Self-Assembly of a Monochromophore-Based Polymer Enables Unprecedented Ratiometric Tracing of Hypoxia

Supramolecular nanotherapeutics based on cucurbiturils

Polymeric biomaterials have important applications in aiding clinical disease treatment, including drug delivery, bioimaging, and tissue engineering. Currently, conventional tumor chemotherapy faces obstacles such as poor solubility/stability, inability to target, and uncontrolled drug release in clinical trials, for which the emergence of supramolecular material therapeutics combining non-covalent interactions with conventional therapies is a very promising candidate. Due to their molecular recognition abilities with a range of biomolecules, cucurbit[n]uril (CB[n]), a type of macrocyclic receptors with robust backbones, hydrophobic cavities, and carbonyl-binding channels, have garnered a lot of attention. Therefore, this paper reviews recent advances in CB[n] material-based supramolecular therapeutics for clinical treatments, including targeted delivery applications and related imaging and sensing systems. This study also covers the distinctive benefits of CB materials for biological applications, as well as the trends and prospects of this interdisciplinary subject, based on numerous state-of-the-art research findings.

Aggregation-Induced Emission Luminogen: Role in Biopsy for Precision Medicine

Biopsy, including tissue and liquid biopsy, offers comprehensive and real-time physiological and pathological information for disease detection, diagnosis, and monitoring. Fluorescent probes are frequently selected to obtain adequate information on pathological processes in a rapid and minimally invasive manner based on their advantages for biopsy. However, conventional fluorescent probes have been found to show aggregation-caused quenching (ACQ) properties, impeding greater progresses in this area. Since the discovery of aggregation-induced emission luminogen (AIEgen) have promoted rapid advancements in molecular bionanomaterials owing to their unique properties, including high quantum yield (QY) and signal-to-noise ratio (SNR), etc. This review seeks to present the latest advances in AIEgen-based biofluorescent probes for biopsy in real or artificial samples, and also the key properties of these AIE probes. This review is divided into: (i) tissue biopsy based on smart AIEgens, (ii) blood sample biopsy based on smart AIEgens, (iii) urine sample biopsy based on smart AIEgens, (iv) saliva sample biopsy based on smart AIEgens, (v) biopsy of other liquid samples based on smart AIEgens, and (vi) perspectives and conclusion. This review could provide additional guidance to motivate interest and bolster more innovative ideas for further exploring the applications of various smart AIEgens in precision medicine.

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Cucurbit[8]uril-based supramolecular theranostics

Different from most of the conventional platforms with dissatisfactory theranostic capabilities, supramolecular nanotheranostic systems have unparalleled advantages via the artful combination of supramolecular chemistry and nanotechnology. Benefiting from the tunable stimuli-responsiveness and compatible hierarchical organization, host-guest interactions have developed into the most popular mainstay for constructing supramolecular nanoplatforms. Characterized by the strong and diverse complexation property, cucurbit[8]uril (CB[8]) shows great potential as important building blocks for supramolecular theranostic systems. In this review, we summarize the recent progress of CB[8]-based supramolecular theranostics regarding the design, manufacture and theranostic mechanism. Meanwhile, the current limitations and corresponding reasonable solutions as well as the potential future development are also discussed.

Cucurbit[8]uril-based water-dispersible assemblies with enhanced optoacoustic performance for multispectral optoacoustic imaging

Organic small-molecule contrast agents have attracted considerable attention in the field of multispectral optoacoustic imaging, but their weak optoacoustic performance resulted from relatively low extinction coefficient and poor water solubility restrains their widespread applications. Herein, we address these limitations by constructing supramolecular assemblies based on cucurbit[8]uril (CB[8]). Two dixanthene-based chromophores (DXP and DXBTZ) are synthesized as the model guest compounds, and then included in CB[8] to prepare host-guest complexes. The obtained DXP-CB[8] and DXBTZ-CB[8] display red-shifted and increased absorption as well as decreased fluorescence, thereby leading to a substantial enhancement in optoacoustic performance. Biological application potential of DXBTZ-CB[8] is investigated after co-assembly with chondroitin sulfate A (CSA). Benefiting from the excellent optoacoustic property of DXBTZ-CB[8] and the CD44-targeting feature of CSA, the formulated DXBTZ-CB[8]/CSA can effectively detect and diagnose subcutaneous tumors, orthotopic bladder tumors, lymphatic metastasis of tumors and ischemia/reperfusion-induced acute kidney injury in mouse models with multispectral optoacoustic imaging.

