Diketopyrrolopyrrole-Based Semiconducting Polymer Nanoparticles for In Vivo Photoacoustic Imaging

Boosting Photoacoustic Effect via Intramolecular Motions Amplifying Thermal-to-Acoustic Conversion Efficiency for Adaptive Image-Guided Cancer Surgery

Photoacoustic (PA) imaging emerges as a promising technique for biomedical applications. The development of new strategies to boost PA conversion without depressing other properties (e.g., fluorescence) is highly desirable for multifunctional imaging but difficult to realize. Here, we report a new phenomenon that active intramolecular motions could promote PA signal by specifically increasing thermal-to-acoustic conversion efficiency. The compound with intense intramolecular motion exhibits amplified PA signal by elevating thermal-to-acoustic conversion, and the fluorescence also increases due to aggregation-induced emission signature. The simultaneously high PA and fluorescence brightness of TPA-TQ3 NPs enable precise image-guided surgery. The preoperative fluorescence and PA imaging are capable of locating orthotopic breast tumor in a high-contrast manner, and the intraoperative fluorescence imaging delineates tiny residual tumors. This study highlights a new design guideline of intramolecular motion amplifying PA effect.

Recent progress in near-infrared photoacoustic imaging

The emergence of the photoacoustic imaging (PAI) expands the application of biomolecules bioimaging in cells, various tissues, and living body to monitor multiple physiological processes in complex internal environments. The PAI possesses intriguing properties such as non-invasive, highly selective excitation, and weak signal attenuation. Especially, the near-infrared (NIR) PAI displays low optical absorption and scattering, good temporal or spatial resolution and deep penetration, holds great potential in biomedical applications. We briefly compare different imaging modalities to provide a comprehensive understanding of their characteristics and related applications, highlighting the feature of the PAI. The principle of PAI is then delineated and the emerging NIR-PAI is discussed. We then focus on elaboration of the recent achievement of typical NIR-PAI contrast and their biomedical applications, especially the strategies used to improve contrast rational design and PAI performance are summarized. The PAI-related multimodal imaging approaches for improving imaging accuracy are also covered in the review. Finally, the challenges and prospective are pointed out for attracting more researchers to accelerate the development of PAI.

The usage of composite nanomaterials in biomedical engineering applications

Nanotechnology is still developing over the decades and it is commonly used in biomedical applications with the design of nanomaterials due to the several purposes. With the investigation of materials on the molecular level has increased the develop composite nanomaterials with exceptional properties using in different applications and industries. The application of these composite nanomaterials is widely used in the fields of textile, chemical, energy, defense industry, electronics, and biomedical engineering which is growing and developing on human health. Development of biosensors for the diagnosis of diseases, drug targeting and controlled release applications, medical implants and imaging techniques are the research topics of nanobiotechnology. In this review, overview of the development of nanotechnology and applications which is use of composite nanomaterials in biomedical engineering is provided.

A Diradicaloid Small Molecular Nanotheranostic with Strong Near-Infrared Absorbance for Effective Cancer Photoacoustic Imaging and Photothermal Therapy

Organic small molecule-based phototheranostics hold great promise for clinical translation by virtue of their distinct chemical structure, easy reproducibility, and high purity. However, reported molecular agents typically have relatively low optical absorbances, particularly over the near-infrared (NIR) region, and this limits their phototheranostic performance. Herein, we first exploit a diradicaloid molecular structure for enhancing NIR absorption to facilitate efficient photoacoustic imaging (PAI)-guided photothermal therapy (PTT). The donor-acceptor interaction in the diradicaloid molecule (DRM) leads to strong charge transfer resulting on obvious diradical characteristics, which is beneficial for NIR absorption. The DRM possesses excellent light-harvesting ability, with a mass extinction coefficient of ∼220 L g^-1 cm^-1, which is much higher than those (∼5-100 L g^-1 cm^-1) of typical organic molecules. After assembling into nanoparticles, they show good water dispersibility, good photostability, and impressive performance for PAI-guided PTT in vitro and in vivo. The impressive in vitro and in vivo performances show that developing small molecules with diradicaloid structures can be an effective approach for enhancing NIR harvesting capability for biomedical applications.

Recent Developments in Semiconducting Polymer Dots for Analytical Detection and NIR-II Fluorescence Imaging

In recent years, semiconducting polymer dots (Pdots) have attracted enormous attention in applications from fundamental analytical detection to advanced deep-tissue bioimaging due to their ultrahigh fluorescence brightness with excellent photostability and minimal cytotoxicity. Pdots have therefore been widely adopted for a variety types of molecular sensing for analytical detection. More importantly, the recent development of Pdots for use in the optical window between 1000 and 1700 nm, popularly known as the "second near-infrared window" (NIR-II), has emerged as a class of optical transparent imaging technology in the living body. The advantages of the NIR-II region over the traditional NIR-I (700-900 nm) window in fluorescence imaging originate from the reduced autofluorescence, minimal absorption and scattering of light, and improved penetration depths to yield high spatiotemporal images for biological tissues. Herein, we discuss and summarize the recent developments of Pdots employed for analytical detection and NIR-II fluorescence imaging. Starting with their preparation, the recent developments for targeting various analytes are then highlighted. After that, the importance of and latest progress in NIR-II fluorescence imaging using Pdots are reported. Finally, perspectives and challenges associated with the emergence of Pdots in different fields are given.

