Light emission enhancement by supramolecular complexation of chemiluminescence probes designed for bioimaging

Point-of-Care Testing of Whole Blood for Liver Injury Auxiliary Diagnosis with Biothiols Activable Chemiluminescent Probe

Liver injury significantly affects a patient's health and quality of life. However, timely and convenient diagnosis of this disease via whole blood detection remains challenging due to the lack of user-friendly and fast readout blood test methods. Herein, we developed such a method for the swift auxiliary diagnosis of liver injury via whole blood detection using a customed point-of-care testing (POCT) system consisting of a biothiols-activatable chemiluminescent probe and a hand-held POCT device. Biothiols served as the target to build the activable chemiluminescence probe due to their abnormal level in liver injury. Compared with fluorescent and electrical POCTs, this method is more convenient and has strong universality. By incorporating cyclodextrin via host-guest chemistry, we intensified chemiluminescence while mitigating chemical hemolysis caused by the dissolution of organic molecules, making this system suitable for whole blood analysis. Preliminary assessments in aqueous solutions, living cells, and mouse models confirmed its sensitivity, reliability, and feasibility. Simply mixing blood with the probe for 30 min yielded a clear signal readout within 15 s on the POCT device. Utilizing this portable detector, the reduced biothiol level was tested in 18 liver injury patient blood samples, and the results were similar to those measured by a commercial kit and in vivo imaging system. Thus, this work provides a universal platform for the fast and convenient detection of other biomarkers in whole blood samples and opens up possibilities for the rapid clinical diagnosis of diseases, enabling patients to conduct home self-examinations with ease.

Cucurbit[7]uril as the host of adamantane-modified dyes for fluorescence enhancement in aqueous environments

Taking advantage of the excellent host-guest complexation ability between an auxochrome (adamantane group) and CB[7], the fluorescence emission performance of dyes in water was effectively improved with the addition of two equivalents of CB[7], which provided an efficient method for increasing fluorescence intensity in aqueous environments. Furthermore, these dyes with the host were successfully used in cell imaging.

Fluorescence Enhancement of Adamantane-Modified Dyes in Aqueous Solution via Supramolecular Interaction with Methyl-β-cyclodextrin and Their Application in Cell Imaging

The fluorescence of functional dyes was generally quenched in aqueous solution, which hindered their application in water-bearing detections. In this work, a novel strategy based on host-guest interaction was provided for the purpose of fluorescence enhancement in aqueous solution and cell imaging. Three adamantane-modified fluorescent dyes (Coum-Ad, NP-Ad, NR-Ad) with coumarin, 1,8-naphthalimide and Nile Red as fluorophores were initially designed and prepared. The ((adamantan-1-yl)methyl)amino group, as the auxochrome of those dyes, complexed with methylated β-cyclodextrin (M-β-CD) via supramolecular interaction, and then fluorescent supramolecular nanoparticles (FSNPs) were formed by self-assembly in water. The inclusion equilibrium constant (K) could be as high as 3.94×104  M-1 . With the addition of M-β-CD, fluorescence quantum yields of these dyes were separately improved to 69.8 %, 32.9 % and 41.3 %. Inspired by the above satisfactory results, six adamantane-modified probes organelle-NPAds with organelle-targeting capability were further obtained. As the formation of hydrogen bonds between organelle-NPAd2 and M-β-CD verified by theoretical calculation, K of organelle-NPAd2 (5.13×104  M-1 ~4.53×105  M-1 ) with M-β-CD was higher than that of organelle-NPAd1 (1.15×104  M-1 ~3.66×104  M-1 ) and their fluorescence quantum yields increased to 32.8 %~83.6 % in aqueous solution. In addition, fluorescence enhancement was realized in cell imaging with the addition of M-β-CD.

