A micro-flame ionization detector (micro-FID) was developed operating with a diffusion flame with a folded flame structure. Unlike conventional FIDs, an air-hydrogen diffusion flame was developed and tested in an encapsulated structure of Quartz-Macor??-Quartz layers. Diffusion flames are generally known to be more controllable and stable than premixed flames, which fits our purpose for the micro-FID, where the stability plays an important role for many applications. Various Macor designs including a burner cavity and a micro-channel were tested to obtain highest output sensitivity over methane test samples. In order to gauge sensitivity of the device, collected electric charge per mole (C/mol) was calculated and taken as a reference value of ionization efficiency. The result was 1.959x10-2 C/mol for methane which was about 34 times higher compared to the result obtained using a counter-flow flame, which was 5.73x10-4 C/mol for methane, while one of the commercial macro FIDs has 10-1 C/mol. This result shows that the micro-FID using the folded flame structure enhances ionization with less leakage of the analytes than the classical counter-flow flame design