NIR-II bioimaging of small organic molecule

In recent years, people have been actively exploring new imaging methods with high biological imaging performance because the clinical image definition and depth in vivo cannot meet the requirements of early diagnosis and prognosis. Based on the traditional near-infrared region I (NIR-I), the molecular probe of the near-infrared region II (NIR-II) is further explored and developed. In the NIR-II region due to the wavelength is longer than the NIR-I region can effectively reduce the molecular scattering, optical absorption of the organization, the organization of spontaneous fluorescence negligible, thus the NIR-II Fluorescence imaging (FI) can get deeper penetration depth, higher signal-to-background ratio (SBR) and better spatiotemporal resolution, FI in NIR-II region are an important and rapidly developing research region for future imaging. In the NIR-II fluorophore, small organic molecule fluorophore has attracted much attention because of its good biocompatibility and good pharmacokinetic properties. In this review, we briefly introduced the existing NIR-II organic small molecule fluorophores, and introduced the existing relatively mature methods for improving quantum yield and water solubility, and the small molecule dyes on FI of various improvement methods, also briefly introduces the small molecules of photoacoustic imaging (PAI), and a brief introduction of imaging-guided surgery (IGS) for some small organic molecules, finally, a reasonable prospect is made for the development of small organic molecules.

Near-infrared small molecule coupled with rigidness and flexibility for high-performance multimodal imaging-guided photodynamic and photothermal synergistic therapy

Photodynamic therapy (PDT) synergized photothermal therapy (PTT) shows superior clinical application prospects than single PDT or PTT. On the other hand, multimodal imaging can delineate comprehensive information about the lesion site and thus help to improve therapy accuracy. However, integrating all these functions into one single molecule is challenging, let alone balancing and maximizing the efficacy of each function. Herein, a near-infrared (NIR) small molecule (ETTC) with an "acceptor-donor-acceptor" structure was designed and synthesized by coupling rigity and flexibility to simultaneously achieve NIR-II fluorescence imaging (NIR-II FLI), photoacoustic imaging, PTT and PDT. The efficacy of each functionality was well balanced and optimized (NIR-II quantum yield: 3.0%; reactive oxygen species generation: 3.2-fold higher than ICG; photothermal conversion efficiency: 52.8%), which may be attributed to the coupling of the rigid and flexible structures in ETTC to tactically manipulate the energy dissipation paths (non-radiative against radiative decay). As a proof-of-concept, under the effective guidance of local-tumor imaging by PA and whole-body imaging by NIR-II FL, complete tumor eradication was achieved via PDT and PTT combinational therapy. This work provides a novel perspective into conceiving and developing single molecule for efficient versatile biomedical applications.

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.

Different PEG-PLGA Matrices Influence In Vivo Optical/Photoacoustic Imaging Performance and Biodistribution of NIR-Emitting π-Conjugated Polymer Contrast Agents

The π-conjugated polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b0]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) with deep-red/near-infrared (NIR) absorption and emission has been investigated as a contrast agent for in vivo optical and photoacoustic imaging. PCPDTBT is encapsulated within poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG_2kDa -PLGA_4kDa or PEG_5kDa -PLGA_55kDa ) micelles or enveloped by the phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (PEG_2kDa -DPPE), to investigate the formulation effect on imaging performance, biodistribution, and biocompatibility. Nanoparticles that meet the quality requirements for parenteral administration are generated with similar physicochemical properties. Optical phantom imaging reveals that both PEG-PLGA systems exhibit a 30% higher signal-to-background ratio (SBR) than PEG_2kDa -DPPE. This trend cannot be observed in a murine HeLa xenograft model following intravenous administration since dramatic differences in biodistribution are observed. PEG_2kDa -PLGA_4kDa systems accumulate more rapidly in the liver compared to other formulations and PEG_2kDa -DPPE demonstrates a higher tumor localization. Protein content in the "hard" corona differs between formulations (PEG_2kDa -DPPE < PEG_2kDa -PLGA_4kDa < PEG_5kDa -PLGA_55kDa ), although this observation alone does not explain biodistribution patterns. PEG_2kDa -PLGA_4kDa systems show the highest photoacoustic amplitude in a phantom, but also a lower signal in the tumor due to differences in biodistribution. This study demonstrates that formulations for conjugated polymer contrast agents can have significant impact on both imaging performance and biodistribution.

Synergistic non-bonding interactions based on diketopyrrolo-pyrrole for elevated photoacoustic imaging-guided photothermal therapy

Synergistic non-bonding interactions in fluorine and chalcogen-substituted diketopyrrolopyrrole nanoagents for elevated photoacoustic imaging-guided photothermal therapy.