Platinum Drug-Incorporating Polymeric Nanosystems for Precise Cancer Therapy

Platinum (Pt) drugs are widely used in clinic for cancer therapy, but their therapeutic outcomes are significantly compromised by severe side effects and acquired drug resistance. With the emerging immunotherapy and imaging-guided cancer therapy, precise delivery and release of Pt drugs have drawn great attention these days. The targeting delivery of Pt drugs can greatly increase the accumulation at tumor sites, which ultimately enhances antitumor efficacy. Further, with the combination of Pt drugs and other theranostic agents into one nanosystem, it not only possesses excellent synergistic efficacy but also achieves real-time monitoring. In this review, after the introduction of Pt drugs and their characteristics, the recent progress of polymeric nanosystems for efficient delivery of Pt drugs is summarized with an emphasis on multi-modal synergistic therapy and imaging-guided Pt-based cancer treatment. In the end, the conclusions and future perspectives of Pt-encapsulated nanosystems are given.

Vision for Ratiometric Nanoprobes: In Vivo Noninvasive Visualization and Readout of Physiological Hallmarks

Lesion areas are distinguished from normal tissues surrounding them by distinct physiological characteristics. These features serve as biological hallmarks with which targeted biomedical imaging of the lesion sites can be achieved. Although tremendous efforts have been devoted to providing smart imaging probes with the capability of visualizing the physiological hallmarks at the molecular level, the majority of them are merely able to derive anatomical information from the tissues of interest, and thus are not suitable for taking part in in vivo quantification of the biomarkers. Recent advances in chemical construction of advanced ratiometric nanoprobes (RNPs) have enabled a horizon for quantitatively monitoring the biological abnormalities in vivo. In contrast to the conventional probes whose dependency of output on single-signal profiles restricts them from taking part in quantitative practices, RNPs are designed to provide information in two channels, affording a self-calibration opportunity to exclude the analyte-independent factors from the outputs and address the issue. Most of the conventional RNPs have encountered several challenges regarding the reliability and sufficiency of the obtained data for high-performance imaging. In this Review, we have summarized the recent progresses in developing highly advanced RNPs with the capabilities of deriving maximized information from the lesion areas of interest as well as adapting themselves to the complex biological systems in order to minimize microenvironmental-induced falsified signals. To provide a better outlook on the current advanced RNPs, nanoprobes based on optical, photoacoustic, and magnetic resonance imaging modalities for visualizing a wide range of analytes such as pH, reactive species, and different derivations of amino acids have been included. Furthermore, the physicochemical properties of the RNPs, the major constituents of the nanosystems and the analyte recognition mechanisms have been introduced. Moreover, the alterations in the values of the ratiometric signal in response to the analyte of interest as well as the time at which the highest value is achieved, have been included for most of RNPs discussed in this Review. Finally, the challenges as well as future perspectives in the field are discussed.

NIR-II Dyad-Doped Ratiometric Nanosensor with Enhanced Spectral Fidelity in Biological Media for In Vivo Biosensing

Ratiometric fluorescence nanosensors provide quantitative biological information. However, spectral shift and distortion of ratiometric nanosensors in biological media often compromise sensing accuracy, limiting in vivo applications. Here, we develop a fluorescent dyad (aBOP-IR1110) in the second near-infrared (NIR-II) window by covalently linking an asymmetric aza-BODIPY with a ONOO^--responsive meso-thiocyanine. The dyad encapsulated in the PEGylated nanomicelle largely improves spectral fidelity in serum culture by >9.4 times compared to that of its noncovalent counterpart. The increased molecular weights (>1480 Da) and hydrophobicity (LogP of 7.87-12.36) lock dyads inside the micelles, which act as the shield against the external environment. ONOO^--altered intramolecular Förster resonance energy transfer (FRET) generates linear ratiometric response with better serum tolerance, enabling us to monitor the dynamics of oxidative stress in traumatic brain injury and evaluate therapeutic efficiency. The results show high correlation with in vitro triphenyltetrazolium chloride staining, suggesting the potential of NIR-II dyad-doped nanosensor for in vivo high-fidelity sensing applications.

