Abstract
We report on a method for selective optical sensing and imaging of potassium ions using a sandwich assembly composed of layers of photonic crystals and an ion-selective membrane. This represents a new scheme for sensing ions in that an ionic strength-sensitive photonic crystal hydrogel layer is combined with a K+-selective membrane. The latter consists of plasticized poly(vinyl chloride) doped with the K+-selective ion carrier, valinomycin. The film has a red color if immersed into plain water, but is green in 5 mM KCl and purple at KCl concentrations of 100 mM or higher. This 3D photonic crystal sensor responds to K+ ions in the 1 to 50 mM concentration range (which includes the K+ concentration range encountered in blood) and shows high selectivity over ammonium and sodium ions. Sensor films were also imaged with a digital camera by exploiting the RGB technique.
Highlights
Monitoring of potassium ions is of large interest in point-of-care diagnostics on a daily basis, because it is a highly significant parameter for recognizing the occurrence of various kinds of infarction
A large variability of the concentration of K+ is indicative of a large number of diseases, for example cardiac arrhythmia or myasthenia [7], alcoholism, diabetes, cancer and others [8]
K+ and to respond to K+ over a wide concentration range that covers the level of K+ encountered in whole blood. We show that such sensor films can be imaged using either a microscope or a digital camera
Summary
Potassium ions govern numerous physiological processes [1], such as the control of blood pressure, nerve signal transmission and muscular strength [2,3]. They regulate the growth of cells [4], affect endothelial function [5] and maintain a concentration gradient (and, the Donnan potential). The determination of potassium concentration [K+], is carried out on a large scale in clinical labs. The [K+] typically is 150 mM, while it is only 4 mM in the extracellular space, for example in serum [9]
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