The preservation of enzymatic activity is a fundamental requirement for exploiting hybrid nano-bio-conjugates, and the control over protein-nanoparticle interactions, leading to stable and catalytically active hybrids, represents the key for designing new biosensing platforms. In this scenario, surface active maghemite nanoparticles (SAMNs) represent a new class of naked magnetic nanoparticles, displaying peculiar electrocatalytic features and the ability to selectively bind proteins. Recombinant aminoaldehyde dehydrogenase from tomato (SlAMADH1) was used as a model protein, and successfully immobilized by self-assembly on the surface of naked SAMNs, where its enzymatic activity resulted preserved for more than 6 months. The hybrid nanomaterial (SAMN@SlAMADH1) was characterized by UV-Vis spectroscopy, mass spectrometry, and TEM microscopy, and applied for the development of a biosensor for the determination of aminoaldehydes in alcoholic beverages. Measurements were carried out in a low volume electrochemical flow cell comprising a SAMN modified carbon paste electrode for the coulometric determination of the NADH produced during the enzymatic catalysis. The present findings, besides representing the first example of an electrochemical biosensor for aminoaldehydes in an alcoholic matrix, open the door to the use of immobilized enzymes on naked metal oxides nanomaterials for biosensing.

Department of Biochemical Sciences A Rossi Fanelli University of Rome La Sapienza and CNR Institute of Biology and Molecular Pathology 00185 Rome Italy

Department of Comparative Biomedicine and Food Science University of Padua Agripolis Viale dell'Università 16 35020 Legnaro PD Italy

Department of Molecular Medicine University of Padua Via Gabelli 63 35121 Padua Italy

Department of Protein Biochemistry and Proteomics Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University in Olomouc Šlechtitelu 11 78371 Olomouc Czech Republic

International Polyamines Foundation ONLUS Via del Forte Tiburtino 98 00159 Rome Italy

Proteomic Center of Padua University VIMM and Padua University Hospital Via G Orus 2b 35129 Padua Italy

Regional Centre of Advanced Technologies and Materials Department of Physical Chemistry Faculty of Science Palacký University in Olomouc 17 Listopadu 12 771 46 Olomouc Czech Republic

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Enzyme Immobilization on Maghemite Nanoparticles with Improved Catalytic Activity: An Electrochemical Study for Xanthine