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.