An ultrathin platinum film sensor to measure biomolecular binding

A sensitive conductimetric immunosensor has been demonstrated based on an u ltrathin platinum film on an oxidized silicon base. The film is about 25 An gstrom thick and is seen to consist of a discontinuous layer with channels 20-30 Angstrom wide. Monoclonal antibodies were bound to the sensor surface using conventional biosensor chemistry. Impedance at fixed frequencies acr oss the film was used to track modification and binding at the surface. Imp edance increased 55% at 20 Hz during the activation of the surface with ant i-alkaline phosphatase (anti-AP). Binding of alkaline phosphatase (A-P) to the prepared surface results in a further increase of 12%. p-Nitrophenyl ph osphate hydrolysis confirmed binding and activity of the AP. About 40 amol AP were bound on the 0.5 cm(2) electrode. Non-specific binding of horseradi sh peroxidase. caused an impedance change < 6%. Control experiments showed small impedance changes and trace enzyme activity. Since the mechanism of e lectrical conduction of the thin film was not established, modeling of thin -film response was used to distinguish between redox processes, capacitance and tunneling mechanisms. The data fit well with the diffusion distributed elements (DE) model as well as a transmission line distribution element (D X) model. The first model, DE, is distributed elements for diffusion. The s econd DX model represents a transmission line. The sensors behave in a dist ributed network or like a transmission line. (C) 2001 Elsevier Science B.V. All rights reserved.