Methods and devices for detecting a target substance on a subject without contacting the subject are disclosed. At least one air jet blows analyte from a surface of the subject into an airflow, the airflow entraining the analyte. A desorption channel desorbs molecules from analyte in a portion of the airflow travelling through the desorption channel. An ionizer forms ions from vapor molecules in the portion of the airflow. At least one mass spectrometer analyzes the ions to detect the target substance. The flow travels without interruption from the subject to the at least one mass spectrometer. The desorption channel causes a sufficient quantity of molecules to desorb from the analyte to enable the at least one mass spectrometer to detect the target substance.