Visualized detection of apo-transferrin based on cyanine dye supramolecular assembly

"One stone, two birds": a mitochondria-targeted fluorescent probe for the detection of viscosity and HSO3- in living cells

The material transport and physiological events of mitochondria need to be supported by a suitable microenvironment. For example, high viscosity will seriously hinder material exchange, and SO2, as the precursor of HSO3-, is an endogenous signal molecule that plays a key role in information transmission. It is very important to detect viscosity and HSO3- in mitochondria. Here, we developed a dual-responsive fluorescent probe (named Hcy-NT) to image the changes in mitochondrial viscosity and HSO3- in a "killing two birds with one stone" manner. Hcy-NT showed an OFF-ON fluorescence signal for the increase in cell viscosity induced by nystatin, while an ON-OFF fluorescence signal for intracellular and endogenous HSO3-. Its limits of detection for HSO3- were calculated by both absorption and fluorescence methods, which were 1.200 and 1.291 μM, respectively. This work provides a valuable tool for the study of viscosity and HSO3- related physiological processes and the diagnosis of potential diseases.

Spectral-fluorescent and photochemical study of 6,6'-di(benzoylamino)trimethine cyanine dyes in solutions as possible probes for DNA

Spectral-fluorescent and photochemical properties of trimethine cyanine dyes T-304, T-306, and T-307, having substituents in 6,6'-positions, in various organic solvents, in aqueous buffer solutions, in the presence of surfactants and ethanol additives, and the effect on these properties of addition of DNA have been studied. Strong aggregation of the dyes in aqueous and aqueous buffer solutions has been shown. This is due to increased hydrophobicity of the dyes, which makes it difficult to use them as spectral-fluorescent probes for DNA. In the presence of DNA, trimethine cyanines partially form highly fluorescent complexes of dye monomers with the biomolecule, with slight decomposition of the initial aggregates and the formation of aggregates on DNA molecules. The formation of different types of dye-DNA complexes, i.e., intercalation and binding in the DNA grooves, was modeled by molecular docking. Dye-DNA complexes were also studied by circular dichroism spectroscopy and by thermal dissociation of DNA. To reveal selectivity of the dyes, their interaction with human serum albumin was briefly studied. The presence of moderate concentrations of nonionic surfactants does not lead to a significant decomposition of aggregates, but leads to a biphasic dependence of the fluorescence intensity on the DNA concentration. At the same time, ethanol additives (15%) lead to a more or less linear concentration dependence of the fluorescence intensity, which makes it possible to use these dyes as fluorescent probes for DNA. The effective binding constants of the dyes to DNA and the limits of DNA detection using the dyes in the presence of 15% ethanol were estimated. Photoisomerization and generation of the triplet states of T-304, T-306, and T-307 have been also studied. Along with the fluorescence growth, complexation with DNA leads to an increase in the yield of the triplet states of the dyes. This creates a prerequisite for using the dyes in targeted PDT. In the presence of DNA, the decay kinetics of the triplet states are biexponential, which indicates different types of dye complexes with DNA. The rate constants of oxygen quenching of the triplet states of the dyes bound to DNA are significantly lower than the diffusion-controlled values (taking into account the spin-statistical factor), which is explained by the shielding effect on the triplet molecules in complexes with DNA. The data obtained show that dyes T-304, T-306 and T-307, with addition of 15% ethanol, can be used as possible fluorescent probes for DNA.

