Donor-acceptor conjugated polymer-based nanoparticles for highly effective photoacoustic imaging and photothermal therapy in the NIR-II window

Laparoscopic hepatectomy using indocyanine green attenuates postoperative inflammatory response for hepatocellular carcinoma: A propensity score matching analysis

BACKGROUND

Improving the intraoperative and postoperative performance of laparoscopic hepatectomy was quite a challenge for liver surgeons.

AIM

To determine the benefits of indocyanine green (ICG) fluorescence imaging in patients with hepatocellular carcinoma (HCC) who underwent laparoscopic hepatectomy during and after surgery.

METHODS

We retrospectively collected the clinicopathological data of 107 patients who successfully underwent laparoscopic hepatectomy at Zhongshan Hospital (Xiamen), Fudan University from June 2022 to June 2023. Whether using the ICG fluorescence imaging technique, we divided them into the ICG and non-ICG groups. To eliminate statistical bias, a 1:1 propensity score matching analysis was conducted. The comparison of perioperative outcomes, including inflammation-related markers and progression-free survival, was analyzed statistically.

RESULTS

Intraoperatively, the ICG group exhibited lower blood loss, a shorter surgical time, lower hepatic inflow occlusion (HIO) frequency, and a shorter total HIO time. Postoperatively, the participation of ICG resulted in a shorter duration of hospitalization (6.5 vs 7.6 days, P = 0.03) and postoperative inflammatory response attenuation (lower neutrophil-lymphocyte ratio on the first day after surgery and platelet-lymphocyte ratio on the third day, P < 0.05). Although the differences were not significant, the levels of all inflammation-related markers were lower in the ICG group. The rates of postoperative complications and the survival analyses, including progression-free and overall survivals showed no significant difference between the groups.

CONCLUSION

The involvement of ICG fluorescence imaging may lead to improved perioperative outcomes, especially postoperative inflammatory response attenuation, and ultimately improve HCC patients' recovery after surgery.

Rational Design of NIR-II Emitting Conjugated Polymer Derived Nanoparticles for Image-Guided Cancer Interventions

Due to the reduced absorption, light scattering, and tissue autofluorescence in the NIR-II (1000-1700 nm) region, significant efforts are underway to explore diverse material platforms for in vivo fluorescence imaging, particularly for cancer diagnostics and image-guided interventions. Of the reported imaging agents, nanoparticles derived from conjugated polymers (CPNs) offer unique advantages to alternative materials including biocompatibility, remarkable absorption cross-sections, exceptional photostability, and tunable emission behavior independent of cell labeling functionalities. Herein, the current state of NIR-II emitting CPNs are summarized and structure-function-property relationships are highlighted that can be used to elevate the performance of next-generation CPNs. Methods for particle processing and incorporating cancer targeting modalities are discussed, as well as detailed characterization methods to improve interlaboratory comparisons of novel materials. Contemporary methods to specifically apply CPNs for cancer diagnostics and therapies are then highlighted. This review not only summarizes the current state of the field, but offers future directions and provides clarity to the advantages of CPNs over other classes of imaging agents.

A NIR-II absorbing conjugated polymer based on tetra-fused isoindigo with ultrahigh photothermal conversion efficiency for cancer therapy

A conjugated polymer, P4TTD-DPP, based on tetra-fused isoindigo-alt-diketopyrrolopyrrole, has been synthesized as a photothermal therapeutic nanotransducer within the near-infrared-II (NIR-II) window. P4TTD-DPP exhibits a notable mass extinction coefficient of 62.8 L g-1 cm-1 at 1064 nm. Additionally, P4TTD-DPP nanoparticles demonstrate remarkable photothermal conversion efficiency of 91.5% at 1064 nm and exhibit excellent anticancer efficacy under photothermal conditions.

Contrast-enhanced near-infrared photoacoustic microscopy and optical coherence tomography imaging of rat fundus

In this paper, we design a multimodal visible/near-infrared photoacoustic microscopy and optical coherence tomography (VIS/NIR-PAM-OCT) system for imaging both retina and retinal pigment epithelium (RPE)/choroid complex layer. F127 and DSPE-PEG-cRGD encapsulated IR-1048 nanoparticles (FINPs) exhibiting absorption peak up to 1,064 nm were utilized as contrast agents to enhance NIR-PAM for in vivo imaging of fundus tissues. The fundus structure and vessels are clearly visualized by the multimodal imaging, and their parameters were quantitatively analyzed. NIR-PAM and OCT imaging of fundus were time-serially monitored over 60 min following the intravenous injection of FINPs into rats. The results indicated a 134 % increase in image signals in PAM at 1 min, along with an 8.23 % intensity enhancement in OCT. Moreover, laser-induced choroidal neovascularization (CNV) was specifically detected and accurately quantified using VIS/NIR-PAM-OCT. Lastly, FINPs demonstrated excellent biocompatibility in hematology analysis and pathology testing.

Semiconducting Polymers Based on Asymmetric Thiadiazoloquinoxaline for Augmented In Vivo NIR-II Photoacoustic Imaging

A photoacoustic (PA) imaging technique using the second near-infrared (NIR-II) window has attracted more and more attention because of its merits of deeper penetration depth and higher signal-to-noise (S/N) ratio than that using the first near-infrared (NIR-I) one. However, the design and development of high-performance PA imaging contrast agents in the NIR-II window is still a challenge. A semiconducting polymer, constructed by asymmetric units, exhibits regiorandom characteristics that effectively increase the distortion of the backbone. This increase in the degree of twist can regulate the twisted intramolecular charge transfer (TICT) effect, resulting in an enhancement of the PA signal. In this paper, an asymmetric structural acceptor strategy is developed to improve the PA signals of the resulting semiconducting polymer (PATQ-MP) in the NIR-II window with improved brightness, higher S/N ratio, and better photothermal conversion efficiency compared to polymers with the same main-chain structure containing a symmetric acceptor. DFT analysis showed that PATQ-MP containing an asymmetric acceptor monomer had a larger dihedral angle, which effectively improved the PA signal intensity by enhancing the TICT effect. The PEG-encapsulated PATQ-MP nanoparticles exhibit promising performance in the PA imaging of mouse tumors in vivo, demonstrating the clear identification of microvessels as small as 100 μm along with rapid metabolism within a span of 5 h. Therefore, this work provides a unique molecular design strategy for improving the signal intensity of PA imaging in the NIR-II window.

