Electrochemical Applications for the Antioxidant Sensing in Food Samples Such as Citrus and Its Derivatives, Soft Drinks, Supplementary Food and Nutrients

Although there are many definitions of antioxidants, the most general description; antioxidants are carried a phenolic function in their structure and prevent the formation of free radicals or intercept from damage to the cell by scavenging existing radicals. Moreover, they are one of the most effective substances that contain essential nutrients for healthy individuals. The importance of these antioxidants, which have an incredible effect on the body and increase the body’s resistance, is increasing day by day for healthy individuals. Numerous studies have been carried out for antioxidants with excellent properties and however new, reliable, selective, sensitive and green analytical methods are sought for their determination at trace levels in food samples. Along with the latest developments, electrochemical methods are of great interest in the world of science because they are fast, reliable, sensitive and environmentally friendly. Electrochemical methods have been frequently applied to analyze antioxidant capacity in many nutrients samples found in different forms such as solid, liquid without any pretreatment applications in the last decade. Furthermore, these methods are preferred because of the short analysis time, the ability to lower detection limits, reduction in a solvent, high sensitivity, portability, low sample consumption, wide working range, and more economical than existing other traditional analytical methods. The antioxidant sensing applications by modern electrochemical methods such as cyclic, square wave, differential pulse, and combined with stripping voltammetric techniques were used to deduce antioxidant capacity (AC) in critical nutrients. Moreover, this chapter includes a description of the classification of electrochemical methods according to the working electrode type, dynamic working range, limit of determination (LOD), limit of quantification (LOQ), sample type, and using standard analyte and so forth for each voltammetric methods. While many articles applied for the determination of antioxidant sensing by electrochemistry have gained momentum in the last two decades, we focused on the studies conducted over the last 4 years in this chapter

Applications of Molecularly Imprinted Films

Molecularly imprinted polymers are materials that have voids that are complementary in shape, size, and electronic environment to a specific molecule used for preparation, known as the template. These voids are specific recognition sites that bind the templates preferentially and are used specifically for biomimetic sensors and for solid-phase extraction. Because the specific surface is very important during this process, the use of films and membranes is preferred. This book contains four articles dedicated to sensor application (three research articles and one review) and one research article dedicated to solid-phase extraction

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 -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.FEDER and both the Spanish Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDER-UE) and the Consejería de Educación -Junta de Castilla y León- (Grant BU297P18). Jesus Garoz-Ruiz thanks Ministerio de Economía y Competitividad for his postdoctoral contracts (CTQ2014-55583-R; CTQ2017-83935-R AEI/FEDER-UE). Fabio Vulcano thanks the ISOF institute of CNR for supporting his PhD Grant. Nicola Porcelli thanks Università di Modena e Reggio Emilia for supporting his stay at the University of Burgos

Exclusive Papers of the Editorial Board Members (EBMs) of the Materials Chemistry Section of Molecules

The book is intended to collect the recent contributions (either research or review papers) to the development of the “Materials Chemistry” research fields by the Editorial Board Members of the Materials Chemistry Section of Molecules. The aim is to present the recent progress in the fields and to highlight the key role of Materials Chemistry in a multidisciplinary research context

Development of nanostructured material based electrochemical sensors for food safety and quality control

