Highly Sensitive Voltammetric Determination of Acrylamide Based on Ibuprofen Capped Mercury Nanoparticles.

Highly stable, small-sized and evenly distributed solid mercury nanoparticles capped with ibuprofen (Ibu-HgNPs) were prepared via reduction with hydrazine and capped with ibuprofen as a stabilizing agent. Characterization of Ibu-HgNPs was carried out by UV-Vis spectrophotometry and transmission electron microscopy (TEM). The prepared Ibu-HgNPs were immobilized onto a glassy carbon electrode (GCE) and used for the first time as the sensing element for voltammetric determination of low concentrations of acrylamide (AA) in aqueous solutions. Various parameters such as the type of supporting electrolyte, voltammetric mode, frequency, deposition time, stirring rate and initial potential were optimized to obtain the highest peak current of AA. The sensor delivered the best results in combination with the square wave voltammetry (SWV) mode, with good repeatability (relative standard deviation (RSD) of 25 repetitions was 1.4% for 1000 ppb AA). The study further revealed that Ibu-HgNPs are strongly adhered to GCE and hence do not contaminate the environment even after several runs. The newly developed AA sensor provides linear calibration dependence in the range of 100-1300 ppb with an R2 value of 0.996 and limit of detection (LOD) of 8.5 ppb. Negligible interference was confirmed from several organic compounds, cations and anions. The developed sensor was successfully applied for AA determination in various types of environmental real water samples to prove its practical usefulness and applicability.

A Laser Reduced Graphene Oxide Grid Electrode for the Voltammetric Determination of Carbaryl.

Laser-reduced graphene oxide (LRGO) on a polyethylene terephthalate (PET) substrate was prepared in one step to obtain the LRGO grid electrode for sensitive carbaryl determination. The grid form results in a grid distribution of different electrochemically active zones affecting the electroactive substance diffusion towards the electrode surface and increasing the electrochemical sensitivity for carbaryl determination. Carbaryl is electrochemically irreversibly oxidized at the secondary amine moiety of the molecule with the loss of one proton and one electron in the pH range from 5 to 7 by linear scan voltammetry (LSV) on the LRGO grid electrode with a scan rate of 300 mV/s. Some interference of the juice matrix molecules does not significantly affect the LSV oxidation current of carbaryl on the LRGO grid electrode after adsorptive accumulation without applied potential. The LRGO grid electrode can be used for LSV determination of carbaryl in fruit juices in the concentration range from 0.25 to 128 mg/L with LOD of 0.1 mg/L. The fabrication of the LRGO grid electrode opens up possibilities for further inexpensive monitoring of carbaryl in other fruit juices and fruits.

Evaluation of human macrophage functional state by voltammetric monitoring of nitrite ions.

The method for assessing the level of nitric oxide (II) (NO) by voltammetric monitoring of nitrite ions was carried out on models M1 and M2 of polarized macrophages induced from monocytes of human peripheral blood with the addition of lipopolysaccharide (LPS) and interleukin-4 (IL-4), respectively. The model of induction of M1 and M2 macrophages was used in the work to achieve the corresponding shifts in the functional status of studied cells. Ethyl nitrite (EtONO) was used as a standard compound of nitrite ions for electrochemical measurements. Electrochemical determination of nitrite ions was performed by anodic linear sweep voltammetry in the first-order derivative mode (ALSV FOD) in Britton-Robinson (BR) buffer with pH 4.02 on carbon ink modified graphite electrode. EtONO calibrations were linear over a concentration range from 2 to 9 µmol L-1 with corresponding regression equation y = 0.768c - 0.048. Limit of detection (LOD) (S/N = 3) was 0.38 µmol L-1. The results of the study showed the fundamental possibility of using voltammetry to assess indirectly the production of nitric oxide by cells in supernatants of the monocytic macrophage lineage. The level of nitric oxide metabolites (nitrite ions) in supernatants was associated with the functional state of macrophages.

