Possibilities and limitations of continuous thyroxine measurement in an optode using the principle of homogeneous fluoroimmunoassay

Abstract

An “optode,” which combines the properties of a fluorescence cuvette with those of a dialysis cell, has been tested for its applicability to continuous hormone measurement, by using thryoxine (T₄) and its specific carrier, thyroxine binding globulin (TBG). The binding of T₄ was monitored by measuring its quenching effect on the fluorescence of the protein.

It was demonstrated that it was not feasible to carry out measurements under equilibrium conditions mainly because of the slow rate of dissociation of the TBG-T₄ complex, once formed. In contrast, the values of the slope of the quench versus time graph, obtained under dynamic conditions, showed good correlation with the concentration of T₄ and could, therefore, be used to measure the concentration of T₄ in the sample solution. However, the utility of this method is limited by progressive saturation of the binder.