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Neurotransmitters are important chemical messengers in the nervous system that play a crucial role in physiological and physical health. Abnormal levels of neurotransmitters have been correlated with physical, psychotic, and neurodegenerative diseases such as Alzheimer’s, Parkinson’s, dementia, addiction, depression, and schizophrenia. Although multiple neurotechnological approaches have been reported in the literature, the detection and monitoring of neurotransmitters in the brain remains a challenge and continues to garner significant attention. Neurotechnology that provides high-throughput, as well as fast and specific quantification of target analytes in the brain, without negatively impacting the implanted region is highly desired for the monitoring of the complex intercommunication of neurotransmitters. Therefore, it is crucial to develop clinical assessment techniques that are sensitive and reliable to monitor and modulate these chemical messengers and screen diseases. This review focuses on summarizing the current electrochemical measurement techniques that are capable of sensing neurotransmitters with high temporal resolution in real time. Advanced neurotransmitter sensing platforms that integrate nanomaterials and biorecognition elements are explored.

This thesis describes investigations into the development of new electrochemical methodologies applicable to organic synthesis. Initial investigations were focused on the development of new strategies for the generation and utilisation of alkoxy radicals under electrochemical conditions. To this end, a new procedure for an electrochemical manganese-catalysed deconstructive chlorination of cycloalkanols was developed. In this study, tertiary cyclopropanols and cyclobutanols were conveniently converted into synthetically useful distally chlorinated ketones via alkoxy radical intermediates. This methodology utilises an inexpensive manganese (II) pre-catalyst to facilitate the synthesis of a diverse range of β- and γ-chloroketones (40 examples, 30-90% yield). Facile scale-up was also performed by employing a recirculating flow-electrochemistry system and mechanistic investigations, including the use of cyclic voltammetry, allowed the proposal of alkoxy radical intermediates. Further work on the electrochemical generation of alkoxy radicals was then performed to overcome the limitations associated with the manganese-catalysed method. This work centred around the use of cerium (III) or (IV) salts to generate alkoxy radicals under electrochemical conditions. Following these unsuccessful investigations, the development of a photoelectrochemical system for the cerium-mediated generation of alkoxy radicals was subsequently explored. Chapter 4 of this thesis then describes investigations into an electrochemical alkene hetero-difunctionalisation procedure that proceeds via a 1,4-nitrile migration. In this study, cyanohydrin substrates bearing a distal alkene were converted into synthetically useful 1,2-azidonitriles using a manganese (II) salt as an azide transfer reagent (28 examples, 27-75% yield). This methodology was then extended to perform electrochemical alkene sulfonylcyanation and trifluoromethylcyanation, as well as to access a trifunctionalised hexanenitrile from a functionalised malononitrile starting material. The utility of the products formed was demonstrated through orthogonal derivatisation, and mechanistic investigations, including cyclic voltammetry studies and a radical clock experiment, allowed the proposal of radical intermediates within the reaction mechanism.

Detailed studies of the electrochemical oxygen reduction reaction (ORR) on catalyst materials are crucial to improving the performance of different electrochemical energy conversion and storage systems (e.g., fuel cells and batteries), as well as numerous chemical synthesis processes. In the effort to reduce the loading of expensive platinum group metal (PGM)-based catalysts for ORR in the electrochemical systems, many carbon-based catalysts have already shown promising results and numerous investigations on those catalysts are in progress. Most of these studies show the catalyst materials’ ORR performance as current density data obtained through the rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) experiments taking cyclic voltammograms (CV) or linear sweep voltammograms (LSV) approaches. However, the provided descriptions or interpretations of those data curves are often ambiguous and recondite which can lead to an erroneous understanding of the ORR phenomenon in those specific systems and inaccurate characterization of the catalyst materials. In this paper, we presented a study of ORR on a newly developed carbon-based catalyst, the nitrogen-doped graphene/metal-organic framework (N-G/MOF), through RDE and RRDE experiments in both alkaline and acidic mediums, taking the LSV approach. The functions and crucial considerations for the different parts of the RDE/RRDE experiment such as the working electrode, reference electrode, counter electrode, electrolyte, and overall RDE/RRDE process are delineated which can serve as guidelines for the new researchers in this field. Experimentally obtained LSV curves’ shapes and their correlations with the possible ORR reaction pathways within the applied potential range are discussed in depth. We also demonstrated how the presence of hydrogen peroxide (H2O2), a possible intermediate of ORR, in the alkaline electrolyte and the concentration of acid in the acidic electrolyte can maneuver the ORR current density output in compliance with the possible ORR pathways.

A nanocomposite is described that consists of TmPO and graphene oxide (GO) and is used to modify a glassy carbon electrode (GCE) to obtain a sensor for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). GO and TmPO were synthesized via the Hummers method and by a hydrothermal method, respectively. The nanocomposite was characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical properties of the modified GCE were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The good performance of the modified GCE results from the synergistic effects between GO with its good electrical conductivity and of TmPO as the electron mediator that accelerates the electron transfer rate. Compared to a bare GCE, a GO/GCE and a TmPO /GCE, the GO/TmPO /GCE exhibits three well-defined and separated oxidation peaks (at -0.05, +0.13 and + 0.26 V vs. SCE). Responses to AA, DA and UA are linear in the 0.1-1.0 mM, 2-20 μM and 10-100 μM concentration ranges, respectively. Graphical abstract Schematic presentation of a nanocomposite that consists TmPO and graphene oxide (GO) and is used to modify a glassy carbon electrode (GCE) to obtain a sensor for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA).

