A Layer-by-Layer Film of Chitosan in a Taste Sensor Application David S. dos Santos, Jr., 1 Antonio Riul, Jr., 2 Roger R. Malmegrim, 3 Fernando J. Fonseca, 4 Osvaldo N. Oliveira, Jr., 1 Luiz H. C. Mattoso* 3 1 Instituto de Fı ´sica de Sa ˜o Carlos, USP, CP 369, 13560-970, Sa ˜o Carlos/SP, Brazil 2 Depto de Fı ´sica, Quı ´mica e Biologia, FCT-UNESP, CP 467, 19060-900, Presidente Prudente/SP, Brazil 3 EMBRAPA Instrumentac¸a ˜o Agropecua ´ria, CP 741, 13560-970, Sa ˜o Carlos/SP, Brazil Fax: (þ55) 16 272 5958; E-mail: mattoso@cnpdia.embrapa.br 4 Laborato ´rio de Microeletro ˆnica, Departamento de Engenharia de Sistemas Eletro ˆnicos, EPUSP, 05508-900, Sa ˜o Paulo/SP, Brazil Received: May 22, 2003; Revised: August 29, 2003; Accepted: August 29, 2003; DOI: 10.1002/mabi.200350027 Keywords:biomaterials; dielectric properties; nanolayers; polysaccharides; sensors Introduction Improvements in product quality in the food and beverage industries requirethe development of sensorsable to provide – automatically and reliably – information on key features of the products being processed. In this context, ‘‘taste sensors’’ are becoming increasingly important for several reasons: they may help prevent humans from being exposed to toxic and unpleasant substances, and they have no loss of sensitivity after long exposure to certain sub- stances, unlike in the case of the human tongue. The taste recognition process is the least understood of the human senses, probably due to the variety of perception mecha- nisms involved. [1–10] Nonetheless, there is general agree- ment that the biological system cannot discriminate each chemical substance present in beverages and foodstuffs. Instead, the gustatory system groups all the information received in different patterns of response produced by neurons to encode the taste quality. [1–10] This is referred to as the global selectivity concept. Therefore, specificity is not a crucial requirement for taste sensors. To mimic the human perception of taste, artificial sensors must be able to distinguish the four basic tastes detected by humans (sweet, salty, sour, and bitter). Most of the ‘‘electronic tongues’’ found in the literature use potentiometry [11–17] and cyclic voltammetry [18–21] as the principle of detection. They employ nonselective sens- ing units generating a response pattern associated with the main characteristics of the samples analyzed. Potentio- metric devices work on the measured charge of positively and negatively lipid membranes, being thus limited to liquids with detectable charged species. With voltammetry, Full Paper: Chitosan is alternated with sulfonated poly- styrene (PSS) to build layer-by-layer (LBL) films that are used as sensing units in an electronic tongue. Using impe- dance spectroscopy as the principle method of detection, an array using chitosan/PSS LBL film and a bare gold electrode as the sensing units was capable of distinguishing the basic tastes – salty, sweet, bitter, and sour– to a concentration below the human threshold. The suitability of chitosan as a sensing material was confirmed by using this sensorto distinguish red wines according to their vintage, vineyard, and brands. PCA Plot for red wine samples obtained from impedance measurements at 1 kHz for the sensor array comprising a 3-bilayer chitosan/PSS film and a bare gold electrode. Macromol. Biosci. 2003, 3, 591–595 591 Macromol. Biosci. 2003, 3, No. 10 DOI: 10.1002/mabi.200350027 ß 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim