In a conventional paper-based sandwich ELISA, the capture antibody is coupled to the cellulose surface by physical adsorption, which results in the desorption of antibodies and less than optimum performance [29]. From previous research, covalently coupling antibodies on the ELISA plate may increase the stability, thus improving performance [10]. In this paper, the cellulose activated by periodate treatment was used for the immobilization of antibodies through the formation of a Schiff base product. The absorption in Fig. 2c at 1646 cm−1 could be assigned to CN stretching presented in the Schiff bases, while the band at 1740 cm-1 decreased, which confirmed the immobilization of antibodies in the aldehyde groups and the reduction. In this process, the N-terminal amino groups, as well as the amino groups from lysine, react with aldehyde groups on the oxidized cellulose. A typical antibody contains over 60 lysine residues [30], a sufficient amount of amino groups for attachment between the antibody and the oxidized cellulose.