Electrochemical H2O2 Sensor Research Articles

In situ growth of FeOOH nanoparticles on physically-exfoliated graphene nanosheets as high performance H2O2 electrochemical sensor

Compared with extensively-used chemically-exfoliated graphene, physically-exfoliated graphene-based heterogeneous structures are rarely used for electrochemical analysis. In this work, physically-exfoliated graphene nanosheets (GN) are used as the substrate material to couple high-activity FeOOH nanoparticles. Multiple characterization technology confirm that a novel hierarchical hybrid composed of physically-exfoliated graphene nanosheets and FeOOH nanoparticles (GN@FeOOH) is easily obtained by a facile solution growth strategy. Plenty of fiber-like FeOOH nanoparticles with size about 20 nm are uniformly anchored on the surface of graphene with robust adhesion. Relative to pristine GN, the electrochemical active area and electron transfer kinetics are greatly boosted for the introduction of high-activity of FeOOH nanoparticles. Benefiting from the remarkably enhanced electrochemical activity, the obtained GN@FeOOH hybrids exhibit excellent electrochemical performance toward the reduction of H2O2. As a result, a novel and rapid electrochemical sensing platform for the detection of H2O2 at low applied potential (-0.25 V vs. SCE) is fabricated with wide linear range (0.25 μM - 1.2 mM) and high sensitivity (265.7 μA mM−1 cm-2), and the limit of detection is as low as 0.08 μM, which is comparable with many other noble metal-based electrochemical sensors and exceeds many non-noble metal-based electrochemical sensors.

Prussian Blue modified boron-doped diamond interfaces for advanced H2O2 electrochemical sensors

We report on the boron-doped diamond (BDD) electrodes modified with Prussian Blue (PB) through electrochemical synthesis, open-circuit deposition, and immobilization of Prussian Blue based nanozymes. The later allowed attaining the utmost sensitivity of the H2O2 sensor (≈0.14 A M−1 cm−2). Compared to conventional graphite electrodes modified with Prussian Blue, the use of BDD provided twenty times decreased oxygen reduction currents resulting in up to ten times increased signal-to-background ratio of the corresponding modified electrodes. The successful combination of exceptional diamond properties (including wide potential window for BDD electrodes) with advantageous performance characteristics of Prussian Blue sensing layers would open new horizons for H2O2 detection as well as biosensors elaboration.

Silver nanoparticles-embedded poly(1-naphthylamine) nanospheres for low-cost non-enzymatic electrochemical H2O2 sensor

In this work, a novel nanocomposite containing silver nanoparticles (AgNPs) embedded poly(1-naphthylamine) nanospheres (Ag/PNA) was prepared by in situ chemical reduction of silver nitrate. The structure, composition, and morphology of the prepared Ag/PNA nanocomposites were established by Fourier transform infrared spectrometry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the PNA and Ag/PNA-modified carbon paste electrodes were analyzed using cyclic voltammetry (cyclic voltammogram) and electrochemical impedance spectroscopy. It is observed that the electrochemical and charge transfer characteristics of PNA have significantly enhanced upon the incorporation of AgNPs. The prepared Ag/PNA nanocomposite has shown impressive electrocatalytic and electrochemical sensing performance toward H2O2. Remarkably, the present Ag/PNA-based enzymeless voltammetric H2O2 sensor showed a wide detection range in the concentration range of 1–3000 μM with a lower detection limit of 0.972 μM. The study revealed that Ag/PNA-modified carbon paste electrodes are an ideal platform for the fabrication of low-cost non-enzymatic H2O2 sensor with high sensitivity, good reproducibility, better selectivity, and stability.

H2O2-sensing abilities of mixed-metal (Fe-Ni) Prussian blue analogs in a wide pH range

