Combined affinity and catalytic biosensor: in situ enzymatic activity monitoring of surface-bound enzymes.

Surface Plasmon Resonance Spectroscopy (SPR) and miniature Fiber Optic Absorbance Spectroscopy (FOAS) were combined to monitor in situ and quantitatively an enzymatic model reaction catalyzed by beta-lactamase. The enzyme was covalently immobilized to the gold surface of a SPR chip, which was functionalized with NeutrAvidin through a biotinylated alkanethiol self-assembled monolayer, thus serving as a highly sensitive affinity biosensor. SPR was used to control the density of the surface-bound enzyme. Nitrocefin as the enzymatic substrate was allowed to react with the immobilized enzyme in the SPR flow cell, and its turnover was detected with the FOAS system acting as the catalytic biosensor. The coupling of the two techniques has a substantial potential for highly controlled on-line monitoring of surface-bound enzyme activity. The FOAS technique may also be easily employed as an add-on device to other types of affinity sensing instruments.