Anupam Yadav1 Richa Pandey2 Ting-Wei Liao1 Kuo-Juei Hu1 Didier Grandjean1 Peter Lievens1 Yosi-Shacham Diamand2

1, KU Leuven, Leuven, , Belgium
2, Tel Aviv University, Tel Aviv, , Israel

A novel biosensor for the ultra-sensitive electrochemical detection of para(p)-aminophenol based on an array of size selected Au clusters deposited on Fluorine doped Tin Oxide (FTO) was produced using a novel magnetron cluster beam deposition (CBD) setup equipped with a particle size-selector. Detailed characterization of the structural and electrochemical properties of the biosensor was performed by a combination of aberration-corrected Scanning Transmission Electron Microscopy (STEM), Scanning Electron Microscope (SEM), Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry.
The fabrication process of the Au-cluster based biosensor is carried out under ultra-high vacuum conditions and involves the production of metal particles in the gas-phase through gas borne aggregation of sputtered gold atoms from a pristine metal target. Next, the formed charged clusters are size-selected (2.5-3.5 nm) based on their kinetic energy using a quadrupole size selector and deposited at a typical coverage of 1 atomic monolayer (~10Λ15 atoms/cm2) on FTO supports. Unique surface modification of FTO by an array of isolated and monodisperse Au clusters with 3.1±0.3 nm size was confirmed by electron microscopy. EIS study reveals that controlled immobilization of these surfactant free Au clusters efficiently decreases the electron exchange resistance between the analyte and bare FTO from 43.12 Ohms to 29.65 Ohms. Cyclic Voltammetry measurements demonstrate the excellent redox activity of Au-cluster modified FTO that is capable of oxidizing para-aminophenol at 0.14 V compared to 0.67 V for bare FTO. This novel biosensor enables the ultra-sensitive electrochemical detection of para-aminophenol in a concentration range of 10 to 80 µg ml-1 with a detection limit of 404 ng ml-1(S/N = 3).

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 607417 (Catsense).