Researchers have developed a nanoscale light-emitting biosensor that uses quantum tunnelling and engineered metasurfaces to achieve efficient, tunable, and label-free detection of biomolecules.
Study: Plasmonic biosensor enabled by resonant quantum tunnelling. Image Credit: Casimiro PT/Shutterstock.com
In a recent Nature Photonics publication, the team introduced a promising approach to nanoscale light emission and biosensing, based on a mechanism called light emission from inelastic tunnelling (LIET).
Background
Electron tunnelling—a quantum phenomenon where electrons pass through energy barriers without a classical conduction path—can emit photons when it occurs inelastically. While this principle has been known, practical implementations have faced challenges, primarily due to inefficient nanostructure designs. Early configurations, like metal-insulator-metal (MIM) structures and plasmonic antennas, showed limited light output and uneven emission patterns, with scalability also proving difficult.
However, advances in nanofabrication now allow researchers to design metasurfaces with precise geometries and periodicities that improve light emission efficiency. Integrating plasmonic elements with tunnelling layers has opened up new ways to amplify these emissions.
The Current Study
In this study, the team used advanced fabrication methods to create metasurfaces composed of nanoantenna arrays with tightly controlled periodic spacing. These arrays feature metallic nanostructures patterned on a substrate, separated from the tunnelling layer by an insulating film. Techniques like electron-beam lithography allowed for nanometer-level control over antenna size and placement. The tunnelling layer was assembled under carefully managed conditions to ensure consistent electron tunnelling under an applied voltage.
Optical characterization was carried out using a customized inverted microscope setup equipped with variable magnification objectives (10× and 50×). Emission from the metasurfaces was analyzed using a spectrometer and EMCCD camera, capturing both wavelength-resolved spectra and spatial emission patterns. The data was then normalized to account for optical throughput, allowing comparisons in units of counts per second per nanometer.
Electrical biasing was precisely managed using a sourcemeter, typically applying voltages around 2.8 V. Device performance was evaluated under different test conditions, including surface coatings with biomolecules like alanine. Structural integrity and morphology were confirmed using SEM, TEM, and AFM imaging.
Theoretical modeling separated the emission into two components: the electronic behavior of the tunnelling current, and the photonic output shaped by the nanoantenna structures. This framework guided device optimization and was backed by numerical simulations that helped clarify emission dynamics.
Results and Discussion
The experiments confirmed that the engineered metasurfaces could generate strong electroluminescence solely through inelastic electron tunnelling. A standout design—featuring a sparse 400 nm-period mesh—outperformed denser 2D nanowire arrays, producing roughly 2.3 times more light. The photon emission rate reached around 1.2 × 10-7 photons per tunnelling electron, aligning well with theoretical expectations.
Notably, the emission was uniform over large areas, suggesting strong potential for scalable applications. The devices also showed a broad spectral response that could be tuned via design changes, as confirmed by simulation. This tunability supports their use in biosensing, where signal changes can indicate the presence of specific biomolecules.
In biosensing tests, the devices detected thin films of materials like PMMA and alanine, with emission intensity increasing as more alanine was deposited. The system was sensitive enough to detect picogram-scale analyte quantities, with emission shifts clearly visible in the spectral data. Sensitivity was quantified using a standard sensor response metric, successfully distinguishing analyte amounts down to the device’s detection limit, defined as three times the noise level.
These findings demonstrate that the device can detect molecular interactions in real time without needing fluorescent labels or elaborate sample preparation.
Conclusion
This study showcases how carefully engineered metasurfaces can efficiently convert tunnelling currents into light, enabling uniform, tunable, and highly sensitive nanoscale electroluminescence. By optimizing nanoantenna array geometry, the researchers significantly boosted emission efficiency, making label-free molecular detection possible under simple biasing conditions.
The work blends theoretical modeling with robust experimental validation, highlighting the promise of LIET-based photonic devices in applications ranging from biosensing to lab-on-chip diagnostics. Compared to traditional fluorescence techniques, these devices simplify workflows while achieving high spatial resolution and detection sensitivity down to the picogram level.
Journal Reference
Lee J., Wu Y., et al. (2025). Plasmonic biosensor enabled by resonant quantum tunnelling. Nature Photonics. DOI: 10.1038/s41566-025-01708-y, https://www.nature.com/articles/s41566-025-01708-y