Small-Molecule Phototheranostic Agent with Extended π-Conjugation for Efficient NIR-II Photoacoustic-Imaging-Guided Photothermal Therapy

Photoacoustic imaging (PAI) and photothermal therapy (PTT) conducted over the near-infrared-II (NIR-II) window offer the benefits of noninvasiveness and deep tissue penetration. This necessitates the development of highly effective therapeutic agents with NIR-II photoresponsivity. Currently, the predominant organic diagnostic agents used in NIR-II PAI-guided PTT are conjugated polymeric materials. However, they exhibit a low in vivo clearance rate and long-term biotoxicity, limiting their clinical translation. In this study, an organic small molecule (CY-1234) with NIR-II absorption and nanoencapsulation (CY-1234 nanoparticles (NPs)) for PAI-guided PTT is reported. Extended π-conjugation is achieved in the molecule by introducing donor-acceptor units at both ends of the molecule. Consequently, CY-1234 exhibits a maximum absorption peak at 1234 nm in tetrahydrofuran. Nanoaggregates of CY-1234 are synthesized via F-127 encapsulation. They exhibit an excellent photothermal conversion efficiency of 76.01% upon NIR-II light irradiation. After intravenous injection of CY-1234 NPs into tumor-bearing mice, strong PA signals and excellent tumor ablation are observed under 1064 nm laser irradiation. This preliminary study can pave the way for the development of small-molecule organic nanoformulations for future clinical applications.

Progress of NIR-II fluorescence imaging technology applied to disease diagnosis and treatment

Near-infrared two-region (NIR-II, 1000-1700 nm) fluorescence imaging has received widespread attention because of its high in vivo penetration depth, high imaging resolution, fast imaging speed and high efficiency, dynamic imaging, and high clinical translatability. This paper reviews the application of NIR-II imaging technology in disease diagnosis and treatment. The paper highlights the latest research progress of commonly used NIR-II imaging materials and the latest progress of multifunctional diagnostic platforms based on NIR-II imaging technology, and discusses the challenges and directions for the development and utilization of novel NIR-II imaging probes.

Isoindigo-Based Dual-Acceptor Conjugated Polymers Incorporated Conjugation Length and Intramolecular Charge Transfer for High-Efficient Photothermal Conversion

Photothermal tumor therapy (PTT) and photoacoustic imaging (PA) have emerged as promising noninvasive diagnostic and therapeutic approaches for cancer treatment. However, the development of efficient PTT agents with high photostability and strong near-infrared (NIR) absorption remains challenging. This study synthesizes three isoindigo-based dual-acceptor conjugated polymers (CPs) (P-IIG-TPD, P-IIG-DPP, and P-IIG-EDOT-BT) via a green and nontoxic direct arylation polymerization (DArP) method and characterizes their optical, electrochemical, and NIR photothermal conversion properties. By incorporating two acceptors into the backbone, the resulting polymers exhibit enhanced photothermal conversion efficiency (PCE) due to improved synergy among conjugation length, planarity, and intramolecular charge transfer (ICT). The nanoparticles (NPs) of P-IIG-EDOT-BT and P-IIG-DPP have a uniform size distribution around 140 nm and exhibit remarkable NIR absorption at 808 nm. In addition, P-IIG-EDOT-BT and P-IIG-DPP NPs exhibit high PCEs of 62% and 78%, respectively. This study promotes the molecular design of CPs as NIR photothermal conversion materials and provides guidance for the development of novel dual-acceptor CPs for tumor diagnosis and treatment.

Novel Application of NIR-I-Absorbing Quinoidal Conjugated Polymer as a Photothermal Therapeutic Agent

Conjugated polymer nanoparticles (CP NPs) that could absorb the first near-infrared (NIR-I) window have emerged as highly desirable therapeutic nanomaterials. Here, a quinoidal-conjugated polymer (QCP), termed PQ, was developed as a novel class of therapeutic agents for photothermal therapy (PTT). Owing to its intrinsic quinoid structure, PQ exhibits molecular planarity and π-electron overlap along the conjugated backbone, endowing it with a narrow band gap, NIR-I absorption, and diradical features. The obtained PQ was coated with a poly(ethylene glycol) (PEG) moiety, affording nanosized and water-dispersed PQ nanoparticles (PQ NPs), which consequently show a high photothermal conversion efficiency (PCE) of 63.2%, good photostability, and apparent therapeutic efficacy for both in vitro and in vivo PTTs under an 808 nm laser irradiation. This study demonstrates that QCPs are promising active agents for noninvasive anticancer therapy using NIR-I light.

Colloidal antibiotic mimics: selective capture and killing of microorganisms by shape-anisotropic colloids

The development of targeted and efficient antimicrobials for the selective killing of pathogenic bacteria is of great importance, yet remains challenging. Here, we propose a targeted approach to selectively capture and kill microorganisms with colloidal antibiotic mimics that are readily prepared by common chemical syntheses. The mimics are shape-anisotropic colloids, which can selectively capture shape-matching microorganisms due to lock-key depletion attractions. Furthermore, after being modified with gold nanoparticles (AuNPs) and irradiated with near-infrared light, the colloidal mimics can kill the selectively captured microorganisms due to the localized photothermal effect of the AuNPs. The work demonstrates the important ability of anisotropic colloids to selectively capture and precisely kill microorganisms, which holds considerable promise for safe and adaptive antibacterial therapies without the risk of antibiotic resistance.

Conjugated Polymer Nanoparticles for Tumor Theranostics

Water-dispersible conjugated polymer nanoparticles (CPNs) have demonstrated great capabilities in biological applications, such as in vitro cell/subcellular imaging and biosensing, or in vivo tissue imaging and disease treatment. In this review, we summarized the recent advances of CPNs used for tumor imaging and treatment during the past five years. CPNs with different structures, which have been applied to in vivo solid tumor imaging (fluorescence, photoacoustic, and dual-modal) and treatment (phototherapy, drug carriers, and synergistic therapy), are discussed in detail. We also demonstrated the potential of CPNs as cancer theranostic nanoplatforms. Finally, we discussed current challenges and outlooks in this field.

