荧光光谱法研究金纳米粒子和槲皮素及牛血红蛋白的相互作用

本文采用荧光光谱法研究了磷酸缓冲溶液(PBS,pH 7.2)中有无金纳米粒子(AuNP)共存时槲皮素(Qct)与牛血红蛋白(BHb)的相互作用,评估了共存AuNP对Qct和BHb的荧光猝灭效应及对Qct-BHb作用的影响。测得了不同温度下Qct-BHb结合反应的平衡常数K和结合摩尔比n,并由所得热力学常数确定了结合的作用力类型。根据F rster偶极-偶极无辐射能量转移理论,求得了Qct-BHb作用的分子间距离r=2.68 nm和能量转移效率E=0.232。     

Fighting Aggregation‐Caused Quenching and Leakage of Dyes in Fluorescent Polymer Nanoparticles: Universal Role of Counterion

Dye‐loaded polymer nanoparticles (NPs) emerge as a powerful tool for bioimaging applications, owing to their exceptional brightness and controlled small size. However, aggregation‐caused quenching (ACQ) and leakage of dyes at high loading remain important challenges of these nanomaterials. The use of bulky hydrophobic counterions has been recently proposed as an effective approach to minimize ACQ and dye leakage, but the role of counterion structure is still poorly understood. Here, a systematic study based on ten counterions, ranging from small hydrophilic perchlorate up to large hydrophobic tetraphenylborate derivatives, reveals how counterion nature can control encapsulation and emission of a cationic dye (rhodamine B octadecyl ester) in NPs prepared by nanoprecipitation of a biodegradable polymer, poly‐lactide‐co‐glycolide (PLGA). We found that increase in counterion hydrophobicity enhances dye encapsulation efficiency and prevents dye adsorption at the particle surface. Cellular imaging studies revealed that ≥95 % encapsulation efficiency, achieved with most hydrophobic counterions (fluorinated tetraphenylborates), is absolutely required because non‐encapsulated dye species at the surface of NPs are the origin of dye leakage and strong fluorescence background in cells. The size of counterions is found to be essential to prevent ACQ, where the largest species, serving as effective spacer between dyes, provide the highest fluorescence quantum yield. Moreover, we found that the most hydrophobic counterions favor dye–dye coupling inside NPs, leading to ON/OFF fluorescence switching of single particles. By contrast, less hydrophobic counterions tend to disperse dyes in the polymer matrix favoring stable emission of NPs. The obtained structure‐property relationships validate the counterion‐based approach as a mature concept to fight ACQ and dye leakage in the development of advanced polymeric nanomaterials with controlled optical properties.     

Target‐Triggered NIR Emission with a Large Stokes Shift for the Detection and Imaging of Cysteine in Living Cells

Background autofluorescence from biological systems generally reduces the sensitivity of a fluorescent probe for imaging biological targets. Addressing this challenge requires the development of fluorescent probes that produce emission in the near‐infrared region. Herein, we report the design and synthesis of a fluorescent probe that generates an NIR emission with a large Stokes shift upon the selective response to Cys over Hcy and GSH. The probe is designed to consist of two Cys‐sensing sites, an acrylate ester and an aldehyde installed ortho to each other. The reaction of the probe with Cys triggers an excited state intramolecular proton transfer process upon photo‐excitation, thereby producing an NIR emission with a large Stokes shift. Accordingly, this probe hold great promise for the selective detection of Cys in biological systems. We further demonstrate the capacity of this probe for Cys imaging in living cells.     

Water-soluble AIE-active Fluorescent Organic Nanoparticles: Design,Preparation and Application for Specific Detection of Cyanide in Water and Food Samples

A dilactosyl-dicyanovinyl-functionalized tetraphenylethene ( TPELC ) was designed, synthesized and used for ratiometric sensing of cyanide. TPELC was comprised of three moieties (tetraphenylethylene, dicyanovinyl group and lactose unit) in one molecule, making TPELC water-soluble and aggregation-induced emission (AIE)-active and selectively reactive to cyanide. Compared with other reported fluorescent probes containing dicyanovinyl group, TPELC is the first AIE luminogen to be assembled as fluorescent organic nanoparticles (FONs) for sensing of cyanide in water without the use of surfactant or the help of organic solvents based on the nucleophilic addition reaction. The detection mechanism was verified by liquid chromatograph mass spectrometry experiments and by protonation of cyanide to reduce the nucleophilicity of cyanide. In addition, TPELC was used for detection of the cyanide content of food samples and test strips were developed to simplify the detection procedure.     

