Release of Amino‐ or Carboxy‐Containing Compounds Triggered by HOCl: Application for Imaging and Drug Design

The overproduction of HOCl is highly correlated with diseases such as atherosclerosis, rheumatoid arthritis, and cancer. Whilst acting as a marker of these diseases, HOCl might also be used as an activator of prodrugs or drug delivery systems for the treatment of the corresponding disease. In this work, a new platform of HOCl probes has been developed that integrates detection, imaging, and therapeutic functions. The probes can detect HOCl, using both NIR emission and the naked eye in vitro, with high sensitivity and selectivity at ultralow concentrations (the detection limit is at the nanomolar level). Basal levels of HOCl can be imaged in HL‐60 cells without special stimulation. Moreover, the probes provided by this platform can rapidly release either amino‐ or carboxy‐containing compounds from prodrugs, during HOCl detection and imaging, to realize a therapeutic effect.     

Near‐Infrared Fluorescent Probe with New Recognition Moiety for Specific Detection of Tyrosinase Activity: Design,Synthesis, and Application in Living Cells and Zebrafish

Fluorescence imaging of tyrosinase (a cancer biomarker) in living organisms is of great importance for biological studies. However, selective detection of tyrosinase remains a great challenge because current fluorescent probes that contain the 4‐hydroxyphenyl moiety show similar fluorescence responses to both tyrosinase and some reactive oxygen species (ROS), thereby suffering from ROS interference. Herein, a new tyrosinase‐recognition 3‐hydroxybenzyloxy moiety, which exhibits distinct fluorescence responses for tyrosinase and ROS, is proposed. Using the recognition moiety, we develop a near‐infrared fluorescence probe for tyrosinase activity, which effectively eliminates the interference from ROS. The high specificity of the probe was demonstrated by imaging and detecting endogenous tyrosinase activity in live cells and zebrafish and further validated by an enzyme‐linked immunosorbent assay. The probe is expected to be useful for the accurate detection of tyrosinase in complex biosystems.     

Confining Free Radicals in Close Vicinity to Contaminants Enables Ultrafast Fenton‐like Processes in the Interspacing of MoS2 Membranes

Heterogenous Fenton‐like reactions are frequently proposed for treating persistent pollutants through the generation of reactive radicals. Despite great efforts to optimize catalyst activity, their broad application in practical settings has been restricted by the low efficiency of hydrogen peroxide or persulfate decomposition as well as ultrafast self‐quenching of the activated radicals. Theoretical calculations predicted that two‐dimensional (2D) metallic 1T phase MoS₂ materials with exposed (001) surfaces and (100) edges should have remarkable affinity towards crucial intermediates in the peroxymonosulfate (PMS) activation process. X‐ray photoelectron spectroscopy and in situ Raman spectroscopy were used to show that the exposed metallic Mo sites accelerate the rate‐limiting step of electron transfer. A lamellar membrane made from a stack of 2D MoS₂ with tunable interspacing was then designed as the catalyst. The non‐linear transport between the MoS₂ nanolayers leads to high water diffusivity so that the short‐lived reactive radicals efficiently oxidize contaminants.     

Ratiometric Fluorescence Assay for Nitroreductase Activity: Locked-Flavylium Fluorophore as a NTR-Sensitive Molecular Probe

Nitroreductases belong to a member of flavin-containing enzymes that can reduce nitroaromatic compounds to amino derivatives with NADH as an electron donor. NTR activity is known to be elevated in the cancerous environment and is considered an advantageous target in therapeutic prodrugs for the treatment of cancer. Here, we developed a ratiometric fluorescent molecule for observing NTR activity in living cells. This can provide a selective and sensitive response to NTR with a distinct increase in fluorescence ratio (FI₅₃₀/FI₆₃₀) as well as color changes. We also found a significant increase in NTR activity in cervical cancer HeLa and lung cancer A549 cells compared to non-cancerous NIH3T3. We proposed that this new ratiometric fluorescent molecule could potentially be used as a NTR-sensitive molecular probe in the field of cancer diagnosis and treatment development related to NTR activity.     

NanoSOSG: A Nanostructured Fluorescent Probe for the Detection of Intracellular Singlet Oxygen

A biocompatible fluorescent nanoprobe for singlet oxygen (¹O₂) detection in biological systems was designed, synthesized, and characterized, that circumvents many of the limitations of the molecular probe Singlet Oxygen Sensor Green^® (SOSG). This widely used commercial singlet oxygen probe was covalently linked to a polyacrylamide nanoparticle core using different architectures to optimize the response to ¹O₂. In contrast to its molecular counterpart, the optimum SOSG‐based nanoprobe, which we call NanoSOSG, is readily internalized by E. coli cells and does not interact with bovine serum albumin. Furthermore, the spectral characteristics do not change inside cells, and the probe responds to intracellularly generated ¹O₂ with an increase in fluorescence.     

Rational Engineering of a Dynamic,Entropy‐Driven DNA Nanomachine for Intracellular MicroRNA Imaging

We rationally engineered an elegant entropy‐driven DNA nanomachine with three‐dimensional track and applied it for intracellular miRNAs imaging. The proposed nanomachine is activated by target miRNA binding to drive a walking leg tethered to gold nanoparticle with a high density of DNA substrates. The autonomous and progressive walk on the DNA track via the entropy‐driven catalytic reaction of intramolecular toehold‐mediated strand migration leads to continuous disassembly of DNA substrates, accompanied by the recovery of fluorescence signal due to the specific release of a dye‐labeled substrate from DNA track. Our nanomachine outperforms the conventional intermolecular reaction‐based gold nanoparticle design in the context of an improved sensitivity and kinetics, attributed to the enhanced local effective concentrations of working DNA components from the proximity‐induced intramolecular reaction. Moreover, the nanomachine was applied for miRNA imaging inside living cells.     

