ORIGINAL PAPER Amperometric xanthine biosensors using glassy carbon electrodes modified with electrografted porous silica nanomaterials loaded with xanthine oxidase Maroua Saadaoui 1,2 & Alfredo Sánchez 2 & Paula Díez 2 & Noureddine Raouafi 1 & José M. Pingarrón 2,3 & Reynaldo Villalonga 2,3 Received: 17 January 2016 /Accepted: 20 March 2016 # Springer-Verlag Wien 2016 Abstract Glassy carbon electrodes were modified with silica materials such as silica nanoparticles, mesoporous silica nano- particles and mesoporous silica thin films with the aim to introduce scaffolds suitable for the immobilization of en- zymes. Xanthine oxidase was selected as a model enzyme, and xanthine as the target analyte. A comparison of the mod- ified electrodes showed the biosensor prepared with mesopo- rous silica nanoparticles to perform best. By using the respec- tive biosensor, xanthine can be amperometrically determined (via measurement of enzymatically formed hydrogen perox- ide) at a working voltage of 0.7 V (vs. Ag/AgCl) with a 0.28 μM detection limit. The biosensor was evaluated in terms of potential interferences, reproducibility and stability, and applied to the determination of fish freshness via sensing of xanthine. Keywords Mesoporous silica . Silica nanospheres . Electrografting . Field–emission scanning electron microscopy . Transmission electron microscopy . Hexacyanoferrate . Brunauer-Emmett-Teller Introduction Incorporation of nanomaterials into electrochemical biosen- sors allows achieving improved bioanalytical performances, enhanced catalytic effects and faster electron–transfer kinetics [1–3]. In particular, silica nanomaterials have been used in nanotechnological applications such as drug delivery [4, 5] and electrochemical sensing [6, 7] thanks to their interesting properties such as chemical inertness, negligible swelling in aqueous solution, tunable porosity and facile chemical modi- fication [8–10]. This makes them good candidates for the im- mobilization of biomacromolecules in the assembly of the hybrid structures. Xanthine was selected as the target analyte to be ad- dressed in this work. As it is well known, xanthine is an important purine metabolite deriving from adenine pathway until the formation of uric acid [11], which is rapidly ex- creted by the kidney. Normal xanthine levels in human urine are ca. 40–160 μM[12]. Higher levels of xanthine are ascribed to metabolic disorders such as xanthinuria, hyperuricemia, gout and renal failure [13]. Regarding food control, xanthine levels are commonly used to ascertain meat freshness [14]. For instance, the concentration of hy- poxanthine in fresh fish is approximately 5 μM[15]. Moreover, xanthine oxidase (XOx) is the most commonly used biocatalytic element in the construction of biosensors to monitor the levels of xanthine in different food samples [16–19]. This enzyme has been immobilized on various types of substrates including conductive and non – Electronic supplementary material The online version of this article (doi:10.1007/s00604-016-1840-5) contains supplementary material, which is available to authorized users. * Noureddine Raouafi n.raouafi@fst.rnu.tn * José M. Pingarrón pingarro@quim.ucm.es * Reynaldo Villalonga rvillalonga@quim.ucm.es 1 Faculty of Sciences, Department of Chemistry, Laboratory of Analytical Chemistry and Electrochemistry (LR99ES15), University of Tunis El–Manar, 2092 Tunis El–Manar, Tunisia 2 Faculty of Chemistry, Department of Analytical Chemistry, Complutense University of Madrid, 28040 Madrid, Spain 3 IMDEA Nanoscience, Campus University of Cantoblanco, C/Faraday, 9, 28049 Madrid, Spain Microchim Acta DOI 10.1007/s00604-016-1840-5