The power of three: Silica-Silver-Titania engineered sensors bearing photocatalytic self-cleaning features

Fouling and passivation are the main challenges faced during electroanalysis of complex matrices, especially those commonly encountered in the biomedical and environmental fields [1]. The production of highly engineered devices, designed ad hoc for specific applications, is the key factor in the direction of overcoming such problems and accessing effective sensors. A performant, reliable and reusable sensor, that could be cleaned simply by irradiation with UV light, would perfectly match this goal. We designed a three-layered transparent electrode, in which silver nanoparticles are embedded between a bottom silica and a top titania layer [2, 3]. Such structure equips the device with multifunctional properties for a complex biomedical challenge: the detection and quantification of catecholamine neurotransmitters. The crucial importance of each component to make our device a robust and efficient electroanalytical system was thoroughly investigated. The size distribution of silver nanoparticles, the device architecture and surface homogeneity were inspected by electron microscopy. The overlayer was made of anatase (the active polymorph of titanium dioxide) as confirmed by X-ray diffraction and by measuring the photodegradation of model contaminants. Electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy) revealed that an highly ordered distribution of silver nanoparticles is the active core of the device, allowing easier electron transfer and better quantification of the analytes even in the presence of typical interferents, e.g. ascorbic acid and uric acid. The high photoactivity of titania top layer allowed total recovery of the device performance in terms of sensitivity after a fast UV-A cleaning step. This self-cleaning property, combined with a remarkable resistance against aging, make our sensor also suitable for on-field applications.