Photonics of Trimethine Cyanine Dyes as Probes for Biomolecules

Cyanine dyes are widely used as fluorescent probes in biophysics and medical biochemistry due to their unique photophysical and photochemical properties (their photonics). This review is focused on a subclass of the most widespread and studied cyanine dyes—trimethine cyanines, which can serve as potential probes for biomolecules. The works devoted to the study of the noncovalent interaction of trimethine cyanine dyes with biomolecules and changing the properties of these dyes upon the interaction are reviewed. In addition to the spectral-fluorescent properties, elementary photochemical properties of trimethine cyanines are considered, including: photoisomerization and back isomerization of the photoisomer, generation and decay of the triplet state, and its quenching by oxygen and other quenchers. The influence of DNA and other nucleic acids, proteins, and other biomolecules on these properties is covered. The interaction of a monomer dye molecule with a biomolecule usually leads to a fluorescence growth, damping of photoisomerization (if any), and an increase in intersystem crossing to the triplet state. Sometimes aggregation of dye molecules on biomolecules is observed. Quenching of the dye triplet state in a complex with biomolecules by molecular oxygen usually occurs with a rate constant much lower than the diffusion limit with allowance for the spin-statistical factor 1/9. The practical application of trimethine cyanines in biophysics and (medical) biochemistry is also considered. In conclusion, the prospects for further studies on the cyanine dye–biomolecule system and the development of new effective dye probes (including probes of a new type) for biomolecules are discussed.

An Improved Method for Quick Quantification of Unsaturated Transferrin

Blood iron levels play a vital role in oxygen metabolism and energy generation whilst transporter protein, transferrin, binds and delivers iron to the transferrin receptor of endosomal compartments of cells. Consequently, the iron-binding capacity of transferrin is an important indicator for many diseases, and its measurements are used in the diagnosis and treatment of anaemias. Various assays, including Total Iron Binding Capacity (TIBC), Unsaturated Iron-Binding Capacity (UIBC) and Transferrin Saturation (TS), were developed to assess the iron-binding capacity of transferrin. Clinically, UIBC is measured in serum by a multi-step liquid ferrozine method and subjected to interference from conditions such as haemolysis and lipemia. Here, we report a quick method that directly measures the concentration of apotransferrin in EDTA-treated plasma, theoretically equivalent to UIBC. Importantly, this supramolecular assembly-based method is more time-efficient, cost-effective and insensitive to serum cation fluctuations. With additional colorimetric property, this method also provides a visual indicator for abnormal health conditions with extreme transferrin statuses such as those found in cancers. Its minimal requirement for equipment would be particularly useful for diagnosis in remote and under-developed regions.

A cysteine and Hg2+ detection method based on transformation supramolecular assembly of cyanine dye by AGRO100

ETC (3,3'-di(3-sulfopropyl)-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine triethylammonium salt), as a derivative of thiazole, is capable of forming various aggregates by the short-range noncovalent interaction forces under specific conditions, accompanying with significant absorbance and fluorescence characteristics. In this work, a label-free probe (ETC) for the detection of Cys (Cysteine) and Hg²⁺ was developed based on transformation between monomers and J-aggregations by AGRO100. AGRO100 can transform between single-stranded DNA and G-quadruplex to realize recognition of Cys and Hg²⁺ in dual-channel mode. These recognitional signals can be captured by UV-visible absorption spectra and fluorescence spectroscopy. ETC exhibits high sensitivity and selectivity with the detection limit of 0.197 nM in a wide range of 0-15 μM, which can apply of Cys and Hg²⁺ detection in human serum.

Meso-aryl-substituted thiacarbocyanine dyes as spectral-fluorescent probes for DNA

The noncovalent interaction of meso-aryl-substituted thiacarbocyanine dyes I and II with dsDNA and ssDNA in aqueous solutions has been studied by spectral-fluorescent methods. Complexation with DNA is accompanied by both aggregation of the dyes and the formation of monomeric strongly fluorescent complexes. Experiments on molecular docking of dyes I and II with dsDNA confirm the previous assumption about the possibility of the formation of complexes of different types: intercalation between base pairs and in the grooves of the double helix of the biopolymer. The possibility of intercalation of the dyes in the complex is confirmed by experiments on thermal dissociation of dsDNA in the presence of dyes I and II, as well as experiments on the interaction of the dyes with ssDNA. An increase in the melting temperatures T_m of dsDNA is obtained in the presence of I and II, similar to that observed for the classical intercalator ethidium bromide. The limits of detection and quantification of DNA, which are important for the use of the dyes as probes for DNA, have been determined. The primary photochemical processes of the dyes in complexes with ssDNA were studied by flash photolysis technique. Complexation with ssDNA hinders photoisomerization and creates favorable conditions for the dye triplet state formation. The decay kinetics of the triplet state of the dyes were monoexponential. The rate constant of quenching of the triplet state by air oxygen was estimated for dye I complexed with ssDNA and was found to be less than the diffusion-controlled limit. This is probably a consequence of the shielding effect of the complex on the triplet quenching process.

