Fluorogenic response from DNA templated micrometer range self-assembled gold nanorod

Plasmonic gold nanorod (AuNR) on a macromolecular matrix exhibits an end-to-end (ETE) long-range self-assembly (AuNR)_n with n > 100. In the case of small molecules as a template, the pre-synthesized macromolecular matrix is missing and this brings a synthetic challenge in directed long-range assembly of AuNR. Self-assembly with thiol-modified small DNA and AuNR shows a much short-range ETE assembly with n < 25 via a simple evaporation technique on a solid surface. In this study, the introduction of two short amine modified probe DNAs (∼2.5 nm) and one 22-mer complementary single strand (ss)-DNA template (∼7 nm) show the long-range ETE self-assembly of (AuNR)_n with n > 130. In the solution state, the zigzag arrangement within the assembled structure controls the typical change in the absorption behavior for (AuNR)_n ETE assembly. The formation of this long-range ETE self-assembly in a solution state was verified from the combined effect of fluorescence resonance energy transfer (FRET) and hotspot-induced fluorescence enhancement. The probe DNAs and templated DNA concentration on fluorescence enhancement have been varied to monitor the effect of (AuNR)_n with n = ∼5-130 in ETE self-assembly. Primarily quenched FRET acceptor in the presence of AuNR decisively exhibits remarkable fluorogenic response in ETE self-assembly with maximum n value. Although the FRET efficiencies among the fluorophores are comparable, the fluorogenic boost in ETE AuNR is due to the increased number of intrinsic navigated hotspots in these assemblies.