Development of a ruthenium(II) complex-based luminescent probe for hypochlorous acid in living cells

Postsynthetic Modification Strategy for Constructing Electrochemiluminescence-Active Chiral Covalent Organic Frameworks Performing Efficient Enantioselective Sensing

Electrochemiluminescence (ECL), integrating the characteristics of electrochemistry and fluorescence, has the advantages of high sensitivity and low background. However, only a few studies have been reported for enantioselective sensing based on the ECL-active platform because of the huge challenges in constructing tunable chiral ECL luminophores. Here, we developed a facile strategy to design and prepare ECL-active chiral covalent organic frameworks (COFs) Ph-triPy+-(R)-Ru(II) for enantioselective sensing. In such an artificial structure, the ionic skeleton of COFs was beneficial to the electron transfer on the working electrode surface and the chiral Ru-ligand was used as the chiral ECL-active luminophore. It was found that Ph-triPy+-(R)-Ru(II) coupled with sodium persulfate (Na2S2O8) as the coreactant exhibited obvious ECL signals. More importantly, a clear difference toward l- and d-enantiomers was observed in the response of the ECL intensity, resulting in a uniform recognition law. That is, for amino alcohols, d-enantiomers (1 mM) measured by Ph-triPy+-(R)-Ru(II) showed a higher ECL intensity compared with l-enantiomers. Differently, amino acids (1 mM) gave an inverse recognition phenomenon. The ECL intensity ratios between l- and d-enantiomers (1 mM) are in the range of 1.25-1.94 for serine, aspartic acid, glutamic acid, valine, leucine, leucinol, and valinol. What is more interesting is that the ECL intensity was closely related to the concentration of l-amino alcohols and d-amino acids, whereas their inverse configurations remained unchanged. In a word, the present concept demonstrates a feasible direction toward chiral ECL-active COFs and their potential for efficient enantioselective sensing.

Fast detection, a precise and sensitive diagnostic agent for breast cancer

Background

Breast cancer targeting diagnostic agent with effective imaging ability is important in guiding plan formulation, prediction, and curative effect evaluation of tumors in clinic. A tumor-targeting nanoprobe based on the functional and programmable Liquid–Liquid phase separation of AS1411 promoted by Ru(II) complex RuPEP may develop into a potential phosphorescence probe to detect breast cancer cells, where AS1411 act as a tumor-targeting guidance moiety to distinguish tumor cells from normal cells and RuPEP act as a light-emitting element to highlight breast cancer cells.

Methods

Here we designed and constructed a nanoprobe AS1411@RuPEP, and the physicochemical and biochemical properties were characterized by TEM, AFM and EDS. The breast cancer targeting diagnostic capacity was evaluated by normal/tumor cell co-culture assay, tumor cells targeting tracking in xenograft model and cancerous area selectively distinguishing in human patient tissue.

Results

Further studies indicated that the nanoprobe exhibits excellent tumor-targeting imaging ability in vitro and in vivo by effectively recognize the over-expressed nucleolin (NCL) on the breast cancer cells membrane. Intriguingly, we discovered that the selectively enrichment of nanoprobe particles in tumor cells is related to ATP-dependent NCL transport processes that rely on the AS1411 component of nanoprobe to recognize NCL. Furthermore, preferential accumulation of nanoprobe is clearly differentiating the human breast cancer tissue surrounding non-cancerous tissue in histological analysis.

Conclusion

This study produce a potent nanoprobe can be used as a convenient tool to highlight and distinguish tumor cells in vivo, and indicate the tumorous grading and staging in human breast cancer patient pathological section, which provides an effective way for breast cancer diagnostic imaging by targeting recognize NCL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02393-3.

