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 Beerʹs 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 3×1013 molecules/cm2, and further aggregate formation, including J-type dimers, is significant above 2×1014 molecules/cm2. 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.