Amperometric determination of reduced glutathione with a new Co-based metal-organic coordination polymer modified electrode

Enzyme-immobilized graphene oxide-based electrochemical biosensor for glutathione detection

Glutathione acts as a natural antioxidant in the human body and the reduction of its content is a sign of oxidative stress. In this study, a sensitive electrochemical sensor was developed using laccase enzyme immobilized onto graphene oxide (GO) for detection of glutathione. The surface of the indium tin oxide (ITO) was modified with GO via a drop casting method. Subsequently, laccase was immobilized onto the modified ITO decorated with GO. The modified electrode was characterized using field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The FTIR spectra of laccase/GO confirmed the successful immobilization of laccase onto GO sheets. FESEM analysis revealed the transformation from a layered, wrinkled structure to a compact, smooth surface with spherical laccase, confirming successful enzyme integration. Raman analysis confirmed successful laccase immobilization onto GO, as evidenced by structural changes in the D and G bands, highlighting the modification of the material. The cyclic voltammetry measurements revealed that laccase/GO/ITO exhibited better electrocatalytic activity toward oxidation of GSH in acetate buffer solution than the bare ITO electrode. This newly developed electrode exhibited a good response to glutathione with a wide linear range from 1 μM to 100 μM, a limit of detection of 0.89 μM and high sensitivity (6.51 μA μM-1). Furthermore, it exhibited excellent selectivity, repeatability, and long-term stability. The modified electrode was successfully used for the detection of GSH in a real sample, offering satisfactory results.

Analytical Methods for Assessing Thiol Antioxidants in Biological Fluids: A Review

Redox metabolism is an integral part of the glutathione system, encompassing reduced and oxidized glutathione, hydrogen peroxide, and associated enzymes. This core process orchestrates a network of thiol antioxidants like thioredoxins and peroxiredoxins, alongside critical thiol-containing proteins such as mercaptoalbumin. Modifications to thiol-containing proteins, including oxidation and glutathionylation, regulate cellular signaling influencing gene activities in inflammation and carcinogenesis. Analyzing thiol antioxidants, especially glutathione, in biological fluids offers insights into pathological conditions. This review discusses the analytical methods for biothiol determination, mainly in blood plasma. The study includes all key methodological aspects of spectroscopy, chromatography, electrochemistry, and mass spectrometry, highlighting their principles, benefits, limitations, and recent advancements that were not included in previously published reviews. Sample preparation and factors affecting thiol antioxidant measurements are discussed. The review reveals that the choice of analytical procedures should be based on the specific requirements of the research. Spectrophotometric methods are simple and cost-effective but may need more specificity. Chromatographic techniques have excellent separation capabilities but require longer analysis times. Electrochemical methods enable real-time monitoring but have disadvantages such as interference. Mass spectrometry-based approaches have high sensitivity and selectivity but require sophisticated instrumentation. Combining multiple techniques can provide comprehensive information on thiol antioxidant levels in biological fluids, enabling clearer insights into their roles in health and disease. This review covers the time span from 2010 to mid-2024, and the data were obtained from the SciFinder® (ACS), Google Scholar (Google), PubMed®, and ScienceDirect (Scopus) databases through a combination search approach using keywords.

The development of a novel copper-loaded mesoporous silica nanoparticle as a peroxidase mimetic for colorimetric biosensing and its application in H2O2 and GSH assay

In recent years, the development of nanomaterials-based peroxidase mimics as enzyme sensors has been attracting considerable interest due to their outstanding features, including potent stability, and cost-effectiveness toward natural enzymes. In this work, mesoporous silica nanoparticles functionalized by copper (Cu-MSN) were prepared as a new artificial enzyme for the first time through the sol-gel procedure. A comprehensive investigation of the catalytic activity of Cu-MSN was done through the oxidation of chromogenic peroxidase substrates, 3,3',5,5'-tetramethylbenzidine (TMB), and (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), in the presence of H₂O₂. The results indicate that the peroxidase-like activity of the as-prepared sample is significantly higher than other nanoparticles. Additionally, for the study, a facile and rapid sensing method based on the enzyme-like activity of Cu-MSN to detect H₂O₂ and glutathione (GSH) was developed to examine the potency of the proposed biosensor. Preliminary analysis revealed that the limit of detection (LOD) of H₂O₂ and GSH is 0.2 and 0.0126 μM, in the range of 0.9-100 and 0.042-1 μM, respectively. These findings support the claims for the efficiency of the sensor in detection fields. Also, human serum was utilized as the real sample to obtain additional evidence.

Engineering MOFs derived metal oxide nanohybrids: Towards electrochemical sensing of catechol in tea samples

In this work, we have successfully developed Cu-MOF/CuO/NiO nanocomposites (NCs) and employed as a novel electrochemical sensing platform in catechol (CC) detection. The Scanning electron microscopy (SEM) along Energy dispersive X-ray Analysis (EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) are carried out to characterize the as-fabricated Cu-MOF/CuO/NiO NCs. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques have used to obtain oxidation peak currents of CC. Glassy carbon electrode (GCE) modified with Cu-MOF/CuO/NiO has exposed the superb EC properties representing low limit of detection (LOD) of 0.0078 µM (S/N = 3). To assess the practicability of Cu-MOF/CuO/NiO based sensing medium, it has been used to detect CC from two varieties of tea, namely black and green. Thus, we anticipate that this structural integration strategy possesses encouraging application potential in sensing podium and material synthesis.

Covalent Organic Frameworks-TpPa-1 as an Emerging Platform for Electrochemical Sensing

Covalent organic frameworks (COFs) are a new type of metal-free porous architecture with a well-designed pore structure and high stability. Here an efficient electrochemical sensing platform was demonstrated based on COFs TpPa-1 constructed by 1,3,5-triformylphloroglucinol (Tp) with p-phenylenediamine (Pa-1), which possesses abundant nitrogen and oxo-functionalities. COFs TpPa-1 exhibited good water dispersibility and strong adsorption affinities for Pd²⁺ and thus was used as loading support to modify Pd²⁺. The Pd²⁺-modified COFs TpPa-1 electrode (Pd²⁺/COFs) showed high electrocatalytic activity for both hydrazine oxidation reaction and nitrophenol reduction reaction. In addition, TpPa-1-derived nitrogen-doped carbon presented high activity for the electro-oxidation of reduced glutathione (GSH), and sensitive electrochemical detection of GSH was achieved. The presented COFs TpPa-1 can be utilized as a precursor as well as support for anchoring electro-active molecules and nanoparticles, which will be useful for electrochemical sensing and electrocatalysis.

Advanced Metal-Organic Frameworks-Based Catalysts in Electrochemical Sensors

Developing efficient catalysts is vital for the application of electrochemical sensors. Metal-organic frameworks (MOFs), with high porosity, large specific surface area, good conductivity, and biocompatibility, have been widely used in catalysis, adsorption, separation, and energy storage applications. In this invited review, the recent advances of a novel MOF-based catalysts in electrochemical sensors are summarized. Based on the structure-activity-performance relationship of MOF-based catalysts, their mechanism as electrochemical sensor, including metal cations, synthetic ligands, and structure, are introduced. Then, the MOF-based composites are successively divided into metal-based, carbon-based, and other MOF-based composites. Furthermore, their application in environmental monitoring, food safety control, and clinical diagnosis is discussed. The perspective and challenges for advanced MOF-based composites are proposed at the end of this contribution.

A photoelectrochemical sensor for glutathione based on Bi2S3-modified TiO2 nanotube arrays

A novel photoelectrochemical sensor for the determination of glutathione based on Bi2S3-modified TiO2 nanotube arrays. Under the excitation of visible light, glutathione can be oxidized by the holes created by the Bi2S3/TiO2 NTAs.

Gold nanoparticle decorated rGO-encapsulated metal-organic framework composite sensor for the detection of dopamine

In this study, by encapsulation of reduced graphene oxide (rGO) into Ni-based metal–organic framework (Ni-MOF) structure, the composite rGO@Ni-MOF was first prepared. Then, gold nanoparticle (AuNP) decorated rGO@Ni-MOF (rGO@Ni-MOF/AuNP) were obtained through the electrodeposition. The morphology and structure of rGO@Ni-MOF/AuNP were characterized by SEM, FTIR, and XRD. The rGO@Ni-MOF/AuNP modified electrode was used for the detection of dopamine. Combining the catalysis from Ni-MOF and AuNP with the conductivity of rGO endowed rGO@Ni-MOF/AuNP with synergetic high catalytic activity to the electrochemical oxidation of dopamine. The developed modified electrode had a good linear relationship with dopamine in the concentration range of 0.5∼120 μM, and the detection limit was 0.33 μM (S/N = 3). Additionally, the potential interferents, electrode stability, reproducibility, and practical applications were also studied and satisfactory results were obtained.

2D metal azolate framework as nanozyme for amperometric detection of glucose at physiological pH and alkaline medium

The synthesis of Co-based two-dimensional (2D) metal azolate framework nanosheets (MAF-5-Co^II NS) is described using a simple hydrothermal method. The product was isostructural to MAF-5 (Zn). The as-prepared MAF-5-Co^II NS exhibited high surface area (1155 m²/g), purity, and crystallinity. The MAF-5-Co^II NS-modified screen-printed electrode (MAF-5-Co^II NS/SPE) was used for nonenzymatic detection of glucose in diluted human blood plasma (BP) samples with phosphate buffer saline (PBS, pH 7.4) and NaOH (0.1 M, pH 13.0) solutions. The MAF-5-Co^II NS nanozyme displayed good redox activity in both neutral and alkaline media with the formation of Co^II/Co^III redox pair, which induced the catalytic oxidation of glucose. Under the optimized detection potential, the sensor presented a chronoamperometric current response for the oxidation of glucose with two wide concentration ranges in PBS-diluted (62.80 to 180 μM and 305 to 8055 μM) and NaOH-diluted (58.90 to 117.6 μM and 180 to 10,055 μM) BP samples, which were within the limit of blood glucose levels of diabetic patients before (4.4-7.2 mM) and after (10 mM) meals (recommended by the American Diabetes Association). The sensor has a limit of detection of ca. 0.25 and 0.05 μM, respectively, and maximum sensitivity of ca. 36.55 and 1361.65 mA/cm²/mM, respectively, in PBS- and NaOH-diluted BP samples. The sensor also displayed excellent stability in the neutral and alkaline media due to the existence of hydrophobic linkers (2-ethyl imidazole) in the MAF-5-Co^II NS, good repeatability and reproducibility, and interference-free signals. Thus, MAF-5-Co^II NS is a promising nanozyme for the development of the disposable type of sensor for glucose detection in human body fluids. Graphical abstract.

Indirect differential pulse voltammetric analysis of cyanide at porous copper based metal organic framework modified carbon paste electrode: Application to different water samples

Carbon paste electrode (CPE) modified with porous copper based metal organic framework (Cu-MOF) nanocomposite is described for analysis of cyanide (CN^-) for the first time. The electrochemical performance of the proposed electrode was investigated by differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The Cu-MOF nanocomposite was characterized using scanning electron microscope (SEM), N₂-adsorption-desorption isotherms, powder X-ray powder diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Under optimal conditions of measurements, the anodic peak (Ipa) decreases linearly in the range of 1.87-25 μM with LOD of 0.60 μM (at S/N = 3). The Cu-MOF/CPE showed good selectivity towards CN^- measurement with no significant interference in pH 7.0 using 0.25 M KCl to increase the medium conductivity and to stabilize the analyte and prevents its volatility. Moreover, the method was successfully applied for determination of CN^- in different environmental water samples.

Luminescent Thermochromic Silver Iodides as Wavelength-Dependent Thermometers

Luminescent thermochromic materials with a dramatic shift of emission band under different temperatures are highly desirable in temperature sensing fields. However, the design of the synthesis of such compounds remains a great challenge. In this work, two new luminescent thermochromic silver iodides, (emIm)Ag₃I₄ (1) and (emIm)Ag₂I₃ (2) (emIm = 1-ethyl-3-methyl imidazole), have been synthesized under solvothermal conditions. Compound 1 features a [Ag₃I₄]^- anionic layer, while compound 2 possesses an infinite [Ag₂I₃]^- chain structure, both of which are charge balanced by emIm⁺ cations. Particularly, they display luminescent thermochromism with a significant wavelength shift of emission maximum with temperature change. They represent rare examples of infinite layered or chain silver iodides that show luminescent thermochromism. Furthermore, the results indicate that compounds 1 and 2 are promising wavelength-dependent luminescent thermometers.

Fabrication of an electrochemical sensor based on metal-organic framework ZIF-8 for quantitation of silver ions: optimizing experimental conditions using central composite design (CCD)

ZIF-8 was synthesized and carbon paste electrodes (CPEs) modified with this metal-organic framework were utilized for quantitation of silver(i) by the differential pulse anodic stripping voltammetry (DPASV) technique.Prepared ZIF-8 and the matrix of the electrodes were distinguished by impedance spectroscopy (EIS), XRD, FT-IR spectroscopy, cyclic voltammetry (CV), TEM and SEM/EDX methods. To obtain the strongest stripping peak currents, several significant variables were optimized with response surface methodology (RSM), including the ligand amount (near 11% w/w), applied potential for preconcentration (approximately -1.36 V), pH of the preconcentration solution (about 8.5) and preconcentration time (about 275 s). A calibration curve was acquired in the limits from 1.0 × 10-10 to 5.0 × 10-7 M with the Pearson correlation coefficient R = 0.9993. The limiting detectable concentration (LDC) was determined to be 1.0 × 10-11 M. The developed sensor has high selectivity for mercury(ii). The excellent pH, potential and especially size-exclusion based selectivity of the prepared sensor are unique characteristics that are very important in the determination of silver ions. The developed method was effectively employed for the quantitation of silver(i) ions in environmental and industrial samples.

Overview and recent advances in electrochemical sensing of glutathione - A review

The present paper is aimed at providing an overview of the recent advances in the electrochemical sensing of glutathione (GSH), an important electrochemically and biologically active molecule, for the period 2012-2018. Herein, the analytical performances of newly developed electrochemical methods, procedures and protocols for GSH sensing are comprehensively and critically discussed with respect to the type of method, electrodes used (new electrode modifications, advanced materials and formats), sample matrices, and basic validation parameters obtained (limit of detection, linear dynamic range, precision, selectivity/evaluation of interferences). This paper considers electrochemical methods used alone as well as the hyphenated methods with electrochemical detection (ECD), such as HPLC-ECD or CE-ECD. The practical applicability of the platforms developed for GSH detection and quantification is mostly focused on pharmaceutical and biomedical analysis. The most significant electrochemical approaches for GSH detection in multicomponent analyte samples and multicomponent matrices and for real-time in vivo GSH analysis are highlighted. The great variability in the electrochemical techniques, electrode approaches, and obtainable performance parameters, discussed in this review, brought new insights not only on current GSH and glutathione disulfide (GSSG) determinations, but, along with this, on the advances in electrochemical analysis from a more general point of view.

Electrochemical determination of 2,4,6-trinitrophenol using a hybrid film composed of a copper-based metal organic framework and electroreduced graphene oxide

A metal organic framework (MOF) of the type copper(II)-1,3,5-benzenetricarboxylic acid (Cu-BTC) was electrodeposited on electroreduced graphene oxide (ERGO) placed on a glassy carbon electrode (GCE). The modified GCE was used for highly sensitive electrochemical determination of 2,4,6-trinitrophenol (TNP). The fabrication process of the modified electrode was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. Differential pulse voltammetry (DPV) demonstrates that the Cu-BTC/ERGO/GCE gives stronger signals for TNP reduction than Cu-BTC/GCE or ERGO/GCE alone. DPV also shows TNP to exhibit three reduction peaks, the first at a potential of -0.42 V (vs. SCE). This potential was selected because the other three similarly-structured compounds (2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol) do not give a signal at this potential. Response is linear in the 0.2 to 10 μM TNP concentration range, with a 0.1 μM detection limit (at S/N = 3) and a 15.98 μA∙μM^-1∙cm^-2 sensitivity under optimal conditions. The applicability of the sensor was evaluated by detecting TNP in spiked tap water and lake water samples. Recoveries ranged between 95 and 101%. Graphical abstract Schematic presentation of an electrochemical sensor that was fabricated by electrodeposition of the metal-organic framework (MOF) of copper(II)-1,3,5-benzenetricarboxylic acid (Cu-BTC) onto the surface of electroreduced graphene oxide (ERGO) modified glassy carbon electrode (GCE). It was applied to sensitive and selective detection of 2,4,6-trinitrophenol (TNP).

