pH sensing in aqueous solutions using a MnO2 thin film electrodeposited on a glassy carbon electrode

BIOSENSOR DEVELOPMENT IN SPORTS DOPING WITH DEXAMETHASONE

ABSTRACT Introduction: Dexamethasone is a type of drug that is considered a steroid. It belongs to a class of drugs known as corticosteroids. Objective: Develop an electrochemical sensor of dexamethasone in a pharmaceutical sample using electrodes modified with nanostructures of MnO2 and reduced graphene oxide (MnO2/rGO). The glassy carbon electrodes (GCE) used to make the GO nanostructures were first modified using a modified Hummers technique before electrochemically reduced. Methods: MnO2 nanomaterials were electrochemically deposited on rGO/GCE. SEM structural investigation indicated vertical tetragonal crystal development of -MnO2 nanostructures in sprayed rGO nanostructures. Results: Because of the high composite surface area, multiple exposed active sites, and the synergistic effect of MnO2 and rGO, the electrocatalytic reaction to dexamethasone of MnO2/rGO/CPE was shown to be broad, selective, stable, and sensitive in electrochemical tests using amperometry. It was established that the linear range, sensitivities, and detection limit of the sensor are 0 to 260 µM, 4.6153µA/µM and 0.005 µM, respectively. The MnO2/rGO/CPE was tested for accuracy and applicability in determining dexamethasone in pharmacological and human urine samples. Conclusion: The results revealed that the sensor could prepare acceptable recovery (96.34%) and RSD (3.58%), suggesting that it could be used as a reliable dexamethasone sensor in clinical samples. Level of evidence II; Therapeutic studies - Investigation of treatment outcomes.

An ultrasensitive electrochemical sensor based on in situ synthesized manganese dioxide/gold nanoparticles nanocomposites for rapid detection of methylmercury in foodstuffs

The inclusion of methylmercury (CH₃Hg⁺) in the environment and food chain has aroused wide concern due to its high neurotoxicity and cumulative effects. Herein, a highly sensitive electrochemical sensor based on manganese dioxide (MnO₂)/gold nanoparticles (AuNPs) composites is fabricated for CH₃Hg⁺ detection in food. The MnO₂/AuNPs nanocomposites were synthesized in situ on the surface of a glassy carbon electrode by an electrodeposition method and were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The resulting MnO₂/AuNPs modified electrode exhibited a large active surface area, enhanced conductivity and excellent electrocatalytic activity toward CH₃Hg⁺ due to the synergistic effect of MnO₂ and AuNPs. Square wave anodic stripping voltammetry (SWASV) was used as the sensing technique for CH₃Hg⁺, and the stripping peak current showed a good linear relationship with CH₃Hg⁺ concentration in the range of 0.7-15 μg L^-1 with a detection limit of 0.051 μg L^-1. Besides, the interference from Hg²⁺ associated with CH₃Hg⁺ detection can be avoided by the addition of diethylene triamine pentaacetic acid (DTPA). The as-prepared sensor was applied to detect CH₃Hg⁺ in various food samples with satisfactory recoveries, thus providing a promising platform for rapid screening of methylmercury residues.

Effect of heat-treatment on the pH sensitivity of stainless-steel electrodes as pH sensors

Effect of heat-treatment on the pH sensitivity of uncoated stainless-steel electrodes was investigated to comprehend the pH sensitivity of metal-oxide coated stainless-steel electrodes as novel pH sensors. The pH sensitivity of stainless-steel electrodes as-received and heat-treated at 500 °C, 600 °C and 700 °C for 24 h were 91 %, 94 %, 102 % and 91 %, respectively. The pH sensitivity tended to increase with increasing heat-treatment time at a given temperature. Thus, the most suitable heat-treatment condition for the stainless-steel electrodes was 600 °C for 24 h. The austenite phase (fcc) was the main phase on the surface of the heat-treated stainless-steel electrodes. Unexpectedly, the change in the martensite phase (bcc) as the second phase with heat-treatment temperature was similar to the pH sensitivity, with the martensite phase affecting the pH sensitivity. Therefore, it appeared that the pH sensitivity of the metal-oxide coated stainless-steel electrodes was affected by the underlying stainless-steel as well as the outer metal-oxide film coating. A prototype stainless-steel tube electrode was used as a working electrode for demonstrating the depth profiling of pH. The stainless-steel tube electrode showed good performance for measuring pH depth profiles compared to commercially available glass electrodes.

New Developments in Smart Bandage Technologies for Wound Diagnostics

The pH of wound fluid has long been recognized as an important diagnostic for assessing wound condition, but as yet there are few technological options available to the clinician. The availability of sensors that can measure wound pH, either in the clinic or at home could significantly improve clinical outcome - particularly in the early identification of complications such as infection. New material designs and electrochemical research strategies that are being targeted at wound diagnostics are identified and a critical overview of emerging research that could be pivotal in setting the direction for future devices is provided.

Molecular Wiring in Smart Dressings: Opening a New Route to Monitoring Wound pH

It has been proposed that fluctuations in wound pH can give valuable insights into the healing processes in chronic wounds, but acquiring such data can be a technological challenge especially where there is little sample available. Developments in voltammetric pH sensing have opened up new avenues for the design of probes that can function in ultra-small volumes and can be inherently disposable but, as yet few can meet the demands of wound monitoring. A preliminary investigation of the pH response of a new redox wire prepared from a peptide homopolymer of tryptophan is presented and its potential applicability as a sensing material for use in smart dressings is critically discussed.

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

This paper presents a review of the redox and electrocatalytic properties of transition metal oxide electrodes, paying particular attention to the oxygen evolution reaction. Metal oxide materials may be prepared using a variety of methods, resulting in a diverse range of redox and electrocatalytic properties. Here we describe the most common synthetic routes and the important factors relevant to their preparation. The redox and electrocatalytic properties of the resulting oxide layers are ascribed to the presence of extended networks of hydrated surface bound oxymetal complexes termed surfaquo groups. This interpretation presents a possible unifying concept in water oxidation catalysis - bridging the fields of heterogeneous electrocatalysis and homogeneous molecular catalysis.