We report energy transfer (ET) from two dyes: Alexa Fluor 514 (AF514) and Alexa Fluor 532 (AF532) to gold nanoparticles (AuNPs) of three different sizes (10, 30, and 53 nm) employing steady-state and time-resolved fluorescence measurements. The results show that the fluorescence intensity and fluorescence lifetimes of donor (D) molecules AF514 and AF532 decrease with increase in the concentration of acceptor (A) AuNPs (2 to 10 μM) upon interaction with AuNPs, thereby confirming the occurrence of ET between D and A. This clearly suggests that these two Alexa Fluor molecules act as efficient donors and AuNPs as excellent acceptors. Interestingly, the Forster distance (Ro) determined for these dyes varies from 212 to 550 Å with increasing size of AuNPs and suggests that the ET from AF514 and AF532 to AuNPs is essentially obeying surface energy transfer (SET) process following 1 / d4 distance dependence. As is well known, Forster resonance energy transfer is efficient for separation distances of up to 100 Å, beyond which its efficiency decreases. Thus, the present results follow dipole-surface type ET from molecule dipole (AF514 and AF532) to nanometal (Au) surface. The influence of size and distance on the SET from AF514 and AF532 to AuNPs is discussed. Further, the quenching of donor fluorescence in the presence of AuNPs and nonradiative ET are analyzed using Stern–Volmer plots. Our study is an experimental quest to explore the potential of such dye–noble metal NPs pairs performing as sensitive chemical and biosensors.
This article highlights the studies on precise measurements of energy transfer efficiency in a steady-state method by adopting sample preparation methods. Steady-state and time-resolved fluorescence measurements were employed to evaluate the cadmium telluride (CdTe) quantum dot (QD) photoluminescence quenching induced by the proximal rhodamine 101 dye (Rh 101) molecule via fluorescence resonance energy transfer (FRET). Further, the evaluation of steady-state measurements in comparison with time-resolved measurements was carried out. The FRET parameters, such as spectral overlap, Förster distance, and intermolecular distance for each donor–acceptor pair, were determined and variation of these parameters with respect to the size of the QD is discussed. Further, efforts to understand the optical and carrier relaxation dynamics of CdTe QDs are made using steady-state and time-resolved fluorescence data.
Quantum dots (QDs), highly luminescent semiconductor nanocrystals, have found extensive applications spanning from optoelectronics to chemo- and biosensors to bioimaging. In addition to these QDs, semiconductor alloy nanostructures with tunable composition provide excellent material platform for biological applications. This paper reports the effect of composition of alloyed QDs on resonance energy transfer between hydrophilic ternary alloyed CdSeS/ZnS QDs (donor) and Rhodamine 640 dye (acceptor) employing steady state and time-resolved fluorescence spectroscopic techniques. Time-resolved decay curves of QDs obtained in the presence and absence of Rhodamine 640 dye have been recorded and the values of spectral overlap, Förster distance, and transfer efficiency are determined. The fluorescence resonance energy transfer of these systems was investigated as a function of spectral overlap between the QD donor emission and acceptor absorption as well as composition of the QDs. It is found that the efficiency significantly increases with varying compositions of the QD. In addition, the fluorescence quenching studies have been carried out using both absorption and emission data. The present study opens up the possibility of such QD-dye pairs performing as sensitive chemical and biosensors.
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