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors

Luminescence chemosensors are one of the most useful tools for the determination and imaging of small biomolecules and ions in situ in real time. Based on the unique photo-physical/-chemical properties of ruthenium(II) (Ru(II)) complexes, the development of Ru(II) complex-based chemosensors has attracted increasing attention in recent years, and thus many Ru(II) complexes have been designed and synthesized for the detection of ions and small biomolecules in biological and environmental samples. In this work, we summarize the research advances in the development of Ru(II) complex-based chemosensors for the determination of ions and small biomolecules, including anions, metal ions, reactive biomolecules and amino acids, with a particular focus on binding/reaction-based chemosensors for the investigation of intracellular analytes’ evolution through luminescence analysis and imaging. The advances, challenges and future research directions in the development of Ru(II) complex-based chemosensors are also discussed.

A bright chemiluminescence conjugated polymer-mesoporous silica nanoprobe for imaging of colonic tumors in vivo

Hypochlorite acid (ClO^-) is one of the major reactive oxygen species (ROS) in colon cancer, providing an effective target for colonic tumor in vivo imaging. For detection of ClO^- and tumor imaging, poly[(9,9-di(2-ethylhexyl)-9H-fluorene-2,7-vinylene)-co-(1-methoxy-4-(2-ethylhexyloxy)-2,5-phenylenevinylene)] (PFV-co-MEHPV, namely CP1) was encapsulated in mesoporous silica nanoparticles (MSNs) that were pre-modified with polyphenylenevinylene (PPV) via in situ polymerization to construct bright PPV@MSN-CP1 nanoparticles. The synthesized nanoparticles were size-stable and not cytotoxic as confirmed by FE-TEM, FE-SEM, and MTT assay. Hypochlorite oxidizes the vinylidene bond of CP1 through π²-π² cycloaddition to form PPV-dioxetane intermediates to generate photons. The CL quantum yield of PPV@MSN-CP1 was 16.7 times higher than that of Pluronic F-127 wrapped CP1. CL nanoparticles PPV@MSN-CP1 have good selectivity for hypochlorite detection among biological oxidants (mainly ROS). The linear range and the LOD of PPV@MSN@CP1 for ClO^- detection are 4-90 and 1.02 μM, respectively. Subsequently, we further coated PPV@MSN@CP1 with folic acid for tumor targeting by phospholipid wrapping. PPV@MSN-CP1@FA was successfully applied for in vivo imaging of endogenously produced ClO^- of tumor tissue in living animals.

An optical strategy for detecting hypochlorite in vitro and cells with high selectivity and stability based on a lanthanide-doped upconversion probe

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans. More importantly, owing to hypochlorite being a biomarker of immune responses in living organisms, its abnormal production can damage nucleic acids and protein molecules, eventually causing many diseases (even cancer). Exploring a reliable, rapid, and non-invasive method to monitor the hypochlorite level in vitro and in cells can be significant. Herein, we report a novel ratiometric fluorescence sensing strategy based on Astrazon Brilliant Red 4G dye-sensitized NaGdF₄:Yb³⁺, Er³⁺@NaYF₄ core–shell upconversion nanoparticles (UCNPs@ABR 4G). Based on the combination mechanism of the fluorescent resonant energy transfer effect (FRET) and redox, a linear model of fluorescence intensity ratio and hypochlorite concentration was constructed for a fast response and high selectivity monitoring of hypochlorite in vitro and in vivo. The detection limit was calculated to be 0.39 μM. In addition, this sensing strategy possessed good stability and circularity, making it valuable both for the quantitative detection of hypochlorite in water and for the visualization of intracellular hypochlorite. The proposed optical probe is promising for the efficient and stable non-invasive detection of hypochlorite.

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans.

Bis-heteroleptic Ru(ii) polypyridine complex-based luminescent probes for nerve agent simulant and organophosphate pesticide

Two bis-heteroleptic Ru(ii) complexes of a 4,7-dihydroxy-1,10-phenanthroline ligand were synthesized for the detection of the nerve agent gas mimic, DCP, and the organophosphate pesticide, dichlorvos, through the “off–on” luminescence response.

