Chaperonins ensure correct functional folding of proteins in cells. Despite their crucial role, their mechanisms of action are still open to questions. In a recent Scientific Report study “Differential conformational modulations of MreB folding upon interactions with GroEL/ES and TRiC chaperonins”, we investigate the action of GroEL/ES and TRiC systems to fold MreB substrate protein.

MreB is a homologue to actin in prokaryotes both structurally and functionally, and plays a central role to control cell shape, division or locomotion. The strength of our approach is to take advantage on complementary time-resolved fluorescence techniques (FCS, anisotropy and FRET) to monitor the conformational rearrangements of MreB occurring in GroEL/ES and TRiC assisted refolding.

Significance:

- We clearly establish that MreB forms complexes with TRiC, GroEL and GroES independently and in concert, and we quantify the complexes sizes and dynamics.

- We demonstrate an unexpected role of GroES acting as an unfoldase to induce a dramatic expansion of MreB and facilitate refolding in the GroEL/ES system. Our analysis importantly provides quantitative distance information about the MreB conformation expansions for both GroEL/ES and TRiC systems.

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Plasmonic nanoantennas provide powerful means to concentrate light into nanoscale dimensions and enhance the fluorescence from single quantum emitters. However, the effects of a resonant plasmonic antenna on Förster resonance energy transfer (FRET) between single molecules remained elusive so far. We address this challengein a recent ACS Photonics publication, and report FRET between single donor and acceptor fluorescent molecules deterministically located inside the nanogap of a resonant gold dimer antenna.

Significance:

- While previous works were limited to moderate nanophotonic effects and lacked position control of the dyes, our gold antennas provide 10x stronger photonic effects on accurately positioned donor and acceptor molecules. This sets unprecedented conditions to explore the limits of nanophotonics to control energy transfer at the nanoscale.

- We conclusively demonstrate enhanced energy transfer rate constants in resonant plasmonic nanoantennas, in good agreement with numerical simulations.

- Our results exemplify the competition between radiative and non-radiative processes in complex nanophotonic systems and highlight geometrical parameters and design rules to optimize nanoantennas for non-radiative energy harvesting.

Quantum plasmonics and the interaction of quantum emitters with metal nanostructures are receiving a large interest. However, coupling two quantum emitters via a surface plasmon waveguide has remained a major technical challenge.

In a recent ACS Nano publication, we take a significant step towards achieving this goal and demonstrate for the first time the plasmon-mediated fluorescence energy transfer between two nanoparticles separated by micron distance. The key technical innovation is brought by a dedicated dual-beam optical microscope, allowing us to find the best configurations that maximize the nanoparticle-nanowire coupling.

Significance:

- We describe the experimental conditions to achieve high figures of merit for coupling nanoemitters with plasmonic waveguides, in excellent agreement with numerical simulations.

- We provide the first demonstration of long-range fluorescence energy transfer between two nanoparticles mediated by nanowire surface plasmons.

Coupling single fluorescent emitters to plasmonic resonators is essential in optimizing solid-state light sources. However, the non-scalability of the current approaches remains still a major challenge. In a recent ACS Nano publication, we overcome the scalability issue and demonstrate the self-assembly of colloidal nanostructures associating a single molecule to optimized gold nanoparticle dimers.

Significance:

- We achieve the large scale bottom-up production of millions of reproducible samples deterministically coupling a single emitter to plasmonic optical antennas.

- The nanoemitters achieve luminescence lifetimes down to a few picoseconds (some of the shortest ever reported) and importantly maintain a high quantum yields of 70 %.

- Our data uniquely quantifies the statistical dispersions of the fluorescence intensity and decay rate enhancements in plasmonic dimer antennas.