| The motivation is primarily from the interest of the National Center for Food Safety and Technology (Summit-Argo, IL) in rapid, low cost methods for detection of bacteria in food. A sensitive conductimetric immunosensor has been demonstrated based on ultrathin platinum film. Surface characterization by X-ray photoelectron spectroscopy (XPS) of Glycidoxypropyldimethylethoxy silane (GOP) layer on platinum demonstrated approximately a monolayer coating. This result was confirmed by ellipsometry. Angle resolved XPS of GOP on silicon oxide (SiO2) shows a monolayer thickness. We have demonstrated for the first time, a stable monolayer coating of GOP on platinum and SiO 2 for biosensor. This layer also provides immobilization of Anti-Alkaline Phosphatase (Anti-AP) to the electrode.; Impedance increases during Anti-AP immobilization and binding with AP. Impedance modulation was greater at 20 Hz than at 800 KHz. Average impedance change of 55% at 20 Hz for Anti-AP immobilization for the sensors at concentration 1 uM. Average impedance change of 12% was confirmed with absorbance measurement indicating layer of AP bound at about .04 fmoles. Non-specific binding sensitivity with peroxidase at 1 uM was less than 6%. Reverse assay showed less impedance change in magnitude and small absorbance change. Control experiments showed small impedance changes and little absorbance.; The simulations of electrode response were to distinguish between redox: processes, capacitance and tunneling mechanisms. For the sensor experiments, without redox couple, data fit well with the diffusion distributed elements (DE) model as well as a transmission line distribution element (DX) model. First model, DE, is distributed elements for axial diffusion where oxygen seems to have diffused into PBS. The second DX model represents a transmission line. The sensors behave in a distributed network or like a transmission line. |
