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 (A_A) (3269 cm⁻¹), amide B (A_B) (3066 cm⁻¹), amide I (A_I) (1618 cm⁻¹), amide II (A_II) (1512 cm⁻¹) are also evidenced