Enhancing sensitivity towards electrochemical miRNA detection using an affordable paper-based strategy.

In the era of liquid biopsy, microRNAs emerge as promising candidates for the early diagnosis and prognosis of cancer, offering valuable insights into the disease's development. Among all the existing analytical approaches, even if traditional approaches such as the nucleic acid amplification ones have the advantages to be highly sensitive, they cannot be used at the point-of-care, while sensors might be poorly sensitive despite their portability. In order to improve the analytical performance of existing electroanalytical systems, we demonstrate how a simple chromatographic paper-based disk might be useful to rationally improve the sensitivity, depending on the number of preconcentration cycles. A paper-based electrochemical platform for miRNA detection has been developed by modifying a paper-based electrode with a methylene blue (MB)-modified single-stranded sequence (ssDNA) complementary to the chosen miRNA, namely miR-224 that is associated with lung cancer. A detection limit of ca. 0.6 nM has been obtained in spiked human serum samples. To further enhance the sensitivity, an external chromatographic wax-patterned paper-based disk has been adopted to preconcentrate the sample, and this has been demonstrated both in standard and in serum solutions. For each solution, three miR-224 levels have been preconcentrated, obtaining a satisfactory lowering detection limit of ca. 50 pM using a simple and sustainable procedure. This approach opens wide possibilities in the field of analytical and bioanalytical chemistry, being useful not only for electrochemistry but also for other architectures of detection and transduction.

Electroanalysis in Pharmacogenomic Studies: Mechanisms of Drug Interaction with DNA.

The review discusses electrochemical methods for analysis of drug interactions with DNA. The electroanalysis method is based on the registration of interaction-induced changes in the electrochemical oxidation potential of heterocyclic nitrogenous bases in the DNA molecule and in the maximum oxidation current amplitude. The mechanisms of DNA-drug interactions can be identified based on the shift in the electrooxidation potential of heterocyclic nitrogenous bases toward more negative (cathodic) or positive (anodic) values. Drug intercalation into DNA shifts the electrochemical oxidation potential to positive values, indicating thermodynamically unfavorable process that hinders oxidation of nitrogenous bases in DNA. The potential shift toward the negative values indicates electrostatic interactions, e.g., drug binding in the DNA minor groove, since this process does not interfere with the electrochemical oxidation of bases. The concentration-dependent decrease in the intensity of electrochemical oxidation of DNA bases allows to quantify the type of interaction and calculate the binding constants.

Recent trends in core/shell nanoparticles: their enzyme-based electrochemical biosensor applications.

Improving novel and efficient biosensors for determining organic/inorganic compounds is a challenge in analytical chemistry for clinical diagnosis and research in biomedical sciences. Electrochemical enzyme-based biosensors are one of the commercially successful groups of biosensors that make them highly appealing because of their low cost, high selectivity, and sensitivity. Core/shell nanoparticles have emerged as versatile platforms for developing enzyme-based electrochemical biosensors due to their unique physicochemical properties and tunable surface characteristics. This study provides a comprehensive review of recent trends and advancements in the utilization of core/shell nanoparticles for the development of enzyme-based electrochemical biosensors. Moreover, a statistical evaluation of the studies carried out in this field between 2007 and 2023 is made according to the preferred electrochemical techniques. The recent applications of core/shell nanoparticles in enzyme-based electrochemical biosensors were summarized to quantify environmental pollutants, food contaminants, and clinical biomarkers. Additionally, the review highlights recent innovations and strategies to improve the performance of enzyme-based electrochemical biosensors using core/shell nanoparticles. These include the integration of nanomaterials with specific functions such as hydrophilic character, chemical and thermal stability, conductivity, biocompatibility, and catalytic activity, as well as the development of new hybrid nanostructures and multifunctional nanocomposites.

Ultrasensitive electrochemical sensor based on synergistic effect of Ag@MXene and antifouling cyclic multifunctional peptide for PD-L1 detection in serum.

