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

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_q) 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.     

Comprehensive study of interaction between biocompatible PEG‐InP/ZnS QDs and bovine serum albumin

Polyethylene glycol (PEG) surface modified biocompatible InP/ZnS quantum dots (QDs) act as a potential alternative for conventional carcinogenic cadmium‐based quantum dots for in vivo and in vitro studies. Comprehensively, we studied the interaction between a model protein bovine serum albumin (BSA) and PEGylated toxic free InP/ZnS QDs using various spectroscopic tools such as absorption, fluorescence quenching, time resolved and synchronous fluorescence spectroscopic measurements. These studies principally show that tryptophan (Trp) residues of BSA have preferable binding affinity towards PEG‐InP/ZnS QDs surface and a blue shift in Trp fluorescence emission is a signature of conformational changes in its hydrophobic microenvironment. Photoluminescence (PL) intensity of Trp is quenched by ground state complex formation (static quenching) at room temperature. However, InP/ZnS@BSA conjugates become unstable with increasing temperature and PL intensity of Trp is quenched via dynamic quenching by PEG‐InP/ZnS QDs. Experimentally determined thermodynamic parameters for these conjugates have shown spontaneity, entropy driven and exothermic nature of bio‐conjugation. The calculated binding affinity (n ? 1, Hill coefficient) suggest that the affinity of InP/ZnS QDs for a BSA protein is not dependent on whether or not other BSA proteins are already bound to the QD surface. Energy transfer efficiency (E), Trp residue to InP/ZnS QDs distances and energy transfer rate (k_T) were all obtained from FÖrster resonance energy.     

Investigating Fluorescence Quenching of ZnS Quantum Dots by Silver Nanoparticles

Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra having an absorbance edge at 300 nm and emission maxima (λ _emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process. The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K _sv value of 9 × 10⁹ M⁻¹. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm.     

Fluorescence Quenching of CdTe Nanocrystals by Bound Gold Nanoparticles in Aqueous Solution

Water-soluble gold nanoparticles with an average diameter of 5 nm were prepared with carboxylic acid terminated thiol ligands. These ligands contain zero to eight methylene moieties. CdTe nanocrystals with an average diameter of 5 nm were synthesized with aminoethanethiol capping. These nanocrystals displayed characteristic absorption and emission spectra of quantum dots. The amine terminated CdTe nanocrystals and carboxylic-acid-terminated gold nanoparticles were conjugated in aqueous solution at pH 5.0 by electrostatic interaction, and the conjugation was monitored with fluorescence spectroscopy. The CdTe nanocrystals were significantly quenched upon binding with gold nanoparticles. The quenching efficiency was affected by both the concentration of gold nanoparticles in the complex and the length of spacer between the CdTe nanocrystal and Au nanoparticle. The observed quenching was explained using Förster resonance energy transfer (FRET) mechanism, and the Förster distance was estimated to be 3.8 nm between the donor–acceptor pair.     

Effect of heteroatom-doped carbon quantum dots on the red emission of metal-conjugated phthalocyanines through hybridization

Quantum dots (QDs) are significant fluorescent materials for energy transfer studies with phthalocyanines (Pcs) and phthalocyanine (Pc)-like biomolecules (such as chlorophylls). Carbon-based QDs, especially, have been used in numerous studies concerning energy transfer with chlorophylls, but the numbers of studies concerning energy transfer between phthalocyanines and carbon-based QDs are limited. In this study, peripherally, hydroxythioethyl terminal group substituted metal-free phthalocyanine (H₂Pc) and zinc phthalocyanine (ZnPc) were noncovalently (electrostatic and/or π–π interaction) attached to carbon QDs containing boron and nitrogen to form QD-Pc nanoconjugates. The QD-Pc conjugates were characterized using different spectroscopic techniques (Fourier transform infrared spectroscopy and transmission electron microscopy). The absorption and fluorescence properties of QD-Pc structures in solution were studied. It was found that the quantum yields of the QDs slightly decreased from 30% to 25% upon doping the QDs with heteroatoms B and N. Förster resonance energy transfer efficiency was calculated as 33% for BCN-QD/ZnPc. For the other conjugates, almost no energy transfer from QDs to Pc cores was observed. It was shown that the energy transfer between QDs to Pc cores was completely different from the energy transfer between QDs and photosynthetic pigments, and therefore we concluded that heteroatom doping in the QD structure and the existence of zinc metal in the phthalocyanine structure is obligatory for an efficient energy transfer.     

