A method and apparatus for detecting trace amounts of a target substance carried by the object, by: applying to the object a flow of air which has been pre-heated, to dislodge substances carried by the object; collecting the heated air after applied to the object; and analyzing the collected heated air for the presence of the target substance. Preferably, a marker substance is introduced into the air before applied to the objects, and the collected heated air is analyzed also for the presence of the marker substance.