FTIR spectra results. (a) Chitosan and (b) ZnS-chitosan bioconjugates at (A) pH 6.0 ± 0.2 and (B) pH = 4.0 ± 0.2. Vibrational regions: 1,750 to 1,475 cm-1 (left) and 1250–950 cm-1 (right). (C) Relative 'red-shift’ of bands associated with the functional groups of chitosan after the formation of ZnS bioconjugates as a function of pH. (D) Schematic representation of some interactions at ZnS-chitosan nanointerfaces (not to scale).