Hydrogen peroxide (H2O2) is generated as a byproduct via enzymatic decomposition reactions of biological molecules; therefore, H2O2-sensing devices that function in wide pH ranges have been developed. Prussian blue (PB) is one of the most promising materials for constructing electrochemical H2O2-sensing devices; however, PB undergoes hydrolytic decomposition via the N-coordinated Fe(III) of the H2O2-sensing active Fe(II)-CN-Fe(III) moieties even in the weak basic condition of pH 8. In this study, it is anticipated that the homogeneously distributed Ni atoms in the partially Ni-displaced PB analog (Fe-Ni PBA, Fe1−xNix[Fe(CN)6]0.67·nH2O) effectively block serious structural damage from hydrolytic decomposition. Fe-Ni PBA nanoparticles (NPs) have been successfully prepared in all of the metal composition ratios between x = 0 and 1 and are stably dispersible into water by a surface modification method using [Fe(CN)6]4−. The spin-coated thin films composed of the Fe-Ni PBA NPs on ITO substrates function as an electrochemical H2O2 sensor even in the weak basic condition of pH 8, showing a linearity of the catalytic currents within the H2O2 concentrations between 2 × 10−4 and 5 × 10−3 mol/dm3.

A glassy carbon electrode modified with a nanocomposite prepared from Pd/Al layered double hydroxide and carboxymethyl cellulose for voltammetric sensing of hydrogen peroxide.

A Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated using carboxymethyl cellulose as a green substrate via co-precipitation method. The synthesized nanocomposite was characterized using different methods such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy, and electrochemical techniques. A glassy carbon electrode (GCE) was then modified with the suspended composite to obtain an electrochemical sensor for hydrogen peroxide (H2O2). The voltammetric (cathodic) current of the modified GCE was measured at -380mV (vs. Ag/AgCl), at the scan rate of 50mV.s-1. Results show a linear dynamic range of 1 to 120μM, and a 0.3 µMlimit of detection (at S/N= 3). Intraday and interday relative standard deviations are in the ranges of 4.9-5.4% and 6.8-7.3%, respectively. The sensor was applied for the determination of H2O2 in basil extracts, milk, and spiked river water samples. The recoveries are between 96.60 and 102.30%. Graphical abstractA Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated via co-precipitation method and was characterized using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy and electrochemical techniques. CMC@Pd/Al-LDH was used to fabricate H2O2 electrochemical sensor.

Elucidation of ultrasonic wave-assisted electrodeposited AgPd nanoalloy from ionic liquid as an efficient bifunctional electrocatalyst for methanol oxidation and hydrogen peroxide reduction

A combined ultrasonic wave-assisted electrodeposition approach has been elucidated for the preparation of AgPd nanoalloy catalyst films on glassy carbon plate from an ionic liquid medium, and explored as a bifunctional electrocatalyst. The synergetic effects of variable frequency ultrasonic-wave and electrodeposition process and related parameters have been analyzed to understand the enhanced electrocatalytic activity towards small molecules, such as methanol electro-oxidation and hydrogen peroxide (H2O2) electro-reduction in an alkaline medium. The characterization techniques like field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), energy dispersive X-ray fluorescence spectroscopy (ED-XRF) and electrochemical techniques like cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to verify the alloy nature of the as-deposited AgPd nanostructure catalysts. Further, the scope of application to construct the nonenzymatic electrochemical sensor for H2O2 with as-prepared nanoalloy electrocatalysts has been also tested. Moreover, among the as-prepared catalysts, the AgPd-USD-45 catalyst exhibits better catalytic activity for both the reactions, suggesting the potential for further development of high performance non-Pt catalysts based alkaline fuel cells and nonenzymatic electrochemical sensor.

Cobalt Nanoparticles and Atomic Sites in Nitrogen-Doped Carbon Frameworks for Highly Sensitive Sensing of Hydrogen Peroxide.

In situ monitoring of hydrogen peroxide (H2 O2 ) during its production process is needed. Here, an electrochemical H2 O2 sensor with a wide linear current response range (concentration: 5 × 10-8 to 5 × 10-2 m), a low detection limit (32.4 × 10-9 m), and a high sensitivity (568.47 µA mm-1 cm-2 ) is developed. The electrocatalyst of the sensor consists of cobalt nanoparticles and atomic Co-Nx moieties anchored on nitrogen doped carbon nanotube arrays (Co-N/CNT), which is obtained through the pyrolysis of the sandwich-like urea@ZIF-67 complex. More cobalt nanoparticles and atomic Co-Nx as active sites are exposed during pyrolysis, contributing to higher electrocatalytic activity. Moreover, a portable screen-printed electrode sensor is constructed and demonstrated for rapidly detecting (cost ≈40 s) H2 O2 produced in microbial fuel cells with only 50 µL solution. Both the synthesis strategy and sensor design can be applied to other energy and environmental fields.

