Raman spectroelectrochemical study of Meldola blue, adsorbed and electropolymerized at a gold electrode

Flow injection enzymatic biosensor for aldehydes based on a Meldola Blue-Ni complex electrochemical mediator

Carbon nanofibers (CNF) are efficient electrode modifiers in electrochemical biosensors that enhance the electrochemical active area, induce electrocatalytic effect toward the oxidation of the enzymatic cofactor nicotinamide adenine dinucleotide (reduced form, NADH), and enable the quantitative immobilization of enzymes. Combining CNF with efficient and stable mediators radically augments the speed of electron transfer between NADH and solid electrodes and leads to electrochemical sensors characterized by high sensitivity and stability. The main aim of this work was to investigate the performance of a novel mediator for NADH with advantageously low solubility in an electrochemical detector based on a screen-printed CNF electrode as well as its potential in biosensing. Using a mediator, prepared from Meldola Blue and Ni hexamine chloride, a stable and sensitive electrochemical NADH sensor is provided with a detection limit of 0.5 μmol L^-1. Further on, covalent immobilization of a recently described aldehyde dehydrogenase from the Antarctic Flavobacterium PL002 strain on the surface of the mediator-modified electrode produced a stable biosensor for the detection of aldehydes. When integrated in a flow injection analysis (FIA) setup with amperometric detection at 0.1 V vs. Ag/AgCl, the measurement of benzaldehyde with a detection limit of 10 μmol L^-1 over a linear range of 30-300 μmol L^-1 is possible. Determination of trace benzaldehyde impurities in a pharmaceutical excipient was also demonstrated and results compared with a chromatographic method. Graphical abstract.

Fabrication of liquid–liquid self-assembled Ag arrays on disposable screen-printed electrodes and their application in the identification and analysis of the adsorption behavior of organic carboxylates through in situ electrochemical surface-enhanced Raman scattering

A disposable Ag array@screen-printed electrode (SPE) was fabricated for the identification and analysis of the adsorption behavior of organic carboxylates in in situ electrochemical surface-enhanced Raman scattering (EC-SERS).

Spectroelectrochemistry, the future of visualizing electrode processes by hyphenating electrochemistry with spectroscopic techniques

Reviewing the future of electrochemistry combined with infrared, Raman, and nuclear magnetic resonance spectroscopy as well as mass spectrometry.

Raman and IR Spectroelectrochemical Methods as Tools to Analyze Conjugated Organic Compounds

In the presented work, two spectroelectrochemical techniques are discussed as tools for the analysis of the structural changes occurring in the molecule on the vibrational level of energy. Raman and IR spectroelectrochemistry can be used for advanced characterization of the structural changes in the organic electroactive compounds. Here, the step-by-step analysis by means of Raman and IR spectroelectrochemistry is shown. Raman and IR spectroelectrochemical techniques provide complementary information about structural changes occurring during an electrochemical process, i.e. allows for the investigation of redox processes and their products. The examples of IR and Raman spectroelectrochemical analysis are presented, in which the products of the redox reactions, both in solution and solid state, are identified.

Detection of aniline oligomers on polyaniline-gold interface using resonance Raman scattering

In situ deposited conducting polyaniline films prepared by the oxidation of aniline with ammonium peroxydisulfate in aqueous media of various acidities on gold and silicon supports were characterized by Raman spectroscopy. Enhanced Raman bands were found in the spectra of polyaniline films produced in the solutions of weak acids or in water on gold surface. These bands were weak for the films prepared in solutions of a strong acid on a gold support. The same bands are present in the Raman spectra of the reaction intermediates deposited during aniline oxidation in water or aqueous solutions of weak or strong acids on silicon removed from the reaction mixture at the beginning of the reaction. Such films are formed by aniline oligomers adsorbed on the surface. They were detected on the polyaniline-gold interface using resonance Raman scattering on the final films deposited on gold. The surface resonance Raman spectroscopy of the monolayer of oligomers found in the bulk polyaniline film makes this method advantageous in surface science, with many applications in electrochemistry, catalysis, and biophysical, polymer, or analytical chemistry.

Phenothiazine derivative-accelerated microbial extracellular electron transfer in bioelectrochemical system

In bioelectrochemical system (BES) the extracellular electron transfer (EET) from bacteria to anode electrode is recognized as a crucial step that governs the anodic reaction efficiency. Here, we report a novel approach to substantially enhance the microbial EET by immobilization of a small active phenothiazine derivative, methylene blue, on electrode surface. A comparison of the currents generated by Shewanella oneidensis MR-1 and its mutants as well as the electrochemical analytical results reveal that the accelerated EET was attributed to enhanced interactions between the bacterial outer-membrane cytochromes and the immobilized methylene blue. A further investigation into the process using in situ Raman spectro-electrochemical method coupled with density functional theory calculations demonstrates that the electron shuttling was achieved through the change of the molecule conformation of phenothiazine in the redox process. These results offer useful information for engineering BES.