| dc.description.abstract | This thesis details the synthesis and characterisation of seven osmium and ruthenium
bipyridyl complexes, reports on their electrochemical characteristics and outlines an
application for one of the synthesised complexes in an electrochemical DNA biosensor.
Complexes synthesised included cis-bis(2,2-bipyridine-N,N)dichlororuthenium, cis-bis(2,2-
bipyridine-N,N)dichloroosmium, [Os(bpy)2-(4 -tetrazine)-Cl](PF6), [Ru(bpy)2(4 -tetrazine)-
C1](PF6), [Os(bpy)2-(pyridine-4-COOH)-Cl](PF6), [Ru(bpy)2-(pyridine-4-COOH)-Cl](PF6),
Ru(bpy)2(4-tetrazine)2(PF6)2- Diffusion coefficients determined using a glassy carbon
electrode ranged from 1.51 x 10' to 3.28 x 10' cm s' for the osmium complexes and from
c c ^ 1 2.39 x 10' to 4.76 x 10“ cm s" for the ruthenium complexes. Using the Laviron approach,
solution phase electron transfer rates ranged from 0.29 cm s' 1 for [Os(bpy)2-(4-tet)-Cl](PF6)
to 1.61 cm s' 1 for Ru(bpy)2(4-tet)2(PF6)2* Self assembled monolayers of [Os(bpy)2-(4-tet)-
C1](PF6)> [Ru(bpy)2-(4-tet)-Cl](PF6) and Ru(bpy)2(4-tet)2(PF6)2 formed spontaneously on
platinum electrodes and electron transfer rate constants were determined as 9.0 x 103, 5.7 x
103 and 1.4 x 104 s_1 respectively. Monolayers of [Os(bpy)2-(pyridine-4-COOH)-Cl](PF6)
and [Ru(bpy)2-(pyridine-4“COOH)-Cl](PF6) were formed on gold electrodes in a two-step
assembly and the former complex shown to spontaneously adsorb on indium tin oxide.
Complexes adsorbed by the two-step assembly exhibited much reduced electron transfer rate
constants for example 33.86 s' 1 for [Os(bpy)2-(pyridine-4-COOH)-Cl](PF6). Rates of
adsorption on platinum were determined in-situ and closely followed Langmurian adsorption
and first order adsorption kinetics. Adsorption rate constants determined for complexes
where adsorption occurred on a single site ranged from 14.30 ± 4.35 M 1 s' 1 for [Os(bpy)2-(4-
tet)-Cl](PF6) to 30.93 ± 9.15 M' 1 s' 1 for Ru(bpy)2(4-tet)2(PF6)2. Rates of desorption followed
first order kinetics for the complexes investigated and desorption rate constants ranged from
2.33 x lO 'V to 5.66 x 10'5s \
In a further two-step assembly procedure, a 5’ thiolated hairpin ssDNA probe specific to the
bacterial genus Salmonella spp.: 5’ SH-(CH2)6- GCA GTA AC A AGA ATA AAA CGC
ACT GC- (CH2)6- NH2 3’ was immobilised on a gold electrode surface and then [Os(bpy)2-
(pyridine-4-COOH)-Cl](PF6) coupled to the amine group at the 3* end using carbodiimide
coupling. This DNA biosensor was capable of hybridisation detection in the presence of a
complementary sequence due to the conformational change in hairpin structure. This is the
first report of the use of a covalently attached osmium bipyridyl complex as a redox label for
the purpose of hybridisation detection. | en |
