cy7, with a PCE of 43.5%. Furthermore, the PCE of CZ-Cy7 is only 13.0% because there is no PET process. Interestingly, PTZ-Cy7 self-assembles into homogeneous nanoparticles exhibiting passive tumor-targeting properties. This study provides a new strategy for excited-state regulation for photoacoustic imaging-guided PTT with high efficiency.

Orderly Self-Assembly of Organic Fluorophores for Sensing and Imaging

Fluorescence imaging utilizing traditional organic fluorophores is extensively applied in both cellular and in vivo studies. However, it faces significant obstacles, such as low signal-to-background ratio (SBR) and spurious positive/negative signals, primarily due to the facile diffusion of these fluorophores. To cope with this challenge, orderly self-assembled functionalized organic fluorophores have gained significant attention in the past decades. These fluorophores can create nanoaggregates via a well-ordered self-assembly process, thus prolonging their residency time within cells and in vivo settings. The development of self-assembled-based fluorophores is an emerging field, and as such, in this review, we present a summary of the progress and challenges of self-assembly fluorophores, focusing on their development history, self-assembly mechanisms, and biomedical applications. We hope that the insights provided herein will assist scientists in further developing functionalized organic fluorophores for in situ imaging, sensing, and therapy.

Medical Applications and Advancement of Near Infrared Photosensitive Indocyanine Green Molecules

Indocyanine green (ICG) is an important kind of near infrared (NIR) photosensitive molecules for PTT/PDT therapy as well as imaging. When exposed to NIR light, ICG can produce reactive oxygen species (ROS), which can kill cancer cells and pathogenic bacteria. Moreover, the absorbed light can also be converted into heat by ICG molecules to eliminate cancer cells. In addition, it performs exceptionally well in optical imaging-guided tumor therapy and antimicrobial therapy due to its deeper tissue penetration and low photobleaching properties in the near-infrared region compared to other dyes. In order to solve the problems of water and optical stability and multi-function problem of ICG molecules, composite nanomaterials based on ICG have been designed and widely used, especially in the fields of tumors and sterilization. So far, ICG molecules and their composite materials have become one of the most famous infrared sensitive materials. However, there have been no corresponding review articles focused on ICG molecules. In this review, the molecular structure and properties of ICG, composite material design, and near-infrared light- triggered anti-tumor, and antibacterial, and clinical applications are reviewed in detail, which of great significance for related research.

Contrast-Enhanced Multispectral Optoacoustic Tomography for Functional Assessment of the Gastrointestinal Tract

Real-time imaging and functional assessment of the intestinal tract and its transit pose a significant challenge to conventional clinical diagnostic methods. Multispectral optoacoustic tomography (MSOT), a molecular-sensitive imaging technology, offers the potential to visualize endogenous and exogenous chromophores in deep tissue. Herein, a novel approach using the orally administered clinical-approved fluorescent dye indocyanine green (ICG) for bedside, non-ionizing evaluation of gastrointestinal passage is presented. The authors are able to show the detectability and stability of ICG in phantom experiments. Furthermore, ten healthy subjects underwent MSOT imaging at multiple time points over eight hours after ingestion of a standardized meal with and without ICG. ICG signals can be visualized and quantified in different intestinal segments, while its excretion is confirmed by fluorescent imaging of stool samples. These findings indicate that contrast-enhanced MSOT (CE-MSOT) provides a translatable real-time imaging approach for functional assessment of the gastrointestinal tract.

Anti-Quenching NIR-II J-Aggregates of Benzo[c]thiophene Fluorophore for Highly Efficient Bioimaging and Phototheranostics

Molecular fluorophores with the second near-infrared (NIR-II) emission hold great potential for deep-tissue bioimaging owing to their excellent biocompatibility and high resolution. Recently, J-aggregates are used to construct long-wavelength NIR-II emitters as their optical bands show remarkable red shifts upon forming water-dispersible nano-aggregates. However, their wide applications in the NIR-II fluorescence imaging are impeded by the limited varieties of J-type backbone and serious fluorescence quenching. Herein, a bright benzo[c]thiophene (BT) J-aggregate fluorophore (BT6) with anti-quenching effect is reported for highly efficient NIR-II bioimaging and phototheranostics. The BT fluorophores are manipulated to have Stokes shift over 400 nm and aggregation-induced emission (AIE) property for conquering the self-quenching issue of the J-type fluorophores. Upon forming BT6 assemblies in an aqueous environment, the absorption over 800 nm and NIR-II emission over 1000 nm are boosted for more than 41 and 26 folds, respectively. In vivo visualization of the whole-body blood vessel and imaging-guided phototherapy results verify that BT6 NPs are excellent agent for NIR-II fluorescence imaging and cancer phototheranostics. This work develops a strategy to construct bright NIR-II J-aggregates with precisely manipulated anti-quenching properties for highly efficient biomedical applications.

