Reconfigurable 3D plasmonic metamolecules

Abstract

A reconfigurable plasmonic nanosystem combines an active plasmonic structure with a regulated physical or chemical control input. There have been considerable e orts on integration of plasmonic nanostructures with active platforms using topdown techniques. The active media include phase-transition materials, graphene, liquid crystals and carrier-modulated semiconductors, which can respond to thermal 1 , electrical 2 and optical stimuli 3-5 . However, these plasmonic nanostructures are often restricted to two-dimensional substrates, showing desired optical response only along specific excitation directions. Alternatively, bottom-up techniques o er a new pathway to impart reconfigurability and functionality to passive systems. In particular, DNA has proven to be one of the most versatile and robust building blocks 6-9 for construction of complex three-dimensional architectures with high fidelity 10-14 . Here we show the creation of reconfigurable three-dimensional plasmonic metamolecules, which execute DNA-regulated conformational changes at the nanoscale. DNA serves as both a construction material to organize plasmonic nanoparticles in three dimensions, as well as fuel for driving the metamolecules to distinct conformational states. Simultaneously, the threedimensional plasmonic metamolecules can work as optical reporters, which transduce their conformational changes in situ into circular dichroism changes in the visible wavelength range.Circular dichroism (CD), that is, differential absorption of left-and right-handed circularly polarized light, of natural chiral macromolecules is highly sensitive to their three-dimensional (3D) conformations 15 . Taking a similar strategy, we create 3D reconfigurable plasmonic chiral metamolecules 4,16 , whose conformation changes are highly correlated with their pronounced and distinct CD spectral changes in the visible wavelength range. Figure 1a shows the design schematic. Two gold nanorods (AuNRs) are hosted on a reconfigurable DNA origami template 7,10 , which consists of two 14-helix bundles (80 nm × 16 nm × 8 nm) folded from a long single-stranded DNA (ssDNA) scaffold with the help of hundreds of staple strands 13 . The two origami bundles are linked together by the scaffold strand passing twice between them at one point. To ensure the mobility of the DNA bundles and avoid the formation of a Holliday junction 17 , 8 unpaired bases are introduced to each ssDNA connector (Supplementary Note 1). Twelve binding sites are extended from each origami bundle for robust assembly of one AuNR (38 nm × 10 nm) functionalized with complementary DNA (Supplementary Note 2). The surface to surface distance of the two AuNRs is roughly 25 nm. Owing to close proximity, the excited plasmons in the two AuNRs can be strongly coupled 18 . The two crossed AuNRs constitute a 3D plasmonic chiral object [19][20][21][22] , which generates a theme of handedness when interacting with left-and right-handed circularly polarized light, giving rise to strong CD. Left-handedRight-handed Two gold nanorods (...

Programmable motion of DNA origami mechanisms

“…In nanoscale design, specific mechanical motion has seldom been explored. Whereas rotational (19,20,32,41,44,[46][47][48][49] and small linear motions (36,(50)(51)(52)(53)(54)(55)(56) have been demonstrated, the mechanics of this motion have not been studied in any detail. Here we use scaffolded DNA origami to integrate stiff double-stranded DNA (dsDNA) and Significance Folding DNA into complex 3D shapes (DNA origami) has emerged as a powerful method for the precise design and fabrication of self-assembled nanodevices.…”

“…The largest triggerable structural change was achieved by Han et al in a DNA origami Möbius strip (one-sided ribbon structure) that could be opened to approximately double in size (45). Constrained motion has been achieved in systems with rotational motion (19,20,32,41,44,46,47) in some cases to open lid-like components (19,20,41) or detect molecular binding (44,48,49). A few of these systems achieved reversible conformational changes (32,41,44,46), although the motion path and flexibility were not studied.…”

Active Nanorheology with Plasmonics

“…However, the power of circular dichroism (CD) spectroscopy is apparent in the strong, sharp chiroptical response of the Au-Fe nanohelix metafluid. At a peak wavelength of 690 nm, it exhibits a molar CD = ~14×10 9 o ·M -1 ·cm -1 , stronger than that observed for other chiral assembled plasmonic systems 11,[42][43][44] . Complex fluids, such as blood, whose rheology we set out to measure generally show no measurable chiroptical response of their own in this spectral region 45 .…”

Chemistry Can Make Strict and Fuzzy Controls for Bio-Systems: DNA Nanoarchitectonics and Cell-Macromolecular Nanoarchitectonics

“…317 Furthermore, DNA origami nanostructure was switched between two different conformations by adding DNA fuel strands. 402 However, DNA origami-based nanomachines which carry out more dynamic mechanistic motions have not yet been constructed. As the first step to their engineering, rotational and linear joints were prepared and used to constrain the motions along a single degree of freedom.…”