Electrochemical detection of substrates

1. A method for determining the presence or absence of a target substrate in a test sample comprising:

providing an electrode comprising:

a conductive surface, and

a probe that is bound to the conductive surface and is capable of binding to a target substrate;

contacting the conductive-surface bound probe with the test sample to form a surface bound target complex if the target substrate is present in the test sample, wherein the surface bound target complex further comprises a redox-catalyst complex that is capable of catalyzing an oxidation-reduction reaction;

contacting the surface bound probe or the surface bound target complex, if present, with a fluid medium comprising a redox transition metal complex that is capable of undergoing an oxidation-reduction reaction when the surface bound target complex comprising the redox-catalyst complex is present;

detecting the oxidation-reduction reaction of the redox transition metal complex that is at least in part catalyzed by the redox-catalyst complex; and

determining the presence or absence of the target substrate in the test sample from the detected oxidation-reduction reaction.

2. The method of claim 1 , wherein the redox-catalyst complex is covalently attached to the target substrate.

3. The method of claim 1 , wherein the electrode is contacted with the redox-catalyst complex after said step of contacting the conductive-surface bound probe with the test sample such that when the surface bound target complex is present, at least a portion of the redox-catalyst complex intercalates into the surface bound target complex.

4. The method of claim 1 , wherein the redox transition metal complex is of the formula:

[M(L) p X q ] m

wherein

m is an integer;

p is an integer from 1 to 6;

q is an integer from 0 to 5;

provided that the sum of p+q is such that M has no more than six binding sites;

M is a transition metal that can exist in at least two stable oxidation sates within the transition metal complex;

each X is a ligand independently selected from the group consisting of a halide, cyanide, pyridine and amine; and

each L is independently an optionally substituted aromatic ligand that comprises one, two or three coordinating atoms each of which is independently selected from the group consisting of nitrogen, oxygen, and phosphorous.

5. The method of claim 4 , wherein each L is independently selected from the group consisting of bipyridine, terpyridine, and phenanthroline, each of which is optionally substituted.

6. The method of claim 4 , wherein M is Co.

7. The method of claim 4 , wherein at least one of the aromatic ligand is substituted with a substituent having a steric bulk volume larger than a methyl group.

8. The method of claim 7 , wherein each L is independently selected from the group consisting of:

wherein

each of R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is independently hydrogen, alkyl, cycloalkyl, aryl, aralkyl, an ester moiety of the formula —CO 2 R 7 , an amide moiety of the formula —CONR 8 R 9 ;

R 7 is alkyl, cycloalkyl, aryl, or aralkyl; and

each of R 8 and R 9 is independently hydrogen, alkyl, cycloalkyl, aryl, or aralkyl; provided at least one of R 1 , R 2 , R 3 , R 4 , or R 5 in L(I), or at least one of R 1 , R 2 , R 3 , or R 4 in L(II), or at least one of R 1 , R 2 , R 3 , R 4 , R 5 , or R 6 in L(III) is a substituent having a steric bulk volume larger than a methyl group.

9. The method of claim 8 , wherein the redox transition metal complex is of the formula: [M(L(I)) 2 ] +m , [M(L(II)) 3 ] +m , or [M(L(III)) 2 ] +m , wherein M and m are those defined in claim 4 .

10. The method of claim 1 , wherein the redox-catalyst complex is of the formula:

[M 1 (L 1 ) a (X 1 ) b ] n   II

wherein

n is an integer;

a is an integer from 1 to 6;

b is an integer from 0 to 5;

provided that the sum of a +b is such that M 1 has no more than six binding sites;

M 1 is a transition metal that can exist in at least two stable oxidation sates within the transition metal complex;

each X 1 is a ligand independently selected from the group consisting of a halide, cyanide, pyridine and amine; and

each L 1 is independently an optionally substituted aromatic ligand that comprises one, two or three coordinating atoms each of which is independently selected from the group consisting of nitrogen, oxygen, and phosphorous, and wherein at least one of the aromatic ligand comprises a linker that is attached to a binding moiety that is capable of binding to a double stranded oligonucleotide.

11. The method of claim 10 , wherein M 1 is Ru, Fe, or Os.

12. The method of claim 10 , wherein at least one of L 1 is of the formula:

wherein

each m is independently an integer from 0 to 4;

each n is independently an integer from 0 to 3;

each of R 11 and R 13 is independently alkyl, or aryl;

each R 12 is independently C 1 -C 12 alkylene; and

each Z is an intercalating moiety that is capable of intercalating into a double stranded oligonucleotide.

13. The method of claim 12 , wherein m is 1.

14. The method of claim 12 , wherein R 11 is methyl.

15. The method of claim 12 , wherein m is 1.

16. The method of claim 12 , wherein n is 0.

17. The method of claim 10 , wherein the redox-catalyst complex is selected from the group consisting of Ru(dppz) 2 Cl 2 , Ru(dmb)(dpphz)Cl 2 , Os(dppz) 2 Cl 2 , Os(bpy) (dpphz)Cl 2 , Os(dpphz)(phen)Cl 2 , Os(dpdphphz)(phen)Cl 2 , [Os(phen)(dpphz)(py)Cl]PF 6 , and [Os(bpy)(dpdphphz)(py)Cl]PF 6 .