Label-Free Electrochemical Biosensors for the Determination of Flaviviruses: Dengue, Zika, and Japanese Encephalitis.

A highly effective way to improve prognosis of viral infectious diseases and to determine the outcome of infection is early, fast, simple, and efficient diagnosis of viral pathogens in biological fluids. Among a wide range of viral pathogens, Flaviviruses attract a special attention. Flavivirus genus includes more than 70 viruses, the most familiar being dengue virus (DENV), Zika virus (ZIKV), and Japanese encephalitis virus (JEV). Haemorrhagic and encephalitis diseases are the most common severe consequences of flaviviral infection. Currently, increasing attention is being paid to the development of electrochemical immunological methods for the determination of Flaviviruses. This review critically compares and evaluates recent research progress in electrochemical biosensing of DENV, ZIKV, and JEV without labelling. Specific attention is paid to comparison of detection strategies, electrode materials, and analytical characteristics. The potential of so far developed biosensors is discussed together with an outlook for further development in this field.

Preparation and Investigation of Silver Nanoparticle⁻Antibody Bioconjugates for Electrochemical Immunoassay of Tick-Borne Encephalitis.

A new simple electrochemical immunosensor approach for the determination of antibodies to tick-borne encephalitis virus (TBEV) in immunological products was developed and tested. The assay is performed by detecting the silver reduction signal in the bioconjugates with antibodies (Ab@AgNP). Here, signal is read by cathodic linear sweep voltammetry (CLSV) through the detection of silver chloride reduction on a gold-carbon composite electrode (GCCE). Covalent immobilization of the antigen on the electrode surface was performed after thiolation and glutarization of the GCCE. Specific attention has been paid to the selection of conditions for stabilizing both the silver nanoparticles and their Ab@AgNP. A simple flocculation test with NaCl was used to select the concentration of antibodies, and the additional stabilizer bovine serum albumin (BSA) was used for Ab@AgNP preparation. The antibodies to TBEV were quantified in the range from 50 IU·mL-1 to 1600 IU·mL-1, with a detection limit of 50 IU·mL-1. The coefficient of determination (r2) is 0.989. The electrochemical immunosensor was successfully applied to check the quality of immunological products containing IgG antibodies to TBEV. The present work paves the path for a novel method for monitoring TBEV in biological fluids.

Electrochemical nonenzymatic sensor for cholesterol determination in food.

The treatment of some inborn metabolism errors requires cholesterol substitution therapy. Cholesterol plays a vital role in the human body. Therefore, the majority of cholesterol determination techniques are targeted to blood and blood serum. Nevertheless, cholesterol determination in food is important as well. In this paper, cholesterol determination using differential pulse voltammetry (DPV) in dairy products (e.g., milk, clotted cream, yogurt, butter, etc.) is reported with a novel nonenzymatic sensor based on diphosphonic acid of 1,4-diacetylglycoluril (DPADGU) as an electrode surface modifier. Stable anodic response was obtained from cholesterol on the modified carbon-based electrode. The sensor has high stability, sensitivity (20 µA mol L-1 cm-2), and a wide linear range from 1 up to 200 µM. The LOD and LOQ values are 1.5 and 5.1 µM, respectively. The developed methods were successfully applied to the above mentioned dairy products. Graphical abstract ᅟ.

Novel, fast, and reliable electrochemical dsDNA biosensor based on O-terminated pristine nanocrystalline boron-doped diamond electrode for DNA interaction studies.

