Plasmonic Nanoparticle Dimers with Reversibly Photoswitchable Interparticle Distances Linked by DNA

We report the assembly and optical characterization of stimulus-responsive gold nanoparticle dimers using azobenzene-modified hairpin DNA. We demonstrate a reversible, light-triggered actuation of the interparticle distance using reversible trans-to-cis photoisomerization of azobenzene. UV exposure leads to an extension of the dimers and concomitant blue shift of their scattering spectra, whereas blue light reverses the process. We use single-particle dark-field scattering spectroscopy to quantify the interparticle distances of the DNA-hairpin-linked nanoparticle heterodimers in the open and closed hairpin states. Analyzing the plasmon peak shifts for nearly 100 dimers with the plasmon ruler equation yields an average interparticle distance of 14.3 +/- 1.7 nm in the closed (transazobenzene) and 17.7 +/- 1.5 nm in the open (cis-azobenzene) state, which are in good agreement with finite-difference time domain (FDTD) electrodynamic simulations of the dimers. We conclude that larger photoreversible plasmon shifts can be achieved by designing photoswitchable linkers that are more rigid in the unzipped state.