Use of self-assembled monolayers as substrates for atomic force imaging ofhydroxyapatite crystals from mammalian skeletal tissues

Atomic force microscopy (AFM) has recently been successfully used to descri be the surface topography of hydroxyapatite crystals from mammalian skeleta l tissues. To further characterize the growth mechanisms of skeletal hydrox yapatite crystals and the role of adsorbed proteins in these processes, ima ging under biological fluids is essential. However, under aqueous solutions , these crystals do not bind to the usual AFM substrates such as mica and g raphite and therefore alternative substrates are necessary. The aim of the present study was to evaluate the use of self-assembled monolayer technolog y with controllable chemical functionality to provide "designer surfaces" f or crystal binding in fluid environments which simulate the normal physiolo gical milieu. We have found that hydroxyapatite crystals from developing en amel are bound most effectively by negatively charged self-assembled monola yer (COO- and SO3-) surfaces, demonstrating an important role for such subs trates in AFM imaging of biological samples under aqueous fluids and sugges ting that the prevalent charge on enamel crystal surfaces is positive.