US Patent 7544979 Ion concentration transistor and dual-mode sensors

An ion concentration sensor produces a signal reflective of the ion concentration within a solution. The ion concentration sensor is based on an ion sensitive transistor having a solution input, a reference input, a diffusion input, and a diffusion output. The ion sensitive transistor is connected as a pass transistor, such that the diffusion output provides an electrical signal indicating an ion concentration in a solution contacting the solution input.