Self-Amplified Photodynamic Therapy through the 1O2-Mediated Internalization of Photosensitizers from a Ppa-Bearing Block Copolymer

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non-selective release of photosensitizers still exist. Herein, we report a ¹O₂-responsive block copolymer (POEGMA-b-P(MAA-co-VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (¹O₂) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The ¹O₂-responsiveness of POEGMA-b-P(MAA-co-VSPpaMA) block copolymer enabled the realization of self-amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.     

A Ratiometric Fluorescent Probe for Cisplatin: Investigating the Intracellular Reduction of Platinum(IV) Prodrug Complexes

The Pt^IV prodrug strategy has emerged as an excellent alternative to tackle the problems associated with conventional Pt^II drug therapy. However, there is a lack of tools to study how this new class of Pt^IV drugs are processed at the cellular level. Herein, we report the first ratiometric probe for cisplatin detection and use it to investigate Pt^IV anticancer complexes in biological systems. The probe was able to distinguish between cisplatin and its Pt^IV derivatives, allowing us to probe the intracellular reduction of Pt^IV prodrug complexes. The correlation between the amount of active Pt^II species available after intracellular reduction of Pt^IV complexes and their cytotoxicity and the role glutathione plays in the reduction of Pt^IV complexes were investigated.     

A General Strategy for Development of Near‐Infrared Fluorescent Probes for Bioimaging

Near‐infrared (NIR) fluorescent dyes with favorable photophysical properties are highly useful for bioimaging, but such dyes are still rare. The development of a unique class of NIR dyes via modifying the rhodol scaffold with fused tetrahydroquinoxaline rings is described. These new dyes showed large Stokes shifts (>110 nm). Among them, WR3, WR4, WR5, and WR6 displayed high fluorescence quantum yields and excellent photostability in aqueous solutions. Moreover, their fluorescence properties were tunable by easy modifications on the phenolic hydroxy group. Based on WR6, two NIR fluorescent turn‐on probes, WSP‐NIR and SeSP‐NIR, were devised for the detection of H₂S. The probe SeSP‐NIR was applied in visualizing intracellular H₂S. These dyes are expected to be useful fluorophore scaffolds in the development of new NIR probes for bioimaging.     

Oxidative Intramolecular 1,2‐Amino‐Oxygenation of Alkynes under AuI/AuIII Catalysis: Discovery of a Pyridinium‐Oxazole Dyad as an Ionic Fluorophore

Oxidative intramolecular 1,2‐amino‐oxygenation reactions, combining gold(I)/gold(III) catalysis, is reported. The reaction provides efficient access to a structurally unique ionic pyridinium‐oxazole dyad with tunable emission wavelengths. The application of these fluorophores as potential biomarkers has been investigated.     

5-氨基-1,10-菲咯啉：可异构化杂环螯合荧光载体作为比例计量型锌离子荧光探针的一种原型

5-amino-l,10-phenanthroline （5-AP）, as a tautomeric heterocyclic aromatic chelating fluorophore （THACF）, can sense Zn^2＋ selectively by shifting emission from 495 to 564 nm upon Zn^2＋ addition in ethanol. The ratiometric fluorescent sensing behavior has been correlated to the tautomerization of 5-AP affected by solvents and metal chelation. The strategy using THACF as ratiometric fluorescent sensor for Zn^2＋ not only simplifies the synthetic procedure but also gives a promising alternative for Zn^2＋ ratiometric fluorescent sensor design.     

High-Performance Quinoline-Malononitrile Core as a Building Block for the Diversity-Oriented Synthesis of AIEgens

In vivo fluorescent monitoring of physiological processes with high-fidelity is essential in disease diagnosis and biological research, but faces extreme challenges due to aggregation-caused quenching (ACQ) and short-wavelength fluorescence. The development of high-performance and long-wavelength aggregation-induced emission (AIE) fluorophores is in high demand for precise optical bioimaging. The chromophore quinoline-malononitrile (QM) has recently emerged as a new class of AIE building block that possesses several notable features, such as red to near-infrared (NIR) emission, high brightness, marked photostability, and good biocompatibility. In this minireview, we summarize some recent advances of our established AIE building block of QM, focusing on the AIE mechanism, regulation of emission wavelength and morphology, the facile scale-up and fast preparation for AIE nanoparticles, as well as potential biomedical imaging applications.     

A Water‐Soluble Perylene Bisimide Cyclophane as a Molecular Probe for the Recognition of Aromatic Alkaloids

Herein, we report a water‐soluble macrocyclic host based on perylene bisimide (PBI) chromophores that recognizes natural aromatic alkaloids in aqueous media by intercalating them into its hydrophobic cavity. The host–guest binding properties of our newly designed receptor with several alkaloids were studied by UV/Vis and fluorescence titration experiments as the optical properties of the chromophoric host change significantly upon complexation of guests. Structural information on the host–guest complexes was obtained by 1D and 2D NMR spectroscopy and molecular modelling. Our studies reveal a structure–binding property relationship for a series of structurally diverse aromatic alkaloids with the new receptor and higher binding affinity for the class of harmala alkaloids. To our knowledge, this is the first example of a chromophoric macrocyclic host employed as a molecular probe for the recognition of aromatic alkaloids.