Quantification of methylene blue aggregation on a fused silica surface and resolution of individual absorbance spectra

The absorbance spectra of individual methylene blue aggregates adsorbed by spin coating on a fused silica surface are resolved. Using singular value decomposition and a model incorporating Beer's Law and elemental conservation, a varied concentration family of UV-Vis spectra are fit. Results indicate that H-dimer formation occurs beginning at a surface concentration of 3 x 10(13) molecules/cm(2), and further aggregate formation, including J-type dimers, is significant above 2 x 10(14) molecules/cm(2). Based on our results, past assumptions that a spin-coated surface (using a millimolar coating solution) results in a monolayer of methylene blue monomers should be reexamined. (C) 2001 Elsevier Science B.V. All rights reserved.