An "all-in-one" strategy based on the organic molecule DCN-4CQA for effective NIR-fluorescence-imaging-guided dual phototherapy

Dual phototherapy combining photodynamic therapy (PDT) and photothermal therapy (PTT) is considered to be a more effective therapeutic method against cancer than single treatment. Therefore, the development of a single material with both near-infrared (NIR)-laser-triggered PDT and PTT abilities is highly desirable but remains a great challenge. A design philosophy for photosensitizers for integrated PDT and PTT treatment has been put forward: (1) a high molar extinction coefficient in the NIR region; (2) suitable LUMO and T1 energy levels to regulate intersystem crossing for effective singlet oxygen (1O2) generation for PDT; and (3) the suppression of fluorescence emission to enhance the process of nonradiative transition with appropriate chemical modifications. Herein, an "all-in-one" functional material, di-cyan substituted 5,12-dibutylquinacridone (DCN-4CQA), for diagnosis and therapy was obtained. DCN-4CQA possesses dual-functional phototherapeutic activity and NIR fluorescence and it was produced via a facile synthesis process from the classic organic photoelectric material quinacridone. We then prepared smart water-soluble nanoparticles (NPs), DCN-4CQA/F127, using Pluronic® 127 (F127) as a drug carrier. The NPs exhibited excellent biocompatibility, robust photostability, NIR fluorescence, a high photothermal conversion efficiency (η = 47.3%), and sufficient 1O2 generation (ΦΔ = 24.3%) under NIR laser irradiation. Remarkably, the DCN-4CQA/F127 NPs significantly inhibited tumor growth in mice subjected to NIR laser irradiation. This study provides a new route for the development of highly efficient, low-cytotoxicity photosensitizers for fluorescence-imaging-guided PTT/PDT.

Immune remodeling triggered by photothermal therapy with semiconducting polymer nanoparticles in combination with chemotherapy to inhibit metastatic cancers

Immune remodeling was triggered by photothermal therapy based on semiconducting polymer nanoparticles in combination with chemotherapy based on a hypoxia-activated antitumor drug (tirapazamine) to efficiently inhibit metastatic tumors.

Terselenophene Regioisomer Conjugated Polymer Materials for High-Performance Cancer Phototheranostics

Molecular isomerization is a fundamental issue in the development of functional materials, with a crucial impact on photophysical properties. However, up to now, their effect on photothermal conversion is rarely investigated. Here, two near-infrared (NIR)-absorbing regioisomer conjugated polymers integrated with cis/trans-terselenophenes are designed and synthesized as efficient photothermal agents to enhance cancer phototheranostics. It is demonstrated that enhanced quinoidal resonance of trans-terselenophenes allows the resulting trans-CP to possess more planar backbone to further increase the effective conjugation length and result in the strong absorption spectra at 808 nm. Characterization of photophysical properties has proved that the photothermal conversion efficiency of trans-CP nanoparticles is up to 61.4%, and they are 210% as strong as cis-CP nanoparticles (29.4%). Further in vitro and in vivo works demonstrate efficient photothermal therapeutic effects with the guidance of photoacoustic imaging. This work affords a new understanding of the molecular isomerization into the development of conjugated materials for high-performance cancer phototheranostics.

Photoacoustic imaging with fiber optic technology: A review

Photoacoustic imaging (PAI) has achieved remarkable growth in the past few decades since it takes advantage of both optical and ultrasound (US) imaging. In order to better promote the wide clinical applications of PAI, many miniaturized and portable PAI systems have recently been proposed. Most of these systems utilize fiber optic technologies. Here, we overview the fiber optic technologies used in PAI. This paper discusses three different fiber optic technologies: fiber optic light transmission, fiber optic US transmission, and fiber optic US detection. These fiber optic technologies are analyzed in different PAI modalities including photoacoustic microscopy (PAM), photoacoustic computed tomography (PACT), and minimally invasive photoacoustic imaging (MIPAI).

Shifting the absorption to the near-infrared region and inducing a strong photothermal effect by encapsulating zinc(II) phthalocyanine in poly(lactic-co-glycolic acid)-hyaluronic acid nanoparticles

By using an oil-in-water single emulsion method, a series of multifunctional hybrid nanoparticles (NPs) were prepared which consisted of a core of poly(lactic-co-glycolic acid) (PLGA) with a lipoid shell of n-hexadecylamine-substituted hyaluronic acid (HA), encapsulating a zinc(II) phthalocyanine-based photosensitizer (ZnPc). As determined by laser light scattering, these hybrid NPs labeled as ZnPc@PLGA-HA NPs possessed a hydrodynamic diameter of 280 nm and a surface charge of -30 mV, showing high stability in serum. The Q-band absorption of ZnPc exhibited a large red-shift from 674 nm for free ZnPc in dimethylsulfoxide to 832 nm for this nanosystem in water. Upon light irradiation at 808 nm, the encapsulated ZnPc induced a strong photothermal effect instead of photodynamic action, which is usually observed for ZnPc-containing NPs. The tumor-targeting effect of these NPs due to the HA coating was investigated against the human colorectal adenocarcinoma HT29 cells and human lung carcinoma A549 cells, both of which overexpress cluster determinant 44 (CD44) receptors, using the CD44-negative human normal hepatic LO2 cells as a negative control. The photothermal cell-killing effect of these NPs was significantly higher for the two CD44-positive cell lines than that for the negative control. Their in vivo photothermal efficacy was also examined on HT29 tumor-bearing nude mice. Upon irradiation, the NPs caused significant temperature increase at the tumor site and ablation of the tumor. The results showed that these multifunctional NPs could serve as an effective photothermal agent for targeted photothermal therapy. Statement of significance Phthalocyanines are well-known photosensitizers for photodynamic therapy. By encapsulating these molecules into various nanoplatforms, a range of multifunctional photosensitizing systems have been developed for cancer therapy. In this study, we have demonstrated that by careful selection of phthalocyanines and the nanocarriers, as well as the self-assembly and encapsulation methods, the encapsulated phthalocyanine molecules could switch the photoinduced action from photodynamic therapy to photothermal therapy as a result of the enhanced aggregation of the macrocyclic molecules in the nanoparticles. The unique packing of the molecules also resulted in a large red-shift of the Q-band absorption to 832 nm, facilitating the in vitro and in vivo photothermal treatment.