Highly sensitive H2O2 sensor based on poly(azure A)-platinum nanoparticles deposited on activated screen printed carbon electrodes

The sensitive determination of hydrogen peroxide has broad analytical applications. In this work, a novel non-enzymatic hydrogen peroxide sensor based on Pt nanoparticles (PtNPs) electrochemically deposited on previously modified and activated screen-printed carbon electrodes (aSPCEs) was constructed. The pretreatment consisted of subjecting the electrodes to a surface activation treatment with hydrogen peroxide followed by the electrodeposition of poly(azure A) films (PAA) in a sodium dodecyl sulfate micellar aqueous solution. The PtNPs/PAA/aSPCEs were characterized by scanning electron microscope, X-Ray photoelectron spectrometry, linear scan voltammetry and electrochemical impedance spectroscopy. Linear sweep voltammograms showed that the oxidation peak potential of H2O2 shifts from ˜1 V at SPCEs to ˜0.1 V at PtNPs/PAA/aSPCEs. The fabricated electrodes showed excellent electrocatalytic activity towards H2O2 oxidation, making its detection possible at 0.1 V. The detection limit was 51.6 nM, which is significantly lower than other modified electrodes found in the literature, and the linear range ranging from 0 to 300 μM. The proposed electrode was successfully applied to the determination of H2O2 in real samples in different areas. Additional experiments against common interfering agents (ascorbic acid, dehydroascorbic acid, glucose, salicylic acid, among other compounds) showed no increase in the current signal and only in the case of ascorbic acid a small interference, not greater than 10% is observed, which indicates high specificity of the sensor. These electrodes open up alternative avenues for the development of highly sensitive, robust and low cost electrochemical H2O2 sensors for field tests.

Pd@CeO2-SnO2 nanocomposite, a highly selective and sensitive hydrogen peroxide electrochemical sensor

In this study, Pd@CeO2-SnO2 nanocomposite was synthesized and various methods such as FE-SEM, TEM, EDS, FT-IR, and XRD were used to characterize the nanocomposite. The electrocatalytic behaviour of the nanocomposite was studied for the reduction of H2O2. After optimization of various experimental parameters including pH, scan rate, rotation rate and potential, the calibration curve was plotted for the reduction reaction of the H2O2 at pHs 7.0 and 8.0. At pH 7.0, the linear range and detection limit were obtained as 0.15–1920 μM and 44 nM, respectively. Also, at pH 8.0, the linear range and detection limit were obtained as 0.12–2170 μM and 36 nM, respectively. In addition, the detection sensitivity of the sensor for the determination of H2O2 at pH 7.0 and 8.0 was 472.40 and 533.07 μA.mM−1. cm-2, respectively. Further, the sensor response to the H2O2 was studied in the presence of various types of potential interference species. The results confirmed the high selectivity of the designed sensor for the reduction of H2O2. Finally, the accuracy and applicability of the H2O2 electrochemical sensor in three different milk samples were evaluated with satisfactory results.

Recent advances in electrochemical nonenzymatic hydrogen peroxide sensors based on nanomaterials: a review

The development of efficient electrochemical hydrogen peroxide (H2O2) sensors has received great attention due to the significance of H2O2 in biological systems and its practical applications in various fields. With the new class of H2O2 sensors, the nonenzymatic detection of the target can provide many attractive characteristics, such as simple fabrication, ultrahigh sensitivity, and excellent stability. Considering the rapid expansion of nonenzymatic H2O2 detection using advanced nanomaterials, an overview of the current state of methods for electrochemical nonenzymatic H2O2 sensors is presented (with 399 refs.). The first part of the review covers the sensors based on the use of nanoparticles consisting of metals, metal oxides/sulfides, and bimetallic nanoparticles/alloys. The next major section discusses sensors that make use of carbon nanomaterials, such as carbon nanotubes, graphene, graphene oxide, carbon dots, and of other carbonaceous materials. Advantages and the intrinsic drawbacks of employing various nanomaterials to detect H2O2 are emphasized.

Amperometric hydrogen peroxide sensor using a glassy carbon electrode modified with a nanocomposite prepared from ferumoxytol and reduced graphene oxide decorated with platinum nanoparticles.

