Indirect detection of alcoholic strength in spirits by fluorescence method using the polyethyleneimine capped ZnO QDs

We synthesized polyethyleneimine capped ZnO quantum dots (PEI-ZnO QDs) which dispersed well in ethanol by using a two-step method. UV–visible absorption spectroscopy, photoluminescence, Fourier transform infrared spectroscopy, high resolution transmission electron microscope, and field emission scanning electron microscope were used to characterize the as-prepared PEI-ZnO QDs. It emitted green-yellow fluorescence (527   nm) for excitation at 355   nm. We used the PEI-ZnO QDs to determine the alcoholic strength because of its different property in water and ethanol which caused decrease in the PEI-ZnO QDs fluorescence intensity with increasing water content. With this method, we determined the alcoholic strength of different artificial samples with a linear range from 20% to 60% vol and detected commercial spirits with satisfactory results.