Nanoscale potassium sensing based on valinomycin-anchored fluorescent gold nanoclusters.

Gold nanoclusters are a smart platform for sensing potassium ions (K+). They have been synthesized using bovine serum albumin (BSA) and valinomycin (Val) to protect and cap the nanoclusters. The nanoclusters (Val-AuNCs) produced have a red emission at 616 nm under excitation with 470 nm. In the presence of K+, the valinomycin polar groups switch to the molecule's interior by complexing with K+, forming a bracelet structure, and being surrounded by the hydrophobic exterior conformation. This structure allows a proposed fluorometric method for detecting K+ by switching between the Val-AuNCs' hydrophilicity and hydrophobicity, which induces the aggregation of gold nanoclusters. As a result, significant quenching is seen in fluorescence after adding K+. The quenching in fluorescence in the presence of K+ is attributed to the aggregation mechanism. This sensing technique provides a highly precise and selective sensing method for K+ in the range 0.78 to 8 µM with LOD equal to 233 nM. The selectivity of Val-AuNCs toward K+ ions was investigated compared to other ions. Furthermore, the Val-AuNCs have novel possibilities as favorable sensor candidates for various imaging applications. Our detection technique was validated by determining K+ ions in postmortem vitreous humor samples, which yielded promising results.

Equipment-Free Detection of K+ on Microfluidic Paper-Based Analytical Devices Based on Exhaustive Replacement with Ionic Dye in Ion-selective Capillary Sensors.

A distance-based analysis of potassium ion (K+) is introduced that is performed on a microfluidic paper-based analytical device (µPAD) coupled to an ion-selective capillary sensor. The concept is based on two sequential steps, the selective replacement of analyte ion with an ionic dye, and the detection of this dye in a distance-based readout on paper. To achieve the first step, the capillary sensor holds a poly(vinyl chloride) (PVC) membrane film layer plasticized by dioctyl sebacate (DOS) that contains the potassium ionophore valinomycin, a lipophilic cation-exchanger and the ionic indicator Thioflavin T (ThT) on its inner wall. Upon introduction of the sample, K+ in the aqueous sample solution is quantitatively extracted into the film membrane and replaced with ThT. To convert the ion exchange signal into a distance-based analysis, this solution was dropped onto the inlet area of a µPAD to flow the ThT along a channel defined by wax printing, resulting in the electrostatic binding of ThT to the cellulose carboxylic groups. The initial amount of K+ determines the amount of ThT in the aqueous solution after ion-exchange, and consequently the distance of ThT-colored area reflects the sample K+ concentration. The ion exchange reaction was operated in a so-called "exhaustive sensing mode" and gave a distinct response in a narrow range of K+ concentration (1-6 mM) that cannot be achieved by the classical optode sensing mode. The absence of hydrogen ions from the equilibrium competition of the capillary sensor contributed to a complete pH-independence, unlike conventional optodes that contain a pH sensitive indicator. A very high selectivity for K+ over Na+ and Ca2+ has been confirmed in separate solutions and mixed solutions tests. K+ measurements in pooled serum samples at concentrations between 2 and 6 mM are successfully demonstrated on a temperature controlled support.

30 s Response Time of K+ Ion-Selective Hydrogels Functionalized with 18-Crown-6 Ether Based on QCM Sensor.

Potassium detection is critical in monitoring imbalances in electrolytes and physiological status. The development of rapid and robust potassium sensors is desirable in clinical chemistry and point-of-care applications. In this study, composite supramolecular hydrogels are investigated: polyethylene glycol methacrylate and acrylamide copolymer (P(PEGMA-co-AM)) are functionalized with 18-crown-6 ether by employing surface initiated polymerization. Real-time potassium ion monitoring is realized by combining these compounds with quartz crystal microbalance. The device demonstrates a rapid response time of ≈30 s and a concentration detection range from 0.5 to 7.0 × 10-3 m. These hydrogels also exhibit high reusability and K+ ion selectivity relative to other cations in biofluids such as Na+ , NH4+ , Mg2+ , and Ca2+ . These results provide a new approach for sensing alkali metal ions using P(PEGMA-co-AM) hydrogels.