Electrode Reactions Coupled with Chemical Reactions of Oxygen, Water and Acetaldehyde in an Ionic Liquid: New Approaches for Sensing Volatile Organic Compounds

Novel Ag3PO4/ZnWO4-modified graphite felt electrode for photoelectrocatalytic removal of harmful algae: Performance and mechanism

A novel Ag3PO4/ZnWO4-modified graphite felt electrode (AZW@GF) was prepared by drop coating method and applied to photoelectrocatalytic removal of harmful algae. Results showed that approximately 99.21% of chlorophyll a and 91.57% of Microcystin-LR (MCLR) were degraded by the AZW@GF-Pt photoelectrocatalytic system under the optimal operating conditions with a rate constant of 0.02617 min-1 and 0.01416 min-1, respectively. The calculated synergistic coefficient of photoelectrocatalytic algal removal and MC-LR degradation by the AZW@GF-Pt system was both larger than 1.9. In addition, the experiments of quenching experiments and electron spin resonance (ESR) revealed that the photoelectrocatalytic reaction mainly generated •OH and •O2- for algal removal and MC-LR degradation. Furthermore, the potential pathway for photoelectrocatalytic degradation of MC-LR was proposed. Finally, the photoelectrocatalytic cycle algae removal experiments were carried out on AZW@GF electrode, which was found to maintain the algae removal efficiency at about 91% after three cycles of use, indicating that the photoelectrocatalysis of AZW@GF electrode is an effective emergency algae removal technology.

Electrochemical detection of the neurotransmitter glutamate and the effect of the psychotropic drug riluzole on its oxidation response

Glutamate is the main excitatory neurotransmitter in the brain and plays a leading role in degenerative diseases, such as motor neuron diseases. Riluzole is a glutamate regulator and a therapeutic drug for motor neuron diseases. In this work, the interaction between glutamate and riluzole was studied using cyclic voltammetry and square-wave voltammetry at a glassy carbon electrode (GCE). It was shown that glutamate underwent a two-electron transfer reaction on the GCE surface, and the electrochemical detection limits of glutamate and riluzole were 483 μmol/L and 11.47 μmol/L, respectively. The results confirm that riluzole can promote the redox reaction of glutamate. This work highlights the significance of electrochemical technology in the sensing detection of the interaction between glutamate and related psychotropic drugs.

Effect of Electrode Surface Chemistry on Ion Structuring of Imidazolium Ionic Liquids

Surface chemistry plays a critical role in the ion structuring of ionic liquids (ILs) at the interfaces of electrodes and controls the overall energy storage performance of the system. Herein, we functionalized the gold (Au) colloid probe of an atomic force microscope with -COOH and -NH₂ groups to explore the effect of different surface chemical properties on the ion structuring of an IL. Aided by colloid-probe atomic force microscopy (AFM), the ion structuring of an imidazolium IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆], abbreviated as BP hereafter), on the Au electrode surface and the ion response to the change in the surface chemistry are investigated. AFM morphologies, contact angles, and approaching force-distance curves of the BP IL on the functionalized Au surfaces exhibited that the IL forms a more obvious layering structure on the -COOH-terminated Au surface (Au-COOH), while it forms heterogeneous and aggregating droplets on the -NH₂ surface (Au-NH₂). The formed uniform and aggregation-free ion layers in the vicinity of the Au-COOH surface are due to the π-π⁺ stacking interaction between the delocalized π⁺ electrons from the imidazolium ring in the IL [BMIM]⁺ cation and the localized π electrons from the sp² carbon on the -COOH group. The in situ observation of nano-friction and torsional resonance frequency at the IL-electrode interfaces further demonstrated the ion structuring of the IL at Au-COOH, which results in a more sensitive electrochemical response associated with a faster capacitive process.

Ho2O3-TiO2 Nanobelts Electrode for Highly Selective and Sensitive Detection of Cancer miRNAs

The design and engineering of effective electrode materials is critical in the development of electrochemical sensors. In the present study, Ho2O3-TiO2 nanobelts were synthesized by an alkaline hydrothermal process. The structure and morphology were investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) measurements. The Ho2O3-TiO2 nanobelts showed a distinctly enhanced (004) reflection peak and rough surfaces and were used for the electrochemical selective sensing of various cancer miRNAs, such as prostate cancer miR-141, osteosarcoma miR-21, and pancreatic cancer miR-1290. Voltammetric measurements showed an oxidation peak at +0.4, +0.2, and +1.53 V for the three different cancer biomarkers, respectively, with the detection limit as low as 4.26 aM. The results suggest that the Ho2O3-TiO2 nanobelts can be used as active materials to detect early cancers, for in vitro screening of anticancer drugs, and molecular biology research.