A sensing interface co-constructed from the two-dimensional conductive material (Ag@MXene) and an antifouling cyclic multifunctional peptide (CP) is described. While the large surface area of Ag@MXene loads more CP probes, CP binds to Ag@MXene to form a fouling barrier and ensure the structural rigidity of the targeting sequence. This strategy synergistically enhances the biosensor's sensitivity and resistance to contamination. The SPR results showed that the binding affinity of the CP to the target was 6.23 times higher than that of the antifouling straight-chain multifunctional peptide (SP) to the target. In the 10 mg/mL BSA electrochemical fouling test, the fouling resistance of Ag@MXene + CP (composite sensing interface of CP combined with Ag@MXene) was 30 times higher than that of the bare electrode. The designed electrochemical sensor exhibited good selectivity and wide dynamic response range at PD-L1 concentrations from 0.1 to 50 ng/mL. The lowest detection limit was 24.54 pg/mL (S/N = 3). Antifouling 2D materials with a substantial specific surface area, coupled with non-straight chain antifouling multifunctional peptides, offer a wide scope for investigating the sensitivity and antifouling properties of electrochemical sensors.

Optimised graphite/carbon black loading of recycled PLA for the production of low-cost conductive filament and its application to the detection of ß-estradiol in environmental samples.

The production, optimisation, physicochemical, and electroanalytical characterisation of a low-cost electrically conductive additive manufacturing filament made with recycled poly(lactic acid) (rPLA), castor oil, carbon black, and graphite (CB-G/PLA) is reported. Through optimising the carbon black and graphite loading, the best ratio for conductivity, low material cost, and printability was found to be 60% carbon black to 40% graphite. The maximum composition within the rPLA with 10 wt% castor oil was found to be an overall nanocarbon loading of 35 wt% which produced a price of less than £0.01 per electrode whilst still offering excellent low-temperature flexibility and reproducible printing. The additive manufactured electrodes produced from this filament offered excellent electrochemical performance, with a heterogeneous electron (charge) transfer rate constant, k0 calculated to be (2.6 ± 0.1) × 10-3 cm s-1 compared to (0.46 ± 0.03) × 10-3 cm s-1 for the commercial PLA benchmark. The additive manufactured electrodes were applied to the determination of ß-estradiol, achieving a sensitivity of 400 nA µM-1, a limit of quantification of 70 nM, and a limit of detection of 21 nM, which compared excellently to other reports in the literature. The system was then applied to the detection of ß-estradiol within four real water samples, including tap, bottled, river, and lake water, where recoveries between 95 and 109% were obtained. Due to the ability to create high-performance filament at a low material cost (£0.06 per gram) and through the use of more sustainable materials such as recycled polymers, bio-based plasticisers, and naturally occurring graphite, additive manufacturing will have a permanent place within the electroanalysis arsenal in the future.

Design of a printed electrochemical strip towards miRNA-21 detection in urine samples: optimization of the experimental procedures for real sample application.

MicroRNAs (miRNAs) are clinical biomarkers for various human diseases, including cancer. They have been found in liquid biopsy samples, including various bodily fluids. They often play an important role in the early diagnosis and prognosis of cancer, and the development of simple and effective analytical methods would be of pivotal importance for the entire community. The determination of these targets may be affected by the different physicochemical parameters of the specimen of interest. In this work, an electrochemical detection platform for miRNA based on a screen-printed gold electrode was developed. In the present study, miRNA-21 was selected as a model sequence, due to its role in prostate, breast, colon, pancreatic, and liver cancers. A DNA sequence modified with methylene blue (MB) was covalently bound to the electrochemical strip and used to detect the selected target miRNA-21. After optimization of selected parameters in standard solutions, including the study of the effect of pH, the presence of interferent species, and NaCl salt concentration in the background, the application of square-wave voltammetry (SWV) technique allowed the detection of miRNA-21 down to a limit in the order of 2 nM. The developed device was then applied to several urine samples. In this case too, the device showed high selectivity in the presence of the complex matrix, satisfactory repeatability, and a limit of detection in the order of magnitude of nM, similarly as what observed in standard solutions.

Electrochemical ELASA: improving early cancer detection and monitoring.

The discovery of new molecular biomarkers of cancer during the last decades and the development of new diagnostic devices exploiting those have significantly contributed to the clinical analysis of cancer and to improve the outcomes. Among those, liquid biopsy sensors exploiting aptamers for the detection of cancer biomarkers in body fluids are useful and accurate tools for a fast and inexpensive non-invasive screening of population. The incorporation of aptamers in electrochemical sandwich biosensors using enzyme labels, a so-called ELASA, has demonstrated its utility to improve the detection schemes. In this review, we overview the existing ELASA assays for numerous cancer biomarkers as alternatives to the traditional ELISA and discuss their possibilities to reach the market, currently dominated by optical immunoassays.

