Interaction and energy transfer studies between bovine serum albumin and CdTe quantum dots conjugates: CdTe QDs as energy acceptor probes

Abstract

In this paper, a systematic investigation of the interaction of bovine serum albumin (BSA) with water-soluble CdTe quantum dots (QDs) of two different sizes capped with carboxylic thiols is presented based on steady-state and time-resolved fluorescence measurements. Efficient Förster resonance energy transfer (FRET) was observed to occur from BSA donor to CdTe acceptor as noted from reduction in the fluorescence of BSA and enhanced fluorescence from CdTe QDs. FRET parameters such as Förster distance, spectral overlap integral, FRET rate constant and efficiency were determined. The quenching of BSA fluorescence in aqueous solution observed in the presence of CdTe QDs infers that fluorescence resonance energy transfer is primarily responsible for the quenching phenomenon. Bimolecular quenching constant (k ) determined at different temperatures and the time-resolved fluorescence data provide additional evidence for this. The binding stoichiometry and various thermodynamic parameters are evaluated by using the van 't Hoff equation. The analysis of the results suggests that the interaction between BSA and CdTe QDs is entropy driven and hydrophobic forces play a key role in the interaction. Binding of QDs significantly shortened the fluorescence lifetime of BSA which is one of the hallmarks of FRET. The effect of size of the QDs on the FRET parameters are discussed in the light of FRET parameters obtained.

Realization of a Model-Free Pathway for Quantum Dot–Protein Interaction Beyond Classical Protein Corona or Protein Complex

“…BSA is often used as a model compound to study protein− ligand binding interactions, as it has 76% sequence homology with human serum albumin (HSA) consisting of three fluorophore units: tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe). 46 BSA has a single polypeptide chain consisting of 583 amino acid residues, where the secondary structure is predominated by the α-helix, and the ternary structure comprises (a) three homologous domains, (b) two tryptophan units situated at positions 135 and 214, and (c) cysteine residues forming disulfide bonds. 47 In the present work, we monitored the conformational changes of BSA in the presence of ZAIS QDs.…”

“…The shorter decay component (τ 1 = 2.95 ns) is attributed mostly to the Trp 135 moiety while the longer decay component (τ 2 = 6.6 ns) is attributed mostly to the Trp 214 moiety. 49 As λ ex is 278 nm, there might only be a small contribution (insignificant) of the Try and Phe moiety, 46 which we have not considered. Generally, it is believed that a quenching process is dynamically controlled if there is a decrease in the average lifetime of the fluorophore.…”

“…The FI of BSA decreases with the addition of ZAIS QDs. It is to be noted that as the Trp moiety contributes 91% ( λ ex = 278 nm) of the intrinsic fluorescence of BSA, we can think that most of the fluorescence changes that have occurred are primarily due to the Trp. We would also like to mention here that the λ em max of BSA is mostly attributed to the buried Trp moiety (Trp 214) which is situated in the hydrophobic interior and participates in the hydrophobic packing interactions at the IIA–IIIA interfacial surface .…”

Ultrasensitive detection of glibenclamide based on its enhancing effect on the fluorescence emission of CdTe quantum dots

“…QDs have exceptional properties such as high photostability, greater quantum efficiency, wide absorption and narrow emission spectra, large Stokes shift, surface functionality and large surface‐to‐volume ratio, which have made them superior to the usual organic fluorescent compounds . However, QDs show quantum‐size behaviors and also can be manufactured in an organized procedure for a specific function . Meanwhile, cadmium telluride quantum dots (CdTe QDs) can be synthesized by a rapid and simple method and have relatively high quantum yield, broad excitation and narrow emission spectrum .…”

A simple FRET system using two‐color CdTe quantum dots assisted by cetyltrimethylammonium bromide and its application to Hg(II) detection

“…Many FRETs have been reported using quantum dots (QDs) such as nanogold, carbon dots and other nanoparticles . and QDs have been favourably adopted for their superior optical and physical properties such as size‐tunable fluorescence, narrow and symmetric emission, broad absorption, high quantum yield and photochemical stability .…”