Synthesis and photophysical studies of CdTe quantum dot-monosubstituted zinc phthalocyanine conjugates

The linkage of unsymmetrically monosubstituted 4-aminophenoxy zinc phthalocyanine (ZnAPPc, 5) to CdTe quantum dots capped with mercaptopropionic acid (MPA), l-cysteine (l-cys) or thioglycolic acid (TGA) has been achieved using the coupling agents ethyl-N(3-dimethylaminopropyl) carbodiimide and N-hydroxy succinimide, which facilitate formation of an amide bond to form the QD-ZnAPPc-linked conjugate. The formation of the amide bond was confirmed using Raman and IR spectroscopies. Atomic force microscopy (AFM) and UV-Vis spectroscopy were used further to characterise the conjugate. Förster resonance energy transfer (FRET) resulted in stimulated emission of ZnAPPc in both the linked (QD-ZnAPPc-linked) and mixed (QD:ZnAPPc-mixed) conjugates. The linked l-cys and TGA QDs conjugates (QD-ZnAPPc-linked) gave the largest FRET efficiencies hence showing the advantages of covalent linking. Fluorescence quantum yields of QDs were decreased in QD:ZnAPPc-mixed and QD:ZnAPPc-linked.     

Triple-FRET Technique for Energy Transfer Between Conjugated Polymer and TAMRA Dye with Possible Applications in Medical Diagnostics

Three-component Förster resonance energy transfer (FRET) has been used to obtain efficient FRET between the cationic conjugated polymer (CCP) as donor and 5-carboxy tetramethylrhodamine (TAMRA) dye as acceptor, by using an intermediate donor, fluorescein. In spite of the fact that there is enough overlap between the emission spectra of CCP and absorption spectra of TAMRA, the efficiency of FRET between CCP and TAMRA is poor. The reason for this is that while the Förster critical distance is not very sensitive to the overlap, the FRET efficiency is extremely sensitive to it. However, it is observed that the FRET efficiency between CCP and TAMRA improves considerably when fluorescein is introduced in the solution. The triple FRET so obtained can be used for deoxyribonucleic acid sequence detection in medical diagnostics because the fluorescence emission from TAMRA is pH-insensitive.     

Investigation on the Interaction of Hydroxyethyl Starch 130/0.4 (Voluven) and Serum Albumin for Pharmacokinetic and Toxicological Implications

The interaction of hydroxyethyl starch 130/0.4 (Voluven) with human serum albumin (HSA) has been investigated by fluorescence (steady state and synchronous), Fourier transforms infrared (FT‐IR), and circular dichroism (CD) spectroscopies. Analysis of the fluorescence quenching data of HSA by Voluven using the Stern–Volmer method revealed the formation of 1:1 ground‐state complex. Evaluation of binding parameters and binding energy indicated that the binding reaction was exothermic. On the basis of fluorescence measurements, it was concluded that electrostatic forces play a crucial role in stabilizing the complex. The binding distance was calculated by using Förster resonance energy transfer (FRET) theory. The conformational changes of HSA were obtained qualitatively as well as quantitatively using synchronous fluorescence, FT‐IR, and CD. The HSA underwent partial unfolding in the presence of Voluven.     

Spectroscopic investigation of water‐soluble alloyed QDs with bovine serum albumin

We present here a systematic investigation on the interaction between a water‐soluble alloyed semiconductor quantum dot and bovine serum albumin using various spectroscopic techniques i.e. fluorescence quenching, resonance light scattering and synchronous fluorescence spectroscopy. The analysis of fluorescence spectrum and fluorescence intensity indicates that the intrinsic fluorescence of bovine serum albumin (BSA) gets quenched by both static and dynamic quenching mechanism. The Stern‐Volmer quenching constants, energy transfer efficiency parameters, binding parameters and corresponding thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) have been evaluated by using van 't Hoff equation at different temperatures. A positive entropy change with a positive enthalpy change was observed suggesting that the binding process was an entropy‐driven, endothermic process associated with the hydrophobic effect. The intermolecular distance (r) between donor (BSA) and acceptor (CdSeS/ZnS quantum dots) was estimated according to Förster's theory of non‐radiative energy transfer. The synchronous fluorescence spectra revealed a blue shift in the emission maxima of tryptophan which is indicative of increasing hydrophobicity. Negative ΔG⁰ values implied that the binding process was spontaneous. It was found that hydrophobic forces played a role in the quenching process. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel fluorescent assay for oxytetracycline hydrochloride based on fluorescence quenching of water‐soluble CdTe nanocrystals

