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In this contribution, we report the study of the FRET (Förster Resonance Energy Transfer) effect between AgInS2 Quantum Dots (QDs) as donor and an organic fluorophore (cyanine 5 – Cy5) as acceptor, with the QD-Cy5 inter-distance d tuned by DNA strands. To this end, the cyanine dye linked to a single-stranded DNA (ssDNA) was first hybridized with its complementary thiolated DNA sequence. The resulting double-stranded DNA (dsDNA) construct was then used to functionalize the QD. The analyses of the optical properties of these nanohybrid assemblies were conducted by fluorescence. We found a characteristic Förster distance R0 = 6 nm for this system with an experimental FRET efficiency of 57 % for a distance d = 6 nm = R0, and 17 % for d = 13 nm ⪆ 2R0 in agreement with the theory. To explore the potential of such assembly for sensing applications based on FRET and DNA hybridization process, we have studied another approach: the QD was first functionalized with thiolated ssDNA single strand, and then the organic fluorophore linked to complementary DNA sequence was added by selective hybridization. Surprisingly, in this second approach, a strong FRET was observed whatever the targeted QD-Cy5 distance (efficiency ⪆70%). We will discuss the reasons for this non-expected effect.
Daveau et al. (2024) studied this question.