Extreme Light–Matter Interactions in Single-Digit Nanospaces and Their Roles in Biosensors, Chemical Processes, and Quantum Photonics

The exploration of extreme light–matter interactions at the nanoscale has become a key area of research driving innovation across various scientific disciplines. In particular, the investigation of these interactions within single-digit nanometer dimensions (i.e., gaps smaller than 10 nm), where light and matter reach their physical boundaries, has significantly expanded the opportunities in biosensing, chemical reactions, and quantum photonics. Advances in fabrication techniques have enabled the manipulation of light at such extreme confinements, resulting in higher sensitivity of biosensors, improving selectivity for chemical reactions and light–matter interactions at the single-molecule level, and expanding photonics into quantum applications through single-photon emitters. This review introduces the fundamental physics of nanogaps and extreme light–matter interactions and highlights recent progress in nanofabrication and their applications in leveraging nanogaps for cutting-edge technologies in biosensors, chemical reactions, and quantum photonics.