Design of Fluorescent Hybrid Materials Based on POSS for Sensing Applications

Polyhedral oligomeric silsesquioxane (POSS) has a nanoscale silicon core and eight organic functional groups on the surface, with sizes from 0.7 to 1.5 nm. The three-dimensional nanostructures of POSS can be used to build all types of hybrid materials with specific performance and controllable nanostructures. The applications of POSS-based fluorescent materials have spread across various fields. In particular, the employment of POSS-based fluorescent materials in sensing application can achieve high sensitivity, selectivity, and stability. As a result, POSS-based fluorescent materials are attracting increasing attention due to their fascinating vistas, including unique structural features, easy fabrication, and tunable optical properties by molecular design. Here, we summarize the current available POSS-based fluorescent materials from design to sensing applications. In the design section, we introduce synthetic strategies and structures of the functionalized POSS-based fluorescent materials, as well as photophysical properties. In the application section, the typical POSS-based fluorescent materials used for the detection of various target objects are summarized with selected examples to elaborate on their wide applications.

Probing the Structural Dynamics of the Coil-Globule Transition of Thermosensitive Nanocomposite Hydrogels

Nanocomposite hydrogels have emerged to exhibit multipurpose properties, boosting especially the biomaterial field. However, the development and characterization of these materials can be a challenge, especially stimuli-sensitive materials with dynamic properties in response to external stimuli. By employing UV-vis spectroscopy and NMR relaxation techniques, we could outline the formation and behavior of thermosensitive nanocomposites obtained by in situ polymerization of poly(N-vinylcaprolactam) (PNVCL) and mesoporous silica nanofibers under temperature stimuli. For instance, inorganic nanoparticles covalently linked to PNVCL changed the pattern of temperature-induced phase transition despite showing similar critical temperatures to neat PNVCL. Thermodynamic parameters indicated the formation of an interconnected system of silica and polymer chains with reduced enthalpic contribution and mobility. The investigation of water molecule and polymer segment motions also revealed that the absorption and release of water happened in a wider temperature range for the nanocomposites, and the polymer segments respond in different ways during the phase transition in the presence of silica. This set of techniques was essential to reveal the polymer motions and structural features in nanocomposite hydrogels under temperature stimuli, demonstrating its potential use as experimental guideline to study multicomponent nanocomposites with diverse functionalities and dynamic properties.

A simple yet effective AIE-based fluorescent nano-thermometer for temperature mapping in living cells using fluorescence lifetime imaging microscopy

We designed and synthesized a novel nano-thermometer using aggregation-induced-emission (AIE) dye as the reporter and household butter as the matrix. This temperature nanosensor showed decreased fluorescence intensities (∼2%/°C) and shorter fluorescence lifetimes (∼0.11 ns/°C) upon increasing the environmental temperature in the physiological temperature range. Such fluorescence responses were reversible and independent of the environmental pH and ionic strength. The application of these nano-thermometers in temperature sensing in living cells using fluorescence lifetime imaging microscopy (FLIM) was also demonstrated. To the best of our knowledge, this is the first example of AIE-based nano-thermometer for temperature sensing in living cells. This work also provides us with a simple and low-cost method for rapid fabrication of an effective nanosensor based on AIE mechanism.

Mesoporous magnetic silica particles modified with stimuli-responsive P(NIPAM-DMA) valve for controlled loading and release of biologically active molecules

Mesoporous magnetic silica particles bearing a stimuli-responsive polymer valve were prepared and their performance as a microcapsule was evaluated. In this study, first, mesoporous magnetic iron oxide (Fe3O4) particles were prepared by a solvothermal method. Then, the magnetic particles were coated with silica and functionalized with vinyl groups using 3-(trimethoxysilyl)-propyl methacrylate (MPS). Subsequently, the Fe3O4/SiO2 composite particles grafted with MPS were used to carry out the seeded precipitation copolymerization of N-isopropylacrylamide (NIPAM) and 2,2-dimethylaminoethyl methacrylate (DMA). Here N,N'-methylenebisacrylamide (MBA) was used as a cross-linker. Brunauer-Emmett-Teller (BET) surface analysis suggested that the mesoporous structure was retained in the final Fe3O4/SiO2/P(NIPAM-DMA-MBA) composite hydrogel particles. The prepared Fe3O4/SiO2/P(NIPAM-DMA-MBA) composite hydrogel microspheres exhibited a pH-dependent volume phase transition. At lower pH values (<7), the inclusion of DMA shifted the volume phase transition to higher temperature because of the protonation of the tertiary amine groups. The composite hydrogel particles possessed a high saturation magnetization (51 emu g-1) and moved under the influence of an external magnetic field. The loading-release behaviour of these biologically active molecules suggested that a portion of the encapsulated guest molecules was released at a temperature below the lower critical solution temperature, LCST (<35 °C).