A high-performance electrochemical H2O2 sensor was prepared by constructing multiple interfaces using platinum nanoparticles (Pt NPs), ferumoxytol (Fer) and reduced graphene oxide (rGO) on a glassy carbon electrode (GCE). The morphology of Fer/rGO and Fer/rGO-Pt was characterized by field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic voltammetry and chronoamperometry were adopted to characterize the electrochemical properties of the sensor. Because of the synergistic catalytic effect of the compositions (rGO, Fer and Pt NPs) on the multiple interfaces, the sensor exhibits particularly high electrocatalytic activity toward the reduction of H2O2 with a low detection limit (~0.38μM), a linear range (0.0004-0.01, 0.0075-4.3 and 4.9-10.8mM), and a high sensitivity (340μAmM-1cm-2, n= 4) operated at a typical working voltage of +0.1V (vs. Ag/AgCl). The electrode is selective and long-term stable. It was successfully applied to the determination of H2O2 in (spiked) milk samples. Graphical abstract Schematic presentation of an electrochemical H2O2 sensor using platinum nanoparticles (Pt NPs), ferumoxytol (Fer) and reduced graphene oxide (rGO) nanocomposites modified glassy carbon electrode (GCE). The sensor was applied to the determination of H2O2 in (spiked) milk samples.

SnO2 nanorod: An efficient non-noble-metal electrocatalyst for non-enzymatic H2O2 sensing

Developing non-noble-metal electrocatalyst for non-enzymatic H2O2 sensing is highly attractive. In this work, we describe the development of SnO2 nanorod grown on carbon cloth (SnO2/CC) as an efficient electrocatalyst for H2O2 reduction in neutral solution. The SnO2/CC electrode reveals superior electrochemical performance as a non-enzymatic electrochemical H2O2 sensor, with an ultra-high sensitivity of 24 840 μA mM−1 cm-2, a low detection limit of 9.94 nM at S/N = 3, a linear range from 0.10 μM to 1.0 mM, and satisfactory reproducibility and stability at −0.40 V.

Novel sensitive amperometric hydrogen peroxide sensor using layered hierarchical porous α-MoO3 and GO modified glass carbon electrode

The nonenzymatic electrochemical H2O2 sensor based on molybdenum oxides has been rarely reported. In this work, a nonenzymatic electrode, hierarchical porous α-MoO3 and graphene oxide decorated glass carbon electrode (α-MoO3/GO/GCE) used for H2O2 electrochemical detection, is firstly fabricated by simple layer-by-layer assemble method, in which the α-MoO3 is derived by one-step pyrolysis of the regular organic-inorganic hybrid [(H2L)2(Mo8O26)]n [HL = N-(pyridin-3-ylmethyl)pyridine- 3-amine] single crystal precursor. The wedge-shaped morphology of the material is accumulated by micro-slices which comprise of nanosheets and small particles with average size of 25 nm. Meanwhile, different types of meso- and macro-pores with the size distributions of 4–6, 20–35 and 100–150 nm are observed, respectively. The α-MoO3/GO/GCE sensor based on the optimal ratio of 1:1 shows excellent electrocatalytic H2O2 property at room temperature. It displays the broad linear detection from 0.92 μM to 2.46 mM and the high sensitivity is calculated to be 391.39 μA mM−1 cm−2 with a low detection limit of 0.31 μM (S/N = 3). The sensor can achieve 95% steady state current within 5 s and present well stability, reproducibility and anti-interference during H2O2 detection. Furthermore, the sensor is applied for the determination of H2O2 in human serum samples. The excellent performances of this sensor are related to the hierarchical porous structure of α-MoO3 and its synergistic effect with GO.

Hierarchical graphene/nanorods-based H2O2 electrochemical sensor with self-cleaning and anti-biofouling properties