Biocompatible Polymer Nano-Constructs: A Potent Platform for Cancer Theranostics

Nano-constructs of biocompatible polymers have drawn wide attention owing to their potential as theranostics for simultaneous therapy and detection of cancer. The present mini review summarizes various nano-architectures of polymers that have been developed as theranostic agents for the simultaneous treatment and diagnosis of cancer in a single platform. Additionally, research prospects of polymeric cancer theranostics for the future have been highlighted.

Soft nano and microstructures for the photomodulation of cellular signaling and behavior

Photoresponsive soft materials are everywhere in the nature, from human's retina tissues to plants, and have been the inspiration for engineers in the development of modern biomedical materials. Light as an external stimulus is particularly attractive because it is relatively cheap, noninvasive to superficial biological tissues, can be delivered contactless and offers high spatiotemporal control. In the biomedical field, soft materials that respond to long wavelength or that incorporate a photon upconversion mechanism are desired to overcome the limited UV-visible light penetration into biological tissues. Upon light exposure, photosensitive soft materials respond through mechanisms of isomerization, crosslinking or cleavage, hyperthermia, photoreactions, electrical current generation, among others. In this review, we discuss the most recent applications of photosensitive soft materials in the modulation of cellular behavior, for tissue engineering and regenerative medicine, in drug delivery and for phototherapies.

Impairing proliferation of glioblastoma multiforme with CD44+ selective conjugated polymer nanoparticles

Glioblastoma is one of the most aggressive types of cancer with success of therapy being hampered by the existence of treatment resistant populations of stem-like Tumour Initiating Cells (TICs) and poor blood-brain barrier drug penetration. Therapies capable of effectively targeting the TIC population are in high demand. Here, we synthesize spherical diketopyrrolopyrrole-based Conjugated Polymer Nanoparticles (CPNs) with an average diameter of 109 nm. CPNs were designed to include fluorescein-conjugated Hyaluronic Acid (HA), a ligand for the CD44 receptor present on one population of TICs. We demonstrate blood-brain barrier permeability of this system and concentration and cell cycle phase-dependent selective uptake of HA-CPNs in CD44 positive GBM-patient derived cultures. Interestingly, we found that uptake alone regulated the levels and signaling activity of the CD44 receptor, decreasing stemness, invasive properties and proliferation of the CD44-TIC populations in vitro and in a patient-derived xenograft zebrafish model. This work proposes a novel, CPN- based, and surface moiety-driven selective way of targeting of TIC populations in brain cancer.

Looking deep inside tissue with photoacoustic molecular probes: a review

Significance

Deep tissue noninvasive high-resolution imaging with light is challenging due to the high degree of light absorption and scattering in biological tissue. Photoacoustic imaging (PAI) can overcome some of the challenges of pure optical or ultrasound imaging to provide high-resolution deep tissue imaging. However, label-free PAI signals from light absorbing chromophores within the tissue are nonspecific. The use of exogeneous contrast agents (probes) not only enhances the imaging contrast (and imaging depth) but also increases the specificity of PAI by binding only to targeted molecules and often providing signals distinct from the background.

Aim

We aim to review the current development and future progression of photoacoustic molecular probes/contrast agents.

Approach

First, PAI and the need for using contrast agents are briefly introduced. Then, the recent development of contrast agents in terms of materials used to construct them is discussed. Then, various probes are discussed based on targeting mechanisms, in vivo molecular imaging applications, multimodal uses, and use in theranostic applications.

Results

Material combinations are being used to develop highly specific contrast agents. In addition to passive accumulation, probes utilizing activation mechanisms show promise for greater controllability. Several probes also enable concurrent multimodal use with fluorescence, ultrasound, Raman, magnetic resonance imaging, and computed tomography. Finally, targeted probes are also shown to aid localized and molecularly specific photo-induced therapy.

Conclusions

The development of contrast agents provides a promising prospect for increased contrast, higher imaging depth, and molecularly specific information. Of note are agents that allow for controlled activation, explore other optical windows, and enable multimodal use to overcome some of the shortcomings of label-free PAI.

Gold-seaurchin based immunomodulator enabling photothermal intervention and αCD16 transfection to boost NK cell adoptive immunotherapy

Despite huge potentials of NK cells in adoptive cell therapy (ACT), formidable physical barriers of the tumor tissue and deficiency of recognizing signals on tumor cells severely prevent NK cell infiltrating, activating and killing performances. Herein, a nano-immunomodulator AuNSP@αCD16 (CD16 antibody encoding plasmid) is explored to remodel the tumor microenvironment (TME) for improving the antitumor effects of adoptive NK cells. The as-prepared AuNSP, with a seaurchin-like gold core and a cationic polymer shell, exhibited a high gene transfection efficiency and a stable NIR-II photothermal capacity. The AuNSP could trigger mild photothermal intervention to partly destroy tumors and collapse the dense physical barriers, making a permeable TME for NK cell infiltration. What's more, the AuNSP could achieve αCD16 gene transfection to modify tumor surface with CD16 antibody, marking a unique structure on tumor cells for NK cell recognition and then lead to strong NK cell activation by CD16-mediated antibody-dependent cellular cytotoxicity (ADCC). As expected, the designed AuNSP@αCD16 induced an immune-favorable TME for NK cell performing killing functions against solid tumors, increasing the release of cytolytic granules and proinflammatory cytokines, which ultimately achieved a robustly boosted NK cell-based immunotherapy. Hence, the AuNSP@αCD16-mediated TME reconstituting strategy provides a substantial perspective for NK-based ACT on solid tumors. STATEMENT OF SIGNIFICANCE: In adoptive cell therapy (ACT), natural killer (NK) cells exhibit greater off-the-shelf utility and improved safety comparing with T cells, but the efficacy of NK cell therapy is severely compromised by formidable physical barriers of the tumor tissue and deficiency of NK cell recognizing signals on tumor cells. Herein, a nano-immunomodulator AuNSP@αCD16, with the abilities of inducing mild photothermal intervention and modifying the tumor cell surface with αCD16, is explored to reconstruct an infiltration-favorable and activation-facilitating tumor microenvironment for NK cells to perform killing functions. Such a simple and safe strategy is believed as a very promising candidate for future NK-based ACT.

An AIPH-decorated semiconducting nanoagonist for NIR-II light-triggered photothermic/thermodynamic combinational therapy

A multifunctional semiconducting nanoagonist with high photothermic conversion efficiency (86.2%) and alkyl radical generation ability was developed. The nanoagonist demonstrated excellent anticancer performance through NIR-II light-triggered photothermic/thermodynamic combinational therapy both in vitro and in vivo.