The issue of foodborne related illnesses due to additives and contaminants poses a significant challenge to food processing industries. Electrochemical-based strategies offer simple and robust analytical tools, which are ideal for food safety and the quality assessment process, in contrast to conventional instrumentation methods. The development of nanomaterials based electrochemical sensors has garnered significant attention due to their capacity for accurate analytical quantification, which has strong potential toward the replacement of conventional techniques by offering advantages such as high sensitivity and selectivity, real-time monitoring, and ease of use. During my Ph.D. study, four distinct types of nanostructured materials were used to develop electrochemical sensors for the detection of food preservatives in food and beverage products. The consumption of excessive amounts of nitrite (NO2-) can be detrimental to the human body. In light of this, we developed an electrochemical sensor based on cobalt oxide nanosheets and gold nanoparticles (Co3O4/Au) for NO2- sensing. The nanomaterial was synthesized through the electrodeposition of gold (Au) on Co3O4 nanosheets. The Co3O4/Au/GCE was capable of electrooxidizing nitrite with a higher anodic peak current, and the sensor exhibited excellent linearity with a limit of detection (LOD) value of 0.11 μM. A nanoporous gold microelectrode was synthesized for the determination of contaminants (hydrazine, N2H4) and preservatives (sulfite (SO32-), nitrite (NO2-)). The fabricated microelectrode was characterized via scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). The nanoporous gold microelectrode exhibited excellent electrochemical performance for the simultaneous electrochemical oxidation of N2H4, SO32-, and NO2-. In addition, the nanoporous gold microelectrode possessed high selectivity and stability. The performance of ii the electrochemical sensor was further validated using actual samples such as water, wine, apple cider beer, and beef with good recovery rates, thereby confirming its potential for food safety and quality control applications. A novel electrochemical sensor was developed using fluorine-doped graphene oxide (F-GO) for the detection of caffeic acid (CA). The fabricated nanomaterial was systematically characterized using SEM and X-ray photoelectron spectroscopy (XPS). The electrochemical investigation of F-GO/GCE for CA oxidation revealed that it demonstrated high electrocatalytic activity compared with other electrodes (e.g., bare GCE and GO/GCE). The analytical quantitation of CA recorded with the F-GO/GCE produced a stable oxidation signal over the selected CA concentration range (0.5 μM to 100.0 μM, R2 = 0.9960) with a LOD value of 0.018 μM. The fabricated sensor successfully exhibited the capacity to directly detect CA in assorted wine samples without pretreatment. To further explore the applications of the F-GO, a nanocomposite material synthesized with Au and F-GO was employed for the development of an Au/F-rGO/GCE sensor for the detection of vanillin. The electrochemical performance and the analytical capabilities of this novel electrochemical sensor were investigated using electrochemical techniques such as CV and DPV. The excellent sensitivity, selectivity, augmented electrocatalytic activity, and reproducibility of these developed electrochemical sensors can be attributed to the high conductivity of the nanostructured materials. The dimensions and morphologies of the developed nanomaterials played a critical role in enhancing the electrochemical performance of these sensors

Voltametrické a amperometrické stanovení nitrofenolů pomocí borem dopované diamantové filmové elektrody

Tato práce je věnována použití borem dopované diamantové (BDD) elektrody pro voltametrické a amperometrické stanovení vybraných nitrofenolů - 2-nitrofenolu (2NP), 4-nitrofenolu (4NP) a 2,4-dinitrofenolu (2,4DNP). Tyto látky jsou vedeny v seznamu United States Environmental Protection Agency (US EPA) jako významné polutanty, neboť mají negativní vliv na organismy. V zemědělství jsou používány jako hnojiva - stimulátory růstu. BDD elektrody jsou používány pro stanovení širokého spektra jak oxidovatelných, tak redukovatelných látek, a pro svoji dostupnost a vynikající mechanické a elektrochemické vlastnosti se staly populárním elektrodovým materiálem. Pro stanovení nitrofenolů byla použita diferenční pulsní voltametrie, a to s použitím jak redukce (pro 2NP, 4NP a 2,4DNP), tak i oxidace (pro 4NP a 2,4DNP). Metoda byla úspěšně aplikována pro stanovení těchto látek v pitné a říční vodě v koncentračním rozsahu od 4×10-7 do 2×10-5 mol.L-1 . Po použití prekoncentrace pomocí extrakce tuhou fází ze 100 ml a z 1000 ml vzorků vody bylo dosaženo meze stanovitelnosti pro tyto látky 2×10-8 mol.L-1 (vzorky pitné vody) a 2×10-7 mol.L-1 (vzorky říční vody). Pro stanovení nitrofenolů byla BDD elektroda úspěšně použita také jako amperometrický detektor ve wall-jet uspořádání pro vysokoúčinnou kapalinovou chromatografii...Presented Ph.D. Thesis is focused on the use of the boron-doped diamond (BDD) electrodes for voltammetric and amperometric determination of selected nitrophenols: 2-nitrophenol (2NP), 4-nitrophenol (4NP), and 2,4-dinitrophenol (2,4DNP). These compounds are listed as "priority pollutants" by United States Environmental Protection Agency (US EPA) due to their negative impact on living organisms and are mainly used in agriculture as plant growth stimulators. BDD electrodes are used for determination of wide range of electrochemically both reducible and oxidisable organic compounds and have become a popular electrode material thanks to its commercial availability and excellent mechanical and electrochemical properties. A differential pulse voltammetric method was developed for the determination of 2NP, 4NP and 2,4DNP at a BDD film electrode using electrochemical reduction and of 4NP and 2,4DNP using electrochemical oxidation. The method was successfully applied for the direct determination of these compounds in drinking and river water in the concentration range from 4×10-7 to 2×10-5 mol.L-1 . To improve the limit of quantification, a preconcentration by solid phase extraction from 100 mL (drinking and river water) and 1000 mL (drinking water) of water samples was used with limit of determination...Katedra analytické chemieDepartment of Analytical ChemistryPřírodovědecká fakultaFaculty of Scienc

