Spectroscopic and molecular modeling study of cyanine dye interacting with human serum transferrin

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.

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

In this work, a new biological probe for human transferrin (hTf) detection based on a cyanine dye ETC supramolecular assembly was designed. In sub-micromolar level, apo-hTf could induced the ETC aggregations transferred from H-aggregations to J-band with color change from pink to blue, while holo-hTf hardly possessed the ability, indicating ETC could specifically identify apo-hTf. The present study allowed for apo-hTf detection in the range of 8-80 nM with a detection limit of 2.8 nM and the sensitivity of visualization was around 70 nM. To further examine the suitability, iron ions were added into apo-hTf to stimulate the transformation from open conformation to the closed one gradually. It has been confirmed through tryptophan internal fluorescence quenching and the decrease of ETC J-aggregation. The interaction between ETC and apo-hTf performed high affinity that K_a was reached to 10⁶ M^-1 with a high selectivity. The potential in practical applications of this method has been tested for detection apo-hTf in human serum.

Specific identification of human transferrin conformations using a cyanine dye supramolecular assembly

A new method to recognize human transferrin open conformation (apo-Tf) was developed using cyanine dye (MTC) supramolecular assembly.