The detection and quantification of heavy metals in the environment are of great importance, due to their high toxicity and their lifetime in soil, air and groundwater. The detection techniques already available are very expensive and difficult to implement. Therefore, there is a real need to develop new detection schemes that are rapid, simple, sensitive and low cost. Electrochemical sensors based on modified surfaces with recognition probes meet these criteria for a fast and easy analysis [1
], and they are likely to be miniaturised to allow the development of detection equipment capable of operating directly on site. These devices could then complete or even replace the existing conventional techniques.
Surface modification by immobilisation of organic molecules is a very important step and search of new methods is constantly developing [3
]. The molecular structure, the homogeneity of the layer, the surface density, bonds stability and processes reproducibility are parameters that determine the performance of subsequent applications of these modified surfaces and therefore, must be perfectly controlled.
Furthermore, the choice of the appropriate ligands to be immobilised on the electrode surface is a crucial issue. The majority of work in this field involves a tedious synthesis of selective macrocyclic ligands for a target metal [5
]. In nature however, metal binding is achieved with high degree of selectivity using peptide motifs [6
The known works in this area refer to the immobilisation of peptides on a gold electrode [7
]. However, the peptide ligands were self-assembled on the surface via a moderately strong gold-sulphur bond. These monolayers are kinetically labile when exposed to moderate temperatures, a chemical attack or application of a potential [9
]. Covalent attachment of monolayers on silicon surface through the formation of silicon-carbon bond is an attractive route, since it offers the best performances in terms of robustness and can be made reproducible, with a high yield [10
]. In this framework, the advances performed in silicon surface chemistry allowed for attaching functional groups upon demand [11
]. Generally, the surface functionalization requires a multi-step reaction scheme [13
]. In addition, the use of porous silicon substrates, allowing for an increased surface interaction area, can enhance the detection signal significantly.
Cyclic voltammetry is an efficient method used extensively to study metal ions complexed to electrodes modified by ligands [15
]. Parallel to experimental investigations, theoretical studies have been developed to predict and interpret the electrochemical behaviour of this new type of electrodes [17
In this work, Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis)-modified PSi was prepared by anchoring the peptide on a carboxyl-terminated PSi surface using N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling agents. Electrochemical behaviour of such prepared electrodes was carried out in the presence of copper ions by means of cyclic voltammetry. Electrochemical parameters were determined as well.