A ruthenium oxide (RuOx) sensor for potentiometric pH sensing is currently being developed for organs-on-chip purposes. The sensor was fabricated from a Ru(OH)3 precursor, resulting in RuOx nanorods after heating. An open-circuit potential of the RuOx electrode showed a near-Nernstian response of −58.05 mV/pH, with good selectivity against potentially interfering ions (lithium, sulfate, chloride, and calcium ions). The preconditioned electrode (stored in liquid) had a long-term drift of −0.8 mV/h, and its response rate was less than 2 s. Sensitivity to oxygen was observed at an order of magnitude lower than other reported metal-oxide pH sensors. Together with miniaturizability, the RuOx pH sensor proves to be a suitable pH sensor for organs-on-chip studies.

In vitro studies which focus on cellular metabolism can benefit from time-resolved readouts from the living cells. pH and O2 concentration are fundamental parameters upon which cellular metabolism is often inferred. This work demonstrates a novel use of a ruthenium oxide (RuO x ) electrode for in vitro studies. The RuO x electrode was characterized to measure both pH and O2 using two different modes. When operated potentiometrically, continuous pH reading can be obtained, and O2 concentration can be measured chronoamperometrically. In this work, we demonstrate the use of the RuO x electrodes in inferring two different types of metabolism of human pluripotent stem cell-derived cardiomyocytes. We also show and discuss the interpretation of the measurements into meaningful extracellular acidification rates and oxygen consumption rates of the cells. Overall, we present the RuO x electrode as a versatile and powerful tool in in vitro cell metabolism studies, especially in comparative settings.

Online, on-chip measurement of nitric oxide (NO) in organ-on-chip devices is desired to study endothelial (dys) function under dynamic conditions. In this work, ruthenium oxide (RuOx) is explored as an amperometric NO sensor and its suitability for organ-on-chip applications. For testing purposes, diethylamine NONOate was used as chemical NO donor. The NONOate's NO generation and electrochemical oxidation of generated NO were confirmed by real-time electrochemical/mass-spectrometry. Using RuOx nanorods electrodes, we show that NO oxidation occurred at a lower onset potential (+675 mV vs. Ag/AgCl) than on bare Pt electrode (+800 mV vs. Ag/AgCl). Due to NO adsorption on the RuOx surface, NO oxidation also delivered a higher current density (33.5 nA.μM − 1 . cm -2 ) compared to bare Pt (19.6 nA.μM − 1 . cm -2 ), making RuOx nanorods a favourable electrode for NO sensing applications. The RuOx electrode's suitability for organ-on-chip applications was successfully tested by using the electrode to detect a few micromolar concentration of NO generated by endothelial cell culture. Overall, the RuOx nanorods proved to be suitable for organ-on-chip studies due to their high sensitivity and selectivity. Our chip-integrated electrode allows for online NO monitoring in biologically relevant in vitro experiments.

Antioxidants are molecules that neutralize reactive oxygen species in the human body, reportedly reducing the risk of cancer and cardiovascular diseases. With multiple dietary products being advertised by their assumed high antioxidant concentration, the need for a proper way of analyzing antioxidant containing beverages becomes apparent.In this research, the antioxidant nature of teas, wines and (superfood) juices is investigated using staircase voltammetry (SV). A new parameter is proposed and evaluated to characterize the antioxidant nature, including its antioxidant capacity and activity: the Antioxidant Index (AI).AI showed green tea to have the best antioxidant nature of teas and red wine to be a better antioxidant than white wine. Superfoods did not show better antioxidant behavior than non-superfoods. AI proved to be a promising way of investigating the antioxidant nature of beverages.

A ruthenium oxide (RuOx) electrode is being developed as potentiometric pH sensor for organs-on-chip applications. Open-circuit potential (OCP) of the RuOx electrode showed a response of −58.05 mV/pH, with no cross-sensitivity to potentially interfering/complexing ions (tested were lithium, sulfate, chloride, and calcium ions). Similar response was observed in complex biological medium. The electrode stored in liquid had a long-term drift of −0.8 mV/hour (corresponding to ΔpH of 0.013/hour) and response time in complex biological medium was 3.7 s. Minimum cross-sensitivity to oxygen was observed as the OCP shifted ~3 mV going from deoxygenated to oxygenated solution. This response is one magnitude lower than previously reported for metal- oxide pH sensors. Overall, the RuOx pH sensor has proven to be a suitable pH sensor for organs- on-chip applications.