Organic nanoparticle-doped microdroplets as dual-modality contrast agents for ultrasound microvascular flow and photoacoustic imaging

Tumor blood vessels are chaotic and abundantly distributed, owing to their heterogeneity. Therefore, imaging techniques which reveal abnormalities of tumor vasculature play significant roles in both mechanistic and clinical diagnostic tumor studies. Photoacoustic (PA) imaging uses the intrinsic characteristics of hemoglobin, to acquire tumor hemodynamic information, while ultrasound (US) imaging provides information about tumoral vessel structures and blood flow. To improve the imaging contrast performance, hydrogel-based microdroplets were designed for both US blood flow and PA imaging in this study. The microdroplets served as carriers for PA contrast agent solution in the innermost part while oil and hydrogel formed the inner and outer layers of the droplets. In vitro experiments firstly demonstrated the dual modality contrast effects of the microdroplets on US flow determination and PA imaging. In vivo experiments were then carried out in both healthy nude mice and nude mice with subcutaneous tumor to validate the contrast effects and to monitor the duration of contrast effects in animals. Using the dual-modality microdroplets, we were able to obtain distinct edges of tumor and blood flow mapping of the tumor microvascular with improved sensitivity up to 11.09 dB for PA and 6.69 dB for US flow. Besides, the in vivo evaluation with microdroplets showed US flow enhancement for more than 60 min. Therefore, the microdroplets are able to provide the contrast effects for both US flow and PA in a relative long duration and have potential to be applied in the tumor related diagnoses and studies.

Biomineralized Biohybrid Algae for Tumor Hypoxia Modulation and Cascade Radio-Photodynamic Therapy

Biomineralization of biomaterials has shown extraordinary potential in cancer treatment, but the exploration of their in vivo applications is still insufficient. Here, we report a biohybrid microalgae system using a biomineralization approach to improve their biocompatibility, while keeping their living activities for radiation and photodynamic synergistic therapy in breast cancer. The biohybrid algae (Algae@SiO₂) synthesized by a one-step biomimetic silicification method could significantly enhance their cytotoxicity and tolerance, improving the living activity in the tumor area. The innate chlorophyll and unique optical property make Algae@SiO₂ possess dual imaging ability, namely, photoacoustic imaging and fluorescence imaging. Algae@SiO₂ accumulated in tumor sites could generate oxygen in situ by external light-mediated photosynthesis, relieve tumor hypoxia, and then enhance the efficiency of radiation therapy. As a natural photosensitizer, the released chlorophyll from Algae@SiO₂ could provide reactive oxygen species to kill the cancer cells for the cascaded photodynamic therapy. The significant suppression of tumor growth in the mice bearing 4T1 tumor successfully demonstrates the promising anti-tumor effect of the Algae@SiO₂-mediated synergistic therapy. Our results show that biohybrid algae, integrated with PAI/FI dual imaging, radiosensitization, and cascaded photothermal therapy, is a promising multifunctional efficient biosystem for cancer treatment.

Enhanced optical imaging properties of lipid nanocapsules as vehicles for fluorescent conjugated polymers

Conjugated polymer nanoparticles (CPNs) have emerged as highly photostable probes for optical and photoacoustic imaging. However, the aggregation of conjugated polymer (CP) molecules upon nanoparticle formation is associated with fluorescence quenching, poor yields and mutable particle sizes. This study investigated whether the CP encapsulation within the liquid midchain triglyceride (MCT) core of lipid nanocapsules (LNCs) may achieve reduced packing of CP chains leading to a stable system with enhanced optical features. The red- and near infrared-emitting CPs, CN-PPV and PCPDTBT, showed precipitation and aggregation-induced quenching with concentrations >~25 µg/mL in MCT alone. Despite this, CP encapsulation within LNCs abolished quenching at concentrations up to 1500 µg/mL. PCPDTBT-LNCs exhibited a quantum yield of 2.8% and a higher signal:background ratio in an optical imaging phantom compared to literature reports of PCPDTBT encapsulated in PEG-PLGA nanoparticles. In contrast, PCPDTBT-LNCs had slightly lower photoacoustic amplitudes than reported PEG-PLGA systems. CP-LNCs were also stable in size (32 ± 0.7 nm) and photoluminescence over 21 days at 4 °C, 25 °C and 37 °C. In summary, encapsulation of CP within the liquid core of lipid nanocapsules enhances the optical properties of fluorescent CP.