Adamantoid Scaffolds for Multiple Cargo Loading and Cellular Delivery as β-Cyclodextrin Inclusion Complexes

There is huge demand for developing guests that bind β-CD and can conjugate multiple cargos for cellular delivery. We synthesized trioxaadamantane derivatives, which can conjugate up to three cargos per guest. 1 H NMR titration and isothermal titration calorimetry revealed these guests form 1 : 1 inclusion complexes with β-CD with association constants in the order of 103  M-1 . Co-crystallization of β-CD with guests yielded crystals of their 1 : 1 inclusion complexes as determined by single-crystal X-ray diffraction. In all cases, trioxaadamantane core is buried within the hydrophobic cavity of β-CD and three hydroxyl groups are exposed outside. We established biocompatibility using representative candidate G4 and its inclusion complex with β-CD (β-CD⊂G4), by MTT assay using HeLa cells. We incubated HeLa cells with rhodamine-conjugated G4 and established cellular cargo delivery using confocal laser scanning microscopy (CLSM) and fluorescence-activated cell sorting (FACS) analysis. For functional assay, we incubated HeLa cells with β-CD-inclusion complexes of G4-derived prodrugs G6 and G7, containing one and three units of the antitumor drug (S)-(+)-camptothecin, respectively. Cells incubated with β-CD⊂G7 displayed the highest internalization and uniform distribution of camptothecin. β-CD⊂G7 showed higher cytotoxicity than G7, camptothecin, G6 and β-CD⊂G6, affirming the efficiency of adamantoid derivatives in high-density loading and cargo delivery.

Enhanced Chemiluminescence under the Nanoconfinement of Covalent-Organic Frameworks and Its Application in Sensitive Detection of Cancer Biomarkers

Chemiluminescence (CL) with intensive emission has been pursued for decades. It is still challenging to find a new mechanism to enhance CL. In this work, confinement-enhanced CL was developed for the first time by the coembedding of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) and Co²⁺ into gold nanoparticle-modified covalent-organic frameworks (COFs). For the consideration of improving the hydrophilicity of COFs and facilitating subsequent biological modification, gold nanoparticles were first reduced on the COF surface (Au-COF) in situ without other reducing reagents. By virtue of the abundant imine bond and π backbones, ABEI and Co²⁺ were embedded in Au-COF synergistically through π-π stacking and coordination. The confinement of ABEI and Co²⁺ into Au-COF brought an over 20-fold enhancement of CL intensity compared to that of adding them to a liquid phase, which benefitted from the three aspects of the confinement effect, including the molecular enrichment effect, the physical constraint effect, and the molecular preorganization effect. As proof of concept, a lipid-protein dual-recognition sandwich strategy based on this CL-functionalized COF was developed for the detection of breast cancer cell line-derived extracellular vesicles (EVs) with four orders of magnitude improvement in the detection limit compared to ELISA. The successful distinction of human epidermal growth factor receptor 2 (HER2)-positive patients from HER2-negative patients indicated the great application potential of the proposed bioassay in HER2-positive breast cancer diagnosis. This work proposed a novel enhancement mechanism for CL based on crystalline porous materials, which provides a new perspective for the development of CL-functionalized materials for biosensors and bioassays.

Fluorophore-based host-guest assembly complexes for imaging and therapy

Recently, supramolecular chemistry with its unique properties has received considerable attention in many fields. Supramolecular fluorescent systems constructed on the basis of macrocyclic hosts are not only effective in overcoming the limitations of imaging and diagnostic reagents, but also in enhancing their performances. This paper summarizes the recent advances in supramolecular fluorescent systems based on host-guest interactions and their application in bioimaging and therapy as well as the challenges and prospects in developing novel supramolecular fluorescent systems.

Reversible dynamic optical sensing based on coumarin modified β-cyclodextrin for glutathione in living cells

Coumarin acting as an optical probe was modified on ethylenediamine β-cyclodextrin, which not only enhanced its molecular binding affinity to glutathione (GSH) by a reversible Michael addition, showing 113 times more affinity than that of coumarin itself, but also achieved dynamic real-time sensing of glutathione in living HeLa cells.

Oxygen-Sensing Chemiluminescent Iridium(III) 1,2-Dioxetanes: Unusual Coordination and Activity

Next generation chemiluminescent iridium 1,2-dioxetane complexes have been developed which consist of the Schaap's 1,2-dioxetane scaffold directly attached to the metal center. This was achieved by synthetically modifying the scaffold precursor with a phenylpyridine moiety, which can act as a ligand. Reaction of this scaffold ligand with the iridium dimer [Ir(BTP)2(μ-Cl)]2 (BTP = 2-(benzo[b]thiophen-2-yl)pyridine) yielded isomers which depict ligation through either the cyclometalating carbon or, interestingly, the sulfur atom of one BTP ligand. Their corresponding 1,2-dioxetanes display chemiluminescent responses in buffered solutions, exhibiting a single, red-shifted peak at 600 nm. This triplet emission was effectively quenched by oxygen, yielding in vitro Stern-Volmer constants of 0.1 and 0.009 mbar-1 for the carbon-bound and sulfur compound, respectively. Lastly, the sulfur-bound dioxetane was further utilized for oxygen sensing in muscle tissue of living mice and xenograft models of tumor hypoxia, depicting the ability of the probe chemiluminescence to penetrate biological tissue (total flux ~ 106 p/s).

