Researchers at École Polytechnique Fédérale de Lausanne (EPFL) have developed a novel self-emitting biosensor based on the quantum tunneling effect that achieves picogram-level molecular detection without any external light source. This breakthrough, published in Nature Photonics, opens new pathways for portable diagnostic devices.

While conventional nanophotonic biosensors require bulky optical systems to focus light to the nanoscale, the EPFL team exploits inelastic electron tunneling: applying a voltage simultaneously generates and detects optical signals. When electrons tunnel through an aluminum oxide insulating layer to an ultrathin gold layer, they excite plasmons and emit photons whose spectral changes reflect biomolecular information in real time.

"We designed nanostructures that increase the quantum tunneling probability by a factor of one million," explained researcher Mikhail Masharin. The sensor's core is a gold nanowire grid metasurface that both promotes electron tunneling and acts as a "nano-antenna" to focus the optical field. Experiments confirmed a detection limit of one part per trillion for molecules such as amino acids, rivaling large commercial instruments.

Fabricated at EPFL's Center of MicroNanoTechnology, the active sensing area is less than 1mm². Project leader Hatice Altug stated: "This fully integrated chip combines light source and detector in one, dramatically reducing system complexity." Former team member Jihye Lee added that by optimizing large-area quantum tunneling, the team achieved stable photon collection efficiency.

The platform is compatible with standard semiconductor processes and can be scaled for point-of-care diagnostics and environmental monitoring. The researchers are currently exploring its potential for rapid infectious disease detection and pollutant screening.