Patent ID: 7538538

Claim:
A method of operating an electrical chemical sensing unit using a silicon semiconductor field effect device having an N-type silicon semiconductor channel having a first channel width and extending a first channel length between and electrically coupled to first source and drain terminals, a gate region formed by depositing a gate insulator in alignment with and over the N-type silicon semiconductor channel, an organic semiconductor field effect device having a P-type organic semiconductor channel deposited on the gate region over a portion of the first channel length of the N-type silicon semiconductor channel and extending a second channel length between and electrically coupled to second source and drain terminals, wherein a surface of the organic semiconductor channel is exposed to the ambient environment, and circuitry for selectively applying voltage potentials to at least the first source and drain terminals and the second source and drain terminals in response to program commands comprising, in the following order, the steps of: a) measuring a first channel current of the N-type silicon semiconductor channel by applying a potential difference between the first source and drain terminals while applying a second voltage potential to the second source and drain terminals; b) charging the organic semiconductor channel by applying a first positive voltage potential to the second source and drain terminals and the second voltage potential to the first source and drain terminals; c) measuring a second channel current of the N-type silicon semiconductor channel by applying a third voltage potential between the first source and drain terminals while applying the first positive voltage potential to the second source and drain terminals; d) applying an analyte to be measured to the surface of the organic semiconductor channel, thereby trapping holes in the organic semiconductor channel by electrostatic coupling; e) stopping the application of the analyte to the surface of the organic semiconductor channel thus releasing analyte from the surface while retaining some trapped charges; f) measuring a third channel current of the N-type silicon semiconductor channel by applying the third voltage potential between the first source and drain terminals with no bias applied; g) calculating the difference between the third and first channel currents as a delta current; and h) correlating the delta current to predetermined measurement data of delta current as a function of analyte concentration.