Detection of dissolved gases in oceans is critically needed for global carbon cycle investigation. However, most in situ optical detection techniques, as far as we know, have restricted measurement efficiency due to large gas consumption. Herein, we develop a sub-mL photoacoustic gas sensor with a simple configuration. A single-mode fiber directly guides the incident laser into the photoacoustic cell without any other free-space optics. Thus, a reduced inner size of 12 mm × 6 mm × 4 mm enables the effective detection of limited dissolved gas. We employ methane (CH4) as an example to demonstrate its sensing performance. The sensor achieves a good linear response with an R-square value of 0.9989 and a minimum detection limit of 1.1 ppmv, corresponding to a normalized noise equivalent absorption coefficient of 7.75 × 10−8 W·cm−1·Hz−1/2.
