Coating of gold substrates with polyaniline through electrografting of aryl diazonium salts

Surface Functionalized Titanium Nitride Electrode for CMOS Compatible Bioelectronic Devices

The development of bioelectronic devices is heading toward high throughput and high resolution. Yet, most electrode materials utilized in electrical biosensing are not compatible with the manufacturing techniques of semiconductor chips, which somehow hinders the integration and miniaturization of these devices. Titanium nitride (TiN) is a durable and economical material that is widely used in CMOS-based integrated circuits, bioelectronic systems, electrocatalytic systems, etc. Considering different application scenarios, new and efficient methods are required to functionalize TiN surface. In this study, a surface functionalization approach by covalent grafting of an organic thin film containing hydroxyl groups on TiN surface via electroreduction of diazonium salt 4-(2-hydroxyethyl)benzenediazonium was presented. Cyclic voltammetry (CV) procedures were carried out at the potential ranges of -0.8 V~0.5 V (vs Ag/AgCl) with varying numbers of potential cycles (i. e., 5, 25, and 50 cycles) in order to study the thickness of modification layer. Then, the electrochemical property, surface morphology, and chemical structures of the sample before and after modifications were investigated via multiple characterization techniques, such as CV, atomic force microscopy (AFM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), etc., thereby confirming the successful grafting of hydroxyl groups onto the TiN surface. The experiments on DNA synthesis aimed to explore the potential of modified TiN electrode as a novel platform for DNA data storage applications and the corresponding proof-of-principle was accomplished by the process of coupling Cy3-phosphoramidite. Finally, the experiments were successfully reproduced on the randomly selected sites of the modified TiN microarray chips demonstrating the potential of technical protocol to extend applications in future bioelectronic devices, such as bio-sensing, high-throughput DNA synthesis, and molecular manipulation.

An electrografted monolayer of polyaniline as a tuneable platform for a glucose biosensor

Polyaniline (PANI), a nanostructured conducting polymer, has shown significant potential in optical and bioelectrochemical devices. However, its performance and stability on various substrates are hindered by weak adhesion to the surface. In this study, a strongly adherent polyaniline conducting polymer layer with a thickness of five nanometers was electrografted onto an initiating monolayer on gold and tin-doped indium oxide substrates. These electrografted monolayers consist of vertically oriented fully oxidized-protonated (pernigraniline salt) and deprotonated (pernigraniline base) forms of polyaniline. The monolayer exhibits pH-dependent colour changes and it is suitable for enzyme compatibility. In light of these findings, we have developed and characterized an electrochemical glucose biosensor based on the monolayer of polyaniline on a gold electrode. The biosensor utilizes glucose oxidase as the biorecognition element for the selective detection of glucose concentrations in real blood plasma samples.

Polyaniline nanowire arrays generated through oriented mesoporous silica films: effect of pore size and spectroelectrochemical response

Indium-tin oxide electrodes modified with vertically aligned silica nanochannel membranes have been produced by electrochemically assisted self-assembly of cationic surfactants (cetyl- or octadecyl-trimethylammonium bromide) and concomitant polycondensation of the silica precursors (tetraethoxysilane). They exhibited pore diameters in the 2-3 nm range depending on the surfactant used. After surfactant removal, the bottom of mesopores was derivatized with aminophenyl groups via electrografting (i.e., electrochemical reduction of in situ generated aminophenyl monodiazonium salt). These species covalently bonded to the ITO substrate were then exploited to grow polyaniline nanofilaments by electropolymerization of aniline through the nanochannels. Under potentiostatic conditions, the length of polyaniline wires is controllable by tuning the electropolymerization time. From cyclic voltammetry characterization performed either before or after dissolution of the silica template, it appeared that both the polyaniline/silica composite and the free polyaniline nanowire arrays were electroactive, yet with much larger peak currents in the latter case as a result of larger effective surface area offered to the electrolyte solution. At identical electropolymerization time, the amount of deposited polyaniline was larger when using the silica membrane with larger pore diameter. All polyaniline deposits exhibited electrochromic properties. However, the spectroelectrochemical data indicated more complete interconversion between the coloured oxidized form and colourless reduced polyaniline for the arrays of nanofilaments in comparison to bulky films. In addition, the template-free nanowire arrays (i.e., after silica dissolution) were characterized by faster electrochromic behaviour than the polyaniline/silica hybrid, confirming the potential interest of such polyaniline nano-brushes for practical applications.

Experimental and Theoretical Study of the Covalent Grafting of Triazole Layer onto the Gold Surface

Finding novel strategies for surface modification is of great interest in electrochemistry and material sciences. In this study, we present a strategy for modification of a gold electrode through covalent attachment of triazole (TA) groups. Triazole groups were electrochemically grafted at the surface of the electrode by a reduction of in situ generated triazolediazonium cations. The resulting grafted surface was characterized before and after the functionalization process by different electrochemical methods (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)) confirming the presence of the grafted layer. The grafting of TA on the electrode surface was confirmed using analysis of surface morphology (by atomic force microscopy), the thickness of the grafted layer (by ellipsometry) and its composition (by X-ray photoelectron spectroscopy). Density functional theory (DFT) calculations imply that the grafted triazole offers a stronger platform than the grafted aryl layers.

Controlling Redox Enzyme Orientation at Planar Electrodes

Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve efficient direct electron transfer by tunneling between enzymes and conductive surfaces. Based on various examples of bioelectrochemical studies described in the recent literature, this review discusses the issue of enzyme immobilization at planar electrode interfaces. The fundamental importance of controlling enzyme orientation, how to obtain such orientation, and how it can be verified experimentally or by modeling are the three main directions explored. Since redox enzymes are sizable proteins with anisotropic properties, achieving their functional immobilization requires a specific and controlled orientation on the electrode surface. All the factors influenced by this orientation are described, ranging from electronic conductivity to efficiency of substrate supply. The specificities of the enzymatic molecule, surface properties, and dipole moment, which in turn influence the orientation, are introduced. Various ways of ensuring functional immobilization through tuning of both the enzyme and the electrode surface are then described. Finally, the review deals with analytical techniques that have enabled characterization and quantification of successful achievement of the desired orientation. The rich contributions of electrochemistry, spectroscopy (especially infrared spectroscopy), modeling, and microscopy are featured, along with their limitations.

Porous silicon–polyaniline hybrid composites synthesized through electroreduction of an aryldiazonium salt: preparation and photocurrent properties

Porous Si–polyaniline composites were realized by electropolymerization with an underlayer of phenylamine. The composite showed photocurrent properties higher than those of porous Si or Si–polyaniline composites realized without underlayer.

Analysis of photocurrent and capacitance of TiO2 nanotube–polyaniline hybrid composites synthesized through electroreduction of an aryldiazonium salt

TiO₂ nanotube–polyaniline hybrid composites were synthesized using an aminophenyl under-layer electrochemically grafted on TiO₂ obtaining improvements in photocurrent and capacitance.