Direct Electron Transfer of Cellobiose Dehydrogenase on Positively Charged Polyethyleneimine Gold Nanoparticles

Efficient conjugation between biomolecules and electrode materials is one of the main challenges in the field of biosensors. Cellobiose dehydrogenase (CDH) is a monomeric enzyme, which consists of two separate domains: one catalytic dehydrogenase domain (DHCDH) carrying strongly bound flavin adenine dinucleotide (FAD) in the active site and a cytochrome domain (CYTCDH) carrying a b-type heme connected by a flexible linker region. Herein, we report on the development of a lactose biosensor, based on direct electron transfer (DET) from CDH from Phanerochaete sordida (PsCDH) electrostatically attached onto polyethyleneimine-stabilized gold nanoparticles (PEI@AuNPs) used to cover a conventional polycrystalline solid gold disk electrode. PEI@AuNPs were synthesized in aqueous solution using PEI as reducing agent for AuIII and as stabilizer for the nanoparticles. The heterogeneous electron-transfer (ET) rate (ks) for the redox reaction of immobilized PsCDH at the modified electrodes was calculated based on the Laviron theory and was found to be (39.6±2.5)s-1. The proposed lactose biosensor exhibits good long term stability as well as high and reproducible sensitivity to lactose with a response time less than 5s and a linear range from 1 to 100μm

Photoelectrochemical Communication between Thylakoid Membranes and Gold Electrodes through Different Quinone Derivatives

Photosynthesis is a sustainable process for the conversion of light energy into chemical energy. Thylakoids in energy-transducing photosynthetic membranes are unique in biological membranes because of their distinguished structure and composition. The quantum trapping efficiency of thylakoid membranes is appealing in photobioelectrochemical research. In this study, thylakoid membranes extracted from spinach are shown to communicate with a gold-nanoparticle-modified solid gold electrode (AuNP-Au) through a series of quinone derivatives. Among these, para-benzoquinone (PBQ) is found to be the best soluble electron-transfer mediator, generating the highest photocurrent of approximately 130 mu Acm(-2) from water oxidation under illumination. In addition, the photocurrent density is investigated as a function of applied potential, the effect of light intensity, quinone concentration, and amount of thylakoid membrane. Finally, the source of photocurrent is confirmed by using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (known by its trade name, Diuron), an inhibitor of photosystem II, which decreases the total photocurrent by 50%

Interaction of polymer-coated gold nanoparticles with cellobiose dehydrogenase : The role of surface charges

Studying the interaction of functional proteins such as enzymes and nanoparticles (NPs) includes the important topic of investigating any possible changes in stability and function of enzymes in nanostructured environments. The effects of NPs on the enzyme activity and stability are governed by their physical and chemical properties such as structure, shape, size, surface chemistry and their surface charges. In this study, the influence of negatively and positively charged AuNPs are investigated on the activity of immobilized Myriococcum thermophilum cellobiose dehydrogenase (MtCDH) and its electron transfer rate with graphite electrodes modified with positively and negatively AuNPs. The MtCDH modified graphite electrode premodified with positively charged AuNPs showed an alkaline shift in the pH of maximum activity from pH5.5 to 8. No change in the pH of maximum activity was observed when MtCDH graphite electrodes were premodified with negatively charged AuNPs. The results clearly demonstrated the effect of surface charge of AuNPs on the activity of the enzyme. The catalytic current density and the KM app value for MtCDH graphite electrode premodified with positively charged AuNPs were enhanced with up to 66 and 8 times, respectively. Two spectroscopic assays were also performed in solution to investigate the influence of the presence of positively or negatively charged AuNPs on the activity of MtCDH in homogeneous solution. The results clearly demonstrated that not only the rate of the heterogeneous electron transfer between the immobilized MtCDH and the electrode but also the rate of the homogeneous electron transfer between soluble MtCDH and the acceptor was highly dependent on the type of surface charge of the AuNPs