A Class of Biocompatible Dye-Protein Complex Optical Nanoprobes

Molecular Engineering of Bright NIR-I/NIR-II Nanofluorophores for High-Resolution Bioimaging and Tumor Detection in Vivo

A comprehensive approach for the construction of NIR-I/NIR-II nanofluorophores with exceptional brightness and excellent chemo- and photostability has been developed. This study first confirmed that the amphiphilic molecules with stronger hydrophobic moieties and weaker hydrophilic moieties are superior candidates for constructing brighter nanofluorophores, which are attributed to its higher efficiency in suppressing the intramolecular charge transfer/aggregation-caused fluorescence quenching of donor-acceptor-donor type fluorophores. The prepared nanofluorophore demonstrates a fluorescence quantum yield exceeding 4.5% in aqueous solution and exhibits a strong NIR-II tail emission up to 1300 nm. The superior performance of the nanofluorophore enabled the achievement of high-resolution whole-body vessel imaging and brain vessel imaging, as well as high-contrast fluorescence imaging of the lymphatic system in vivo. Furthermore, their potential for highly sensitive fluorescence detection of tiny tumors in vivo has been successfully confirmed, thus supporting their future applications in precise fluorescence imaging-guided surgery in the early stages of cancer.

Facile and green fabrication of tumor- and mitochondria-targeted AIEgen-protein nanoparticles for imaging-guided photodynamic cancer therapy

In recent years, aggregation-induced emission (AIE)-active materials have been emerging as a promising means for bioimaging and phototherapy. However, the majority of AIE luminogens (AIEgens) need to be encapsulated into versatile nanocomposites to improve their biocompatibility and tumor targeting. Herein, we prepared a tumor- and mitochondria-targeted protein nanocage by the fusion of human H-chain ferritin (HFtn) with a tumor homing and penetrating peptide LinTT1 using genetic engineering technology. The LinTT1-HFtn could serve as a nanocarrier to encapsulate AIEgens via a simple pH-driven disassembly/reassembly process, thereby fabricating the dual-targeting AIEgen-protein nanoparticles (NPs). The as designed NPs exhibited an improved hepatoblastoma-homing property and tumor penetrating ability, which is favorable for tumor-targeted fluorescence imaging. The NPs also presented a mitochondria-targeting ability, and efficiently generated reactive oxygen species (ROS) upon visible light irradiation, making them valuable for inducing efficient mitochondrial dysfunction and intrinsic apoptosis in cancer cells. In vivo experiments demonstrated that the NPs could provide the accurate tumor imaging and dramatic tumor growth inhibition with minimal side effects. Taken together, this study presents a facile and green approach for fabrication of tumor- and mitochondria-targeted AIEgen-protein NPs, which can serve as a promising strategy for imaging-guided photodynamic cancer therapy. STATEMENT OF SIGNIFICANCE: AIE luminogens (AIEgens) show strong fluorescence and enhanced ROS generation in the aggregate state, which would facilitate the image-guided photodynamic therapy [12-14]. However, the major obstacles that hinder biological applications are their lack of hydrophilicity and selective targeting [15]. To address this issue, this study presents a facile and green approach for the fabrication of tumor‑ and mitochondria‑targeted AIEgen-protein nanoparticles via a simple disassembly/reassembly of the LinTT1 peptide-functionalized ferritin nanocage without any harmful chemicals or chemical modification. The targeting peptide-functionalized nanocage not only restricts the intramolecular motion of AIEgens leading to enhanced fluorescence and ROS production, but also confers good targeting to AIEgens.

Orchestrated Strategies for Developing Fluorophores for NIR-II Imaging

Fluorescence imaging (FLI), a non-invasive, real-time, and highly sensitive imaging modality, allows for investigating the molecular/cellular level activities to understand physiological functions and diseases. The emergence of the second near-infrared window (NIR-II, 1000-1700 nm) has endowed fluorescence imaging with deeper tissue penetration and unprecedented clarity. Among the various NIR-II imaging fluorophores, the organic fluorescent probes have occupied a pivotal position in bioimaging due to their higher biocompatibility, safety, and potential for clinical applications compared with those of the inorganic probes. To obtain high-quality organic dyes, diverse strategies have been taken. In this review, different strategies for optimizing NIR-II organic fluorophores are summarized, including traditional chemical modifications, and emerging bioengineering operations, which have not previously been elaborated on and summarized. Moreover, the bioengineering strategies are highlighted using endogenous serum proteins and even exogenous gene-editing proteins, which would provide fresh insights to design good-performance dyes and help develop NIR-II probes with clinical translation potential in the future. A critical perspective on the direction of the design strategies of NIR-II dyes for disease imaging is also proposed.

