Improving the design of ion track-based biosensors

In the last decade we had developed new types of biosensors, by cladding the inner walls of transparent etched swift heavy ion tracks in thin polymer foils with enzymes. The enzymatic reaction products of appropriate analytes penetrating into narrow tracks are enriched in the track’s confinement, and they change the electrical track properties if their charge states differ from those of the analytes. It was yet unknown how to design these sensors so that their best efficiency and highest possible sensitivity is achieved. This requires the accurate knowledge of the optimum track radius and the degree of product enrichment within the tracks. These questions were answered by appropriate experiments described here. The above studies restricted to transparent tracks only. After it became evident that also thin membranes can be formed within such tracks – thus separating transparent tracks into two adjacent semi-transparent segments each – we were curious in how far such structures might also become useful as sensors. In fact, two promising approaches emerged, one that uses these structures as polarization-induced capacitive biosensors, and another one that considers the semitransparent track segments as neighboring “electrostatic bottles” which can be discharged by pulse-wise product emission. Preliminary results indicate that the latter sensor type is superior in its performance to all other ones.