Supramolecular Host-Guest System as Ratiometric Fe3+ Ion Sensor Based on Water-Soluble Pillar[5]arene

Developing a specific, ratiometric, and reversible detection method for metal ions is significant to guard against the threat of metal-caused environmental pollution and organisms poisoning. Here a supramolecular host-guest system (WP5⊃G) based on water-soluble pillar[5]arene (WP5) and water-soluble quaternized perylene diimide derivative (G) was constructed. Morphological transformation was achieved during the process of adding WP5 into G aqueous solution, and a fluorescence "turn-off" phenomenon was observed which was caused by supramolecular photoinduced electron transfer (PET). Meanwhile, hydrophobic effect and electrostatic interaction played important roles in this supramolecular process, which was confirmed by isothermal titration calorimeter (ITC) and ζ potential experiments. Furthermore, the supramolecular host-guest system could be a "turn-on" fluorescent probe for Fe³⁺ ion detection through the process of interdicting supramolecular PET. Moreover, the Fe³⁺ ion detection showed specific, ratiometric, and reversible performances with a detection limit of 2.13 × 10^-7 M, which might have great potentials in biological and environmental monitoring.

Investigation of Drug-Induced Hepatotoxicity and Its Remediation Pathway with Reaction-Based Fluorescent Probes

Drug-induced liver injury (DILI) is considered a serious problem related to public health, due to its unpredictability and acute response. The level of peroxynitrite (ONOO^-) generated in liver has long been regarded as a biomarker for the prediction and measurement of DILI. Herein we present two reaction-based fluorescent probes (Naph-ONOO^- and Rhod-ONOO^-) for ONOO^- through a novel and universally applicable mechanism: ONOO^--mediated deprotection of α-keto caged fluorophores. Among them, Rhod-ONOO^- can selectively accumulate and react in mitochondria, one of the main sources of ONOO^-, with a substantial lower nanomolar sensitivity of 43 nM. The superior selectivity and sensitivity of two probes enable real-time imaging of peroxynitrite generation in lipopolysaccharide-stimulated live cells, with a remarkable difference from cells doped with other interfering reactive oxygen species, in either one- or two-photon imaging modes. More importantly, we elucidated the drug-induced hepatotoxicity pathway with Rhod-ONOO^- and revealed that CYP450/CYP2E1-mediated enzymatic metabolism of acetaminophen leads to ONOO^- generation in liver cells. This is the first time to showcase the drug-induced hepatotoxicity pathways by use of a small-molecule fluorescent probe. We hence conclude that fluorescent probes can engender a deeper understanding of reactive species and their pathological revelations. The reaction-based fluorescent probes will be a potentially useful chemical tool to assay drug-induced hepatotoxicity.

Sodium-Selective Fluoroionophore-Based Optodes for Seawater Salinity Measurement

A new fluorescent sensor for Na⁺ is presented. The sensor relies on a Na⁺ selective fluoroionophore based on a bright red-emitting BODIPY chromophore. The fluorescence of the fluoroionophore is enhanced upon binding of Na⁺-ions to the highly selective aza-crown ether receptor due to reduction of the photoinduced electron transfer (PET) quenching. Solid state sensing materials were prepared by physically embedding the fluoroionophore into water-swellable biocompatible polymer matrices (polyurethane hydrogels), thus enabling continuous measurements of aqueous samples. Despite the simple design, the sensor showed no leaching of the indicator and featured fast and reversible response. Among different polyurethane hydrogels investigated, the hydrogel D1 featuring the highest water uptake was found to be the most suitable due to the highest dynamics between "off" and "on" states. Due to little or no cross sensitivity to other ions (e.g., Mg²⁺, Ca²⁺, K⁺) and its insensitivity to potential changes in pH, this sensor is promising for use in clinical diagnostics and for biological and marine applications. Fiber-optic sensors based on referenced read-out with a compact phase fluorimeter were prepared. To demonstrate their practical applicability, the sensors were used to determine the salinity in the seawater and brackish water of the Baltic Sea.

Low-Affinity Zinc Sensor Showing Fluorescence Responses with Minimal Artifacts

The study of the zinc biology requires molecular probes with proper zinc affinity. We developed a low-affinity zinc probe (HBO-ACR) based on an azacrown ether (ACR) and an 2-(2-hydroxyphenyl)benzoxazole (HBO) fluorophore. This probe design imposed positive charge in the vicinity of a zinc coordination center, which enabled fluorescence turn-on responses to high levels of zinc without being affected by the pH and the presence of other transition-metal ions. Steady-state and transient photophysical investigations suggested that such a high tolerance benefits from orchestrated actions of proton-induced nonradiative and zinc-induced radiative control. The zinc bioimaging utility of HBO-ACR has been fully demonstrated with the use of human pancreas epidermoid carcinoma, PANC-1 cells, and rodent hippocampal neurons from cultures and acute brain slices. The results obtained through our studies established the validity of incorporating positively charged ionophores for the creation of low-affinity probes for the visualization of biometals.

Metallacycle-cored supramolecular assemblies with tunable fluorescence including white-light emission

Control over the fluorescence of supramolecular assemblies is crucial for the development of chemosensors and light-emitting materials. Consequently, the postsynthetic modification of supramolecular structures via host-guest interactions has emerged as an efficient strategy in recent years that allows the facile tuning of the photophysical properties without requiring a tedious chemical synthesis. Herein, we used a phenanthrene-21-crown-7 (P21C7)-based 60° diplatinum(II) acceptor 8 in the construction of three exohedral P21C7 functionalized rhomboidal metallacycles 1-3 which display orange, cyan, and green emission colors, respectively. Although these colors originate from the dipyridyl precursors 10-12, containing triphenylamine-, tetraphenylethene-, and pyrene-based fluorophores, respectively, the metal-ligand coordination strongly influences their emission properties. The metallacycles were further linked into emissive supramolecular oligomers by the addition of a fluorescent bis-ammonium linker 4 that forms complementary host-guest interactions with the pendant P21C7 units. Notably, the final ensemble derived from a 1:1 mixture of 1 and 4 displays a concentration-dependent emission. At low concentration, i.e., <25 µM, it emits a blue color, whereas an orange emission was observed when the concentration exceeds >5 mM. Moreover, white-light emission was observed from the same sample at a concentration of 29 µM, representing a pathway to construct supramolecular assemblies with tunable fluorescence properties.

Highly sensitive and selective fluorescent sensor for copper(ii) based on salicylaldehyde Schiff-base derivatives with aggregation induced emission and mechanoluminescence

The present study provides valuable information for designing materials with AIE, Cu²⁺ sensor and MFC properties based on Schiff-bases.

Fluorescent chemical probes for accurate tumor diagnosis and targeting therapy

This review focuses on small molecular ligand-targeted fluorescent imaging probes and fluorescent theranostics, including their design strategies and applications in clinical tumor treatment.

Pillararene-based fluorescent chemosensors: recent advances and perspectives

This feature article summarizes recent research in the pillararene-based fluorescent chemosensor field in terms of ion sensing, small molecule recognition, biomolecule detection, fluorescent supramolecular aggregates, and biomedical imaging.

A supramolecular self-assembly host–guest system from cyclodextrin as an absolute water-soluble fluorescence sensor for aluminium ions: synthesis, characterization and sensing activity

In the study, an organic molecule derived from paeonol and anthraniloyl hydrazine (L) was synthesized via a Schiff-base reaction.