Tris(4'-Nitrobiphenyl)amine─An Octupolar Chromophore with High Two-Photon Absorption Cross-Section and Its Application for Uncaging of Calcium Ions in the Near-Infrared Region

Compounds with high two-photon absorption (2PA) performance in the near-infrared region have attracted great attention because of their application in the material and biological science. In this study, we have developed a simple and novel octupolar chromophore, tris(4'-nitrobiphenyl)amine 1, with three nitro peripheral groups attached to a triphenylamine core via biphenyl linkers. A mono-branched analogue 2 has also been prepared to investigate the effects of octupolar and dipolar systems on photophysical and 2PA behaviors. Compound 1, despite having a much simpler structure than the previous three-branched scaffolds, exhibits comparable σ₂ values, reaching 1330 GM at 730 nm and 900 GM at 820 nm in toluene. Combined with an outstanding σ₂/MW ratio (2.2 GM g^-1 mol) and a high fluorescence quantum yield (0.51), 1 displays potential as a promising two-photon (2P) probe for bioimaging. Subsequently, the ethylene glycol tetraacetic acid-substituted derivatives featuring octupolar (3 and 5) or dipolar (4 and 6) character have been synthesized and their one-photon (1P) and 2P photochemical reactions have been examined. Finally, 1P- and 2P-triggered uncaging of Ca²⁺ from these calcium chelators has been confirmed.

Surfactant-chaperoned donor-acceptor-donor NIR-II dye strategy efficiently circumvents intermolecular aggregation to afford enhanced bioimaging contrast

Fluorescence emission in the near-infrared-II (NIR-II) optical window affords reduced autofluorescence and light scattering, enabling deep-tissue visualization for both disease detection and surgical navigation. Small-molecule NIR-II dyes are preferable for clinical bioimaging applications, as the flexibility in their molecular synthesis allows for precise control of their optical and pharmacokinetic properties. Among the various types of dye, donor-acceptor-donor-based (D-A-D) dyes demonstrate exceptional photostability, whereas the frequently used PEGylation approach does not keep their intrinsic brightness enough in water environments due to their inherent effect of self-assembly. Here, we demonstrate that the commercially-available surfactants can serve as a dispersant to prevent molecular aggregation of PEGylated D-A-D dyes. Due to the favorable energetics for co-assembly between D-A-D dyes and surfactants, the formed surfactant-chaperoned dye strategy dramatically increases dye brightness. Accordingly, this effect provides remarkably improved performance for in vivo bioimaging applications. In parallel, we also investigate the D-A-D dye uptake and signal enhancement properties in the liver of murine models and demonstrate that the lumen-lining Kupffer cells can potentially disassemble PEGylated D-A-D aggregates such that their inherent brightness is restored. This phenomenon is similar to the surfactant-chaperoned dye strategy and our investigations provide a positive addition to better use of the current NIR-II fluorophores, especially for visualizing high-brightness required events.

Chemiluminescent Cucurbit[n]uril-Based Chemosensor for the Detection of Drugs in Biofluids

Chemiluminescence-based detection methods offer a superior signal-to-noise ratio and are commonly adopted for biosensors. This work presents the design and implementation of a supramolecular assay based on a chemiluminescent chemosensor. Specifically, an indicator displacement assay (IDA) with the supramolecular host-guest complex of chemiluminescent phenoxy 1,2-dioxetane and cucurbit[8]uril enables the low-micromolar detection of drugs in human urine and human serum samples. Cucurbit[8]uril thereby acts as a non-surfactant chemiluminescence enhancer and a synthetic receptor. Additionally, we show that adding an equimolar amount of cucurbit[8]uril to a commercially available dioxetane used in standard enzymatic chemiluminescence immunoassays enhances the chemiluminescence by more than 15 times. Finally, we demonstrate that a chemiluminescence resonance energy transfer between a unimolecular macrocyclic cucurbit[7]uril-dye conjugate and a phenoxy 1,2-dioxetane can be utilized to detect the herbicide paraquat at a micromolar concentration in aqueous media.

