The hierarchical assembly of inorganicand organic building blocksis an efficient strategy to produce high-performance materials whichhas been demonstrated in various biomaterials. Here, we report a layer-by-layer(LBL) assembly method to fabricate ultrathin hybrid films from nanometer-scaleionic clusters and proteins. Two types of cationic clusters (hydrolyzedaluminum clusters and zirconium-glycine clusters) were assembled withnegatively charged bovine serum albumin (BSA) protein to form high-qualityhybrid films, due to their strong electrostatic interactions and hydrogenbonding. The obtained hybrid films were characterized by scanningelectron microscope (SEM), UV–vis, Raman spectroscopy, Fouriertransform infrared spectroscopy (FTIR), X-ray fluorescence (XRF),and X-ray diffraction (XRD). The results demonstrated that the cluster-proteinhybrid films exhibited structural homogeneity, relative transparency,and bright blue fluorescence. More importantly, these hybrid filmsdisplayed up to a 70% increase in hardness and up to a 100% increasein reduced Young’s modulus compared to the pure BSA film. Thesehybrid cluster-protein films could be potentially used as biomedicalcoatings in the future because of their good transparency and excellentmechanical properties. [ABSTRACT FROM AUTHOR]