Tuning molecular aggregation to achieve highly bright AIE dots for NIR-II fluorescence imaging and NIR-I photoacoustic imaging

Currently, bright aggregation-induced emission luminogens (AIEgens) with high photoluminescence quantum yields (PLQYs) in the NIR-II region are still limited, and thus an efficient strategy to enhance NIR-II fluorescence performance through tuning molecular aggregation is proposed here. The synthesized donor-acceptor tailored AIEgen (DTPA-TBZ) not only exhibits an excellent absorptivity in the NIR-I region, but also good fluorescence signals in the NIR-II region with an emission extending to 1200 nm. Benefiting from such improved intramolecular restriction and aggregation, a significant absolute PLQY value of 8.98% was obtained in solid DTPA-TBZ. Encouragingly, the resulting AIE dots also exhibit a high relative PLQY of up to 11.1% with IR 26 as the reference (PLQY = 0.5%). Finally, the AIE dots were applied in high performance NIR-II fluorescence imaging and NIR-I photoacoustic (PA) imaging: visualization of abdominal vessels, hind limb vasculature, and cerebral vessels with high signal to background ratios was performed via NIR-II imaging; Moreover, PA imaging has also been performed to clearly observe tumors in vivo. These results demonstrate that by finely tuning molecular aggregation in DTPA-TBZ, a good NIR-I absorptivity and a highly emissive fluorescence in the NIR-II region can be achieved simultaneously, finally resulting in a promising dual-modal imaging platform for real-world applications to achieve precise cancer diagnostics.

Grafted semiconducting polymer amphiphiles for multimodal optical imaging and combination phototherapy

Semiconducting polymer nanoparticles (SPNs) have gained growing attention in biomedical applications. However, the preparation of SPNs is usually limited to nanoprecipitation in the presence of amphiphilic copolymers, which encounters the issue of dissociation. As an alternative to SPNs, grafted semiconducting polymer amphiphiles (SPAs) composed of a semiconducting polymer (SP) backbone and hydrophilic side chains show increased physiological stability and improved optical properties. This review summarizes recent advances in SPAs for cancer imaging and combination phototherapy. The applications of SPAs in optical imaging including fluorescence, photoacoustic, multimodal and activatable imaging are first described, followed by the discussion of applications in imaging-guided phototherapy and combination therapy, light-triggered drug delivery and gene regulation. At last, the conclusion and future prospects in this field are discussed.

Polymerization-induced photothermy: A non-donor-acceptor approach to highly effective near-infrared photothermal conversion nanoparticles

Photothermal conversion nanoagents based on conjugated polymers (CPs) are attracting increasing attention for in vivo disease theranostics and high-performing ones are in urgent pursuit. Herein, we report a new and non-donor-acceptor approach to photothermal conversion CPs that combine several merits including low bandgaps, strong near-infrared absorption, low intersystem crossing rate and non-emissive nature. Three CPs based on 6,7; 6',7'-fused isoindigos (nIIDs), i.e., P2IIDV, P3IIDV and P4IIDV that have optical bandgaps of 1.30, 1.22 and 1.17 eV, respectively, are synthesized. The nanoparticles (NPs) of the CPs in water are prepared via nanocoprecipitation, which are non-fluorescent due to the rapid intramolecular twisting in the CP backbone within NPs, enabling most of the excitation energy flow to generate heat. The photothermal conversion efficiencies of the NPs as measured under irradiation at 808, 880 and 980 nm are 62.4%, 40.5% and 15.8% for P2IIDV, 65.1%, 41.0% and 38.9% for P3IIDV and 71.5%, 48.9% and 41.7% for P4IIDV, which are significantly higher than indocyanine green and many popularly reported photothermal conversion materials. In vivo studies using xenograft 4T1 tumor-bearing mouse model demonstrate that the P4IIDV NPs can serve as a rather effective photothermal conversion nanoagent for enhanced photoacoustic imaging and photothermal therapy of tumors.

Rational design of semiconducting polymer brushes as cancer theranostics

Photonic theranostics (PTs) generally contain optical agents for the optical sensing of biomolecules and therapeutic components for converting light into heat or chemical energy. Semiconducting polymer nanoparticles (SPNs) as advanced PTs possessing good biocompatibility, stable photophysical properties, and sensitive and tunable optical responses from the ultraviolet to near-infrared (NIR) II window (300-1700 nm) have recently aroused great interest. Although semiconducting polymers (SPs) with various building blocks have been synthesized and developed to meet the demands of biophotonic applications, most of the SPNs were made by a nanoprecipitation method that used amphiphilic surfactants to encapsulate SPs. Such binary SP micelles usually exhibit weakened photophysical properties of SPs and undergo dissociation in vivo. SP brushes (SPBs) are products of functional post-modification of SP backbones, which endows unique features to SPNs (e.g. enhanced optical properties and multiple chemical reaction sites for the conjunction of organic/inorganic imaging agents and therapeutics). Furthermore, the SPB-based SPNs can be highly stable due to supramolecular self-assembly and/or chemical crosslinking. In this review, we highlight the recent progress in the development of SPBs for advanced theranostics.

