Self-assembly of ultra-small gold nanoparticles on an indium tin oxide electrode for the enzyme-free detection of hydrogen peroxide

Flexible Sensors for Hydrogen Peroxide Detection: A Critical Review

Hydrogen peroxide (H₂O₂) is a common chemical used in many industries and can be found in various biological environments, water, and air. Yet, H₂O₂ in a certain range of concentrations can be hazardous and toxic. Therefore, it is crucial to determine its concentration at different conditions for safety and diagnostic purposes. This review provides an insight about different types of sensors that have been developed for detection of H₂O₂. Their flexibility, stability, cost, detection limit, manufacturing, and challenges in their applications have been compared. More specifically the advantages and disadvantages of various flexible substrates that have been utilized for the design of H₂O₂ sensors were discussed. These substrates include carbonaceous substrates (e.g., reduced graphene oxide films, carbon cloth, carbon, and graphene fibers), polymeric substrates, paper, thin glass, and silicon wafers. Many of these substrates are often decorated with nanostructures composed of Pt, Au, Ag, MnO₂, Fe₃O₄, or a conductive polymer to enhance the performance of sensors. The impact of these nanostructures on the sensing performance of resulting flexible H₂O₂ sensors has been reviewed in detail. In summary, the detection limits of these sensors are within the range of 100 nM-1 mM, which makes them potentially, but not necessarily, suitable for applications in health, food, and environmental monitoring. However, the required sample volume, cost, ease of manufacturing, and stability are often neglected compared to other detection parameters, which hinders sensors' real-world application. Future perspectives on how to address some of the substrate limitations and examples of application-driven sensors are also discussed.

Recent Advances in Electrochemical Sensing of Hydrogen Peroxide (H2O2) Released from Cancer Cells

Cancer is by far the most common cause of death worldwide. There are more than 200 types of cancer known hitherto depending upon the origin and type. Early diagnosis of cancer provides better disease prognosis and the best chance for a cure. This fact prompts world-leading scientists and clinicians to develop techniques for the early detection of cancer. Thus, less morbidity and lower mortality rates are envisioned. The latest advancements in the diagnosis of cancer utilizing nanotechnology have manifested encouraging results. Cancerous cells are well known for their substantial amounts of hydrogen peroxide (H₂O₂). The common methods for the detection of H₂O₂ include colorimetry, titration, chromatography, spectrophotometry, fluorimetry, and chemiluminescence. These methods commonly lack selectivity, sensitivity, and reproducibility and have prolonged analytical time. New biosensors are reported to circumvent these obstacles. The production of detectable amounts of H₂O₂ by cancerous cells has promoted the use of bio- and electrochemical sensors because of their high sensitivity, selectivity, robustness, and miniaturized point-of-care cancer diagnostics. Thus, this review will emphasize the principles, analytical parameters, advantages, and disadvantages of the latest electrochemical biosensors in the detection of H₂O₂. It will provide a summary of the latest technological advancements of biosensors based on potentiometric, impedimetric, amperometric, and voltammetric H₂O₂ detection. Moreover, it will critically describe the classification of biosensors based on the material, nature, conjugation, and carbon-nanocomposite electrodes for rapid and effective detection of H₂O₂, which can be useful in the early detection of cancerous cells.

A high-efficiency cathodic sodium nitroprusside/luminol/H2O2 electrochemiluminescence system in neutral media for the detection of sodium nitroprusside, glucose, and glucose oxidase

Sodium nitroprusside (SNP) is an anti-hypertension drug used in vascular surgery, chronic cardiovascular disease, and in the management of acute myocardial infarction by the spontaneous release of nitric oxide. Herein, for the first time, we extend its application to electrochemiluminescence (ECL). The NO generated from the electrochemical reduction of SNP reacts with H₂O₂ to generate reactive oxygen species, which subsequently reacts with luminol to produce intense ECL. The ECL signal of the new SNP/H₂O₂/luminol system under neutral conditions (pH 7.4) is almost equivalent to the classic luminol/H₂O₂ system at pH 10, making this system highly attractive for bioanalysis that directly or indirectly liberates H₂O₂ under neutral conditions. At the optimum experimental conditions, the ECL intensity increases proportionally with the log of H₂O₂ and SNP concentration over the range from 0.2 μM-1000 μM and 0.08 mM-1.8 mM with the detection limits of 0.078 μM and 0.038 mM, respectively. The RSD for ten analyses of H₂O₂ is 4.25%. Recoveries from 97.2% to 101.7% were obtained for real sample analysis. Since H₂O₂ participates in numerous important enzymatic reactions, the application of this system was further investigated using glucose oxidase (GODx) and glucose as a representative enzyme and substrate, respectively, thus liberating H₂O₂ as a reaction product. The concentrations of glucose and the activity of GODx were directly proportional to the ECL intensities over a range of 5-1000 μM and 0.0025-1 units per mL with the limits of detection of 2.65 μM and 0.0012 units per mL (S/N = 3), respectively.

Multi-tasking Schiff base ligand: a new concept of AuNPs synthesis

Multi-tasking 3,4-dihydroxysalophen Schiff base tetradentate ligand (3,4-DHS) as reductant, stabilizer, and catalyst in a new concept of gold nanoparticles (AuNPs) synthesis is demonstrated. 3,4-DHS is able to reduce HAuCl4 in water, acting also as capping agent for the generation of stable colloidal suspensions of Schiff base ligand-AuNPs assemblies of controlled size by providing a robust coating to AuNPs, within a unique reaction step. Once deposited on carbon electrodes, 3,4-DHS-AuNPs assemblies show a potent electrocatalytic effect towards hydrazine oxidation and hydrogen peroxide oxidation/reduction.