New Direct Competition Free but Not Label Free Immunosensor Method for IgG Determination

In the last few years we fabricated several competitive immunosensors for the analysis of IgG proteins [1-7]. In the present study, to reduce the excessively long time required for each competition measurement, we developed an innovative “direct” immunosensor method for IgG determination. Of course other immunosensors for the direct measurement of several different antigens have already been described in the literature [8-13]; these devices usually do not involve any “competition” procedure and generally do not make use of a marker, because in these probes the signal is often obtained directly as a result of immunocomplex formation (which may, for example, be a cause of potential variation in the membrane). These devices are usually unsuccessful for various reasons (low signal, high noise and scarce selectivity) even though they afford a considerable reduction in analysis time. Nevertheless, we recently resumed studies on direct immunosensor types as part of research conducted on new electrochemical “competition free” immunosensors developed for the analysis of other proteins [14,15] and designed to perform measurements using different operating schemes. In the latter case, however, unlike what is usually reported in the literature for this kind of immunosensor, an enzymatic marker was again used to perform the electrochemical measurement while the transducer used was of the classic amperometric type [14,15]. In the present research a slightly different approach, although of the same type, was used for the measurement of IgG, while the electrochemical transducer was of the potentiometric type. The new geometry of the direct method selected by us was also discussed on the basis of several different label free immunosensor methods reported in the literature.