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

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

RBC Membrane Camouflaged Semiconducting Polymer Nanoparticles for Near-Infrared Photoacoustic Imaging and Photothermal Therapy

Semiconducting conjugated polymer nanoparticles (SPNs) represent an emerging class of phototheranostic materials with great promise for cancer treatment. In this report, low-bandgap electron donor-acceptor (D-A)-conjugated SPNs with surface cloaked by red blood cell membrane (RBCM) are developed for highly effective photoacoustic imaging and photothermal therapy. The resulting RBCM-coated SPN (SPN@RBCM) displays remarkable near-infrared light absorption and good photostability, as well as high photothermal conversion efficiency for photoacoustic imaging and photothermal therapy. Particularly, due to the small size (< 5 nm), SPN@RBCM has the advantages of deep tumor penetration and rapid clearance from the body with no appreciable toxicity. The RBCM endows the SPNs with prolonged systematic circulation time, less reticuloendothelial system uptake and reduced immune-recognition, hence improving tumor accumulation after intravenous injection, which provides strong photoacoustic signals and exerts excellent photothermal therapeutic effects. Thus, this work provides a valuable paradigm for safe and highly efficient tumor photoacoustic imaging and photothermal therapy for further clinical translation.

Calixarene-Based Supramolecular AIE Dots with Highly Inhibited Nonradiative Decay and Intersystem Crossing for Ultrasensitive Fluorescence Image-Guided Cancer Surgery

Host-guest complexation between calix[5]arene and aggregation-induced emission luminogen (AIEgen) can significantly turn off both the energy dissipation pathways of intersystem crossing and thermal deactivation, enabling the absorbed excitation energy to mostly focus on fluorescence emission. The co-assembly of calix[5]arene amphiphiles and AIEgens affords highly emissive supramolecular AIE nanodots thanks to their interaction severely restricting the intramolecular motion of AIEgens, which also show negligible generation of cytotoxic reactive oxygen species. In vivo studies with a peritoneal carcinomatosis-bearing mouse model indicate that such supramolecular AIE dots have rather low in vivo side toxicity and can serve as a superior fluorescent bioprobe for ultrasensitive fluorescence image-guided cancer surgery.

Multifunctional phototheranostic nanomedicine for cancer imaging and treatment

Cancer, as one of the most life-threatening diseases, shows a high fatality rate around the world. When improving the therapeutic efficacy of conventional cancer treatments, researchers also conduct extensive studies into alternative therapeutic approaches, which are safe, valid, and economical. Phototherapies, including photodynamic therapy (PDT) and photothermal therapy (PTT), are tumor-ablative and function-reserving oncologic interventions, showing strong potential in clinical cancer treatment. During phototherapies, the non-toxic phototherapeutic agents can be activated upon light irradiation to induce cell death without causing much damage to normal tissues. Besides, with the rapid development of nanotechnology in the past decades, phototheranostic nanomedicine also has attracted tremendous interests aiming to continuously refine their performance. Herein, we reviewed the recent progress of phototheranostic nanomedicine for improved cancer therapy. After a brief introduction of the therapeutic principles and related phototherapeutic agents for PDT and PTT, the existing works on developing of phototheranostic nanomedicine by mainly focusing on their categories and applications, particularly on phototherapy-synergized cancer immunotherapy, are comprehensively reviewed. More importantly, a brief conclusion and future challenges of phototheranostic nanomedicine from our point of view are delivered in the last part of this article.

Rational design of near-infrared platinum(ii)-acetylide conjugated polymers for photoacoustic imaging-guided synergistic phototherapy under 808 nm irradiation

We have developed a novel near-infrared Pt-acetylide conjugated polymer CP3 with highly efficient photoconversion behaviors for synergistic cancer phototherapy.

Design of superior phototheranostic agents guided by Jablonski diagrams

This review summarizes how Jablonski diagrams guide the design of advanced organic optical agents and improvement of disease phototheranostic efficacies.

Regulating the Photophysical Property of Organic/Polymer Optical Agents for Promoted Cancer Phototheranostics

On the basis of the Jablonski diagram, the photophysical properties of optical agents are highly associated with biomedical function and efficacy. Herein, the focus is on organic/polymer optical agents and the recent progress in the main strategies for regulating their photophysical properties to achieve superior cancer diagnosis/phototheranostics applications are highlighted. Both the approaches of nanoengineering and molecular design, which can lead to optimized effectiveness of required biomedical function, are discussed.

Photophysical and Optical Properties of Semiconducting Polymer Nanoparticles Prepared from Hyaluronic Acid and Polysorbate 80

A nanoprecipitation procedure was utilized to prepare novel diketopyrrolopyrrole-based semiconducting polymer nanoparticles (SPNs) with hyaluronic acid (HA) and polysorbate 80. The nanoprecipitation led to the formation of spherical nanoparticles with average diameters ranging from 100 to 200 nm, and a careful control over the structure of the parent conjugated polymers was performed to probe the influence of π-conjugation on the final photophysical and thermal stability of the resulting SPNs. Upon generation of a series of novel SPNs, the optical and photophysical properties of the new nanomaterials were probed in solution using various techniques including transmission electron microscopy, dynamic light scattering, small-angle neutron scattering, transient absorption, and UV-vis spectroscopy. A careful comparison was performed between the different SPNs to evaluate their excited-state dynamics and photophysical properties, both before and after nanoprecipitation. Interestingly, although soluble in organic solution, the nanoparticles were found to exhibit aggregative behavior, resulting in SPNs that exhibit excited-state behaviors that are very similar to aggregated polymer solutions. Based on these findings, the formation of HA- and polysorbate 80-based nanoparticles does not influence the photophysical properties of the conjugated polymers, thus opening new opportunities for the design of bioimaging agents and nanomaterials for health-related applications.

