Self-assembled multilayer surfaces of highly fluorescent spirobifluorene-based dye for label-free protein recognition

The preparation of smart surfaces for protein detection is a challenging field of research. With the aim to achieve label-free detection in the solid state, we report on the organic surface functionalization for protein recognition without the need of previous chemical modification of the fluorophore. Layer-by-layer deposition of polyelectrolyte poly(vinyl benzyl tetramethylammonium) chloride (p(VBTMA)Cl) and a tetrasulfonate water-soluble low molecular weight fluorophore (1) based on spirobifluorene leads to modified glass and quartz substrates with outstanding photophysical properties in response to bovine serum albumin (BSA). The absorbance, photoluminescence as well as the fluorescence lifetimes were recorded for all surfaces. The surface structure and height of the different number of bilayers polymer/fluorophore were characterized by atomic force microscopy and ellipsometry. The results show linear trends in the absorption, fluorescence and height of the multilayer with increasing number of functionalization steps. Upon incubation with BSA the multilayer shows an increase in fluorescence up to 3-fold, which is also detectable with the naked eye. In conclusion, we report an easy, fast and biocompatible approach for the construction of protein sensors by self-assembly.