Plasmonic Toroidal Nanoantennae Achieve 99.9% Molecular Transition Switching with 2840-fold Radiative Enhancement

Controlling the behaviour of molecules with light holds immense potential for advances in sensing and photonics, and now, Arda Gulucu and Emre Ozan Polat, both from Bilkent University and UNAM’s National Nanotechnology Research Center, demonstrate a new method for achieving this with unprecedented precision. The researchers successfully switch molecular transition energies using specifically designed plasmonic nanoantennae, achieving a remarkable 99. 9% modulation depth and over 2840-fold enhancement of radiative properties. This breakthrough stems from the unique ability of these toroidal nanoantennae to focus intense light fields around individual molecules, manipulating how they absorb and emit light, and even suppressing energy loss. By carefully controlling the antenna’s geometry and positioning, the team not only achieved complete switching of molecular transitions but also created systems capable of individually addressing multiple molecules, paving the way for highly sensitive spectral detection and advanced photonic processing.

Nanoscale Light Control via Plasmonics

This research area focuses on nanophotonics, specifically manipulating light at the nanoscale to achieve desired optical properties and functionalities. A central theme is plasmonics, the study of collective electron oscillations at the interface between a metal and a dielectric, which enhances light-matter interactions. Researchers are investigating nanoresonators and metamaterials, engineered structures exhibiting resonant optical properties, and exploring their interaction with quantum systems to advance quantum technologies and optical devices. Integration of these nanophotonic devices onto chips and the use of waveguides to guide light at the nanoscale are also crucial areas of development, supporting applications like single-molecule detection, biosensing, gas sensing, and the creation of advanced optical switches and modulators.

The research encompasses a range of applications and technologies, including biosensors for medical diagnostics, gas sensors for environmental monitoring, optical switches and modulators for controlling light flow, and quantum technologies for computing and communication. Scientists are also developing single-photon sources for quantum cryptography and photonic integrated circuits on chips, while further exploration includes super-resolution imaging and nonlinear optics. In summary, this field represents a rapidly evolving area of nanophotonics, with diverse applications ranging from biosensing and environmental monitoring to quantum technologies and optical communication, drawing upon expertise in physics, materials science, chemistry, and engineering.

Toroidal Nanoantennas Control Molecular Light Emission

Scientists engineered a system combining quantum emitters and toroidal nanoantennas to achieve unprecedented control over molecular transition energies and significantly enhance radiative emission. This breakthrough relies on the unique geometry of the toroidal nanoantennas, which focus intense three-dimensional electric fields through their toroidal moment, allowing precise positioning around the quantum emitters. Experiments varied the aspect ratio of the nanoantennas to tune the plasmonic resonance wavelength, achieving a broad spectrum of resonance wavelengths from the near-infrared to the ultraviolet-visible range. Detailed analysis revealed that reducing the aspect ratio redshifts the resonance wavelength and compresses the effective mode volume, increasing the local density of states and enhancing the Purcell factor.

Within an optimal range of aspect ratios, this enhancement preferentially couples to radiative channels, transforming the plasmonic nanoantenna into a resonant cavity. The team meticulously characterized the system, providing a comprehensive parameter set including aspect ratio, resonance wavelength, and decay rates, establishing a benchmark for spectral sensing and manipulation of quantum states. This innovative approach establishes plasmonic nanoantennas as a promising architecture for high-sensitivity spectral detection and enables the implementation of mode switches for applications in bioimaging, quantum sensing, and programmable photonic circuits.

Toroidal Nanoantennas Control Molecular Energy Switching

Scientists achieved complete switching of molecular transition energies with a modulation depth of 99. 9%, accompanied by a 2840-fold increase in radiative enhancement and a 1056-fold enhancement of non-radiative decay channels, using toroidal nanoantennas and quantum objects. This is achieved by positioning a quantum emitter near a toroidal nanoantenna and tuning the nanoantenna’s aspect ratio to shift the resonance from the near-infrared to the ultraviolet-visible spectrum. The unique geometry of the nanoantennas focuses intense three-dimensional electric fields, allowing precise positioning around the emitters and optimizing spectral enhancement.

The team demonstrated that a molecule with specific dielectric properties, when resonant with the quantum emitter’s emission, completely suppresses both radiative and non-radiative decay, a phenomenon not previously observed in plasmon-exciton studies. Further investigations with multiple quantum objects revealed that spectral degeneracy broadens the transmission range, while detuning generates distinct minima, enabling individual addressability of each object’s response. These results establish plasmonic nanoantennas as a promising architecture for highly sensitive spectral detection of single or multiple molecules and enable the implementation of quantum mode switches for photonic processing, anticipating applications in bioimaging, quantum sensing, programmable photonic circuits, and display technologies.

Fano Interference Boosts Light-Matter Interaction

This research demonstrates a toroidal nanoantenna capable of precisely controlling the interaction between light and molecular objects, achieving complete switching of molecular transition energies with a modulation depth of 99. 9%. This control is achieved by exploiting Fano interference, arising from the interaction between the broad plasmonic response of the nanoantenna and the narrow spectral transitions of the molecular objects. The study extends this principle to systems incorporating multiple molecular objects, revealing that spectral degeneracy broadens the range of light transmission, while spectral detuning creates distinct minima, enabling individual addressability of each molecule’s response.

This level of control establishes the nanoantenna as a promising architecture for highly sensitive spectral detection of single or multiple molecules, with potential applications in label-free biomolecular sensing and advanced photonic processing. The authors suggest that extending this design into arrays and fabricating diverse nanoantenna geometries are future directions, highlighting the functional versatility of the nanoantenna across a broad range of geometries and compatibility with existing nanofabrication techniques. The ability to suppress both radiative and non-radiative decay pathways also suggests possibilities for programmable light emission in future photonic systems.