Subcellular visualization: Organelle-specific targeted drug delivery and discovery

Organelles perform critical biological functions due to their distinct molecular composition and internal environment. Disorders in organelles or their interacting networks have been linked to the incidence of numerous diseases, and the research of pharmacological actions at the organelle level has sparked pharmacists' interest. Currently, cell imaging has evolved into a critical tool for drug delivery, drug discovery, and pharmacological research. The introduction of advanced imaging techniques in recent years has provided researchers with richer biological information for viewing and studying the ultrastructure of organelles, protein interactions, and gene transcription activities, leading to the design and delivery of precision-targeted drugs. Therefore, this reviews the research on organelles-targeted drugs based upon imaging technologies and development of fluorescent molecules for medicinal purposes. We also give a thorough analysis of a number of subcellular-level elements of drug development, including subcellular research instruments and methods, organelle biological event investigation, subcellular target and drug identification, and design of subcellular delivery systems. This review will make it possible to promote drug research from the individual/cellular level to the subcellular level, as well as give a new focus based on newly found organelle activities.

Restriction of molecular motion to a higher level: Towards bright AIE dots for biomedical applications

In the late 19th century, scientists began to study the photophysical differences between chromophores in the solution and aggregate states, which breed the recognition of the prototypical processes of aggregation-caused quenching and aggregation-induced emission (AIE). In particular, the conceptual discovery of the AIE phenomenon has spawned the innovation of luminogenic materials with high emission in the aggregate state based on their unique working principle termed the restriction of intramolecular motion. As AIE luminogens have been practically fabricated into AIE dots for bioimaging, further improvement of their brightness is needed although this is technically challenging. In this review, we surveyed the recent advances in strategic molecular engineering of highly emissive AIE dots, including nanoscale crystallization and matrix-assisted rigidification. We hope that this timely summary can deepen the understanding about the root cause of the high emission of AIE dots and provide inspiration to the rational design of functional aggregates.

NIR-II Imaging-Guided Mitochondrial-Targeting Organic Nanoparticles for Multimodal Synergistic Tumor Therapy

Effectively interfering energy metabolism in tumor cells and simultaneously activating the in vivo immune system to perform immune attacks are meaningful for tumor treatment. However, precisely targeted therapy is still a huge challenge. Herein, a mitochondrial-targeting phototheranostic system, FE-T nanoparticles (FE-T NPs) are developed to damage mitochondria in tumor cells and change the tumor immunosuppressive microenvironment. FE-T NPs are engineered by encapsulating the near-infrared (NIR) absorbed photosensitizer IR-FE-TPP within amphiphilic copolymer DSPE-SS-PEG-COOH for high-performing with simultaneous mitochondrial-targeting, near-infrared II (NIR-II) fluorescence imaging, and synchronous photothermal therapy (PTT) /photodynamic therapy (PDT) /immune therapy (IMT). In tumor treatment, the disulfide in the copolymer can be cleaved by excess intracellular glutathione (GSH) to release IR-FE-TPP and accumulate in mitochondria. After 808 nm irradiation, the mitochondrial localization of FE-T NPs generated reactive oxygen species (ROS), and hyperthermia, leading to mitochondrial dysfunction, photoinductive apoptosis, and immunogenic cell death (ICD). Notably, in situ enhanced PDT/PTT in vivo via mitochondrial-targeting with FE-T NPs boosts highly efficient ICD toward excellent antitumor immune response. FE-T NPs provide an effective mitochondrial-targeting phototheranostic nanoplatform for imaging-guided tumor therapy.

