  We show that a multi-walled carbon nanotube film can be used as the sensing
element of a low-cost sensor for the alcoholic concentration in liquid
solutions. To this purpose, we investigate the electrical resistance of the
film as a function of the isopropanol concentration in a water solution. The
analysis reveals a growing resistance with increasing isopropanol concentration
and a fast response. The sensing element is re-usable as the initial resistance
value is restored once the solution has evaporated. The electrical resistance
increases linearly when the multi-walled carbon nanotube film is exposed to
common beverages with increasing alcoholic content. This work paves the way for
the development of low-cost, miniaturized MWCNT-based sensors for quality
monitoring and control of alcoholic beverages and general liquid solutions.