We present a novel application of a nanocrystalline boron-doped diamond electrode (B-NCDE) for the construction of an electrochemical DNA biosensor based on double-stranded DNA (dsDNA) for various bioanalytical applications. Surface characterization of the transducer surface (prior and after the fabrication of negatively charged O-terminated surface - O-B-NCDE) was performed by scanning electron microscopy (SEM), Raman spectroscopy, and linear sweep voltammetry (LSV) that was further used for the voltammetric determination, scan rate dependence investigation, and repeatability examination of dsDNA electrochemical oxidation at the O-B-NCDE. The fabrication of a dsDNA/O-B-NCDE biosensor via electrostatic adsorption of dsDNA involved a thorough optimization process of deposition potential (Edep), deposition time (tdep), and optimal saturation concentration (cg(satur)) with optimal values of 0.3 V, 3 min, and 10 mg/mL. The bioanalytical applicability of the fabricated dsDNA/O-B-NCDE biosensor was verified by examining the nature of the interaction between dsDNA and five selected DNA intercalators - namely thioridazine hydrochloride (TR), trimipramine maleate (TRIM), levomepromazine maleate (LEV), imipramine hydrochloride (IMI), and prochlorperazine maleate (PER) - where intercalation was proven for all of the five tested compounds. Moreover, the proposed novel bioanalytical test offers the possibility to selectively distinguish between the phenothiazine representatives (TR, LEV, and PER) and representatives of tricyclic antidepressants group (TRIM and IMI).

Voltammetric studies of the interaction of genotoxic 2-nitrofluorene with DNA.

The interaction of genotoxic environmental pollutant 2-nitrofluorene (2-NF) with double-stranded DNA has been studied using a hanging mercury drop electrode (HMDE) as an electrochemical sensor. Two types of DNA damage were investigated and electrochemically detected using cyclic voltammetry and differential pulse voltammetry: (i) DNA damage caused by the direct interaction with 2-NF and (ii) DNA damage caused by short-lived radicals generated by the electrochemical reduction of 2-NF. For the study of the direct interaction, the HMDE was modified by DNA and the interaction of DNA with 2-NF was studied after their mutual interaction right at the HMDE surface, or DNA was preincubated with 2-NF in solution and, subsequently, the interaction was studied voltammetrically. Using both detection techniques, the formation of DNA-2-NF complex was observed and the mutual interaction was interpreted as an intercalation between DNA base pairs. On the basis of obtained results, we suppose that expected formation of 8-oxoguanosine leads to guanosine-cytidine base pair interruption and DNA double-strand break formation. The binding constants (K) of the DNA-2-NF complex formed in solution and on the HMDE surface (DNA/HMDE) were determined from the changes in the voltammetric peaks of the studied analyte.

Graphene derivatives-based electrodes for the electrochemical determination of carbamate pesticides in food products: A review.

Graphene (GR) composites have great potential for the determination of carbamates pesticides (CPs) by electrochemical methods. Since the beginning of the 20th century, GR has shown remarkable promise as electrode material for various sensors. The contamination of food products with harmful CPs is a major problem as they do not always damage human health immediately, but can be harmful after prolonged exposure. A range of advantages can be gained from their electrochemical determination, such as high sensitivity, reasonably selectivity, rapid detection, low limit of detection, and easy electrode fabrication. Furthermore, these electrochemical techniques are robust, reproducible, user-friendly, and conform to both "green" and "white" analytical chemistry. This review is focused on results published in the last ten years in the field of electrochemical determination of CPs in food products using GR and its derivatives.

Determination of 1-hydroxypyrene in human urine by HPLC with electrochemical detection at a boron-doped diamond film electrode.

