Abstract
Graphite electrodes were modified with triangular (AuNTrs) or spherical (AuNPs) nanoparticles and further modified with fructose dehydrogenase (FDH). The present study reports the effect of the shape of these nanoparticles (NPs) on the catalytic current of immobilized FDH pointing out the different contributions on the mass transfer–limited and kinetically limited currents. The influence of the shape of the NPs on the mass transfer–limited and the kinetically limited current has been proved by using two different methods: a rotating disk electrode (RDE) and an electrode mounted in a wall jet flow-through electrochemical cell attached to a flow system. The advantages of using the wall jet flow system compared with the RDE system for kinetic investigations are as follows: no need to account for substrate consumption, especially in the case of desorption of enzyme, and studies of product-inhibited enzymes. The comparison reveals that virtually identical results can be obtained using either of the two techniques. The heterogeneous electron transfer (ET) rate constants (kS) were found to be 3.8 ± 0.3 s−1 and 0.9 ± 0.1 s−1, for triangular and spherical NPs, respectively. The improvement observed for the electrode modified with AuNTrs suggests a more effective enzyme-NP interaction, which can allocate a higher number of enzyme molecules on the electrode surface.Graphical abstractThe shape of gold nanoparticles has a crucial effect on the catalytic current related to the oxidation of D-(-)-fructose to 5-keto-D-(-)-fructose occurring at the FDH-modified electrode surface. In particular, AuNTrs have a higher effect compared with the spherical one.
Highlights
Nanostructuration of electrodes seems to play a crucial role in the development of biodevices, such as biosensors and enzymatic fuel cells (EFCs) [1, 2], which are based on a direct electron transfer (DET) communication between the biological material and the electrode [3, 4]
fructose dehydrogenase (FDH) from Gluconobacter japonicus NCBR 3260 is a membrane-bound flavocytochrome oxidoreductase belonging to the hemoflavoprotein family and is a heterotrimeric membrane-bound enzyme complex with a molecular mass of 146.4 kDa, consisting of three subunits, viz. subunit I (DHFDH), which is the catalytic dehydrogenase domain with a covalently bound flavin adenine dinucleotide (FAD) cofactor, where D-(-)-fructose is involved in a 2H+/2e− oxidation to 5-dehydro-D-(-)-fructose; subunit II (CYTFDH), a cytochrome domain acting as a built-in electron acceptor with three heme c moieties covalently bound to the enzyme scaffold and two of them are involved, one by one, in the electron transfer pathway; and subunit III, which is not involved in the electron transfer but plays a key role for the stability of the enzyme complex [20, 21]
Cyclic voltammetry (CV) experiments were performed with modified graphite electrodes in absence and in presence of substrate in order to assess the contribution of the electrode nanostructuration using differently shaped AuNPs on the catalytic current related to the oxidation of D-(-)-fructose to 5-keto-D-(-)-fructose catalyzed by FDH
Summary
Nanostructuration of electrodes seems to play a crucial role in the development of biodevices, such as biosensors and enzymatic fuel cells (EFCs) [1, 2], which are based on a direct electron transfer (DET) communication between the biological material and the electrode [3, 4]. Graphite electrodes have been modified with triangular (AuNTrs) and spherical gold (AuNSphs) nanoparticles to investigate whether the shape of the NPs can affect both the mass transfer–limited and the kinetically limited currents by using two different methods: a rotating disk electrode (RDE) and an electrode mounted in a wall jet flow-through electrochemical cell attached to a flow system. The differently prepared electrodes were further modified by drop-casting FDH directly on the top of the AuNTrs/G and AuNSphs/G electrodes Both methods allowed quantifying the influence of the shape of the NPs on the mass transfer–limited current and the heterogeneous electron transfer rate constant (kS). The solution containing a mixture of gold nanotriangles (AuNTrs) and byproducts (spherical particles) was redispersed in 2 mL of pure water and purified by using a depletion-induced flocculation method. The electrochemical system was equipped with a flow system consisting of a peristaltic pump (Gilson, Villier-le-Bel, France) and a six-port valve electrical injector (Rheodyne, Cotati, CA, USA) [62]
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