Reduced Graphene Oxide and Polyaniline Nanofibers Nanocomposite for the Development of an Amperometric Glucose Biosensor.

The control of glucose concentration is a crucial factor in clinical diagnosis and the food industry. Electrochemical biosensors based on reduced graphene oxide (rGO) and conducting polymers have a high potential for practical application. A novel thermal reduction protocol of graphene oxide (GO) in the presence of malonic acid was applied for the synthesis of rGO. The rGO was characterized by scanning electron microscopy, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, and Raman spectroscopy. rGO in combination with polyaniline (PANI), Nafion, and glucose oxidase (GOx) was used to develop an amperometric glucose biosensor. A graphite rod (GR) electrode premodified with a dispersion of PANI nanostructures and rGO, Nafion, and GOx was proposed as the working electrode of the biosensor. The optimal ratio of PANI and rGO in the dispersion used as a matrix for GOx immobilization was equal to 1:10. The developed glucose biosensor was characterized by a wide linear range (from 0.5 to 50 mM), low limit of detection (0.089 mM), good selectivity, reproducibility, and stability. Therefore, the developed biosensor is suitable for glucose determination in human serum. The PANI nanostructure and rGO dispersion is a promising material for the construction of electrochemical glucose biosensors.

Single-walled carbon nanotube based coating modified with reduced graphene oxide for the design of amperometric biosensors.

In this study a polycarbonate filter membrane (PcFM) with 400 nm diameter holes was covered/protruded by single walled carbon nanotubes (SWCNT) and then formed PcFM/SWCNT structure was covered by thin layer of graphene oxide (GO) or reduced graphene oxide (rGO) in order to get the multilayered PcFM/SWCNT/GO and PcFM/SWCNT/rGO coatings, respectively. It was determined that the SWCNTs filaments were able to form a layer on the polycarbonate membrane having a number of carbon nanotube arranged in different orientations. A fraction of SWCNT filaments protruded through the holes of polycarbonate membrane and in such way significantly enhanced the adhesion of SWCNT-based layer and provided electrical conductivity across the PcFM. Atomic force microscopy (AFM), scanning electron microscopy (SEM) images and Raman spectroscopy-based evaluation revealed the characteristic morphology features: wide distribution of height profile, separate GO/rGO flakes on the top of PcFM/SWCNT/GO structure and close attachment of rGO flakes on the top of multilayered PcFM/SWCNT/rGO coating. Performed contact angle measurement (CAM) enabled to determine the surface energy components and wettability data of prepared coatings. Both PcFM/SWCNT/GO and PcFM/SWCNT/rGO coatings were modified with glucose oxidase (GOx). Amperometric measurements revealed that multilayered PcFM/SWCNT/rGO/GOx coating is the most suitable structure for glucose biosensor design.

Synthesis of Reduced Graphene Oxide with Adjustable Microstructure Using Regioselective Reduction in the Melt of Boric Acid: Relationship Between Structural Properties and Electrochemical Performance.

The melt of H3BO3 was used to reach a controllable reduced graphene oxide (rGO) synthesis protocol using a graphene oxide (GO) precursor. Thermogravimetric analysis and differential scanning calorimetry (TG/DSC) investigation and scanning electron microscopy (SEM) images have shown that different from GO powder, reduction of GO in the melt of H3BO3 leads to the formation of less disordered structure of basal graphene planes. Threefold coordinated boron atom acts as a scavenger of oxygen atoms during the process of GO reduction. Fourier-transform infrared (FTIR) spectra of synthesized products have shown that the complex of glycerol and H3BO3 acts as a regioselective catalyst in epoxide ring-opening reaction and suppress the formation of ketone C=O functional groups at vacancy sites. Thermal treatment at 800 °C leads to the increased concentration of point defects in the backbone structure of rGO. Synthesized materials were tested electrochemically. The electrochemical performance of these materials essentially differs depending on the preparation protocol. The highest charge/discharge rate and double-layer capacitance were found for a sample synthesized in the melt of H3BO3 in the presence of glycerol and treated at 800 °C. The effect of optimal porosity and high electrical conductivity on the electrochemical performance of prepared materials also were studied.

Graphene oxide-dye nanocomposites: effect of molecular structure on the quality of laser-induced graphene.

