METHODS FOR BONDING MOLECULES TO RUTHENIUM SURFACES
A bifunctional linker of general structure A-L-Z is used to covalently bond a bridge molecule to ruthenium electrodes in sensor circuits. The A group comprises a diazonium salt, a diazo group or a carbene precursor such as an imidazolium ring. L is a bivalent tether configured to adjust the spacing of Z from the ruthenium surface and to alter conductivity through the circuit. An end of the bridge molecule to be bonded to ruthenium through the linker is configured with a functional group that participates in a condensation reaction or click-chemistry with the Z group of the bifunctional linker.
1 . A sensor circuit comprising:
a pair of ruthenium electrodes comprising a first ruthenium electrode and a second ruthenium electrode spaced-apart from the first ruthenium electrode by a nanogap; and
a bridge molecule comprising a first reactive group RG A configured at or near a first end, and a second reactive group RG B configured at a second end, the bridge molecule electrically wired to each of the first and second ruthenium electrodes and spanning the nanogap;
wherein the first reactive group RG A is conjugated to a first reactive group Z 1 covalently bonded to the first ruthenium electrode through a first bivalent tether L, and the second reactive group RG B is conjugated to a second reactive group Z 2 covalently bonded to the second ruthenium electrode through a second bivalent tether L′.
2 . The sensor circuit of claim 1 , wherein the bridge molecule comprises a polypeptide, a protein, a protein fragment, a protein alpha-helix, DNA, RNA, a single-stranded oligonucleotide, a double-stranded oligonucleotide, a peptide nucleic acid duplex, a peptide nucleic acid-DNA hybrid duplex, an antibody, an antibody Fab binding domain, a carbon nanotube, a graphene-like polycyclic aromatic nanoribbon, other natural polymers, or (poly)thiophene.
3 . The sensor circuit of claim 1 , wherein RG A and RG B are independently selected from —CO 2 H, —NH 2 , —OH, —SH, —CH═CH 2 , —C≡CH, and —N 3 .
4 . The sensor circuit of claim 1 , wherein L and L′ are independently selected from —CH—; —(CH 2 ) y —; or —(CH 2 CH 2 O) y —, wherein y=1 to 25.
5 . The sensor circuit of claim 1 , wherein L further comprises a phenyl ring or substituted phenyl ring covalently bonded to the first ruthenium electrode.
6 . The sensor circuit of claim 1 , wherein L′ further comprises a phenyl ring or substituted phenyl ring covalently bonded to the second ruthenium electrode.
7 . A bifunctional linker configured to covalently bond a molecule to a ruthenium surface, the bifunctional linker molecule having a structure, A-L-Z, wherein:
X=Cl—, Br—, I—, BF 4 —, ClO 4 —, or (SO 4 2− ) 1/2 ;
Z=—CO 2 H, —NH 2 , —OH, —OC(O)C(CH 3 ) 2 —Br, —CH═CH 2 , —SH, —C≡CH or N 3 ;
L is a bivalent tether selected from -G-CH—; -G-(CH 2 ) y —; or -G-(CH 2 CH 2 O) y —, wherein y=1 to 25 and G is an optional aryl linkage —Ar—;
M=N or S, and E is a heterocycle selected from imidazole, imidazoline, thiazole, or triazole; and
R 1 and R 2 are independently selected from an electron pair, H, an aliphatic substituent, or an aryl substituent.
8 . The bifunctional linker of claim 7 , wherein A is a diazonium salt and Z is —CO 2 H, —NH 2 , —OH, —OC(O)C(CH 3 ) 2 —Br, —CH═CH 2 , —SH, —C≡CH or N 3 .
9 . The bifunctional linker of claim 7 , wherein A is a diazo group and Z is —CO 2 H, —NH 2 , —OH, —OC(O)C(CH 3 ) 2 —Br, —CH═CH 2 , —SH, —C≡CH or N 3 .
10 . The bifunctional linker of claim 7 , wherein A is an imidazolium ring and Z is —CO 2 H, —NH 2 , —OH, —OC(O)C(CH 3 ) 2 —Br, —CH═CH 2 , —SH, —C≡CH or N 3 .
11 . A method of forming a sensor circuit, the method comprising:
depositing a pair of ruthenium electrodes on a substrate, the pair of ruthenium electrodes comprising a first ruthenium electrode and a second ruthenium electrode spaced-apart from the first ruthenium electrode by a nanogap;
exposing the first ruthenium electrode to a bifunctional linker having a structure A-L-Z 1 to functionalize the first ruthenium electrode with a plurality of exposed Z 1 groups;
conjugating at least one exposed Z 1 group to a first reactive group RG A configured at or near a first end of a bridge molecule, the bridge molecule further comprising a second reactive group RG B configured at a second end of the bridge molecule;
exposing the second ruthenium electrode to a bifunctional linker having a structure A′-L′-Z 2 to functionalize the second ruthenium electrode with a plurality of exposed Z 2 groups; and
conjugating at least one exposed Z 2 group to the second reactive group RG B configured at or near the second end of the bridge molecule.
12 . The method of claim 11 , wherein:
A and A′ are independently,
X=Cl—, Br—, I—, BF 4 —, ClO 4 —, or (SO 4 2− ) 1/2 ;
Z 1 and Z 2 are independently selected from:
—CO 2 H, —NH 2 , —OH, —OC(O)C(CH 3 ) 2 —Br, —CH═CH 2 , —SH, —C≡CH, and N 3 ;
L and L′ are each a bivalent tether independently selected from -G-CH—; -G-(CH 2 ) y —;
or -G-(CH 2 CH 2 O) y —, wherein y=1 to 25 and G is an optional aryl linkage —Ar—;
M=N or S, and E is a heterocycle selected from imidazole, imidazoline, thiazole, or triazole; and
R 1 and R 2 are independently selected from an electron pair, H, an aliphatic substituent, or an aryl substituent.
13 . The method of claim 11 , further comprising a step of polarizing the first ruthenium electrode prior to exposing the first ruthenium electrode to a bifunctional linker having a structure A-L-Z′ such that the bifunctional linker covalently bonds to the first ruthenium electrode via electrochemical reduction.
14 . The method of claim 11 , further comprising a step of polarizing the second ruthenium electrode prior to exposing the second ruthenium electrode to a bifunctional linker having a structure A′-L′-Z 2 such that the bifunctional linker covalently bonds to the first ruthenium electrode via electrochemical reduction.
15 . The method of claim 11 , wherein the bridge molecule comprises a polypeptide, and RG A and RG B are independently selected from —CO 2 H, —NH 2 , —OH, —SH, —CH═CH 2 , —C≡CH, and —N 3 .