Conventional electrochemical sensors use voltammetric and amperometric methods with external power supply and modulation systems, which hinder the flexibility and application of the sensors. To avoid the use of an external power system and to minimize the number of electrochemical cell components, a self-powered electrochemical sensor (SPES) for hydrogen peroxide was investigated here. Iron phthalocyanine, an enzyme mimetic material, and Ni were used as a cathode catalyst and an anode material, respectively. The properties of the iron phthalocyanine catalyst modified by graphene nanoplatelets (GNPs) were investigated. Open circuit potential tests demonstrated the feasibility of this system. The GNP-modulated interface helped to solve the problems of aggregation and poor conductivity of iron phthalocyanine and allowed for the achievement of the best analytical characteristics of the self-powered H2O2 sensor with a low detection limit of 0.6 µM and significantly higher sensitivity of 0.198 A/(M·cm2) due to the enhanced electrochemical properties. The SPES demonstrated the best performance at pH 3.0 compared to pH 7.4 and 12.0. The sensor characteristics under the control of external variable load resistances are discussed and the cell showed the highest power density of 65.9 μW/cm2 with a 20 kOhm resistor. The practical applicability of this method was verified by the determination of H2O2 in blood serum.

Conductive ink deposited on flexible substrates through simple methods such as dyeing or printing is one of the most promising approaches for scalable fabrication of wearable electronics. However, excessive chemical additives or a complex preparation process has limited the practical applications of conductive inks. Herein, a highly stable and antibacterial AgNPs/CNT/rGO (SACR) conductive ink with the only assistance of sustainable silk sericin (SS) is developed through a green one-step strategy. SS functions as not only the reductant of silver ions and GO by donating electrons but also the dispersant and stabilizer of CNTs through strong noncovalent interactions. The universality of SACR ink is demonstrated by depositing on various flexible substrates through handwriting, screen-printing, and dyeing techniques; meanwhile, the mechanical reliability between SACR ink and substrates is validated by peeling, bending, and twisting measurements. In addition, the synergistic effects of the multilevel hierarchical 0D/1D/2D structure and abundant interfacial interactions in SACR ink are advantageous to enhancing sensing performance. An SACR ink-based strain sensor and hydrogen peroxide (H2O2) sensor are fabricated to detect physical and biochemical indicators, demonstrating the enormous potential of SACR ink in intelligent wearables for active health monitoring in early care.

Aging is closely related to redox regulation. In our previous work, we proposed a new concept, \"redox-stress response capacity (RRC),\" and found that the decline in RRC was a dynamic characteristic of aging. However, the mechanism of RRC decline during aging remains unknown. In this study, using the senescent human fibroblast cell model and Caenorhabditis elegans model, we identified that peroxiredoxin 2 (PRDX2), as a hydrogen peroxide (H2O2) sensor, was involved in mediating RRC. PRDX2 knockdown led to a decline of RRC and accelerated senescence in fibroblasts and prdx-2 mutant C. elegans also showed decreased RRC. The mechanism study showed that the decreased sensor activity of PRDX2 was related to the increase in hyperoxidation of PRDX2 in senescent cells. Moreover, the level of PRDX2 hyperoxidation also increased in old C. elegans. Simultaneous overexpression of both PRDX2 and sulfiredoxin (SRX) rescued the reduced RRC and delayed senescence. The increase in PRDX2 hyperoxidation in senescent cells led to a decrease in its sensor activity, resulting in the decreased cellular response to H2O2, which is similar to the mechanism of insulin resistance due to the lower insulin receptor sensitivity. Treatment of young cells with a high level of H2O2 to induce a higher level of PRDX2-SO3 resulted in mimicking the RRC decline in senescent cells, which is also similar to a model of insulin resistance induced by high levels of insulin. All these results thrillingly indicate that there is an insulin-resistance-like phenomenon in senescent cells, we named it redox-stress response resistance, RRR. RRR in senescent cells is an important new discovery that explains RRC decline during aging and reveals the internal relationship between redox regulation and aging from a new perspective.

