Semiconducting Photosensitizer-Incorporated Copolymers as Near-Infrared Afterglow Nanoagents for Tumor Imaging

Acidity-activatable upconversion afterglow luminescence cocktail nanoparticles for ultrasensitive in vivo imaging

Activatable afterglow luminescence nanoprobes enabling switched "off-on" signals in response to biomarkers have recently emerged to achieve reduced unspecific signals and improved imaging fidelity. However, such nanoprobes always use a biomarker-interrupted energy transfer to obtain an activatable signal, which necessitates a strict distance requisition between a donor and an acceptor moiety (<10 nm) and hence induces low efficiency and non-feasibility. Herein, we report organic upconversion afterglow luminescence cocktail nanoparticles (ALCNs) that instead utilize acidity-manipulated singlet oxygen (1O2) transfer between a donor and an acceptor moiety with enlarged distance and thus possess more efficiency and flexibility to achieve an activatable afterglow signal. After in vitro validation of acidity-activated afterglow luminescence, ALCNs achieve in vivo imaging of 4T1-xenograft subcutaneous tumors in female mice and orthotopic liver tumors in male mice with a high signal-to-noise ratio (SNR). As a representative targeting trial, Bio-ALCNs with biotin modification prove the enhanced targeting ability, sensitivity, and specificity for pulmonary metastasis and subcutaneous tumor imaging via systemic administration of nanoparticles in female mice, which also implies the potential broad utility of ALCNs for tumor imaging with diverse design flexibility. Therefore, this study provides an innovative and general approach for activatable afterglow imaging with better imaging performance than fluorescence imaging.

A Highly Bright Near-Infrared Afterglow Luminophore for Activatable Ultrasensitive In Vivo Imaging

Afterglow luminescence imaging probes, with long-lived emission after cessation of light excitation, have drawn increasing attention in biomedical imaging field owing to their elimination of autofluorescence. However, current afterglow agents always suffer from an unsatisfactory signal intensity and complex systems consisting of multiple ingredients. To address these issues, this study reports a near-infrared (NIR) afterglow luminophore (TPP-DO) by chemical conjugation of an afterglow substrate and a photosensitizer acting as both an afterglow initiator and an energy relay unit into a single molecule, resulting in an intramolecular energy transfer process to improve the afterglow brightness. The constructed TPP-DO NPs emit a strong NIR afterglow luminescence with a signal intensity of up to 108  p/s/cm2 /sr at a low concentration of 10 μM and a low irradiation power density of 0.05 W/cm2 , which is almost two orders of magnitude higher than most existing organic afterglow probes. The highly bright NIR afterglow luminescence with minimized background from TPP-DO NPs allows a deep tissue penetration depth ability. Moreover, we develop a GSH-activatable afterglow probe (Q-TPP-DO NPs) for ultrasensitive detection of subcutaneous tumor with the smallest tumor volume of 0.048 mm3 , demonstrating the high potential for early diagnosis and imaging-guided surgical resection of tumors.

Development of novel polymeric nanoagents and their potential in cancer diagnosis and therapy runing title: Polymeric nanoagents for cancer theranostics

Cancer has been one of the leading factors of death around the world. Cancer patients usually have low 5-year survival rates and poor life quality requiring substantial improvement. In clinic, the presenting diagnostic strategies lack sensitivity with only a small proportion of patients can be accurately identified. For diagnosed patients, most of them are at the advanced stages thus being delayed to receive treatment. Therefore, it is eager to investigate and develop highly effective and accurate techniques for cancer early diagnosis and individualized therapy. Various nanoplatforms are emerging as imaging agents and drug carriers for cancer theranostics recently. Novel polymeric nanoagents, as a potent exemplar, have extraordinary merits, such as good stability, high biosafety and high drug loading efficacy, showing the great prospect for cancer early diagnosis and precise treatment. Herein, we review the recent advances in novel polymeric nanoagents and elucidate their synthesis procedures. We further introduce the applications of novel polymeric nanoagents in cancer diagnosis, treatment, and theranostics, as well as associated challenges and prospects in this field.

Organic persistent luminescence imaging for biomedical applications

Persistent luminescence is a unique visual phenomenon that occurs after cessation of excitation light irradiation or following oxidization of luminescent molecules. The energy stored within the molecule is released in a delayed manner, resulting in luminescence that can be maintained for seconds, minutes, hours, or even days. Organic persistent luminescence materials (OPLMs) are highly robust and their facile modification and assembly into biocompatible nanostructures makes them attractive tools for in vivo bioimaging, whilst offering an alternative to conventional fluorescence imaging materials for biomedical applications. In this review, we give attention to the existing limitations of each class of OPLM-based molecular bioimaging probes based on their luminescence mechanisms, and how recent research progress has driven efforts to circumvent their shortcomings. We discuss the multifunctionality-focused design strategies, and the broad biological application prospects of these molecular probes. Furthermore, we provide insights into the next generation of OPLMs being developed for bioimaging techniques.

