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Compared to enzymes, Au nanocatalysts show better long-term stability and are more easily prepared. Au nanoparticles (AuNPs) are used as catalytic labels to achieve ultrasensitive DNA detection via fast catalytic reactions. In addition, magnetic beads (MBs) are employed to permit low nonspecific binding of DNA-conjugated AuNPs and to minimize the electrocatalytic current of AuNPs as well as to take advantage of easy magnetic separation. In a sandwich-type electrochemical sensor, capture-probe-conjugated MBs and an indium-tin oxide electrode modified with a partially ferrocene-modified dendrimer act as the target-binding surface and the signal-generating surface, respectively. A thiolated detection-probe-conjugated AuNP exhibits a high level of unblocked active sites and permits the easy access of p-nitrophenol and NaBH 4 to these sites. Electroactive p-aminophenol is generated at these sites and is then electrooxidized to p-quinoneimine at the electrode. The p-aminophenol redox cycling by NaBH 4 offers large signal amplification. The nonspecific binding of detection-probe-conjugated AuNPs is lowered by washing DNA-linked MB-AuNP assemblies with a formamide-containing solution, and the electrocatalytic oxidation of NaBH 4 by AuNPs is minimized because long-range electron transfer between the electrode and the AuNPs bound to MBs is not feasible. The high signal amplification and low background current enable the detection of 1 fM target DNA.

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We present a facile and simple method to synthesize a thin layer of platinum on gold as Au@Pt core−shell nanoparticles on the surface of reduced graphene oxide (rGO) via Cu under potential deposition (UPD) followed by galvanic Pt replacement reaction. The difference in the reduction potential is the driving force for the reaction where Pt 4+ ions reduced and deposited simultaneously on the surface of Au by replacing the Cu surface. The as synthesized catalyst was characterized by scanning electron microscope (SEM), energy dispersive X-ray mapping analysis (EDAX), high resolution transmission electron microscope (HRTEM), High angle annular dark-field scanning/transmission electron microscopy (STEM-HAADF), X-ray diffraction (XRD), Raman spectroscopy and electrochemical studies. It exhibits an excellent electrocatalytic activity towards methanol and ethanol oxidation in alkaline medium due to enhanced mass and specific activities. Galvanic replacement method paves an important role in the architecture of a thin layer of Pt on Au surface. On the other hand, rGO surface acts as a solid