A facile turn-on chemiluminescence probe for sensitive imaging on aminopeptidase N activity

Aminopeptidase N, as a target for drug discovery, shows remarkable relationship with many diseases, especially liver injury and cancer. Herein, we explored a chemiluminescence (CL) probe for sensing APN by tethering APN-specific substrate group to the ortho-acrylated phenoxy-dioxetane scaffold. In this manner, two CL probes (APN-CL and BAPN-CL) were designed with non-capped leucine and butoxy-carbonyl capped leucine as the protecting group to preserve the chemiexcitation energy. The uncovered leucine was demonstrated to be essential for detection of APN activity by comparing the CL intensity of two CL probes. Probe APN-CL was turned on upon APN cleavage, resulting in a high chemiluminescent emission, while the chemiexcitation energy of probe BAPN-CL was still restrained even with the high-level APN. The result was elucidated by molecular docking simulation in further. Probe APN-CL exhibited fast response and high sensitivity with a detection limit of 0.068 U/L, and an excellent specificity for the discrimination of APN from biological ions, small molecules and other proteases commonly found in living system. By virtue of good stability and cell viability, probe APN-CL imaged abnormal level of APN in tumor cells and tumor-bearing mice. Moreover, this probe APN-CL could be easily used to evaluate APN inhibitors and APN level in plasma samples from 20 patients. Overall, as a facile and cost-effective probe, APN-CL will be a promising alternative in the early diagnosis of pathologies and cost-effective screening on inhibitors.

Multicharged cyclodextrin supramolecular assemblies

Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.

Supramolecular Mitigation of the Cyanine Limit Problem

Currently, there is a substantial research effort to develop near-infrared fluorescent polymethine cyanine dyes for biological imaging and sensing. In water, cyanine dyes with extended conjugation are known to cross over the "cyanine limit" and undergo a symmetry breaking Peierls transition that favors an unsymmetric distribution of π-electron density and produces a broad absorption profile and low fluorescence brightness. This study shows how supramolecular encapsulation of a newly designed series of cationic, cyanine dyes by cucurbit[7]uril (CB7) can be used to alter the π-electron distribution within the cyanine chromophore. For two sets of dyes, supramolecular location of the surrounding CB7 over the center of the dye favors a nonpolar ground state, with a symmetric π-electron distribution that produces a sharpened absorption band with enhanced fluorescence brightness. The opposite supramolecular effect (i.e., broadened absorption and partially quenched fluorescence) is observed with a third set of dyes because the surrounding CB7 is located at one end of the encapsulated cyanine chromophore. From the perspective of enhanced near-infrared bioimaging and sensing in water, the results show how that the principles of host/guest chemistry can be employed to mitigate the "cyanine limit" problem.

Chemiluminescent 1,2-Dioxetane Iridium Complexes for Near-Infrared Oxygen Sensing

Chemiluminescent iridium-based sensors which demonstrate oxygen dependent responses have been developed. The molecular probes, named IrCL-1, IrCL-2 and IrCL-3 consist of oxygen-sensitive iridium complexes attached to a spiroadamantane 1,2 dioxetane and operate via energy transfer from the chemiexcited benzoate to the corresponding iridium(III) complex. Complexing the iridium(III) center with π-extended ligands results in emission in the biologically relevant, near-infrared (NIR) region. All probes demonstrate varying oxygen tolerance, with IrCL-1 being the most oxygen sensitive. These probes have been further utilized for in vitro ratiometric imaging of oxygen, as well as for intraperitoneal, intramuscular and intratumoral imaging in live mice. To our knowledge, these are the first iridium-based chemiluminescent probes that have been employed for in vitro ratiometric oxygen sensing, and for in vivo tumor imaging.

Chemiluminescent Probes Based on 1,2-dioxetane Structures For Bioimaging

Chemiluminescent probes based on 1,2-dioxetane scaffold are one of the most sensitive imaging modalities for detecting disease-related biomarkers and can obtain more accurate biological information in cells and in vivo . Due to the elimination of external light excitation, the background autofluorescence problem in fluorescence technology can be effectively avoided, providing ultra-high sensitivity and signal-to-noise ratio for various applications. In this minireview, we highlight a comprehensive but concise overview of activatable 1,2-dioetxane-based chemiluminescent probes by reporting significant advances in accurate detection and bioimaging. The design principles and applications for reactive species, enzymes, and other disease-related biomarkers are systematically discussed and summarized. The challenges and potential prospects of chemiluminescent probes are also discussed to further promote the development of new chemiluminescence methods for biological analysis and diagnosis.

