Solid-state sensing tip for zinc ion with double parallel optical fibers embedded in fluorescent hydrogel

Abstract

A tip-shaped zinc ion solid-state sensor is made by two parallel optical fibers embedded closely in a sensing hydrogel film. The film is made of poly(2-hydroxyethyl methacrylate) (poly HEMA) hydrogel mixed with the selective fluorescent probe meso-2,6-Dichlorophenyltripyrrinone (TPN-Cl-2) with weight ratio of 0.025 wt%. A 405 nm laser output is sent from one fiber and the 622 nm fluorescence of the doped hydrogel is collected by the second fiber. Each fiber diameter is 370 mu m (core is 300 mu m), whose sum is roughly the tip diameter. The 0.4 cm by 0.5 cm tip has real-time response for zinc ion concentration over 10(-6) M, with marginal signal for 10(-7) M. The tip is inserted inside an oyster and successfully detects the zinc ions, showing that the sensor works in complex body fluid and tolerates certain mechanical stress. To show the potential application for medicine, the sensing film is applied for primary neuronal cultures. We report for the first time zinc ions release at concentration levels 10(-6)-10(-7) M to the medium under stress conditions of ischemia, inflammation, and intoxication. Furthermore, this correlates with the zinc levels detected by biochemical assay. Such sensing tip has great potential for biomedical monitoring ex vivo or in vivo. (C) 2015 Elsevier B.V. All rights reserved.