Phage as a molecular recognition element in biosensors immobilized by physical adsorption

Biosensors based on landscape phages immobilized by physical adsorption on the surface of a quartz crystal microbalance was used for detection of beta-galactosidase from Escherichia coli. The sensor had a detection limit of a few nanomoles and a response time of a similar to 100 s over the range of 0.003-210 nM. The binding dose-response curve had a typical sigmoid shape and the signal was saturated at the beta-galactosidase concentration of about 200 nM. A marked selectivity for beta-galactosidase over BSA was observed in mixed solutions even when the concentration of BSA exceeded the concentration of beta-galactosidase by a factor of similar to 2000. The apparent value of the dissociation constant (K-d) of the interaction of free phage with beta-galactosidase (9.1 +/- 0.9 mu M) was smaller compared with the one calculated for the bound phage (1.7 +/- 0.5 nM). The binding was specific with three binding sites needed to bind a single molecule of beta-galactosidase. The Kd obtained from the enzyme-linked immunosorbent assay (ELISA) for the phage and the monoclonal anti-beta-galactosidase antibodies were 21 +/- 2 and 26 +/- 2 nM, respectively. Although the method of physical adsorption is simpler and more economical in comparison with Langmuir-Blodgett and molecular assembling methods the performances of the sensors made by these technologies compare well. This work provides evidence that phage can be used as a recognition element in biosensors using physical adsorption method for immobilization of phage on the sensor surface. (c) 2006 Elsevier B.V. All rights reserved.