Mechanochemiluminescent hydrogels for real-time visualization of chemical bond scission

Quantitative and real-time characterization of mechanically induced bond scission events taken place in polymeric hydrogels is essential to uncover their fracture mechanics. Herein, a class of mechanochemiluminescent swelling hydrogels have been synthesized through a facile micellar copolymerization method using chemiluminescent bis(adamantyl)-1,2-dioxetane (Ad) as a crosslinker. This design and synthetic strategy ensure intense mechanochemiluminescence from Ad located in a hydrophobic network inside micelles. Moreover, the mechanochemiluminescent colors can be tailored from blue to red by mixing variant acceptors. Taking advantages of the transient nature of dioxetane chemiluminescence, the damage distribution and crack evolution of the hydrogels can be visualized and analyzed with high spatial and temporal resolution. The results demonstrate the strengths of the Ad mechanophore and micellar copolymerization method in the study of damage evolution and fracture mechanism of swelling hydrogels.

A H2O2-responsive theranostic platform for chemiluminescence detection and synergistic therapy of tumor

Chemiluminescence substances that respond to hydrogen peroxide (H2O2) in the tumor microenvironment have the potential to achieve accurate tumor imaging. Here, Pluronic F-127 (PF127) and polymers containing oxalate ester (POE)...

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

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.

Universal Access to Protease Chemiluminescent Probes through Solid-Phase Synthesis

Protease chemiluminescent probes exhibit extremely high detection sensitivity for monitoring activity of various proteolytic enzymes. However, their synthesis, performed in solution, involves multiple synthetic and purification steps, thereby generating a major limitation for rapid preparation of such probes with diverse substrate scope. To overcome this limitation, we developed a general solid-phase-synthetic approach to prepare chemiluminescent protease probes, by peptide elongation, performed on an immobilized chemiluminescent enol-ether precursor. The enol-ether precursor is immobilized on a 2-chlorotrityl-chloride resin through an acrylic acid substituent by an acid-labile ester linkage. Next, a stepwise elongation of the peptide is performed using standard Fmoc solid-phase peptide synthesis. After cleavage of the peptide-enol-ether precursor from the resin, by hexafluoro-iso-propanol, a simple oxidation of the enol-ether yields the final chemiluminescent dioxetane protease probe. To validate the applicability of the methodology, two chemiluminescent probes were efficiently prepared by solid-phase synthesis with dipeptidyl substrates designed for activation by aminopeptidase and cathepsin-B proteases. A more complex example was demonstrated by the synthesis of a chemiluminescent probe for detection of PSA, which includes a peptidyl substrate of six amino acids. We anticipate that the described methodology would be useful for rapid preparation of chemiluminescent protease probes with vast and diverse peptidyl substrates.

Prevent or Cure-The Unprecedented Need for Self-Reporting Materials

Self-reporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than self-healing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of self-reporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring self-reporting research concepts from the laboratory to the real world. Especially in the space of diagnostic self-reporting systems, the recent SARS-CoV-2 (COVID-19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a self-reporting fashion.

Photoactivatable Red Chemiluminescent AIEgen Probe for In Vitro/Vivo Imaging Assay of Hydrazine

Here, we have developed a novel photoactivatable red chemiluminescent AIEgen probe (ACL), based on the combination of the red-emission AIEgen fluorophore (TPEDC) that shows excellent singlet oxygen (¹O₂)-generation ability and the precursor of Schaap's dioxetane (the linker connected to adamantane is the C═C bond) that can be modified to target various analytes, for in vitro and in vivo measurement of hydrazine. Prior to applying for sensing detection, the C═C bond connected to adamantane in ACL was first converted into dioxetane by irradiation to form the activated chemiluminescent AIEgen probe (ACLD). Then, the self-immolative reaction was triggered upon the deprotection of the acylated phenolic hydroxyl group in ACLD in the presence of hydrazine, resulting in the release of the high energy held in the 1,2-dioxetanes, and then, the chemiexcitation was triggered, thereby producing red chemiluminescence through the intramolecular chemiluminescence resonance energy transfer from Schaap's dioxetane to TPEDC. This chemiluminescent AIEgen probe was evaluated in a clean buffer environment as well as using living cells and mouse models.