Fabrication of Fluorescent Silica Nanoparticles Hybridized with AIE Luminogens and Exploration of Their Applications as Nanobiosensors in Intracellular Imaging

Highly emissive inorganic–organic nanoparticles with core–shell structures are fabricated by a one‐pot, surfactant‐free hybridization process. The surfactant‐free sol–gel reactions of tetraphenylethene‐ (TPE) and silole‐functionalized siloxanes followed by reactions with tetraethoxysilane afford fluorescent silica nanoparticles FSNP‐ 1 and FSNP‐ 2 , respectively. The FSNPs are uniformly sized, surface‐charged and colloidally stable. The diameters of the FSNPs are tunable in the range of 45–295 nm by changing the reaction conditions. Whereas their TPE and silole precursors are non‐emissive, the FSNPs strongly emit in the visible vision, as a result of the novel aggregation‐induced emission (AIE) characteristics of the TPE and silole aggregates in the hybrid nanoparticles. The FSNPs pose no toxicity to living cells and can be utilized to selectively image cytoplasm of HeLa cells.     

Amphiphilic Invertible Polyesters as Reducing and Stabilizing Agents in the Formation of Metal Nanoparticles

Metal nanoparticles of various size and shape are prepared by the reduction of metal precursors in polymer micellar architectures (nanoreactors). The nanoreactors are developed from the amphiphilic invertible polyesters solved over a wide concentration range in solvents that strongly differ in polarity. In a non‐polar medium, the micelle core contains hydrophilic [poly(ethylene oxide)] fragments, which acts as a reducing agent of metal ions. Nanoparticle stabilization occurs because of the presence of hydrophobic (polymethylene) fragments outside of the micelle structure. The size and shape of the nanoreactors may be altered by the polyester composition and molecular weight as well as by the solvent polarity and concentration of the amphiphilic polyester.

     

Use of Selenium to Detect Mercury in Water and Cells: An Enhancement of the Sensitivity and Specificity of a Seleno Fluorescent Probe

Seleno fluorescent probe : An organoselenium fluorescent probe (FSe‐1) for mercury was designed based on the irreversible deselenation mechanism. FSe‐1 exhibits an ultrahigh selectivity and sensitivity for Hg²⁺ detection only for reactive selenium atom sites, due the strong affinity between Se and Hg. Furthermore, the new probe has been successfully used for imaging mercury ions in RAW 264.7 cells (a mouse macrophage cell line; see figure).

     

Effect of Soft Preheating of Bovine Serum Albumin on the Complexation with Oligochitosan: Structure and Conformation of BSA in the Complex

Phase analysis, spectroscopic, and light scattering methods are applied to investigate the peculiarities of the interaction of oligochitosan (OCHI) with native and preheated bovine serum albumin (BSA) as well as the conformational and structural changes of BSA in BSA/OCHI complex. As shown, untreated BSA binds with OCHI mainly forming soluble electrostatic nanocomplexes, with the binding causing an increase in BSA helicity without a change in the local tertiary structure and thermal stability of BSA. In contrast, soft preheating at 56 °C enhances the complexation of BSA with OCHI and slightly destabilizes the secondary and local tertiary structures of BSA within the complex particles. Preheating at 64 °C (below the irreversible stage of BSA thermodenaturation) leads to further enhancement in the complexation and formation of insoluble complexes stabilized by both Coulomb forces and hydrophobic interactions. The finding can be promising for the preparation of biodegradable BSA/chitosan-based drug delivery systems.     

Conformational Stability of Bovine Serum Albumin in Aqueous Amides: A Further Insight into the Mechanism of Urea Acting on the Protein

The binding distances of fluorescein to bovine serum albumin (BSA) in formamide‐water and N,N‐dimethyl‐ formamide‐water mixtures were determined by fluorescence quenching method and compared with the values in urea‐water mixtures in our previous work. The results, together with the analysis of fluorescence spectra, were utilized to probe the conformational stability of protein in aqueous amides, providing a further insight into the mechanism of urea acting on protein. The spectral properties of BSA showed significant difference in the aqueous solutions of the three kinds of amide and indicated that both NH₂ group and C=O group could form hydrogen bond with the protein, serving as donor and acceptor, respectively. However, the results revealed that the multiple hydrogen bonds of NH₂ group with back bond and hydrophilic side chains of the protein played a key role in the nonspecific urea‐mediated network of intramolecular interaction due to its higher hydrogen bonding capability compared to C=O group.