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Herein, we report the synthesis, characterisation and glucose sensor study of prepared compounds and composite. The prepared samples reported here for glucose-sensing applications were doped (Mn.NiO) and un-doped metal oxide (NiO) and their composite with 2D layered material (Mn-doped-NiO/rGO). The structural analysis of the samples was done by conventional technique called as X-rays diffraction (×RD). Spectral and functional groups' analysis was elucidated by FTIR spectroscopy. The electron microscopy (SEM) was used for morphological features study. The electrochemical measurements were carried out to analyse biosensing response. Carbon fibre cloth was used as a substrate material to fabricate Mn-doped-NiO/rGO nanocomposite-based biosensor for glucose detection. The analytical performance of the synthesised material was evaluated in terms of electrochemical sensitivity, linear response and limit of detection (LOD). The results showed that the material exhibited an excellent electrochemical sensitivity towards glucose detection with wider range of linear responses. The LOD for Mn-doped-NiO/rGO nanocomposite was 0.11 µM, regression equation for the low concentration was I(µA) = 1477.1C + 165.19 with correlation coefficient value R2 = 0.9849. Conclusively, the rGO-based Mn-doped-NiO nanocomposite experienced robust potential as non-enzymatic sensor for detection of glucose. [ABSTRACT FROM AUTHOR]

In this study, a new amperometric biosensor was developed for glucose determination. For this purpose, polyaniline–polypyrrole–poly(sodium‐4‐styrenesulfonate) film was prepared by electropolymerization of aniline and pyrrole with poly(sodium‐4‐styrenesulfonate) on a platinum plate. The best working conditions of the polyaniline–polypyrrole–poly(sodium‐4‐styrenesulfonate) film were determined. The glucose oxidase enzyme was immobilized by the entrapment method in polyaniline–polypyrrole–poly(sodium‐4‐styrenesulfonate) film. Glucose determination was made based on the oxidation of hydrogen peroxide, which is formed as a result of the enzymatic reaction on the surface of the prepared biosensor at +0.40 V. The working range for the glucose determination of the biosensor was determined. The effects of pH and temperature on the response of the glucose biosensor were investigated. The reusability and shelf life of the biosensor were determined. The effects of interference in biological environments on the response of the biosensor were investigated. Glucose determination was made in the biological fluid (blood) with the prepared biosensor. This study has a feature that sheds light on biosensor studies to be developed for the detection of substances in the human body, such as glucose, uric acid, and urea. This article will set an example for future scientific research on the development of a sensor for other biological fluids in the human body, such as the sensor developed for blood samples. In addition, this developed sensor provides an innovation that improves the quality of life of patients by allowing them to constantly monitor their glucose levels and intervene when necessary. [ABSTRACT FROM AUTHOR]

Enzyme-based portable amperometric biosensors are precise and low-cost medical devices used for rapid cancer biomarker screening. Sarcosine (Sar) is an ideal biomarker for prostate cancer (PCa). Because human serum and urine contain complex interfering substances that can directly oxidize at the electrode surface, rapid Sar screening biosensors are relatively challenging and have rarely been reported. Therefore, highly sensitive and selective amperometric biosensors that enable real-time measurements within <1.0 min are needed. To achieve this, a chitosan–polyaniline polymer nanocomposite (CS–PANI NC), a carrier for dispersing mesoporous carbon (MC), was synthesized and modified on a screen-printed carbon electrode (SPCE) to detect hydrogen peroxide (H2O2). The sarcosine oxidase (SOx) enzyme-immobilized CS–PANI–MC-2 ternary NCs were referred to as supramolecular architectures (SMAs). The excellent electron transfer ability of the SMA-modified SPCE (SMA/SPCE) sensor enabled highly sensitive H2O2 detection for immediate trace Sar biomarker detection. Therefore, the system included an SMA/SPCE coupled to a portable potentiostat linked to a smartphone for data acquisition. The high catalytic activity, porous architecture, and sufficient biocompatibility of CS–PANI–MC ternary NCs enabled bioactivity retention and immobilized SOx stability. The fabricated biosensor exhibited a detection limit of 0.077 μM and sensitivity of 8.09 μA mM−1 cm−2 toward Sar, demonstrating great potential for use in rapid PCa screening. [ABSTRACT FROM AUTHOR]

We report the development of amperometric biosensors (ABSs) employing flavocytochrome b2 (Fcb2) coupled with nanoparticles (NPs) of noble metals on graphite electrode (GE) surfaces. Each NPs/GE configuration was evaluated for its ability to decompose hydrogen peroxide (H2O2), mimicking peroxidase (PO) activity. The most effective nanoPO (nPO) was selected for developing ABSs targeting L-lactate. Consequently, several Fcb2/nPO-based ABSs with enhanced sensitivity to L-lactate were developed, demonstrating mediated ET between Fcb2 and the GE surface. The positive effect of noble metal NPs on Fcb2-based sensor sensitivity may be explained by the synergy between their dual roles as both PO mimetics and electron transfer mediators. Furthermore, our findings provide preliminary data that may prompt a re-evaluation of the mechanism of L-lactate oxidation in Fcb2-mediated catalysis. Previously, it was believed that L-lactate oxidation via Fcb2 catalysis did not produce H2O2, unlike catalysis via L-lactate oxidase. Our initial research revealed that the inclusion of nPO in Fcb2-based ABSs significantly increased their sensitivity. Employing other PO mimetics in ABSs for L-lactate yielded similar results, reinforcing our hypothesis that trace amounts of H2O2 may be generated as a transient intermediate in this reaction. The presence of nPO enhances the L-lactate oxidation rate through H2O2 utilization, leading to signal amplification and heightened bioelectrode sensitivity. The proposed ABSs have been successfully tested on blood serum and fermented food samples, showing their promise for L-lactate monitoring in medicine and the food industry. [ABSTRACT FROM AUTHOR]

The biological recognition of enzymes was the basis of enzyme-based chemical biosensors. It is essential for a biosensor to function under normal operating conditions so that enzymes can catalyze biochemical reactions. The mechanism of a modified enzyme-membrane electrode in a catalytic cycle was described using a mathematical model. The nonlinear terms associated with enzyme kinetics were presented in this model. The Akbari-Ganji's method (AGM) was used to calculate the semi-analytical expressions for species concentration and normalized current. For all possible values of the Thiele modulus, normalized surface concentration of the oxidized mediator, and normalized surface concentration of the substrate, a simple and approximate hyperbolic expression of concentrations of an oxidized mediator, substrate, and reduced mediator were derived. The numerical simulation was then verified using semi-analytical results. The numerical simulation and semi-analytical predictions agreed well with each other.