Two-photon-excited tumor cell fluorescence targeted imaging based on transferrin-functionalized silicon nanoparticles

Transferrin-functionalized silicon nanoparticles (Trf-SiNPs) were fabricated and utilized for targeted fluorescence imaging in tumor cells. Silicon nanoparticles (SiNPs) was firstly synthesized by microwave irradiation method, and then coupled with transferrin in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The structural informations of Trf-SiNPs were measured by transmission electron microscope and Fourier transform infrared spectrometer. The optical properties of Trf-SiNPs were characterized by ultraviolet absorption spectrum, fluorescence emission spectrum, fluorescence quantum yield, fluorescence lifetime, photo-stability, and so on. MTT assay evidenced the low toxicity of Trf-SiNPs. Finally, Trf-SiNPs were successfully applied in HeLa cells and HepG2 cells for targeted fluorescence imaging under single-photon excitation and two-photon excitation.

"Switch-Off-On" Detection of Fe3+ and F- Ions Based on Fluorescence Silicon Nanoparticles and Their Application to Food Samples

An approach to the detection of F⁻ ions in food samples was developed based on a “switch-off-on” fluorescence probe of silicon nanoparticles (SiNPs). The fluorescence of the synthetic SiNPs was gradually quenched in the presence of Fe³⁺ ion and slightly recovered with the addition of F⁻ ion owing to the formation of a stable and colorless ferric fluoride. The fluorescence recovery exhibited a good linear relationship (R² = 0.9992) as the concentration of F⁻ ion increased from 0 to 100 μmol·L⁻¹. The detection limit of the established method of F⁻ ion was 0.05 μmol·L⁻¹. The recovery experiments confirmed the accuracy and reliability of the proposed method. The ultraviolet–visible spectra, fluorescence decays, and zeta potentials evidenced the fluorescence quenching mechanism involving the electron transfer between the SiNPs and Fe³⁺ ion, while the fluorescence recovery resulted from the formation of ferric fluoride. Finally, SiNPs were successfully applied to detect F⁻ ions in tap water, Antarctic krill, and Antarctic krill powder.

Photonics of meso-substituted carbocyanine dyes in solutions and in complexes with DNA

Spectral-fluorescent and photochemical properties (photoisomerization and generation of the triplet state) of meso-substituted cationic carbocyanine dyes, 3,3'-di-(β-hydroxyethyl)-5,5'-dimethoxy-9-ethylthiacarbocyanine iodide (K1) and 3,3'-di-(β-hydroxyethyl)-9-methylthiacarbocyanine iodide (K2), have been studied in solutions and in the presence of DNA. In solutions, on passing from acetonitrile to dioxane, a growth of fluorescence of the dyes is observed due to a shift of the equilibrium of cis/trans isomers toward the fluorescent trans-isomer. Upon flash photolysis of dye solutions in dioxane, the formation and subsequent decay of the cis-photoisomers of the dyes are observed. In aqueous solutions, the interaction with DNA leads to the formation of noncovalent complexes of K1 and K2 with DNA, which is accompanied by a significant increase in the fluorescence intensity. The results of the molecular docking experiments showed the possibility of several types of binding, which was confirmed by the data obtained from other experiments. The effects of temperature and additions of NaCl on the stability of the dye-DNA complexes were studied. The spectral-fluorescent data were used to estimate the binding constants of the dyes with DNA and other characteristics of the dyes that are important for their use as probes. Upon flash photolysis of the dyes in complexes with DNA, photoisomerization is not observed, but the quantum yield of intersystem crossing to the triplet state increases. The decay of the triplet states occurs by a two-exponential law. The rate constants for quenching of the triplet states of the dyes complexed with DNA by oxygen were found to be lower than the expected values for diffusion-controlled quenching (taking into account the spin statistical factor 1/9), which is explained by the steric factor of complexation.