Detection of H2O2 in bio-fluids plays an important role in early-diagnosis of many diseases, and thus the development of electrochemical H2O2 sensors has been explored. However, constructing robust sensors that could self-clean and avoid biofouling is still challenging, because the complex compositions of bio-fluids could easily absorb to or even passivate the sensor electrode. In this work, we reported the development of H2O2 electrochemical sensor based on hierarchical vertical graphene/nanorods structure (vG/NRs) with self-cleaning and anti-biofouling properties. The hierarchical vG/NRs structure consisted of ZnO nanorods branched on vertical graphene nanowalls, which were fabricated through multiple steps of plasma enhanced chemical vapor deposition, atomic layer deposition and hydrothermal growth. The hierarchical vG/NRs after fluorination (vG/NRs-F) displayed excellent liquid repellence and anti-platelet adhesion properties. The vG/NRs-F was utilized as working electrodes and integrated as electrochemical sensors. H2O2 molecules in solution could access to the vG/NRs surface, inducing electrochemical signals for detection with reasonable sensitivity and selectivity. Meanwhile, the vG/NRs-F electrode could resist the contamination of biocomponents in blood serum after sensing experiment, enabling stable sensing of H2O2 without interfering by biofouling. Our work offers a promising strategy to design self-cleaning and anti-biofouling sensors with extended applicability for detection in complex biological fluids.

Ultrathin Phthalocyanine-Conjugated Polymer Nanosheet-Based Electrochemical Platform for Accurately Detecting H2O2 in Real Time.

As a vital biological mediator and a widely used industrial oxidant, the accurate detection of hydrogen peroxide (H2O2) is of significance for both academic purpose and practical applications. Herein, we report a novel approach for the development of a high-performance electrochemical H2O2 sensor constructed by iron phthalocyanine (FePc)-based diyne-linked conjugated polymeric nanosheets (NSs), FePc-CP NSs. The FePc-CP NSs were delaminated from the bulk material via a defect- and disorder-induced synthetic strategy. By the quasi-Langmuir-Shäfer method, the prepared FePc-CP NSs were self-assembled into multilayer films with controllable thickness on electrodes. Owing to the highly exposed active centers on the surfaces, the FePc-CP NS film-modified electrodes exhibited excellent H2O2 determination performance with a wide linear detection range (0.1-1000 μM), a short response time (the response current approached the maximum value within 0.1 s), a low limit of detection (0.017 μM), and excellent sensitivity (97 μA cm-2 mM-1), which are comparable to the best results reported so far for electrochemical H2O2 sensors. In addition, the fabricated electrochemical H2O2 sensor also displayed satisfactory stability, reproducibility, and selectivity. Furthermore, the obtained FePc-CP NS film sensor can be applied in real-time monitoring of H2O2 in commercial orange juice and beer as well as H2O2 secreted from A549 live cells, revealing its application potential toward the accurate detection of H2O2 in real-sample analysis.

A novel H2O2 electrochemical sensor based on NiCo2S4 functionalized reduced graphene oxide

In this work, we successfully prepared NiCo2S4 nanoparticles decorated reduced graphene oxide through a facile method. The obtained NiCo2S4/rGO hybrids could be modified on a glassy carbon electrode to construct a highly sensitive non−enzymatic H2O2 sensor. The morphology and structure of the obtained NiCo2S4/rGO were characterized by transmission electron microscopy (TEM), X−ray powder diffraction (XRD) and X−ray photoelectron spectroscopy (XPS). The electrochemical performance of the NiCo2S4/rGO hybrids toward the reduction of H2O2 was reflected through the cyclic voltammetry and chronoamperometry data. The hybrids exhibit a fast response time within 5 s, wide linear range of 0.025–11.25 mM, high sensitivity of 118.5 μA mM−1 cm−2, as well as low detection limit of 0.19 μM. Such results demonstrate NiCo2S4/rGO hybrids is a promising candidate for the quantitative detection of H2O2.

Facile synthesis of a zeolitic imidazolate framework-8 with reduced graphene oxide hybrid material as an efficient electrocatalyst for nonenzymatic H2O2 sensing.

A zeolitic imidazolate framework-8 (ZIF-8)/reduced graphene oxide (rGO) nanocomposite was formed by using an efficient synthetic method. The morphology and structure of the ZIF-8/rGO nanocomposite were characterized by scanning electron spectroscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) mapping. The ZIF-8/rGO nanocomposites were immobilized on a carbon paste electrode (CPE) to construct a high-performance nonenzymatic electrochemical H2O2 sensor. A cyclic voltammetry (CV) study showed that the ZIF-8/rGO nanocomposites displayed better electrocatalytic activity toward H2O2 reduction compared to that of ZIF-8. An amperometric study indicated that the H2O2 sensor displayed high performance, which offered a low detection limit (0.05 μM) (S/N = 3), a high sensitivity (4.01 μA mM−1 cm−2), and a wide linear range (from 1.0 to 625 μM). An electrochemical reaction mechanism was proposed for H2O2 reduction on the ZIF-8/rGO/CPE. Importantly, the as-fabricated H2O2 sensor exhibited good reproducibility and excellent selectivity. Furthermore, the constructed high-performance sensor was utilized to monitor the H2O2 levels in real samples, and satisfactory results were obtained. These results demonstrated that the ZIF-8/rGO nanocomposite can be used as a good electrochemical sensor material in practical applications.