Phenolic compounds impact human health and the environment in both beneficial and undesirable manners. While some phenols are known to be antioxidants, others function as hormones or neurotransmitters, some are significant environmental contaminants, and others have the potential to cause cancer or disturb the endocrine system. To track the amount of toxicity, it is essential to identify and measure these phenols in food, the environment, and human samples. A novel phenol sensing amperometric enzymatic biosensor with a gold electrode was fabricated based on covalent immobilisation of synthesised laccase nanoparticles (LacNPs). The process of synthesising laccase nanoparticles was examined using UV–visible spectrophotometry, FTIR, transmission electron microscopy, zeta potential, and dynamic light scattering techniques. For analysis of electrode fabrication (LacNPs-AuE), scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectra including Nyquist plots and Bode's plot were examined. Optimisation and evaluation of fabricated biosensor were investigated using cyclic voltammetry studies. The LacNPs-AuE biosensor's overall characteristics were enhanced by the direct immobilisation of laccase nanoparticles, enabling the analysis at a lower detection limit (0.3 μM), wider linear range (0.1–100 μM and 100 to 600 μM), faster response time (3 s), and high recovery (92–98%). Tea, alcohol, and pharmaceutical samples were tested for total phenolic content using the biosensor; the results were compared with spectrophotometric data. [ABSTRACT FROM AUTHOR]

AbstractThis study reports the design and development of a disposable amperometric biosensor for the determination of L-glutamate. Glutamate oxidase (GlOx) was immobilized onto a screen-printed carbon electrode (SPE) modified with poly-L-Aspartic acid (PAsp), carbon quantum dots (CQD), and platinum nanoparticles (PtNP) for the construction of the biosensor. The surface composition of the modified SPE was optimized using the one variable at a time method. The morphological properties of the biosensor were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The electrochemical behavior of the modified electrodes was studied by cyclic voltammetry. Under the optimized experimental conditions the linear working range, detection limit and sensitivity of the GlOx/PtNP/CQD/PAsp/SPE were found to be 1.0 − 140 µM, 0.3 µM and 0.002 µA µM−1, respectively. The GlOx/PtNP/CQD/PAsp/SPE biosensor also exhibited good measurement repeatability. The as-developed biosensor was applied for the determination of L-glutamate in spiked serum samples and the average analytical recovery of added glutamate was 98.9 ± 3.9%. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution to the model. By solving the system of nonlinear reaction-diffusion equations using Akbari–Ganji's method (AGM), we can derive the semi-analytical expressions for substrate and oxidized and reduced mediator concentrations. These models provide information about enzyme electrode mechanisms and their kinetics. These modeling results can be helpful for sensor design, optimization, and determining how the electrode will react. Further, we studied the effects of many physical and biological parameters on model prediction. The mathematical equations, which are nonlinear partial differential equations, are solved using AGM. Also, we derived the semi-analytical results for concentrations for saturated and unsaturated kinetics. It is verified that the proposed solution is validated by comparing it with numerical solutions. [ABSTRACT FROM AUTHOR]

Enzyme-based portable amperometric biosensors are precise and low-cost medical devices used for rapid cancer biomarker screening. Sarcosine (Sar) is an ideal biomarker for prostate cancer (PCa). Because human serum and urine contain complex interfering substances that can directly oxidize at the electrode surface, rapid Sar screening biosensors are relatively challenging and have rarely been reported. Therefore, highly sensitive and selective amperometric biosensors that enable real-time measurements within 2O2). The sarcosine oxidase (SOx) enzyme-immobilized CS–PANI–MC-2 ternary NCs were referred to as supramolecular architectures (SMAs). The excellent electron transfer ability of the SMA-modified SPCE (SMA/SPCE) sensor enabled highly sensitive H2O2 detection for immediate trace Sar biomarker detection. Therefore, the system included an SMA/SPCE coupled to a portable potentiostat linked to a smartphone for data acquisition. The high catalytic activity, porous architecture, and sufficient biocompatibility of CS–PANI–MC ternary NCs enabled bioactivity retention and immobilized SOx stability. The fabricated biosensor exhibited a detection limit of 0.077 μM and sensitivity of 8.09 μA mM−1 cm−2 toward Sar, demonstrating great potential for use in rapid PCa screening.

We report the development of amperometric biosensors (ABSs) employing flavocytochrome b2 (Fcb2) coupled with nanoparticles (NPs) of noble metals on graphite electrode (GE) surfaces. Each NPs/GE configuration was evaluated for its ability to decompose hydrogen peroxide (H2O2), mimicking peroxidase (PO) activity. The most effective nanoPO (nPO) was selected for developing ABSs targeting L-lactate. Consequently, several Fcb2/nPO-based ABSs with enhanced sensitivity to L-lactate were developed, demonstrating mediated ET between Fcb2 and the GE surface. The positive effect of noble metal NPs on Fcb2-based sensor sensitivity may be explained by the synergy between their dual roles as both PO mimetics and electron transfer mediators. Furthermore, our findings provide preliminary data that may prompt a re-evaluation of the mechanism of L-lactate oxidation in Fcb2-mediated catalysis. Previously, it was believed that L-lactate oxidation via Fcb2 catalysis did not produce H2O2, unlike catalysis via L-lactate oxidase. Our initial research revealed that the inclusion of nPO in Fcb2-based ABSs significantly increased their sensitivity. Employing other PO mimetics in ABSs for L-lactate yielded similar results, reinforcing our hypothesis that trace amounts of H2O2 may be generated as a transient intermediate in this reaction. The presence of nPO enhances the L-lactate oxidation rate through H2O2 utilization, leading to signal amplification and heightened bioelectrode sensitivity. The proposed ABSs have been successfully tested on blood serum and fermented food samples, showing their promise for L-lactate monitoring in medicine and the food industry.

This work aims to develop new H2O2-sensing elements and nanozyme-oxidase-based sensors for the detection of hydrogen peroxide, glucose, and galactose. Methods. Chemical synthesis. Assay of enzymatic activity. Scanning electron microscope. Results. Hexacyanoferrates of several transient metals were synthesized and tested for their nanozymes (HCF NZs) (certificial peroxidase) activity in solution. The best representative nanozymes (NZs) were used for the construction of H2O2-sensitive sensors and nanozyme-oxidase-based biosensors. The NZs-based sensors: nAuHCF/GE and nPtHCF/GE demonstrated higher sensitivity (7.5 and 9.4-fold) than the biosensor with natural peroxidase. The developed biosensors GOX/nPtHCF/GE and GaOx/nPtHCF/GE for the detection of glucose and galactose showed enhanced sensitivity: 900 and 540 A·M-1·m-2, respectively, broad linear range (0.02-0.2 mM). Along with a broad linear range of detection these biosensors possess low limits of detection -- 4.0 μM for glucose and 6.0 μM for galactose. Additionally, these biosensors exhibited improved stability when compared to the control. Conclusions. The novelty of the presented work is related to the synthesis of new peroxidase-like NZs and the evaluation of their functionality as the chemosensors on H2O2 and as the sensing components in the oxidase-based-biosensors for assay of glucose and galactose. The nPtHCF and nAuHCF NZs exhibit high sensitivity for the target analytes, a broad linear range, and satisfactory storage stability. The main advantages of the proposed nanozyme-oxidase-based biosensors are the simple architecture of the sensing layer and the ability to operate at low working electrode potentials. [ABSTRACT FROM AUTHOR]