A plasmon-enhanced fluorescent gold coated novel lipo-polymeric hybrid nanosystem: synthesis, characterization and application for imaging and photothermal therapy of breast cancer

This study reports a hybrid lipo-polymeric nanosystem (PDPC NPs) synthesized by a modified hydrogel-isolation technique. The ability of the nanosystem to encapsulate hydrophilic and hydrophobic molecules has been demonstrated, and their enhanced cellular uptake has been observed in vitro. The PDPC NPs, surface coated with gold by in situ reduction of chloroauric acid (PDPC-Au NPs), showed a photothermal transduction efficacy of ∼65%. The PDPC-Au NPs demonstrated an increase in intracellular ROS, triggered DNA damage and resulted in apoptotic cell death when tested against breast cancer cells (MCF-7). The disintegration of PDPC-Au NPs into smaller nanoparticles with near-infrared (NIR) laser irradiation was understood using transmission electron microscopy imaging. The lipo-polymeric hybrid nanosystem exhibited plasmon-enhanced fluorescence when loaded with IR780 (a NIR dye), followed by surface coating with gold (PDPC-IR-Au NPs). This paper is one of the first reports on the plasmon-enhanced fluorescence within a nanosystem by simple surface coating of Au, to the best of our knowledge. This plasmon-enhanced fluorescence was unique to the lipo-polymeric hybrid system, as the same was not observed with a liposomal nanosystem. The plasmon-enhanced fluorescence of PDPC-IR-Au NPs, when applied for imaging cancer cells and zebrafish embryos, showed a strong fluorescence signal at minimal concentrations of the dye. The PDPC-IR-Au NPs were also applied for photothermal therapy of breast cancer in vitro and in vivo, and the results depicted significant therapeutic benefits.

Multifunction-Harnessed Afterglow Nanosensor for Molecular Imaging of Acute Kidney Injury In Vivo

Afterglow is superior to other optical modalities for biomedical applications in that it can exclude the autofluorescence background. Nevertheless, afterglow has rarely been applied to the high-contrast "off-to-on" activatable sensing scheme because the complicated afterglow systems hamper the additional inclusion of sensory functions while preserving the afterglow luminescence. Herein, a simple formulation of a multifunctional components-incorporated afterglow nanosensor (MANS) is developed for the superoxide-responsive activatable afterglow imaging of cisplatin-induced kidney injury. A multifunctional iridium complex (Ir-OTf) is designed to recover its photoactivities (phosphorescence and the ability of singlet oxygen-generating afterglow initiator) upon exposure to superoxide. To construct the nanoscopic afterglow detection system (MANS), Ir-OTf is incorporated with another multifunctional molecule (rubrene) in the polymeric micellar nanoparticle, where rubrene also plays dual roles as an afterglow substrate and a luminophore. The multiple functions covered by Ir-OTf and rubrene renders the composition of MANS quite simple, which exhibits superoxide-responsive "off-to-on" activatable afterglow luminescence for periods longer than 11 min after the termination of pre-excitation. Finally, MANS is successfully applied to the molecular imaging of cisplatin-induced kidney injury with activatable afterglow signals responsive to pathologically overproduced superoxide in a mouse model without autofluorescence background.

Near-Infrared Afterglow Luminescence of Chlorin Nanoparticles for Ultrasensitive In Vivo Imaging

Afterglow imaging holds great potential for ultrasensitive biomedical imaging. As it detects photons after the cessation of real-time light excitation, autofluorescence can therefore be effectively eliminated. However, afterglow imaging is still in its infant stage due to the lack of afterglow agents with satisfactory lifetime, biocompatibility, and high luminescence brightness, particularly afterglow in the near-infrared region for in vivo applications. To address these issues, this study for the first time reports chlorin nanoparticles (Ch-NPs) emitting afterglow luminescence peaking at 680 nm with a half-life of up to 1.5 h, which is almost 1 order of magnitude longer than those of other reported organic afterglow probes. In-depth experimental and theoretical studies revealed that the brightness of the afterglow luminescence is strongly correlated with the singlet oxygen (¹O₂) capacity and the oxidizability of the chlorins. Benefitting from the ultralong half-life and the minimized imaging background, small metastatic tumor foci of 3 mm³ were successfully resected under the guidance of the afterglow luminescence generated upon a single shot of activation prior to the injection, which was impossible for conventional near-infrared fluorescence imaging due to tissue autofluorescence.

