A colorimetric paper sensor for lactate assay using a cellulose-Binding recombinant enzyme

A new fabrication technology for effective preparation of paper-based biosensors using affinity-binding enzymes is developed. Lactate dehydrogenase (LDH) fused with a cellulose binding domain (CBD) is produced to allow one-step purification and immobilization of the enzyme on paper. Results demonstrate that the binding capacity of the recombinant enzyme is as high as 22 mg-enzyme/g-paper, with much improved stability (by a factor of 25-fold) in comparison to the native parent enzyme. That ensures the solid phase bioassay reactions on surface of the paper sensor are not limited by enzyme availability, and affords much extended sensor shelf life at the same time. The paper sensor shows a linear detection range of 0.5-8 mM of lactate, with changes in color intensity detectable within a much broader concentration range examined (up to 16 mM). The colorimetric display is suited for readouts using either human eyes or hand-held imaging devices such as smart phones. This work promises of a new strategy of developing high performance paper-based sensors for point-of-care diagnosis applications.