Formation of a nickel hydroxide monolayer on Au through a self-assembled monolayer of 5,5'-dithiobis(2-nitrobenzoic acid): voltammetric, SERS and XPS investigations of the modified electrodes

The formation of self-assembled monolayers (SAM) of 5,5'-dithiobis (2-nitrobenzoic acid), DNBA on gold has enabled further derivatization of the electrode surface with functional moieties anchored to the surface bound molecules. A SAM of DNBA was formed on the Au surface. Nickel ions tethered to the SAM-covered Au surface, were subsequently derivatized electrochemically to yield nickel hydroxide overlayers, thereby showing the possibility of preparing ultra-thin films of metal oxides through solution chemistry. The nickel hydroxide surface coverage obtained on bare and SAM-covered electrodes was estimated from voltammetric peaks and it varied from one monolayer to about 300 monolayers. The formation of a monolayer of nickel hydroxide has been achieved for the first time by electrochemical modification. Further, the modified electrodes were subjected to SERS and XPS studies to understand their surface characteristics. Modified electrodes provide a catalytic pathway involving nickel hydroxide for the electro-oxidation of glucose in alkaline solutions

Ferrocene probe-assisted fluorescence quenching of PEI-carbon dots for NO detection and the logic gates based sensing of NO enabled by trimodal detection

Abstract Our research demonstrates the effectiveness of fluorescence quenching between polyethyleneimine functionalised carbon dots (PEI-CDs) and cyclodextrin encapsulated ferrocene for fluorogenic detection of nitric oxide (NO). We confirmed that ferrocene can be used as a NO probe by observing its ability to quench the fluorescence emitted from PEI-CDs, with NO concentrations ranging from 1 × 10–6 M to 5 × 10–4 M. The photoluminescence intensity (PL) of PEI-CDs decreased linearly, with a detection limit of 500 nM. Previous studies have shown that ferrocene is a selective probe for NO detection in biological systems by electrochemical and colorimetric methods. The addition of fluorogenic NO detection using ferrocene as a probe enables the development of a three-way sensor probe for NO. Furthermore, the triple mode NO detection (electrochemical, colorimetric, and fluorogenic) with ferrocene aids in processing sensing data in a controlled manner similar to Boolean logic operations. This work presents key findings on the mechanism of fluorescence quenching between ferrocene hyponitrite intermediate and PEI-CDs, the potential of using ferrocene for triple channel NO detection as a single molecular entity, and the application of logic gates for NO sensing

Self-assembled monolayers of 2-mercaptobenzimidazole on gold: stripping voltammetric determination of Hg(II)

Monomolecular level modification of electrode surfaces through a self-assembly approach is, of late, gaining importance in view of its many functional applications in areas such as molecular electronics, molecular recognition, electron transfer studies and electroanalysis. Self-assembled monolayer (SAM) modification of a gold electrode with 2-mercaptobenzimidazole (MBI) has been achieved. On this modified electrode, anodic stripping voltammetric determination of mercury at ppm/sub-ppm level concentrations has been successfully attempted. Pre-concentration, prior to stripping, has been effected through a non-electrolytic process involving chemical interactions between MBI and Hg(II). The results are described and discussed with a plausible scheme. Keywords: 2-Mercaptobenzimidazole, Self-assembled monolayer, Mercury(II), Anodic stripping voltammetr

Electron transfer studies through mixed self-assembled monolayers of thiophenol and thioctic acid

Mixed self-assembled monolayer of thiols were formed on the electrode surface using aromatic and aliphatic thiols and the modified interface were used to demonstrate charge trapping behavior at the modified interface. The electrode surface was modified by two schemes. In Scheme 1, electrode surface modified with methylene blue (MB) shows charge trapping behavior when contacts the electrolyte containing potassium ferricyanide. In Scheme 2, a redox-active bilayer is constructed using hexamineruthenium (II) chloride and methylene blue. This redox-active bilayer assembly exhibits unidirectional flow of current

Highly sensitive detection of proteins using voltammetric assay in the presence of silver nanostructures

A novel voltammetric protein assay has been demonstrated using bovine serum albumin in the presence of silver nanostructures (AgNs) formed electrochemically on gold substrates modified by self-assembled monolayer of thioctic acid. It is shown that the prepared AgNs exhibit voltammetric response characteristic of Ag and shows near Nernstian response at physiological pH. The advantages of the electrochemical assay compared to conventional protein analysis are the wide linear concentration range (10-4-10-11 g/mL) and trace level detection limits (50 pg/mL). The result of this electrochemical analysis agreed well with an independent spectrophotometric method using Bradford reagent, but the detection limit is far superior using the electrochemical method. Further, the modified electrode exhibits high sensitivity and long term stability. We invoke a new concept of surface enhanced activity of Ag+ ions at the electrochemical interface by the negatively charged bovine serum molecules

Novel effects of metal ion chelation on the properties of lipoic acid-capped Ag and Au nanoparticles

The effects of the interactions of metal ions with lipoic acid-capped Ag and Au nanoparticles have been studied by the combined use of electronic absorption spectroscopy and transmission electron microscopy. Three types of effects that are dependent on the metal ion concentration can be distinguished. First, in the dilute regime, there is reversible chelation of the metal ions, causing a marked dampening of the plasmon resonance band of the nanoparticles, but there is no aggregation. The magnitude of plasmon dampening depends on the nature as well as the concentration of the metal ions. In the intermediate concentration regime, aggregation occurs, but in the high concentration regime, there is precipitation. These different regimes are clearly evidenced in the changes in the electronic spectra and in the electron micrographs