Intracellular hydrogen peroxide (H2O2) levels can oscillate from low, physiological concentrations, to intermediate, signaling ones, and can participate in toxic reactions when overcoming certain thresholds. Fluorescent protein-based reporters to measure intracellular H2O2 have been developed in recent decades. In particular, the redox-sensitive green fluorescent protein (roGFP)-based proteins fused to peroxiredoxins are among the most sensitive H2O2 biosensors. Using fission yeast as a model system, we recently demonstrated that the gradient of extracellular-to-intracellular peroxides through the plasma membrane is around 300:1, and that the concentration of physiological H2O2 is in the low nanomolar range. Here, we have expressed the very sensitive probe roGFP2-Tpx1.C169S in two other model systems, budding yeast and human Jurkat cells. As in fission yeast, the biosensor is ~40-50% oxidized in these cell types, suggesting similar peroxide steady-state levels. Furthermore, probe oxidation upon the addition of extracellular peroxides is also quantitatively similar, suggesting comparable plasma membrane H2O2 gradients. Finally, as a proof of concept, we have applied different concentrations of zinc to all three model systems and have detected probe oxidation, demonstrating that an excess of this metal can cause fluctuations of peroxides, which are moderate in yeasts and severe in mammalian cells. We conclude that the principles governing H2O2 fluxes are very similar in different model organisms.

A metal-free porphyrazine derivative with peripheral phthalimide substituents was metallated with a nickel(II) ion. The purity of the nickel macrocycle was confirmed using HPLC, and characterized by MS, UV-VIS, and 1D (1H, 13C) and 2D (1H-13C HSQC, 1H-13C HMBC, 1H-1H COSY) NMR techniques. The novel porphyrazine was combined with various carbon nanomaterials, such as carbon nanotubes-single walled (SWCNTs) and multi-walled (MWCNTs), and electrochemically reduced graphene oxide (rGO), to create hybrid electroactive electrode materials. The carbon nanomaterials\' effect on the electrocatalytic properties of nickel(II) cations was compared. As a result, an extensive electrochemical characterization of the synthesized metallated porphyrazine derivative on various carbon nanostructures was carried out using cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). An electrode modified with carbon nanomaterials GC/MWCNTs, GC/SWCNTs, or GC/rGO, respectively, was shown to have a lower overpotential than a bare glassy carbon electrode (GC), allowing for the measurement of hydrogen peroxide in neutral conditions (pH 7.4). It was shown that among the tested carbon nanomaterials, the modified electrode GC/MWCNTs/Pz3 exhibited the best electrocatalytic properties in the direction of hydrogen peroxide oxidation/reduction. The prepared sensor was determined to enable a linear response to H2O2 in concentrations ranging between 20-1200 µM with the detection limit of 18.57 µM and sensitivity of 14.18 µA mM-1 cm-2. As a result of this research, the sensors produced here may find use in biomedical and environmental applications.

The development of efficient H2O2 sensors is crucial because of their multiple functions inside and outside the biological system and the adverse effects that a higher concentration can cause. This work reports a highly sensitive and selective non-enzymatic electrochemical H2O2 sensor achieved through the hybridization of Co3S4 and graphitic carbon nitride nanosheets (GCNNS). The Co3S4 is synthesized via a hydrothermal method, and the bulk g-C3N4 (b-GCN) is prepared by the thermal polycondensation of melamine. The as-prepared b-GCN is exfoliated into nanosheets using solvent exfoliation, and the composite with Co3S4 is formed during nanosheet formation. Compared to the performances of pure components, the hybrid structure demonstrates excellent electroreduction towards H2O2. We investigate the H2O2-sensing performance of the composite by cyclic voltammetry, differential pulse voltammetry, and amperometry. As an amperometric sensor, the Co3S4/GCNNS exhibits high sensitivity over a broad linear range from 10 nM to 1.5 mM H2O2 with a high detection limit of 70 nM and fast response of 3 s. The excellent electrocatalytic properties of the composite strengthen its potential application as a sensor to monitor H2O2 in real samples. The remarkable enhancement of the electrocatalytic activity of the composite for H2O2 reduction is attributed to the synergistic effect between Co3S4 and GCNNS.

Nanomaterial-based mimetic enzymes, called nanozymes, received more and more attention in recent decades; however, their lack of biocompatibility limited the biomedical applications, which could be solved by surface modification. In this work, the Co3O4 nanoplates were modified by different functional groups, including the amino group, carboxyl group, hydroxyl group, and sulfhydryl group (NH2-Co3O4, COOH-Co3O4, OH-Co3O4, and SH-Co3O4). And the modified Co3O4 nanoplates were characterized by XRD, SEM, TEM, XPS, FTIR, TG, and the Zeta potential, verifying the successful modification of different functional groups. Their mimetic peroxidase properties and kinetics process were further studied and showed that the order of their catalytic activities was as follows: NH2-Co3O4 > SH-Co3O4 > COOH-Co3O4 > pure Co3O4 > OH-Co3O4, and the catalysis of modified Co3O4 nanozymes all followed Michaelis-Menten kinetics. The results indicated that the different functional groups changed their electron transfer ability, and further affected their catalytic activity. H2O2 detection was selected as an application model system to evaluate the modified Co3O4 nanozymes. Compared with other Co3O4 nanozymes, a wider linear range from 0.01 to 40 mmol L-1 and a lower detection limit of 1.5 μmol L-1 was constructed with NH2-Co3O4 nanozymes. The results suggested that surface modification by functional groups was a robust strategy to improve the application of Co3O4 nanozymes. The enhanced catalytic activity and good biocompatibility of modified Co3O4 nanozymes provided valuable materials for the relative application, such as medical detection and antioxidation.

