Electrochemical Sensor for the Quantification of Dopamine Using Glassy Carbon Electrodes Modified with Single-Wall Carbon Nanotubes Covalently Functionalized with Polylysine

Surface grafting of poly-L-lysine via diazonium chemistry to enhance cell adhesion to biomedical electrodes

The ability to study and regulate cell behavior at a biomaterial interface requires a strict control over its surface chemistry. Significance of studying cell adhesion in vitro and in vivo has become increasingly important, particularly in the field of tissue engineering and regenerative medicine. A promising surface modification route assumes using organic layers prepared by the method of electrografting of diazonium salts and their further functionalization with biologically active molecules as cell adhesion promoters. This work reports the modification of platinum electrodes with selected diazonium salts and poly-L-lysine to increase the number of sites available for cell adhesion. As-modified electrodes were characterized in terms of their chemical and morphological properties, as well as wettability. In order to monitor the process of cell attachment, biofunctionalized electrodes were used as substrates for culturing human neuroblastoma SH-SY5Y cells. The experiments revealed that cell adhesion is favored on the surface of diazonium-modified and poly-L-lysine coated electrodes, indicating proposed modification route as a valuable strategy enhancing the integration between bioelectronic devices and neural cells.

Development of Electrochemical Sensors/Biosensors to Detect Natural and Synthetic Compounds Related to Agroalimentary, Environmental and Health Systems in Argentina. A Review of the Last Decade

Electrochemical sensors and biosensors are analytical tools, which are in continuous development with the aim of generating new analytical devices which are more reliable, cheaper, faster, sensitive, selective, and robust than others. In matrices related to agroalimentary, environmental, or health systems, natural or synthetic compounds occur which fulfil specific roles; some of them (such as mycotoxins or herbicides) may possess harmful properties, and others (such as antioxidants) beneficial ones. This imposes a challenge to develop new tools and analytical methodologies for their detection and quantification. This review summarises different aspects related to the development of electrochemical sensors and biosensors carried out in Argentina in the last ten years for application in agroalimentary, environmental, and health fields. The discussion focuses on the construction and development of electroanalytical methodologies for the determination of mycotoxins, herbicides, and natural and synthetic antioxidants. Studies based on the use of different electrode materials modified with micro/nanostructures, functional groups, and biomolecules, complemented by the use of chemometric tools, are explored. Results of the latest reports from research groups in Argentina are presented. The main goals are highlighted.

Carbon Nanotube Film Electrodes with Acrylic Additives: Blocking Electrochemical Charge Transfer Reactions

Carbon nanotubes (CNTs) processed into conductive films by liquid phase deposition technologies reveal increasing interest as electrode components in electrochemical device platforms for sensing and energy storage applications. In this work we show that the addition of acrylic latex to water-based CNT inks not only favors the fabrication of stable and robust flexible electrodes on plastic substrates but, moreover, sensitively enables the control of their electrical and electrochemical transport properties. Importantly, within a given concentration range, the acrylic additive in the films, being used as working electrodes, effectively blocks undesired faradaic transfer reactions across the electrode-electrolyte interface while maintaining their capacitance response as probed in a three-electrode electrochemical device configuration. Our results suggest a valuable strategy to enhance the chemical stability of CNT film electrodes and to suppress non-specific parasitic electrochemical reactions of relevance to electroanalytical and energy storage applications.

A novel electrochemical sensor based on carbon nanotubes array for selective detection of dopamine or uric acid

A novel single-walled carbon nanotubes array-modified glassy carbon electrode (SWCNTs array-GCE) has been fabricated through a simple electrochemical technique. Benefitting from their vertically aligned configuration on the electrode surface, the modified single-walled carbon nanotubes can be used more efficiently in comparison with other modified method. The as-fabricated SWCNTs array-GCE can separate the anodic oxidation potential of dopamine (DA), uric acid (UA) and ascorbic acid (AA) with well-defined peak separation in the presence of each other, and thus employs as a new electrochemical sensor for selective determination of DA and UA. It can make a further improvement of the electrocatalytic ability of the electrode to perform an acetone pretreatment to SWCNTs array-GCE before electrochemical detection, which has been confirmed by atomic force microscope and electrochemical impedance spectroscopic measurements. Especially, unlike other carbon nanotubes-based electrode at which only two redox pairs are observed for dopamine oxidations, a third two-electron oxidation of 5,6-dihydroxyindole to indole-5,6-quinone can be clearly observed at acetone-pretreated SWCNTs array-GCE, showing the excellent electrocatalytic performance of as-fabricated electrode toward dopamine. The practicability of SWCNTs array-GCE was evaluated for the selective detection of DA and UA in real sample solutions of human serum and urine. It revealed acceptable recovery results in the range of 94-104%, indicating that it might be a promising platform for further biosensor development.

Electrochemical dopamine sensor based on the use of a thermosensitive polymer and an nanocomposite prepared from multiwalled carbon nanotubes and graphene oxide

An electrochemical dopamine sensor with a temperature-controlled switch was constructed by using a mixture of thermo-sensitive block copolymers (type tBA-PDEA-tBA), graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs). If the temperature is below 26 °C, the polymer on the glassy carbon electrode (GCE) is stretched, the distance between the MWCNTs is large, and the charge transfer resistance (R_ct) of the composite also is large. In the presence of dopamine, the electron transfer at the electrode is strongly retarded and in the "off" state. At above 38 °C, the polymer is shrunk and the R_ct is much smaller. The presence of dopamine results in a rapid electron transfer at the GCE, and this is referred to as the "on" state. At temperatures between 26 and 38 °C, the polymer shrinks slightly and has a "spring-like" state. There is a linear relationship between the response current (typically measured at a potential as low as 0.16 V vs. Ag/AgCl) and temperature. The response to dopamine is linear in the 0.06 to 4.2 μM and 4.2 to 18.2 μM concentration range, and the detection limit is 42 nM. Conceivably, this approach provides a novel approach towards the design of electrochemical sensors based on the use of thermo-sensitive polymers. Graphical abstract Schematic presentation of reversible and temperature-controlled electrochemical response of dopamine on the thermo-sensitive block copolymers (tBA-PDEA-tBA) / multi-walled carbon nanotubes (MWCNTs) / graphene oxide (GO) / glassy carbon electrode (GCE).

Simultaneous Detection of Dopamine and Uric Acid Using a Poly(l-lysine)/Graphene Oxide Modified Electrode

A novel, simple and selective electrochemical method was investigated for the simultaneous detection of dopamine (DA) and uric acid (UA) on a poly(l-lysine)/graphene oxide (GO) modified glassy carbon electrode (PLL/GO/GCE) by differential pulse voltammetry (DPV). The electrochemically prepared PLL/GO sensory platform toward the oxidation of UA and DA exhibited several advantages, including high effective surface area, more active sites and enhanced electrochemical activity. Compared to the PLL-modified GCE (PLL/GCE), GO-modified GCE and bare GCE, the PLL/GO/GCE exhibited an increase in the anodic potential difference and a remarkable enhancement in the current responses for both UA and DA. For the simultaneous detection of DA and UA, the detection limits of 0.021 and 0.074 μM were obtained, while 0.031 and 0.018 μM were obtained as the detection limits for the selective detection of UA and DA, using DPV in the linear concentration ranges of 0.5 to 20.0 and 0.5 to 35 μM, respectively. In addition, the PLL/GO/GCE demonstrated good reproducibility, long-term stability, excellent selectivity and negligible interference of ascorbic acid (AA). The proposed modified electrode was successfully implemented in the simultaneous detection of DA and UA in human blood serum, urine and dopamine hydrochloride injection with satisfactory results.