Fiber Optic Sensor for Ca2+ Based on an Induced Change in the Conformation of the Protein Calmodulin

Abstract

A fiber optic sensor that exploits the natural selectivity of the Ca2+-binding protein calmodulin (CaM) is described. In this sensor, a dialysis membrane is used to entrap a fluorescein-labeled CaM (F-CaM) solution at the common end of a bifurcated fiber optic bundle. Ca2+ ions in a sample solution can diffuse through the membrane and bind to the F-CaM. Upon binding with Ca2+, CaM undergoes a conformational change that induces a change in the fluorescence of the attached fluorescein tag. This change in fluorescence can be related to the concentration of Ca2+ in the sample solution. The detection limit for the sensor is 5 × 10−8 M Ca2+. The sensor has no interference by Mg2+ at concentrations as high as 10−2 M. © 1994, American Chemical Society. All rights reserved.