New devices to monitor oxidative stress biomarkers in point-of-care: a new tool for cancer prevention

According to the most recent World Health Organization (WHO) data, cancer is the second leading cause of death worldwide, accounting for 9.6 million deaths in 2018. In particular, cancer diseases have caused 26% of the total deaths in Portugal in 2016. Among the complex mechanisms associated to cancer development, Oxidative Stress (OS) seems to play an important role at the origin of the disease. Thus, early diagnosis of multiple OS biomarkers may be a fundamental tool in cancer prevention and in more efficient therapeutic strategies. Despite the development and the research efforts that are being made, accurate and early detection methods for cancer are still lacking. The demand for specific OS biomarker assays carried out in wide screening programs in point-of-care (POC) is undoubtedly a difficult but potentially useful challenge for biomedical research and health. So far, current methods for cancer diagnosis based upon pathological examination alone are insufficient for detecting early tumour progression. Thus, to overcome this need, the present project aims the development of quick, simple and accurate detection of selected OS biomarkers, collected using minimally invasive methods, in order to allow rapid and reliable diagnosis at early stages of the disease. Under this scope, the design of sensitive biosensing materials integrated with novel conductive substrates for POC screening of OS biomarkers will be presented. In order to achieve a specific and highly selective bio-chemical recognition process, molecular imprinting strategy was used to create the artificial recognition sites. During the fabrication of electrochemical transduction platforms, paper was introduced as a novel alternative to the conventional support materials usually incorporated in electrode systems. Overall, it is expected that the outcome of this plan will contribute, in the future, to the development and application of a multi-analyte platform for simultaneous fast screening of cancer biomarkers in POC context

Biofuel Cell Anode for NAD-Dependent Enzymes

Enzymatic biofuel cells are a very attractive young technology based on utilization of natural, renewable and plentiful resources that offer an alternative energy source. Most fuel cells run on hydrogen; but it is extremely expensive and difficult to obtain, which is why research has moved to target fuels that are already available in nature, avoiding high costs of production, both economically and environmentally. Several biofuels with very high energy densities are available to us in abundance, but the challenges to make use of them are plenty. These biofuels contain several carbon-to-carbon bonds which make their oxidation processes significantly more complex than those of hydrogen. Examples of these biofuels are sugars and alcohols. If we refer back to nature, we have learned that enzymes play a very important role in oxidizing these types of fuels to obtain energy. If we could mimic such processes in a fuel cell, we would be able to harvest the energy of the fuels and convert it into electrical power. There are several advantages to using enzymes as catalysts for biofuel cells including their availability, easiness to produce in large quantities and selectivity. The main pitfall when mimicking natures pathways to oxidize biofuels by enzymatic action is that they usually require multiple oxidation steps. The full energy potential of biofuels can only be attained if all of the reaction steps are completed achieving the complete oxidation to CO2. This must be achieved by including all individual enzymes that catalyze each step of the oxidation of biofuels. Several of the necessary enzymes for those oxidation steps depend on the diffusive cofactor NAD+/NADH which by itself presents a great challenge. The optimal performance of a biofuel cell requires continuous operation and oxidation of the fuel which can only be achieved if the enzymes\u27 cofactors are constantly regenerated. NADH oxidation has been a practical challenge in biotechnology over decades, since it requires very large overpotentials. In this work, we evaluated the utilization of standardized fuel cell apparatus built for cross-lab analysis by preparing poly-(MG) electrocatalysts for NADH oxidation onto different electrode materials. These electrocatalysts have been studied and characterized both electrochemically and structurally in order to develop NAD+-dependent enzyme anodes. Immobilization of enzymes also represents an important design aspect. One immobilization technique is chosen in this research; based on the combination of porous chitosan scaffolds and multi-walled carbon nanotubes that stabilizes enzymes while enabling mass transport of fuels and providing electrical conductivity. This research ultimately introduces a common technology platform for NADH re-oxidation in a flow through electrode format that can sustain single- or multi-enzyme anodes into biofuel cell technology. Future directions and optimization of the design are discussed.\u2