Fabrication, Potentiometric Characterization, and Application of Screen-Printed RuO2 pH Electrodes for Water Quality Testing

Direct electrochemical sensing of ampicillin in aqueous media by a ruthenium oxide electrode decorated with a molecularly imprinted polymer

Ampicillin (AMP) ranks third among the top ten most frequently sold antibiotic combinations globally, raising concerns due to its extensive use. Improper disposal practices in agriculture, aquaculture, and healthcare have led to environmental contamination of water sources with elevated AMP levels. Current methods for detecting such contamination are costly, require sophisticated equipment, and depend on skilled personnel and unstable natural receptors. To address these limitations, we introduce AMP sensor for direct electrochemical detection of AMP in aqueous media. This sensor employs a molecularly imprinted polymer (MIP) integrated with a ruthenium oxide electrode, which serves as both a substrate transducer and an internal redox-active probe, eliminating the need for an external probe solution. The sensor exhibited a low limit of detection (LOD) of 6 nM and high recovery rates (98-114 %) in pond water samples, highlighting its sensitivity and practical application. This study demonstrates the potential of MIP-based electrochemical sensors for affordable, rapid, and accurate detection of antibiotic contaminants in water, contributing to improved tools for environmental and public health protection.

Targeting JAK/STAT3 in glioblastoma cells using an alginate-PNIPAm molecularly imprinted hydrogel for the sustained release of ruxolitinib

Glioblastoma (GBM) is a notoriously aggressive primary brain tumor characterized by elevated recurrence rates and poor overall survival despite multimodal treatment. Local treatment strategies for GBM are safer and more effective alternatives to systemic chemotherapy, directly tackling residual cancer cells in the resection cavity by circumventing the blood-brain barrier. Molecularly imprinted polymers (MIPs) are promising drug delivery systems due to their high-affinity binding cavities that enable tailored release kinetics. This study reports the development of a semi-synthetic polysaccharide MIP-based hydrogel intended for the post-surgical management of GBM. The biodegradable implant, made of calcium-crosslinked alginate-poly(N-isopropylacrylamide) graft copolymer, was designed for the sustained release of ruxolitinib (RUX) in the resection cavity, targeting the Janus kinase/Signal Transducer and Activator of Transcription-3 signaling pathway. The molecularly imprinted hydrogel demonstrated thermo-thickening and shear-thinning behavior, high entrapment efficiency of RUX (84.59 ± 0.73 %), and sustained release over 14 days, underscoring the advantages that molecular imprinting of the alginate matrix provides compared to conventional MIPs. The dose-dependent inhibitory effects of the imprinted hydrogel against U251 and A172 GBM cells were demonstrated by increased apoptosis, reduced confluence, colony formation, and delayed wound healing, whereas the non-imprinted hydrogel was biocompatible. The MIP hydrogel could be a safe and effective GBM treatment.

pH Sensing Properties of Co3O4-RuO2-Based Electrodes and Their Application in Baltic Sea Water Quality Monitoring

Water is critical for the sustenance of life and pH is an important parameter in monitoring its quality. Solid-state pH sensors provide a worthy alternative to glass-based electrodes due to many advantages such as low cost, longer shelf life, simpler manufacturing, easier operation, miniaturization, and integration into electronic systems. Cobalt oxides are relatively cheaper and more abundantly available than ruthenium oxide. This work aims to reduce the environmental impact of screen-printed pH sensors by mixing Co3O4 and RuO2 in five molar proportions (30%, 40%, 50%, 60%, and 70%) and investigating the influence of oxide proportions on the pH-sensing properties of the resulting composition using potentiometric characterization, scanning electron microscopy, X-ray diffraction, surface profilometry, and electron dispersive spectroscopy. Although all the developed compositions showed super- or near-Nernstian sensitivity with good linearity, the sensors based on 50 mol% Co3O4-50 mol% RuO2 were the best due to superior sensitivity, selectivity, and stability. Fabricated sensors were applied in real-life environmental, municipal, and commercial water samples, including those from various depths in the Baltic Sea, and were found to be accurate in comparison to a glass electrode.