An activity-based fluorescent probe and its application for differentiating alkaline phosphatase activity in different cell lines

Herein, a new fluorescent probe, AE-Phos, is reported for detecting the ALP activity with the combined advantages of aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT). Further detailed fluorescence experiments demonstrated that AE-Phos exhibited excellent selectivity and sensitivity, a large Stokes shift, and a fast response towards ALP. Furthermore, AE-Phos was applied to imaging the ALP activity in different cell lines quantitatively.

Coal-Tar Dye-based Coordination Cages and Helicates

A strategy to implement four members of the classic coal-tar dye family, Michler's ketone, methylene blue, rhodamine B, and crystal violet, into [Pd2 L4 ] self-assemblies is introduced. Chromophores were incorporated into bis-monodentate ligands using piperazine linkers that allow to retain the auxochromic dialkyl amine functionalities required for intense colors deep in the visible spectrum. Upon palladium coordination, ligands with pyridine donors form lantern-shaped dinuclear cages while quinoline donors lead to strongly twisted [Pd2 L4 ] helicates in solution. In one case, single crystal X-ray diffraction revealed rearrangement to a [Pd3 L6 ] ring structure in the solid state. For nine examined derivatives, showing colors from yellow to deep violet, CD spectroscopy discloses different degrees of chiral induction by an enantiomerically pure guest. Ion mobility mass spectrometry allows to distinguish two binding modes. Self-assemblies based on this new ligand class promise application in chiroptical recognition, photo-redox catalysis and optical materials.

Multicolor Chemiluminescent Resonance Energy-Transfer System for In Vivo High-Contrast and Targeted Imaging

Chemiluminescence (CL) resonance energy transfer (CRET) has received great attention due to its fascinating applications in in vivo imaging and photodynamic therapy. Here, we report a highly efficient CRET polymer dot (CRET-Pdots)-based system using catalytic CL reagents as energy donors and fluorescent polymers and dyes as energy acceptors. CRET-Pdots consist of Fe(III) deuteroporphyrin IX (CL catalyst), fluorescent polymers, and dyes. The CL intensity and duration are markedly enhanced by using ultrasensitive catalytic CL reaction of luminol analogue-H₂O₂, and the CL emission wavelength can be adjusted by one-step/two-step energy-transfer strategies. CRET-Pdots show intensive multicolor CL (about 3000× enhanced), an adjustable emission wavelength (470-720 nm), long CL duration (over 8 h), and a high CRET efficiency (50%). CRET-Pdots possess excellent biocompatibility, sensitive response to reactive oxygen species (ROS), and ultrahigh catalytic activity. They are successfully used for high-contrast real-time ROS imaging and in vivo tumor-targeted imaging with an excellent signal-to-noise ratio (over 90).

Self-Immolative Difluorophenyl Ester Linker for Affinity-Based Fluorescence Turn-on Protein Detection

Currently most fluorogenic probes are developed for the analysis of enzymes, where a bond breaking or rearrangement reaction is required to transform a nonfluorescent enzymatic substrate into a fluorescent product. However, this approach cannot be used for proteins that do not possess enzymatic activities. In this article, we show that fluorogenic probes with a self-immolative difluorophenyl ester linker can mimic the bond disassembly processes of fluorogenic enzyme substrates for the rapid analysis of nonenzymatic proteins. Although numerous self-immolative reagents have shown promising applications in sensors, drug delivery systems, and material chemistry, all of them are triggered by either enzymes or small reactive molecules. In our strategy, the probe binds to the protein via a specific protein-ligand interaction, inducing a chemical reaction between the self-immolative linker and an amino acid of the protein, thereby triggering a cascade reaction that leads to the activation and release of the fluorogenic reporter. In contrast, a phenyl ester linker without the difluoro substituent cannot be triggered to release the fluorogenic reporter. With this probe design, live-cell imaging of extracellular and intracellular endogenous tumor marker proteins can be achieved with high selectivity and sensitivity.

