Ion Sensitive Field Effect Transistors (ISFETs) for sensing change in ionic concentration in biological
systems can be used for detecting critical conditions like Myocardial Ischemia. Having the ability to yield
steady signal characteristics can be used to observe the ionic concentration gradients which mark the onset
of ischemia. Two ionic concentrations, pH and [K+], have been considered as the indicator for Myocardial
Ischemia in this study. The ISFETs in this study have an organic
semi-conductor film as the electronically
active component. Poly-3 hexylthiophene was chosen for its compatibility to the solution processing, which
is a simple and economical method of thin film fabrication. The gate electrode, which regulates the current in the active layer, has been employed as the sensor element. The devices under study here were fabricated on a flexible substrate PEN. The pH sensor was designed with the Tantalum Oxide gate dielectric as the ion selective component. The charge accumulated on the surface of the metal oxide acts as the source of the effecter electric field. The device was tested for pH values between 6.5 and 7.5, which comprises the variation observed during ischemic attack. The potassium ion sensor has got a floating gate electrode which is functionalized to be selective to potassium ion. The device was tested for potassium ion concentration between 5 and 25 mM, which constitutes the variation in extra cellular potassium ion concentration during ischemic attack. The device incorporated a monolayer of Valinomycin, a potassium specific ionophore, on top of the gate electrode.