Amino acid L-arginine (Arg), usually presented in food products and biological liquids, can serve both as a useful indicator of food quality and an important biomarker in medicine. The biosensors based on Arg-selective enzymes are the most promising devices for Arg assay. In this research, three types of amperometric biosensors have been fabricated. They exploit arginine oxidase (ArgO), recombinant arginase I (ARG)/urease, and arginine deiminase (ADI) coupled with the ammonium-chelating redox-active nanoparticles. Cadmium-copper nanoparticles (nCdCu) as the most effective nanochelators were used for the development of ammonium chemosensors and enzyme-coupled Arg biosensors. The fabricated enzyme/nCdCu-containing bioelectrodes show wide linear ranges (up to 200 µM), satisfactory storage stabilities (14 days), and high sensitivities (A⋅M−1⋅m−2) to Arg: 1650, 1700, and 4500 for ADI-, ArgO- and ARG/urease-based sensors, respectively. All biosensors have been exploited to estimate Arg content in commercial juices. The obtained data correlate well with the values obtained by the reference method. A hypothetic scheme for mechanism of action of ammonium nanochelators in electron transfer reaction on the arginine-sensing electrodes has been proposed. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOD) immobilized poly(o-toluidine) (POT) coated Pt electrode was designed for glucose-sensitive biosensor. Since POT film structure affects enzyme activity, parameters of enzyme immobilization and POT synthesis conditions were optimized. Optimal monomer concentration for POT film synthesis was determined as 40 mM and the scanning rate was determined as 50 mV/s. As for the immobilization process results, GOD, glutaraldehyde (GAL) and chitosan (Chi) concentrations were decided as 2 mg/ml 0.10%, and 0.5% for the Pt/POT electrode. Zinc ferrite nanoparticle (ZnFe2O4NP) was immobilized together with POT film in the presence of GOD enzyme. It was revealed that ZnFe2O4NP increased the current responses and stability of the Pt/POT electrode. [ABSTRACT FROM AUTHOR]

This article examines a mathematical model for stable urea amperometric biosensors with non-competitive inhibition under homogenous conditions. The system is based on reaction and diffusion equations with a non-linear component associated with the Michaelis-Menten kinetics of the enzyme reaction. Theoretical findings in this study can be used to examine the impact of various factors, including the Michaelis-Menten constant and the Thiele modulus. The steady-state non-linear reaction–diffusion equations were solved using two effective and widely used analytical approaches, the Akbari-Ganji method (AGM) and the differential transform method (DTM). The generalized approximation analytical solution for the concentrations of the substrate, inhibitor, and product, as well as the current for the experimental values of the parameter, is developed. The current can also be used to analyze the resistance and sensitivity of biosensors. The digital simulation was carried out utilizing MATLAB software. The numerical results help to validate the analytical results. The impact of membrane thickness, maximum enzymatic rate, and substrate concentration on biosensor response was evaluated.

The aim of this work was to create the new biosensor of alanine transaminase (ALT) activity detection in water samples. A platinum disk electrode was used to transduce chemical reactions into amperometry measured signal. Nanosize polyphenylendiamine (PPD) was applied to improve the selectivity of the transducer. In the work, the most effective isomer PD was selected and the stability of the additional membrane based on it was checked. The bioselective element was formed by the immobilization of glutamate oxidase on the surface of the transducer covered by a semipermeable P-meta-PD membrane. There was reported the method of ALT activity measurement. There was also reported the optimal conditions to create this biosensor (including enzyme immobilization parameters and substrates concentrations). The analytical characteristics were investigated including the sensitivity, the linear range, the minimum limit of detection, time of measurement, duration of analysis, stability, etc. Also, there was explored the biosensor selectivity to different interferents, e.g., electroactive molecules and amino acids. For the purpose to test the fundamental possibility of this biosensor to measure the ALT activity in real samples, the operation of the biosensor was tested in a solution with an ionic composition close to serum. [ABSTRACT FROM AUTHOR]

Catalytically active nanomaterials, in particular, nanozymes, are promising candidates for applications in biosensors due to their excellent catalytic activity, stability and cost-effective preparation. Nanozymes with peroxidase-like activities are prospective candidates for applications in biosensors. The purpose of the current work is to develop cholesterol oxidase-based amperometric bionanosensors using novel nanocomposites as peroxidase (HRP) mimetics. To select the most electroactive chemosensor on hydrogen peroxide, a wide range of nanomaterials were synthesized and characterized using cyclic voltammetry (CV) and chronoamperometry. Pt NPs were deposited on the surface of a glassy carbon electrode (GCE) in order to improve the conductivity and sensitivity of the nanocomposites. The most HRP-like active bi-metallic CuFe nanoparticles (nCuFe) were placed on a previously nano-platinized electrode, followed by conjugation of cholesterol oxidase (ChOx) in a cross-linking film formed by cysteamine and glutaraldehyde. The constructed nanostructured bioelectrode ChOx/nCuFe/nPt/GCE was characterized by CV and chronoamperometry in the presence of cholesterol. The bionanosensor (ChOx/nCuFe/nPt/GCE) shows a high sensitivity (3960 A·M−1·m−2) for cholesterol, a wide linear range (2–50 µM) and good storage stability at a low working potential (−0.25 V vs. Ag/AgCl/3 M KCl). The constructed bionanosensor was tested on a real serum sample. A detailed comparative analysis of the bioanalytical characteristics of the developed cholesterol bionanosensor and the known analogs is presented. [ABSTRACT FROM AUTHOR]

L-Lactate is an indicator of food quality, so its monitoring is essential. Enzymes of L-Lactate metabolism are promising tools for this aim. We describe here some highly sensitive biosensors for L-Lactate determination which were developed using flavocytochrome b2 (Fcb2) as a bio-recognition element, and electroactive nanoparticles (NPs) for enzyme immobilization. The enzyme was isolated from cells of the thermotolerant yeast Ogataea polymorpha. The possibility of direct electron transfer from the reduced form of Fcb2 to graphite electrodes has been confirmed, and the amplification of the electrochemical communication between the immobilized Fcb2 and the electrode surface was demonstrated to be achieved using redox nanomediators, both bound and freely diffusing. The fabricated biosensors exhibited high sensitivity (up to 1436 A·M−1·m−2), fast responses, and low limits of detection. One of the most effective biosensors, which contained co-immobilized Fcb2 and the hexacyanoferrate of gold, having a sensitivity of 253 A·M−1·m−2 without freely diffusing redox mediators, was used for L-Lactate analysis in samples of yogurts. A high correlation was observed between the values of analyte content determined using the biosensor and referenced enzymatic-chemical photometric methods. The developed biosensors based on Fcb2-mediated electroactive nanoparticles can be promising for applications in laboratories of food control. [ABSTRACT FROM AUTHOR]