Intensive and Persistent Chemiluminescence System Based on Nano-/Bioenzymes with Local Tandem Catalysis and Surface Diffusion

A chemiluminescence (CL) system with long persistent and intensive emission is essential for accurate CL quantitative analysis and imaging assay. However, with most known CL systems being flash-type, it is still a great challenge to develop long-lasting CL systems. Here, by combining an iron porphyrin metal-organic frameworks (FePorMOFs) based peroxidase mimic with natural glucose oxidase (GOx), an intensive and persistent CL system is presented on the basis of local tandem catalysis and surface diffusion of the nano-/bioenzymes (FePorMOF/GOx). FePorMOF synthesized by iron porphyrin linker and zirconium ion node possesses high peroxidase catalytic activity and stability. Using luminol and glucose as substrate, the FePorMOF/GOx CL system can produce intensive CL emission containing a plateau period of 7.5 h. The strong CL signal is due to the local tandem generation and reaction of H₂O₂ by GOx and FePorMOF, which avoids the diffusion-limited kinetics and leads to a high catalytic efficiency of the nano-/bioenzymes. On the other hand, the long persistent CL emission is attributed mainly to the enzymatic reaction-controlled H₂O₂ supply and surface diffusion-controlled CL reaction. The proposed CL system is explored for CL imaging sensing of glucose and homogeneous immunoassay of α-fetoprotein. The nano-/bioenzymes CL system exhibits intensive and long constant CL emission in physiological condition, showing promising applications in real-time bioassay and bioimaging.

One-step fabrication of trimetallic alloy nanozyme catalyzer for luminol-H2O2 chemiluminescence and its application for miRNA-21 detection coupled with miRNA walking machine

PtCuCo trimetallic alloys (PtCuCo-TAs) are synthesized by one-step reduction. The chemiluminescence (CL) properties of PtCuCo-TAs are studied systemically. PtCuCo-TAs show good catalyzing for luminol-H₂O₂ system. A CL platform is developed for the detection of miRNA-21 using PtCuCo-TAs as nanozyme catalyzer. In the CL detection platform, H1 (Hairpin DNA1) is immobilized onto magnetic beads (MBs) firstly. In the presence of miRNA-21, H1 is opened. H2 (Hairpin DNA2) then hybridizes with H1. Meanwhile, a "cleat" in the end of miRNA-21 with a fewer bases complementary is formed to prevent miRNA-21 dissociating from H1. This miRNA-21 hybridizes to another H1. When cpDNA-PtCuCo-TAs which consisted with cDNA (Complementary strand of probe DNA) and pDNA-PtCuCo-TAs (PtCuCo-TAs labeled with probe DNA) are added, the ssDNA region of H1 reacts with the toehold domain of probe DNA and cDNA is released resulting pDNA-PtCuCo-TAs being captured. With this process repeatedly, a lot of pDNA-PtCuCo-TAs are captured onto MBs. After separation and washing, the precipitate and H₂O₂ are put into the 96-well and luminol solution is injected. The CL signal is produced by PtCuCo-TAs catalyzing luminol-H₂O₂ system. The amount of miRNA-21 is detected with CL signal. This CL platform performs with limit of detection 0.167 fM and has good selectivity over other RNA.

Highly sensitive chemiluminescent sensing of intracellular Al3+ based on the phosphatase mimetic activity of cerium oxide nanoparticles

Nanomaterials with enzyme-like characteristics (also called nanozymes) have attracted increasing attention in the area of analytical chemistry. Nevertheless, most of the nanozymes used for analytical applications are oxidoreductase mimics, and their enzyme-like activities are usually demonstrated by using chromogenic and/or fluorogenic substrates. Herein, the phosphatase mimetic activity of cerium oxide nanoparticles (nanoceria) was investigated by using CDP-star as the chemiluminescent (CL) substrate. Interestingly, we found that the phosphatase mimetic activity of nanoceria can be remarkably inhibited by the addition of Al³⁺. Based on this finding, a highly sensitive and selective CL method for Al³⁺ detection is proposed. The CL intensity of the nanoceria/CDP-star system decreased with the increasing Al³⁺ concentrations in the range from 30 nM to 3.5 μM. A detection limit as low as 10 nM was obtained. Finally, the CL detection of intracellular Al³⁺ was achieved, demonstrating the utility of the CL method in complex biological samples.

