Chromatic Transitions in Polydiacetylene Langmuir-Blodgett Films due to Molecular Recognition at the Film Surface Studied by Spectroscopic Methods and Surface Analysis

Abstract

Langmuir-Blodgett films of polydiacetylene are used to create a biosensor on the basis of a surface hostguest recognition process. Functionalizing a 10 wt.% fraction of the diacetylene monomer with biotin leads to a visually observable color change in the resulting polymerized film when streptavidin in the molar ratio streptavidin: biotin = 1:2 is added. The chromatic transition, caused by a shortening of the conjugation length of the π-electron system in the polydiacetylene backbone, is investigated by monitoring the change of visible optical absorption and Raman spectroscopy. Chemical species and to some extent also the presence of surface-immobilized peptide are identified via time-of-flight secondary-ion mass spectrometry (TOF-SIMS) signal assignment and XPS studies.