Sonochemical synthesis of silver nanoparticles anchored reduced graphene oxide nanosheets for selective and sensitive detection of glutathione

Developed here an eco-friendly, one-pot approach toward rapid synthesis of silver nanoparticles anchored reduced graphene oxide (AgNPs_(TMSPED)-rGO) nanosheets via sonochemical irradiation method, using an aqueous solution mixture of GO and AgNO₃ in the presence of N-[3(trimethoxysilyl)propyl] ethylenediamine (TMSPED) without any reducing agent. As synthesized decorated nanosheets was thoroughly characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Pristine AgNPs_(TMSPED), pristine rGO_(TMSPED) and as prepared AgNPs_(TMSPED)-rGO materials were employed to modify the glassy carbon (GC) electrode and demonstrated its excellent electrocatalytic activities towards glutathione (GSH). Voltammetry and amperometry measurements were utilized to assess the electrochemical properties towards the glutathione detection. When the Ag nanoparticles were anchored onto the rGO surface, the observed results illustrated that the electrocatalytic properties of rGO might be enhanced. The resulting sensor exhibits excellent repeatability and long-term stability. Furthermore, AgNPs_(TMSPED)-rGO/GC electrode able to be employed for the selective determination of GSH in amperometric analysis in the presence of ascorbic acid (AA), dopamine (DA), uric acid (UA) and glucose. Finally, this modified electrode was effectively applied to determine glutathione in real samples with good recoveries.

Glassy carbon electrode modified with 7,7,8,8-tetracyanoquinodimethane and graphene oxide triggered a synergistic effect: Low-potential amperometric detection of reduced glutathione

A sensitive electrochemical sensor based on the synergistic effect of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and graphene oxide (GO) for low-potential amperometric detection of reduced glutathione (GSH) in pH 7.2 phosphate buffer solution (PBS) has been reported. This is the first time that the combination of GO and TCNQ have been successfully employed to construct an electrochemical sensor for the detection of glutathione. The surface of the glassy carbon electrode (GCE) was modified by a drop casting using TCNQ and GO. Cyclic voltammetric measurements showed that TCNQ and GO triggered a synergistic effect and exhibited an unexpected electrocatalytic activity towards GSH oxidation, compared to GCE modified with only GO, TCNQ or TCNQ/electrochemically reduced GO. Three oxidation waves for GSH were found at -0.05, 0.1 and 0.5V, respectively. Amperometric techniques were employed to detect GSH sensitively using a GCE modified with TCNQ/GO at -0.05V. The electrochemical sensor showed a wide linear range from 0.25 to 124.3μM and 124.3μM to 1.67mM with a limit of detection of 0.15μM. The electroanalytical sensor was successfully applied towards the detection of GSH in an eye drop solution.

Fabrication of Palladium Nanoparticles on Porous Aromatic Frameworks as a Sensing Platform to Detect Vanillin

Here, we report the fabrication of palladium nanoparticles on porous aromatic frameworks (Pd/PAF-6) using a facile chemical approach, which was characterized by various spectro- and electrochemical techniques. The differential pulse voltammetry (DPV) response of Pd/PAF-6 toward the vanillin (VA) sensor shows a linear relationship over concentrations (10-820 pM) and a low detection limit (2 pM). Pd/PAF-6 also exhibited good anti-interference performance toward 2-fold excess of ascorbic acid, nitrophenol, glutathione, glucose, uric acid, dopamine, ascorbic acid, 4-nitrophenol, glutathione, glucose, uric acid, dopamine, and 100-fold excess of Na(+), Mg(2+), and K(+) during the detection of VA. The developed electrochemical sensor based on Pd/PAF-6 had good reproducibility, as well as high selectivity and stability. The established sensor revealed that Pd/PAF-6 could be used to detect VA in biscuit and ice cream samples with satisfactory results.

Reduced graphene oxide uniformly decorated with Co nanoparticles: facile synthesis, magnetic and catalytic properties

A facile and eco-friendly strategy was developed to deposit highly dispersed tiny Co nanoparticles on RGO sheets, which exhibit excellent magnetic and catalytic properties.

AuNp@MOF composite as electrochemical material for determination of bisphenol A and its oxidation behavior study

A hybrid material on the carbon paste electrode exhibited a greater electroactivity for the determination of an endocrine disruptor.