C4nr03643c 12515..12523 ++

Metallic nanoparticles (MNPs) are known to alter the emission of vicinal fluorophores through the nearfield interaction, leading to either fluorescence quenching or enhancement. Much ambiguity remains in the experimental outcome of such a near-field interaction, particularly for bulk colloidal solution. It is hypothesized that the strong far-field interference from the inner filter effect of the MNPs could mask the true near-field MNP–fluorophore interaction significantly. Thus, in this work, a reliable internal control capable of decoupling the near-field interaction from far-field interference is established by the use of the DNA toehold concept to mediate the in situ assembly and disassembly of the MNP–fluorophore conjugate. A model gold nanoparticle (AuNP)–Cy3 system is used to investigate our proposed toeholdmediated internal control system. The maximum fluorescence enhancement is obtained for large-sized AuNP (58 nm) separated from Cy3 at an intermediate distance of 6.8 nm, while fluorescence quenching is observed for smaller-sized AuNP (11 nm and 23 nm), which is in agreement with the theoretical values reported in the literature. This work shows that the toehold-mediated internal control design can serve as a central system for evaluating the near-field interaction of other MNP–fluorophore combinations and facilitate the rational design of specific MNP–fluorophore systems for various applications.