Development of an immunosensor based on pressure transduction.

Traditional strategies for signal transduction in immunosensors are based on piezoelectric, thermometric, electrochemical, magnetic and optical methods. The use of pressure as a signal transduction method in immunosensors has not been reported previously. An immunosensor incorporating the detection of a change in pressure as the signal-transducing mechanism was investigated. A commercially available ultra-low pressure sensor was used in conjunction with a sealed chamber to assess the feasibility of this strategy. A key feature of the current approach is the use of a thin membrane (or film) in which to perform an immunoassay and subsequently to detect production of gas. The thinness contributes to efficient gas evolution and minimizes the effect of liquid acting as a "sink" for gas molecules. This feature also simplifies measurement of evolved gas, which traditionally was based on the use of bulk solutions, shaking and pH changes to "release" dissolved gas (especially carbon dioxide). Gas generation in the current approach is achieved by the coupling of catalase to haptens or antibodies for use in competitive or sandwich immunoassays, respectively. Hydrogen peroxide is used as the substrate. Performance characteristics of the sensor apparatus were assessed in several ways. Injection of various volumes of air from a gas-tight syringe produced an essentially linear relationship from 0.2 to 2.0 microl of injected volume, with a slope of approximately 5 V/microl. Depending on the duration of the sampling period, specific signals in excess of 2 V have been obtained for 0.01 units of catalase (approximately 0.4 ng of protein). Development and use of this sensing apparatus will be described for both competitive and sandwich immunoassays.