Method and system for sensing

1. A system for detecting changes in an electrical property, comprising:

a sensing element comprising a transistor having a gate electrode and a semiconductor nanostructure connecting between a source electrode and a drain electrode and being modified by a functional moiety covalently attached thereto; and

a voltage source connected to said gate electrode;

a controller configured for controlling a gate voltage applied by said voltage source to said gate electrode such as to reverse a redox reaction occurring when said moiety contacts a redox reactive agent; and

a circuit for detecting changes in an electrical property of said nanostructure.

2. The system of claim 1 , wherein said functional moiety is a redox reactive moiety.

3. The system of claim 1 , wherein said functional moiety comprises at least one functional group capable of reversible change in an oxidation number or oxidation state of at least one of its atoms.

4. The system of claim 1 , wherein said functional moiety comprises a quinone.

5. The system of claim 2 , wherein said functional moiety comprises a quinone.

6. The system of claim 1 , wherein said functional moiety comprises an aromatic quinone.

7. The system of claim 2 , wherein said functional moiety comprises an aromatic quinone.

8. The system of claim 1 , wherein said functional moiety or comprises a functional group elected from the group consisting of quinone, benzoquinone, anhraquinone, and phenanthrenequinone, each being substituted or unsubstituted.

9. The system of claim 2 , wherein said functional moiety or comprises a functional group elected from the group consisting of quinone, benzoquinone, anhraquinone, and phenanthrenequinone, each being substituted or unsubstituted.

10. The system of claim 1 , wherein said electrical property comprises electron or charge density on a surface of said nanostructure.

11. The system of claim 2 , wherein said electrical property comprises electron or charge density on a surface of said nanostructure.

12. The system of claim 1 , wherein said nanostructure is a nanowire.

13. The system of claim 1 , wherein said semiconductor nanostructure comprises silicon.

14. The system of claim 1 , wherein said sensing element comprises at least one additional transistor having a nanostructure modified by a non-redox active moiety, wherein said detector circuit is configured to subtract signals received from said nanostructure modified by said redox active moiety, from signals received from said nanostructure modified by said non-redox active moiety.

15. The system according to claim 1 , being contained in a skin-attachable sticker.

16. The system according to claim 1 , being contained in a housing implantable in a living body.

17. A method of sensing metabolic activity in a living organism, comprising:

contacting the living organism with a sensing element comprising a transistor having a gate electrode and a semiconductor nanostructure connecting between a source electrode and a drain electrode and being modified by a functional moiety covalently attached thereto;

detecting changes in an electrical property of said nanostructure resulting from redox reaction occurring during said contact; and

applying gate voltage to said gate electrode so as to reverse said redox reaction.

18. The method according to claim 17 , wherein said gate voltage is selected to maintain a generally constant population of said functional moiety on said nanostructure.

19. The system according to claim 1 , wherein said gate voltage is constant.

20. The system according to claim 1 , wherein said gate voltage is from about −3 volts to about +3 volts.