Molecular Probes for Autofluorescence-Free Optical Imaging

Optical imaging is an indispensable tool in clinical diagnostics and fundamental biomedical research. Autofluorescence-free optical imaging, which eliminates real-time optical excitation to minimize background noise, enables clear visualization of biological architecture and physiopathological events deep within living subjects. Molecular probes especially developed for autofluorescence-free optical imaging have been proven to remarkably improve the imaging sensitivity, penetration depth, target specificity, and multiplexing capability. In this Review, we focus on the advancements of autofluorescence-free molecular probes through the lens of particular molecular or photophysical mechanisms that produce long-lasting luminescence after the cessation of light excitation. The versatile design strategies of these molecular probes are discussed along with a broad range of biological applications. Finally, challenges and perspectives are discussed to further advance the next-generation autofluorescence-free molecular probes for in vivo imaging and in vitro biosensors.

ROS-responsive probes for low-background optical imaging: a review

Optical imaging is a facile tool for visualizing biological processes and disease progression, but its image quality is largely limited by light-induced autofluorescence or background signals. To overcome this issue, low-background optical-imaging techniques including chemiluminescence imaging, afterglow imaging and photoacoustic imaging have been developed, based on their unique working mechanisms, which are: the detection of light emissions from chemical reactions, the cessation of light excitation before signal collection, and the detection of ultrasonic signals instead of light signals, respectively. Stimuli-responsive probes are highly desirable for improved imaging results since they can significantly reduce surrounding interference signals. Reactive oxygen species (ROS), which are closely implicated in a series of diseases such as cancer and inflammation, are frequently employed as initiators for responsive agents to selectively change the imaging signal. Thus, ROS-responsive agents incorporated into low-background imaging techniques can achieve a more promising imaging quality. In this review, recent advances in ROS-responsive probes for low-background optical-imaging techniques are summarized. Moreover, the approaches to improving the sensitivity of probes and tissue penetration depth are discussed in detail. In particular, we highlight the reaction mechanisms between the probes and ROS, revealing the potential for low-background optical imaging.

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.

Highly stable semiconducting polymer nanoparticles for multi-responsive chemo/photothermal combined cancer therapy

Rationale: Structural stability and size controllability are critical issues to semiconducting polymer nanoparticles (SPNs), which currently show great potential for theranostic applications.

Methods: Herein, multi-responsive semiconducting polymer semi-interpenetrating nanoparticles (PDPP3T@PNIPAMAA IPNs) with highly stable structure and uniform size have been successfully designed by semi-interpenetrating technique.

Results: It is proposed for the first time that PDPP3T@PNIPAMAA IPNs were prepared with “reinforced concrete” particle structure, which is even resistant to organic solvent such as ethanol and THF. By adjusting the polymerization time, the obtained PDPP3T@PNIPAMAA IPNs exhibit uniform and controllable particle size with extremely low polydispersity index (~0.037) at 1 h of reaction time. The presence of pH/light/GSH multi-responsive semi-interpenetrating network in PDPP3T@PNIPAMAA IPNs dramatically increase their drug loading efficiency (92.64%), which is significantly higher than previously reported comparable SPNs-based drug delivery systems. Additionally, PDPP3T@PNIPAMAA-DOX IPNs further provide improved therapeutic efficacy by the combination of chemotherapy and photothermal therapy with controllably regulated release of doxorubicin (DOX). In vitro and in vivo results indicate that PDPP3T@PNIPAMAA-DOX IPNs are able to release drugs at controlled rate by pH/light/GSH regulation and offer PAI-guided chemo/photothermal combined therapy with excellent therapeutic efficacy.

Conclusions: The semi-interpenetrating network method may be generally extended for the preparation of a wide range of organic polymer nanoparticles to achieve ultrahigh structural stability, precise particle size controllability and excellent drug loading capacity.

