A BODIPY-luminol chemiluminescent resonance energy-transfer (CRET) cassette for imaging of cellular superoxide

Activatable Dual-Optical Molecular Probe for Bioimaging Superoxide Anion in Epilepsy

Superoxide anion (O2•-) plays a pivotal role in the generation of other reactive oxygen species within the body and is closely linked to epilepsy. Despite this connection, achieving precise imaging of O2•- during epilepsy pathology remains a formidable challenge. Herein, we develop an activatable molecular probe, CL-SA, to track the fluctuation of the level of O2•- in epilepsy through simultaneous fluorescence imaging and chemiluminescence sensing. The developed probe CL-SA demonstrated its efficacy in imaging of O2•- in neuronal cells, showcasing its dual optical imaging capability for O2•- in vitro. Furthermore, CL-SA was successfully used to observe aberrantly expressed O2•- in a mouse model of epilepsy. Overall, CL-SA provides us with a valuable tool for chemical and biomedical studies of O2•-, promoting the investigation of O2•- fluctuations in epilepsy, as well as providing a reliable means to explore the diagnosis and therapy of epilepsy.

Aggregation-Induced Emission-Based Chemiluminescence Systems in Biochemical Analysis and Disease Theranostics

Chemiluminescence (CL) is of great significance in biochemical analysis and imaging due to its high sensitivity and lack of need for external excitation. In this review, we summarized the recent progress of AIE-based CL systems, including their working mechanisms and applications in biochemical analysis, bioimaging, and disease diagnosis and treatment. In ion and molecular detection, CL shows high selectivity and high sensitivity, especially in the detection of dynamic reactive oxygen species (ROS). Further, the integrated NIR-CL single-molecule system and nanostructural CL platform harnessing CL resonance energy transfer (CRET) have remarkable advantages in long-term imaging with superior capability in penetrating deep tissue depth and high signal-to-noise ratio, and are promising in the applications of in vivo imaging and image-guided disease therapy. Finally, we summarized the shortcomings of the existing AIE-CL system and provided our perspective on the possible ways to develop more powerful CL systems in the future. It can be highly expected that these promoted CL systems will play bigger roles in biochemical analysis and disease theranostics.

BODIPY-Based Molecules for Biomedical Applications

BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives have attracted attention as probes in applications like imaging and sensing due to their unique properties like (1) strong absorption and emission in the visible and near-infrared regions of the electromagnetic spectrum, (2) strong fluorescence and (3) supreme photostability. They have also been employed in areas like photodynamic therapy. Over the last decade, BODIPY-based molecules have even emerged as candidates for cancer treatments. Cancer remains a significant health issue world-wide, necessitating a continuing search for novel therapeutic options. BODIPY is a flexible fluorophore with distinct photophysical characteristics and is a fascinating drug development platform. This review provides a comprehensive overview of the most recent breakthroughs in BODIPY-based small molecules for cancer or disease detection and therapy, including their functional potential.

A Fast-Response, Phenanthroimidazole-Based Fluorescent Probe for Selective Detection of HClO

A new phenanthroimidazole-based fluorescence probe for selective detection of HClO was synthesized and characterized using 1HNMR, 13CNMR, IR, and HRMS. With benzenesulfonohydrazide as the identification group, the probe demonstrated a fast fluorescence response from yellow-green to blue when the HC = N double bond was oxidized and broken into an aldehyde group by HClO. The probe showed high selectivity and sensitivity towards HClO with approximately 4.5-fold fluorescence enhancement and has been successfully applied in the molecular logic gate, determination of HClO in environmental water samples, and portable HClO detection.

BODIPY-Based Fluorescent Probes for Selective Visualization of Endogenous Hypochlorous Acid in Living Cells via Triazolopyridine Formation

In this work, the two pyridylhydrazone-tethered BODIPY compounds (2 and 3) were synthesized. These compounds aimed to detect hypochlorous acid (HOCl) species via cyclic triazolopyridine formation. The open forms and the resulting cyclic forms of BODIPYs (2, 3, 4, and 5) were fully characterized by nuclear magnetic resonance, mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. These two probes can selectively detect HOCl through a fluorescence turn-on mechanism with the limit of detections of 0.21 µM and 0.77 µM for compounds 2 and 3, respectively. This fluorescence enhancement phenomenon could be the effect from C = N isomerization inhibition due to HOCl-triggered triazolopyridine formation. In cell imaging experiments, these compounds showed excellent biocompatibility toward RAW 264.7 murine live macrophage cells and greatly visualized endogenous HOCl in living cells stimulated with lipopolysaccharide.

