Ultrasensitive electrochemical detection of DNA hybridization using Au/Fe3O4magnetic composites combined with silver enhancementElectronic supplementary information (ESI) available: the distribution of diameter of Fe3O4/PSS/PDDA/Au composites using DLS method; LSV recorded at a GC electrode for the determination of Ag誉. The calibration plots of the determination of Ag誉. Effect of the dilution ratio of Fe3O4/PSS/PDDA/Au–probe 2 conjugate upon the anodic stripping peak current. See DOI: 10.1039/b923847f

A novel method is described for the highly effective amplifying electrochemical response of DNA based on oligonucleotides functionalized with Au/Fe3O4nanocomposites by the aid of silver (Ag) enhancement. Viaelectrostatic layer-by-layer (LBL) assembly, the prepared Fe3O4nanoparticles form nano-clusters coated with a bilayer composed of polystyrene sulfonate sodium salt (PSS) and poly(diallyldimethylammonium chloride) (PDDA), which are in favor of adsorbing lots of gold nanoparticles (AuNPs) on the surface. The application of magnetic Fe3O4made the procedures much more simple, convenient and feasible. The resulting composites were then used as labels viathe Au–S bond for the DNA hybridization, followed by catalytic deposition of silver on the gold tags. Such an assay is then combined with a sensitive anodic stripping voltammetry (ASV) measurement of multiple silver nanoparticle tracers. A 27-mer sequence DNA target is detected at a glassy carbon (GC) electrode with a detection limit down to ca.100 aM, which is 800 times lower than that obtained using gold nanoparticles only as labels in the control experiments. This Fe3O4/PSS/PDDA/Au composite offers a great promising future for the ultrasensitive detection of other biorecognition events. [ABSTRACT FROM AUTHOR]