Cerium-terephthalic acid metal-organic frameworks for ratiometric fluorescence detecting and scavenging·OH from fuel combustion gas

Hydroxyl radical (•OH) in fuel combustion gas seriously damages human health. The techniques for simultaneously detecting and scavenging •OH in these gases are limited by poor thermal resistance. To meet this challenge, herein, metal organic frameworks (MOFs) with high thermal stability (80-400 °C) and dual function (•OH detection and elimination) are developed by coordinating Ce ions with terephthalic acid (TA) (Ce-BDC). Due to the reversible conversion between Ce³⁺ and Ce⁴⁺, and the high concentration of Ce³⁺ on the surface of Ce-BDC MOFs (89.6%), an •OH scavenging efficiency over 90% is realized. Ratiometric fluorescence (I_440 nm/I_355 nm) detection of •OH with a low detection limit of ∼4 μM is established by adopting Ce ions as an internal standard and TA as an •OH-responsive fluorophore. For real applications, the Ce-BDC MOFs demonstrate excellent •OH detection sensitivity and high •OH scavenging efficiency in gas produced from cigarettes, wood fiber and machine oil. Mouse model results show that the damage caused by •OH in cigarette smoke can be greatly reduced by Ce-BDC MOFs. This work provides a promising strategy for sensitively detecting and efficiently eliminating •OH in fuel combustion gas.

Rational Design of a Near-Infrared Ratiometric Probe with a Large Stokes Shift: Visualization of Polarity Abnormalities in Non-Alcoholic Fatty Liver Model Mice

Tracking liver polarity with noninvasive and dynamic imaging techniques is helpful to better understand the non-alcoholic fatty liver (NAFL). Herein, a novel near-infrared (NIR) fluorescent probe Cy-Mp is constructed using a "symmetry collapse" strategy. The structure modification leads to the conversion of locally excited state fluorescence to charge transfer state fluorescence. Cy-Mp emits at near-infrared (NIR) wavelengths with high photostability as well as a large Stokes shift. Cy-Mp exhibits a ratiometric response to polarity, providing more accurate analysis of intracellular polarity via the built-in internal reference correction. Most importantly, the in vivo studies indicate that Cy-Mp can accumulate in the liver and the decreased polarity in the liver of mice with NAFL is verified by the ratiometric imaging, implying the great potential of Cy-Mp in the diagnosis of NAFL.

NIR-II J-Aggregated Pt(II)-Porphyrin-Based Phosphorescent Probe for Tumor-Hypoxia Imaging

The luminescence of traditional phosphorescence-based hypoxia probes is limited to the visible and first near-infrared wavelength regions (<1000 nm), which has defects of higher light scattering and lower penetration depth in contrast with the second near-infrared wavelength window (NIR-II, 1000-1700 nm) for optical bioimaging. Herein, 5,15-bis(2,6-bis(dodecyloxy)phenyl)-porphyrin platinum(II) (PpyPt) with J-aggregation induced NIR-II phosphorescence is reported. J-aggregates of PpyPt are confirmed by the X-ray diffraction data in the crystalline state. Moreover, the emission and excitation spectra of PpyPt in the solid states reveal NIR-II luminescence feature of PpyPt in J-aggregates. More importantly, by preparation of water-soluble PpyPt nanoparticles (PpyPt NPs_4.76 ) with J-aggregates, it has NIR-II phosphorescent lifetime of microseconds and good oxygen-sensitivity in water. Moreover, the good biological hypoxia-sensing potential of PpyPt NPs_4.76 is demonstrated in cells and 4T1-tumor-bearing mice. This study provides an efficient strategy to design NIR-II phosphorescent probe for sensitive tumor-hypoxia detection through the construction of J-aggregates.