In Vivo Optical Performance of a New Class of Near-Infrared-Emitting Conjugated Polymers: Borylated PF8-BT

Borylated poly(fluorene-benzothiadiazoles) (PF8-BT) are π-conjugated polymers (CPs) with deep-red/near-infrared (NIR) absorption and emission profiles suitable for in vivo optical imaging. A fully borylated PF8-BT derivative (P4) was encapsulated in pegylated poly(lactic-co-glycolic acid) (PEG-PLGA) nanoparticles and compared with a reference NIR-emitting CP (PCPDTBT) or indocyanine green (ICG). All formulations satisfied quality requirements for parenterally administered diagnostics. P4 nanoparticles had higher quantum yield (2.3%) than PCPCDTBT (0.01%) or ICG nanoparticles (1.1%). The signal/background ratios (SBRs) of CP systems P4 and PCPDTBT in a phantom mouse (λ_em = 820 nm) increased linearly with fluorophore mass (12.5-100 μg/mL), while the SBRs of ICG decreased above 25 μg/mL. P4 nanoparticles experienced <10% photobleaching over 10 irradiations (PCPDTBT: ∼25% and ICG: >44%). In a mouse tumor xenograft model, P4 nanoparticles showed a 5-fold higher SBR than PCPDTBT particles with fluorophore accumulation in the liver > spleen > tumor. Blood chemistry and tissue histology showed no abnormalities compared to untreated animals after a single administration.

Organic semiconducting polymer amphiphile for near-infrared-II light-triggered phototheranostics

Development of near-infrared-II (NIR-II) light responsive nano-agents with high photothermal stability, high photothermal conversion efficiency (PCE), and excellent biocompatibility for photoacoustic (PA) imaging-guided photothermal therapy (PTT) is of tremendous significance. In spite of the superiority of organic semiconducting polymer nanoparticles (OSPNs) in PA imaging-guided PTT, the limited absorption in the first NIR (NIR-I) window and metastable nanostructure of OSPNs resulting from commonly used preparation methods based on nanoprecipitation or reprecipitation compromise their in vivo phototheranostic performance. Herein we design and synthesize a novel NIR-II absorbing organic semiconducting polymer amphiphile (OSPA) to enhance the structural stability of OSPNs. With prominent optical properties, low toxicity, and a suitable size, OSPA not only efficiently labels and kills cancer cells under NIR-II irradiation but also accumulates at the tumor of living mice upon intravenous injection, allowing efficient NIR-II light-triggered phototheranostics toward tumor. The developed OSPA has promising potential for fabricating multifunctional nanoplatforms to enable multimodal theranostics.

Near-Infrared Light-Harvesting Fullerene-Based Nanoparticles for Promoted Synergetic Tumor Phototheranostics

A synergetic phototheranostic system, combining diagnostic photo-imaging and phototherapies [such as photothermal therapy and photodynamic therapy (PDT)], shows great potential in today's tumor precise therapy. Herein, we fabricate near-infrared (NIR) light-harvesting fullerene-based nanoparticles (DAF NPs) for photoacoustic (PA) imaging-guided synergetic tumor photothermal and PDT. The fullerene derivatives (DAF) absorbing in the NIR region have been synthesized by conjugating NIR-absorbing antenna with fullerene. In addition, DAF NPs with good biocompatibility have been fabricated via a nanoprecipitation approach. The as-prepared DAF NPs can accumulate and generate PA signals around the tumor site 6 h post injection via enhanced permeability and retention effect in vivo. More importantly, the DAF NPs exhibit better reactive oxygen species and heat generation efficacy compared with fullerene and antenna nanoparticles (DA NPs), respectively. Further in vitro and in vivo studies demonstrate that DAF NPs can effectively inhibit tumor growth through synergetic photodynamic and photothermal therapies, which provides a new sight of photosensitizer design for enhanced cancer phototheranostics.

Massively Evoking Immunogenic Cell Death by Focused Mitochondrial Oxidative Stress using an AIE Luminogen with a Twisted Molecular Structure

Immunogenic cell death (ICD) provides momentous theoretical principle for modern cancer immunotherapy. However, the currently available ICD inducers are still very limited and photosensitizer-based ones can hardly induce sufficient ICD to achieve satisfactory cancer immunotherapy by themselves. Herein, an organic photosensitizer (named TPE-DPA-TCyP) with a twisted molecular structure, strong aggregation-induced emission activity, and specific ability is reported for effectively inducing focused mitochondrial oxidative stress of cancer cells, which can serve as a much superior ICD inducer to the popularly used ones, including chlorin e6 (Ce6), pheophorbide A, and oxaliplatin. Furthermore, more effective in vivo ICD immunogenicity of TPE-DPA-TCyP than Ce6 is also demonstrated using a prophylactic tumor vaccination model. The underlying mechanism of the effectiveness and robustness of TPE-DPA-TCyP in inducing antitumor immunity and immune-memory effect in vivo is verified by immune cell analyses. This study thus reveals that inducing focused mitochondrial oxidative stress is a highly effective strategy to evoke abundant and large-scale ICD.

