An organic molecule – o-phenylene diamine (OPD) – is selected as an aldehyde sensing material. It is studied for selectivity to aldehyde vapours both by experiment and simulation. A chemiresistor based sensor for detection of aldehyde vapours is fabricated. An o-phenylene diamine–carbon black composite is used as the sensing element. The amine groups in the OPD would interact with the carbonyl groups of the aldehydes. The selectivity and cross-sensitivity of the OPD–CB sensor to VOCs – aldehyde, ketone and alcohol – are studied. The sensor shows good response to aldehydes compared to other VOCs. The higher response for aldehydes is attributed to the interaction of the carbonyl oxygen of aldehydes with –NH₂ groups of OPD. The surface morphology of the sensing element is studied by scanning electron microscopy. The OPD–CB sensor is responsive to 10 ppm of formaldehyde. The interaction of the VOCs with the OPD–CB nanocomposite is investigated by molecular dynamics studies. The interaction energies of the analyte with the OPD–CB nanocomposite were calculated. It is observed that the interaction energies for aldehydes are higher than those for other analytes. Thus the OPD–CB sensor shows selectivity to aldehydes. The simulated radial distribution function is calculated for the O–H pair of analyte and OPD which further supports the finding that the amine groups are involved in the interaction. These results suggest that it is important and easy to identify appropriate sensing materials based on the understanding of analyte interaction properties.