Sensing apparatus and method

1. A sensing apparatus comprising two ion sensitive field effect transistors, which are arranged to generate an electrical output signal in response to a chemical reaction to which the transistors are exposed and means for discriminating discrete fluctuation in the electrical output signal, the discrete fluctuations indicating reaction intermediaries occurring during the chemical reaction, a first of the transistors being provided with an enzyme linked layer and a second of the transistors being provided with a non-enzyme linked layer; and said apparatus further comprising means for determining the difference between the electrical signals generated by said first and second transistors to provide said electrical output signal.

2. The sensing apparatus according to claim 1 , wherein said first and second transistors are connected to first and second operational amplifiers, and the outputs of the operational amplifiers are passed to a differential amplifier which provides the electrical output signal.

3. The sensing apparatus according to claim 2 , wherein the electrical output signal is passed to an electrode located in the reagent mixture, to maintain voltages applied to said first and second transistors at a constant level.

4. The sensing apparatus according to claim 2 or claim 3 , wherein said and second transistors are arranged to form part of the first and second operational amplifiers respectively.

5. The sensing apparatus according to claim 1 , wherein said two ion sensitive field effect transistors are both PMOS transistors arranged to operate in the weak inversion region.

6. The sensing apparatus according to claim 1 , wherein said two ion sensitive field effect transistors are both NMOS transistors arranged to operate in the weak inversion region.

7. The sensing apparatus according to claim 1 , wherein the apparatus is configured to generate an electrical output signal in response to ion consumption or ion liberation.

8. The sensing apparatus according to claim 1 , wherein said first and second ion sensitive field effect transistors are provided with a layer of silicon nitride.

9. The sensing apparatus according to claim 1 , wherein the enzyme of said enzyme-linked layer is provided over a layer of silicon nitride.

10. The sensing apparatus according to claim 1 , wherein said first and second ion sensitive field effect transistors are provided as part of an integrated circuit which is substantially covered by epoxy resin and the field effect transistors are not covered by the epoxy resin.

11. The sensing apparatus according to claim 1 , wherein the enzyme-linked layer comprises polymerase.

12. The sensing apparatus according to claim 11 , wherein said chemical reaction to be detected is nucleotide chain extension, the enzyme of said enzyme-linked layer comprises polymerase and the insertion of a di-deoxynucleotide triphosphate (ddNTP) at the end of the chain is detected.

13. The sensing apparatus according to claim 11 , wherein the chemical reaction to be detected is DNA synthesis, the enzyme of said enzyme-linked layer comprises a polymerase and the discrete fluctuations in electrical signal indicate the insertion of one or more deoxynucleotide triphosphates (dNTPs) or termination of DNA synthesis by insertion of a di-deoxynucleotide triphosphate (ddNTP).

14. The sensing apparatus according to claim 13 which further comprises monitoring means arranged to monitor the time at which the discrete fluctuations occur and the magnitude of the discrete fluctuations to allow sequencing of DNA or mRNA.

15. The sensing apparatus according to claim 1 which is configured to generate the electrical output signal in response to a pyrophosphate hydrolysis reaction.