Luminescent probes for hypochlorous acid in vitro and in vivo

HClO/ClO^- is the most effective antibacterial active oxygen in neutrophils. However, its excessive existence often leads to the destruction of human physiological mechanisms. In recent years, the developed luminescent probes for the detection of HClO/ClO^- are not only conducive to improve the sensitivity and selectivity of HClO/ClO^- detection, but also play a crucial role in understanding the biological functions of HClO/ClO^-. In addition, luminescent probe-based biological imaging for HClO/ClO^- at sub-cellular resolution has become a powerful tool for biopathology and medical diagnostic research. This article reviews a variety of luminescent probes for the detection of HClO/ClO^-in vitro and in vivo with different design principles and mechanisms, including fluorescence, phosphorescence, and chemiluminescence. The photophysical/chemical properties and biological applications of these luminescent probes were outlined. Finally, we summarized the merits and demerits of the developed luminescent probes and discussed their challenges and future development trends. It is hoped that this review can provide some inspiration for the development of luminescent probe-based strategies and to promote the further research of biomedical luminescent probes for HClO/ClO^-.

Responsive Upconversion Nanoprobe for Background-Free Hypochlorous Acid Detection and Bioimaging

Responsive nanoprobes play an important role in bioassay and bioimaging, early diagnosis of diseases and treatment monitoring. Herein, a upconversional nanoparticle (UCNP)-based nanoprobe, Ru@UCNPs, for specific sensing and imaging of hypochlorous acid (HOCl) is reported. This Ru@UCNP nanoprobe consists of two functional components,, i.e., NaYF₄ :Yb, Tm UCNPs that can convert near infrared light-to-visible light as the energy donor, and a HOCl-responsive ruthenium(II) complex [Ru(bpy)₂ (DNCH-bpy)](PF₆ )₂ (Ru-DNPH) as the energy acceptor and also the upconversion luminescence (UCL) quencher. Within this luminescence resonance energy transfer nanoprobe system, the UCL OFF-ON emission is triggered specifically by HOCl. This triggering reaction enables the detection of HOCl in aqueous solution and biological systems. As an example of applications, the Ru@UCNPs nanoprobe is loaded onto test papers for semiquantitative HOCl detection without any interference from the background fluorescence. The application of Ru@UCNPs for background-free detection and visualization of HOCl in cells and mice is successfully demonstrated. This research has thus shown that Ru@UCNPs is a selective HOCl-responsive nanoprobe, providing a new way to detect HOCl and a new strategy to develop novel nanoprobes for in situ detection of various biomarkers in cells and early disgnosis of animal diseases.

"Chemistry-on-the-complex": functional RuII polypyridyl-type sensitizers as divergent building blocks

Ruthenium polypyridyl type complexes are potent photoactive compounds, and have found - among others - a broad range of important applications in the fields of biomedical diagnosis and phototherapy, energy conversion schemes such as dye-sensitized solar cells (DSSCs) and molecular assemblies for tailored photo-initiated processes. In this regard, the linkage of RuII polypyridyl-type complexes with specific functional moieties is highly desirable to enhance their inherent photophysical properties, e.g., with a targeting function to achieve cell selectivity, or with a dye or redox-active subunits for energy- and electron-transfer. However, the classical approach of performing ligand syntheses first and the formation of Ru complexes in the last steps imposes synthetic limitations with regard to tolerating functional groups or moieties as well as requiring lengthy convergent routes. Alternatively, the diversification of Ru complexes after coordination (termed "chemistry-on-the-complex") provides an elegant complementary approach. In addition to the Click chemistry concept, the rapidly developing synthesis and purification methodologies permit the preparation of Ru conjugates via amidation, alkylation and cross-coupling reactions. In this regard, recent developments in chromatography shifted the limits of purification, e.g., by using new commercialized surface-modified silica gels and automated instrumentation. This review provides detailed insights into applying the "chemistry-on-the-complex" concept, which is believed to stimulate the modular preparation of unpreceded molecular assemblies as well as functional materials based on Ru-based building blocks, including combinatorial approaches.