Escherichia coli (E. coli) O157:H7 is a pathogenic bacterium that causes serious toxic effects in the human gastrointestinal tract. In this paper, a method for its effective analytical control in a milk sample was developed. To perform rapid (1 h) and accurate analysis, monodisperse Fe3O4@Au magnetic nanoparticles were synthesized and used in an electrochemical sandwich-type magnetic immunoassay. Screen-printed carbon electrodes (SPCE) were used as transducers, and electrochemical detection was performed by chronoamperometry using a secondary horseradish peroxidase-labeled antibody and 3,3′,5,5′-tetramethylbenzidine. This magnetic assay was used to determine the E. coli O157:H7 strain in the linear range from 20 to 2 × 106 CFU/mL, with a limit of detection of 20 CFU/mL. The selectivity of the assay was tested using Listeria monocytogenes p60 protein, and the applicability of the assay was assessed by analyzing a commercial milk sample, demonstrating the usefulness of the synthesized nanoparticles in the developed magnetic immunoassay. [ABSTRACT FROM AUTHOR]

The determination of L-glutamate in biological media is very important, as it is the most common excitatory neurotransmitter related to some neurological diseases, such as Parkinson’s, communication dysfunction, stroke, epilepsy and schizophrenia. When aiming to study the pathways of these diseases, as well as for the evaluation of medical treatments, it is very important to have rapid and reliable methods for the determination of L-glutamate. This study presents the new approach of an enzyme-based biosensor operating at −0.1 V, which ensures its good sensitivity and selectivity. The reduced graphene oxide used in the biosensor allowed for the monitoring of L-glutamate via the electro-oxidation of the NH3 released during the reaction catalyzed by Glutamate oxidase.

Nafion®-nanostructured polyaniline (nsPANi) composite film is prepared using cyclic voltammetry (CV) and immobilized with creatinine deiminase (CD) enzyme and is used to sense creatinine in a buffer phosphate solution. The conditions for preparing Nafion®-nsPANi composite film are optimized by using a mixture design for which the sensitivity is the response. The relationship between the sensitivity of the amperometric creatinine biosensor (y) and the normalized aniline concentration (Y1), HCl concentration (Y2) and scanning rate (Y3) is y = 119.44Y1 + 45.23Y2 + 100.93Y3 + 255.69Y1Y2 + 313.16Y1Y3 + 430.56Y1Y2Y3The maximum sensitivity of an amperometric creatinine biosensor that is constructed using Nafion®-nsPANi composite film in 0.0943 M aniline, 0.9024 M HCl and using a scanning rate of 27.88 mV s − 1 is 2013.2 μA mM−1 cm−2, which is 54.9% better than the sensitivity of a conventional experimental technique. The amperometric creatinine biosensor is 6.60% less sensitive after sensing 0.15 mM creatinine 240 times. The amperometric creatinine biosensor incurs insignificant interference in 0.138 mM urea, 0.085 mM ascorbic acid (AA) and 5.54 mM glucose.

The detection of lactate is an important indicator of the freshness, stability, and storage stability of products as well as the degree of fermentation in the food industry. In addition, it can be used as a diagnostic tool in patients' healthcare since it is known that the lactate level in blood increases in some pathological conditions. Thus, the determination of lactate level plays an important role in not only the food industry but also in health fields. As a result, biosensor technologies, which are quick, cheap, and easy to use, have become important for lactate detection. In the current study, amperometric lactate biosensors based on lactate oxidase immobilization (with Nafion 5% wt) were designed and the limit of detection, linear range, and sensitivity values were determined to be 31 μM, 50–350 μM, and 0.04 μA μM−1 cm−2, respectively. Then, it was used for the measurement of lactic acid that produced by six different and morphologically identified presumptive lactic acid bacteria (LAB) which are isolated from different naturally fermented cheese samples. The biosensors were then used to successfully perform lactate measurements within 3 min for each sample, even though a few of them were out of the limit of detection. Thus, electrochemical biosensors should be used as an alternative and quick solutions for the measurement of lactate metabolites rather than the traditional methods which require long working hours. This is the first study to use a biosensor to measure lactate produced by foodborne LAB in a real sample. [ABSTRACT FROM AUTHOR]

Sugar and artificial sweeteners are additives in packaged food and beverage products that are widely used, where excessive sugar consumption can cause an increase in various diseases. Detection and classification of natural sugars sucrose, fructose, glucose, and artificial sweetener aspartame are needed to determine the effects of consuming these sweeteners. This study uses an amperometric biosensor integrated biochip-D, which uses Saccharomyces cerevisiae as a bioreceptor through cellular metabolic respiration activity expressed in dissolved oxygen (DO) levels. The variations of sweetener concentration used were in the range of 50 mM to 250 mM. The measurement results showed that the higher the concentration of sugar and artificial sweeteners, the lower DO levels would be measured. It was due to the yeast cell respiration in consuming oxygen (O2) and producing carbon dioxide (CO2), where the decrease in DO levels of sucrose was 14.24%, fructose was 18.02%, glucose was 16.59%, and aspartame was 20.45% at a concentration of 250 mM. The measurement data was clustered and classified using principal component analysis (PCA), which resulted in data variance percentages of 92.80% and 89.40% for the two main components. In the application studies of the biosensor, sensitive determination of sugar in the beverage samples was investigated. [ABSTRACT FROM AUTHOR]

The aim of the current research is to design alcohol oxidase-based amperometric biosensors (ABSs) using hybrid metallic nanoparticles as artificial peroxidases (PO) or PO-like nanozymes (NZs). A lot of metallic PO-like NZs were synthesized and tested with respect to their ability to substitute natural PO in solution and on amperometric electrode. The most effective PO mimetics were coupled with alcohol oxidase (AOX) on graphite electrodes (GEs) and characterized. Two types of modified GEs, namely, the AOX/nAuCePt/GE and the AOX/nFePtAu/GE show the highest sensitivities to ethanol (2600 A⋅M−1⋅m−2 and 1250 A⋅M−1⋅m−2, respectively), low limits of detection (1.5 µM and 2.2 µM), broad linear ranges (5 – 100 µM and 12 – 120 µM), as well as satisfactory storage stabilities. The most sensitive bioelectrode AOX/nAuCePt/GE was used as ABS for ethanol determination in real samples. The practical feasibility of the constructed ABS was demonstrated by determination of ethanol in beverages, human blood and saliva. [ABSTRACT FROM AUTHOR]

We report two novel genosensors for the quantification of SARS-CoV-2 nucleic acid using glassy carbon electrodes modified with a biocapture nanoplatform made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with avidin (Av) as a support of the biotinylated-DNA probes. One of the genosensors was based on impedimetric transduction offering a non-labelled and non-amplified detection of SARS-CoV-2 nucleic acid through the increment of [Fe(CN)6]3-/4- charge transfer resistance. This biosensor presented an excellent analytical performance, with a linear range of 1.0 × 10−18 M - 1.0 × 10−11 M, a sensitivity of (5.8 ± 0.6) x 102 Ω M−1 (r2 = 0.994), detection and quantification limits of 0.33 aM and 1.0 aM, respectively; and reproducibilities of 5.4% for 1.0 × 10−15 M target using the same MWCNTs-Av-bDNAp nanoplatform, and 6.9% for 1.0 × 10−15 M target using 3 different nanoplatforms. The other genosensor was based on a sandwich hybridization scheme and amperometric transduction using the streptavidin(Strep)-biotinylated horseradish peroxidase (bHRP)/hydrogen peroxide/hydroquinone (HQ) system. This genosensor allowed an extremely sensitive quantification of the SARS-CoV-2 nucleic acid, with a linear range of 1.0 × 10−20 M - 1.0 × 10−17 M, detection limit at zM level, and a reproducibility of 11% for genosensors prepared with the same MWCNTs-Av-bDNAp1 nanoplatform. As a proof-of-concept, and considering the extremely high sensitivity, the genosensor was challenged with highly diluted samples obtained from SARS-CoV-2 RNA PCR amplification.

Bacterial infections in marine fishes are linked to mass mortality issues; hence, rapid detection of an infection can contribute to achieving a faster diagnosis using point-of-care testing. There has been substantial interest in identifying diagnostic biomarkers that can be detected in major organs to predict bacterial infections. Aspartate was identified as an important biomarker for bacterial infection diagnosis in olive flounder (Paralichthys olivaceus) fish. To determine aspartate levels, an amperometric biosensor was designed based on bi-enzymes, namely, glutamate oxidase (GluOx) and aspartate transaminase (AST), which were physisorbed on copolymer reduced graphene oxide (P-rGO), referred to as enzyme nanosheets (GluOx-ASTENs). The GluOx-ASTENs were drop casted onto a Prussian blue electrodeposited screen-printed carbon electrode (PB/SPCE). The proposed biosensor was optimized by operating variables including the enzyme loading amount, coreactant (α-ketoglutarate) concentration, and pH. Under optimal conditions, the biosensor displayed the maximum current responses within 10 s at the low applied potential of −0.10 V vs. the internal Ag/AgCl reference. The biosensor exhibited a linear response from 1.0 to 2.0 mM of aspartate concentrations with a sensitivity of 0.8 µA mM−1 cm−2 and a lower detection limit of approximately 500 µM. Moreover, the biosensor possessed high reproducibility, good selectivity, and efficient storage stability. [ABSTRACT FROM AUTHOR]

Laccase is a copper-containing enzyme that does not require hydrogen peroxide as a co-substrate or additional cofactors for an enzymatic reaction. Nanomaterials of various chemical structures are usually applied to the construction of enzyme-based biosensors. Metals, metal oxides, semiconductors, and composite NPs perform various functions in electrochemical transformation schemes as a platform for the enzyme immobilization, a mediator of an electron transfer, and a signal amplifier. We describe here the development of amperometric biosensors (ABSs) based on laccase and redox-active micro/nanoparticles (hereafter—NPs), which were immobilized on a graphite electrode (GE). For this purpose, we isolated a highly purified enzyme from the fungus Trametes zonatus, and then synthesized bi- and trimetallic NPs of noble and transition metals, as well as hexacyanoferrates (HCF) of noble metals; these were layered onto the surfaces of GEs. The electroactivity of many of the NPs immobilized on the GEs was characterized by cyclic voltammetry (CV) experiments. The most effective mediators of electron transfer were selected as the platform for the development of laccase-based ABSs. As a result, a number of catechol-sensitive ABSs were constructed and characterized. The laccase/CuCo/GE was demonstrated to possess the highest sensitivity to catechol (4523 A·M−1·m−2) among the tested ABSs. The proposed ABSs may be promising for the analysis of phenolic derivatives in real samples of drinking water, wastewater, and food products. [ABSTRACT FROM AUTHOR]

The availability of fast and non-expensive analytical methods for the determination of widespread interest analytes such as glucose is an object of large relevance; this is so not only in the field of analytical chemistry, but also in medicinal and in food chemistry. In this context, electrochemical biosensors have been proposed in different arrangements, according to the mode of electron transfer between the bioreceptor and the electrode. An efficient immobilization of an enzyme on the electrode surface is essential to assure satisfactory analytical performances of the biosensor in terms of sensitivity, limit of detection, selectivity, and linear range of employment. Here, we report the use of a thiophene monomer, (2,5-di(2-thienyl)thieno [3,2-b]thiophene (dTT-bT), as a precursor of an electrogenerated conducting film to immobilize the glucose oxidase (GOx) enzyme on Pt, glassy carbon (GC), and Au electrode surfaces. In addition, the polymer film electrochemically synthetized on a glassy carbon electrode was modified with graphene oxide before the deposition of GOx; the analytical performances of both the arrangements (without and with graphene oxide) in the glucose detection were compared. The biosensor containing graphene oxide showed satisfactory values of linear dynamic range (1.0–10 mM), limit of detection (0.036 mM), and sensitivity (9.4 µA mM−1 cm−2). Finally, it was tested in the determination of glucose in fruit juices; the interference from fructose, saccharose, and ascorbic acid was evaluated. [ABSTRACT FROM AUTHOR]

Catalytically active nanomaterials, in particular, nanozymes, are promising candidates for applications in biosensors due to their excellent catalytic activity, stability and cost-effective preparation. Nanozymes with peroxidase-like activities are prospective candidates for applications in biosensors. The purpose of the current work is to develop cholesterol oxidase-based amperometric bionanosensors using novel nanocomposites as peroxidase (HRP) mimetics. To select the most electroactive chemosensor on hydrogen peroxide, a wide range of nanomaterials were synthesized and characterized using cyclic voltammetry (CV) and chronoamperometry. Pt NPs were deposited on the surface of a glassy carbon electrode (GCE) in order to improve the conductivity and sensitivity of the nanocomposites. The most HRP-like active bi-metallic CuFe nanoparticles (nCuFe) were placed on a previously nano-platinized electrode, followed by conjugation of cholesterol oxidase (ChOx) in a cross-linking film formed by cysteamine and glutaraldehyde. The constructed nanostructured bioelectrode ChOx/nCuFe/nPt/GCE was characterized by CV and chronoamperometry in the presence of cholesterol. The bionanosensor (ChOx/nCuFe/nPt/GCE) shows a high sensitivity (3960 A·M−1·m−2) for cholesterol, a wide linear range (2–50 µM) and good storage stability at a low working potential (−0.25 V vs. Ag/AgCl/3 M KCl). The constructed bionanosensor was tested on a real serum sample. A detailed comparative analysis of the bioanalytical characteristics of the developed cholesterol bionanosensor and the known analogs is presented.

• A whole cell-based electrochemical biosensor was applied for the assay of methylamine. • A method of enrichment of yeast cells with a target enzyme and nanozyme has been proposed. • Recombinant methylamine oxidase was employed as a specific enzyme. • A synergistic effect of enzyme and nanoparticles inside yeast cells for enhanced catalytic activity was demonstrated. • Selective and sensitive determination of methylamine in food products was demonstrated. Microbial biosensors, particularly when combined with nanotechnologies, are fast and affordable tools for different analytical purposes. Most microbial biosensors are based on the use of genetically modified cells, capable of over-producing a target enzyme, which is advantageous in terms of their sensitivity and selectivity. However, the loss of a plasmid or changes in the number of copies of the plasmid is a significant drawback. In this context, the application of alternative nanotechnological approaches for increasing the catalytic activity of sensing cells is of paramount importance. In the current research, a novel strategy of additional loading of recombinant yeast cells with a target enzyme and nanozyme has been proposed to develop methylamine (MA)-selective biosensor. To construct an amperometric sensor, the Saccharomyces cerevisiae yeast cells were enriched with the enzyme and nanozyme by combining three ways of genetic and nanotechnological engineering: on the genetic level – by overexpression of the methylamine oxidase (MAO) gene coding for MAO in recombinant cells; under nanotechnological approaches – by the additional enrichment of the cells with the purified enzyme MAO, co-immobilized with peroxidase mimetics, i.e. , nCdTe or nCeAu. Fluorescent nCdTe as the most effective peroxidase-mimetic was used to develop hydrogen peroxide chemosensors and as a carrier for delivery of MAO inside the cells. The most effective cells-MAO-nCdTe-containing electrode shows wide range (0.001–0.02 µM) of linear response and high sensitivity (5450 A⋅M−1⋅m−2) to MA. The proposed approaches for increasing catalytic efficiency of sensing cells can be used for elaboration of other microbial sensors based on their enzymatic activity. [Display omitted] [ABSTRACT FROM AUTHOR]

Escherichia coli (E. coli) O157:H7 is a pathogenic bacterium that causes serious toxic effects in the human gastrointestinal tract. In this paper, a method for its effective analytical control in a milk sample was developed. To perform rapid (1 h) and accurate analysis, monodisperse Fe3O4@Au magnetic nanoparticles were synthesized and used in an electrochemical sandwich-type magnetic immunoassay. Screen-printed carbon electrodes (SPCE) were used as transducers, and electrochemical detection was performed by chronoamperometry using a secondary horseradish peroxidase-labeled antibody and 3,3′,5,5′-tetramethylbenzidine. This magnetic assay was used to determine the E. coli O157:H7 strain in the linear range from 20 to 2 × 106 CFU/mL, with a limit of detection of 20 CFU/mL. The selectivity of the assay was tested using Listeria monocytogenes p60 protein, and the applicability of the assay was assessed by analyzing a commercial milk sample, demonstrating the usefulness of the synthesized nanoparticles in the developed magnetic immunoassay.

L-Lactate is an indicator of food quality, so its monitoring is essential. Enzymes of L-Lactate metabolism are promising tools for this aim. We describe here some highly sensitive biosensors for L-Lactate determination which were developed using flavocytochrome b2 (Fcb2) as a bio-recognition element, and electroactive nanoparticles (NPs) for enzyme immobilization. The enzyme was isolated from cells of the thermotolerant yeast Ogataea polymorpha. The possibility of direct electron transfer from the reduced form of Fcb2 to graphite electrodes has been confirmed, and the amplification of the electrochemical communication between the immobilized Fcb2 and the electrode surface was demonstrated to be achieved using redox nanomediators, both bound and freely diffusing. The fabricated biosensors exhibited high sensitivity (up to 1436 A·M−1·m−2), fast responses, and low limits of detection. One of the most effective biosensors, which contained co-immobilized Fcb2 and the hexacyanoferrate of gold, having a sensitivity of 253 A·M−1·m−2 without freely diffusing redox mediators, was used for L-Lactate analysis in samples of yogurts. A high correlation was observed between the values of analyte content determined using the biosensor and referenced enzymatic-chemical photometric methods. The developed biosensors based on Fcb2-mediated electroactive nanoparticles can be promising for applications in laboratories of food control.

The regulation of nervous and cardiovascular systems and some brain-related behaviors, such as stress, panic, anxiety, and depression, are strictly dependent on the levels of the main catecholamines of clinical interest, dopamine (DA), epinephrine (EP), and norepinephrine (NEP). Therefore, there is an urgent need for a reliable sensing device able to accurately monitor them in biological fluids for early diagnosis of the diseases related to their abnormal levels. In this paper, we present the first tyrosinase (Tyr)-based biosensor based on chitosan nanoparticles (ChitNPs) for total catecholamine (CA) detection in human urine samples. ChitNPs were synthetized according to an ionic gelation process and successively characterized by SEM and EDX techniques. The screen-printed graphene electrode was prepared by a two-step drop-casting method of: (i) ChitNPS; and (ii) Tyr enzyme. Optimization of the electrochemical platform was performed in terms of the loading method of Tyr on ChitNPs (nanoprecipitation and layer-by-layer), enzyme concentration, and enzyme immobilization with and without 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as cross-linking agents. The Tyr/EDC-NHS/ChitNPs nanocomposite showed good conductivity and biocompatibility with Tyr enzyme, as evidenced by its high biocatalytic activity toward the oxidation of DA, EP, and NEP to the relative o-quinone derivatives electrochemically reduced at the modified electrode. The resulting Tyr/EDC-NHS/ChitNPs-based biosensor performs interference-free total catecholamine detection, expressed as a DA concentration, with a very low LOD of 0.17 μM, an excellent sensitivity of 0.583 μA μM−1 cm−2, good stability, and a fast response time (3 s). The performance of the biosensor was successively assessed in human urine samples, showing satisfactory results and, thus, demonstrating the feasibility of the proposed biosensor for analyzing total CA in physiological samples. [ABSTRACT FROM AUTHOR]

