1IntroductionNowadays,m agnetic-gold nanoparticles (Fe 3 O 4 @Aus eed nanoparticles,F e 3 O 4 @AuN Ps) have attracted considerable attention due to their advantages,s uch as catalytic effect, ease of handling,a nd good biocompatibility [1][2][3][4]. Fe 3 O 4 @Aus eed nanoparticles have been used in some fields such as biochemical sensing [5-9] medicali maging [10],d rug targeting delivery [ 11,12],p rotein purification [13,14],c ancer therapy [ 15],b iological separation [16,17],a nd catalysis [18].D ecoratingm agneticn anoparticles with gold, either as as hell or as seeds on their surface,m ust be performed in ac ontrollable way.T he gold shell is helpful to increase the biocompatibility and electroconductivity of Fe 3 O 4 nanoparticles as well as to enlarge the surface area, which is,t ogetherw ith the high affinity of gold towardsS H-groups,g ood for immobilizing biomolecules.T herefore,F e 3 O 4 @Aus eed nanoparticles hold promise for biosensor applications.Biosensors are usefula nalytical devices in various industries; for example, in the control of food quality and its freshness [19][20][21][22][23][24][25][26].C onventional alternative techniques are chromatography,s pectrophotometry and others. These methods are often time-consuming and expensive. Well-trained operators and occasionally the extraction of the analyte or other sample pretreatment procedures are also required. Food and drink industries need rapid and reliable methodst od etermine some compounds of interest [20,27].B iosensors are simple alternatives to facilitate the analysis in manufacturing industrial products,e specially alcoholic beverages such as beer, wines,a nd spirits. Thed etermination of alcoholicc ompounds,p articularly of ethanol, is relevant in food industry.I nt he case of ethanol, an umber of enzyme-based electrochemical devices have been developed involving two kinds of enzyme, alcohol oxidase (AOx) and alcohold ehydrogenase.B iosensorsb ased on AOxs howed limited storage stability [28] whereas biosensors using ADH and the cofactor nicotin- ,areproducibility of 4.0 %R SD,a nd ar epeatability of 2.7 %R SD. Ther esults for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 -108.8 %.
