Competitive Immunological Detection of Progesterone by Means of the Ion-step Induced Response of an ImmunoFET

The ion-step method was originally designed to measure immunoreactions via the change in charge density which occurs in an antibody loaded membrane, deposited on an ISFET, upon reaction with a charged antigen. In this paper we show the possibility of detecting an immunoreaction involving a non-charged antigen, progesterone, by using competitive binding of progesterone and a charged progesterone-lysozyme conjugate in the membrane. Both the immunoreaction and the non-specific binding could unequivocally be measured. The detection limit was approximately lo-* M of progesterone in the sample solution. This proves that the ion-step method is suitable for detection of both charged and non-charged antigens. tions can be determined, provided they cause a change in charge density in the membrane. Details of the detection method are described by Schasfoort et al. [ 1, 21. The purpose of this paper is to show an application of the ion-step method to an immunochemical model system, in which the analyte is uncharged. As a model system we have chosen the immunological reaction between progesterone and anti-progesterone. As before, the antibody is incorporated in the membrane which is deposited on an ISFET. Progesterone is an uncharged molecule, so it cannot be detected directly by using the ion-step method. However detection can Introduction Potential generation Recently we introduced a new method to operate an immunological field-effect transistor (an ImmunoFET) by detecting a change in charge density in a membrane, deposited on an ISFET, resulting from an immunological reaction [ 11. Transient potentials can be measured, arising from transient transport of ions across the membrane, which are caused by stepwise changes in electrolyte concentration (an ion-step) (see Fig. 1). Ta, OS SiO,