Electrochemical and spectroscopic properties of dendritic cobalto-salicylaldiimine DNA biosensor

A metallodendrimer-based electrochemical DNA biosensor was constructed by a layer-by-layer assembly of cobalt(II) salicylaldiimine metallodendrimer (SDD-Co(II)) and a 21 bases oligonucleotide NH2-5'-GAGGAGTTGGGGGAGCACATT-3' (pDNA) on a gold electrode. The complementary oligonucleotide was 5'-AATGTGCTCCCCCAACTCCTC-3' (tDNA). UV-visible spectra of SDD-Co(II) in 1:1 (v/v) acetone-ethanol solution showed absorption bands at 325 nm and 365-420 nm related to pi-pi* intra-dendrimer transitions and d-pi* metal-dendrimer charge transfer transitions, respectively. Square-wave voltammetry (SWV) characterisation of the Au vertical bar SDD-Co(II)vertical bar pDNA biosensor system in phosphate buffer saline solution of pH 7.4, indicated a reversible one-electron electrochemical process with a formal potential, E degrees', value of +210 mV. Electrochemical impedance spectroscopy (EIS) data confirmed that the hybridisation of the biosensor's pDNA with the tDNA to form double-stranded DNA (dsDNA) resulted in an increase of the impedimetric charge transfer resistance, R-ct, value from 6.52 to 12.85 k Omega. The limit of detection (LOD), calculated as 3 sigma of the background noise, and sensitivity of the sensor were 1.29 k Omega/nmol L-1 and 0.34 pmol L-1, respectively. (C) 2009 Elsevier Ltd. All rights reserved.