Photo-renewable electroanalytical sensor for neurotransmitters detection: The role of silver ion nanoparticles

A sandwich-like structure electrode of silver nanoparticles embedded in a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. In comparison with literature data on bare silver nanoparticles-modified electrodes [3-5], the new device features a pronounced electrocatalytic effect on the silver oxidation peak together with a great increase in the current intensity (Figure a). 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 were found to gain a partially positive charge [7], quickly decreasing with the distance from the TiO2 surface. These joint theoretical and experimental studies demonstrated that the device could be considered as a “charged silver nanoparticles-based electrode”, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure was found to be of a highly convenient use for sensor applications. As a proof-of-concept, this device performed efficiently for the determination of neurotransmitters such as dopamine, norepinephrine and serotonin in simulated biological matrices (liquor, serum and urine). Moreover, this optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 µM, which makes it appealing for clinical purposes), but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids). Furthermore, the fouling of the electrode surface, typical which is unavoidable for this kind of analytes, could be easily overcome by irradiating the device with UVA-light, which restored the initial sensor sensitivity. This feature allows the possibility to reactivate the sensor on site, i.e. directly in solution, to yield a system capable of working in continuous, able to be used in an integrated monitoring system. 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. Acknowledgements This work has been supported by Fondazione Cariplo (Milano, Italy), grant no. 2014-1285. We acknowledge the CINECA and the Regione Lombardia award under the LISA initiative (grant SURGREEN) for the availability of high performance computing resources. We also thank the Chemistry Department for funding through the Development Plan of Athenaeum grant – line B1 (UNIAGI 17777).