We report an electrochemical glucose biosensor made with layer-by-layer (LbL) films of functionalized reduced graphene oxide (rGO) and glucose oxidase (GOx). The LbL assembly using positively and negatively charged rGO multilayers represents a simple approach to develop enzymatic biosensors. The electron transport properties of graphene were combined with the specificity provided by the enzyme. rGO was obtained and functionalized using chemical methods, being positively charged with poly(diallyldimethylammonium chloride) to form GPDDA, and negatively charged with poly(styrene sulfonate) to form GPSS. Stable aqueous dispersions of GPDDA and GPSS are easily obtained, enabling the growth of LbL films on various solid supports. The use of graphene in the immobilization of GOx promoted Direct Electron Transfer, which was evaluated by Cyclic Voltammetry. Amperometric measurements indicated a detection limit of 13.4μmol·L(-1) and sensitivity of 2.47μA·cm(-2)·mmol(-1)·L for glucose with the (GPDDA/GPSS)1/(GPDDA/GOx)2 architecture, whose thickness was 19.80±0.28nm, as determined by Surface Plasmon Resonance (SPR). The sensor may be useful for clinical analysis since glucose could be detected even in the presence of typical interfering agents and in real samples of a lactose-free milk and an electrolyte solution to prevent dehydration.

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AA 2024 aluminum alloy is widely employed in aeronautic and automobilist industries. Its hardness and low density are attractive properties for such industrial areas. However, since it contains copper, it undergoes severe corrosion in aggressive media as saline or low Earth orbit environments. In this work, it was investigated the properties of films deposited by PECVD on AA 2024 aluminum alloy as well as the corrosion resistance of the film/substrate systems under different corrosive atmospheres. Films were prepared in a plasma atmosphere composed of 50% of oxygen and 50% of hexamethyldisiloxane resulting in a total gas pressure of 4.0 Pa. Plasma ignition was promoted by the application of radiofrequency signal (13.56 MHz) to the sample holder while grounding the topmost electrode. The plasma excitation power, P, was changed from 10 to 80 W in the six different set of experiments. Film thickness, measured by profilometer, increases by 5 times as P was elevated from 10 to 80 W. As demonstrated by the infrared spectra of the samples, films are essentially organosilicons with preservation of functional groups of the precursor molecule and with creation of different ones. The oxide proportion and the structure crosslinking degree are affected by the plasma excitation power. According to the results obtained by sessile drop technique, hydrophilic to moderately hydrophobic films are produced with changing P from 10 to 80 W. The corrosion resistance, evaluated by salt spray and electrochemical impedance spectroscopy, EIS, experiments, in general increases after film deposition. It is demonstrated that film deposition improves, in up to 36 times, the resistance of the alloy to salt spray attack. It is also shown an improvement of about 240 times in the alloy resistance under NaCl solution by the EIS data. Micrographs acquired by Scanning Electron Microscopy after the corrosion tests furnish further information on the importance of the layer physical stability on its barrier properties. Furthermore, films highly protect the alloy against the oxygen attack. Interpretations are proposed based on the modification of the plasma kinetics with P, altering film structure, composition and properties.

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