Nanostructured organic photosensitizer aggregates in disease phototheranostics

Aggregate science provides promising opportunities for the discovery of novel disease phototheranostics. Under the guidance of aggregology and the Jablonski energy level diagram, photosensitizer aggregates with tunable photophysical properties can consequently result in tailorable diagnosis and treatment modalities. This review summarizes recent advances in the formation of nanostructured organic photosensitizer aggregates, their photophysical processes (e.g., radiative emission, vibrational relaxation, and intersystem crossing), and particularly, their applications in disease phototheranostics such as fluorescence imaging and sensing, photothermal therapy, photoacoustic imaging, and photodynamic therapy. It is expected that this comprehensive summary will provide guidance for the construction of nanostructured organic photosensitizer aggregates, for establishment of aggregation-photophysical property relationships and the development of novel disease phototheranostic nanomedicines. Teaser: This article reviews the electron-delocalized π system-caused formation of nanostructured organic photosensitizer aggregates, which undergo radiative emission, vibrational relaxation, or intersystem crossing pathways to achieve fluorescence imaging and sensing, photothermal therapy, photoacoustic imaging, and photodynamic therapy.

Biobased Agents for Single-Particle Detection with Optoacoustics

Optoacoustic (OA, photoacoustic) imaging synergistically combines rich optical contrast with the resolution of ultrasound within light-scattering biological tissues. Contrast agents have become essential to boost deep-tissue OA sensitivity and fully exploit the capabilities of state-of-the-art OA imaging systems, thus facilitating the clinical translation of this modality. Inorganic particles with sizes of several microns can also be individually localized and tracked, thus enabling new applications in drug delivery, microrobotics, or super-resolution imaging. However, significant concerns have been raised regarding the low bio-degradability and potential toxic effects of inorganic particles. Bio-based, biodegradable nano- and microcapsules consisting of an aqueous core with clinically-approved indocyanine green (ICG) and a cross-linked casein shell obtained in an inverse emulsion approach are introduced. The feasibility to provide contrast-enhanced in vivo OA imaging with nanocapsules as well as localizing and tracking individual larger microcapsules of 4-5 µm is demonstrated. All components of the developed capsules are safe for human use and the inverse emulsion approach is known to be compatible with a variety of shell materials and payloads. Hence, the enhanced OA imaging performance can be exploited in multiple biomedical studies and can open a route to clinical approval of agents detectable at a single-particle level.

A Photoacoustic Contrast Nanoagent with a Distinct Spectral Signature for Ovarian Cancer Management

Photoacoustic imaging (PAI) has tremendous potential for improving ovarian cancer detection. However, the lack of effective exogenous contrast agents that can improve PAI diagnosis accuracy significantly limits this application. This study presents a novel contrast nanoagent with a specific spectral signature that can be easily distinguished from endogenous chromophores in cancer tissue, allowing for high-contrast tumor visualization. Constructed as a 40 nm biocompatible polymeric nanoparticle loaded with two naphthalocyanine dyes, this agent is capable of efficient ovarian tumor accumulation after intravenous injection. The developed nanoagent displays a spectral signature with two well-separated photoacoustic peaks of comparable PA intensities in the near-infrared (NIR) region at 770 and 860 nm, which remain unaffected in cancer tissue following systemic delivery. In vivo experiments in mice with subcutaneous and intraperitoneal ovarian cancer xenografts validate that this specific spectral signature allows for accurate spectral unmixing of the nanoagent signal from endogenous contrast in cancer tissue, allowing for sensitive noninvasive cancer diagnosis. In addition, this nanoagent can selectively eradicate ovarian cancer tissue with a single dose of photothermal therapy by elevating the intratumoral temperature to ≈49 °C upon exposure to NIR light within the 700-900 nm range.