No abstract

Neurotransmitters are molecules that transfer chemical signals between neurons to convey messages for any action conducted by the nervous system. All neurotransmitters are medically important; the detection and analysis of these molecules play vital roles in the diagnosis and treatment of diseases. Among analytical strategies, electrochemical techniques have been identified as simple, inexpensive, and less time-consuming processes. Electrochemical analysis is based on the redox behaviors of neurotransmitters, as well as their metabolites. A variety of electrochemical techniques are available for the detection of biomolecules. However, the development of a sensing platform with high sensitivity and selectivity is challenging, and it has been found to be a bottleneck step in the analysis of neurotransmitters. Nanomaterials-based sensor platforms are fascinating for researchers because of their ability to perform the electrochemical analysis of neurotransmitters due to their improved detection efficacy, and they have been widely reported on for their sensitive detection of epinephrine, dopamine, serotonin, glutamate, acetylcholine, nitric oxide, and purines. The advancement of electroanalytical technologies and the innovation of functional nanomaterials have been assisting greatly in in vivo and in vitro analyses of neurotransmitters, especially for point-of-care clinical applications. In this review, firstly, we focus on the most commonly employed electrochemical analysis techniques, in conjunction with their working principles and abilities for the detection of neurotransmitters. Subsequently, we concentrate on the fabrication and development of nanomaterials-based electrochemical sensors and their advantages over other detection techniques. Finally, we address the challenges and the future outlook in the development of electrochemical sensors for the efficient detection of neurotransmitters.

Nitrite (NO 2 −) is one of the most intensively studied species in foods owing to its detrimental effects on the human body. Here we report on a high-performance electrochemical sensor based on cobalt oxide nanosheets and gold nanoparticles (Co 3 O 4 /Au) for the detection of NO 2 − . The structural morphology and chemical composition of the nanomaterial were examined using a scanning electron microscope and energy dispersive X-ray spectroscopy. The Au/Co 3 O 4 /GCE (glassy carbon electrode) was capable of electrooxidizing NO 2− at a low onset potential with a higher anodic peak current over other modified electrodes (bare GCE, Co 3 O 4 /GCE, and Au/GCE). The analytical performance of the electrochemical sensor was tested using square wave voltammetry. The sensor exhibited good linearity in the selected concentration range from 1.0 to 4000.0 μM with an R 2 value of 0.999 and the limit of detection (LOD) of 0.11 μM. The Au/Co 3 O 4 /GCE demonstrated high selectivity and good stability. Moreover, the Au/Co 3 O 4 /GCE showed a good anti-interference capacity in the presence of other potential co-existing ions. The performance of the developed sensor was scrutinized further with commercial bottled water and a beef sample with good recovery rates, thereby confirming its plausible applications in food and beverage safety and quality control.

4-hydroxy-3-methoxybenzaldehyde (vanillin) is a biophenol compound that is relatively abundant in the world’s most popular flavoring ingredient, natural vanilla. As a powerful antioxidant chemical with beneficial antimicrobial properties, vanillin is not only used as a flavoring agent in food, beverages, perfumery, and pharmaceutical products, it may also be employed as a food-preserving agent, and to fight against yeast and molds. The widespread use of vanilla in major industries warrants the need to develop simple and cost-effective strategies for the quantitative determination of its major component, vanillin. Herein, we explore the applications of a selective and sensitive electrochemical sensor (Au electrodeposited on a fluorine-doped reduced-graphene-oxide-modified glassy-carbon electrode (Au/F-rGO/GCE)) for the detection of vanillin. The electrochemical performance and analytical capabilities of this novel electrochemical sensor were investigated using electrochemical techniques including cyclic voltammetry and differential pulse voltammetry. The excellent sensitivity, selectivity, and reproducibility of the proposed electrochemical sensor may be attributed to the high conductivity and surface area of the formed nanocomposite. The high performance of the sensor developed in the present study was further demonstrated with real-sample analysis.

L-hydroxyproline (Hyp) is one of the significant amino acids present in connective tissue proteins such as collagen, elastin, and gelatin. The quantitative analysis of Hyp levels in bodily fluids is critical to assist with diagnosing diseases and early treatments. In the present study, for the first time, we report on a facile electrochemical method for the detection of Hyp using gold nanoparticles (AuNPs), which were electrochemically deposited on a glassy carbon electrode (GCE). The electrochemical behavior of the AuNPs/GCE for the oxidation of Hyp was examined using cyclic voltammetry, demonstrating higher electrocatalytic activity in contrast to GCE and bulk Au electrodes. Additionally, the mechanism for the electrochemical oxidation of Hyp was investigated using in situ Fourier transform infrared (FT-IR) spectroscopy. Moreover, the electrochemical sensing performance of the AuNPs was investigated using differential pulse voltammetry (DPV), exhibiting a low limit of detection (0.026 mM) and high sensitivity (8.5 μA (mM cm2)−1). The interference of other amino acids present in collagen and urine has been further tested, demonstrating high selectivity and good reproducibility. The novel electrochemical sensing approach described in the present study may lead to a facile non-enzymatic technique for the sensitive detection of Hyp, a significant biomarker.