Synthesis of Donor–Acceptor Copolymers Derived from Diketopyrrolopyrrole and Fluorene via Eco-Friendly Direct Arylation: Nonlinear Optical Properties, Transient Absorption Spectroscopy, and Theoretical Modeling

A series of PFDPP copolymers based on fluorene (F) and diketopyrrolopyrrole (DPP) monomers were synthesized via direct arylation polycondensation using Fagnou conditions which involved palladium acetate as catalyst (a gradual catalyst addition of three different percentages were used), potassium carbonate as the base, and neodecanoic acid in N, N-dimethylacetamide. This synthesis provides a low cost compared with traditional methods of transition-metal-catalyzed polymerization. Among the different amounts of catalyst used in the present work, 12% was optimal because it gave the highest reaction yield (81.5%) and one of the highest molecular weights (Mn = 13.8 KDa). Copolymers’ chemical structures, molecular weight distributions, and optical and thermal properties were analyzed. The linear optical properties of PFDPP copolymers resulted very similarly independently to the catalyst amounts used in the synthesis of the PFDPP copolymers: two absorptions bands distinctive of donor–acceptor copolymers, Stokes shifts of 41 nm, a good quantum yield of fluorescence around 47%, and an optical bandgap of 1.7 eV were determined. Electronic nonlinearities were observed in these copolymers with a relatively high two-photon absorption cross-section of 621 GM at 950 nm. The dynamics of excited states and aggregation effects were studied in solutions, nanoparticles, and films of PFDPP. Theoretical calculations modeled the ground-state structures of the (PFDPP)n copolymers with n = 1 to 4 units, determining the charge distribution by the electrostatic potential and modeling the absorption spectra determining the orbital transitions responsible for the experimentally observed leading bands. Experimental and theoretical structure–properties analysis of these donor–acceptor copolymers allowed finding their best synthesis conditions to use them in optoelectronic applications.

Vehicle-Free Nanotheranostic Self-Assembled from Clinically Approved Dyes for Cancer Fluorescence Imaging and Photothermal/Photodynamic Combinational Therapy

Phototherapy, including photothermal therapy (PTT) and photodynamic therapy (PDT) has attracted growing attention as a noninvasive option for cancer treatment. At present, researchers have developed various "all-in-one" nanoplatforms for cancer imaging and PTT/PDT combinational therapy. However, the complex structure, tedious preparation procedures, overuse of extra carriers and severe side effects hinder their biomedical applications. In this work, we reported a nanoplatform (designated as ICG-MB) self-assembly from two different FDA-approved dyes of indocyanine green (ICG) and methylene blue (MB) without any additional excipients for cancer fluorescence imaging and combinational PTT/PDT. ICG-MB was found to exhibit good dispersion in the aqueous phase and improve the photostability and cellular uptake of free ICG and MB, thus exhibiting enhanced photothermal conversion and singlet oxygen (1O2) generation abilities to robustly ablate cancer cells under 808 nm and 670 nm laser irradiation. After intravenous injection, ICG-MB effectively accumulated at tumor sites with a near-infrared (NIR) fluorescence signal, which helped to delineate the targeted area for NIR laser-triggered phototoxicity. As a consequence, ICG-MB displayed a combinational PTT/PDT effect to potently inhibit tumor growth without causing any system toxicities in vivo. In conclusion, this minimalist, effective and biocompatible nanotheranostic would provide a promising candidate for cancer phototherapy based on current available dyes in clinic.

Benzobisthiadiazole and Its Derivative-Based Semiconducting Polymer Nanoparticles for Second Near-Infrared Photoacoustic Imaging

Photoacoustic (PA) imaging has received more and more attention on disease diagnosis and fundamental scientific research. It is still challenging to amplify their imaging ability and reduce the toxicity of inorganic materials and exogenous contrast agents. Semiconducting polymer nanoparticles (SPNs), as a new type of contrast agent, have the advantages of low toxicity, flexible structure adjustment, good photostability, and excellent photothermal conversion efficiency. SPNs containing benzo(1,2-c;4,5-c′)bis(1,2,5)thiadiazole (BBT) units, as the most classic second near-infrared window (NIR-II, 1,000–1700 nm) PA contrast agents, can achieve light absorption in the NIR-II region, thereby effectively reducing light loss in biological tissues and improving imaging resolution. This mini review summarizes the recent advances in the design strategy of BBT and its derivative-based semiconducting polymer nanoparticles for second near-infrared photoacoustic imaging. The evolution process of BBT blocks provides a unique perspective for the design of high-performance NIR-II PA contrast agents.

Peptide-based semiconducting polymer nanoparticles for osteosarcoma-targeted NIR-II fluorescence/NIR-I photoacoustic dual-model imaging and photothermal/photodynamic therapies

Background

The overall survival rate of osteosarcoma (OS) patients has not been improved for 30 years, and the diagnosis and treatment of OS is still a critical issue. To improve OS treatment and prognosis, novel kinds of theranostic modalities are required. Molecular optical imaging and phototherapy, including photothermal therapy (PTT) and photodynamic therapy (PDT), are promising strategies for cancer theranostics that exhibit high imaging sensitivity as well as favorable therapeutic efficacy with minimal side effect. In this study, semiconducting polymer nanoparticles (SPN-PT) for OS-targeted PTT/PDT are designed and prepared, using a semiconducting polymer (PCPDTBT), providing fluorescent emission in the second near-infrared window (NIR-II, 1000 - 1700 nm) and photoacoustic (PA) signal in the first near-infrared window (NIR-I, 650 - 900 nm), served as the photosensitizer, and a polyethylene glycolylated (PEGylated) peptide PT, providing targeting ability to OS.

Results

The results showed that SPN-PT nanoparticles significantly accelerated OS-specific cellular uptake and enhanced therapeutic efficiency of PTT and PDT effects in OS cell lines and xenograft mouse models. SPN-PT carried out significant anti-tumor activities against OS both in vitro and in vivo.

Conclusions

Peptide-based semiconducting polymer nanoparticles permit efficient NIR-II fluorescence/NIR-I PA dual-modal imaging and targeted PTT/PDT for OS.

