Determination of ethyl alcohol content in red wines with an optical alcohol meter based on nanostructured silicon

A rapid analytical method for selectively monitoring ethyl alcohol in red wines without sample pretreatment, based on the use of an optical sensor, has been developed exploiting a porous silicon microcavity. The optical structure, realized by alternating layers of different porosities, was stabilized by thermal oxidation, and the resonant peak shift of the microcavity (projected at 600 nm) was monitored in the presence of more than 20 red wines. The resonant peak shows an increasing red shift depending on the wine alcoholic strength, which is ascribable to a change of refractive index due to physisorption/condensation of ethanol vapors inside the pores' structure. The linear response of the PS oxidized microcavity to the wine alcoholic strength insures the determination of the ethanol amount with a high accuracy and reliability. The calculated values differ by less than 0.5% to those obtained with the official method in accordance with the limits imposed by European laws. Moreover, a user-friendly interface, allowing the sensor to be used by unskilled persons, and portable packaging, able to ensure in situ measurements, have been developed.