Optical Sensor for Organic Ammonium Ions and Its Application to Lysine Biosensing

Publisher Summary This chapter discusses an optical sensor for organic ammonium ions and its application to lysine biosensing. The detection scheme is based on the use of lysine decarboxylase immobilized in a flowbed reactor. The organic amine formed by enzymatic action is detected by optical means using a PVC-based optrode membrane containing lipophilic tartrates acting as the cadaverine carrier. Transport of the positively charged cadaverine cation into the membrane is accompanied by a release of a proton from protonated rhodamine dye contained in the membrane. This results in a strong and fully reversible change in the fluorescence properties of the sensing membrane. The major advantage of sensors based on measurement of the amount of organic amine formed in an enzymatic reaction is because of the fact that in many real samples, there is a low and fairly constant background of organic amines. This is in contrast to sensors where transduction based on the measurement of oxygen consumption or carbon dioxide production where the background level of the respective gas has to be kept constant or needs to be measured in an independent assay.