the present invention relates to a modular chemiresistive sensor . in particular , a modular chemiresistive sensor for hypergolic fuel and oxidizer leak detection , carbon dioxide monitoring and detection of disease biomarkers . the sensor preferably has two gold or platinum electrodes mounted on a silicon substrate where the electrodes are connected to a power source and are separated by a gap of 0 . 5 to 4 . 0 μm . a polymer nanowire or carbon nanotube spans the gap between the electrodes and connects the electrodes electrically . the electrodes are further connected to a circuit board having a processor and data storage , where the processor can measure current and voltage values between the electrodes and compare the current and voltage values with current and voltage values stored in the data storage and assigned to particular concentrations of a pre - determined substance such as those listed above or a variety of other substances .