A molecular emission detector on a chip employing a direct current microplasma

An optical emission detector is presented realized on a glass chip. The device employs a direct current helium plasma for molecular fragmentation and excitation. The plasma was generated in a chamber of 50 nL volume at a typical operating pressure of 130 Torr. The plasma stability and the current/voltage/pressure behavior were investigated. Comparison with the theoretical behavior of downscaled plasma devices shows that the properties of the microplasma do not fundamentally differ from those of larger plasmas. Using the plasma as an excitation source, methane could be detected with a detection limit of 3 x 10^-12 g/s (600 ppm), by observing the emission of the CH radical. The lifetime of the present device was limited to ~2 h by sputtering of the cathode material. When lifetime is increased, the device looks to be a promising detector for on-chip integration with gas chromatography.