When one molecule meets a photon
A magnifying lens can be used to light a piece of paper on fire by concentrating the sun's rays. Fibre optic cables can be used to guide light and transmit information over long distances. As instrumentation and experimental techniques become more and more advanced, a window has opened on the quantum world with impact on the study of light-matter interactions and just about everything else. More recently, interaction of light with metal nanoparticles can induce collective electron oscillations known as localised surface plasmon resonances. Researchers launched the EU-funded project 'Single-molecule spectroscopy in the near field of plasmonic metal nanoparticles' (1MOLECULENEARPLASMON) to lay the foundations for manipulating single photons with single molecules. The work focused on implementation of single-molecule spectroscopy with special nanomaterials (plasmonic materials) that exploit electromagnetic waves produced by coupling with incident light. Researchers developed and built the setup required to observe modifications in coupling of a plasmonic antenna to single molecules in a solid at cryogenic temperatures. Experiments at cryogenic temperatures are technically challenging but they will overcome major limitations with similar tests at room temperature. Measurements of the coupling are much more difficult and less accurate at room temperature due to the instability of the molecules at this temperature. Each antenna can only interact with one molecule at room temperature compared to many at cryogenic, allowing comparison of the antenna effect at different positions. Finally, photobleaching due to molecular movement is suppressed at low temperatures such that optical properties remain strong. The short two-year 1MOLECULENEARPLASMON project delivered the required advanced experimental setup for cryogenic single-molecule spectroscopy and selected the host-guest system and a promising nanoantenna. Preliminary spectroscopic experiments were conducted. Continuing research promises to yield pioneering results in the field of plasmonics and optical antennae for enhancing the efficiency of light-matter interactions.