The nanocomposite coatings made using graphene oxide (GO) and six different organic dyes were used to produce the laser-induced graphene (LIG) coatings by means of near infrared picosecond laser irradiation. The coatings were investigated by means of contact angle measurement with three liquids (1-bromonaphtalene, glycerol and water), Raman spectroscopy, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis. It was found that the more hydrophilic is the precursor surface the more hydrophobic LIG surface is produced after the laser treatment. Contact angle values obtained on LIG produced from pure GO reached 143°. FTIR spectra have shown that the interaction between GO and dye molecules is realized through the nitrogen atoms. Raman spectra have shown that the best quality LIG coating is obtained using a GO-neutral red nanocomposite precursor. A correlation among contact angle, Raman spectra and topological indices of dye molecules was found, and will serve for the further investigation of the mechanism of LIG production and development of low-defect coatings.

Thermally reduced graphene oxide: The study and use for reagentless amperometric D-fructose biosensors.

Aiming to create reagentless amperometric D-fructose biosensor, graphene based electrode materials have been synthesized by newly proposed thermal reduction of graphene oxide. The method allowed to separate and collect different fractions of thermally reduced graphene oxide (TRGO) with different physicochemical properties. The structural characteristics and surface morphologies of TRGO fractions were evaluated using SEM, XRD, TGA analysis, Raman spectroscopy and BET measurements. Three different fractions of TRGO were tested as electrode materials for D-fructose amperometric biosensors. The direct electron transfer (DET) from the active site of D-fructose dehydrogenase (FDH) to the electrode was achieved with all TRGO fractions. High values of the sensitivity (up to 14.5 µA mM(-1) cm(-2)) are of the same order as these for other D-fructose sensors based on the synergistic mediated processes. The relationships between the structure of TRGO fractions and the molecular processes determining the effect of DET in bioelectrocatalysis by FDH have been studied. Stability of the D-fructose biosensors was also assessed. The best results were achieved when immobilization of FDH was performed using a crosslinking with glutaraldehyde. For the best group, after a period of 5 days the sensitivity of the biosensor for D-fructose determination decreased by less than 20%.

Fine structure and related properties of the assembleable carbon nanotubes based electrode for new family of biosensors with chooseable selectivity.

Surfaces of constituent parts of biosensors based on single wall carbon nanotube layer were investigated and compare for properly functioning and faulty biosensors. Though the original technology is acceptable for changing of the selectivity, only glucose sensitive biosensors are investigated. Based on the results of the study, a correlation between the features of the nanoscale structures and parameters of amperiometric biosensors for assemblage of which an innovative approach is described. Original template of the electrodes has been prepared on a base of single wall carbon nanotube layer deposited on the supporting polycarbonate membrane. Original immobilisation of enzymes within special membrane allows functional modification of biosensors being accomplished by simple replacement of the enzymatic membrane. The original technology leads to a novel family of biosensors acceptable for detection of wide range of carbohydrates. The morphology and the local electric properties of the constituent parts of the biosensors are characterized by scanning probe microscopy. The sensitivity, selectivity and stability are described for typical types of the biosensors.

Modified graphitized carbon black as transducing material for reagentless H2O2 and enzyme sensors.

Direct electron transfer between redox enzymes and electrodes is the basis for the third generation biosensors. We established direct electron transfer between quinohemoprotein alcohol dehydrogenase (PQQ-ADH) and modified carbon black (CBs) electrodes. Furthermore, for the first time, this phenomenon was observed for pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (PQQ-GDH). Reagentless enzyme biosensors suitable for the determination of ethanol, glucose and sensors for hydrogen peroxide were designed using CB electrodes and screen-printing technique. Aiming to create an optimal transducing material for biosensors, a set of CB batches was synthesized using the matrix of Plackett-Burman experimental design. Depending on the obtained surface functional groups as well as the nano-scale carbon structures in CBs batches, the maximal direct electron transfer current of glucose and ethanol biosensors can vary from 20 to 300 nA and from 30 to 6300 nA for glucose and ethanol, respectively. Using modified CB electrodes, an electrocatalytic oxidation of H(2)O(2) takes place at more negative potentials (0.1-0.4V versus Ag/AgCl). Moreover, H(2)O(2) oxidation efficiency depends on the amount and morphology of fine fraction in the modified CBs.