SAMs & EDMs OF THIOLS ON Au BY EIS AND AFM


Self-Assembly is a spontaneous process in which organic molecules (alkanethiols, silanes) are chemisorbed on a 2D substrate (gold, glass, silicon, ceramic materials as Al2O3, TiO2, ZnO2 et cetera) forming a highly ordered monolayer architecture.

Self Assembled Monolayers (SAMs) of thiols are building elements (nanoLego’s, Fig.1) for (bio)sensors designed to detect analytes as well as Hg(0), Hg(II), ochratoxin-A, E.coli. Although the implementation is extremely easy, an overnight treatment after cleaning of the substrate (Au electrodes) by cyclic voltammetry (CV), (insert in Fig.3,) is required. SAM are deposed not only on WE, but also on RE and AE.

Electrochemically Deposed Multilayers (EDMs) are commonly adopted in our labs for immobilisation of molecular structures in order to obtain (bio)sensors for several analytes (Fig.1). Constant potential drives thiols in proximity of a single AuWE (not AE or RE) in an array (Fig.2) allowing their reaction on the Au surface and forming an EDM in only 50s (Fig.3) instead of hours as for SAMs. Thiols as well as cysteamine (CYS) or 4-mercaptobenzoic acid (MBA) have been deposed as SAMs or EDMs on AuWEs. Both the layers have been studied with Electrochemical Impedance Spectroscopy (EIS) (Fig.4) and Atomic Force Microscopy (AFM) (Fig.5).

EDMs seem to be thicker (Fig.3) than SAMs. SAM shows Au electrodes poorly covered with a thinner film with holes where the bare Au electrode is exposed (poor electrochemical performances of further obtained biosensors). On the contrary the substrate covered with EDMs shows a higher and a more homogeneous and smooth surface (Fig.5, roughness parameters).

 

 

 

 

 

 

 

 

 

 

 

 

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