Chemical Detection by Analyte-Induced Change in Electrophoretic Deposition of Gold Nanoparticles

The electrophoretic deposition (EPD) of citrate-stabilized Au nanoparticles (cit-Au NPs) occurs on indium tin oxide (ITO)-coated glass electrodes upon electrochemical oxidation of hydroquinone (HQ) due to the release of hydronium ions. Anodic stripping voltammetry (ASV) for Au oxidation allows the determination of the amount of Au NP deposition under a specific EPD potential and time. The binding of Cr3+ to the cit-Au NPs inhibits the EPD by inducing aggregation and/or reducing the negative charge, which could lower the effective NP concentration of the cit-Au NPs and/or lower the electrophoretic mobility. This lowers the Au oxidation charge in the ASV, which acts as an indirect signal for Cr3+. The binding of melamine to cit-Au NPs similarly leads to aggregation and/or lowers the negative charge, also resulting in reduction of the ASV Au oxidation peak. The decrease in Au oxidation charge measured by ASV increases linearly with increasing Cr3+ and melamine concentration. The limit of detection (LOD) for Cr3+ is 21.1 ppb and 16.0 ppb for 15.1 and 4.1 nm diameter cit-Au NPs, respectively. Improving the sensing conditions allows for as low as 1 ppb detection of Cr3+. The LOD for melamine is 45.7 ppb for 4.1 nm Au NPs.

Unified pH Measurements of Ethanol, Methanol, and Acetonitrile, and Their Mixtures with Water

Measurement of pH in aqueous-organic mixtures with different compositions is of high importance in science and technology, but it is, at the same time, challenging both from a conceptual and practical standpoint. A big part of the difficulty comes from the fundamental incomparability of conventional pH values between solvents (spH, solvent-specific scales). The recent introduction of the unified pH (pHabs) concept opens up the possibility of measuring pH, expressed as pHabsH2O, in a way that is comparable between solvent, and, thereby, removing the conceptual problem. However, practical issues remain. This work presents the experience of the authors with measuring pHabsH2O values in mixtures of methanol, ethanol, and acetonitrile, with water, but without the presence of buffers or other additives. The aim was to assigned pHabsH2O values to solvent–water mixtures using differential potentiometry and the ‘pHabs-ladder’ method. Measurements were made of the potential difference between glass electrodes immersed in different solutions, separated by an ionic liquid salt bridge. Data were acquired for a series of solutions of varying solvent content. This work includes experiences related to: a selection of commercial electrodes, purity of starting material, and comparability between laboratories. Ranges of pHabsH2O values for selected compositions of solvent–water mixtures are presented.

Development of stretchable metallic glass electrodes

Stretchable metallic glass electrodes achieved by folding apporoach.

Tripartite Mechanism of Neural Memory: Proof-of-Concept with Neuromimetic Impedence Electrodes

The idea that neural signaling is the basis of mental processes has a long history. We graphically summarize salient developments in the neurobiology of signaling, as a Timeline. In particular, we review the “tripartite mechanism” of neural memory, which centers on the interactions between a neuron with its surrounding extracellular matrix (nECM) doped with metals and neurotransmitters (NTs). Essentially, the neuron employs the nECM as its “memory material”, wherein it uses dopants to encode cognitive units of information (termed “cuinfo”). The NTs, which elicit bodily reactions (feelings), also encode past feelings as emotions, which “color” mental states in real-time and in memory. In the interest of developing experimental tests of the tripartite mechanism, impedance glass electrodes were covalently coated with an exemplar NT (oxytocin) or a sulfated tetra-saccharide analog of the nECM, were constructed and tested. The two types of coated, neuro-mimetic electrodes, termed “neulectrodes”, were capable of detecting metals, such as Hg+2, Pb+2, Cd+2, Cu+2, and Zn+2 with very high selectivity and sensitivity. The “neulectrodes” demonstrated that the chemodynamic interactions of metal cations with NTs or nECM-saccharide analogues can translate into electrodynamic signals. They experimentally validate the concept of the tripartite mechanism that underlies the chemo-electric encoding of neural memory.

Symmetric Potentiometric Cells for the Measurement of Unified pH Values

A unified pH scale of absolute values (pHabs scale) enables the comparison of acidities in different solvents. To date, very few different experimental setups have been used for the measurement of values on this scale. The article describes the design and performance of the different symmetric cells used for unified pH measurement by several institutions. Well-established and reliable standard aqueous buffer solutions are the first step of method validation necessary to achieve a robust metrological level for more complex media. The pH of aqueous standard buffers was measured by differential potentiometry, where the potential between two glass electrodes is measured directly. All the tested electrochemical cells prove to be suitable for unified pH measurements. This validation highlights that the method is, to a large extent, independent of the used equipment, including the cell geometry. The inherent symmetry of the cell design helps to reduce the experimental workload and improve the accuracy of obtained results.

Potentiometric E-Tongue System for Geosmin/Isoborneol Presence Monitoring in Drinkable Water

A potentiometric E-tongue system based on low-selective polymeric membrane and chalcogenide-glass electrodes is employed to monitor the taste-and-odor-causing pollutants, geosmin (GE) and 2-methyl-isoborneol (MIB), in drinkable water. The developed approach may permit a low-cost monitoring of these compounds in concentrations near the odor threshold concentrations (OTCs) of 20 ng/L. The experiments demonstrate the success of the E-tongue in combination with partial least squares (PLS) regression technique for the GE/MIB concentration prediction, showing also the possibility to discriminate tap water samples containing these compounds at two concentration levels: the same OTC order from 20 to 100 ng/L and at higher concentrations from 0.25 to 10 mg/L by means of PLS-discriminant analysis (DA) method. Based on the results, developed multisensory system can be considered a promising easy-to-handle tool for express evaluation of GE/MIB species and to provide a timely detection of alarm situations in case of extreme pollution before the drinkable water is delivered to end users.

Effect of Temperature on pH Meter Based on Arduino Uno With Internal Calibration

pH Meter is a device used to express the level of acidity or basicity possessed by a substance or solution. Normal pH has a value of 7 while the pH value> 7 indicates that the substance has alkaline properties while the pH value <7 indicates acidic properties. pH 0 shows a high degree of acidity, and pH 14 shows the highest degree of alkalinity. pH Meter reads the pH and temperature values ​​in a sample. The author uses glass electrodes as a pH sensor, DS18B20 as a temperature sensor and LCD to make pH and temperature values. This module is equipped with an internal calibration that is used to set the module to read the pH value properly and correctly using a pH buffer and equipped with internal storage and this module facilitates battery usage. Based on pH measurements on the module the error value in buffer 4 calibration is 5.39%, in buffer 7 is 1.76%, in buffer 10 is 1.04%. The highest error value in the measurement sample is 3.54% and the lowest error value is 0.03%. The temperature of the sample is very influential on the reading of the pH value because the higher the temperature the pH value also increases even though it is not so significant.