Near-Infrared Phosphorescent Switch of Diarylethene Phenylpyridinium Derivative and Cucurbit[8]uril for Cell Imaging

Near-infrared (NIR) pure organic room-temperature phosphorescence (RTP) materials have received growing research interest due to their wide application in the fields of high-resolution bioimaging and luminescent materials. In this work, the authors report a macrocycle-confined pure organic RTP supramolecular assembly, which is constructed by diarylethene phenylpyridinium derivative (DTE-TP) and cucurbit[8]uril (CB[8]). Compared with CB[6] and CB[7], the larger cavity of CB[8] induces molecular folding and enhances the intramolecular charge transfer interactions, which leads to the obtained assembly emitting efficient NIR phosphorescence at 700 nm. Due to the photochromism of the diarylethene core, the NIR phosphorescence is reversibly regulated by light irradiation at wavelengths of 365 and >600 nm. Furthermore, cell-based experiments show that this supramolecular assembly is located in the lysosomes and displays a NIR phosphorescence at 650-750 nm. In addition, by means of phosphorescence resonance energy transfer, the obtained assembly exhibits a red-shifted NIR emission at 817 nm. This supramolecular phosphorescent switch provides a convenient path for the modular design of water-soluble pure organic room-temperature NIR phosphorescent materials.

Dissecting extracellular and intracellular distribution of nanoparticles and their contribution to therapeutic response by monochromatic ratiometric imaging

Efficient delivery of payload to intracellular targets has been identified as the central principle for nanomedicine development, while the extracellular targets are equally important for cancer treatment. Notably, the contribution of extracellularly distributed nanoparticles to therapeutic outcome is far from being understood. Herein, we develop a pH/light dual-responsive monochromatic ratiometric imaging nanoparticle (MRIN), which functions through sequentially lighting up the intracellular and extracellular fluorescence signals by acidic endocytic pH and near-infrared light. Enabled by MRIN nanotechnology, we accurately quantify the extracellular and intracellular distribution of nanoparticles in several tumor models, which account for 65-80% and 20-35% of total tumor exposure, respectively. Given that the majority of nanoparticles are trapped in extracellular regions, we successfully dissect the contribution of extracellularly distributed nanophotosensitizer to therapeutic efficacy, thereby maximize the treatment outcome. Our study provides key strategies to precisely quantify nanocarrier microdistribtion and engineer multifunctional nanomedicines for efficient theranostics.

Phosphorescent NIR emitters for biomedicine: applications, advances and challenges

Application of NIR (near-infrared) emitting transition metal complexes in biomedicine is a rapidly developing area of research. Emission of this class of compounds in the "optical transparency windows" of biological tissues and the intrinsic sensitivity of their phosphorescence to oxygen resulted in the preparation of several commercial oxygen sensors capable of deep (up to whole-body) and quantitative mapping of oxygen gradients suitable for in vivo experimental studies. In addition to this achievement, the last decade has also witnessed the increased growth of successful alternative applications of NIR phosphors that include (i) site-specific in vitro and in vivo visualization of sophisticated biological models ranging from 3D cell cultures to intact animals; (ii) sensing of various biologically relevant analytes, such as pH, reactive oxygen and nitrogen species, RedOx agents, etc.; (iii) and several therapeutic applications such as photodynamic (PDT), photothermal (PTT), and photoactivated cancer (PACT) therapies as well as their combinations with other therapeutic and imaging modalities to yield new variants of combined therapies and theranostics. Nevertheless, emerging applications of these compounds in experimental biomedicine and their implementation as therapeutic agents practically applicable in PDT, PTT, and PACT face challenges related to a critically important improvement of their photophysical and physico-chemical characteristics. This review outlines the current state of the art and achievements of the last decade and stresses the most promising trends, major development prospects, and challenges in the design of NIR phosphors suitable for biomedical applications.

Nonconventional luminophores: characteristics, advancements and perspectives

Nonconventional luminophores devoid of remarkable conjugates have attracted considerable attention due to their unique luminescence behaviors, updated luminescence mechanism of organics and promising applications in optoelectronic, biological and medical fields. Unlike classic luminogens consisting of molecular segments with greatly extended electron delocalization, these unorthodox luminophores generally possess nonconjugated structures based on subgroups such as ether (-O-), hydroxyl (-OH), halogens, carbonyl (CO), carboxyl (-COOH), cyano (CN), thioether (-S-), sulfoxide (SO), sulfone (OSO), phosphate, and aliphatic amine, as well as their grouped functionalities like amide, imide, anhydride and ureido. They can exhibit intriguing intrinsic luminescence, generally featuring concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence and prevailing phosphorescence. Herein, we review the recent progress in exploring these nonconventional luminophores and discuss the current challenges and future perspectives. Notably, different mechanisms are reviewed and the clustering-triggered emission (CTE) mechanism is highlighted, which emphasizes the clustering of the above mentioned electron rich moieties and consequent electron delocalization along with conformation rigidification. The CTE mechanism seems widely applicable for diversified natural, synthetic and supramolecular systems.

