Soft Nanogaps

DNA nanotechnology and polymers for plasmonic applications

DNA folding at the nanoscale

Light-matter interactions at the nanoscale can be challenging and looking at the behaviour of single-molecules in plasmonic cavities requires sub-nanometric accuracy. With DNA nanotechnology and DNA origami, single-molecules such as chromophores, proteins and quantum dots can be positioned in optical cavities with high precision using the natural dimensions of DNA base-pairs (< 0.5 nm). Not only can DNA nanostructures be used as molecular breadboards for single-molecule observations, but they can also be combined with more complex molecules, such as polymers, to create bio-compatible nanomachines for targeted drug delivery in the human body.[2]

A rectangular DNA nanostructure (grey) is used to place single dye molecules (red star) in a plasmonic gap between a gold nanoparticle and a gold surface. Adapted from [1].
A DNA origami nanomachine whose movement is controlled by the thermoresponsive polymer PNIPAM. Adapted from [3].

Key publications:

[1] Rochetti et al, Amplified plasmonic forces from DNA origami-scaffolded single dyes in nanogaps, Nano Lett., 2023, 23, 13, 5959–5966

[2] Ojambati et al, Quantum electrodynamics at room temperature coupling a single vibrating molecule with a plasmonic nanocavity, Nature Comm., 2019, 10, 1049

[3] Turek et al, Thermo-responsive actuation of a DNA origami flexor, Adv. Func. Mat., 28, 25

People working on the topic: Sara Rocchetti, Thieme Schmidt

Monitoring polymers within the nanogap

Understanding the redox process of conjugated polymers remains challenging due to the limitation of powerful tools with high precision. Electrochromic nanoparticles-on-mirror (eNPoMs) offer an extraordinary opportunity to precisely monitor the in-situ redox process of conjugated polymers within the nanogap. [1-3] Based on eNPoMs, the details of redox doping mechanisms[2] and associated microstructure rearrangements[3] for different conjugated polymers can be revealed at the nanoscale (<100 nm3), impossible to achieve with conventional approaches.

The redox state of the conjugated polymers in an eNPoM can be precisely modulated by electrical bias. Adapted from [1].
Drastically different redox doping mechanisms revealed by eNPoMs made of different conjugated polymer gaps. Sequential electron transfer mechanism dominates for low-conductivity polymers, while disproportionation mechanism prevails in high-conductivity polymers. Adapted from [2].
The nanostructure rearrangement induced by the metal-insulator transition in conducting polymers revealed by the eNPoM structures. The decrease of the shell thickness leads to well-aligned conducting polymer crystallites with face-on orientation parallel to the Au mirror. Adapted from [3].

Key publications:

[1] Peng et al., Scalable electrochromic nanopixels using plasmonics, Science Advances, 2019, 5, 5

[2] Peng et al., In-situ spectro-electrochemistry of conductive polymers using plasmonics to reveal doping mechanisms, ACS Nano, 2022, 16, 12, 21120-21128

[3] Xiong et al., Metal to insulator transition for conducting polymers in plasmonic nanogaps, Light: Science & Applications, 2023, accepted.

People working on the topic: Yuling Xiong, Shangzhi Chen