Engineers at EPFL have developed a new type of optical biosensor that can detect biomolecules without needing an external light source. The sensor uses a quantum effect to generate and measure light on a single chip.
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The study, published in Nature Photonics, removes a major barrier to the application of optical biosensors in healthcare and environmental monitoring contexts.
Optical biosensors are essential for precision diagnostics, personalized medicine, and environmental analysis. They work by using light waves to detect specific molecules. Incorporating nanophotonic structures that compress light at the chip’s surface, concentrating it down to the scale of proteins or amino acids, makes these sensors substantially more sensitive.
However, the use of nanophotonic structures in rapid or point-of-care settings has been limited by the bulky and expensive equipment required to produce and detect light.
To eliminate the need for external light, engineers at EPFL’s School of Engineering, in the Bionanophotonic Systems Laboratory, have created a biosensor that uses an applied electrical voltage instead to both generate and detect light. The researchers achieved this using a quantum phenomenon called inelastic electron tunneling.
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.
Mikhail Masharin, Bionanophotonic Systems Lab Researcher, EPFL
Trillionth-Of-A-Gram Detection
The team designed their nanostructure to have the perfect conditions for an electron passing upward through it to cross an aluminum oxide barrier to an ultrathin layer of gold. During this process, the electron transfers energy to a collective excitation known as a plasmon, which then emits a photon. The intensity and spectrum of this emitted light changes in response to nearby biomolecules, enabling 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.
Hatice Altug. Head, Bionanophotonic Systems Laboratory
A Dual-Purpose Metasurface
The team's breakthrough is based on dual functionality using a gold metasurface layer. This layer has unique features that enable quantum tunneling while simultaneously controlling the subsequent light emission. This control is made possible by arranging the metasurface into a mesh of gold nanowires that operate as ‘nanoantennas’, which focus the light into the ultra-small volumes required to detect biomolecules effectively.
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.
Jihye Lee, Former Bionanophotonic Systems Lab Researcher and Study First Author and Engineer, Samsung Electronics
In addition to being small and sensitive, the team's quantum platform, created at EPFL's Center of MicroNanoTechnology, is scalable and compatible with sensor production techniques. With an active sensing area smaller than a square millimeter, the nanochip has potential for use in handheld biosensors, offering an alternative to the benchtop systems currently used.
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.
Ivan Sinev, Bionanophotonic Systems Lab Researcher, EPFL
Journal Reference:
Lee, J., et al. (2025) Plasmonic biosensor enabled by resonant quantum tunneling. Nature Photonics. doi.org/10.1038/s41566-025-01708-y