Modulation of Plasmon-Enhanced Resonance Energy Transfer to Gold Nanoparticles by Protein Survivin Channeled-Shell Gating

The resonance energy transfer (RET) from excited fluorescent probe molecules to plasmonic gold nanoparticles (AuNPs) can be gated by modulating the width of channels (gates) in submonolayer protein shells surrounding AuNPs. We have explored the gated-RET (gRET) processes using an antiapoptotic protein survivin (Sur) as the gating material, citrate-capped gold nanoparticles (AuNP@Cit), and fluorescein isothiocyanate as the fluorescent probe. Despite the electrostatic repulsive forces between these components, a strong modulation of RET efficiency by Sur down to 240 pM (S/N = 3) is possible. Using piezometric measurements, we have confirmed the Sur adsorbability on Cit-coated Au surfaces with monolayer coverage: γ_Sur = 5.4 pmol/cm² and Langmuirian adsorption constant K_L,Sur = 1.09 × 10⁹ M^–1. The AuNP@Cit/Sur stability has been corroborated using resonance elastic light scattering. The quantum mechanical calculations indicate that multiple hydrogen bonding between Cit ligands and −NH₃⁺, =NH₂⁺, and −NH₂ groups of lysines and arginines of Sur have likely facilitated Sur bonding to nanoparticles. A theoretical model of gated-RET has been developed, enabling predictions of the system behavior. In contrast to the positive slope of the Stern–Volmer quenching dependence (F₀/F) = f(Q_A), a negative slope has been obtained for gRET relationship (F₀/F) = f(c_P), attributed to the dequenching.