High fluorescence of thioflavin T confined in mesoporous silica xerogels

Deciphering amyloid fibril molecular maturation through FLIM-phasor analysis of thioflavin T

The investigation of amyloid fibril formation is paramount for advancing our understanding of neurodegenerative diseases and for exploring potential correlated therapeutic strategies. Moreover, the self-assembling properties of amyloid fibrils show promise for the development of advanced protein-based biomaterials. Among the methods employed to monitor protein aggregation processes, fluorescence has emerged as a powerful tool. Its exceptional sensitivity enables the detection of early-stage aggregation events that are otherwise challenging to observe. This research underscores the pivotal role of fluorescence analysis, particularly in investigating the aggregation processes of hen egg white lysozyme, a model protein extensively studied for insights into amyloid fibril formation. By combining classical spectroscopies with fluorescence microscopy and by exploiting the fluorescence properties (intensity and lifetime) of the thioflavin T, we were able to noninvasively monitor key and complex molecular aspects of the process. Intriguingly, the fluorescence lifetime imaging-phasor analysis of thioflavin T fluorescence lifetime on structures at different stages of aggregation allowed to decipher the complex fluorescence decay behavior, highlighting that their changes rise from the combination of specific binding to amyloid typical cross-β structures and of the rigidity of the molecular environment.

Measuring Solvent Exchange in Silica Nanoparticles with Rotor-Based Fluorophore

Measuring the diffusivity of molecules is the first step toward understanding their dependence and controlling diffusion, but the challenge increases with the decrease of molecular size, particularly for non-fluorescent and non-reactive molecules such as solvents. Here, the capability to monitor the solvent exchange process within the micropores of silica with millisecond time resolution is demonstrated, by simply embedding a rotor-based fluorophore (thioflavin T) in colloidal silica nanoparticles. Basically, the silica provides an extreme case of viscous microenvironment, which is affected by the polarity of the solvents. The fluorescence intensity traces can be well fitted to the Fickian diffusion model, allowing analytical solution of the diffusion process, and revealing the diffusion coefficients. The validation experiments, involving the water-to-ethanol and ethanol-to-water solvent exchange, the comparison of different drying conditions, and the variation in the degree of cross-linking in silica, confirmed the effectiveness and sensitivity of this method for characterizing diffusion in silica micropores. This work focuses on the method development of measuring diffusivity and the high temporal resolution in tracking solvent exchange dynamics over a short distance (within 165 nm) opens enormous possibilities for further studies.

Regulation of light-harvesting antenna based on silver ion-enhanced emission of dye-doped coordination polymer nanoparticles

The design and construction of artificial light-harvesting systems for solar energy conversion to chemical energy has been an active research field. A variety of molecules and materials have been used to mimic the function of the light-harvesting antenna. However, the improvement or regulation of the antenna effect of the existing artificial light-harvesting systems is less explored. Coordination polymers have aroused extensive concern due to their applications in light-harvesting and energy conversion. Herein, it is found that silver ion can dramatically enhance the emission of dye encapsulated in the coordination polymer nanoparticles (CPNs). The mechanism of Ag⁺-induced fluorescence enhancement is elucidated. Taking advantage of the effect of Ag⁺ ions, the regulation of CPN-based light-harvesting system by Ag⁺ is achieved for the first time. The antenna effect could be up to 2.3 times the original value by adding Ag⁺ ions. The present work provides a new approach to regulate the antenna effect of the light-harvesting system with the advantages of convenience, rapidity, low cost, and flexibility.

Hysteresis in the temperature dependence of the IR bending vibration of deeply cooled confined water

Using Fourier Transform Infrared (FTIR) spectroscopy, we investigate the temperature dependence of the bending vibrations of water confined in the pores of a silica hydrogel in the temperature interval of 270-180 K. We also investigate the presence of thermal hysteresis by cooling and reheating temperature scans. The results clearly show the presence, at about 230 K, of a crossover in the temperature dependence of the IR spectra; moreover, the presence of hysteresis is clearly demonstrated. By comparing FTIR data with neutron diffraction data and previous calorimetric data on the same samples, we conclude that the crossover and the hysteretical behavior do not involve a water glass transition or crystallization but are related to a first-order-like liquid-liquid transition.

