Bilayer fluidity and melting as a function nanoparticle loading determined by fluorescence anisotropy. Fluorescence anisotropy of diphenylhexatriene in DPPC bilayers was measured as a function of the DPPC/AgNP weight ratio and temperature (1°C/min). DPPC/AgNP samples prepared at 1 mM were diluted 1000-fold for analysis. Anisotropy, <r>, is a measure of lipid ordering and the bilayer microviscosity. Gel phase bilayers exhibit high anisotropy and fluid phase bilayers exhibit low anisotropy. The transition from high to low anisotropy with increasing temperature denotes the gel to fluid melting transition. The midpoint of the transition is taken as the melting temperature.