Protein-conjugated, glucose-sensitive surface using fluorescent dendrimer porphyrin

A multi-functional dendrimer-coated surface has been prepared for the effective protein immobilization and detection of protein activity. The silicon surface was first modified with positively-charged amino groups using 3-aminopropyltriethoxysilane (APTES), and subsequently coated with ionic dendrimer porphyrin (DP) by electrostatic interaction. Fluorescence and atomic force microscopy (AFM) studies showed that the dendrimer was homogeneously coated on the APTES-modified silicon surface as dome-shaped features that protruded 1.0-2.5 nm above the surface and had diameters ranging from 50 nm to 100 nm. The dendrimer-modified surface showed a higher capacity to covalently bind proteins, compared to the control surfaces, and the protein activity was higher by a factor of two. Using the fluorescent property of the porphyrin core, the relative amounts of dendrimer and the enzyme-catalyzed reactions on the dendrimer-coated surface were examined by fluorescence microscopy. Glucose oxidase (GOX)-mediated glucose oxidation quenched fluorescence emission from the focal porphyrin core through a peroxidase-coupled system and from the quantitative relationship between quenching and glucose concentration, the GOX-catalyzed reaction could be characterized.