Rational design of Nd2O3 decorated functionalized carbon nanofiber composite for selective electrochemical detection of carbendazim fungicides in vegetables, water, and soil samples.

Abuse of carbendazim (CBZ) leaves excessive pesticide residues on agricultural products, which endangers human health because of the residues' high concentrations. Hence, a composite consisting of functionalized carbon nanofibers (f-CNF) with neodymium oxide (Nd2O3) was fabricated to monitor CBZ at trace levels. The Nd2O3/f-CNF composite-modified electrode displays higher electro-oxidation ability towards CBZ than Nd2O3 and f-CNF-modified electrodes. The combined unique properties of Nd2O3 and f-CNF result in a substantial specific surface area, superior structural stability, and excellent electrocatalytic activity of the composite yielding enhanced sensitivity to detecting CBZ with a detection limit of 4.3 nM. Also, the fabricated sensor electrode can detect CBZ in the linear concentration range of up to 243.0 µM with high selectivity, appropriate reproducibility, and stability. A demonstration of the sensing capability of CBZ in vegetables, water, and soil samples was reported paving the way for its use in practical applications.

Comparative MIP sensor technique: photopolymerization or thermal polymerization for the sensitive determination of anticancer drug Regorafenib in different matrixes.

Regorafenib (REG) is a diphenylurea derivative oral multikinase inhibitor. It plays an important role in the treatment of colorectal cancer, metastatic gastrointestinal stromal tumors, and hepatocellular carcinoma. Molecularly imprinted polymer (MIP) based glassy carbon electrodes (GCE) were fabricated using photopolymerization (PP) and thermal polymerization (TP) methods. The characterizations of the proposed sensors were investigated by electrochemical techniques, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Several parameters were studied in detail for the optimum conditions of MIP-based sensors, such as dropping volume, photopolymerization and thermal polymerization durations, removal medium and time, and rebinding time. Both sensors' analytical validation and electroanalytical performance comparison were made in different REG concentrations ranging between 0.1 nM and 2.5 nM in standard solution and commercial human serum samples. The limit of detection (LOD) of PP-REG@MIP/GCE and TP-REG@MIP/GCE were 9.13 × 10-12 M and 1.44 × 10-11 M in standard solutions and 2.04 × 10-11 M and 2.02 × 10-11 M in serum samples, respectively. The applicability of the proposed sensors was tested using commercial human serum samples and pharmaceutical form of REG with high recovery values (PP-REG@MIP/GCE and TP REG@MIP/GCE sensors, 99.56-101.59%, respectively). The selectivity of the sensor for REG was investigated in the presence of similar molecules: Sorafenib, Sunitinib, Nilotinib, and Imatinib. The developed techniques and sensors checked the possible biological compounds and ions' effects and storage stability.

Electrochemically reduced graphene oxide films from Zn-C battery waste for the electrochemical determination of paracetamol and hydroquinone.

Contributing to the development of sustainable electroanalytical chemistry, electrochemically reduced graphene oxide (ERGO) films obtained from residual graphite of discharged Zn-C batteries are proposed in this work. Graphite from the cathode of discarded Zn-C batteries was recovered and used in the synthesis of graphene oxide (GO) by the modified Hummer's method. The quality of the synthesized GO was verified using different characterization methods (FT-IR, XRD, SEM, and TEM). GO films were deposited on a glassy carbon electrode (GCE) by the drop coating method and then electrochemically reduced by cathodic potential scanning using cyclic voltammetry. The electrochemical features of the ERGO films were investigated using the ferricyanide redox probe, as well as paracetamol (PAR) and hydroquinone (HQ) molecules as model analytes. From the cyclic voltammetry assays, enhanced heterogeneous electron transfer rate constants (k0) were observed for all redox systems studied. In analytical terms, the ERGO-based electrode showed higher analytical sensitivity than the bare and GO-modified GCE. Using differential pulse voltammetry, wide linear response ranges and limits of detection of 0.14 µmol L-1 and 0.65 µmol L-1 were achieved for PAR and HQ, respectively. Furthermore, the proposed sensor was successfully applied to the determination of PAR and HQ in synthetic urine and tap water samples (recoveries close to 100%). The outstanding electrochemical and analytical properties of the proposed ERGO films are added to the very low cost of the raw material, being presented as a green-based alternative for the development of electrochemical (bio)sensors with unsophisticated resources.

