Atomic force microscopy (AFM) has recently been successfully used to describe the surface topography of hydroxyapatite crystals from mammalian skeletal tissues. To further characterize the growth mechanisms of skeletal hydroxyapatite crystals and the role of adsorbed proteins in these processes, imaging under biological fluids is essential. However, under aqueous solutions, these crystals do not bind to the usual AFM substrates such as mica and graphite and therefore alternative substrates are necessary. The aim of the present study was to evaluate the use of self-assembled monolayer technology with controllable chemical functionality to provide "designer surfaces" for crystal binding in fluid environments which simulate the normal physiological milieu. We have found that hydroxyapatite crystals from developing enamel are bound most effectively by negatively charged self-assembled monolayer (COO- and SO3-) surfaces, demonstrating an important role for such substrates in AFM imaging of biological samples under aqueous fluids and suggesting that the prevalent charge on enamel crystal surfaces is positive.