Jerome Wenger NanoBioPhotonics

FRET is highly sensitive to the mutual orientation of donor and acceptor dipoles, and can be strongly prohibited for perpendicularly oriented dipoles. However, all previous studies combining FRET with nanophotonics largely overlooked this orientation effect. In a recent Nano Letters article "Plasmonic Nanoantennas Enable Forbidden Förster Dipole–Dipole Energy Transfer and Enhance the FRET Efficiency", we show for the first time how to exploit the orientation dependence in FRET using plasmonic nanoantennas.

Significance:

- Nanoantennas can allow FRET even for perpendicularly oriented donor and acceptor pairs. This provides a new strategy using nanophotonics to reveal FRET interactions that would otherwise be impossible to probe with diffraction-limited microscopy.

- While all previous work were dominated by the plasmonic losses which compete with FRET and decrease the FRET efficiency, our approach exploiting the dipolar orientation effect overcomes the losses. We report the first gain in FRET efficiency using nanophotonics, which even reaches up to 50%.

- Numerical simulations elucidate this new FRET enhancement and reveal the crucial role of the simultaneous presence of electric field components along all three directions of space inside the nanogap. This bridges the gap between FRET orientation effects and near-field optics.

Plasmonic optical antennas enhance light-matter interactions at the nanoscale, yet this phenomenon is currently limited by the ohmic losses in the metal. Silicon-based nanophotonics is an appealing alternative approach to implement cost-effective CMOS-compatible molecular sensors. So far, the fluorescence experiments with silicon-based antennas did not reach the single molecule level to demonstrate clearly the phenomenon and explore its physical origins. We bridge this gap in a recent Nano Letters publication “All-Dielectric Silicon Nanogap Antennas to Enhance the Fluorescence of Single Molecules”.

Significance:

- This report provides the first experimental evidence that silicon nanoantennas achieve single molecule fluorescence enhancements above 200-fold together with a detection volume of 140 e-21 L that allows the detection of individual molecules at micromolar concentration using dielectric materials only.

- The fluorescence enhancement results from a combination of excitation intensity and radiative rate enhancement within the nanogap region. These effects are quantified in excellent agreement with numerical simulations.

- These results open new routes to implement high sensitivity molecular (bio)sensors with on-chip photonic devices that are CMOS compatible.

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.