Gold nanoparticles-decorated peptide hydrogel for antifouling electrochemical dopamine determination.

A reliable and brief ultralow fouling electrochemical sensing system capable of monitoring targets in complex biological media was constructed and validated based on gold nanoparticles-peptide hydrogel-modified screen-printed electrode. The self-assembled zwitterionic peptide hydrogel was prepared by a newly designed peptide sequence of Phe-Phe-Cys-Cys-(Glu-Lys)3 with the N-terminal modified with a fluorene methoxycarbonyl group. The thiol groups on cysteine of the designed peptide are able to self-assemble with AuNPs to form a three-dimensional nanonetwork structure, which showed satisfactory antifouling capability in complex biological media (human serum). The developed gold nanoparticles-peptide hydrogel-based electrochemical sensing platform displayed notably sensing properties for dopamine determination, with a wide linear range (from 0.2 nM to 1.9 µM), a low limit of detection (0.12 nM), and an excellent selectivity. This highly sensitive and ultralow fouling electrochemical sensor was fabricated via simple preparation with concise components that avoid the accumulation of layers with single functional material and complex activation processes. This ultralow fouling and highly sensitive strategy based on the gold nanoparticles-peptide hydrogel with a three-dimensional nanonetwork offers a solution to the current situation of various low-fouling sensing systems facing impaired sensitivity and provides a potential path for the practical application of electrochemical sensors.

Electrochemical sensor using cobalt oxide-modified porous carbon for uric acid determination.

An electrochemical sensor for the detection of uric acid was constructed using cobalt oxide-modified porous carbon@multi-walled carbon nanotube (MWCNTs) composite material for the modification of the electrode. Firstly, ZIF-67 is generated on carbon nanotubes using the surfactant cetylammonium bromide (CTAB) as template. The vesicles generated by CTAB act as nucleation sites for the in situ growth of ZIF-67. Then, cobalt oxide-modified porous carbon was obtained after high-temperature carbonization of ZIF-67, leading to the formation of cobalt oxide-modified porous carbon@MWCNT composite materials. Co-N and Co-O active sites on the composite material can improve the oxidation of uric acid on the electrode surface, leading to enhanced sensitivity and selectivity for uric acid detection. The sensor has a good linear range from 1 to 40 µM for uric acid detection with a detection limit of 0.09 µM. The sensor was utilized for determination of uric acid in actual serum samples.

Boron-doped diamond nanosheet volume-enriched screen-printed carbon electrodes: a platform for electroanalytical and impedimetric biosensor applications.

This paper focuses on the development of a novel electrode based on boron-doped diamond nanosheet full-volume-enriched screen-printed carbon electrodes (BDDPE) for use as an impedimetric biosensor. Impedimetric biosensors offer high sensitivity and selectivity for virus detection, but their use as point-of-care devices is limited by the complexity of nanomaterials' architecture and the receptor immobilisation procedures. The study presents a two-step modification process involving the electroreduction of diazonium salt at the BDDPE and the immobilisation of antibodies using zero-length cross-linkers for a selective impedimetric biosensor of Haemophilus influenzae (Hi). The incorporation of diamond nanosheets into BDDPE leads to enhanced charge transfer and electrochemical behaviour, demonstrating greatly improved electrochemically active surface area compared with unmodified screen-printed electrodes (by 44% and 10% on average for [Ru(NH3)6]Cl2 and K3[Fe(CN)6], respectively). The presented sensing system shows high specificity towards protein D in Hi bacteria, as confirmed by negative controls against potential interference from other pathogens, with an estimated tolerance limit for interference under 12%. The Hi limit of detection by electrochemical impedance spectroscopy was 1 CFU/mL (measured at - 0.13 V vs BDDPE pseudo-reference), which was achieved in under 10 min, including 5 min sample incubation in the presence of the analyte.

Extraction-assisted voltammetric determination of homocysteine using magnetic nanoparticles modified with molecularly imprinted polymer.

