Fluorescent S-layer protein colloids

Four different coloured pH dependent biocolloids have been designed with fluorescent S-layer fusion proteins. The intrinsic self assembling capability of the S-layer protein SgsE on silicon dioxide particles lead to crystalline p2 lattice symmetry which was combined with the fluorescent properties of fused cyan ECFP, green EGFP, yellow YFP and red mRFP1. Confocal microscopy was used to monitor the pH dependence of the fluorescent S-layer coating. Electrophoretic measurements were carried out to understand the colloidal behaviour of the S-layer protein coated particles. It was found with flow cytometry that the stable SgsE-ECFP, SgsE-EGFP, SgsE-YFP and SgsE-mRFP bioparticle suspensions lost 50% of their fluorescence emission at the pK(a) of the chromophores. These novel fluorescent S-layer biocolloids can be used as pH sensors and might have an important role in surface pH determination.