Fabrication and characterization of all-covalent nanocomposite functionalized screen-printed voltammetric sensors

•Screen printed electrodes were covalently functionalized by gold nanoparticles.•The covalent grafting of AuNPs was achieved via diazonium salt chemistry.•Two grafting methods and two types of AuNPs were compared.•Carboxylate ligands were grafted on these nanostructured electrodes.•Good preliminary responses towards lead analysis were obtained by SW-ASV.

We report in this paper an all-covalent method to obtain highly nanostructured carbon screen printed electrodes (SPEs) bearing gold nanoparticles (AuNPs) functionalized by complexing groups using diazonium salts chemistry. SPEs were first modified with 4-aminophenyl functions (SPE-Ph-NH2). The amino moieties were then converted into diazonium salts (SPE-Ph-N2+ Cl−). These reactive SPEs were then used to immobilize AuNPs by electrochemical or spontaneous method. The spontaneous method proved to be a more efficient grafting approach. Two types of AuNPs suspensions were compared: AuNPs obtained via the well-known Turkevich method, citrate-stabilized and having a diameter of about 20 nm, and AuNPs obtained by the method recently described by Eah et al., stabilizer-free with an average diameter of 4 nm. We show that the size of the Au-NPs, their concentration and their surface properties are key parameters that affect the electrochemical properties of the final nanostructured SPEs. The covalent grafting of 4-carboxyphenyl ligands through diazonium chemistry, able to complex metallic cations, at the surface of SPE-Ph-AuNPs allowed their use for the detection of Pb(II). Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, Scanning Electron Microscopy, Rutherford Backscattering and X-ray Photoelectron Spectroscopy were used to characterize these nanostructured materials.