Suspended Nanophotonic Waveguide for Isotope-Specific CO₂ Detection

Spectroscopic detection of gases and their stable isotopes holds significant value in bio-sciences and climate studies. However, achieving high precision has long been confined to bulky and costly equipment. In this work, we introduce a nanophotonic waveguide that is capable of detecting CO₂ gas down to 20 parts per billion, and for the first time perform accurate stable isotope ratio measurements. The waveguide leverages a suspended membrane design with microstructured cladding, providing a 102% high evanescent field confinement factor, moderate loss of 3.4 dB/cm, and effective suppression of etalons. The δ¹³C isotope ratio precision of 0.2‰ was achieved, replicating the performance of high-end laser absorption spectrometers on a photonic chip. This marks the inaugural instance of on-chip, isotope-specific gas detection facilitating a compact and cost-efficient system scalable to sensor networks.