A self-assembled periodic superlattice material was obtained by integrating positively charged semiconductive sheets of a Zn-NiAl layered double hydroxide (LDH) and negatively charged layers of reduced graphene oxide (rGO). The material was used to modify a glassy carbon electrode which then is shown to be a viable sensor for the diagnostic parameters dopamine (DA), uric acid (UA) and ascorbic acid (AA). The modified GCE displays excellent electrocatalytic activity towards these biomolecules. This is assumed to be due to the synergistic effects of (a) excellent interfacial electrical conductivity that is imparted by direct neighboring of conductive rGO to semiconductive channels of LDHs, (b) the superb intercalation feature of LDHs, and (c) the enlarged surface with an enormous number of active sites. The biosensor revealed outstanding electrochemical performances in terms of selectivity, sensitivity, and wide linear ranges. Typically operated at working potentials of −0.10, +0.13 and + 0.27 V vs. saturated calomel electrode, the lower detection limits for AA, DA and UA are 13.5 nM, 0.1 nM, and 0.9 nM, respectively, at a signal-to-noise ratio of 3. The sensor was applied to real-time tracking of dopamine efflux from live human nerve cells. Graphical abstract Schematic of the preparation of a superlattice self-assembled material by integrating positively charged semiconductive sheets of Zn-NiAl layered double hydroxide (LDH) with negatively charged reduced graphene oxide (rGO) layers. It was applied to simultaneous electrochemical detection of dopamine (DA), uric acid and ascorbic acid.

The interactions of compounds with DNA have been studied since the recognition of the role of nucleic acid in organisms. The design of molecules which specifically interact with DNA sequences allows for the control of the gene expression. Determining the type and strength of such interaction is an indispensable element of pharmaceutical studies. Cognition of the therapeutic action mechanisms is particularly important for designing new drugs. Owing to their sensitivity, simplicity, and low costs, electrochemical methods are increasingly used for this type of research. Compared to other techniques, they require a small number of samples and are characterized by a high reliability. These methods can provide information about the type of interaction and the binding strength, as well as the damage caused by biologically active molecules targeting the cellular DNA. This review paper summarizes the various electrochemical approaches used for the study of the interactions between pharmaceuticals and DNA. The main focus is on the papers from the last decade, with particular attention on the voltammetric techniques. The most preferred experimental approaches, the electrode materials and the new methods of modification are presented. The data on the detection ranges, the binding modes and the binding constant values of pharmaceuticals are summarized. Both the importance of the presented research and the importance of future prospects are discussed.

The article describes innovative procedures for determining In(III) using anodic stripping voltammetry (ASV) and adsorptive stripping voltammetry (AdSV) with cupferron as a chelating agent. In both procedures, an environmentally friendly solid bismuth microelectrode (SBiµE) with a diameter of 25 µm was used as the working electrode. In both procedures, 0.1 mol L−1 acetate buffer with a pH of 3.0 ± 0.05 was used as the supporting electrolyte. The electrochemical measurement conditions were as follows: −2.4 V for a 20 s activation step and −1.2 V for a 20 s accumulation step for ASV, and −2.5 V for a 45 s activation step and −0.65 V for a 10 s accumulation step for AdSV. The signal was recorded as a result of a positive potential change from −1.0 to −0.3 V in the case of the ASV procedure and as a result of a negative potential change from −0.4 to −1.0 V in the case of the AdSV procedure. The calibration graph was linear from 5 × 10−9 mol L−1 to 5 × 10−7 mol L−1 with a detection limit of 1.4 × 10−9 mol L−1 for ASV and from 1 × 10−9 mol L−1 to 1 × 10−7 mol L−1 with a detection limit of 3.9 × 10−10 mol L−1 for AdSV. The effect of interferents such as surfactants, humic substances and EDTA on the analytical signal was compared in the case of signal recording using the ASV technique with the signal recorded using the AdSV technique. Based on the results obtained, it was determined how the charge of interferents affects the signal depending on the technique used. To validate the practical application of the developed procedures, an analysis of In(III) recovery from samples of the Baltic Sea and Synthetic Sea Water was performed.

A composite was prepared from a Co(II)-based zeolitic imidazolate framework (ZIF-67) and graphene oxide (GO) by an in situ growth method. The material was electrodeposited on a glassy carbon electrode (GCE). The modified GCE was used for the simultaneous voltammetric determination of dopamine (DA) and uric acid (UA), typically at working potentials of 0.11 and 0.25 V (vs. SCE). The morphology and structure of the nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The modified electrode exhibits excellent electroanalytical performance for DA and UA owing to the synergistic effect of the high electrical conductivity of GO and the porosity of ZIF-67. By applying differential pulse voltammetry, a linear response is found for DA in the 0.2 to 80 μM concentration range, and for UA between 0.8 and 200 μM, with detection limits of 50 and 100 nM (at S/ N  = 3), respectively. Further studies were performed on the effect of potential interferents, and on electrode stability and reproducibility. The modified GCE was applied to the simultaneous detection of DA and UA in spiked human urine and gave satisfying recoveries. Graphical abstract Schematic of the preparation procedure of GO-ZIF67 and electrochemical reaction mechanisms of UA and DA at the GO-ZIF67-modified glassy carbon electrode (GCE). GO: graphene oxide; ZIF-67: Co(II)-based zeolitic imidazolate framework.