The non-enzymatic electrochemical sensing platform for hydrogen peroxide by using Pt-based nanoparticle was investigated. The characterization of PtNiCo-NPs was done by XRD, TEM, HRTEM, EDS, and XPS. A simple drop-casting technique was used to fabricate the nanomaterial on FTO electrode. The amperometric and cyclic voltammetric results illustrated that PtNiCo-NPs on FTO had excellent electrochemical performance over other mono or bimetallic materials. The catalytic performance for H2O2 sensing based on PtNiCo-NPs possessed a wide linear range from 5 μM to 16.5 mM with a low detection limit of 0.37 μM and a good sensitivity of 1374.4 μA mM-1 cm-2 at a scan rate of 20 mV s-1 (vs. Ag/AgCl). This work presents a new way to produce a ternary nanomaterial for H2O2 sensing with excellent electrochemical performance. In addition, the fabricated nanomaterial showed no interferences for common interfering agents, which indicates the high specificity of the sensor. The PtNiCo-NPs have excellent stability and good reproducibility in real samples.

Hydrogen peroxide (H2O2) is generated as a by-product of metabolic reactions during oxygen use by aerobic organisms, and can be toxic or participate in signaling processes. Cells, therefore, need to be able to sense and respond to H2O2 in an appropriate manner. This is often accomplished through thiol switches: Cysteine residues in proteins that can act as sensors, and which are both scarce and finely tuned. Bacteria and eukaryotes use different types of such sensors-either a one-component (OxyR) or two-component (Pap1-Tpx1) redox relay, respectively. However, the biological significance of these two different signaling modes is not fully understood, and the concentrations and peroxides driving those types of redox cascades have not been determined, nor the intracellular H2O2 levels linked to toxicity. Here we elucidate the characteristics, rates, and dynamic ranges of both systems.
By comparing the activation of both systems in fission yeast, and applying mathematical equations to the experimental data, we estimate the toxic threshold of intracellular H2O2 able to halt aerobic growth, and the temporal gradients of extracellular to intracellular peroxides. By calculating both the oxidation rates of OxyR and Tpx1 by peroxides, and their reduction rates by the cellular redoxin systems, we propose that, while Tpx1 is a sensor and an efficient H2O2 scavenger because it displays fast oxidation and reduction rates, OxyR is strictly a H2O2 sensor, since its reduction kinetics are significantly slower than its oxidation by peroxides, and therefore, it remains oxidized long enough to execute its transcriptional role. We also show that these two paradigmatic H2O2-sensing models are biologically similar at pre-toxic peroxide levels, but display strikingly different activation behaviors at toxic doses.
Both Tpx1 and OxyR contain thiol switches, with very high reactivity towards peroxides. Nevertheless, the fast reduction of Tpx1 defines it as a scavenger, and this efficient recycling dramatically changes the Tpx1-Pap1 response to H2O2 and connects H2O2 sensing to the redox state of the cell. In contrast, OxyR is a true H2O2 sensor but not a scavenger, being partially insulated from the cellular electron donor capacity.

A facile approach was developed for preparing the multilayer hybrid films of mixed (phthalocyaninato) (porphyrinato) europium(III) triple-decker compound (Pc)Eu(Pc)Eu[trans-T(COOCH3)2PP] (1) and graphene oxide (GO) using the solution-processing QLS method. The combination of the nature of relatively high conductivity and great surface area for GO with the electroactive and semiconductive triple-decker compound in ITO electrode renders the hybrid film excellent sensing property for H2O2, due to the optimized triple-decker molecular packing in the uniform-sized nanoparticles (ca. 70 nm) formed on the GO surface. The amperometric responses are linearly proportional to the concentration of H2O2 in the range of 0.05-1800 μM with a fast response time of 0.03 s μM-1, a low detection limit of 0.017 μM, and good sensitivity of 7.4 μA mM-1. The present work represents the best result of tetrapyrrole-based nonenzymatic electrochemical sensor for H2O2. Nevertheless, the triple-decker/GO/ITO also shows excellent stability, reproducibility, and selectivity, indicating the great potential of electroactive tetrapyrrole rare earth sandwich compounds in combination with GO in the field of nonenzymatic electrochemical sensors.