Silver nanoparticles/nanostructured TiO2 interface: a photo-renewable “silver-ions electrode” for neurotransmitters detection

Silver nanoparticles were embedded in a TiO2 (anatase polymorph) photoactive layer in a sandwich-like nanostructured electrode. [1-2] The device was (photo)electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. In comparison with literature data on electrodes modified with silver nanoparticles [3-5], the new sensor presents a pronounced electrocatalytic effect on the silver oxidation peak together with a great increase in the current intensity. Parallel plane-wave 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 anatase polymorph. The silver atoms close to the semiconductor were found to gain a partially positive charge, quickly decreasing with the distance from the TiO2 surface. Comparing the theoretical and experimental results it could be concluded that the device may be considered as a \u201cpositively charged silver nanoparticles-based electrode\u201d, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge. The final sensor performed efficiently in the electroanalytical determination of some neurotransmitters (e.g. dopamine, norepinephrine and serotonin) in simulated biological matrices (liquor, serum and urine). The optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 \ub5M, 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). Last but not least, the fouling and passivation of the electrode surface, an unavoidable drawback during the detection of this kind of analytes, could be easily overcome by irradiating the device with UVA-light, which restored the initial sensor sensitivity. The photo-renewability allows 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), 1486 \u2013 1494. [2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances, 5, (2015), 71210 \u2013 71214. [3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc., 132, (2010), 70\u201372. [4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B, 109, (2005), 1204-1209. [5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C, 112, (2008), 17820\u201317827. [6] G. Kresse, J. Furthm\ufcller, Phys. Rev. B, 54:11169, (1996). 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 \u2013 line B1 (UNIAGI 17777)