Rapid Response Fluorescence Probe Enabled In Vivo Diagnosis and Assessing Treatment Response of Hypochlorous Acid-Mediated Rheumatoid Arthritis

Diagnosis and early assessment of the treatment response of rheumatoid arthritis (RA) necessitates a reliable bioanalytical method for rapid, sensitive, and specific detection of the hypochlorous acid (HOCl) biomarker in inflammatory diseases. Herein, two fluorescence probes, Probe-1 and Probe-2 are developed for quantitative monitoring and visualization of inflammatory response-related HOCl levels in vitro and in vivo. In the presence of HOCl, fluorescence "OFF-ON" response is obtained for both the probes as a result of specific HOCl-triggered C=N bond cleavage reaction. Probe-1 and Probe-2 feature rapid response (<4 s), a high degree of sensitivity and selectivity toward HOCl, which allow them to be used for quantification of HOCl in a simulated physiological condition. Using Probe-2 as the probe, fluorescence imaging and flow cytometry analysis of HOCl levels in lysosome of inflammatory mimic cells, visualization of HOCl generation in endotoxin-induced inflammation of adult zebrafish and RA of mice are possible. Probe-2 exhibits high effectiveness for early assessment of the treatment response of HOCl-mediated RA in mice with an antiarthritic drug, methotrexate (MTX). The results demonstrate that Probe-2 is a powerful tool for future studies on diagnosis and monitoring treatment efficiency in a broad range of inflammatory diseases, including RA.

Covalent and Non-covalent Conjugation of Few-Layered Graphene Oxide and Ruthenium(II) Complex Hybrids and Their Energy Transfer Modulation via Enzymatic Hydrolysis

Pyrene-containing ruthenium(II) tris-bipyridine complexes have been prepared. These complexes have been non-covalently attached onto the few-layered graphene oxide (GO) sheets through their high binding affinity for flat π-surfaces. Alternatively, the reduced graphene oxide (rGO) sheets have also been covalently functionalized with the ruthenium(II) tris-bipyridine complex. The prepared conjugates have been characterized by transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, thermogravimetric analysis (TGA), and UV-visible absorption spectroscopy. The energy transfer properties of the resulted conjugates between the graphene and transition metal complexes have been studied via esterase hydrolysis. The energy transfer efficiencies were found to vary with the separation between the donor and the acceptor units.

A coumarin Schiff's base two-photon fluorescent probe for hypochlorite in living cells and zebrafish

Selective and sensitive fluorescent probes for ClO⁻ are desirable due to the importance of ClO⁻ in biological processes. Here, a coumarin Schiff's base, compound 1, has been developed and successfully used as a one- and two-photon fluorescent probe for ClO⁻ with high selectivity. This probe can recognize ClO⁻ with obvious color change from yellow-green to colorless and green to blue fluorescence emission, which can be observed by the naked eye. The properties of low cytotoxicity and good cell permeability allow it to be used for ClO⁻ detection in living cells and zebrafish by both one- and two-photon microscopy imaging. All these results indicate that the compound is a sensitive probe with potential for analysis of ClO⁻ in biological samples. The mechanism by which probe 1 recognizes ClO⁻ is possibly nucleophilic addition followed by hydrolysis.

A coumarin Schiff's base compound can selectively recognize ClO⁻ and can be successfully applied to the detection of ClO⁻ in living cells and zebrafish by one- and two-photon fluorescence modes.

A naphthalimide based fast and selective fluorescent probe for hypochlorous acid/hypochlorite and its application for bioimaging

A reversible and mitochondria targetable fluorescent probe (Nap-Se) bearing 1,8-naphthalimide and a selenomorpholine fragment was designed and synthesized.

A fast response fluorescence probe specific for hypochlorous acid detection and its applications in bioimaging

The features ofDNPH-NA, including its high sensitivity, selectivity, and reliability at physiological pH, together with a rapid response, enable its successful application in the detection of endogenous HOClin vitroandin vivo.

