Barbituric Acid Based Fluorogens: Synthesis, Aggregation-Induced Emission, and Protein Fibril Detection.

Fluorescent dyes, especially those emitting in the long wavelength region, are excellent candidates in the area of bioassay and bioimaging. In this work, we report a series of simple organic fluorescent dyes consisting of electron-donating aniline groups and electron-withdrawing barbituric acid groups. These dyes are very easy to construct while emitting strongly in the red region in their solid state. The photophysical properties of these dyes, such as solvatochromism and aggregation-induced emission, are systematically characterized. Afterward, the structure-property relationships of these barbituric acid based fluorogens are discussed. Finally, we demonstrate their potential applications for protein amyloid fibril detection.

Phenol-yne Click Polymerization: An Efficient Technique to Facilely Access Regio- and Stereoregular Poly(vinylene ether ketone)s.

Alkyne-based click polymerizations have been well-established. However, in order to expand the family to synthesize polymers with new structures and novel properties, new types of click polymerizations are highly demanded. In this study, for the first time, we established a new efficient and powerful phenol-yne click polymerization. The activated diynes and diphenols could be facilely polymerized in the presence of the Lewis base catalyst of 4-dimethylaminopyridine (DMAP) under mild reaction conditions. Regio- and stereoregular poly(vinylene ether ketone)s (PVEKs) with high molecular weights (up to 35 200) were obtained in excellent yields (up to 99.0 %). The reaction mechanism was well explained under the assistance of density functional theory (DFT) calculation. Furthermore, since the vinyl ether sequence acts as a stable but acid-liable linkage, the polymers could be decomposed under acid conditions, rendering them applicable in biomedical and environmental fields.

A polytriazole synthesized by 1,3-dipolar polycycloaddition showing aggregation-enhanced emission and utility in explosive detection.

The metal-free click polymerizations (MFCPs) of activated alkynes and azides have become a powerful technique for the preparation of functional polytriazoles. Recently, a new MFCP of activated azide and alkyne has been established, but no functional polytriazole is prepared. In this paper, polytriazole PIa with aggregation-enhanced emission (AEE) characteristics is prepared by this efficient polymerization in excellent yield (97.9%). PIa is thermally stable, with 5% loss of its weight at temperature as high as 440 °C. Thanks to its unique AEE feature of PIa, its nanoaggregates can be used to detect explosives with a superamplification quenching effect.

A novel red-emitting aggregation-induced emission probe for determination of ß-glucosidase activity.

ß-Glucosidase (ß-Glu) is a ubiquitous enzyme which has multiple roles in medical diagnosis, food production, agriculture, etc. Existing ß-Glu assays have limitations such as complex operation, long running time, and high background noise. Here we report a red-emissive probe TBPG for measuring the activity of ß-Glu. The probe was synthesized through conjugating a ß-Glu targeting glucoside to an aggregation-induced emission (AIE) fluorophore. In the presence of ß-Glu, TBPG was hydrolyzed and exhibited a fluorescence turn-on process. The detection conditions including time, temperature, pH value, buffer, and probe concentration were optimized systematically. Afterwards, fluorescence titration was conducted showing an excellent linearity (R2 = 0.998), a wide linear dynamic range (0-5.0 U/mL), and a limit of detection as low as 0.6 U/L. The detection specificity and ion interference were evaluated by adding various biological species and ions to probe without or with ß-Glu. Next, we demonstrate the applicability of probe TBPG in determining the ß-Glu activity in living cells using confocal microscopy and flow cytometry. Finally, this newly established assay was applied to real soil samples. Comparable results were obtained as the commercial assay, manifesting its great potential in soil enzyme analysis.

Correction: In situ synthesis of silver nanowire gel and its super-elastic composite foams.

Correction for 'In situ synthesis of silver nanowire gel and its super-elastic composite foams' by Shu Huang et al., Nanoscale, 2020, 12, 19861-19869, https://doi.org/10.1039/D0NR03958F.

Detection of Urinary Albumin Using a "Turn-on" Fluorescent Probe with Aggregation-Induced Emission Characteristics.

Human serum albumin (HSA) is a broadly used biomarker for the diagnosis of various diseases such as chronic kidney disease. Here, a fluorescent probe TC426 with aggregation-induced emission (AIE) characteristics is reported as a sensitive and specific probe for HSA. This probe is non-emissive in aqueous solution, meanwhile it shows bright fluorescence upon interacting with HSA, which makes it applicable in detecting HSA with a high signal to noise ratio. Besides, the fluorescence of TC426 exhibits a high linear correlation with the concentration of albumin in the range of microalbumin (20-200 mg/L), which has a significant importance for the early diagnosis of glomerulus related diseases. Compared with previously reported HSA probes TPE-4TA and BSPOTPE, TC426 shows comparable anti-interference ability towards creatinine and other major components in urine but is excited by a longer excitation wavelength at the visible light range. Finally, with the established assay, TC426 shows excellent performance in detecting HSA in real human urine, indicating its great potential in practical urinalysis.