A magnetic graphite-epoxy composite (m-GEC) electrochemical sensor is presented based on magnetic imprinted polymer (mag-MIP) to determine homocysteine (Hcy). Mag-MIP was synthesized via precipitation polymerization, using functionalized magnetic nanoparticles (Fe3O4) together with the template molecule (Hcy), the functional monomer 2-hydroxyethyl methacrylate (HEMA), and the structural monomer trimethylolpropane trimethacrylate (TRIM). For mag-NIP (magnetic non-imprinted polymer), the procedure was the same in the absence of Hcy. Morphological and structural properties of the resultant mag-MIP and mag-NIP were examined using TEM, FT-IR, and Vibrating Sample Magnetometer. Under optimized conditions, the m-GEC/mag-MIP sensor showed a linear range of 0.1-2 µmol L-1, with a limit of detection (LOD) of 0.030 µmol L-1. In addition, the proposed sensor responded selectively to Hcy compared to several interferents present in biological samples. The recovery values determined by differential pulse voltammetry (DPV) were close to 100% for natural and synthetic samples, indicating good method accuracy. The developed electrochemical sensor proves to be a suitable device for determining Hcy, with advantages related to magnetic separation and electrochemical analysis.

Carbon Fiber Paper Sensor for Determination of Trimethoprim Antibiotic in Fish Samples.

The increase in anthropogenic pollution raises serious concerns regarding contamination of water bodies and aquatic species with potential implications on human health. Pharmaceutical compounds are a type of contaminants of emerging concern that are increasingly consumed and, thus, being frequently found in the aquatic environment. In this sense, an electrochemical sensor based on an unmodified and untreated carbon fiber paper (CPS-carbon paper sensor) was simply employed for the analysis of trimethoprim antibiotic in fish samples. First, the analytical conditions were thoroughly optimized in order for the CPS to achieve maximum performance in trimethoprim determination. Therefore, an electrolyte (0.1 M Britton-Robinson buffer) pH of 7 was selected and for square wave voltammetry parameters, optimum values of amplitude, frequency and step potential corresponded to 0.02 V, 50 Hz, and 0.015 V, respectively, whereas the deposition of analyte occurred at +0.7 V for 60 s. In these optimum conditions, the obtained liner range (0.05 to 2 µM), sensitivity (48.8 µA µM-1 cm-2), and LOD (0.065 µM) competes favorably with the commonly used GCE-based sensors or BDD electrodes that employ nanostructuration or are more expensive. The CPS was then applied for trimethoprim determination in fish samples after employing a solid phase extraction procedure based on QuEChERS salts, resulting in recoveries of 105.9 ± 1.8% by the standard addition method.

Multiple Pulse Amperometry-An Antifouling Approach for Nitrite Determination Using Carbon Fiber Microelectrodes.

Nitrite is a ubiquitous pollutant in modern society. Developing new strategies for its determination is very important, and electroanalytical methods present outstanding performance on this task. However, the use of bare electrodes is not recommended because of their predisposition to poisoning and passivation. We herein report a procedure to overcome these limitations on carbon fiber microelectrodes through pulsed amperometry. A three-pulse amperometry approach was used to reduce the current decay from 47% (after 20 min under constant potential) to virtually 0%. Repeatability and reproducibility were found to have an RSD lower than 0.5% and 7%, respectively. Tap water and synthetic inorganic saliva samples were fortified with nitrite, and the results obtained with the proposed sensor were in good agreement with the amount added.

Electrochemical Behavior of ß-Cyclodextrin-Ni-MOF-74/Reduced Graphene Oxide Sensors for the Ultrasensitive Detection of Rutin.

Rutin, as a biological flavonoid glycoside, has very important medicinal value. The accurate and rapid detection of rutin is of great significance. Herein, an ultrasensitive electrochemical rutin sensor based on ß-cyclodextrin metal-organic framework/reduced graphene oxide (ß-CD-Ni-MOF-74/rGO) was constructed. The obtained ß-CD-Ni-MOF-74 was characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption and desorption. The ß-CD-Ni-MOF-74/rGO presented good electrochemical properties benefiting from the large specific surface area and good adsorption enrichment effect of ß-CD-Ni-MOF-74 and the good conductivity of rGO. Under optimal conditions for the detection of rutin, the ß-CD-Ni-MOF-74/rGO/GCE showed a wider linear range (0.06-1.0 µM) and lower detection limit (LOD, 0.68 nM, (S/N = 3)). Furthermore, the sensor shows good accuracy and stability for the detection of rutin in actual samples.