Preparation and application of a Cu-doped antimony electrode to improve the performance of pH measurement in seawater

Antimony-based electrodes are widely used in various fields for pH detection due to their low cost. However, their application in the marine environment is significantly hampered by the significant potential drift observed in seawater pH measurements. This study focuses on enhancing the stability of a pure antimony electrode by doping various amounts of copper without compromising its pH response. A series of electrochemical tests demonstrated that the fabricated alloy electrodes exhibited excellent pH response characteristics, including sensitivity, ion selectivity, response time, reversibility, and temperature coefficients. Moreover, the alloy electrodes were more resistant to corrosion than the pure antimony electrode, thereby guaranteeing the stability. Notably, the alloy electrodes containing 63 at% and 70 at% antimony exhibited superior electrochemical characteristics. The surface analysis elucidated that the alloy electrode had reduced oxidation, surface cracks and antimony peeling compared to the pure antimony electrode. Furthermore, the prepared alloy electrodes exhibited excellent pH response and stability in simulated high-salinity seawater and real seawater. The above results highlight that doping cheap copper into antimony can improve the electrode stability by enhancing the corrosion resistance and slowing down the oxidation rate, thus enabling reliable long-time operation in a relatively stable state. These findings provide experimental support for developing novel pH electrodes based on non-noble metals for use in challenging environments such as seawater.

Integrated pH Sensors Based on RuO2/GO Nanocomposites Fabricated Using the Aerosol Jet Printing Method

An aerosol jet printing (AJP) process for depositing ruthenium dioxide (RuO2) as a promising material for pH sensing is reported. Graphene oxide (GO) with a large surface area was used for the in situ sol-gel deposition of RuO2 nanoparticles on its surface. The cosolvent ratio and solid loading of the solution are adjusted to form a printable and stable ink. The monodispersed aerosol was atomized on the surface of the screen-printed carbon electrode in order to develop an integrated pH sensor. The RuO2-GO pH sensor demonstrates excellent performance, with a rapid response time of less than 5 s and high sensitivity in the pH range of 4-10. Compared to traditional carbon electrodes, the RuO2-GO sensor shows up to four times higher sensitivity. The increased sensitivity is a result of the consistent attachment of small-crystallized RuO2 nanoparticles onto the surface of GO sheets, leading to a synergistic effect. Thanks to the AJP method as a facile and cost-effective integration technique, the fabricated electrodes can serve as an alternative to traditional rigid pH electrodes for accurate pH measurement.

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.

Fabrication and Optimization of Nafion as a Protective Membrane for TiN-Based pH Sensors

In this study, a solid-state modified pH sensor with RF magnetron sputtering technology was developed. The sensor consists of an active electrode consisting of a titanium nitride (TiN) film with a protective membrane of Nafion and a reference glass electrode of Ag/AgCl. The sensitivity of the pH sensor was investigated. Results show a sensor with excellent characteristics: sensitivity of 58.6 mV/pH for pH values from 2 to 12, very short response time of approximately 12 s in neutral pH solutions, and stability of less than 0.9 mV in 10 min duration. Further improvement in the performance of the TiN sensor was studied by application of a Nafion protective membrane. Nafion improves the sensor sensitivity close to Nernstian by maintaining a linear response. This paves the way to implement TiN with Nafion protection to block any interference species during real time applications in biosensing and medical diagnostic pH sensors.

Highly Sensitive and Selective Sol-Gel Spin-Coated Composite TiO2-PANI Thin Films for EGFET-pH Sensor

A highly selective and sensitive EGFET-pH sensor based on composite TiO2-PANI had been developed in this work. A sol-gel titanium dioxide (TiO2) and the composite of TiO2 with semiconducting polyaniline (PANI) were deposited using a simple spin-coating method on an indium tin oxide (ITO) substrate. The films have been explored as a sensing electrode (SE) of extended gate field-effect transistor (EGFET) for pH applications in the range of pH 2 to 12. The pH sensitivities between TiO2, TiO2-PANI bilayer composite, and TiO2-PANI composite thin films were discussed. Among these, the TiO2-PANI composite thin film showed a super-Nernstian behavior with high sensitivity of 66.1 mV/pH and linearity of 0.9931; good repeatability with a standard deviation of 0.49%; a low hysteresis value of 3 mV; and drift rates of 4.96, 5.54, and 3.32 mV/h in pH 4, 7, and 10, respectively, for 6 h. Upon applying the TiO2-PANI composite as the SE for nitrate measurement, low sensitivity of 12.9 mV/dec was obtained, indicating that this film is a highly selective sensing electrode as a pH sensor. The surface morphology and crystallinity of the thin films were also discussed.