Molecular Design of Monochromophore-Based Bifunctional Photosensitizers for Simultaneous Ratiometric Oxygen Reporting and Photodynamic Cancer Therapy

Monitoring the tumor oxygen level when implementing photodynamic therapy (PDT) on malignant cancer has vital significance but remains challenging yet. Herein, by structurally manipulating a 2,4-dimethylpyrrole-engineered asymmetric BODIPY scaffold with different kinds, numbers, and positions of halogen atoms, we rationally designed several monochromophore-based bifunctional photosensitizers, named BDPs (BDP-I, BDP-II, and BDP-III), with self-sensitized photooxidation characteristics for accurate oxygen reporting and photodynamic tumor ablation. We show that different ways of halogen regulation allow available tuning of BDPs' oxygen-dependent ratiometric fluorescence turn-ons upon light irradiation as well as type-II PDT efficiencies before and after self-sensitized photooxidation. Encouragingly, measuring the specific ratiometric signals of the most promising BDP-II enabled the direct observation of initial oxygen concentration in both living 4T1 cells and a tumor-bearing mice model, affording an alternative way for evaluating oxygen supplementation strategies. Meanwhile, the "always on" PDT effect of BDP-II ensured efficient tumor ablation via apoptosis. Our research was thus believed to be of instructive significance for future application of oxygen-related auxiliary strategies and the design of unimolecular multifunctional PDT agents for cancer precision therapy.

Photoresponsive metallopolymer nanoparticles for cancer theranostics

Over the past decades, transition metal complexes have been successfully used in anticancer phototherapies. They have shown promising properties in many different areas including photo-induced ligand exchange or release, rich excited state behavior, and versatile biochemical properties. When encorporated into polymeric frameworks and become part of nanostructures, photoresponsive metallopolymer nanoparticles (MPNs) show enhanced water solubility, extended blood circulation and increased tumor-specific accumulation, which greatly improves the tumor therapeutic effects compared to low-molecule-weight metal complexes. In this review, we aim to present the recent development of photoresponsive MPNs as therapeutic nanomedicines. This review will summarize four major areas separately, namely platinum-containing polymers, zinc-containing polymers, iridium-containing polymers and ruthenium-containing polymers. Representative MPNs of each type are discussed in terms of their design strategies, fabrication methods, and working mechanisms. Current challenges and future perspectives in this field are also highlighted.

The development of phosphorescent probes for in vitro and in vivo bioimaging

Phosphorescence is a process that slowly releases the photoexcitation energy after the removal of the excitation source. Although transition metal complexes and purely organic room-temperature phosphorescence (RTP) materials show excellent phosphorescence property, their applications in in vitro and in vivo bioimaging are limited due to their poor solubility in water. To overcome this issue, phosphorescent materials are modified with amphiphilic or hydrophilic polymers to endow them with biocompatibility. This review focuses on recent advances in the development of phosphorescent probes for in vitro and in vivo bioimaging. The photophysical mechanism and the design principles of transition metal complexes and purely organic RTP materials for the stabilization of the triplet excited state for enhanced phosphorescence are first discussed. Then, the applications in in vitro and in vivo bioimaging using transition metal complexes including iridium(iii) complexes, platinum(ii) complexes, rhodium(i) complexes, and purely organic RTP materials are summarized. Finally, the current challenges and perspectives for these emerging materials in bioimaging are discussed.

Regulation of the Switchable Luminescence of Tridentate Platinum(II) Complexes by Photoisomerization

Organoplatinum (II) complexes are promising candidates for the construction of smart supramolecular materials due to their unique flat structures. This accompanied by intriguing luminescent properties, prompts the molecules to aggregate after external stimuli. Nevertheless, the utilization of photo-responsive subunits to modulate their assemble behaviors and functions are still rarely explored. In this work, azobenzene (azo)-appended tridentate platinum (II) complexes with different linkers have been designed and synthesized. The intermolecular hydrogen bonding, π-π stacking, and metal-metal interactions were finely controlled through the tiny alteration of the linkers, which was found to play a vital role in self-assembly, and photophysical and photoisomerization properties. Some of them exhibited dual emission bands originating from metal-perturbed triplet intraligand (3IL) and metal-metal to ligand charge transfer (3MMLCT) excited states due to the different intermolecular interactions. Based on this, the manipulation of switchable luminescence as well as the controllable morphologies have been realized by photoisomerization.

