Scientists at EPFL have created a revolutionary biosensor that doesn’t need a light source—it makes its own glow using quantum tunneling.
By guiding electrons through a nanostructure of gold and aluminum oxide, the sensor emits light and detects molecules at astonishingly small concentrations, down to a trillionth of a gram. With no bulky equipment, it opens the door to powerful, compact diagnostic tools that could be used anywhere, from hospitals to remote environments.
Nanophotonic Biosensors Go Quantum
Optical biosensors work by shining light onto molecules and reading how that light changes. They are vital tools for pinpoint-accurate medical tests, tailoring treatments to individuals, and checking the health of our environment. The smaller the light can be squeezed—right down to nanometers, about the size of a protein—the sharper the detection becomes. Yet shrinking the optics normally demands laser setups and detectors so large and costly that portable or rapid-response testing is almost impossible.
EPFL engineers have now revealed a clever workaround: they replaced the external light source with quantum mechanics. Their chip taps into a phenomenon called inelastic electron tunneling. Give the device a small electric voltage, and electrons leap across an ultrathin barrier, releasing light on the spot. That same burst of light immediately probes any molecules sitting on the sensor.
“If you think of an electron as a wave, rather than a particle, that wave has a certain low probability of ‘tunneling’ to the other side of an extremely thin insulating barrier while emitting a photon of light. What we have done is create a nanostructure that both forms part of this insulating barrier and increases the probability that light emission will take place,” explains Bionanophotonic Systems Lab researcher Mikhail Masharin.
Picogram-Level Sensitivity Achieved
In short, the design of the team’s nanostructure creates just the right conditions for an electron passing upward through it to cross a barrier of aluminum oxide and arrive at an ultrathin layer of gold. In the process, the electron transfers some of its energy to a collective excitation called a plasmon, which then emits a photon. Their design ensures that the intensity and spectrum of this light changes in response to contact with biomolecules, resulting in a powerful method for extremely sensitive, real-time, label-free detection.
“Tests showed that our self-illuminating biosensor can detect amino acids and polymers at picogram concentrations – that’s one-trillionth of a gram – rivaling the most advanced sensors available today,” says Bionanophotonic Systems Laboratory head Hatice Altug.
The work has been published in Nature Photonics in collaboration with researchers at ETH Zurich, ICFO (Spain), and Yonsei University (Korea).
Metasurface Engineered Light Control
At the heart of the team’s innovation is a dual functionality: their nanostructure’s gold layer is a metasurface, meaning it exhibits special properties that create the conditions for quantum tunneling, and control the resulting light emission. This control is made possible thanks to the metasurface’s arrangement into a mesh of gold nanowires, which act as ‘nanoantennas’ to concentrate the light at the nanometer volumes required to detect biomolecules efficiently.
“With potential applications ranging from point-of-care diagnostics to detecting environmental contaminants, this technology represents a new frontier in high-performance sensing systems.”
Bionanophotonic Systems Lab researcher Ivan Sinev
“Inelastic electron tunneling is a very low-probability process, but if you have a low-probability process occurring uniformly over a very large area, you can still collect enough photons. This is where we have focused our optimization, and it turns out to be a very promising new strategy for biosensing,” says former Bionanophotonic Systems Lab researcher and first author Jihye Lee, now an engineer at Samsung Electronics.
In addition to being compact and sensitive, the team’s quantum platform, fabricated at EPFL’s Center of MicroNanoTechnology, is scalable and compatible with sensor manufacturing methods. Less than a square millimeter of active area is required for sensing, creating an exciting possibility for handheld biosensors, in contrast to current tabletop setups.
“Our work delivers a fully integrated sensor that combines light generation and detection on a single chip. With potential applications ranging from point-of-care diagnostics to detecting environmental contaminants, this technology represents a new frontier in high-performance sensing systems,” summarizes Bionanophotonic Systems Lab researcher Ivan Sinev.
Reference: “Plasmonic biosensor enabled by resonant quantum tunnelling” by Jihye Lee, Yina Wu, Ivan Sinev, Mikhail Masharin, Sotirios Papadopoulos, Eduardo J. C. Dias, Lujun Wang, Ming Lun Tseng, Seunghwan Moon, Jong-Souk Yeo, Lukas Novotny, F. Javier García de Abajo and Hatice Altug, 26 June 2025, Nature Photonics.
DOI: 10.1038/s41566-025-01708-y
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