Electrochemical behaviour of glassy carbon electrodes modified with aryl groups

Electrochemically induced Meerwein arylation as a green strategy for the synthesis of arylbenzoquinone derivatives under batch and flow conditions

An electrochemical Meerwein arylation reaction was reported for the synthesis of aryl-benzoquinone derivatives. In this work, efficient electrochemical synthesis of aryl-benzoquinone derivatives by direct electrolysis of aqueous solution containing hydroquinone and aryldiazonium salts in batch and a homemade continuous-flow cells is reported. In the batch system, the products were obtained in a simple undivided cell equipped with a copper anode and a stainless steel cathode. In the continuous flow system, the products were obtained simply by passing hydroquinone and the aryldiazonium salt through a tube made of copper with a stainless steel rod in the center. All equipment required in both cell types is obtained from common commercial sources. This protocol is green and cost-effective due to the use of electricity and is performed under mild and safe conditions without the use of toxic solvents and catalysts.

Recent advances in development of glucose nanosensors for cellular analysis and other applications

Diabetes mellitus is a disease that affects a large number of people around the world. There are no effective methods to completely cure diabetes, and patients have to constantly monitor their blood sugar levels, so there is still a need for improved sensors. In addition to diabetes, quantitative values of glucose levels affect the development of some endocrine diseases and problems with nervous tissue. In this review, we will describe existing developments, the principles of glucose measurement, sensor designs, the materials they are made of, and how nanotechnology is improving the sensors under development by increasing sensitivity and surface area and improving catalytic properties.

Diazonium Salts: Versatile Molecular Glues for Sticking Conductive Polymers to Flexible Electrodes

Adhesion of polymers to surfaces is of the upmost importance in timely applications such as protective coatings, biomaterials, sensors, new power sources and soft electronics. In this context, this work examines the role of molecular interactions in the adhesion of polypyrrole thin films to flexible Indium Tin Oxide (ITO) electrodes grafted with aryl layers from various diazonium salts, namely 4-carboxybenzenediazonium (ITO-CO2H), 4-sulfonicbenzenediazonium (ITO-SO3H), 4-N,N-dimethylbenzenediazonium (ITO-N(CH3)2), 4-aminobenzenediazonium (ITO-NH2), 4-cyanobenzenediazonium (ITO-CN) and 4-N-phenylbenzenediazonium (ITO-NHPh). It was demonstrated that PPy thin layers were adherent to all aryl-modified surfaces, whereas adhesive failure was noted for bare ITO following simple solvent washing or sonication. Adhesion of polypyrrole was investigated in terms of hydrophilic/hydrophobic character of the underlying aryl layer as probed by contact angle measurements. It was found that sulfonic acid-doped polypyrrole (PPy-BSA) thin films were preferably deposited on the most hydrophobic surfaces. More importantly, the redox properties and electrochemical impedance of PPy were closely related to the hydrophobic character of the aryl layers. This work demonstrates that diazonium compounds are unique molecular glues for conductive polymers and permit to tune their interfacial properties. With robust, diazonium-based architectured interfaces, one can design high performance materials for e.g., sensors, printed soft electronics and flexible thermoelectrics.

Mapping nanometric electronic property changes induced by an aryl diazonium sub-monolayer on HOPG

The morphology as well as the electric and electronic properties of aryl diazonium, in particular 4-nitrobenzene-diazonium (NBD), films on HOPG surfaces have been studied at the nanoscale level.

Electrodeposition of gold nanoparticles on aryl diazonium monolayer functionalized HOPG surfaces

Gold nanoparticle electrodeposition on a modified HOPG surface with a monolayer organic film based on aryl diazonium chemistry has been studied. This organic monolayer is electrochemically grown with the use of 2,2-diphenyl-1-picrylhydrazyl (DPPH), a radical scavenger. The electrodeposition of gold on this modified surface is highly favored resulting in an AuNP surface density comparable to that found on glassy carbon. AuNPs grow only in the areas covered by the organic monolayer leaving free clean HOPG zones. A progressive mechanism for the nucleation and growth is followed giving hemispherical AuNPs, homogeneously distributed on the surface and their sizes can be well controlled by the applied electrodeposition potential. By using AFM, C-AFM and electrochemical measurements with the aid of two redox probes, namely Fe(CN)6(4-)/Fe(CN)6(3-) and dopamine, relevant results about the electrochemical modified surface as well as the gold nanoparticles electrodeposited on them are obtained.

Electrochemical modification of gold electrodes with azobenzene derivatives by diazonium reduction

An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X-ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi-reversible voltammogram of the Fe(CN)6 (3-/4-) redox couple on bare Au and a sigmoidal shape for the GBC- and FBK-modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)6 (3-/4-) response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)6 (3-/4-) redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge-transfer rates to the Fe(CN)6 (3-) probe for the GBC- and FBK-modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer.