A novel pH sensor with application to milk based on electrochemical oxidative quinone-functionalization of tryptophan residues

Construction of an electrochemical pH sensor using one-pot synthesis of a molybdenum diselenide/nitrogen doped graphene oxide screen-printed electrode

In this study, a one-pot synthesis of a molybdenum diselenide/nitrogen-doped graphene oxide (MoSe2/NGO) composite was demonstrated and used for the fabrication of an electrochemical pH sensor. The MoSe2/NGO composite was characterized using powder X-ray diffraction, infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller analysis. The electrochemical behavior at different pH values was determined by recording the open-circuit potential. When applied for pH detection, the MoSe2/NGO modified screen-printed electrode (SPE) showed good linearity with a sensitivity of 61.3 mV pH-1 over a wide pH range of 2-14. In addition, the pH sensor exhibited a remarkably stable response, high reproducibility, and selectivity. The sensor was used to measure the acidity or alkalinity of real food and beverage samples. The results for these samples showed a relative error of less than 10% compared with the results obtained with the commercial pH meter. The portable sensor produced by screen printing electrodes paves the way for the development of simple, cost-effective, real-time, and robust pH sensors for the pH analysis of various sample matrices for clinical diagnostics, biosensing, and cost-effective applications.

Binary RuO2-CuO Electrodes Outperform RuO2 Electrodes in Measuring the pH in Food Samples

Glass electrodes are the only type of pH-sensitive electrodes currently used in the food industry. While widely used, they have several disadvantages, especially in the areas of brittleness and price. Ruthenium(IV) oxide (RuO₂) pH electrodes are a well-known alternative to conventional glass electrodes, providing improved durability and lower price. Nevertheless, partial substitution of RuO₂ with cupric oxide (CuO) would further lower the price and reduce the toxicity of the electrode. In this paper, we present the applicability of RuO₂-CuO electrodes for pH measurement in food samples. The electrodes were fabricated by screen printing and covered with a protective Nafion membrane. In the experiments with food samples, the RuO₂-CuO electrodes outperformed RuO₂ electrodes in measuring the pH with an almost twofold higher rate of accurate measurements. The utilization of CuO for the fabrication of pH electrodes allowed the accurate measurement of pH in a larger variety of food samples without compromising the response time.

Recent Advances in Optical, Electrochemical and Field Effect pH Sensors

Although its first definition dates back to more than a century ago, pH and its measurement are still studied for improving the performance of current sensors in everyday analysis. The gold standard is the glass electrode, but its intrinsic fragility and need of frequent calibration are pushing the research field towards alternative sensitive devices and materials. In this review, we describe the most recent optical, electrochemical, and transistor-based sensors to provide an overview on the status of the scientific efforts towards pH sensing.

Novel Coordination Polymer of Cadmium (II) with L-Tryptophan

A new cadmium (II) polymeric coordination compound with tryptophan (Trp) of general formula {[Cd(L-Trp)₂(H₂O)Cl]∙(Trp)∙(H₂O)}_n was synthesized. The monocrystals of the investigated complex were obtained using the method of slow evaporation. The crystal and molecular structure was determined. The compound was crystallized in the orthorhombic P2₁2₁2₁ space group. The cadmium atom was seven coordinates by two oxygen atoms from one bidentate-chelating carboxylate group of bridging Trp, two oxygen atoms from one bidentate-chelating carboxylate group from a monodentate organic ligand, one oxygen atom of water molecule, one nitrogen atom of the amino group from bridging Trp and one chlorine atom, which means that every tridentate Trp substituent was bridging towards one cadmium atom and bidentate chelating towards one another. The monodentate Trp is a zwitterionic molecule. The coordination led to the formation of 1D supramolecular chains entrapping water and Trp molecules.