Organic fluorescent nanoparticles with NIR-II emission for bioimaging and therapy

Fluorescence imaging technology in the second near-infrared bio-channel (NIR-II) has the advantages of low light scattering and weak autofluorescence. It can obtain high spatial resolution imaging in deeper biological tissues and realize accurate diagnosis in the lesion. As a new cancer treatment method, photothermal therapy has the characteristics of obvious curative effect and small side effects. However, the hydrophobicity and non-selectivity of many fluorescent materials, aggregation-induced fluorescence quenching, and other problems lead to undesirable imaging results. Here, we reviewed the structure of the NIR-II fluorescent molecules and these dyes whose fluorescence tail emission is in the NIR-II bio-channel, discussed in detail how to realize the redshift of the dye wavelength, including modifying the push-pull electron system, extending the conjugated chain, and forming J-aggregates and other methods. We also summarize some strategies to improve brightness, including responsiveness, targeting, adjustment of aggregation mode, and aggregation-induced emission effect, thereby improving the imaging performance and therapeutic effect of NIR-II fluorescent dyes.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

Supramolecular ensembles modified by near-infrared dyes and their biological applications

Near-infrared dyes possess the qualities of lower interference with biological autofluorescence, low photon scattering, and deep tissue penetration, and are being increasingly involved in the development of biomaterials for sensing and precision medicine. However, dyes usually suffer from the disadvantages of poor water solubility and photobleaching, factors that limit their application in vivo. The introduction of supramolecular ensembles can provide an ideal solution. This review presents recently developed supramolecular ensembles modified by near-infrared dyes. Compared with small-molecule fluorophores, the specific size of a supramolecular-based fluorophore endows it with longer circulation time in the bloodstream, increasing its chances of reaching a specific target. In addition, the construction of supramolecule-based fluorophores with versatile functions can be achieved by simple encapsulation or doping, instead of by complicated chemical synthesis. Thus, supramolecular-complex-based fluorophores offer high potential in diagnosis and therapy. This review outlines four different species of near-infrared dye based ensembles in terms of their method of formation, including simple encapsulation or doping and copolymerisation. Recently, a new technology has employed modified fluorophores for in situ self-assembly that form supramolecular ensembles at a specific position, thus solving the problem of poor uptake of nanoparticles by cells, and is included in this review. Finally, the future of this field is considered.

Ultralong purely organic aqueous phosphorescence supramolecular polymer for targeted tumor cell imaging

Purely organic room-temperature phosphorescence has attracted attention for bioimaging but can be quenched in aqueous systems. Here we report a water-soluble ultralong organic room-temperature phosphorescent supramolecular polymer by combining cucurbit[n]uril (CB[7], CB[8]) and hyaluronic acid (HA) as a tumor-targeting ligand conjugated to a 4-(4-bromophenyl)pyridin-1-ium bromide (BrBP) phosphor. The result shows that CB[7] mediated pseudorotaxane polymer CB[7]/HA-BrBP changes from small spherical aggregates to a linear array, whereas complexation with CB[8] results in biaxial pseudorotaxane polymer CB[8]/HA-BrBP which transforms to relatively large aggregates. Owing to the more stable 1:2 inclusion complex between CB[8] and BrBP and the multiple hydrogen bonds, this supramolecular polymer has ultralong purely organic RTP lifetime in water up to 4.33 ms with a quantum yield of 7.58%. Benefiting from the targeting property of HA, this supramolecular polymer is successfully applied for cancer cell targeted phosphorescence imaging of mitochondria.

Design strategy of optical probes for tumor hypoxia imaging

Clinical manifestations of tumors indicate that malignant phenotypes developing in the hypoxic microenvironment lead to resistance to cancer treatment, rendering chemotherapy, radiotherapy, and photodynamic therapy less sensitive and effective in patients with tumor. Visualizing the oxygen level in the tumor environment has garnered much attention due to its implications in precision tumor therapy. Following the rapid development of biomaterials in nanotechnology, various nanomaterials have been designed to visualize the oxygen levels in tumors. Here, we review recent research on detecting oxygen levels in solid tumors for tumor hypoxia imaging. To monitor the hypoxic level of tumors, two main strategies were investigated: directly detecting oxygen levels in tumors and monitoring the hypoxia-assisted reduced microenvironment. We believe that hypoxia as a tumor-specific microenvironment can be a breakthrough in the clinical treatment of tumors.