Synthesis of 2-acyl-benzo[1,3-d]selenazoles via domino oxidative cyclization of methyl ketones with bis(2-aminophenyl) diselenide

The synthesis of unprecedented 2-acyl-benzo[1,3-d]selenazoles is presented using bis(2-aminophenyl) diselenide and aryl methyl ketones under conventional heating and microwave irradiation.

A visual and reversible assay for temperature using thioflavin T-doped lanthanide/nucleotide coordination polymers

In this work, we prepared a type of thioflavin T (ThT)-doped lanthanide/nucleotide coordination polymer by the self-assembly of ThT, europium ions (Eu(3+)) and nucleotides (guanosine monophosphate, GMP) in aqueous solution (i.e. ThT/Eu/GMP). The Eu/GMP coordination polymers show excellent adaptive inclusion properties for ThT in a convenient one-step approach, which can readily enhance the fluorescence of ThT via the restricted effect. Moreover, the as-prepared hydrophilic ThT/Eu/GMP coordination polymers have the capability to act as a temperature-sensitive, visual and reversible sensor in aqueous solution under the irradiation of visible light. Our proposed design is cost-effective and simple to prepare without chemical modification or fluorescence labeling.

Detection of oligomers and fibrils of α-synuclein by AIEgen with strong fluorescence

We report a fluorophore, TPE-TPP, with AIE characteristics which is utilized as a fluorescence probe to monitor the α-synuclein (α-Syn) fibrillation process. Compared with ThT, TPE-TPP shows a higher sensitivity in the detection of α-Syn oligomers as well as fibrils with a stronger fluorescence. The performance of TPE-TPP was evaluated using fluorescence, AFM, dot blot, and SEC.

Modulation of Amyloid-β Fibrils into Mature Microrod-Shaped Structure by Histidine Functionalized Water-Soluble Perylene Diimide

Alzheimer's disease (AD) is associated with different types of amyloid peptide aggregates including senile plaques, fibrils, protofibrils, and oligomers. Due to these difficulties, a powerful strategy is needed for the disaggregation of amyloid aggregates by modulating their self-aggregation behavior. Herein, we report a unique approach toward transforming the aggregated amyloidogenic peptides using an amino acid functionalized perylene diimide as a molecular modulator, which is a different nondestructive approach as compared to inhibiting the aggregation of peptides. The histidine functionalized perylenediimide (PDI-HIS) molecule could coassemble with amyloid β (Aβ) peptides via hydrogen bonding that leads to the enhancement in the π-π interactions between Aβ and PDI-HIS moieties. The Thioflavin T (ThT) assay and various spectroscopic and microscopic techniques establish that the PDI-HIS molecules accelerate the Aβ1-40 and the amyloid aggregates in CSF into micro size coassembled structures. These results give rise to a new and unique complementary approach for modulating the biological effects of the aggregates in amyloidogenic peptides.

Ratiometric fluorescence detection of silver ions using thioflavin T-based organic/inorganic hybrid supraparticles

A novel ratiometric fluorescent probe for detecting silver ions was developed using thioflavin T-based functional organic/inorganic hybrid supraparticles.

Experimental evidence for a liquid-liquid crossover in deeply cooled confined water

In this work we investigate, by means of elastic neutron scattering, the pressure dependence of mean square displacements (MSD) of hydrogen atoms of deeply cooled water confined in the pores of a three-dimensional disordered SiO2 xerogel; experiments have been performed at 250 and 210 K from atmospheric pressure to 1200 bar. The "pressure anomaly" of supercooled water (i.e., a mean square displacement increase with increasing pressure) is observed in our sample at both temperatures; however, contrary to previous simulation results and to the experimental trend observed in bulk water, the pressure effect is smaller at lower (210 K) than at higher (250 K) temperature. Elastic neutron scattering results are complemented by differential scanning calorimetry data that put in evidence, besides the glass transition at about 170 K, a first-order-like endothermic transition occurring at about 230 K that, in view of the neutron scattering results, can be attributed to a liquid-liquid crossover. Our results give experimental evidence for the presence, in deeply cooled confined water, of a crossover occurring at about 230 K (at ambient pressure) from a liquid phase predominant at 210 K to another liquid phase predominant at 250 K; therefore, they are fully consistent with the liquid-liquid transition hypothesis.

Fluorescent molecular rotors based on the BODIPY motif: effect of remote substituents

The fluorescence properties of the target rotor are strongly affected by aryl substituents at the lower rim.