Atomic force microscopic determination of substrate effects on the structure of deposited biomineral phosphates

Abstract

Periodicity observed by atomic force microscopy on the surface of two biological crystals, hydroxyapatite (HA) and brushite (DCPD), has allowed identification of crystal planes indicative of preferred orientation on several substrates. From isolated HA crystal clusters, deposited on to a glass substrate, two crystal planes were identified. The 〈001〉 and 〈110〉 spacings of HA are in agreement with published values taken from crystallographic data. Measurements made on DCPD platelets, deposited on to glass, yielded atomic spacings presumed to be those of the 〈110〉 crystal plane. For both minerals, comparison of atomic-scale imaging showed differences between deposits on glass or freshly cleaved mica. Larger scale structure was also found to differ when the mineral deposits were compared on gold, glass and mica. A very ordered structure was found when HA was deposited on to a gold substrate that had been modified with a monolayer of an alkane thiol. These observations suggest that different substrates influence the final structure of the crystals as determined by atomic force microscopic surface characterization.