Selim et al. Nanoscale Research Letters 2011, 6:528 http://www.nanoscalereslett.com/content/6/1/528 Page 5 of 9 Figure 3 TEM images of (a) mercaptoacetic acid-coated CSNPs and (b) ICSNPs. hand, the average sizes of ICSNPs were about 38 nm. The size of the particles as determined by DLS was con- siderably larger than that determined by TEM, most likely because the DLS technique gives the mean hydro- dynamic diameter of the core of CSNPs surrounded by Table 1 Atomic percent of CSNPs, PCSNPs, and ICSNPs calculated from ESCA survey scan spectra Sample CSNP PCSNP ICSNP C 30.04 62.09 56.79 O 17.35 22.09 35.81 Atomic percent (%) N - 1.59 2.72 S 16.26 6.71 1.33 Cd 36.35 7.52 3.35 organic and solvated layers, which is influenced by the viscosity and concentration of the solution. On the other hand, TEM gives the diameter of the core alone [30]. Cell proliferation The proliferation of fibroblasts was evaluated by two different methods, BrdU assay and morphological obser- vation. Figure 5 shows the pattern of fibroblast prolifera- tion as measured by BrdU assay after 6 and 24 h of culture in media containing CSNPs, PCSNPs, and ICSNPs. A significant difference in the acceleration of cell growth was not observed after 6 h of culture with CSNPs (Figure 6b), PCSNPs (Figure 6c), ICSNPs (Figure 6d), or without nanoparticles (Figure 6a). This could be attributed to the non-interference of particles during the short incubation period. In this case, fibroblasts adhe- sion occurs due to the influence of FBS-containing media only. However, after 24 h of culture, cell prolif- eration in media containing ICSNPs was significantly accelerated compared to that in media only. However, cell proliferation in media containing PCSNPs or CSNPs was not significantly different from that in media only (p < 0.004). Fibroblast proliferation was suppressed in media containing CSNPs. This low cell proliferation was probably due to the negative charge of the surface car- boxyl groups on CSNPs [19]. Cell proliferation in media containing PEG-immobilized CSNPs (PCSNPs) was almost the same as that in the control culture dish. This was because the biocompatibility of PEG has already been proven [17]. On the other hand, fibroblast prolif- eration in media containing ICSNPs was the highest, probably because immobilized insulin molecules suffi- ciently and continuously stimulate receptors expressed on the plasma membrane surface as well as downstream signal transduction proteins without internalization of ligand-receptor complexes [18]. These results suggest that the binding of immobilized insulin with insulin receptors is essential for the acceleration of the cell pro- liferation. Similar studies have been reported elsewhere [31,32]. Kim et al. [20] prepared insulin-immobilized polyurethanes and evaluated their interaction with human fibroblasts. As a result, cells were more rapidly proliferated onto insulin-immobilized polyurethanes compared to that on both polyurethane (PU) control and PEO-grafted PU when cultured in the presence of