BODIPY-Pyridylhydrazone Probe for Fluorescence Turn-On Detection of Fe3+ and Its Bioimaging Application

A novel pyridylhydrazone-tethered BODIPY (BODIPY-PH) was synthesized, fully characterized via nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopic (FTIR), and single-crystal X-ray diffraction (SC-XRD) techniques, and developed for the selective detection of Fe3+ through fluorescent enhancement process. This derivative showed 1:1 binding with Fe3+ in an acetonitrile-water mixture (1:9 v/v) with the binding constant (K) of 5.4 × 104 M−1 and the limit of detection of 0.58 µM. The Fe3+ complexation reaction has been proved to be a reversible process and could be effectively repeated up to three cycles. The electronic properties of BODIPY-PH and its Fe3+ complex modeled by the density functional theory (DFT) method suggested the presence of chelation-enhanced fluorescence (CHEF) effect in the Fe3+ binding reaction. The X-ray absorption spectroscopy (XAS) probed at Fe K-edge confirmed the complex formation between BODIPY-PH and the Fe3+ in an octahedral geometry. Finally, bioimaging against human embryonic kidney (Hek293) cell, through confocal fluorescence microscopic technique indicated that the BODIPY-PH displayed good permeability and low toxicity toward the tested cell lines and showed enhanced fluorescent signal in the cells incubated with Fe3+ proving its capability for Fe3+ analysis in cellular matrix.

BODIPY and 2,3-Dihydrophthalazine-1,4-Dione Conjugates As Heavy Atom-Free Chemiluminogenic Photosensitizers

We disclose an interesting concept for developing heavy atom-free chemiluminogenic photosensitizers. To accomplish this, conjugates 2 and 3, which are composed of boron-dipyrromethene (BODIPY) and 2,3-dihydrophthalazine-1,4-dione units, are investigated. 2 and 3 are compared in terms of their photophysical properties, chemiluminescence responses, and singlet oxygen production. Strikingly, the results indicate that decoration of BODIPY with the 2,3-dihydrophthalazine-1,4-dione scaffold boosts the singlet oxygen generation. Furthermore, treatment of epidermoid laryngeal carcinoma Hep-2 (Hep-2) cells with conjugates 2 and 3 results in efficient cellular internalization which ensures live- cell imaging of Hep-2 cells. Finally, it is noteworthy that in vitro cytotoxicity assays reveal that both 2 and 3 induce cytotoxicity when illuminated with red light. Thus, 2 and 3 represent heavy atom-free chemiluminogenic photosensitizers.

Self-Illuminated, Oxygen-Supplemented Photodynamic Therapy via a Multienzyme-Mimicking Nanoconjugate

Current photodynamic therapy (PDT) faces several intrinsic limitations, including insufficient oxygen supply and limited penetration of external light sources. Herein, we report a nanoconjugate, which, in response to the elevated hydrogen peroxide levels associated with tumor tissues, can supplement the oxygen needed for PDT and provide local self-illumination. Consisting of a MnFe₂O₄ core, a metal-organic framework shell loaded with the chemiluminescence reagent luminol, and a hyaluronic acid surface coating, the nanoconjugate is highly effective for suppressing cancer tissues in vivo via PDT in the absence of externally delivered light.

Acridone and acridinium constructs with red-shifted emission

Acridinium 9-carboxylic acid derivatives have been extensively used as chemiluminescent labels in diagnostic assays. Triggering acridinium with basic hydrogen peroxide produces a highly strained dioxetanone intermediate, which converts into an acridone in an electronically excited state and emits light at 420-440 nm. Here, we introduce a novel acridinium-fluorescein construct emitting at 530 nm, in which fluorescein is covalently attached to the acridinium N-10 nitrogen via a propyl sulfonamide linker. To characterize the spectral properties of the acridinium-fluorescein chemiluminophores, we synthesized the analogous acridone-fluorescein constructs. Both acridinium and acridone were linked to either 5- or 6-carboxyfluorescein and independently synthesized as individual structural isomers. Using fluorescent acridone-fluorophore tandems, we investigated and optimized the diluent composition to prevent dye aggregation. As monomolecular species, the acridone isomers demonstrated similar absorption, excitation, and emission spectra, as well as the expected fluorescence lifetimes and molecular brightness. Chemical triggering of acridinium-fluorescein tandems, as well as direct excitation of their acridone-fluorescein analogs, resulted in a nearly complete energy transfer from acridone to fluorescein. Acridone-based dyes can be studied with steady-state spectroscopy. Thus, they will serve as useful tools for structure and solvent optimizations, as well as for studying chemiluminescent energy transfer mechanisms in related acridinium-fluorophore tandems. Direct investigations of the light-emitting molecules generated in the acridinium chemiluminescent reaction empower further development of chemiluminescent labels with red-shifted emission. As illustrated by the two-color HIV model immunoassay, such labels can find immediate applications for multicolor detection in clinical diagnostic assays.