Materials for Chemical Sensing: A Comprehensive Review on the Recent Advances and Outlook Using Ionic Liquids, Metal–Organic Frameworks (MOFs), and MOF-Based Composites

The ability to measure and monitor the concentration of specific chemical and/or gaseous species (i.e., “analytes”) is the main requirement in many fields, including industrial processes, medical applications, and workplace safety management. As a consequence, several kinds of sensors have been developed in the modern era according to some practical guidelines that regard the characteristics of the active (sensing) materials on which the sensor devices are based. These characteristics include the cost-effectiveness of the materials’ manufacturing, the sensitivity to analytes, the material stability, and the possibility of exploiting them for low-cost and portable devices. Consequently, many gas sensors employ well-defined transduction methods, the most popular being the oxidation (or reduction) of the analyte in an electrochemical reactor, optical techniques, and chemiresistive responses to gas adsorption. In recent years, many of the efforts devoted to improving these methods have been directed towards the use of certain classes of specific materials. In particular, ionic liquids have been employed as electrolytes of exceptional properties for the preparation of amperometric gas sensors, while metal–organic frameworks (MOFs) are used as highly porous and reactive materials which can be employed, in pure form or as a component of MOF-based functional composites, as active materials of chemiresistive or optical sensors. Here, we report on the most recent developments relative to the use of these classes of materials in chemical sensing. We discuss the main features of these materials and the reasons why they are considered interesting in the field of chemical sensors. Subsequently, we review some of the technological and scientific results published in the span of the last six years that we consider among the most interesting and useful ones for expanding the awareness on future trends in chemical sensing. Finally, we discuss the prospects for the use of these materials and the factors involved in their possible use for new generations of sensor devices.

Highly Stable Low-Cost Electrochemical Gas Sensor with an Alcohol-Tolerant N,S-Codoped Non-Precious Metal Catalyst Air Cathode

The emerging applications of electrochemical gas sensors (EGSs) in Internet of Things-enabled smart city and personal health electronics bring out a new challenge for common EGSs, such as alcohol fuel cell sensors (AFCSs) to reduce the dependence on a pricy Pt catalyst. Here, for the first time, we propose a low-cost novel N,S-codoped metal catalyst (FeNSC) to accelerate oxygen reduction reaction (ORR) and replace the Pt catalyst in the cathode of an AFCS. The optimal FeNSC shows high ORR activity, stability, and alcohol tolerance. Furthermore, the FeNSC-based AFCS not only demonstrates excellent linearity, low detection limit, high stability, and superior sensitivity to that of the commercial Pt/C-based AFCS but also outperforms commercial Pt/C-based AFCS in the exposed cell regarding great linearity, high sensitivity, and great stability. Such a promising sensor performance not just proves the concept of the FeNSC-based ACFS but enlightens the next-generation designs toward low-cost, highly sensitive, and durable EGSs.

4-Hydroxy-2-nonenal, a lipid peroxidation product, as a biomarker in diabetes and its complications: challenges and opportunities

Over 30 million Americans are diagnosed with diabetes and this number is only expected to increase. There are various causes that induce complications with diabetes, including oxidative stress. In oxidative stress, lipid peroxidation-derived reactive carbonyl species such as 4-hydroxy-2-nonenal (4-HNE) is shown to cause damage in organs that leads to diabetic complications. We provided evidence to show that 4-HNE or/and 4-HNE-protein adducts are elevated in various organ systems of diabetic patients and animal models. We then discussed the advantages and disadvantages of different methodologies used for the detection of 4-HNE in diabetic tissues. We also discussed how novel approaches such as electrochemistry and nanotechnology can be used for monitoring 4-HNE levels in biological systems in real-time. Thus, this review enlightens the involvement of 4-HNE in the pathogenesis of diabetes and its complications and efficient methods to identify it. Furthermore, the article presents that 4-HNE can be developed as a biomarker for end-organ damage in diabetes such as diabetic cardiac complications.

Adsorption and Electrochemistry of Carbon Monoxide at the Ionic Liquid-Pt Interface

In this work, CO adsorption and oxidation processes were studied with cyclic voltammetry and anodic adsorptive stripping chronoamperometry in two structural different ionic liquids (ILs) (i.e., 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [Bmpy][NTf₂] and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Bmim][NTf₂]). Multiple redox processes were observed in the ILs. During the anodic oxidation processes, the NTf₂^- anion is oxidized to form NTf₂^• radical and CO is oxidized to CO₂ and produces a proton in these ILs when a trace amount of water is present. The products of oxidation processes (NTf₂^• radical and proton) can be reduced at cathodic processes. Results show that the cation in these ILs can facilitate the formation of an electrolyte-electrode interface structure that influences the amount of CO adsorbed as well as the subsequent CO oxidation current and charge. By selecting the anodic and cathodic potentials, we developed an innovative electroanalytical method for CO sensing based on a simple double-potential adsorptive stripping chronoamperometry. The method allows calibration of the concurrent NTf₂^- anion and CO redox processes as well as the double-layer charging and discharging processes in the IL with the presence of a trace amount of water providing quantitative analysis of CO concentration with high accuracy and sensitivity. The reported method is the first work to show that quantitative CO detection can be achieved in the presence of complex dynamic interfacial processes in the ILs. The trace water present in the ILs is beneficial for CO oxidation, but a large amount of water is detrimental for the CO oxidation in ambient condition.