An aggregation-induced emission dye-powered afterglow luminogen for tumor imaging

Semiconducting polymer (SP)-based afterglow luminogens are showing increasing potential for in vivo imaging because of their long-life luminescence and the associated benefits (e.g., zero-autofluorescence background and high signal-to-noise ratio). However, such organic afterglow luminescence agents are still rare and their application is usually limited by their relatively low afterglow intensity and short afterglow duration. Herein, we report an aggregation-induced emission (AIE) dye-powered SP afterglow luminogen by leveraging on the unique characteristics of an AIE dye to circumvent the concentration-quenching effect, enhance afterglow intensity and prolong afterglow duration. The underlying working mechanism is investigated by a series of experiments and it is found that the AIE dye provides sufficient 1O2 to excite SPs and form massive amounts of high-energy intermediates, and then the SP intermediates emit photons that can activate the AIE dye to generate 1O2 and simultaneously trigger the energy transfer process between the SPs and AIE dye, resulting in a deep-red emission. It is this closed-loop of "photon-1O2-SP intermediates-photon" that provides the afterglow emission even after the cessation of the excitation light. The as-prepared luminogen shows good performance in in vivo tumour imaging. This study demonstrates the advantages of AIE-facilitated afterglow luminescence and discloses its mechanism, and hopefully it could inspire the development of other innovative designs for cancer theranostics.

Advanced Nanotechnology Leading the Way to Multimodal Imaging-Guided Precision Surgical Therapy

Surgical resection is the primary and most effective treatment for most patients with solid tumors. However, patients suffer from postoperative recurrence and metastasis. In the past years, emerging nanotechnology has led the way to minimally invasive, precision and intelligent oncological surgery after the rapid development of minimally invasive surgical technology. Advanced nanotechnology in the construction of nanomaterials (NMs) for precision imaging-guided surgery (IGS) as well as surgery-assisted synergistic therapy is summarized, thereby unlocking the advantages of nanotechnology in multimodal IGS-assisted precision synergistic cancer therapy. First, mechanisms and principles of NMs to surgical targets are briefly introduced. Multimodal imaging based on molecular imaging technologies provides a practical method to achieve intraoperative visualization with high resolution and deep tissue penetration. Moreover, multifunctional NMs synergize surgery with adjuvant therapy (e.g., chemotherapy, immunotherapy, phototherapy) to eliminate residual lesions. Finally, key issues in the development of ideal theranostic NMs associated with surgical applications and challenges of clinical transformation are discussed to push forward further development of NMs for multimodal IGS-assisted precision synergistic cancer therapy.

Near-Infrared Afterglow Semiconducting Nano-Polycomplexes for the Multiplex Differentiation of Cancer Exosomes

The detection of exosomes is promising for the early diagnosis of cancer. However, the development of suitable optical sensors remains challenging. We have developed the first luminescent nanosensor for the multiplex differentiation of cancer exosomes that bypasses real-time light excitation. The sensor is composed of a near-infrared semiconducting polyelectrolyte (ASPN) that forms a complex with a quencher-tagged aptamer. The afterglow signal of the nanocomplex (ASPNC), being initially quenched, is turned on in the presence of aptamer-targeted exosomes. Because detection of the afterglow takes place after the excitation, background signals are minimized, leading to an improved limit of detection that is nearly two orders of magnitude lower than that of fluorescence detection in cell culture media. Also, ASPNC can be easily tailored to detect different exosomal proteins by changing the aptamer sequence. This enables an orthogonal analysis of multiple exosome samples, potentially permitting an accurate identification of the cellular origin of exosomes for cancer diagnosis.

Recent Advances in Cell Membrane-Camouflaged Nanoparticles for Cancer Phototherapy

Phototherapy including photothermal therapy (PTT) and photodynamic therapy (PDT) employs phototherapeutic agents to generate heat or cytotoxic reactive oxygen species (ROS), and has therefore garnered particular interest for cancer therapy. However, the main challenges faced by conventional phototherapeutic agents include easy recognition by the immune system, rapid clearance from blood circulation, and low accumulation in target sites. Cell-membrane coating has emerged as a potential way to overcome these limitations, owing to the abundant proteins on the surface of cell membranes that can be inherited to the cell membrane-camouflaged nanoparticles. This review summarizes the recent advances in the development of biomimetic cell membrane-camouflaged nanoparticles for cancer phototherapy. Different sources of cell membranes can be used to coat nanoparticles uisng different coating approaches. After cell-membrane coating, the photophysical properties of the original phototherapeutic nanoparticles remain nearly unchanged; however, the coated nanoparticles are equipped with additional physiological features including immune escape, in vivo prolonged circulation time, or homologous targeting, depending on the cell sources. Moreover, the coated cell membrane can be ablated from phototherapeutic nanoparticles under laser irradiation, leading to drug release and thus synergetic therapy. By combining other supplementary agents to normalize tumor microenvironment, cell-membrane coating can further enhance the therapeutic efficacy against cancer.