Abstract Achieving chemical specificity in trace detection of small molecules is a challenge. Here we describe a highly selective method for detection of trace chemicals using photoacoustic spectroscopy of adsorbed molecules on a quartz crystal tuning fork. The technique is demonstrated in an open environment without the need of a resonant cavity. Mid-infrared quantum cascade lasers are used as the light source with cyclotrimethylenetrinitromine (RDX) residue being the target analyte. The results show absorption peaks matching those of earlier literature.