Porosity effect of ion-exchange polymers on the performances of electroanalytical sensors

In the last couple of decades, electrode coatings based on proton conducting polymers were extensively adopted in the electroanalytical field for the preparation of modified electrodes to be used as more performing sensors. In fact, these devices offer several advantages: they reduce adsorption phenomena, suppress the inclusion of interfering species, protect the electroactive surface from passivation and fouling, act as pre-concentrating agents towards selected analytes, modify the process kinetics and diffusion yielding high sensitivity and selectivity [1-3]. Commercially available polymers most currently found in the literature as electrode modifiers are Nafion®, Eastman AQ55® (both cation-exchange polymers), and Tosflex® (anion-exchange polymer). Among them, Nafion® is the most widely adopted ion-exchange polymer, founding many diverse electroanalytical applications although initially developed for fuel cell membranes. Scarce use of other polymers was present in the Literature. In this context, in this presentation we would like to show some results on the use of sulphonated poly(aryl ether sulphone) (SPAES), an innovative polymer in this field, whose properties can be appropriately designed, tailored and used as electrode modifier for electroanalytical applications. Since connectivity and morphology of the modifier polymer are critical factors in controlling conductivity, stability, active surface and diffusion mechanism of the modified electrode, much attention was devoted to the polymer casting conditions and procedure on the glassy carbon support electrode. Four solvents, characterized by different boiling points and polarity were tested: dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP). In the case of NMP a better membrane organization, probably allowing a thin layer diffusion mechanism or a preconcentration step, appears to be responsible for the increased peak currents. Moreover, since the effect of polymer porosity seems to play a crucial role in electroanalytical performances, particularly modifying the absorption and pre-concentration of the analyte or its diffusion mechanism (from planar to convergent or to thin-layer [4-5]), an ad hoc study was performed considering different modified electrodes obtained by electrospinning a PLLA polymer in different structures. Three types of porous layers were obtained (nanometric (300-600 nm), micrometric (2-4 μm) and meso/microporous micrometric (2-5 μm)) in three different thickness. The results show a strong effect of mesoporosity in the enhancement of the CV peak height, which is fully consistent with a thin-layer model diffusion mechanism inside the porous structure. This evidence confirms Literature theoretical and experimental data on electrodes modified with carbon nanotubes [5-6]. Acknowledgements This work has been supported by MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca) in the framework of the PRIN 2012 Project (20128ZZS2H). References [1] G. Inzelt, M. Pineri, J. Schultze, M. Vorotyntsev, Electrochim. Acta 45, 2000, pp 2403–2421. [2] P. Ugo, L.M. Moretto, F. Vezzà, Chem. Phys. Chem. 3, 2002, pp 917–925. [3] C. Gouveia-Caridade, C. Brett, Strategies, Curr. Anal. Chem. 4, 2008, pp 206–214. [4] I. Streeter, R. Baron, R.G. Compton, J. Phys. Chem. C 111, 2007, pp 17008–17014. [5] M.C. Henstridge, E.J.F. Dickinson, M. Aslanoglu, C. Batchelor-McAuley, R.G. Compton, Sensors Actuators B Chem. 145, 2010, pp 417–427. [6] V. Pifferi, G. Cappelletti, C. Di Bari, D. Meroni, F. Spadavecchia, L. Falciola, Electrochim. Acta 146, 2014, pp 403-410.