SERS-based chip for discrimination of formaldehyde and acetaldehyde in aqueous solution using silver reduction

A method is described for surface-enhanced Raman scattering (SERS) discrimination of formaldehyde (FA) and acetaldehyde (AA) in aqueous sample solutions. It is based on the use of a paper strip containing 4-aminothiophenol (Atp)-modified reduced graphene oxide (rGO)/[Ag(NH₃)₂]⁺ (rGO/[Ag(NH₃)₂]⁺/Atp). The addition of FA or AA induces the conversion of [Ag(NH₃)₂]⁺ complex to silver nanoparticles (AgNPs) because of aldehyde-induced silver reduction reaction. The AgNPs possess strong SERS activity. The average interparticle gaps between the AgNPs can be fine-tuned by controlling the experimental conditions, this leading to the formation of optimized SERS hot spots. It is also found that the changes in the spectral shapes and the relative intensity ratio of the bands at 1143 and 1072 cm^-1 result from the difference in the pH value of the surrounding solution. This effect enables the selective discrimination of FA and AA. The paper strip can be used as a SERS dipstick and swab for on-site determination of FA or AA in wine and human urine via the differences in the intensity of the SERS peaks. The assay works over a wide range of concentrations (0.45 ng·L^-1 to 480 μg·L^-1) for FA and AA, and the respective detection limits are 0.15 and 1.3 ng·L^-1. Graphical abstract Schematic presentation of the preparation procedure of 4-aminothiophenol (Atp)-modified reduced graphene oxide (rGO)/[Ag(NH₃)₂]⁺ hybrid paper and its surface-enhanced Raman scattering discrimination of formaldehyde and acetaldehyde based on silver reduction.

Volatile aldehydes sensing in headspace using a room temperature ionic liquid-modified electrochemical microprobe

The cyclic voltammetric behaviour of propionaldehyde (PA) and hexanaldehyde (HA), in 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTF₂]), 1-butyl-3-methylimidazolium hydrogen sulphate ([BMIM][HSO₄]) and 1-butyl-3-methylimidazolium hydroxide ([BMIM][OH]) was investigated at a platinum microelectrode. A clear oxidation process for both aldehydes was recorded only in [BMIM][OH]. On the basis of these evidences, an electrochemical microprobe (EMP), incorporating [BMIM][OH] as electrolyte, was assembled for sensing these aldehydes in gaseous phases. The EMP exposed in the headspace of the liquid aldehydes displayed voltammetric and amperometric responses, which depended on the aldehyde vapour pressures and, consequently, on the temperature employed. The usefulness of the [BMIM][OH] coated EMP for practical applications was assessed in the detection of HA vapour released from squalene (i.e., a lipid simulant matrix) samples spiked with known amounts of the aldehyde. Calibration plots were constructed at 40 °C, 50 °C and 60 °C, using both voltammetry and chronoamperometry. In both cases, good linearity between current and HA concentration in squalene was obtained over the range 3-300 ppm, with correlation coefficients higher than 0.991. Reproducibility, evaluated from at least three replicates, was within 5%. Detection limits, evaluated for a signal-to-noise ratio of 3, were in any case lower than 1.7 ppm. These analytical performances are suitable for monitoring VAs coming from lipid oxidation processes in food. An application concerning the determination of VAs in headspace of sunflower oil during an induced oxidative test to establish its thermal stability was also performed.

Continuous amperometric hydrogen gas sensing in ionic liquids

Continuous and real-time ionic liquid based hydrogen gas sensor with high sensitivity, selectivity, speed, accuracy, repeatability and stability.

Hydrogen Electrooxidation in Ionic Liquids Catalyzed by the NTf2 Radical

Hydrogen electrooxidation via a "hydrogen abstraction" mechanism in an aprotic ionic liquid 1-butyl-1-methylpyrrolidinium bis-(trifluoromethylsulfonyl) [Bmpy][NTf2] under anaerobic conditions was investigated using cyclic voltammetry and density functional theory (DFT). It is found that a platinum bound NTf2 radical (NTf2•) formed by the oxidation of NTf2- at anodic potential can catalyze the oxidation of hydrogen and enhance its reaction rate. Both experimental and theoretical studies (DFT) have supported a mechanism involving a NTf2• radical intermediate that catalyzes the hydrogen redox processes.