Accurate glutamate monitoring in foodstuffs by a sensitive and interference-free glutamate oxidase based disposable amperometric biosensor

Glutamate oxidase sheets-Prussian blue grafted amperometric biosensor for the real time monitoring of glutamate release from primary cortical neurons

Glutamate (GLU) is a primary excitatory neurotransmitter, and its dysregulation is associated with several neurodegenerative disorders. A major challenge in GLU estimation is the existence of other biomolecules in the brain that could directly get oxidized at the electrode. Hence, highly selective electroenzymatic biosensors that enable rapid estimation of GLU are needed. Initially, a copolymer, poly(2-dimethylaminoethyl methacrylate- styrene) was synthesized through reversible addition-fragmentation chain transfer polymerization to noncovalently functionalize reduced graphene oxide (rGO), named DS-rGO. Glutamate oxidase macromolecule immobilized DS-rGO formed enzyme nanosheets, which was drop-coated over Prussian blue electrodeposited disposable electrodes to fabricate the GLU biosensor. The interconnectivity between the enzyme nanosheets and the Prussian blue endows the biosensor with enhanced conductivity and electrochemical activity. The biosensor exhibited a linearity: 3.25-250 μM; sensitivity: 3.96 μA mM-1 cm-2, and a limit of detection: 0.96 μM for GLU in the Neurobasal Medium. The biosensor was applied to an in vitro primary rat cortical model to discriminate GLU levels in Neurobasal Medium, before and after KCl mediated depolarization, which provides new insights for elucidating neuronal functioning in the brain.

Recent Advances in Electrochemical Enzyme-Based Biosensors for Food and Beverage Analysis

Food analysis and control are crucial aspects in food research and production in order to ensure quality and safety of food products. Electrochemical biosensors based on enzymes as the bioreceptors are emerging as promising tools for food analysis because of their high selectivity and sensitivity, short analysis time, and high-cost effectiveness in comparison to conventional methods. This review provides the readers with an overview of various electrochemical enzyme-based biosensors in food analysis, focusing on enzymes used for different applications in the analysis of sugars, alcohols, amino acids and amines, and organic acids, as well as mycotoxins and chemical contaminants. In addition, strategies to improve the performance of enzyme-based biosensors that have been reported over the last five years will be discussed. The challenges and future outlooks for the food sector are also presented.

A Facile Method for the Fabrication of the Microneedle Electrode and Its Application in the Enzymatic Determination of Glutamate

Herein, a simple method has been used in the fabrication of a microneedle electrode (MNE). To do this, firstly, a commercial self-dissolving microneedle patch has been used to make a hard-polydimethylsiloxane-based micro-pore mold (MPM). Then, the pores of the MPM were filled with the conductive platinum (Pt) paste and cured in an oven. Afterward, the MNE made of platinum (Pt-MNE) was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). To prove the electrochemical applicability of the Pt-MNE, the glutamate oxidase enzyme was immobilized on the surface of the electrode, to detect glutamate, using the cyclic voltammetry (CV) and chronoamperometry (CA) methods. The obtained results demonstrated that the fabricated biosensor could detect a glutamate concentration in the range of 10-150 µM. The limits of detection (LODs) (three standard deviations of the blank/slope) were also calculated to be 0.25 µM and 0.41 µM, using CV and CA, respectively. Furthermore, the Michaelis-Menten constant (KMapp) of the biosensor was calculated to be 296.48 µM using a CA method. The proposed biosensor was finally applied, to detect the glutamate concentration in human serum samples. The presented method for the fabrication of the mold signifies a step further toward the fabrication of a microneedle electrode.

Development of an Enzymatic Biosensor Using Glutamate Oxidase on Organic-Inorganic-Structured, Electrospun Nanofiber-Modified Electrodes for Monosodium Glutamate Detection

Herein, dendrimer-modified montmorillonite (Mt)-decorated poly-Ɛ-caprolactone (PCL) and chitosan (CHIT)-based nanofibers were prepared. Mt was modified with a poly(amidoamine) generation 1 (PAMAM_G1) dendrimer, and the obtained PAMAM_G1-Mt was incorporated into the PCL-CHIT nanofiber's structure. The PCL-CHIT/PAMAM_G1-Mt nanofibers were conjugated with glutamate oxidase (GluOx) to design a bio-based detection system for monosodium glutamate (MSG). PAMAM_G1-Mt was added to the PCL-CHIT backbone to provide a multipoint binding side to immobilize GluOx via covalent bonds. After the characterization of PCL-CHIT/PAMAM_G1-Mt/GluOx, it was calibrated for MSG. The linear ranges were determined from 0.025 to 0.25 mM MSG using PCL-CHIT/Mt/GluOx and from 0.0025 to 0.175 mM MSG using PCL-CHIT/PAMAMG₁-Mt/GluOx (with a detection limit of 7.019 µM for PCL-CHIT/Mt/GluOx and 1.045 µM for PCL-CHIT/PAMAMG₁-Mt/GluOx). Finally, PCL-CHIT/PAMAMG₁-Mt/GluOx was applied to analyze MSG content in tomato soup without interfering with the sample matrix, giving a recovery percentage of 103.125%. Hence, the nanofiber modification with dendrimer-intercalated Mt and GluOx conjugation onto the formed nanocomposite structures was performed, and the PCL-CHIT/PAMAM_G1-Mt/GluOx system was successfully developed for MSG detection.

