Electropolymerised pH Insensitive Salicylic Acid Reference Systems: Utilization in a Novel pH Sensor for Food and Environmental Monitoring

This work summarizes the electrochemical response of a salicylic acid-based carbon electrode for use as a novel solid-state reference electrode in a redox-based pH sensor. This novel reference produces a pH insensitive response over a range of pH 3–10 in solutions with low buffer concentrations, different compositions, conductivities, and ionic strengths is produced. The pH of the local environment is shown to be determined by the chemistry and the electrochemical response of the redox active species on the surface of the electrode; the local pH can be controlled by the electropolymerized salicylic acid moieties due to the acid concentration on the surface, avoiding any perturbation in environmental pH and leading to a stable novel reference system. Sensitivities of −7.1 mV/pH unit, −2.4 mV/pH unit, −0.2 mV/pH unit, and 2.5 mV/pH units were obtained for different food medias, hydroponic solution, seawater, and cell-culture media, respectively, confirming its ability to control the local pH of the electrode. This reference system is paired with a new pH sensing element based on electropolymerized flavanone to provide a calibration free, pH sensitive sensor to effectively and accurately measure the pH of various media with high viscosity, low conductivity, low/high buffer concentration or cell-culture environment, presenting a maximum error of +/−0.03 pH units.

Spectroscopic and Computational Study of the Protonation Equilibria of Amino-Substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as Novel pH-Sensing Materials

We present the synthesis and analytical, spectroscopic and computational characterization of three amino-substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as novel pH probes with a potential application in pH-sensing materials. The designed systems differ in the number and position of the introduced isobutylamine groups on the pentacyclic aromatic core, which affects their photophysical and acid-base properties. The latter were investigated by UV-Vis absorption and fluorescence spectroscopies and interpreted by DFT calculations. An excellent agreement in experimentally measured and computationally determined pKa values and electronic excitations suggests that all systems are unionized at neutral pH, while their transition to monocationic forms occurs at pH values between 3 and 5, accompanied by substantial changes in spectroscopic responses that make them suitable for detecting acidic conditions in solutions. Computations identified imidazole imino nitrogen as the most favorable protonation site, further confirmed by analysis of perturbations in the chemical shifts of 1H and 13C NMR, and showed that the resulting basicity emerges as a compromise between the basicity-reducing effect of a nearby nitrile and a favorable contribution from the attached secondary amines. With this in mind, we designed a system with three amino substituents for which calculations predict pKa = 7.0 that we suggest as an excellent starting point for a potential pH sensor able to capture solution changes during the transition from neutral towards acidic media.

Reaction Center of Rhodobacter Sphaeroides, a Photoactive Protein for pH Sensing: A Theoretical Investigation of Charge Transport Properties

Featured Application: Bio-electronic devices take advantages of some specific duties of biological matter. The specific ability of some proteins to use sunlight is considered for the realization of photo-electronic devices . Here the focus is on the role of the pH, whose variations seem to affect the protein conductance

Comparison of Magnesium and Titanium Doping on Material Properties and pH Sensing Performance on Sb2O3 Membranes in Electrolyte-Insulator-Semiconductor Structure

In this research, electrolyte-insulator-semiconductor (EIS) capacitors with Sb2O3 sensing membranes were fabricated. The results indicate that Mg doping and Ti-doped Sb2O3 membranes with appropriate annealing had improved material quality and sensing performance. Multiple material characterizations and sensing measurements of Mg-doped and Ti doping on Sb2O3 sensing membranes were conducted, including of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These detailed studies indicate that silicate and defects in the membrane could be suppressed by doping and annealing. Moreover, compactness enhancement, crystallization and grainization, which reinforced the surface sites on the membrane and boosted the sensing factor, could be achieved by doping and annealing. Among all of the samples, Mg doped membrane with annealing at 400 °C had the most preferable material properties and sensing behaviors. Mg-doped Sb2O3-based with appropriate annealing are promising for future industrial ionsensing devices and for possible integration with Sb2O3-based semiconductor devices.

Effects of NH3 Plasma and Mg Doping on InGaZnO pH Sensing Membrane

In this study, the effects of magnesium (Mg) doping and Ammonia (NH3) plasma on the pH sensing capabilities of InGaZnO membranes were investigated. Undoped InGaZnO and Mg-doped pH sensing membranes with NH3 plasma were examined with multiple material analyses including X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and transmission electron microscope, and pH sensing behaviors of the membrane in electrolyte-insulator-semiconductors. Results indicate that Mg doping and NH3 plasma treatment could superpositionally enhance crystallization in fine nanostructures, and strengthen chemical bindings. Results indicate these material improvements increased pH sensing capability significantly. Plasma-treated Mg-doped InGaZnO pH sensing membranes show promise for future pH sensing biosensors.