A novel assay for oxytetracycline hydrochloride (OTC) based on fluorescence quenching was developed from the interaction between functionalized cadmium telluride quantum dots (CdTe QDs) and OTC. Optimum conditions for the detection of OTC were found after investigating all factors. Under optimum conditions, luminescence of CdTe nanocrystals (λ_ex = 365 nm, λ_em = 562 nm) was quenched by OTC in a concentration‐dependent manner best described by a modified Stern‐Volmer type equation. Good linearity was obtained with a regression coefficient of 0.9999 in the range of 1.34 ~ 13.4 x 10^‐5 mol/L and a limit of detection of 3.08 x 10^‐7 mol/L. In addition, the quenching mechanism was also established. The results imply that the close proximity of OTC‐CdTe was driven by electrostatic attraction and the resulting effective electron transfer from OTC to QDs could be responsible for fluorescence quenching of CdTe‐QDs. Copyright © 2012 John Wiley & Sons, Ltd.     

The investigation of the interaction between orientin and bovine serum albumin by spectroscopic analysis

In this paper, the interaction between orientin and bovine serum albumin (BSA) was examined using fluorescence and absorbance spectroscopy. The analysis of the quenching mechanism was done using Stern–Volmer plots which exhibit upward (positive) deviation. A linear response to orientin was shown in the concentration range between 3 and 50 μM. The experimental results showed the presence of a static quenching process between orientin and BSA. The thermodynamic parameters ΔH, ΔS and ΔG were also calculated and suggested that the hydrophobic and electrostatic interactions played an important role in the interaction between orientin and BSA. Furthermore, the distances between BSA and orientin were determined according to Förster non‐radiation energy transfer theory. In addition, the results of the synchronous fluorescence obtained indicated that the binding of orientin with BSA could affect conformation in BSA. Copyright © 2013 John Wiley & Sons, Ltd.     

Multi-spectroscopic,thermodynamic and molecular docking studies to investigate the interaction of eplerenone with human serum albumin

The binding of small molecular drugs with human serum albumin (HSA) has a crucial influence on their pharmacokinetics. The binding interaction between the antihypertensive eplerenone (EPL) and HSA was investigated using multi-spectroscopic techniques for the first time. These techniques include ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), native fluorescence spectroscopy, synchronous fluorescence spectroscopy and molecular docking approach. The fluorescence spectroscopic study showed that EPL quenched HSA inherent fluorescence. The mechanism for quenching of HSA by EPL has been determined to be static in nature and confirmed by UV absorption and fluorescence spectroscopy. The modified Stern–Volmer equation was used to estimate the binding constant (K_b) as well as the number of bindings (n). The results indicated that the binding occurs at a single site (K_b = 2.238 × 10³ L mol⁻¹at 298 K). The enthalpy and entropy changes (∆H and ∆S) were 58.061 and 0.258 K J mol⁻¹, respectively, illustrating that the principal intermolecular interactions stabilizing the EPL–HSA system are hydrophobic forces. Synchronous fluorescence spectroscopy revealed that EPL binding to HSA occurred around the tyrosine (Tyr) residue and this agreed with the molecular docking study. The Förster resonance energy transfer (FRET) analysis confirmed the static quenching mechanism. The esterase enzyme activity of HSA was also evaluated showing its decrease in the presence of EPL. Furthermore, docking analysis and site-specific markers experiment revealed that EPL binds with HSA at subdomain IB (site III).     

Synthesis and study on the binding of thiazol‐2(3H)‐ylidine derivative with human serum albumin using spectroscopic and molecular docking methods

In this article, a facile and convenient synthesis of thiazol‐2(3H)‐ylidine derivatives of fatty acid ( 3a – c ) is described. The binding of N′‐(4,5‐dimethyl‐3‐penylthiazol‐2(3H)‐ylidine)octadec‐9‐enehydrazide ( 3a ) with human serum albumin (HSA) is explored using various spectral methods and molecular docking. Fluorescence quenching results show that 3a induces conformational changes in HSA and the polarity around the tryptophan residues is increased. Stern–Volmer quenching plots at different temperatures (298, 305 and 312 K) show that the fluorescence quenching mechanism is static quenching. Synchronous fluorescence, 3D fluorescence spectra, circular dichroism and Fourier transform infrared spectroscopy are used to determine the structural change in HSA on interaction with 3a . Förster resonance energy transfer analysis shows that the binding distance (r₀ = 2.78 nm) between HSA (Trp214) and 3a is within the of range 2–8 nm for quenching to occur. The molecular docking study also confirms that 3a is located in subdomain IIA (site I) of HSA and is stabilized by hydrogen bonding and hydrophobic forces.     