A high-performance liquid chromatographic method with electrochemical detection (HPLC-ED) at a boron-doped diamond film electrode with preliminary separation and preconcentration by solid-phase extraction (SPE) has been developed for the determination of 1-hydroxypyrene (1-HP) in human urine. 1-HP is among the most widely used biomarkers of exposure to polycyclic aromatic hydrocarbons. Optimal HPLC-ED conditions have been found: mobile phase methanol-0.05 mol L(-1) phosphate buffer pH 5.0 (80:20, v/v), detection potential +1,000 mV versus Ag/AgCl (3 mol L(-1) KCl), and flow rate 0.8 mL min(-1). For SPE, LiChrolut(®) RP-18 E cartridges were used. The extraction yield was (87.0 ± 5.8)% (n = 5). The concentration dependence of 1-HP was measured in the concentration range from 0.01 to 10 µmol L(-1) (2.18-2,180 µg L(-1)) using methanolic solutions resulting from the SPE pretreatment of spiked human urine samples. The limit of detection (signal-to-noise ratio 3) and the limit of quantification (signal-to-noise ratio 10) of the biomarker were 0.013 µmol L(-1) (2.84 µg L(-1)) and 0.043 µmol L(-1) (9.39 µg L(-1)), respectively, which is sufficient for its determination in the urine of persons exposed to polycyclic aromatic hydrocarbons.

The use of silver solid amalgam electrodes for voltammetric and amperometric determination of nitrated polyaromatic compounds used as markers of incomplete combustion.

Genotoxic nitrated polycyclic aromatic hydrocarbons (NPAHs) are formed during incomplete combustion processes by reaction of polycyclic aromatic hydrocarbons (PAHs) with atmospheric nitrogen oxides. 1-Nitropyrene, 2-nitrofluorene, and 3-nitrofluoranthene as the dominating substances are used as markers of NPAHs formation by these processes. In the presented study, voltammetric properties and quantification of these compounds and of 5-nitroquinoline (as a representative of environmentally important genotoxic heterocyclic compounds) have been investigated using a mercury meniscus modified silver solid amalgam electrode (m-AgSAE), which represent a nontoxic alternative to traditional mercury electrodes. Linear calibration curves over three orders of magnitude and limits of determination mostly in the 10(-7) mol L(-1) concentration range were obtained using direct current and differential pulse voltammetry. Further, satisfactory HPLC separation of studied analytes in fifteen minutes was achieved using 0.01 mol L(-1) phosphate buffer, pH 7.0 : methanol (15 : 85, v/v) mobile phase, and C(18) reversed stationary phase. Limits of detection of around 1 · 10(-5) mol L(-1) were achieved using amperometric detection at m-AgSAE in wall-jet arrangement for all studied analytes. Practical applicability of this technique was demonstrated on the determination of 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, and 5-nitroquinoline in drinking water after their preliminary separation and preconcentration using solid phase extraction with the limits of detection around 1 · 10(-6) mol L(-1).

Influence of different covalent immobilization protocols on electroanalytical performance of laccase-based biosensors.

This paper presents a simple and effective flow-through electrochemical biosensor, consisting of Trametes versicolor laccase (Lac)-based mini-reactor and a tubular detector of silver solid amalgam (TD-AgSA), capable of rapid and selective detection of phenolic compounds. Amperometric detection relies on the reduction of the quinone molecule (formed during the enzymatic reaction in a mini-reactor) on TD-AgSA at -50 mV vs SCE. Since different enzyme immobilization techniques may contribute to differing biosensor performances, four covalent strategies for Lac attachment were compared: (i) through glutaraldehyde to supports -NH2, (ii) via disuccinimidyl suberate to supports -NH2, (iii) using EDC/NHS for Lac coupling by its -COOH groups to supports -NH2, and (iv) using EDC/NHS to supports -COOH. Additionally, five supports (mesoporous silica (SBA-15, MCM-41), cellulose, carbon-based (glassy carbon, graphite) powders) were investigated. It was found that different methods of immobilization, as well as different types of supports, significantly affect the amount of immobilized Lac and, in turn, the analytical characteristics of the obtained biosensors. Thus, TD-AgSA with enzymatic mini-reactor based on Lac covalently attached via glutaraldehyde to aminated MCM-41 proved to be the most promising biosensor, providing the best detection limit (18.3 µmol L-1) and the long-term stability (47.9 % of the initial response/4 months/100 measurements).

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review.

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

Crystallic silver amalgam--a novel electrode material.

