Portable Diagnosis Method of Hyperkalemia Using Potassium-Recognizable Poly(<i>N</i>‑isopropylacrylamide-<i>co</i>-benzo-15-crown-5-acrylamide) Copolymers

Abstract

A novel, simple, portable, and low-cost method for diagnosis of hyperkalemia by using K⁺-recognizable poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-benzo-15-crown-5-acrylamide) [poly­(NIPAM-<i>co</i>-B15C5Am)] linear copolymer as indicator is presented in this work. The pendent 15-crown-5 units in the linear copolymers can selectively and specifically recognize K⁺ to form stable 2:1 “sandwich” host–guest complexes, which cause the copolymer chains to change from the hydrophilic state to the hydrophobic state isothermally, whereas other tested metal ions (e.g., Li⁺, Na⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, Fe³⁺, Pb²⁺, Cd²⁺, Cr³⁺) cannot be recognized. With increasing the 15-crown-5 content or the K⁺ concentration, the poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymers exhibit higher sensitivity to K⁺. The hyperkalemia can be simply diagnosed by observing the K⁺-induced optical transmittance change of human blood samples with poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer as an indicator. Normal blood samples with low potassium level containing the poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer are almost transparent since the copolymer is hydrophilic and soluble at the operating temperature. However, severe hyperkalemia samples with high potassium level become completely cloudy since the copolymer is hydrophobic and insoluble at this temperature. The presented diagnosis method with poly­(NIPAM-<i>co</i>-B15C5Am) linear copolymer as indicator is quite simple and low-cost, and it would bring a new candidate material to design simple and portable tools for diagnosis of hyperkalemia in the general population. Moreover, the results in this work provide valuable guidance for building novel poly­(NIPAM-<i>co</i>-B15C5Am)-based artificial K⁺-recognizable “smart” or “intelligent” systems in various application fields