Graphic Abstract

NIR-II Functional Materials for Photoacoustic Theranostics

Photoacoustic imaging (PAI) has attracted great attention in the diagnosis and treatment of diseases due to its noninvasive properties. Especially in the second near-infrared (NIR-II) window, PAI can effectively avoid the interference of tissue spontaneous fluorescence and light scattering, and obtain high resolution images with deeper penetration depth. Because of its ideal spectral absorption and high conversion efficiency, NIR-II PA contrast agents overcome the absorption or emission of NIR-II light by endogenous biomolecules. In recent years, a series of NIR-II PA contrast agents have been developed to improve the performance of PAI in disease diagnosis and treatment. In this paper, the research progress of NIR-II PA contrast agents and their applications in biomedicine are reviewed. PA contrast agents are classified according to their composition, including inorganic contrast agents, organic contrast agents, and hybrid organic-inorganic contrast agents. The applications of NIR-II PA contrast agents in medical imaging are described, such as cancer imaging, inflammation detection, brain disease imaging, blood related disease imaging, and other biomedical application. Finally, the research prospects and breakthrough of NIR-II PA contrast agents are discussed.

Electron-acceptor density adjustments for preparation conjugated polymers with NIR-II absorption and brighter NIR-II fluorescence and 1064 nm active photothermal/gas therapy

Designing conjugated polymers (CPs) with both efficient second near-infrared wavelength (NIR-II) fluorescence and NIR-II photothermal therapy performance remains a huge challenge, as the introduction of excessively strong electron donor and acceptor units significantly increase non-radiative decay. Herein, we describe an "electron acceptor density adjustment" strategy to address this problem, since a lower electron acceptor density in the conjugated polymer backbone can enhance the radiative rate constant and improve NIR-II fluorescence brightness. We used quaterthiophene (4T) with four repeated thiophene chain units and bithiophene (2 TC) modified with long alkyl side chains to reduce the electron acceptor density in the conjugated polymer backbone. The resultant 1064 nm absorption polymer, TTQ-2TC-4T displayed approximately 7.30-folds enhancement in NIR-II emission intensity compared to that of undoped TTQ-1T at the same mass concentration in toluene solution. Furthermore nanoparticles (TTQ-MnCO NPs) based on TTQ-2TC-4T and CO donors (Mn₂(CO)₁₀) were developed to realize NIR-II FI-guided 1064 nm laser-triggered NIR-II PTT/Gas synergistic therapy. The TTQ-MnCO NPs nanoparticles exhibited high photothermal conversion efficiency (η) of 44.43% at 1064 nm and high specific NIR-II fluorescence imaging of the cerebral vasculature of live mice. The in vivo results demonstrate that TTQ-MnCO NPs nanoparticles have excellent PTT/Gas synergistic therapeutic effects in MCF-7 tumor-bearing mice under 1064 nm laser irradiation. This study provides a new approach for optimizing both NIR-II fluorescence and NIR-II photothermal performance of NIR-II absorption conjugated polymers.

The Chemistry of Organic Contrast Agents in the NIR-II Window

Optical imaging, especially fluorescence and photoacoustic imaging, possesses non-invasiveness, high spatial and temporal resolution, and high sensitivity, etc., compared to positron emission tomography (PET) or magnetic resonance imaging (MRI). Due to the merits from the second near infrared (NIR-II) window imaging, like deeper penetration depth, high signal-to-noise ratio, high resolution, and low tissue damage, researchers devote great efforts to develop contrast agents with NIR-II absorption or emission. In this review, we summarized recently developed organic luminescent and photoacoustic materials, ranging from small molecules to conjugated polymers. Then, we systematically introduced engineering strategies and their imaging performance, classified by the skeleton cores. Finally, we elucidated the challenges and prospective of these NIR-II organic dyes for potential clinical applications. We hope our summary can inspire further development of NIR-II contrast agents.

Biodegradable Polyimidazole Particles as Contrast Agents Produced by Direct Arylation Polymerization

Conjugated polymer particles provide an important platform for the development of theranostic nanoagents. However, the number of biocompatible and foremost biodegradable π-conjugated polymers is limited. Imidazole is a π-conjugated motif that is abundant in biological systems. Oxidative degradation of imidazole is present in nature via enzymatic or free radical processes. In this work, we introduce polymer particles consisting purely of polyimidazole. We employ direct arylation polymerization and adapt it to a dispersion polymerization protocol to yield uniform and narrowly dispersed nanoparticles. We employ this mechanism to produce linear and cross-linked polymer particles to tune the optical properties from fluorescent to photoacoustically active. We show that the particles can be degraded by H₂O₂ as well as by reactive oxygen species produced by cells and we detect the degradation products. Altogether, our results suggest that polyimidazole particles represent ideal candidates for theranostic applications.

NIR-II Organic Nanotheranostics for Precision Oncotherapy

Precision oncotherapy can remove tumors without causing any apparent iatrogenic damage or irreversible side effects to normal tissues. Second near-infrared (NIR-II) nanotheranostics can simultaneously perform diagnostic and therapeutic modalities in a single nanoplatform, which exhibits prominent perspectives in tumor precision treatment. Among all NIR-II nanotheranostics, NIR-II organic nanotheranostics have shown an exceptional promise for translation in clinical tumor treatment than NIR-II inorganic nanotheranostics in virtue of their good biocompatibility, excellent reproducibility, desirable excretion, and high biosafety. In this review, recent progress of NIR-II organic nanotheranostics with the integration of tumor diagnosis and therapy is systematically summarized, focusing on the theranostic modes and performances. Furthermore, the current status quo, problems, and challenges are discussed, aiming to provide a certain guiding significance for the future development of NIR-II organic nanotheranostics for precision oncotherapy.

Recent Progress on NIR-II Photothermal Therapy

Photothermal therapy is a very promising treatment method in the field of cancer therapy. The photothermal nanomaterials in near-infrared region (NIR-I, 750-900 nm) attracts extensive attention in recent years because of the good biological penetration of NIR light. However, the penetration depth is still not enough for solid tumors due to high tissue scattering. The light in the second near-infrared region (NIR-II, 1000-1700 nm) allows deeper tissue penetration, higher upper limit of radiation and greater tissue tolerance than that in the NIR-I, and it shows greater application potential in photothermal conversion. This review summarizes the photothermal properties of Au nanomaterials, two-dimensional materials, metal oxide sulfides and polymers in the NIR-II and their application prospects in photothermal therapy. It will arouse the interest of scientists in the field of cancer treatment as well as nanomedicine.

