Electrocatalytic and bioelectroanalytical system based on metal deposition

Abstract

The underpotential deposition of silver and lead on Au(111) is performed sequentially to produce a thin composite layer. Ag was deposited underpotentially in 1 mM $Ag_2SO_4$ and 0.1 M $H_2SO_4$ at 0.400 V and 0.005 V vs Ag wire. Cyclic Voltammetry (CV) on this Ag/Au(111) electrode in $Pb^{2+}$ electrolyte with 0.1 M $HClO_4$ exhibited contributions of both Au and Ag substrates and in-situ STM images show unusual multilayer morphology of Pb upd on Ag/Au(111). CV demonstrated the stability and existence of Ag adlayer in $Pb^{2+}$ electrolyte. In the presence of sodium nitrate, this composite system shows the catalytic effect for nitrate reduction which is not observed in Au(111), Ag/Au(111), Pb/Au(111), Ag(111) and Pb/Ag(111) alone. All results demonstrate that the Ag-Pb/Au(111) composite system has the enhanced catalytic effect for nitrate reduction. We demonstrate the amplified detection of a target DNA based on the enzymatic deposition of silver. In this method, the target DNA and a biotinylated detection DNA probe hybridize to a capture DNA probe tethered onto a gold electrode. Neutravidin-conjugated alkaline phosphatase (Av-ALP) binds to the biotin of the detection probe on the electrode surface and converts the nonelectroactive substrate of the enzyme, p-aminophenyl phosphate (p-APP), into the reducing agent, p-aminophenol (p-AP). The latter, in turn, reduces metal ions in solutions leading to deposition of the metal onto the electrode surface and DNA backbone. This process, which we term biometallization, leads to a great enhancement in signal due to the accumulation of metallic silver by a catalytically generated enzyme product, and thus the electrochemical amplification of a biochemically amplified signal. The anodic stripping current of enzymatically deposited silver provides a measure of the extent of hybridization of the target oligomers. This biometallization process is highly sensitive, detecting as little as 100 aM (10 zmol) of DNA. We also success...