In Vivo Fluorescence Imaging-Guided Development of Near-Infrared AIEgens

In vivo fluorescence imaging has received extensive attention due to its distinguished advantages of excellent biosafety, high sensitivity, dual temporal-spatial resolution, real-time monitoring ability, and non-invasiveness. Aggregation-induced emission luminogens (AIEgens) with near-infrared (NIR) absorption and emission wavelengths are ideal candidate for in vivo fluorescence imaging for their large Stokes shift, high brightness and superior photostability. NIR emissive AIEgens provide deep tissue penetration depth as well as low interference from tissue autofluorescence. Here in this review, we summarize the molecular engineering strategies for constructing NIR AIEgens with high performances, including extending π-conjugation system and strengthen donor (D)-acceptor (A) interactions. Then the encapsulation strategies for increasing water solubility and biocompatibility of these NIR AIEgens are highlighted. Finally, the challenges and prospect of fabricating NIR AIEgens for in vivo fluorescence imaging are also discussed. We hope this review would provide some guidelines for further exploration of new NIR AIEgens.

Lanthanide porphyrinoids as molecular theranostics

In recent years, lanthanide (Ln) porphyrinoids have received increasing attention as theranostics. Broadly speaking, the term 'theranostics' refers to agents designed to allow both disease diagnosis and therapeutic intervention. This Review summarises the history and the 'state-of-the-art' development of Ln porphyrinoids as theranostic agents. The emphasis is on the progress made within the past decade. Applications of Ln porphyrinoids in near-infrared (NIR, 650-1700 nm) fluorescence imaging (FL), magnetic resonance imaging (MRI), radiotherapy, and chemotherapy will be discussed. The use of Ln porphyrinoids as photo-activated agents ('phototheranostics') will also be highlighted in the context of three promising strategies for regulation of porphyrinic triplet energy dissipation pathways, namely: regioisomeric effects, metal regulation, and the use of expanded porphyrinoids. The goal of this Review is to showcase some of the ongoing efforts being made to optimise Ln porphyrinoids as theranostics and as phototheranostics, in order to provide a platform for understanding likely future developments in the area, including those associated with structure-based innovations, functional improvements, and emerging biological activation strategies.

Fabrication of avidin-stabilized gold nanoclusters with dual emissions and their application in biosensing

Protein-stabilized gold nanoclusters (Prot-Au NCs) have been widely used in biosensing and cell imaging owing to their excellent optical properties and low biotoxicity. However, several Prot-Au NCs reported in the literature do not retain the biological role of the protein, which greatly limits their ability to directly detect biomarkers. This study demonstrated for the first time the successful synthesis of dual-function avidin-stabilized gold nanoclusters (Av–Au NCs) using a one-pot method. The resulting Av–Au NCs exhibited intense blue and red emissions under 374 nm excitation. Furthermore, the Av–Au NCs retained the native functionality of avidin to bind to biotin. When DNA strands modified with biotin at both ends (i.e., linker chains) were mixed with Av–Au NCs, large polymers were formed, indicating that Av–Au NCs could achieve fluorescence signal amplification by interacting with biotin. Taking advantage of the aforementioned properties, we constructed a novel enzyme-free fluorescent biosensor based on the Av–Au NCs-biotin system to detect DNA. The designed fluorescent biosensor could detect target DNA down to 0.043 nM, with a wide line range from 0.2 nM to 20 µM. Thus, these dual-functional Av–Au NCs were shown to be an excellent fluorescent material for biosensing.

Avidin-stabilized gold nanoclusters (Av–Au NCs) were synthesized for the first time by a water-bath method.

The synthesized Av–Au NCs not only exhibited intense blue and red emissions under 374 nm excitation, but also retained the native functionality of avidin to bind to biotin.

The fluorescent signal amplification system constructed by the interaction of Av–Au NCs with biotin was successfully applied to detect target DNA in vitro.

NIR-I Dye-Based Probe: A New Window for Bimodal Tumor Theranostics

Near-infrared (NIR, 650–1700 nm) bioimaging has emerged as a powerful strategy in tumor diagnosis. In particular, NIR-I fluorescence imaging (650–950 nm) has drawn more attention, benefiting from the high quantum yield and good biocompatibility. Since their biomedical applications are slightly limited by their relatively low penetration depth, NIR-I fluorescence imaging probes have been under extensive development in recent years. This review summarizes the particular application of the NIR-I fluorescent dye-contained bimodal probes, with emphasis on related nanoprobes. These probes have enabled us to overcome the drawbacks of individual imaging modalities as well as achieve synergistic imaging. Meanwhile, the application of these NIR-I fluorescence-based bimodal probes for cancer theranostics is highlighted.