Photoluminescence properties of hybrid SiO2‐coated CdTe/CdSe quantum dots

Hybrid SiO₂‐coated CdTe/CdSe quantum dots (QDs) were prepared using CdTe/CdSe QDs prepared by hydrothermal synthesis. A CdSe interlayer made CdTe/CdSe cores with unique type II heterostructures. The hybrid SiO₂‐coated CdTe/CdSe QDs revealed excellent photoluminescence (PL) properties compared with hybrid SiO₂‐coated CdTe QDs. Because of the existence of spatial separations of carriers in the type II CdTe/CdSe core/shell QDs, the hybrid QDs had a relatively extended PL lifetime and high stability in phosphate‐buffered saline buffer solutions. This is ascribed to the unique components and stable surface state of hybrid SiO₂‐coated CdTe/CdSe QDs. During the stabilization test in phosphate‐buffered saline buffer solutions, both static and dynamic quenching occurred. The quenching mechanism of the hybrid QDs was not suited with the Stern–Volmer equation. However, the relative stable surface of CdTe/CdSe QDs resulted in lower degradation and relative high PL quantum yields compared with hybrid SiO₂‐coated CdTe QDs. As a result, hybrid SiO₂‐coated CdTe/CdSe QDs can be used in bioapplications. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectroscopic exploration and thermodynamic characterization of desvenlafaxine interacting with fluorescent bovine serum albumin

The mechanism of the interaction between bovine serum albumin (BSA) and desvenlafaxine was studied using fluorescence, ultraviolet absorption, 3‐dimensional fluorescence spectroscopy, circular dichroism, synchronous fluorescence spectroscopy, cyclic voltametry, differential scanning calorimetry, and attenuated total reflection–Fourier transform infrared spectroscopic techniques under physiological condition at pH 7.4. Stern‐Volmer calculations authenticate the fluorescence of BSA that was quenched by desvenlafaxine in a collision quenching mode. The fluorescence quenching method was used to evaluate number of binding sites “n” and binding constant K _A that were measured, and various thermodynamic parameters were evaluated at different temperatures by using the van't Hoff equation and differential scanning calorimetry technique, which indicated a spontaneous and hydrophobic interaction between BSA and desvenlafaxine. According to the Förster theory we calculate the distance between the donor, BSA and acceptor, desvenlafaxine molecules. Furthermore, circular dichroism and attenuated total reflection–Fourier transform infrared spectroscopy indicate nominal changes in the secondary structure of the protein.     

Coupling of different isolated photosynthetic light harvesting complexes and CdSe/ZnS nanocrystals via Förster resonance energy transfer

The present work describes results obtained on hybrid systems formed in aqueous buffer solution by self-assembly of different CdSe quantum dots (QDs) surrounded by a ZnS shell and functionalized by covering the surface with anionic and cationic groups and various isolated pigment-protein complexes from the light-harvesting antennae of photosynthetic organisms (light-harvesting complexes 1 and 2 (LH1 and LH2, respectively) from purple bacteria, phycobiliproteins (PBPs) from cyanobacteria and the rod-shaped PBP from the cyanobacterium Acaryochloris marina). Excitation energy transfer (EET) from QDs to PBP rods was found to take place with varying and highly temperature-dependent efficiencies of up to 90%. Experiments performed at room temperature on hybrid systems with different QDs show that no straightforward correlation exists between the efficiency of EET and the parameter J/(R(12)(6)) given by the theory of F?rster resonance energy transfer (FRET), where J is the overlap integral of the normalized QD emission and PBP absorption and R(12) the distance between the transition dipole moments of donor and acceptor. The results show that the hybrid systems cannot be described as randomly orientated aggregates consisting of QDs and photosynthetic pigment-protein complexes. Specific structural parameters are inferred to play an essential role. The mode of binding and coupling seems to change with the size of QDs and with temperature. Efficient EET and fluorescence enhancement of the acceptor was observed at particular stoichiometric ratios between QDs and trimeric phycoerythrin (PE). At higher concentrations of PE, a quenching of its fluorescence is observed in the presence of QDs. This effect is explained by the existence of additional quenching channels in aggregates formed within hybrid systems. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Förster Energy Transfer in the Vicinity of Two Metallic Nanospheres (Dimer)

We present a detailed theoretical analysis of the Förster energy transfer process when a pair of molecules (donor and acceptor) is located nearby a cluster of two metallic nanospheres (dimer). We consider the case in which plasmonic resonances are within the overlap between the donor emission and acceptor absorption spectra, as well as the case that excludes such resonances from the aforementioned spectral overlap. Moreover, we explore the dependence of the Förster energy transfer rate on different dimer configurations (size and separation of nanospheres) and several dipole orientations of molecules. The dimer perturbs strongly the Förster energy transfer rate when plasmons are excited, donor dipole is oriented along the longitudinal axis of the dimer, and the radii of nanospheres and the sphere-gap distance are on the order of a few nanometers. In case of plasmonic excitation, the Förster energy transfer rate is degraded as the sphere-gap distance and size of the nanoparticles increase due to the dephasing of electronic motion arising from ohmic losses of metal. Also, we study the Förster efficiency influenced by the dimer, finding that the high efficiency region (delimited by the Förster radius curve) is reduced as a consequence of significant enhancement of the direct donor decay rate. Our study could impact applications that involve Förster energy transfer.     