A remotely controlled NIR-II photothermal-sensitive transgene system for hepatocellular carcinoma synergistic therapy

Photothermal therapy (PTT) exhibits an excellent therapeutic effect in cancer treatment, but some cancers are still facing rapid recurrence due to the presence of heat-resistant cells, which express heat shock proteins (HSP) to defend against hyperthermia. Inspired by optogenetics, we firstly designed a caged TNF-related apoptosis-inducing ligand (TRAIL) expressing plasmid under HSP70 protomer (HSP70-TRAIL) as the thermal-activated gene therapy agent to induce the apoptosis of heat resistant cells. Then, the caged HSP70-TRAIL was decorated on the surface of the photothermal agent (semiconducting nanoparticles, SPNs) through electrostatic adsorption to obtain SPN@HSP70-TRAIL-GFP (SPNHT). Under 1064 nm near-infrared second region (NIR-II) laser irradiation, the SPNHT acted as an emerging photothermal agent for PTT. Importantly, the caged HSP70-TRAIL could be further activated by PTT to express TRAIL on demand to concurrently kill survival cells for overcoming the problem of tumor recurrence after PTT. Both in vitro and in vivo studies demonstrated that the SPNHT nano-system with the ability of NIR-II photothermal-triggered TRAIL in situ expression possessed an admirable synergistic anti-cancer efficacy for HCC. This work offers new tactics for effective treatment of cancer, which showed a great significance for reducing the rate of cancer recurrence after PTT treatment.

Tumor Microenvironment Triggered Cascade-Activation Nanoplatform for Synergistic and Precise Treatment of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and deadliest malignancy cancers, which remains a major global health problem. At present, over 50% of patients with HCC have implemented systemic therapies, such as interventional therapy or local chemotherapy that are scarcely effective and induce serious side effects to the remaining normal liver, further limiting their clinical outcomes. Herein, a tumor microenvironment triggered cascade-activation nanoplatform (A-NPLap/TPZ ) is prepared based on β-lapachone (β-Lap) and tirapazamine (TPZ) for the synergistic therapy of HCC. The A-NPLap/TPZ exerts its targeting effect by binding to the receptor of tumor cells with an external aptamer. In the tumor microenvironment, the nanoplatform can realize H2 O2 -triggered disassembly to release β-Lap and TPZ. The released β-Lap generates ROS to induce tumor cell apoptosis under the catalysis of the tumor cell over-expressed NAD(P)H-quinone oxidoreductase-1 (NQO1) enzyme. In this process, oxygen is consumed to intensify tumor hypoxia, and eventually cascade activates TPZ to exert the anti-tumor effect. The studies in vitro and in vivo consistently demonstrate that the as-prepared A-NPLap/TPZ nanoplatform possesses an excellent synergistic anti-tumor effect. This design of nanoplatform with cascade activation effect provides a promising strategy for HCC treatment.

In vivo Multi-scale Photoacoustic Imaging Guided Photothermal Therapy of Cervical Cancer based on Customized Laser System and Targeted Nanoparticles

BACKGROUND

Effective treatment strategy for cervical carcinoma is subject to the limitation of its anatomical location and histological characteristics. Comprehensive imaging before cervical carcinoma treatment is of great significance for the patients. Current imaging methods cannot meet the requirements of high resolution, deep imaging depth and non-invasive imaging at the same time. Fortunately, Photoacoustic imaging (PAI) is a novel imaging method that combines rich optical contrast, high ultrasonic spatial resolution, and deep penetration depth in a single modality. Moreover, PAI-guided photothermal therapy (PTT) by aid of targeting nanoparticles is an emerging and effective cancer treatment in recent years.

METHODS

Here, strong near-infrared region (NIR) absorption-conjugated polymer PIIGDTS (PD) nanoparticles with folic acid (FA) modification (namely, PD-FA) that targeted at Hela cell were specifically designed as cervical tumor imaging contrast agents and photothermal agents.

RESULTS

The obtained PD-FA nanoparticles exhibited admirable photoacoustic contrast-enhancing ability and desirable PTT behavior with the photothermal conversion efficiency as high as 62.6% in vitro. Furthermore, the PAI performance and PTT efficiency were tested in HeLa tumor-bearing nude mice after injection of PD-FA nanoparticles. In vivo multi-scale, PAI provided B-san and 3D dimension imaging for intuitive and comprehensive information of Hela tumor. Moreover, the Hela tumor can be completely eliminated within 18 days after PTT, with no toxicity and side effects.

CONCLUSION

In summary, PD-FA injection combined with PAI and PTT systems provides a novel powerful tool for early diagnosis and precise treatment of cervical cancer.

Strategy for Achieving Long-Wavelength Near-Infrared Luminescence of Diimineplatinum(II) Complexes

Although many strategies have been used to help design effective near-infrared (NIR) luminescent materials, it is still a huge challenge to realize long-wavelength NIR luminescence of diimineplatinum(II) complexes in the solid state. Herein, we have successfully achieved long-wavelength NIR luminescence of a family of diimineplatinum(II) complexes based on a new strategy that combines a one-dimensional (1D) "Pt wire" structure with the electronic effect of the substituent. The structures of six solvated diimineplatinum(II) complexes based on 4,4-dichloro-2,2'-bipyridine or 4,4-dibromo-2,2'-bipyridine and 4-substituted phenylacetylene ligands have been determined, namely, 1·¹/₂toluene, 2·¹/₂THF, 3·¹/₈toluene, 4·¹/₂THF, 5·¹/₈CH₂Cl₂, and 6·¹/₄toluene. All of them crystallize in the monoclinic space group C2/c or C2/m and stack in the 1D "Pt wire" structure. In the solid state, six complexes exhibited unusual long-wavelength metal-metal-to-ligand charge-transfer luminescence that peaked at 984, 1044, 972, 990, 1022, and 935 nm, respectively. Interestingly, 2·¹/₂THF has the shortest Pt···Pt distance and the longest emission wavelength among the six complexes. As far as we know, the luminescence of 2·¹/₂THF at 1044 nm is the longest emission wavelength among known diimineplatinum(II) complexes. Systematic studies revealed that good molecular planarity, suitable substituent position, weak hydrogen-bond-forming ability of the substituents, appropriate molecular bending, and weakening of the interaction between solvated molecules and platinum molecules are conducive to the construction of a 1D "Pt wire" structure of the diimineplatinum(II) complex. Furthermore, the emission energy of the complex is mainly determined by the strength of the Pt-Pt interaction and electronic effect of the substituent.