New three-enzyme lactose amperometric biosensor based on platinum disc electrode modified by nanosized semipermeable poly (meta-phenylenediamine) film was developed in this work. It was studied the influence of different conditions of meta-phenylenediamine electropolymerization on the parameters (sensitivity and selectivity) of the amperometric transducers. The most optimal parameters were achieved after performing the electropolymerization of 5 mM meta-phenylenediamine applying 10–13 cyclic voltammograms. The bioselective element of lactose biosensor consisted of three enzymes (β-galactosidase, mutarotase, glucose oxidase) that were immobilized on the surface of modified working electrode. The analytical characteristics of the developed biosensor were studied. The linear range of lactose determination extended from 0.01 mM to 1.25 mM. The response time of the biosensor was 30 s. The biosensor showed high signal reproducibility (RSD = 1.16%), high sensitivity (LOD = 0.005 mM) and high selectivity. The proposed biosensor was tested for measurement of lactose concentration in milk samples. The high correlation between results obtained with lactose biosensor and HPLC was shown (R = 0.96%). Thus, the developed biosensor is suited for rapid, inexpensive, sensitive, selective and simple determination of lactose in milk samples. [ABSTRACT FROM AUTHOR]

Abstract Histamine is an important biogenic amine because of its role in immune responses and the regulation of physiological functions. It is also used as a food freshness indicator, so its maximum concentration in fish is legally regulated. Although several robust and sensitive methods for histamine detection are already available, it continues to be a challenge to develop simple and portable devices that allow rapid histamine screening at any point of the fish production chain. Thus, in this work, a simple, miniaturized and low-cost sensor for histamine analysis was developed. The construction of the sensor only takes 30 min and consists of the immobilization of the enzyme diamine oxidase on the surface of a screen-printed carbon electrode by cross-linking. The quantification of histamine was achieved by chronoamperometry (+ 0.2V, 120 s) using hexacyanoferrate (III) as a redox mediator. This selective sensor provided a low limit of detection (0.97 mg L−1) and accurate and precise results and was successfully applied to the analysis of spiked tuna and mackerel extracts, obtaining recovery values of 99–100%. Moreover, the sensor shows good stability, maintaining 87.7% of its initial signal after 35 days.

A mathematical model of an amperometric biosensor response for uncompetitive inhibition detection is discussed. The model is based on a system of reaction–diffusion equations containing a nonlinear term related to Michaelis–Menten kinetics of the enzymatic reaction. Two highly accurate and easily accessible analytical methods are used to solve the nonlinear differential equations that describe the diffusion coupled with a reaction term. Semi-analytical expressions for the concentrations of substrate, inhibitor, and product in addition to the corresponding current response are derived. The effects of various parameters such as layer thickness, bulk substrate concentration, Michaelis–Menten constant, maximum reaction velocity on current, and the sensitivity and resistance of a biosensor are investigated. A direct comparison with a numerical solution of the governing system is presented to confirm the accuracy of the derived approximate analytical solutions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of soybean oil/vanillin-based polymers morphology on biosensor parameters. • Usage of positron annihilation lifetime spectroscopy and electrochemical approaches. • Dependence of sensor characteristics on polymer chemical composition. • Possibility to adapt the biosensor to parameters according to the needs of analysis. Network properties on local free volume and biosensor parameters of polymers based on acrylated epoxidized soybean oil (AESO), a combination of AESO with vanillin dimethacrylate (VDM) in ratio 1:0.25 mol, and its combination with vanillin diacrylate (VDA) with the same molar ratio, used as laccase-holding matrixes for the construction of amperometric biosensors, were tested and compared. The formed polymer matrixes were investigated using Positron Annihilation Lifetime Spectroscopy (PALS) as bulk samples and applying electrochemical methods as sensor films. PALS results showed that the lifetime of the ortho -positronium component and corresponding intensity are almost similar for both polymers, indicating no significant difference from the point of view of their morphology. However, the cyclic voltammetric and chronoamperometric analysis demonstrated significant differences in the bioelecrodes' operational parameters formed by the AESO:VDM polymer compared to AESO:VDA. The AESO:VDA-based bioelectodes were characterized with a twice higher affinity toward ABTS (K M app = 0.158 ± 0.022 mM vs. 0.326 ± 0.043 mM). At the same time, their sensitivity was about twice less compared to AESO:VDM-based (902 A·M−1·m−2 vs. 1608 A·M−1·m−2), and a start concentration of the linear frame was 7-folds higher (14 μM vs. 2 μM ABTS). It was shown early, that the operational parameters of amperometric biosensors are greatly dependent on morphological characteristics of polymer matrixes (e.g., crosslink density, cavities size, thermal expansion of free-volume hole, etc.). The matrix morphology affects on efficacity of physical diffusion of the substrate to the enzyme, and electroactive product toward the electrode, as well as provides a comfortable environment for the incorporated enzyme. Here, we describe the usage of polymer matrixes with the same morphological properties but different chemical compositions, analyzing the effect of chemical structure on the operational parameters of biosensors. Thus, it was demonstrated that the sensor operational parameters depend not only on the morphological properties of the polymer holding matrixes, providing enzyme fixation and substrate/product diffusion, but also on their chemical composition, which opens a possibility to adapt the biosensor characteristics according to the required needs of analysis. [ABSTRACT FROM AUTHOR]

This study describes the development of a highly sensitive amperometric biosensor for the analysis of phenolic compounds such as catechol. The biosensor architecture is based on the immobilization of tyrosinase (Tyr) on a screen-printed carbon electrode (SPE) modified with nanodiamond particles (ND), 1-butyl-3-methylimidazolium hexafluorophosphate (IL) and poly- l -lysine (PLL). Surface morphologies of the electrodes during the modification process were evaluated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical characteristics of the modified electrodes. Owing to the synergistic effect of the modification materials, the Tyr/PLL/ND−IL/SPE exhibited high sensitivity (328.2 μA mM−1) towards catechol with a wide linear range (5.0 × 10−8 – 1.2 × 10−5 M) and low detection limit (1.1 × 10−8 M). Furthermore, the method demonstrated good reproducibility and stability. The amperometric response of the biosensor towards other phenolic compounds such as bisphenol A, phenol, p -nitrophenol, m -cresol, p -cresol and o -cresol was also investigated. The analytical applicability of the biosensor was tested by the analysis of catechol in tap water. The results of the tap water analysis showed that the Tyr/PLL/ND−IL/SPE can be used as a practical and effective method for catechol determination. [Display omitted] • A novel amperometric catechol biosensor based on tyrosinase was developed. • Tyrosinase was immobilized on nanodiamond, ionic liquid, poly- l -lysine modified screen-printed carbon electrode. • The biosensor showed high sensitivity towards catechol. • The amperometric response of the presented biosensor towards other phenolic compounds was also investigated. • The biosensor was successfully applied for catechol determination in tap water. [ABSTRACT FROM AUTHOR]

