The present invention provides methods and devices for detecting and distinguishing various types of gas molecules or volatile organic compounds (VOCs), the methods and devices have enhanced sensing ability; namely response magnitude, sensitivity, detection limit and selectivity (i.e., classification capability). In one embodiment, the present invention provides methods and devices for diagnosing a disease in a subject or a health status of a subject through the detection of VOCs indicative of the disease or health status in question from breath of the subject. In one embodiment, the present invention provides methods and devices for detecting the existence of lung cancer or the stage of lung cancer in a subject through the detection of VOCs indicative of the existence of lung cancer from breath of the subject.