Fabrication of a photonic crystal sensor on a plant membrane

Ethanol, as a food additive, can effectively extend product shelf-life and improve food texture. However, its dosage requires stringent control, making ethanol quantification a critical quality assurance requirement in baked goods. Consequently, developing a rapid and simple method for detecting ethanol in baked food products is of great practical significance. This study fabricated a three-dimensional photonic crystal (PC) membrane by integrating plant membranes and a PC, utilizing an onion epidermal membrane as the natural substrate. PC arrays were imprinted onto the onion membrane at room temperature. The resulting onion-derived PC membrane biosensor demonstrated not only high sensitivity but also excellent selectivity towards ethanol. During detection, the spectral reflection peak of the onion–PC film shifted towards the red as the ethanol concentration increased, achieving signal stabilization within 5 min. Moreover, ethanol detection induced visually observable structural color changes (yellow-green to orange-red) on the membrane. The biosensor exhibited excellent practicability and retained stable performance after multiple reuse cycles. Overall, this onion–PC membrane demonstrates significant potential for the visual and rapid detection of ethanol in baked foods.