Synthesis and characterization of a sensitive and selective Fe3+ fluorescent sensor based on novel sulfonated calix[4]arene‐based host‐guest complex

Eu-doped ZIF-8 as a ratiometric fluorescence-scattering probe for the anthrax biomarker in food samples based on competitive coordination

Bacillus anthracis spores can cause contagious anthrax, so it is significant for the public safety to detect its biomarker dipicolinic acid (DPA). Ratiometric fluorescent probes for DPA have attracted great interest because of the self-calibration effect, but they suffer from the complicated construction of dual-emitting materials. With combining fluorescence and second-order scattering (SOS), Eu-doped Zn-based metal-organic framework (ZIF-8) was here designed as a ratiometric probe for DPA, avoiding the completed construction of dual-emitting materials. Eu-doped ZIF-8 exhibited no fluorescence but possessed strong SOS ascribed to the nanostructure. However, the competitive coordination of DPA not only triggered the antenna effect of Eu3+ but also caused the decomposition of Eu-doped ZIF-8. As a consequence, the fluorescence enhancement and the SOS weakness were observed upon the addition of DPA to Eu-doped ZIF-8. And thus, a ratiometric probe for DPA was constructed based on Eu-doped ZIF-8 by integrating fluorescence with SOS. The probe as-constructed could quantify DPA in a wide range of 0.1-150 μM with a rapid response (1 min) and a low detection limit (31 nM). It also displayed excellent manifestation for the analysis of food samples with reasonable accuracy (recoveries, 90.0%-101.5%) and satisfactory precision (RSDs, 0.6%-5.7%), offering a reliable tool for the supervision of the public safety.

A summary of calixarene-based fluorescent sensors developed during the past five years

Calixarenes are "chalice like" phenol-based macrocycles that are one of the most fascinating studied scaffolds in supramolecular chemistry. Their preorganized nonpolar cavities and ion binding sites, and their well-defined conformations all lay important foundations for forming host-guest complexes. Conjugation of calixarene scaffolds with various fluorophores at either upper or lower rims has led to the development of smart fluorescent probes for inorganic molecules or ions, aliphatic or aromatic compounds, biomolecules, temperature and hypoxia, even multi-component traditional Chinese medicine (TCM). Moreover, significant advancements have been made for biological applications. This review critically summarizes the recent advances made in these areas.

Multi-Responsive Molecular Encapsulation and Release Based on Hydrogen-Bonded Azo-Macrocycle

Research on stimuli-responsive host-guest systems is at the cutting edge of supramolecular chemistry, owing to their numerous potential applications such as catalysis, molecular machines, and drug delivery. Herein, we present a multi-responsive host-guest system comprising azo-macrocycle 1 and 4,4'-bipyridinium salt G1 for pH-, photo-, and cation- responsiveness. Previously, we reported a novel hydrogen-bonded azo-macrocycle 1. The size of this host can be controlled through light-induced E↔Z photo-isomerization of the constituent azo-benzenes. The host is found in this work to be capable of forming stable complexes with bipyridinium/pyridinium salts, and implementing guest capture and release with G1 under light in a controlled manner. The binding and release of the guest in the complexes can also be easily controlled reversibly by using acid and base. Moreover, the cation competition-induced dissociation of the complex 1a₂⊃G1 is achieved. These findings are expected to be useful in regulating encapsulation for sophisticated supramolecular systems.

A novel portable smart phone sensing platform based on a supramolecular fluorescence probe for quick visual quantitative detection of picric acid

Picric acid (PA) is a lethal explosive substance that is easily soluble in water and harmful to the environment. Here, a supramolecular polymer material BTPY@Q[8] with aggregation induced emission (AIE) was prepared by supramolecular self-assembly of cucurbit uril (Q[8]) and 1,3,5-tris[4-(pyridin-4-yl) phenyl] benzene derivative (BTPY), which exhibited aggregation-induced fluorescence enhancement. To this supramolecular self-assembly, the addition of a number of nitrophenols was found to have no obvious effect on the fluorescence, however on addition of PA, the fluorescence intensity underwent a dramatic quench. For PA, BTPY@Q[8] had sensitive specificity and effective selectivity. Based on this, a quick and simple on-site visual PA fluorescence quantitative detection platform was developed using smart phones, and the platform was used to monitor temperature. Machine learning (ML) is a popular pattern recognition technology, which can accurately predict the results from data. Therefore, ML has much more potential for analyzing and improving sensing data than the widely used statistical pattern recognition method. In the field of analytical science, the sensing platform offers a reliable method for the quantitative detection of PA that can be applied to other analytes or micropollutant screening.

Disposable paper-based PET fluorescence probe linked with calix[4]arene for lithium and phosphate ion detection

As a part of our ongoing research, we have synthesized a new fluorescence probe, p-C4A, based on a calix[4]arene substituted with 4-aminoquinoline moieties with amide linkages for lithium and phosphate ions.