A crystallic silver amalgam was found to be a suitable working electrode material for voltammetric determination of electrochemically reducible organic nitro-compounds. Optimum conditions for crystal growth were found, the crystal surface was investigated by atomic force microscopy in tapping mode and single crystals were used for the preparation of quasi-cylindrical single crystal silver amalgam electrode (CAgAE). An electrochemical behavior of this alternative electrode material was investigated in aqueous media by direct current voltammetry, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and adsorptive stripping voltammetry (AdSV) using 4-nitrophenol as a model compound. Applicable potential windows of the CAgAE were found comparable with those obtained at a hanging mercury drop electrode, providing high hydrogen overpotential, and polished silver solid amalgam electrode. Thanks to the smooth single crystal electrode surface, the effect of the passivation is not too pronounced, direct DPV determination of 100 µmol l(-1) of 4-nitrophenol at CAgAEs in 0.2 mol l(-1) acetate buffer pH 4.8 provides a RSD around 1.5% (n = 15). DPV calibration curves of 4-nitrophenol are linear in the whole concentration range 1-100 µmol l(-1) with a limit of quantification of 1.5 µmol l(-1). The attempt to increase sensitivity by application of AdSV was not successful. The mechanism of 4-nitrophenol reduction at CAgAE was investigated by CV.

Differential pulse voltammetric determination of homovanillic acid as a tumor biomarker in human urine after hollow fiber-based liquid-phase microextraction.

Novel method for the determination of a tumor marker homovanillic acid (HVA) in human urine was developed. Combination of hollow fiber - based liquid-phase microextraction (HF-LPME) and differential pulse voltammetry (DPV) at a cathodically pre-treated boron doped diamond electrode (BDDE) was applied for these purposes. Optimum conditions were: butyl benzoate as supported liquid membrane (SLM) formed on polypropylene HF, 0.1 mol L-1 HCl as donor phase, 0.1 mol L-1 sodium phosphate buffer of pH 6 as acceptor phase, and 30 min extraction time. HF-LPME-DPV concentration dependence was linear in the range from 1.2 to 100 µmol L-1. Limits of quantification (LOQ) and detection (LOD) were 1.2 and 0.4 µmol L-1, respectively. The applicability of the developed method was verified by analysis of human urine. Standard addition method was used, found HVA concentration was 13.5 ± 1.3 µmol L-1, RSD = 9.3% (n=5).

A critical comparison of natural enzymes and nanozymes in biosensing and bioassays.

Nanozymes (NZs) are nanomaterials that mimic enzyme-like catalytic activity. They have attracted substantial attention due to their inherent physicochemical properties for use as promising alternatives to natural enzymes (NEs) in a variety of research fields. Particularly, in biosensing and bioassays, NZs have opened a new horizon to eliminate the intrinsic limitations of NEs, including their denaturation at extreme pH values and temperatures, poor reusability and recyclability, and high production costs. Moreover, the catalytic activity of NZs can be modulated in the preparation step by following an appropriate synthesis strategy. This review aims to gain insight into the potential substitution of NEs by NZs in biosensing and bioassays while considering both the pros and cons.

A copper nanoparticle-based electrochemical immunosensor for carbaryl detection.

A hapten-protein conjugate with copper nanoparticles (Hap-Car-BSA@CuNPs) was first synthesized in the present work for the determination of carbaryl. The copper nanoparticles (CuNPs) of the conjugate were used as electrochemical labels in the direct solid-phase competitive determination of carbaryl residues in flour from different crops. The signal was read by linear sweep anodic stripping voltammetry (LSASV) of copper (through the electrochemical stripping of accumulated elemental copper) on a gold-graphite electrode (GGE). To form a recognition receptor layer of monoclonal antibodies against the carbaryl on the surface of the GGE, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 1-hydroxy-2,5-pyrrolidinedione (NHS) were used as the best covalent cross-linkers. The concentrations of the antibodies and the Hap-Car-BSA@CuNPs conjugate were optimized for carbaryl detection by the electrochemical immunosensor. The electrochemical immunosensor can be used for highly sensitive determination of carbaryl residues in flour samples in the concentration range 0.8-32.3 µg·kg-1, with a limit of detection 0.08 µg·kg-1. The present work paves the path for a novel method for monitoring carbaryl in other food products, drinks, and soil samples.

