Counting crystal clusters – a neutron reflectometry study of calcium phosphate nano-cluster adsorption at the air–liquid Interface

Abstract

The formation and adsorption of pre-nucleation clusters (PNCs) is widely postulated as the initial step in calcium phosphate biomineralization on organic surfaces. Here, in situ neutron reflectometry was successfully applied to study the initial stages of calcium phosphate nucleation on a deuterated-hexadecanoic acid (d-HDA) monolayer and zein protein films assembled at the air–liquid interface of a simulated body fluid (SBF). Modeled reflectivity profiles show the formation of a mineral thin film 11 Å in thickness. We hypothesize this film originates from aggregation of calcium phosphate prenucleation clusters (PNC), which adsorb electrostatically on the organic films to nucleate subsequent mineral layer development.