Recent advances in development of electrochemical biosensors for the detection of biogenic amines

Biogenic amines (BAs) are widely found in food as a consequence of diverse factors including free amino acid availability, microbial production of decarboxylases, and variations in processing and storage conditions. Hence, BAs are considered as an important marker for determining the freshness and quality of food. Owing to the documentation of BAs in different dietary products, their numerous negative impacts on human health have reported to be a serious concern in past few decades. Therefore, the quantification of these chemical species in food becomes crucial as it can immensely contributes toward control of new episodes on food intoxication in humans. In this line, various chromatographic and colorimetric methods have been developed to detect BAs. However, these methods are in use from a longer time, still are limited by high cost, lengthy procedures, huge infrastructure and skilled personnel requirements that hinder their on-field application. In pursuit of a reliable method offering accurate detection of BAs, this review presents the state-of-the-art of electrochemical strategies for BAs sensing in food. The core of the review discusses about the widely employed electrochemical transducers, such as amperometric, potentiometric, impedimetric and conductometric-based BAs biosensors with significant findings of research work conducted previously. The application of electrochemical sensors to analyze BAs in different fields including food systems (fermented and non-fermented types) and smart packaging systems has been reviewed. Moreover, existing challenges and further available prospects for the development of rapid, facile, and sensitive electrochemical strategies for on-site determination of BAs have also been discussed.

Glutamate Oxidase-Integrated Biomimetic Metal-Organic Framework Hybrids as Cascade Nanozymes for Ultrasensitive Glutamate Detection

The hybrid coupling of biocatalysts and chemical catalysts plays a vital role in the fields of catalysis, sensing, and medical treatment due to the integrated advantages in the high activity of natural enzymes and the excellent stability of nanozymes. Herein, a new nanozyme/natural enzyme hybrid biosensor was established for ultrasensitive glutamate detection. The MIL-88B(Fe)-NH₂ material with remarkable peroxidase mimic activity and stability was used as a nanozyme and carrier for immobilizing glutamate oxidase (GLOX) through Schiff base reaction to construct a chem-enzyme cascade detector (MIL-88B(Fe)-NH₂@GLOX). The resultant MIL-88B(Fe)-NH₂@GLOX exhibited a wide linear range (1-100 μM), with a low detection limit of 2.5 μM for glutamate detection. Furthermore, the MIL-88B(Fe)-NH₂@GLOX displayed excellent reusability and storage stability. After repeated seven cycles, MIL-88B(Fe)-NH₂-GLOX (GLOX was adsorbed on MIL-88B(Fe)-NH₂) lost most of its activity, whereas MIL-88B(Fe)-NH₂@GLOX still retained 69% of its initial activity. Meanwhile, MIL-88B(Fe)-NH₂@GLOX maintained 60% of its initial activity after storage for 90 days, while free GLOX only retained 30% of its initial activity. This strategy of integrating MOF mimics and natural enzymes for cascade catalysis makes it possible to design an efficient and stable chemo-enzyme composite catalysts, which are promising for applications in biosensing and biomimetic catalysis.

A novel and disposable GP- based impedimetric biosensor using electropolymerization process with PGA for highly sensitive determination of leptin: Early diagnosis of childhood obesity

This study presents a novel, single-use electrochemical biosensor for the leptin biomarker, which may have potential use for early diagnosis of childhood obesity. The graphite paper working electrode was used for the first time in impedimetric biosensors. All immobilization procedure, investigation of the optimal parameters and characterization of biosensors were followed and evaluated using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV). The Scanning Electron Microscope (SEM) was utilized to visualize the morphology of the electrode surface during the immobilization steps of the immunosensor. Moreover, the characterization of the interactions between anti-leptin and leptin was investigated by using Single Frequency Technique (SFI). The applicability of the designed biosensor for real serum samples was tested for clinical use. It was observed that the biosensor allows high sensitivity in the analyte detection (leptin) in real serum samples. Moreover, it was suggested that the developed biosensor presents advantages such as long shelf life (5% loss of activity after 8 weeks and 60% loss after 10 weeks), ability to determine analyte concentrations at picogram level (0.2 pg mL^-1 -20 pg mL^-1), low limit of detection (0.00813 pg mL^{- 1}), reproducibility, reusability (12 times) and high sensitivity.

Biosensors for Biogenic Amines: A Review

Biogenic amines (BAs) are well-known biomolecules, mostly for their toxic and carcinogenic effects. Commonly, they are used as an indicator of quality preservation in food and beverages since their presence in higher concentrations is associated with poor quality. With respect to BA’s metabolic pathways, time plays a crucial factor in their formation. They are mainly formed by microbial decarboxylation of amino acids, which is closely related to food deterioration, therefore, making them unfit for human consumption. Pathogenic microorganisms grow in food without any noticeable change in odor, appearance, or taste, thus, they can reach toxic concentrations. The present review provides an overview of the most recent literature on BAs with special emphasis on food matrixes, including a description of the typical BA assay formats, along with its general structure, according to the biorecognition elements used (enzymes, nucleic acids, whole cells, and antibodies). The extensive and significant amount of research that has been done to the investigation of biorecognition elements, transducers, and their integration in biosensors, over the years has been reviewed.