In situ nano-mechanical mapping was performed on an iron substrate with a pre-adsorbed Mefp-1 layer, immersed in the citric acid buffer solution and the 10 μM FeCl3 solution, respectively. The topography images are shown in Fig. 4, presenting the starting surface in the buffer solution at pH 7–8 (Fig. 4a). Since the iron surface was pre-conditioned in 10% NaOH, the surface mainly consists of Fe2O3 as confirmed by the CRM measurement. The Rq value is 3.91 nm over a 500 nm × 500 nm scanned area. The topograpical images of the Mefp-1 layer adsorbed on the iron surface in the buffer solution and in the FeCl3 solution are shown in Fig. 4b and c, respectively. The adsorption of the protein leads to a smearing of the features seen on the surface prior to the Mefp-1 adsorption, compare Fig. 4a and b. By comparing the Z-range of the surface with and without the Mefp-1 film (Table 1), it is seen that the adsorption of Mefp-1 does not lead to any significant change in the height variation, which indicates a full coverage of the Mefp-1 film on the surface. Fig. 4c presents the topography of the Mefp-1 film exposed to the FeCl3 solution; by comparing with Fig. 4b and the Z-range in Table 1, it is observed that the introduction of Fe3+ induced a negligible decrease in the height variation, which remains predominantly due to the roughness of the substrate surface.
FeCl3
10 μM
μM
solution
pH 7–8
pH
NaOH
10%
%
Rq value
3.91 nm
nm
scanned area
500 nm × 500 nm
nm