Internal standard fluorogenic probe based on vibration-induced emission for visualizing PTP1B in living cells

Herein, as a proof of concept, we developed the first enzymatic VIE fluorogenic probe for protein tyrosine phosphatase 1B (PTP1B).

Catalase-Integrated Hyaluronic Acid as Nanocarriers for Enhanced Photodynamic Therapy in Solid Tumor

Photodynamic therapy (PDT) as a treatment method has many advantages such as minimal invasiveness, repeatable dosage, and low systemic toxicity. Issues with conventional PDT agents include the limited availability of endogenous oxygen and difficulty in accumulation at the tumor site, which has hindered the successful treatment of tumors. Herein, we developed catalase-encapsulated hyaluronic-acid-based nanoparticles loaded with adamantane-modified photosensitizer for enhanced PDT of solid tumors. Chlorin e6 (Ce6) as the photosensitizer was modified with adamantane to yield adamantane-modified Ce6 (aCe6). The obtained nanosystem (HA-CAT@aCe6) could target overly expressed CD44 receptors on cancer cells, supplying oxygen by converting endogenous hydrogen peroxide (H₂O₂) to oxygen, and improving PDT efficacy upon light irradiation. HA-CAT@aCe6 nanoparticles showed high colloidal stability and monodispersity in aqueous solution. The uptake and targeting property of HA-CAT@aCe6 were demonstrated by confocal microscopy and flow cytometry in the MDA-MB-231 cell line possessing overly expressed CD44 receptors. The encapsulated catalase was able to decompose the endogenous H₂O₂ to generate O₂ in situ for relieving hypoxia in cells incubated under hypoxic conditions. Cell viability assays indicated that HA-CAT@aCe6 possessed minimal cytotoxicity in the dark, while presenting high cellular toxicity under 660 nm light irradiation at normoxic conditions. As a result of the catalase capability in relieving hypoxia, HA-CAT@aCe6 also exhibited high cellular cytotoxicity under hypoxic condition. In vivo experiments revealed selective tumor accumulation of HA-CAT@aCe6 in MDA-MB-231 tumor bearing nude mice. Significant tumor regression was observed after intravenous injection of HA-CAT@aCe6 under light irradiation in comparison to the control system without loading catalase. Thus, HA-CAT@aCe6 demonstrated a great potential in overcoming hypoxia for targeted PDT.

Ratiometric Nanoparticle Array-Based Near-Infrared Fluorescent Probes for Quantitative Protein Sensing

Quantitative detection of protein biomarkers is crucial to medical diagnosis. Fluorescent probes have been frequently used for protein detection, but they suffered from various weaknesses such as lack of versatility. In particular, most of the reported probes were not capable of simultaneous qualitative and quantitative detection for various proteins. In this paper, we developed novel nanoparticle array-based near-infrared (NIR) ratiometric probes for potent protein analysis, in which the specific protein was able to be distinguished and quantitated within a group of 11 common proteins. The activity of β-galactosidases (β-gal) was temporarily inhibited by the adsorption to magnetic nanoparticles and restored to certain content by replacement with detected proteins, leading to distinctive readout of the enzyme-activatable NIR probe (DCM-β-gal). The readout of the sensor array against 11 proteins, as verified by isothermal titration calorimetry, was processed and transformed into canonical factors with the help of linear discrimination analysis. Moreover, the ratiometric signals of DCM-β-gal were translated to quantitatively detect proteins within the concentration range of 0-100 μg/mL. Based on clear differentiation within both two-dimensional and three-dimensional plots, different proteins could be detected with 100% accuracy with their concentration simultaneously determined, which endowed the sensing system with great potential in clinical diagnosis.

Aggregation/dispersion-mediated peroxidase-like activity of MoS2 quantum dots for colorimetric pyrophosphate detection

Peroxidase-like activity of MoS₂ quantum dots can be manipulated by aggregation/dispersion in the presence of Fe³⁺ or a mix of Fe³⁺ and pyrophosphate (PPi). Based on this finding, a simple and reliable method for colorimetric PPi detection is developed.