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 β-galactosidase from Escherichia coli. The sensor had a detection limit of a few nanomoles and a response time of a ∼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 β-galactosidase concentration of about 200 nM. A marked selectivity for β-galactosidase over BSA was observed in mixed solutions even when the concentration of BSA exceeded the concentration of β-galactosidase by a factor of ∼2000. The apparent value of the dissociation constant (Kd) of the interaction of free phage with β-galactosidase (9.1 ± 0.9 pM) 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 β-galactosidase. The Kd obtained from the enzyme-linked immunosorbent assay (ELISA) for the phage and the monoclonal anti-β-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.