A fluorosensor for two-dimensional measurements of extracellular enzyme activity in marine sediments

A novel planar fluorosensor has been developed for measuring two-dimensional activity distributions of the extracellular enzyme, leucine-aminopetidase (Leu-AP), in marine sediments. The sensor is a foil consisting of an enzyme substrate l-leucine 7-amido-4-methylcoumarin hydrochloride (Leu-MCA) and a Hydromed D4 membrane, backed by a polyester sheet. In its present application, the sensor foil is introduced into surficial deposits to a depth of ~ 10–15 cm, and time dependent fluorescence production occurring in successive digital images is used to resolve enzyme activity patterns. Corrections for microenvironmental variability (e.g., diffusion and adsorption properties) and background reflectance were made. The planar fluorosensor technique was standardized by comparison with traditional slurry based methods using homogenized sediment sections. Spatially averaged, vertical enzyme activity profiles measured using the imaging sensor system were contrasted with the traditional method to verify the reliability of this new approach. The new system resolves enzyme activity on a submillimeter scale over relatively large areas (~ 50–100 cm2). In addition to allowing rapid determination of enzyme activity patterns in undisturbed material, the transparent nature of the sensing foils permits direct correlation of enzyme distributions to heterogeneous biological and physical structure.