Self-Illuminating Agents for Deep-Tissue Optical Imaging

Optical imaging plays an indispensable role in biology and medicine attributing to its noninvasiveness, high spatiotemporal resolution, and high sensitivity. However, as a conventional optical imaging modality, fluorescence imaging confronts issues of shallow imaging depth due to the need for real-time light excitation which produces tissue autofluorescence. By contrast, self-luminescence imaging eliminates the concurrent light excitation, permitting deeper imaging depth and higher signal-to-background ratio (SBR), which has attracted growing attention. Herein, this review summarizes the progress on the development of near-infrared (NIR) emitting self-luminescence agents in deep-tissue optical imaging with highlighting the design principles including molecular- and nano-engineering approaches. Finally, it discusses current challenges and guidelines to develop more effective self-illuminating agents for biomedical diagnosis and treatment.

Activity-Based Optical Sensing Enabled by Self-Immolative Scaffolds: Monitoring of Release Events by Fluorescence or Chemiluminescence Output

Functional molecular scaffolds comprised of self-immolative adaptors are being used in widespread applications in the fields of enzyme activity analyses, signal amplification, and bioimaging. Optically detected chemical probes are very promising compounds for sensing and diagnosis, since they present several attractive features such as high specificity, low detection limits, fast response times, and technical simplicity. During the last two decades, we have developed several distinct molecular scaffolds that harness the self-immolative disassembly feature of these adaptors to amplify chromogenic output for diagnosis and drug delivery applications. In order to study the molecular behavior of the various amplification systems, an optical output, used to monitor the progress of the disassembly pattern, was required. Therefore, over the course of our research, diverse molecular scaffolds that produce an optical signal in response to a disassembly step, were evaluated. These optically active scaffolds have been incorporated into self-immolative dendrimers and self-immolative polymers to implement unique disassembly properties that result with linear and exponential signal amplification capabilities. In addition, some scaffolds, aimed for linker technology, were used in delivery systems to monitor release of drug molecules. The optical signal used to monitor the release event could be produced by analysis of reporter molecules with chromogenic or fluorogenic properties. Recently, we have also developed molecular scaffolds modified to produce a chemiluminescent signal to monitor the self-immolative disassembly step. The main advantage of these scaffolds over others is the use of chemiluminescence as an output signal. It is well-known that chemiluminescence is considered as one the most sensitive diagnostic methods due to its high signal-to-noise ratio. The unique structures of the self-immolative chemiluminescence scaffolds have been used in the design of three different distinctive concepts: self-immolative chemiluminescence polymers, auto-inductive amplification systems with chemiluminescence signal and monitoring of drug release by a chemiluminescence output. Furthermore, we reported the design and synthesis of the first theranostic prodrug for the monitoring of drug release achieved by a chemiluminescence mode of action. Quinone-methide elimination has proven to serve as a valuable functional tool for composing molecular scaffolds with self-immolative capabilities. Such scaffolds function as molecular adaptors that can almost simultaneously release a target molecule with an accompanied emission of a light signal that is used to monitor the release event. We anticipate that these self-immolative scaffolds will continue to find utility as functional linkers in various chemical and biological research areas such as drug delivery, theranostic applications, and as molecular sensors with signal amplification.

Recent Advances and Challenges in Luminescent Imaging: Bright Outlook for Chemiluminescence of Dioxetanes in Water

Chemiluminescence is gradually being recognized as a powerful tool for sensing and imaging. Most known light-emitting compounds undergo chemiexcitation through spontaneous decomposition of cyclic peroxide moieties. A ground-breaking milestone in the chemistry of such compounds was achieved 30 years ago with the discovery of triggerable dioxetanes by Schaap's group. Our group has recently developed a distinct methodology to significantly improve the light emission efficiency of such phenoxy-dioxetane luminophores under physiological conditions. Introduction of an electron-withdrawing substituent at the ortho position of the phenoxy-dioxetane resulted in an approximately 3000-fold increase of the chemiluminescence quantum yield in aqueous media. Furthermore, we discovered that the emission wavelength and the kinetics of the chemiexcitation could be determined by the electronic nature of the substituent incorporated on the dioxetane luminophore. This recent development has provided scientists with new powerful chemiluminophores that can act as single-component probes for in vivo and in vitro detection and imaging of various analytes and enzymes. This outlook describes the recent progress toward applications of synthetic chemiluminescence luminophores suitable for sensing and imaging in aqueous environments.