In this paper we present a new method to electrodeposit highly porous gold (h-PG) onto a polycrystalline solid gold electrode without any template. The electrodeposition is carried out by first cycling the electrode potential between +0.8 and 0 V in 10 mM HAuCl with 2.5 M NHCl and then applying a negative potential for the production of hydrogen bubbles at the electrode surface. After that the modified electrode was characterized in sulfuric acid to estimate the real surface area ( A) to be close to 24 cm, which is roughly 300 times higher compared to the bare gold electrodes (0.08 cm). The electrode was further incubated overnight with three different thiols (4-mercaptobenzoic acid (4-MBA), 4-mercaptophenol (4-MPh), and 4-aminothiophenol (4-APh)) in order to produce differently charged self-assembled monolayers (SAMs) on the electrode surface. Finally a fructose dehydrogenase (FDH) solution was drop-cast onto the electrodes. All the modified electrodes were investigated by cyclic voltammetry both under nonturnover and turnover conditions. The FDH/4-MPh/h-PG exhibited two couples of redox peaks for the heme c and heme c of the cytochrome domain of FDH and as well as a well pronounced catalytic current density (about 1000 μA cm in the presence of 10 mM fructose) due to the presence of -OH groups on the electrode surface, which stabilize and orientate the enzyme layer on the electrode surface. The FDH/4-MPh/h-PG based electrode showed the best analytical performance with an excellent stability (90% retained activity over 90 days), a detection limit of 0.3 μM fructose, a linear range between 0.05 and 5 mM, and a sensitivity of 175 ± 15 μA cm mM. These properties were favorably compared with other fructose biosensors reported in the literature. The biosensor was successively tested to quantify the fructose content in food and beverage samples. No significant interference present in the sample matrixes was observed.

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In this paper, an efficient direct electron transfer (DET) reaction was achieved between fructose dehydrogenase (FDH) and a glassy-carbon electrode (GCE) upon which anthracene-modified single-walled carbon nanotubes were deposited. The SWCNTs were activated in situ with a diazonium salt synthesized through the reaction of 2-aminoanthracene with NaNO 2 in acidic media (0.5 M HCl) for 5 min at 0 °C. After the in situ reaction, the 2-aminoanthracene diazonium salt was electrodeposited by running cyclic voltammograms from +1000 to −1000 mV. The anthracene-SWCNT-modified GCE was further incubated in an FDH solution, allowing enzyme adsorption. Cyclic voltammograms of the FDH-modified electrode revealed two couples of redox waves possibly ascribed to the heme c 1 and heme c 3 of the cytochrome domain. In the presence of 10 mM fructose two catalytic waves could clearly be seen and were correlated with two heme cs (heme c 1 and c 2 ), with a maximum current density of 485 ± 21 μA cm −2 at 0.4 V at a sweep rate of 10 mV s −1 . In contrast, for the plain SWCNT-modified GCE only one catalytic wave and one couple of redox waves were observed. Adsorbing FDH directly onto a GCE showed no nonturnover electrochemistry of FDH, and in the presence of fructose only a slight catalytic effect could be seen. These differences can be explained by considering the hydrophobic pocket close to heme c 1 , heme c 2 , and heme c 3 of the cytochrome domain at which the anthracenyl aromatic structure could interact through π−π interactions with the aromatic side chains of the amino acids present in the hydrophobic pocket of FDH.

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