Photoacoustic Imaging and Photothermal Therapy of Semiconducting Polymer Nanoparticles: Signal Amplification and Second Near-Infrared Construction

Photoacoustic (PA) imaging and photothermal therapy (PTT) have attracted extensive attention in disease diagnosis and treatment. Although many exogenous contrast agents have been developed for PA imaging and PTT, the design guidelines to amplify their imaging and therapy performances remain challenging and are highly demanded. Semiconducting polymer nanoparticles (SPNs) composed of polymers with π-electron delocalized backbones can be designed to amplify their PA imaging and PTT performance, because of their clear structure-property relation and versatility in modifying their molecular structures to tune their photophysical properties. This review summarizes the recent advances in the photoacoustic imaging and photothermal therapy applications of semiconducting polymer nanoparticles with a focus on signal amplification and second near-infrared (NIR-II, 1000-1700 nm) construction. The strategies such as structure-property screening, fluorescence quenching, accelerated heat dissipation, and size-dependent heat dissipation are first discussed to amplify the PA brightness of SPNs for in vivo PA. The molecular approaches to shifting the absorption of SPNs for NIR-II PA imaging and PTT are then introduced so as to improve the tissue penetration depth for diagnosis and therapy. At last, current challenges and perspectives of SPNs in the field of imaging and therapy are discussed.

Localized NIR-II photo-immunotherapy through the combination of photothermal ablation and in situ generated interleukin-12 cytokine for efficiently eliminating primary and abscopal tumors

Recently, photothermal therapy (PTT) in the second near-infrared (NIR-II) biowindow has emerged as a promising treatment modality; however, its therapeutic outcomes are still limited by heterogeneous heat distribution and insufficient control of metastatic lesions. Tremendous efforts have been made to overcome the PTT's shortcomings by combining PTT with immunotherapy, but unfortunately current strategies still suffer from low response rates, primary/acquired resistance or severe immune-related adverse events. Herein, a novel photothermal agent and gene co-delivery nanoparticle (CSP), with CuS inside the SiO2 pore channels and PDMAEMA polycation on the outside of SiO2 surface, is explored for tumor localized NIR-II PTT and in situ immunotherapy through local generation of IL-12 cytokine. The resulting CSP integrated with the plasmid encoding IL-12 gene (CSP@IL-12) exhibited good gene transfection efficiency, outstanding NIR-II PTT effect and excellent therapeutic outcomes both in vitro and in vivo. Meanwhile, such an in situ joint therapy modality could significantly induce systemic immune responses including promoting DC maturation, CD8+ T cell proliferation and infiltration to efficiently eliminate possible metastatic lesions through abscopal effects. Hence, this creative combinational strategy of NIR-II PTT and IL-12 cytokine therapy might provide a more efficient, controllable and safer alternative strategy for future photo-immunotherapy.

Double-acceptor conjugated polymers for NIR-II fluorescence imaging and NIR-II photothermal therapy applications

Nanoparticles based double-acceptor conjugated polymers were developed by conventional methods. And subsequently NPs with bright NIR-II fluorescence signals and superior NIR-II PTT efficiency were successfully applied for NIR-II FI guided NIR-II PTT.

Second near-infrared photothermal materials for combinational nanotheranostics

This review summarizes the recent development of second near-infrared photothermal combinational nanotheranostics for cancer, infectious diseases and regenerative medicine.

Another decade of photoacoustic imaging

Photoacoustic imaging - a hybrid biomedical imaging modality finding its way to clinical practices. Although the photoacoustic phenomenon was known more than a century back, only in the last two decades it has been widely researched and used for biomedical imaging applications. In this review we focus on the development and progress of the technology in the last decade (2010-2020). From becoming more and more user friendly, cheaper in cost, portable in size, photoacoustic imaging promises a wide range of applications, if translated to clinic. The growth of photoacoustic community is steady, and with several new directions researchers are exploring, it is inevitable that photoacoustic imaging will one day establish itself as a regular imaging system in the clinical practices.

Preparation, Biosafety, and Cytotoxicity Studies of a Newly Tumor-Microenvironment-Responsive Biodegradable Mesoporous Silica Nanosystem Based on Multimodal and Synergistic Treatment

Patients with triple negative breast cancer (TNBC) often suffer relapse, and clinical improvements offered by radiotherapy and chemotherapy are modest. Although targeted therapy and immunotherapy have been a topic of significant research in recent years, scientific developments have not yet translated to significant improvements for patients with TNBC. In view of these current clinical treatment shortcomings, we designed a silica nanosystem (SNS) with Nano-Ag as the core and a complex of MnO₂ and doxorubicin (Dox) as the surrounding mesoporous silica shell. This system was coated with anti-PD-L1 to target the PD-L1 receptor, which is highly expressed on the surface of tumor cells. MnO₂ itself has been shown to act as chemodynamic therapy (CDT), and Dox is cytotoxic. Thus, the full SNS system presents a multimodal, potentially synergistic strategy for the treatment of TNBC. Given potential interest in the clinical translation of SNS, the biological safety and antitumor activity of SNS were evaluated in a series of studies that included physicochemical characterization, particle stability, blood compatibility, and cytotoxicity. We found that the particle size and zeta potential of SNS were 94.6 nm and -22.1 mV, respectively. Ultraviolet spectrum analysis showed that Nano-Ag, Dox, and MnO₂ were successfully loaded into SNS, and the drug loading ratio of Dox was about 10.2%. Stability studies found that the particle size of SNS did not change in different solutions. Hemolysis tests showed that SNS, at levels far exceeding the anticipated physiologic concentrations, did not induce red blood cell lysis. Further in vitro and in vivo experiments found that SNS did not activate platelets or cause coagulopathy and had no significant effects on the total number of blood cells or hepatorenal function. Cytotoxicity experiments suggested that SNS significantly inhibited the growth of tumor cells by damaging cell membranes, increasing intracellular ROS levels, inhibiting the release of TGF-β1 cytokines by macrophages, and inhibiting intracellular protein synthesis. In general, SNS appeared to have favorable biosafety and antitumor effects and may represent an attractive new therapeutic approach for the treatment of TNBC.

