A Highly Sensitive and Selective Optical Sensor for the On-Line Detection of Cesium in Water.

In this study, we have undertaken the development of two fluorescent sensors based on calixarene compounds for the purpose of detecting cesium in water. By introducing the sulfonate functional groups, we have considerably improved the water solubility of sensors, enabling complete dissolution of products in aqueous media and direct analysis of polluted water samples. Through rigorous experiments, we have demonstrated that the complexation of Cs+ ions with sensors 1 and 2 in water leads to a remarkable enhancement of fluorescence. This fluorescence enhancement serves as a reliable indication of cesium presence and allows for sensitive detection. To further advance the practical application of our sensors, we have successfully integrated calixarene sensors 1 and 2 into a microfluidic sensor chip. This integration has enabled real-time, on-line measurements and has resulted in the development of a portable detection device capable of detecting cesium ions in water samples at parts per billion (ppb) levels. This device holds great promise for environmental monitoring and assessment, providing a convenient and efficient solution for cesium detection. Our work represents a significant advancement in the field of cesium detection, displaying the efficacy of calixarene-based fluorescent sensors and their integration into microfluidic systems. The enhanced water solubility, fluorescence response, and portability of our detection device offers tremendous potential for applications in environmental monitoring, water quality assessment, and emergency response scenarios where rapid and accurate cesium detection is crucial.

Dynamic Spirals of Nanoparticles in Light-Responsive Polygonal Fields.

Nanoparticles tend to aggregate once integrated into soft matter and consequently, self-assembling nanoparticles into large-scale, regular, well-defined, and ultimately chiral patterns remains an ongoing challenge toward the design and realization of organized superstructures of nanoparticles. The patterns of nanoparticles that are reported in liquid crystals so far are all static, and this lack of responsiveness extends to assemblies of nanoparticles formed in topological singularities and other localized structures of anisotropic matter. Here, it is shown that gold nanoparticles form spiral superstructures in polygonal fields of cholesteric liquid crystals. Moreover, when the cholesteric liquid crystals incorporate molecular photoswitches in their composition, the pitch of the nanoparticulate spirals follows the light-induced reorganization of the cholesteric liquid crystals. These experimental findings indicate that chiral liquid crystals can be used as chiral and dynamic templates for soft photonic nanomaterials. Controlling the geometry of these spirals of nanoparticles will ultimately allow modulating the plasmonic signature of hybrid and chiral systems.

A Highly Selective Potassium Sensor for the Detection of Potassium in Living Tissues.

The development of highly selective sensors for potassium is of great interest in biology. Two new hydrosoluble potassium sensors (Calix-COU-Alkyne and Calix-COU-Am) based on a calix[4]arene bis(crown-6) and an extended coumarin were synthesized and characterized. The photophysical properties and complexation studies of these compounds have been investigated and show high molar extinction coefficients and high fluorescence quantum yields. Upon complexation with potassium in the millimolar concentration range, an increase of one- and two-photon fluorescence emission is detected. A twofold fluorescence enhancement is observed upon excitation at λ=405 nm. The ligands present excellent selectivity for potassium in the presence of various competitive cations in water and in a physiological medium. The photophysical properties are not affected by the presence of a large amount of competing cations (Na+ , Ca2+ , Mg2+ , etc.). Ex vivo measurements on mouse hippocampal slices show that Calix-COU-Alkyne accumulates extracellularly and does not alter the neuronal activity. Furthermore, the sensor can be utilized to monitor slow extracellular K+ increase induced by inhibition of K+ entry into the cells.

Fluorinated Azobenzenes for Shape-Persistent Liquid Crystal Polymer Networks.

Liquid crystal polymer networks respond with an anisotropic deformation to a range of external stimuli. When doped with molecular photoswitches, these materials undergo complex shape modifications under illumination. As the deformations are reversed when irradiation stops, applications where the activated shape is required to have thermal stability have been precluded. Previous attempts to incorporate molecular switches into thermally stable photoisomers were unsuccessful at photogenerating macroscopic shapes that are retained over time. Herein, we show that to preserve photoactivated molecular deformation on the macroscopic scale, it is important not only to engineer the thermal stability of the photoswitch but also to adjust the cross-linking density in the polymer network and to optimize the molecular orientations in the material. Our strategy resulted in materials containing fluorinated azobenzenes that retain their photochemical shape for more than eight days, which constitutes the first demonstration of long-lived photomechanical deformation in liquid-crystal polymer networks.

Calixarene-Based Fluorescent Sensors for Cesium Cations Containing BODIPY Fluorophore.

New fluorescent molecular sensors based on a calix[4]arene biscrown-6 ether as coordination site and BODIPY derivative as signaling unit were synthesized, and their photophysical properties were characterized. The complexation properties of these sensors with potassium and cesium cations were investigated using both steady-state and time-resolved fluorescence methods. The studies show that the sensitivity with cations depends upon the position of substituted coordination site on the BODIPY core. The complexation with cations does not have much effect on the absorption and emission wavelength when the coordination site (calix[4]arene biscrown-6 ether) is introduced at the meso position of the BODIPY core. In contrast, the same calix[4]arene biscrown-6 ether attached via a styryl linker to the α-position of BODIPY core leads to a sensitive sensor for alkali cations thanks to the better conjugation between the coordination site and the BODIPY core. The complexation of cations induces a hypsochromic shift of the absorption and emission maximums due to the diminution of donor character of the oxygen atoms in the coordination site. The stability constants of complexes with potassium and cesium ion were measured.

Aggregation-induced emission enhancement upon Al3+ complexation with a tetrasulfonated calix[4]bisazacrown fluorescent molecular sensor.

Aggregation-induced emission and aggregation-induced emission enhancement have attracted much attention due to their great potential in real-world applications. Up to now most of the reports are based on the restriction of free rotation of the luminogens in the aggregates. In the present work, we found that the dansyl fluorophore with typical intramolecular charge transfer characteristic also exhibited aggregation-induced emission enhancement, which was based on the change of micro-environmental polarity of the fluorophore. In the light of the phenomenon, a new water-soluble ligand bearing a tetrasulfonated calix[4]arene was constructed for ratiometric detection of Al(3+) based on an aggregation-induced emission enhancement mechanism. It displayed a distinct selectivity to Al(3+) among the tested cations in lutidine buffer solution (pH 6-7) with a detection limit of 1.8 µM. A reversible response was also demonstrated by the addition of EDTA or F(-).