Voltammetric detection of damage to DNA caused by nitro derivatives of fluorene using an electrochemical DNA biosensor.

An electrochemical DNA biosensor based on the screen printed carbon paste electrode (SPCPE) with an immobilized layer of calf thymus double-stranded DNA has been used for in vitro investigation of the interaction between genotoxic nitro derivatives of fluorene (namely 2-nitrofluorene and 2,7-dinitrofluorene) and DNA. Two types of DNA damage have been detected at the DNA/SPCPE biosensor: first, that caused by direct association of the nitrofluorenes, for which an intercalation association has been found using the known DNA intercalators [Cu(phen)(2)](2+) and [Co(phen)(3)](3+) as competing agents, and, second, that caused by short-lived radicals generated by electrochemical reduction of the nitro group (observable under specific conditions only).

Non-enzymatic electrochemical approaches to cholesterol determination.

Cholesterol plays a vital role in a human body. It is known as one of the most important sterols, because it forms cell walls and participates in signal transduction. Moreover, cholesterol was recognized as biomarker of cardiovascular diseases and of some metabolic disorders. As a result, cholesterol blood levels should be controlled in a variety of diseases such as ischemic heart disease, cerebrovascular ischemia, stroke, hypertension, type II diabetes, and many others. Hence, the accurate cholesterol quantification plays an important role in diagnosis and treatment of these diseases. Modern voltammetric and amperometric methods are increasingly used for cholesterol monitoring. Consequently, the problem of electrode fabrication for cholesterol detection has high importance for clinical tests. Novel electrode materials initiated the fast growth of electrochemical biosensors. Biomaterials are still the most frequently used modifiers for cholesterol sensors due to their high selectivity. However, biomaterials have low stability complicating their practical applications. This fact is crucial for analytical parameters such as limit of detection (LOD) and sensitivity. Therefore, nanomaterials are used to eliminate disadvantages of biomaterials and to improve sensors performance by increasing the electrode surface, conductivity and sensitivity. This review is focused on the use of non-enzymatic electrodes for cholesterol quantification and on different approaches to their fabrication. Firstly, the necessity and role of modifier is discussed. Afterwards, the advantages and disadvantages of currently used modifiers are critically compared together with all aspects and approaches to sensors fabrication. Finally, the prospects of non-enzymatic electrodes application for cholesterol sensors engineering are summarised.

A novel voltammetric approach to the detection of primary bile acids in serum samples.

An innovative voltammetric approach to the detection of cholic and chenodeoxycholic acids is presented. These two primary bile acids are important biomarkers of liver function in humans and are involved in many physiological processes in the human body. Herein we describe a way to reproducibly convert the hard-to-detect bile acid molecule into an easily detectable derivative in situ using 0.1 M HClO4 in acetonitrile (water content 0.55%). Under these conditions the bile acids are dehydrated and the resulting alkenes can be subsequently oxidized electrochemically on polished boron-doped diamond electrode under unchanged conditions at approximately +1.2 V vs. Ag/AgNO3 in acetonitrile. After optimization, differential pulse voltammetry provides competitive limits of detection of 0.5 µM and 1.0 µM for cholic and chenodeoxycholic acid, respectively, with a linear course of calibration dependency to the minimum of 80 µM. The method was applied for detection of cholic and chenodeoxycholic acids in artificial and human serum samples using single solid phase extraction on C-18 cartridge for preliminary separation of the analytes. High recoveries of 80-90% were consistently obtained by the proposed voltammetric method and reference HPLC with fluorescence detection for human serum samples, confirming good selectivity for real-life samples.