The above mentioned techniques were used to study the immobilization of glucose oxidase (GOx) enzyme from Aspergillus niger, on an SiO2 surface. GOx is a dimeric globular protein having overall dimensions of 6.0��5.2��7.7 nm3. It catalyzes the oxidation of ��-d-glucose to ��-gluconolactone by a reaction that can be summarized in two steps: i) glucose oxidation with the enzyme reduction, ii) re-oxidation of the enzyme with consumption of molecular oxide (O2) and production of hydrogen peroxide (H2O2) [8]. For this reason GOx is commonly used to monitor the glucose concentration in the blood; hence, a GOx based micro-biosensor [9] would have immediate applications in monitoring diabetes [10].

In order to visualize the enzyme with XPS, it was labelled with gold nanoparticles having a diameter of 1.

4 nm. Au is regularly used to label the amino groups of biological molecules in solution when transmission electron microscopy measurements are performed [11]. GOx molecules contain two disulphide bonds and two accessible thiol groups [12]. Since GOx amino groups were used to immobilize the protein on the solid surface, the free sulfydryl groups were labelled with functionalized gold nanoparticles [13]. Gold labelling in this study had a twofold purpose: to provide conclusive proof of the presence of the enzyme and as internal reference for XPS measurements. To verify the preservation of enzyme activity after immobilization, a spectrophotometric technique was used.

It was based on the use of peroxidase to monitor hydrogen peroxide production.

The aims of this work were the definition of an optimized immobilization protocol that would allow the maximum surface coverage without any loss in the Entinostat GOx enzyme performances and the characterization of the deposited organic layer using standard microelectronic techniques.2.?Results and DiscussionThe most promising immobilization protocol Batimastat reported in literature (see ref. [2]) was tested on bulk SiO2 samples, mainly using XPS measurements. The results were compared with those obtained from a sample where a modified protocol was applied.

The main difference with respect to the fist protocol was the addition of an oxide activation step at the beginning of the processing (see the experimental section for details). The XPS survey spectra of the reference (top spectrum, in black) and three fully processed samples (differently prepared) are shown in Figure 1.Figure 1.XPS survey spectra of reference (black) and three fully processed samples: processed without SSC (red, Full-SSC), processed with SSC (green, Full+SSC), processed with SSC and GOx labelled with Au nanoparticles (blue, Full+SSC+Au). In the inset, a zoom …