LED-Based Photoacoustic NO₂ Sensor with a Sub-ppb Detection Limit

A high-sensitivity light-emitting diode (LED)-based photoacoustic NO₂ sensor is demonstrated. Sensitive photoacoustic gas sensors based on incoherent light sources are typically limited by background noise and drifts due to a strong signal generated by light absorbed at the photoacoustic cell walls. Here, we reach a sub-ppb detection limit and excellent stability using cantilever-enhanced photoacoustic detection and perform a two-channel relative measurement. A white-light LED is used as a light source, and the spectrum is divided into two wavelength channels with a dichroic filter. The photoacoustic signals generated by the two wavelength channels are measured simultaneously and used to solve the NO₂ concentration. The background signal is highly correlated between the two channels, and its variations are suppressed in the relative measurement. A noise level below 1 ppb is reached with an averaging time of 70 s. This is, to the best of our knowledge, the first time a sub-ppb detection limit is demonstrated with an LED-based photoacoustic NO₂ sensor. As LEDs are available at a wide selection of emission wavelengths, the results show great potential for development of cost-effective and sensitive detectors for a variety of other trace gasses as well.