Direct growth of ordered PdCu and Co doped PdCu nanoparticles on graphene oxide based on a one-step hydrothermal method for ultrasensitive sensing of H2O2 in living cells.

Ordered PdCu and Co doped PdCu nanoparticles have been synthesized on graphene oxide (GO). The obtained Co-PdCu/GO composites were used to fabricate a H2O2 electrochemical sensor which exhibits an ultralow LOD (limit of detection) of 1.2 nM and an extra broad linear range of 5 nM-5.774 mM, and has been used to detect H2O2 in living cells successfully.

Ultralow-platinum-loading nanocarbon hybrids for highly sensitive hydrogen peroxide detection

Detecting the trace amount of hydrogen peroxide (H2O2) is essential for various industrial and biological applications. Platinum (Pt) based electrochemical H2O2 sensors have good sensing performances. Considering the high cost of Pt, it is desirable to develop high-performance H2O2 sensors with low Pt mass loadings. Here, we use a cathodic polarization treatment method to deposit ultralow mass loading of Pt nanoparticles on a high surface area porous carbon hybrid comprised of reduced graphene oxide nanosheets (rGO) and carbon nanotubes (CNTs). Under multiple cyclic voltammetry (CV) cycles in electrolytes without Pt precursors, Pt can be leached from a Pt mesh anode, and then migrate through electrolyte and anchor on the rGO-CNT hybrid as nanoparticles with narrow size distribution. Varying the number of CV cycles can precisely control the Pt mass loadings. The optimized Pt/rGO-CNT hybrid obtained after 3000 CV cycles contains about 4.8 wt.% Pt nanoparticles with the size of around 3–6 nm. The morphological and physicochemical properties of the synthesized Pt/rGO-CNT hybrids were characterized to understand their synthesis-structure-sensitivity relationship. The Pt/rGO-CNT hybrid show superior H2O2 sensing performances with a low detection limit of 1 μM, linear detection up to 15 mM, and high sensitivity of 2027 μA/ mM cm2, which is the best among the recently reported Pt/carbon material based H2O2 sensors. It can also detect trace amount of H2O2 in milk, and juice samples below the permitted residual level in food packaging, demonstrating its excellent practical application potential in food processing.

FeSx-graphene heterostructures: Nanofabrication-compatible catalysts for ultra-sensitive electrochemical detection of hydrogen peroxide

Hydrogen peroxide (H2O2) is one of the most important redox-active metabolites in biological processes, from cell signaling to oxidative stress. Incorporation of catalytic nano-phase heterostructures can significantly improve the detection limit of H2O2 electrochemical sensors. Here, we report an iron sulfide (FeSx)/graphene heterostructure for detection of H2O2 down to ∼500 picoMolar pM, with a dynamic range over six orders of magnitude. By relying on the Fenton reaction, the developed catalyst enables selective detection of H2O2 vs. common redox-active metabolites in physiological condition. Electrochemical analysis reveals a strong substrate-dependent performance, where the type and doping of the graphene layer dramatically impact sensitivity. Specifically, for the first time, the electrochemical performance of chemical vapor deposited versus epitaxial graphene (EG) layers is examined and compared in a systematic way. The results demonstrate that a heterostructure of FeSx with chemical vapor deposited graphene (CVD-G) exhibits the highest reduction in charge transfer resistance (more than 16×), leading to a significantly higher sensitivity compared to n-doped and p-doped EG. Furthermore, the excellent sensitivity and material stability of the developed heterostructures enable in situ detection of redox changes due to heat shock-induced oxidative stress on E. coli cells. Since the developed heterostructures are directly-grown, they can be patterned with nanometer-scale resolution. Hence, this work can open up new possibilities for developing ultracompact devices for monitoring redox changes in situ, with high spatial resolution.