Highly hydrophobic TEMPO-functionalized conducting copolymers for solid-contact ion-selective electrodes.

Solid-contact ion-selective electrodes (SCISEs) emerged as the best electrode embodiment for miniaturized, wearable and disposable sensors for ion/electrolyte measurements in body fluids. The commercialization of inexpensive single-use "calibration-free" electrodes requires large scale manufacturing of electrodes with reproducible calibration parameters, e.g. E0. This is perhaps the most important shortcoming of SCISEs, beside the many advantages over their conventional liquid-contact counterparts. However, adjusting the E0 value for optimal potential stability is challenging for all state-of-the-art solid-contact materials, which may combine several types of transducing mechanism (e.g. capacitive and redox materials or their combination) for enhanced potential stability and analytical performance. Therefore, here we introduce for the first time the galvanostatic intermittent titration technique (GITT) to determine the best preadjusment potential. The proof of concept is shown for a novel type of solid-contact based on the copolymerization of 3,4-ethylenedioxythiophene with perfluorinated alkyl side chain (EDOTF) and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl modified 3,4-ethylenedioxythiophene (EDOT-TEMPO). Such materials that are compliant with local electrodeposition and provide multiple functionalities, i.e. high hydrophobicity by the perfluorinated alkyl side chain, electron-to-ion transduction by the conducting polymer (EDOT) backbone and the confinement of well-defined redox couple (TEMPO), are expected to prevail as solid-contacts.

TEMPO-Functionalized Carbon Nanotubes for Solid-Contact Ion-Selective Electrodes with Largely Improved Potential Reproducibility and Stability.

Solid-contact ion-selective electrodes (SCISEs) can overcome essential limitations of their counterparts based on liquid contacts. However, attaining a highly reproducible and predictable E0, especially between different fabrication batches, turned out to be difficult even with the most established solid-contact materials, i.e., conducting polymers and large-surface-area conducting materials (e.g., carbon nanotubes), that otherwise possess excellent potential stability. An appropriate batch-to-batch E0 reproducibility of SCISEs besides aiding the rapid quality control of the electrode manufacturing process is at the core of their "calibration-free" application, which is perhaps the last major challenge for their routine use as single-use "disposable" or wearable potentiometric sensors. Therefore, here, we propose a new class of solid-contact material based on the covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with a chemically stable redox molecule, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This material combines the advantages of (i) the large double-layer capacitance of MWCNT layers, (ii) the adjustable redox couple ratio provided by the TEMPO moiety, (iii) the covalent confinement of the redox couple, and (iv) the hydrophobicity of the components to achieve the potential reproducibility and stability for demanding applications. The TEMPO-MWCNT-based SC potassium ion-selective electrodes (K+-SCISEs) showed excellent analytical performance and potential stability with no sign of an aqueous layer formation beneath the ion-selective membrane nor sensitivity toward O2, CO2, and light. A major convenience of the fabrication procedure is the E0 adjustment of the K+-SCISEs by the polarization of the TEMPO-MWCNT suspension prior to its use as solid contact. While most E0 reproducibility studies are limited to a single fabrication batch of SCISEs, the use of prepolarized TEMPO-MWCNT resulted also in an outstanding batch-to-batch potential reproducibility. We were also able to overcome the hydration-related potential drifts for the use of SCISEs without prior conditioning and to feature application for accurate K+ measurements in undiluted blood serum.

3D-printed manifold integrating solid contact ion-selective electrodes for multiplexed ion concentration measurements in urine.

Urinalysis is a simple and non-invasive approach for the diagnosis and monitoring of various health disorders. While urinalysis is predominantly confined to clinical laboratories the non-invasive sample collection makes it applicable in wide range of settings outside of central laboratory confinements. In this respect, 3D printed devices integrating sensors for measuring multiple parameters may be one of the most viable approaches to ensure cost-effectiveness for widespread use. Here we evaluated such a system for the multiplexed determination of sodium, potassium and calcium ions in urine samples with ion-selective electrodes based on state of the art octadecylamine-functionalized multi-walled carbon nanotube (OD-MWCNT) solid contacts. The electrodes were tested in the clinically relevant concentration range, i.e. ca. 10-4 - 10-1 mol L-1 and were proven to have Nernstian responses under flow injection conditions. The applicability of the 3D printed flow manifold was investigated through the analysis of synthetic samples and two certified reference materials. The obtained results confirm the suitability of the proposed system for multiplexed ion analysis in urine.

Stimulation of the cyanide-resistant alternative respiratory pathway by oxygen in Acremonium chrysogenum correlates with the size of the intracellular peroxide pool.

The relationship between oxygen input and activity of the cyanide-resistant alternative respiration of submerged cultures of Acremonium crysogenum was investigated. The volumetric oxygen transfer coefficient of the respective cultures correlated positively within almost two ranges of magnitude with the size of the intracellular peroxide pool, which in turn, correlated with the activity of the cyanide-resistant alternative respiratory pathway. Increased aeration also stimulated the glucose uptake rate but had no effect on the total respiration rate or the growth rate. Addition of the lipid peroxyl radical scavenger DL-alpha-tocopherol to A. chrysogenum cultures decreased the rate of intracellular peroxide production as well as glucose uptake. An increase in the cyanide-resistant fraction of total respiration was observed, while growth and the total respiratory activity remained unchanged. We conclude that intracellular peroxides may stimulate the alternative respiration in A. chrysogenum.