Systematic investigation of interactions between papain and MPA-capped CdTe quantum dots

Fluorescent quantum dots (QDs) have been widely applied in biological and biomedical areas, but relatively little is known about the interaction of QDs with some natural enzymes. Herein, the interactions between 3-mercaptopropionic acid-capped CdTe QDs (MPA-QDs) and papain were systematically investigated by UV–Vis absorption spectra, fluorescence spectra and circular dichroism (CD) spectra under the physiological conditions. The fluorescence spectra results indicated that MPA-QDs quenched the fluorescence intensity of papain. The modified Stern–Volmer quenching constant K _a at different temperatures and the corresponding thermodynamic parameters ΔH, ΔG and ΔS were also calculated. The binding of MPA-QDs and papain is a result of the formation of QDs-papain complex and the electrostatic interactions play a major role in stabilizing the complex. The CD technique was further used to analyze the conformational changes of papain induced by MPA-QDs and the results indicated that the biological activity of papain was affected by MPA-QDs dramatically.     

Facile synthesis and photophysical characterization of luminescent CdTe quantum dots for Forster resonance energy transfer based immunosensing of staphylococcal enterotoxin B

Aqueous phase synthesis of CdTe quantum dots (QDs) with surface functionalization for bioconjugation remains the best approach for biosensing and bioimaging applications. We present a facile aqueous phase method to prepare CdTe QDs by adjusting precursor and ligand concentrations. CdTe QDs had photoluminescence quantum yield up to ≈33% with a narrow spectral distribution. The powder X‐ray diffraction profile elucidated characteristic broad peaks of zinc blende cubic CdTe nanoparticles with 2.5–3 nm average crystalline size having regular spherical morphology as revealed by transmission electron microscopy. Infra‐red spectroscopy confirmed disappearance of characteristic absorptions for –SH thiols inferring thiol coordinated CdTe nanoparticles. The effective molar concentration of 1 : 2.5 : 0.5 respectively for Cd²⁺/3‐mercaptopropionic acid/HTe^– at pH 9 ± 0.2 resulted in CdTe quantum dots of 2.2–3.06 nm having band gap in the range 2.74–2.26 eV respectively. Later, QD₅₂₃ and QD₆₀₁ were used for monitoring staphylococcal enterotoxin B (SEB; a bacterial superantigen responsible for food poisoning) using Forster resonance energy transfer based two QD fluorescence. QD₅₂₃ and QD₆₀₁ were bioconjugated to anti‐SEB IgY antibody and SEB respectively according to carbodiimide protocol. The mutual affinity between SEB and anti‐SEB antibody was relied upon to obtain efficient energy transfer between respective QDs resulting in fluorescence quenching of QD₅₂₃ and fluorescence enhancement of QD₆₀₁. Presence of SEB in the range 1–0.05 µg varied the rate of fluorescence quenching of QD₅₂₃, thereby demonstrating efficient use of QDs in the Forster resonance energy transfer based immunosensing method by engineering the QD size. Copyright © 2012 John Wiley & Sons, Ltd.     

Study on the fluorescence resonance energy transfer between CdS quantum dots and Eosin Y

Water‐soluble CdS quantum dots (QDs) were prepared using mercaptoacetic acid (TGA) as the stabilizer in an aqueous system. A fluorescence resonance energy transfer (FRET) system was constructed between water‐soluble CdS QDs (donor) and Eosin Y (acceptor). Several factors that impacted the fluorescence spectra of the FRET system, such as pH (3.05–10.10), concentration of Eosin Y (2–80 mg/L) and concentration of CdS QDs (2–80 mg/L), were investigated and refined. Donor‐to‐acceptor ratios, the energy transfer efficiency (E) and the distance (r) between CdS QDs and Eosin Y were obtained. The results showed that a FRET system could be established between water‐soluble CdS QDs and Eosin Y at pH 5.0; donor‐to‐acceptor ratios demonstrated a 1: 8 proportion of complexes; the energy transfer efficiency (E) and the distance (r) between the QDs and Eosin Y were 20.07% and 4.36 nm,respectively. Copyright © 2014 John Wiley & Sons, Ltd.