Silver cations electroanalytical sensor: sensitivity and selectivity iIn the detection of neurotransmitters

A composite electrode with a sandwich structure combining the properties of silver nanoparticles and a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. A pronounced electrocatalytic effect was observed along with a great increase in the current intensity of the silver oxidation peak (Figure 1). Results are compared with literature data on bare silver nanoparticles [3-5]. Theoretical DFT calculations, performed using the VASP code [6], described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor gain a partially positive charge [7], which quickly decreases with the distance from the TiO2 surface. This joint theoretical and experimental study allows us to conclude that the device could be considered as a “silver cations electrode”, with silver ions protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure can be conveniently used for sensor applications. For example, we successfully applied our device for the determination of neurotransmitters such as dopamine, norepinephrine and serotonin in simulated biological matrices (liquor, serum and urine). Our optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 µM) but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids). Moreover, the device shows under UV light self-cleaning properties of its titania overlayer, with complete removal of fouling, originated by the chemisorption of analytes and byproducts. Irradiating the device with UVA light, the initial sensor sensitivity was restored, making it reusable and suggesting its employment in integrated monitoring systems. 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. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, pp 1486 – 1494. [2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances 5, 2015, pp 71210 – 71214. [3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc. 132, 2010, pp 70–72. [4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B 109, 2005, pp 1204-1209. [5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C 112, 2008, pp 17820–17827. [6] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter 59, 1999, pp 1758−1775. [7] W. Tang, E. Sanville, and G. Henkelman, J. Phys. Condens. Matter 2009, 21, 084204.