The application of bacteria-derived dehydrogenases and oxidases in the synthesis of gold nanoparticles

In this work the green synthesis of gold nanoparticles (Au-NPs) using the oxidoreductive enzymes Myriococcum thermophilum cellobiose dehydrogenase (Mt CDH), Glomerella cingulata glucose dehydrogenase (Gc GDH), and Aspergillus niger glucose oxidase (An GOX)) as bioreductants was investigated. The influence of reaction conditions on the synthesis of Au-NPs was examined and optimised. The reaction kinetics and the influence of Au ions on the reaction rate were determined. Based on the kinetic study, the mechanism of Au-NP synthesis was proposed. The Au-NPs were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The surface plasmon resonance (SPR) absorption peaks of the Au-NPs synthesised with Mt CDH and Gc GDH were observed at 535 nm, indicating an average size of around 50 nm. According to the image analysis performed on a TEM micrograph, the Au-NPs synthesized with Gc GDH have a spherical shape with an average size of 2.83 and 6.63 nm after 24 and 48 h of the reaction, respectively. KEY POINTS: • The Au NPs were synthesised by the action of enzymes CDH and GDH. • The synthesis of Au-NPs by CDH is related to the oxidation of cellobiose. • The synthesis of Au-NPs by GDH was not driven by the reaction kinetic.

Nanoparticles for Biomedical Application and Their Synthesis

Tremendous developments in nanotechnology have revolutionized the impact of nanoparticles (NPs) in the scientific community and, more recently, in society. Nanomaterials are by their definition materials that have at least one dimension in range of 1 to 100 nm. Nanoparticles are found in many types of different technological and scientific applications and innovations, from delicate electronics to state-of-the-art medical treatments. Medicine has recognized the importance of polymer materials coated with NPs and utilizes them widely thanks to their excellent physical, chemical, antibacterial, antimicrobial, and protective properties. Emphasis is given to their biomedical application, as the nanoscale structures are in the range of many biological molecules. Through this, they can achieve many important features such as targeted drug delivery, imaging, photo thermal therapy, and sensors. Moreover, by manipulating in a "nano-scale" range, their characteristic can be modified in order to obtain the desired properties needed in particular biomedical fields, such as electronic, optical, surface plasmon resonance, and physic-chemical features.

Scanning electrochemical microscope as a tool for the electroporation of living yeast cells

In this study, a scanning electrochemical microscope (SECM) was for the first time adapted to perform the electroporation process of living yeast cells. We have demonstrated that relatively low voltage pulses of 1-2 V vs. Ag/AglCl,Cl^-_sat applied to gold-based ultramicroelectrode (Au-UME) are performing reversible electroporation of yeast cells immobilized on fluorine-doped tin oxide (FTO)/glass surface. SECM and electrochemical impedance spectroscopy (EIS) were used for the determination of quantitative electrochemical characteristics before and after the electroporation. The electrochemical impedance spectroscopy (EIS) illustrated significant electrochemical changes of electroporated yeast cells, while SECM feedback mode surface vertical scan current-distance curves showed that the diameter of the area affected by the electrical pulse is about 25 times larger than the diameter of the Au-UME used for the electroporation process. The results presented in this research open up a possibility to develop a targeted electroporation system which will affect only the selected area of tissue or some other cell-covered surface. Such model is promising for the selective treatment of selected cells in tissues and/or other sensitive biological systems while selecting the location and size of electroporated areas.

Au nanoflower film-based stretchable biosensors for in situ monitoring of superoxide anion release in cell mechanotransduction

Cell mechanotransduction plays an important role in vascular regulation and disease development.

Effect of the driving force on nanoparticles growth and shape: an opto-electrochemical study

Most protocols developed to synthesize nanoparticles (NPs) and to control their shape are inspired from nucleation and growth theories. However, to rationalize the mechanisms of the shape-selective synthesis of NPs, experimental strategies allowing to probe in situ the growth of NPs are needed. Herein, metal Au or Ag nanoparticles (NPs) are produced by reaction of a metallic ion precursor with a reversible redox reducer. The process is explored by an oxidative electrosynthesis strategy using a sacrificial Au or Ag ultramicroelectrode to both trigger the metallic ion generation and control the local concentrations of the different reactants. The effect of the driving force for the metallic ion reduction over metal NP growth dynamics is inspected in situ and in real time at the single NP level by high-resolution optical microscopy from the tracking of the Brownian trajectories of the growing NPs in solution. The NP reductive growth/oxidative etching thermodynamics, and consequently the NP shape, are shown to be controlled electrochemically by the reversible redox couple, while the intervention of an Au(i) intermediate ion is suggested to account for the formation of gold nanocubes.

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 (DH_CDH ) carrying strongly bound flavin adenine dinucleotide (FAD) in the active site and a cytochrome domain (CYT_CDH ) 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 Au^III and as stabilizer for the nanoparticles. The heterogeneous electron-transfer (ET) rate (k_s ) 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 5 s and a linear range from 1 to 100 μm.

Tailored gold nanostructure arrays as catalysts for oxygen reduction in alkaline media and a single molecule SERS platform

Although plenty of functional nanomaterials are widely applied in science and technology, cost-efficient, controlled and reproducible fabrication of metallic nanostructures is a considerable challenge. Automated electrorefining by scanning electrochemical microscopy (SECM) provides an effective approach to circumvent some drawbacks of traditional homogeneous syntheses of nanoparticles, providing precise control over the amount, time and place of reactant delivery. The precursor is just a raw metal, which is the most economically viable source. This approach ensures reproducibility and the opportunity for fabrication of micropatterns, which can be rapidly analyzed by scanning probe techniques. Here, a cost-effective methodology for the preparation of naked (ligand-free) metallic nanostructures, from polycrystalline gold using a moving microelectrode, is presented. Automated micropatterning of bare gold on indium tin oxide (ITO) demonstrates the versatility of this method to tune the size and shape of the nanostructures. The morphology of the obtained materials and thus their catalytic and plasmonic properties can be tuned using the electrorefining parameters. Programmable fabrication of sample microarrays by microprinting followed by comparative SECM studies or spectroscopic analysis allows quick optimization and characterization for specific purposes. Electrocatalytic oxygen reduction in alkaline media and surface-enhanced Raman spectroscopy (SERS) of single porphycene molecules are presented as model examples.

Cellobiose dehydrogenase modified electrodes: advances by materials science and biochemical engineering

The flavocytochrome cellobiose dehydrogenase (CDH) is a versatile biorecognition element capable of detecting carbohydrates as well as quinones and catecholamines. In addition, it can be used as an anode biocatalyst for enzymatic biofuel cells to power miniaturised sensor-transmitter systems. Various electrode materials and designs have been tested in the past decade to utilize and enhance the direct electron transfer (DET) from the enzyme to the electrode. Additionally, mediated electron transfer (MET) approaches via soluble redox mediators and redox polymers have been pursued. Biosensors for cellobiose, lactose and glucose determination are based on CDH from different fungal producers, which show differences with respect to substrate specificity, pH optima, DET efficiency and surface binding affinity. Biosensors for the detection of quinones and catecholamines can use carbohydrates for analyte regeneration and signal amplification. This review discusses different approaches to enhance the sensitivity and selectivity of CDH-based biosensors, which focus on (1) more efficient DET on chemically modified or nanostructured electrodes, (2) the synthesis of custom-made redox polymers for higher MET currents and (3) the engineering of enzymes and reaction pathways. Combination of these strategies will enable the design of sensitive and selective CDH-based biosensors with reduced electrode size for the detection of analytes in continuous on-site and point-of-care applications.