Ion-Partitioning Bulk Membrane CHEMFET as Highly Sensitive Calcium Probe

The development of a novel, highly sensitive calcium CHEMFET‐based sensor system is presented. The CHEMFET utilizes a bulk phase ion‐partitioning membrane as the chemical recognition element while the signal transduction is achieved via a pH‐ISFET. The ion‐partitioning membrane is doped with two different ionophores, one selective to calcium, and the other to protons. Calcium ions partitioned into the bulk of the membrane phase will displace protons of equal charge out of the membrane for electroneutrality reasons, and towards the pH‐ISFET's gate, generating the observed signal. It is shown that the increase of the calcium to proton carrier concentration ratio in the membrane phase, the use of a strong calcium ionophore, and a weak proton carrier contribute to the increase of the sensor sensitivity. The performance of the optimized Ca‐CHEMFET is evaluated by the successful determination of the free calcium ion activity in blood serum samples.