Development of a novel europium complex-based luminescent probe for time-gated luminescence imaging of hypochlorous acid in living samples

Luminescent lanthanide complexes are key reagents used in the time-gated luminescence bioassay technique, but functional lanthanide complexes that can act as luminescent probes for specifically responding to analytes are very limited. In this work, we designed and synthesized a novel Eu³⁺ complex-based luminescence probe for hypochlorous acid (HOCl), NPPTTA-Eu³⁺, by using terpyridine polyacid-Eu³⁺, dinitrophenyl, and hydrazine as luminophore, quencher and HOCl-recognizer moieties, respectively. In the absence of HOCl, the probe is non-luminescent due to the strong luminescence quenching of the dinitrophenyl group in the complex. However, upon reaction with HOCl, the dinitrophenyl moiety is rapidly cleaved from the probe, which affords a strongly luminescent Eu³⁺ complex CPTTA-Eu³⁺, accompanied by a ∼900-fold luminescence enhancement with a long luminescence lifetime of 1.41 ms. This unique luminescence response of NPPTTA-Eu³⁺ to HOCl allowed NPPTTA-Eu³⁺ to be conveniently used as a probe for highly selective and sensitive detection of HOCl under the time-gated luminescence mode. In addition, by loading NPPTTA-Eu³⁺ into RAW 264.7 macrophage cells and Daphnia magna, the generation of endogenous HOCl in RAW 264.7 cells and the uptake of exogenous HOCl by Daphnia magna were successfully imaged on a true-color time-gated luminescence microscope. The results demonstrated the practical applicability of NPPTTA-Eu³⁺ as an efficient probe for time-gated luminescence imaging of HOCl in living cells and organisms.

A mitochondria-targeting time-gated luminescence probe for hypochlorous acid based on a europium complex

A europium complex-based mitochondria-targeting probe has been developed for the time-gated luminescence imaging of hypochlorous acid in living samples.

Combining Ruthenium(II) Complexes with Metal-Organic Frameworks to Realize Effective Two-Photon Absorption for Singlet Oxygen Generation

Singlet oxygen ((1)O2), as a reactive oxygen species, has garnered serious attention in physical, chemical, and biological studies. In this paper, we designed and synthesized a new type of singlet-oxygen generation system by exchanging cationic ruthenium complexes (RCs) into anionic bio-MOF-1. The resulting bio-MOF-1&RCs can be used as effective photocatalysts for generation of singlet oxygen under both single-photon and two-photon excitation. Especially, the excellent two-photon absorption (TPA) behavior of bio-MOF-1&RCs aroused our interest greatly because their two-photon absorption band lies in the optical window of biological tissue. Here, we measured the ability of bio-MOF-1&RCs to generate (1)O2 by irradiation under both 490 and 800 nm wavelength light in DMF. 1,3-Diphenylisobenzofuran (DPBF) and 2',7'-dichlorofluorescein (DCFH) were used as typical (1)O2 traps to detect and evaluate the efficiency of generation of (1)O2 under single-photon and two-photon excitation, respectively. Results indicated that bio-MOF-1&[Ru(phen)3](2+) was able to effectively generate (1)O2 under both conditions. Our work creates a novel synergistic TPA system with the excellent photophysical properties of RCs and the unique microporous structure benefit of MOFs, which may open a new avenue for creation of a cancer treatment system with both photodynamic therapy and chemotherapy.

Kinetic studies on the reaction of cob(II)alamin with hypochlorous acid: Evidence for one electron oxidation of the metal center and corrin ring destruction

Kinetic and mechanistic studies on the reaction of a major intracellular vitamin B₁₂ form, cob(II)alamin (Cbl(II)), with hypochlorous acid/hypochlorite (HOCl/OCl^-) have been carried out. Cbl(II) (Co(II)) is rapidly oxidized by HOCl to predominately aquacobalamin/hydroxycobalamin (Cbl(III), Co(III)) with a second-order rate constant of 2.4×10⁷M^-1s^-1 (25.0°C). The stoichiometry of the reaction is 1:1. UHPLC/HRMS analysis of the product mixture of the reaction of Cbl(II) with 0.9mol equiv. HOCl provides support for HOCl being initially reduced to Cl and subsequent H atom abstraction from the corrin macrocycle occurring, resulting in small amounts of corrinoid species with two or four H atoms fewer than the parent cobalamin. Upon the addition of excess (H)OCl further slower reactions are observed. Finally, SDS-PAGE experiments show that HOCl-induced damage to bovine serum albumin does not occur in the presence of Cbl(II), providing support for Cbl(II) being an efficient HOCl trapping agent.