GOD was immobilized onto polypyrrole (PPy) or poly(o-anisidine) (POA) coated Pt electrode to construct glucose sensitive biosensor. Because polymer film properties and enzyme activity affect the current response, PPy and POA synthesis conditions and also enzyme immobilization parameters were optimized in detail. The optimal monomer concentrations were determined as 25 and 50 mM for PPy and POA, respectively, whereas scan rate was 50 mV/s for both polymer films. In case of immobilization procedure, the optimal Chitosan (Chi), glucose oxidase (GOD) and glutaraldehyde (GAL) concentrations were determined as 0.5%, 2 mg/ml and 0.05% for PPy and 0.5%, 4 mg/ml and 0.075% for POA, respectively. Zinc oxide nanoparticles (ZnONP) were co-immobilized with GOD enzyme and it was revealed that ZnONP modification enhanced the efficiencies of both electrodes in terms of current responses and stabilities. Nyquist diagrams showed that enzyme electrodes were sensitive to glucose molecule and ZnONP modification improved the sensor efficiency.

Triclosan is a compound with antimicrobial activity broadly used in consumer products. Because of its well-documented toxicity, the amount of triclosan present in different products needs to be tightly controlled. This paper outlines a new amperometric sensor for triclosan detection consisting of a screen-printed carbon nanotube electrode (SPCNE) modified with Guinea grass peroxidase (GGP). The GGP-modified SPCNE was able to detect an enhanced electrochemical response of triclosan, unlike the bare SPCNE. The cyclic voltammograms of the GGP-modified SPCNE in a solution of potassium ferrocyanide showed an increase in the current values and linearity between scan rates and oxidation peak currents, suggesting a surface-controlled process. The GGP-modified SPCNE showed an excellent electrocatalytic activity to triclosan oxidation, at a redox potential of 370 mV, in the presence of hydrogen peroxide, exhibiting a linear response between 20 mM to 80 mM and a detection limit of 3 µM. This new amperometry system, based on carbon nanotubes integrated with GGP, becomes a potential tool for environmental analysis and food quality control.

An amperometric biosensor for the indirect determination of Hg(II) has been developed based on inhibition of urease (EC 3.5.1.5) immobilized into alginate–chitosan polyelectrolyte complexes membrane. The biosensor response was monitored by following the reduction peak of hydrolyzed urea at around -0.15 V. The amperometric biosensor has a dynamic range 40–90 ppb Hg(II) with limit of detection of 66.45 ppb toward Hg(II) ions, repeatability (CV) value of 0.86% and only Ag(I) as the main potential interference. The sensor shows a stable and reproducible response for more than 2 weeks when it stored dry at 4 °C. The analytical results of Hg(II)-spiked water sample showed a good agreement with those obtained by atomic absorption spectrometry method, suggesting that the developed method may be applied in the determination of Hg(II) in the water samples.

Laccase is a copper-containing enzyme that does not require hydrogen peroxide as a co-substrate or additional cofactors for an enzymatic reaction. Nanomaterials of various chemical structures are usually applied to the construction of enzyme-based biosensors. Metals, metal oxides, semiconductors, and composite NPs perform various functions in electrochemical transformation schemes as a platform for the enzyme immobilization, a mediator of an electron transfer, and a signal amplifier. We describe here the development of amperometric biosensors (ABSs) based on laccase and redox-active micro/nanoparticles (hereafter—NPs), which were immobilized on a graphite electrode (GE). For this purpose, we isolated a highly purified enzyme from the fungus Trametes zonatus, and then synthesized bi- and trimetallic NPs of noble and transition metals, as well as hexacyanoferrates (HCF) of noble metals; these were layered onto the surfaces of GEs. The electroactivity of many of the NPs immobilized on the GEs was characterized by cyclic voltammetry (CV) experiments. The most effective mediators of electron transfer were selected as the platform for the development of laccase-based ABSs. As a result, a number of catechol-sensitive ABSs were constructed and characterized. The laccase/CuCo/GE was demonstrated to possess the highest sensitivity to catechol (4523 A·M−1·m−2) among the tested ABSs. The proposed ABSs may be promising for the analysis of phenolic derivatives in real samples of drinking water, wastewater, and food products.

Bacterial infections in marine fishes are linked to mass mortality issues; hence, rapid detection of an infection can contribute to achieving a faster diagnosis using point-of-care testing. There has been substantial interest in identifying diagnostic biomarkers that can be detected in major organs to predict bacterial infections. Aspartate was identified as an important biomarker for bacterial infection diagnosis in olive flounder (Paralichthys olivaceus) fish. To determine aspartate levels, an amperometric biosensor was designed based on bi-enzymes, namely, glutamate oxidase (GluOx) and aspartate transaminase (AST), which were physisorbed on copolymer reduced graphene oxide (P-rGO), referred to as enzyme nanosheets (GluOx-ASTENs). The GluOx-ASTENs were drop casted onto a Prussian blue electrodeposited screen-printed carbon electrode (PB/SPCE). The proposed biosensor was optimized by operating variables including the enzyme loading amount, coreactant (α-ketoglutarate) concentration, and pH. Under optimal conditions, the biosensor displayed the maximum current responses within 10 s at the low applied potential of −0.10 V vs. the internal Ag/AgCl reference. The biosensor exhibited a linear response from 1.0 to 2.0 mM of aspartate concentrations with a sensitivity of 0.8 µA mM−1 cm−2 and a lower detection limit of approximately 500 µM. Moreover, the biosensor possessed high reproducibility, good selectivity, and efficient storage stability.

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Today, the concentration of glutamate in the patient′s blood is an important indicator in medical diagnostics; therefore, it is necessary to have a simple, accurate, and fast tool to obtain the data. Here, a recently developed amperometric glutamate‐sensitive biosensor was optimized to improve its characteristics. The platinum disk electrode was used as a transducer. As a bioselective element we used the enzyme glutamate oxidase, covalently crosslinked with bovine serum albumin by glutaraldehyde. Circumstances of enzyme immobilization on the transducer's surface were optimized (enzyme and glutaraldehyde concentrations and immobilization duration). To test the ability of this biosensor to work in biological environments containing complex biological substances, the influence of the working solution was investigated (concentration of the working buffer, its temperature, presence of the protein in the analyzed sample). The linear range of biosensor was from 5 to 600 μM of glutamate and the sensitivity was 150–200 nA/mM. Measurements of glutamate concentrations in the blood plasma were performed by biosensor and glutamate dehydrogenase assay. The linear correlation between the methods was found in a range of 50.4–182.5 μM (R2=0.99). Thus, it has been shown that the developed biosensor makes it possible to measure the concentration of glutamate in blood plasma. [ABSTRACT FROM AUTHOR]