  The measurement of acetone in human breath, a known biomarker for diabetes,
can act as an effective screening method for diabetes. While gas chromatography
and mass spectroscopy based methods can detect gases in low concentration, they
are costly, bulky, need complex sample preparation and are slow. Solid state
devices such as Field Effect Transistors (FETs) can perform this faster and at
a lower cost. In this work, we present the results of acetone gas sensing by
molybdenum disulfide (MoS2) based FETs. MoS2 channel was functionalized with
polymethyl methacrylate (PMMA). When acetone molecules bind to PMMA, an
electrostatic gating effect takes place and changes the electrical
characteristics of the FET. More the number of acetone molecules that bind to
the PMMA layer, the higher the shift in the drain current-voltage (Id-Vg) curve
of the FET. This shift is modeled as a change in the threshold voltage of the
FET. The Id-Vg curve was observed to shift downwards, as the acetone
concentration increases. The limit of detection was observed to be 0.4 parts
per million (ppm). This is the first sub-ppm concentration acetone detection at
room temperature using a solid state device.