A dinuclear ruthenium(II) complex as turn-on luminescent probe for hypochlorous acid and its application for in vivo imaging

A dinuclear ruthenium(II) complex Ruazo was designed and synthesized, in which oxidative cyclization of the azo and o-amino group was employed for the detection of hypochlorous acid (HClO) in aqueous solution. The non-emissive Ruazo formed highly luminescent triazole-ruthenium(II) complex in presence of HClO and successfully imaged HClO in living cell and living mouse.

Recent progress in chromogenic and fluorogenic chemosensors for hypochlorous acid

Due to the biological and industrial importance of hypochlorous acid, the development of optical probes for HOCl has been an active research area. Hypochlorous acid and hypochlorite can oxidize electron-rich analytes with accompanying changes in molecular sensor spectroscopic profiles. Probes for such processes may monitor HOCl levels in the environment or in an organism and via bio-labeling or bioimaging techniques. This review summarizes recent developments in the area of chromogenic and fluorogenic chemosensors for HOCl.

Development of a BODIPY-based ratiometric fluorescent probe for hypochlorous acid and its application in living cells

A BODIPY-based ratiometric fluorescent probe for HOCl has been designed based on the transduction of thioether to sulfoxide function. This probe features a marked absorption and emission blue-shift upon the HOCl-promoted rapid transduction, enabling the highly selective and ratiometric detection. In addition, the probe works excellently within a wide pH range of 4-10, addressing the existing pH dependency issue. Living cells studies demonstrate that the probe is cell membrane permeable and can be employed successfully to image endogenous HOCl generation in macrophage cells.

Synthesis, structures and photophysical properties of luminescent cyanoruthenate(ii) complexes with hydroxylated bipyridine and phenanthroline ligands

Two luminescent cyanoruthenate(ii) complexes with hydroxylated ligands were obtained and their solvatochromism, pH effect and cationic effect on the photophysical properties have been studied.

Ruthenium bistridentate complexes with non-symmetrical hexahydro-pyrimidopyrimidine ligands: a structural and theoretical investigation of their optical and electrochemical properties

The optical and electronic properties of six Ru complexes with non-symmetrical tridentate ligands have been investigated and, as corroborated by electrochemical data, the presence of the hpp ligand strongly affects the oxidation potential of the metal ion.

White emission magnetic nanoparticles as chemosensors for sensitive colorimetric and ratiometric detection, and degradation of ClO⁻ and SCN⁻ in aqueous solutions based on a logic gate approach

Fluorescent chemosensors for detecting single anions have been largely synthesized. However, the simultaneous detection and degradation of multiple anions remain a major challenge. Herein we report the synthesis of a white emission nanoprobe on the basis of a Coumarin-Rhodamine CR1-Eu complex coordinated to dipicolinic acid (dpa)-PEG-Fe3O4 nanoparticles for the selective detection of ClO(-) and SCN(-) ions on controlling by a logic gate. The obtained nanoprobe exhibits three individual primary colors (blue, green, and red) as well as white emission at different excitation energies. Interestingly, this nanoprobe shows a marked rose red to violet emission color change in response to ClO(-), a reversible violet to rose red emission color change in response to SCN(-), and high ClO(-) and SCN(-) selectivity and sensitivity with a detection limit of 0.037 and 0.250 nM, respectively. Furthermore, the SCN(-) and ClO(-) can degrade simultaneously through the redox reaction between ClO(-) and SCN(-).