Optically Active Nanomaterials for Bioimaging and Targeted Therapy

Non-invasive tracking for monitoring the selective delivery and transplantation of biotargeted agents in vivo has been employed as one of the most effective tools in the field of nanomedicine. Different nanoprobes have been developed and applied to bioimaging tissues and the treatment of diseases ranging from inflammatory and cardiovascular diseases to cancer. Herein, we will review the recent advances in the development of optics-responsive nanomaterials, including organic and inorganic nanoparticles, for multimodal bioimaging and targeted therapy. The main focus is placed on nanoprobe fabrication, mechanistic illustrations, and diagnostic, or therapeutical applications. These nanomedicine strategies have promoted a better understanding of the biological events underlying diverse disease etiologies, thereby facilitating diagnosis, illness evaluation, therapeutic effect, and drug discovery.

Tumor Targeting Strategies of Smart Fluorescent Nanoparticles and Their Applications in Cancer Diagnosis and Treatment

Advantages such as strong signal strength, resistance to photobleaching, tunable fluorescence emissions, high sensitivity, and biocompatibility are the driving forces for the application of fluorescent nanoparticles (FNPs) in cancer diagnosis and therapy. In addition, the large surface area and easy modification of FNPs provide a platform for the design of multifunctional nanoparticles (MFNPs) for tumor targeting, diagnosis, and treatment. In order to obtain better targeting and therapeutic effects, it is necessary to understand the properties and targeting mechanisms of FNPs, which are the foundation and play a key role in the targeting design of nanoparticles (NPs). Widely accepted and applied targeting mechanisms such as enhanced permeability and retention (EPR) effect, active targeting, and tumor microenvironment (TME) targeting are summarized here. Additionally, a freshly discovered targeting mechanism is introduced, termed cell membrane permeability targeting (CMPT), which improves the tumor-targeting rate from less than 5% of the EPR effect to more than 50%. A new design strategy is also summarized, which is promising for future clinical targeting NPs/nanomedicines design. The targeting mechanism and design strategy will inspire new insights and thoughts on targeting design and will speed up precision medicine and contribute to cancer therapy and early diagnosis.

Listening to tissues with new light: recent technological advances in photoacoustic imaging

Photoacoustic tomography (PAT), or optoacoustic tomography, has achieved remarkable progress in the past decade, benefiting from the joint developments in optics, acoustics, chemistry, computing and mathematics. Unlike pure optical or ultrasound imaging, PAT can provide unique optical absorption contrast as well as widely scalable spatial resolution, penetration depth and imaging speed. Moreover, PAT has inherent sensitivity to tissue's functional, molecular, and metabolic state. With these merits, PAT has been applied in a wide range of life science disciplines, and has enabled biomedical research unattainable by other imaging methods. This Review article aims at introducing state-of-the-art PAT technologies and their representative applications. The focus is on recent technological breakthroughs in structural, functional, molecular PAT, including super-resolution imaging, real-time small-animal whole-body imaging, and high-sensitivity functional/molecular imaging. We also discuss the remaining challenges in PAT and envisioned opportunities.

Precision Cancer Theranostic Platform by In Situ Polymerization in Perylene Diimide-Hybridized Hollow Mesoporous Organosilica Nanoparticles

Phototheranostics refers to advanced photonics-mediated theranostic methods for cancer and includes imaging-guided photothermal/chemotherapy, photothermal/photodynamic therapy, and photodynamic/chemotherapy, which are expected to provide a paradigm of modern precision medicine. In this regard, various phototheranostic drug delivery systems with excellent photonic performance, controlled drug delivery/release, and precise photoimaging guidance have been developed. In this study, we reported a special "in situ framework growth" method to synthesize novel phototheranostic hollow mesoporous nanoparticles by ingenious hybridization of perylene diimide (PDI) within the framework of small-sized hollow mesoporous organosilica (HMO). The marriage of PDI and HMO endowed the phototheranostic silica nanoparticles (HMPDINs) with largely amplified fluorescence and photoacoustic signals, which can be used for enhanced fluorescence and photoacoustic imaging. The organosilica shell can be chemically chelated with isotope ⁶⁴Cu for positron emission tomography imaging. Moreover, in situ polymer growth was introduced in the hollow structure of the HMPDINs to produce thermosensitive polymer (TP) in the cavity of HMPDINs to increase the loading capacity and prevent unexpected leakage of the hydrophobic drug SN38. Furthermore, the framework-hybridized PDI generated heat under near-infrared laser irradiation to trigger the deformation of TP for controlled drug release in the tumor region. The fabricated hybrid nanomedicine with organic-inorganic characteristic not only increases the cancer theranostic efficacy but also offers an attractive solution for designing powerful theranostic platforms.