Response Patterns of Chromoionophore-Based Bulk Optodes Containing Lipophilic Electrolytes: Toward Background-Independent pH-Sensing

Despite a number of advantages of ion-selective optical sensors (optodes), their practical application is limited by their response mechanism, which leads to the dependence of the signal on the activity of two ions (analyte ion and the so-called reference ion) in the solution at the same time. Here, we show that the introduction of a lipophilic electrolyte into the polymeric optode membrane allows assessing the ionic activity of H+ cations regardless of the concentration of the background electrolyte containing a hydrophilic cation, with NaCl as an example of such an electrolyte. For the first time, the applicability of this approach is proven theoretically utilizing the numerical simulation of optode response. A correlation between the interfacial potential stability and the single-ion optical response is established. The predicted optical response is independent of background cation concentration to a significant extent. Theoretical conclusions are supported by experimental data obtained with chromoionophore-based optodes doped with various lipophilic electrolytes, including ionic liquids, by thin-film spectrophotometry and macrophotography coupled with digital color analysis. Most of the experimental sensor characteristics, such as the response range and its median, as well as its independence from the background electrolyte concentration are in quantitative agreement with the proposed theoretical description.

Photoelectric current as a highly sensitive readout for potentiometric sensors

The photocurrent at a working electrode coated with a ZnSe/r-GO composite can be modulated by a polymeric membrane ion-selective electrode that works as a reference electrode.

Determination of blood potassium using a fouling-resistant PVDF–HFP-based optode

Monitoring potassium levels in blood is a significant aspect of clinical analysis. Here, we report a system for determination of potassium in blood which has the additional advantage of being blood-fouling resistant for safe and easy in situ sensing.

Ionophore-based optical sensors

This review provides an overview of the key aspects of designing ionophore-based optical sensors (IBOS). Exact response functions are developed and compared with a simplified, generalized equation. We also provide a brief introduction into less established but promising working principles, namely dynamic response and exhaustive exchange. Absorbance and fluorescence are the main optical readout strategies used in the evaluation of a sensor response, but they usually require a robust referencing technique for real-world applications. Established referencing schemes using IBOS as well as those from other optical sensors are also discussed. Finally, the power of recently developed photoresponsive ion extraction/release systems is outlined and discussed in view of dynamically switchable IBOS or regenerative exhaustive exchange IBOS.

Fluorescence lifetime-based sensing of sodium by an optode

We report a 1,2,3-triazol fluoroionophore for detecting Na⁺ that shows in vitro enhancement in Na⁺-induced fluorescence intensity and decay time.