A light-driven three-dimensional plasmonic nanosystem that translates molecular motion into reversible chiroptical function

Abstract

Nature has developed striking light-powered proteins such as bacteriorhodopsin, which can convert light energy into conformational changes for biological functions. Such natural machines are a great source of inspiration for creation of their synthetic analogues. However, synthetic molecular machines typically operate at the nanometre scale or below. Translating controlled operation of individual molecular machines to a larger dimension, for example, to 10-100 nm, which features many practical applications, is highly important but remains challenging. Here we demonstrate a light-driven plasmonic nanosystem that can amplify the molecular motion of azobenzene through the host nanostructure and consequently translate it into reversible chiroptical function with large amplitude modulation. Light is exploited as both energy source and information probe. Our plasmonic nanosystem bears unique features of optical addressability, reversibility and modulability, which are crucial for developing all-optical molecular devices with desired functionalities.

Figure 1. Light-induced conformation changes of DNA origami nanostructures.

(a) Trans–cis photoisomerization of an azobenzene molecule by ultraviolet (UV) and visible (VIS) light illumination. (b) Hybridization and dehybridization of azobenzene-modified DNA oligonucleotides controlled by trans–cis photoisomerization of azobenzene through UV and VIS light illumination. (c) Photoregulation of the DNA origami template between the locked and relaxed states by UV and VIS light illumination. The active function of the origami structure is enabled by introducing the azobenzene-modified DNA segment (red) in b on the template, which works as a recognition site to receive light stimuli for triggering light-induced motion.

Figure 2. Structural characterization of the DNA origami nanostructures.

(a) TEM image of the DNA origami nanostructures after ultraviolet (UV) light illumination. (b) Statistic histogram of the acute angle between two linked origami bundles after UV light illumination. The number of the analysed structures: 463. A broad distribution over angles is observed. (c) TEM image of the DNA origami nanostructures after visible (VIS) light illumination. The locked state is designed to be right-handed. (d) Statistic histogram of the acute angle between two linked origami bundles after VIS light illumination. The number of the analysed structures: 541. A maximum magnitude over angles occurs around 50°, which is in accordance to our structure design. (e) Enlarged view of the origami structures in the locked state. The dsDNA branch, which links the two origami bundles to define the angle, is clearly visible. (f) Averaged TEM image reconstructed from locked origami structures. It evidently demonstrates the excellent structural homogeneity and high angle accuracy within the locked structures. Scale bars, 100 nm (a,c); 50 nm (e).

Figure 3. Light-driven 3D plasmonic nanosystem.

(a) Schematic of the 3D plasmonic nanosystem regulated by ultraviolet (UV) and visible (VIS) light illumination for switching between the locked right-handed and relaxed states. Two AuNRs are assembled on one origami template to form a 3D plasmonic chiral nanostructure. (b) TEM images of the plasmonic nanostructures in the locked right-handed state. Scale bars, 200 and 50 nm in the large image and in the inset image, respectively. (c) Measured CD spectra after UV (purple) and VIS (blue) illumination. (d) Kinetic characterization of the 3D plasmonic nanostructures switching from the locked right-handed state to the relaxed state and vice versa on UV and VIS illumination. The experimental data can be well fit by first-order reaction kinetics with rate constants of 5 × 10⁻³ and 1.3 × 10⁻² s⁻¹ for UV and VIS illumination, respectively. The error bars represent one s.d. from the mean.

Figure 4. ‘Writing', ‘erasing' and ‘reading' of the 3D plasmonic nanostructures by light.

(a) Reversible conversion of the plasmonic nanostructures between the relaxed and locked right-handed states by ultraviolet (UV) and visible (VIS) light illumination, which performs the ‘erasing' and ‘writing' behaviour, respectively. The resulting conformation states are probed by circularly polarized light (CPL) in real time, which performs the ‘reading' behaviour. (b) CD intensity recorded at 720 nm (Fig. 3c) during alternative UV and VIS illumination in multiple cycles. Excellent reversibility of the chiroptical response is achieved between the two states with large signal modulations. The error bars represent one s.d. from the mean.