Construction of a Highly Sensitive Thiol-Reactive AIEgen-Peptide Conjugate for Monitoring Protein Unfolding and Aggregation in Cells.

Impairment of the protein quality control network leads to the accumulation of unfolded and aggregated proteins. Direct detection of unfolded protein accumulation in the cells may provide the possibility for early diagnosis of neurodegenerative diseases. Here a new platform based on a peptide-conjugated thiol-reactive aggregation-induced emission fluorogen (AIEgen), named MI-BTD-P (or D1), for labeling and tracking unfolded proteins in cells is reported. In vitro experiments with model proteins show that the non-fluorescent D1 only becomes highly fluorescent when reacted with the thiol group of free cysteine (Cys) residues on unfolded proteins but not glutathione or folded proteins with buried or surface exposed Cys. When the labeled unfolded proteins form aggregates, D1 fluorescence intensity is further increased, and fluorescence lifetime is prolonged. D1 is then used to measure unfolded protein loads in cells by flow cytometry and track the aggregate formation of the D1 labeled unfolded proteins using confocal microscopy. In combination with fluorescence lifetime imaging technique, the proteome at different folding statuses can be better differentiated, demonstrating the versatility of this new platform. The rational design of D1 demonstrates the outlook of incorporation of diverse functional groups to achieve maximal sensitivity and selectivity in biological samples.

In situ synthesis of silver nanowire gel and its super-elastic composite foams.

Noble-metal aerogels (NMAs) including silver aerogels have drawn increasing attention because of their highly conductive networks, large surface areas, and abundant optically/catalytically active sites. However, the current approaches of fabricating silver aerogels are tedious and time-consuming. In this regard, it is highly desirable to develop a simple and effective method for preparing silver aerogels. Herein, we report a facile strategy to fabricate silver gels via the in situ synthesis of silver nanowires (AgNWs). The obtained AgNW aerogels show superior electrical conductivity, ultralow density, and good mechanical robustness. AgNW aerogels with a density of 24.3 mg cm-3 display a conductivity of 2.1 × 105 S m-1 and a Young's modulus of 38.7 kPa. Furthermore, using an infiltration-air-drying-crosslinking technique, polydimethylsiloxane (PDMS) was introduced into 3 dimensional (3D) AgNW networks for preparing silver aerogel/elastomer composite materials. The obtained AgNW/PDMS aerogel composite exhibits outstanding elasticity while retaining excellent electrical conductivity. The fast piezoresistive response proves that the aerogel composite has a potential application for vibration sensors.

Specific and Quantitative Detection of Albumin in Biological Fluids by Tetrazolate-Functionalized Water-Soluble AIEgens.

The analysis of albumin has clinical significance in diagnostic tests and obvious value to research studies on the albumin-mediated drug delivery and therapeutics. The present immunoassay, instrumental techniques, and colorimetric methods for albumin detection are either expensive, troublesome, or insensitive. Herein, a class of water-soluble tetrazolate-functionalized derivatives with aggregation-induced emission (AIE) characteristics is introduced as novel fluorescent probes for albumin detection. They can be selectively lighted up by site-specific binding with albumin. The resulting albumin fluorescent assay exhibits a low detection limit (0.21 nM), high robustness in aqueous buffer (pH = 6-9), and a broad tunable linear dynamic range (0.02-3000 mg/L) for quantification. The tetrazolate functionality endows the probes with a superior water solubility (>0.01 M) and a high binding affinity to albumin (KD = 0.25 µM). To explore the detection mechanism, three unique polar binding sites on albumin are computationally identified, where the multivalent tetrazolate-lysine interactions contribute to the tight binding and restriction of the molecular motion of the AIE probes. The key role of lysine residues is verified by the detection of poly-l-lysine. Moreover, we applied the fluorogenic method to quantify urinary albumin in clinical samples and found it a feasible and practical strategy for albumin analysis in complex biological fluids.

Effect of ionic interaction on the mechanochromic properties of pyridinium modified tetraphenylethene.

A pyridinium modified tetraphenylethene-based salt shows aggregation-induced emission enhancement properties and irreversible mechanochromic behaviours.