Optical fiber spectroelectrochemical device for detection of catechol at press-transferred single-walled carbon nanotubes electrodes

Design of optoelectrodes for the remote imaging of cells and in situ electrochemical detection of neurosecretory events

Optical fibers have opened avenues for remote imaging, bioanalyses and recently optogenetics. Besides, miniaturized electrochemical sensors have offered new opportunities in sensing directly redox neurotransmitters. The combination of both optical and electrochemical approaches was usually performed on the platform of microscopes or within microsystems. In this work, we developed optoelectrodes which features merge the advantages of both optical fibers and microelectrodes. Optical fiber bundles were modified at one of their extremity by a transparent ITO deposit. The electrochemical responses of these ITO-modified bundles were characterized for the detection of dopamine, epinephrine and norepinephrine. The analytical performances of the optoelectrodes were equivalent to the ones reported for carbon microelectrodes. The remote imaging of model neurosecretory PC12 cells by optoelectrodes was performed upon cell-staining with common fluorescent dyes: acridine orange and calcein-AM. An optoelectrode placed by micromanipulation at a few micrometers-distance from the cells offered remote images with single cell resolution. Finally, in situ electrochemical sensing was demonstrated by additions of K⁺-secretagogue solutions near PC12 cells under observation, leading to exocytotic events detected as amperometric spikes at the ITO surface. Such dual sensors should pave the way for in vivo remote imaging, optogenetic stimulation, and simultaneous detection of neurosecretory activities.

Prussian blue-doped nanosized polyaniline for electrochemical detection of benzenediol isomers

Simultaneous speciation of benzenediol isomers (BDIs), 1,2-benzenediol (catechol, CC), 1,3-benzenediol (resorcinol, RS), and 1,4-benzenediol (hydroquinone, HQ), was investigated by differential pulse voltammetry (DPV) using a graphite paste electrode (GPE) modified with Prussian blue-polyaniline nanocomposite. The modified GPE showed good stability, sensitivity, and selectivity properties for all the three BDIs. Prussian blue-doped nanosized polyaniline (PBNS-PANI) was synthesized first by using mechanochemical reactions between aniline and ferric chloride hexahydrate as the oxidants and then followed by the addition of potassium hexacyanoferrate(II) in a solid-state and template-free technique. The material was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The DPV measurements are performed in phosphate electrolyte solution with pH 4.0 at a potential range of - 0.1 to 1.0 V. The proposed modified electrode displayed a strong, stable, and continuous three well-separated oxidation peaks towards electrooxidation at potentials 0.20, 0.31, and 0.76 V for HQ, CC, and RS, respectively. The calibration curves were linear from 1 to 350.5 μM for both HQ and CC, while for RS, it was from 2 to 350.5 μM. The limit of detection was determined to be 0.18, 0.01, and 0.02 μM for HQ, CC, and RS, respectively. The analytical performance of the PBNS-PANI/GPE has been evaluated for simultaneous determination of HQ, CC, and RS in creek water, commercial hair dye, and skin whitening cream samples with satisfactory recoveries between 90 and 106%. Overall, we demonstrated that the presence of NS-PANI and PB resulted in a large redox-active surface area that enabled a promising analytical platform for simultaneous detection of BDIs. Graphical abstract.

A Flexible Platform of Electrochemically Functionalized Carbon Nanotubes for NADH Sensors

A flexible electrode system entirely constituted by single-walled carbon nanotubes (SWCNTs) has been proposed as the sensor platform for β-nicotinamide adenine dinucleotide (NADH) detection. The performance of the device, in terms of potential at which the electrochemical process takes place, significantly improves by electrochemical functionalization of the carbon-based material with a molecule possessing an o-hydroquinone residue, namely caffeic acid. Both the processes of SWCNT functionalization and NADH detection have been studied by combining electrochemical and spectroelectrochemical experiments, in order to achieve direct evidence of the electrode modification by the organic residues and to study the electrocatalytic activity of the resulting material in respect to functional groups present at the electrode/solution interface. Electrochemical measurements performed at the fixed potential of +0.30 V let us envision the possible use of the device as an amperometric sensor for NADH detection. Spectroelectrochemistry also demonstrates the effectiveness of the device in acting as a voltabsorptometric sensor for the detection of this same analyte by exploiting this different transduction mechanism, potentially less prone to the possible presence of interfering species.

Optically transparent electrodes for spectroelectrochemistry fabricated with graphene nanoplatelets and single-walled carbon nanotubes

Hybrid optically transparent electrodes based on single-walled carbon nanotubes and graphene nanoplatelets have been fabricated. The new methodology can be used with other carbon nanomaterials.

Concluding remarks: there's nowt so queer as carbon electrodes

This contribution provides a personal overview and summary of Faraday Discussion 172 on “Carbon in Electrochemistry”, covering some of the key points made at the meeting within the broader context of other recent developments on carbon materials for electrochemical applications. Although carbon electrodes have a long history of use in electrochemistry, methods and techniques are only just becoming available that can test long-established models and identify key features for further exploration. This Discussion has highlighted the need for a better understanding of the impact of surface structure, defects, local density of electronic states, and surface functionality and contamination, in order to advance fundamental knowledge of various electrochemical processes and phenomena at carbon electrodes. These developments cut across important materials such as graphene, carbon nanotubes, conducting diamond and high surface area carbon materials. With more detailed pictures of structural and electronic controls of electrochemistry at carbon electrodes (and electrodes generally), will come rational advances in various technological applications, from sensors to energy technology (particularly batteries, supercapacitors and fuel cells), that have been well-illustrated at this Discussion.