LED based photoacoustic NO$_2$ sensor with sub-ppb detection limit

TL;DR

This paper presents a highly sensitive LED-based photoacoustic NO$_2$ sensor achieving sub-ppb detection limits through dual-wavelength measurement and background noise suppression, demonstrating potential for cost-effective trace gas detection.

Contribution

The study introduces a novel LED-based photoacoustic sensor with sub-ppb detection limit using a two-channel relative measurement technique for enhanced stability.

Findings

Achieved sub-ppb detection limit with LED source

Implemented dual-wavelength measurement for noise suppression

Demonstrated sensor stability over 70 seconds averaging

Abstract

A high-sensitivity LED based photoacoustic NO$_2$ 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 by using cantilever-enhanced photoacoustic detection and performing 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 NO$_2$ 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 NO$_2$ sensor. As LEDs are available at 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.