A rainbow of acridinium chemiluminescence

Multicolor chemiluminescent acridinium derivatives were synthesized by attaching various common fluorophores to the N¹⁰ -acridinium position through a piperazine linker. Triggering of each acridinium derivative using alkaline hydrogen peroxide resulted in a chemiluminescence spectrum dominated by a strong emission (>95%) from the attached fluorophore. The highly quenched emission from the triggered acridinium, acting as a donor, points to a highly efficient intramolecular energy transfer in acridinium-based chemiluminophore-fluorophore tandems. A variable, and in many cases minimal, spectral overlap between the donor emission and the acceptor absorption may indicate that in such tandems the energy transfer follows the Dexter electron exchange mechanism. Moreover, fluorophores affixed through the acridinium 9-position produce a typical acridinium emission profile, demonstrating the need for close distances and favorable intramolecular orientation of the donor and acceptor moieties for the energy transfer to occur. A family of red-shifted chemiluminescent labels, all sharing a uniform triggering method, will find immediate application in multicolor ligand-receptor assays. Along with the multiplexing capabilities, the red-shifted chemiluminescent detection offers a higher tolerance to green-colored biological interferences and will therefore benefit many screening and diagnostic clinical tests.

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).

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

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

Chemiluminescence for bioimaging and therapeutics: recent advances and challenges

The current progress, design principles in bioimaging and therapeutic applications, and future perspectives of various chemiluminescent platforms are reviewed.

Catalytic Chemiluminescence Polymer Dots for Ultrasensitive In Vivo Imaging of Intrinsic Reactive Oxygen Species in Mice

Chemiluminescence (CL) is a promising bioimaging method due to no interferences of light source and autofluorescence. However, compared to fluorescent emission, most CL reactions show short emission time and wavelength and weak emission intensity, which limit their applications in in vivo imaging. Here, we report mimic-enzyme catalytic CL polymer dots (hemin-Pdots) consisting of hemin and fluorescent conjugated polymer based on chemiluminescence resonance energy transfer. Hemin-Pdots show about 700× enhanced CL and over 10 h light emission in the presence of CL substrates and H₂O₂. These properties are mainly due to high-catalytic activity of hemin-Pdots and slow-diffusion-controlled heterogeneous reaction. Hemin-Pdots also possess excellent biocompatibility, good stability, emission wavelength redshift, and ultrasensitive response to reactive oxygen species (ROS), and they were successfully used for real-time imaging ROS levels in the peritoneal cavity and normal and tumor tissues of mice. Hemin-Pdots as new CL probes have wide applications in bioassays, bioimaging, and photodynamic therapy.

The emergence of aqueous chemiluminescence: new promising class of phenoxy 1,2-dioxetane luminophores

For the first time, science now have a single-entity chemiluminescent luminophore that can serve to prepare effective diagnostic probes to evaluate biological processesin vitroandin vivo.

A chemiluminescent platform for smartphone monitoring of H2O2 in human exhaled breath condensates

Noninvasive measurement of oxidative markers in clinical samples has the potential to rapidly provide information for disease management, but is limited by the need for expensive analytical instrumentation that precludes home monitoring or point-of-care applications. We have developed a simple to use diagnostic platform for airway hydrogen peroxide (H₂O₂) that combines optimized reaction-based chemiluminescent designs with an inexpensive home-built darkbox and readily available smartphone cameras. Specialized photography software applications and analysis of pixel intensity enables quantification of sample concentrations. Using this platform, sample H₂O₂ concentrations as low as 264nM can be detected. The platform has been used to measure H₂O₂ in the exhaled breath condensates of human subjects, showing good agreement with the standard Amplex Red assay.

In Vivo Chemiluminescent Imaging Agents for Nitroreductase and Tissue Oxygenation

Tissue oxygenation is a driving parameter of the tumor microenvironment, and hypoxia can be a prognostic indicator of aggressiveness, metastasis, and poor response to therapy. Here, we report a chemiluminescence imaging (CLI) agent based on the oxygen-dependent reduction of a nitroaromatic spiroadamantane 1,2-dioxetane scaffold. Hypoxia ChemiLuminescent Probe 2 (HyCL-2) responds to nitroreductase with ∼170-fold increase in luminescence intensity and high selectivity for enzymatic reductase versus other small molecule reductants. HyCL-2 can image exogenous nitroreductase in vitro and in vivo in living mice, and total luminescent intensity is increased by ∼5-fold under low oxygen conditions. HyCL-2 is demonstrated to report on tumor oxygenation during an oxygen challenge in H1299 lung tumor xenografts grown in a murine model as independently confirmed using multispectral optoacoustic tomography (MSOT) imaging of hemoglobin oxygenation.

Broad-spectrum chemiluminescence covering a 400–1400 nm spectral region and its use as a white-near infrared light source for imaging

Broad-spectrum chemiluminescence has been achieved and used as a white-near infrared light source for imaging techniques.