A thieno-isoindigo derivative-based conjugated polymer nanoparticle for photothermal therapy in the NIR-II bio-window

Photothermal therapy (PTT), a powerful tool for non-invasive cancer treatment, has been recognized as an alternative strategy for cancer therapy in the clinic, and it is promoted by optical absorbing agents (photothermal agents) that can intensively convert near-infrared (NIR) light into thermal energy for cancer ablation. Conjugated polymer nanoparticles (CPNs) have recently attracted extensive attention owing to their excellent photothermal properties. However, the absorption of typical CPNs is mostly located in the traditional near-infrared region (NIR-I, 700-900 nm), which suffers from low tissue penetration, so the penetration depth is still limited and severely restricts their further applications. Compared with the NIR-I light, the second near-infrared window light (NIR-II, 1000-1700 nm) could efficiently enhance the tissue penetration depth, however, CPNs which absorb NIR-II region light are still especially limited and need further exploration. Here, a thieno-isoindigo derivative-based Donor-Acceptor (D-A) polymer (BTPBFDTS), which exhibited excellent absorption characteristics from the NIR-I to NIR-II window, was prepared. After formation of nanoparticles and surface functionalization, the prepared nanoparticles (NPsBTPBFDTS@HA NPs) exhibited obvious targeting ability, high photothermal conversion efficiency and photoacoustic imaging effects under 1064 nm irradiation. Both in vitro and in vivo studies demonstrate that our obtained NPsBTPBFDTS@HA nanoparticles possess excellent PTT efficacy including extremely high cancer cell killing ability and admirable tumor elimination efficiency. Hence, this work developed a promising photothermal conversion agent based on CPNs for cancer ablation.

Nano-delivery vehicle based on chlorin E6, photodynamic therapy, doxorubicin chemotherapy provides targeted treatment of HER-2 negative, ανβ3-positive breast cancer

The prognosis for patients with HER-2 negative breast cancer is currently poor, largely due to the lack of efficacious targeted therapeutics. Photodynamic nanomaterial technologies have rapidly developed in recent years, but their anti-tumor effects are often limited by poor targeting, low transformation efficiency, toxicity, and other factors. Thus, we prepared a new type of nanoparticles (Ce6/Dox@NPs-cRGD, CDNR) with cyclo(Arg-Gly-Asp-d-Phe-Cys) (c(RGDfC)) that target the ανβ3 receptor. We loaded those nanoparticles (NPs) with a combination of the doxorubicin (Dox) and photosensitizer chlorin E6 (Ce6) to test synergy between chemotherapy and photodynamic therapy (PDT) for the treatment of ανβ3 receptor positive and HER-2 negative breast cancer. Through analysis of the Fourier transform infrared and UV-vis spectra of these NPs, we found that Ce6 and Dox were successfully loaded into the CDNR. According to dynamic light scattering (DLS) analyses, CDNR particles had a diameter of 112.6 nm (polydispersity index 0.11), which was also confirmed via TEM characterization. The zeta potential was about -21.5 mV. Stability studies showed that CDNR particle size was stable in ddH₂O, PBS, and DMEM + 5 % FBS for 16 days. The drug loading content of Dox and Ce6 were 5.3 and 6.8 %, respectively. Release studies of CDNR showed that the slow release of Dox was accelerated with increasing GSH concentration, and there was no burst release effect. From studying the absorbance of 9,10-dimethylanthrancene (ABDA), we found that CDNR produces high levels of ROS after excitation with a 670 nm laser, and ROS production increased with increasing radiation time. CDNR was significantly taken up by MCF-7 cells at 6 h because of cRGD targeting. In a CCK8 test, the relative growth rate (RGR) of CDNR +670 nm laser for MCF-7 cells was less than 75 % at 20 μg/mL after 24 h treatment and 15 μg/mL after 48 h treatment. We found that CDNR's effects on RGR were concentration dependent. Live-cell staining with a DCFH-DA kit and flow cytometry assay further supported that a CDNR +670 nm laser provided the maximum chemotherapy-PDT toxicity and production of intracellular ROS, and that cell death was mainly caused by necrosis and apoptosis. In vivo experiments showed that using the cRGD-targeting strategy, CDNR had a stronger affinity and increased half-life relative to Ce6/Dox@NPs in mice with MCF-7 xenograft tumors. Further, the C_max of CDNR in the transplanted tumor occurred 8 h post-injection (HPI) and there was still detectable signal at 24 HPI. In addition, MCF-7 bearing mice that were treated with CDNR +670 nm PDT at 8 HPI had a significantly decreased tumor volume (P < 0.05) and prolonged survival time compared to other groups. Thus, CDNR plus 670 nm PDT was associated with favorable anti-tumor activity with no appreciable impact on body weight or the major organs in mice, as determined by immunohistochemistry/immunofluorescence and hematoxylin-eosin staining. In conclusion, CDNR with 670 nm laser irradiation represents a promising new potential treatment paradigm for the management of breast cancers that are ανβ3-receptor positive and HER-2 negative.

Intelligent Hybrid Hydrogels for Rapid In Situ Detection and Photothermal Therapy of Bacterial Infection

Diseases induced by bacterial infections increasingly threaten the health of people all over the world; thus, it is urgent and significant to early diagnose and effectively eliminate infections to save people's lives. To this end, we synthesized an intelligent hydrogel that integrated in situ visualized diagnosis and photothermal therapy of bacterial infections. By simply and subtly incorporating pH-sensitive bromothymol blue (BTB) and near-infrared (NIR)-absorbing conjugated polymer (termed as PTDBD) into thermosensitive chitosan (CS)-based hydrogel, the synthesized BTB/PTDBD/CS hydrogel can diagnose the acidic microenvironment of Staphylococcus aureus (S. aureus) biofilm and infected wounds by showing visualized color change. After rapid diagnosis, the hydrogel can immediately treat the infection site by local hyperthermia under irradiation of NIR laser (808 nm) and even the stubborn biofilm that is difficult to eradicate. Since the dominating antibacterial mechanism is hyperthermia, the hybrid hydrogel shows broad-spectrum antibacterial activity against Gram-positive, Gram-negative, and drug-resistant bacteria. In addition, it has low cytotoxicity to normal cells and no effect on the main organs of mice. It paves a brand new avenue to develop smart and facile diagnosis and a treatment platform for bacterial infections.