Fig. 3

ATR-FTIR spectrum illustrating the presence of Prussian blue (Fe4[Fe(CN)6]3), through the presence of the typical vibration of the C–N bond, at 2074 cm−1. The main protein bands, amide A (AA) (3269 cm−1), amide B (AB) (3066 cm−1), amide I (AI) (1618 cm−1), amide II (AII) (1512 cm−1) are also evidenced