The ensemble and single molecule (SM) fluorescence properties of Nile Red embedded in polystyrene (PS) films on glasses were investigated. The ensemble spectra showed dual emission bands and SM spectra exhibited distribution with two emission maxima. These results indicate that two distinct environments exist in the thin PS film on a glass: a low polarity environment in the PS bulk and a high polarity environment near the PS/glass interface. It was also found that a PS film of ca. 10 nm thick is sufficient to separate fluorophores from the charged species on glass surfaces. (c) 2006 Elsevier B.V. All rights reserved.