Galvanic Redox Potentiometry for Fouling-Free and Stable Serotonin Sensing in a Living Animal Brain.

Serotonin (5-HT) is a major neurotransmitter broadly involved in many aspects of feeling and behavior. Although its electro-activity makes it a promising candidate for electrochemical sensing, the persistent generation of fouling layers on the electrode by its oxidation products presents a hurdle for reliable sensing. Here, we present a fouling-free 5-HT sensor based on galvanic redox potentiometry. The sensor efficiently minimizes electrode fouling as revealed by in situ Raman spectroscopy, ensuring a less than 3 % signal change in a 2 hour continuous experiment, whereas amperometric sensors losing 90 % within 30 min. Most importantly, the sensor is highly amenable for in vivo studies, permitting real-time 5-HT monitoring, and supporting the mechanism associated with serotonin release in brain. Our system offers an effective way for sensing different neurochemicals having significant fouling issues, thus facilitating the molecular-level understanding of brain function.

An electrochemical method for detecting the biomarker 4-HPA by allosteric activation of Acinetobacterbaumannii reductase C1 subunit.

The C1 (reductase) subunit of 4-hydroxy-phenylacetate (4-HPA) 3-hydroxylase (HPAH) from the soil-based bacterium Acinetobacterbaumannii catalyzes NADH oxidation by molecular oxygen, with hydrogen peroxide as a by-product. 4-HPA is a potent allosteric modulator of C1, but also a known urinary biomarker for intestinal bacterial imbalance and for some cancers and brain defects. We thus envisioned that C1 could be used to facilitate 4-HPA detection. The proposed test protocol is simple and in situ and involves addition of NADH to C1 in solution, with or without 4-HPA, and direct acquisition of the H2O2 current with an immersed Prussian Blue-coated screen-printed electrode (PB-SPE) assembly. We confirmed that cathodic H2O2 amperometry at PB-SPEs is a reliable electrochemical assay for intrinsic and allosterically modulated redox enzyme activity. We further validated this approach for quantitative NADH electroanalysis and used it to evaluate the activation of NADH oxidation of C1 by 4-HPA and four other phenols. Using 4-HPA, the most potent effector, allosteric activation of C1 was related to effector concentration by a simple saturation function. The use of C1 for cathodic biosensor analysis of 4-HPA is the basis of the development of a simple and affordable clinical routine for assaying 4-HPA in the urine of patients with a related disease risk. Extension of this principle to work with other allosteric redox enzymes and their effectors is feasible.

Biorecognition of hydrogen peroxide using a novel electrochemical platform designed with Glossoscolex paulistus giant hemoglobin.

The giant extracellular hemoglobin of the annelid Glossoscolex paulistus (HbGp; 3.6 MDa) is a valuable and underexplored supramolecular hemoprotein system for the biorecognition of reactive oxygen species. In this work, an efficient and simple electrochemical platform was designed for analyzing H2O2, using HbGp covalently immobilized on Nafion®-modified glassy carbon electrode, named as HbGp/Nafion/GCE. Voltammetric and spectroscopic studies revealed the importance of prior modification of the electrodic support with the conducting polymer to obtain satisfactory hemoglobin electroactivity, as well as a biocompatible microenvironment for its immobilization. In terms of biological activity, it was observed a greater reactivity of the biomolecule in acidic medium, enabling the detection of the analyte by a quasi-reversible mechanism, whose kinetics was limited by analyte diffusion. In the presence of H2O2, the native structure of hemoglobin (oxy-HbGp (Fe2+)) oxidizes to ferryl-HbGp (Fe4+) and this redox reaction can be monitored on HbGp/Nafion/GCE with a detection limit of 8.5 × 10‒7  mol L-1. In addition to high sensitivity, the electrochemical biosensor also provided reproducible, consistent, and accurate measurements. The electroanalytical method showed an appropriate performance to quantify different levels of H2O2 in milk samples, proving the potential of HbGp/Nafion/GCE for this purpose.