Optimization of the FRET De-Excitation Lifetime Based Optical Dissolved Ammonia Sensor

Forster or Fluorescence Resonance Energy Transfer (FRET) is a distance-dependent interaction between the electronic excited states of two dye molecules (henceforth referred to as 'Donor' and 'Acceptor') in which the de-excitation of fluorophore's Donor is done by the means of dipole-dipole interaction between the Donor and Acceptor without emission and absorption of photon. The efficiency of the energy transfer of any FRET molecular system is governed by three major parameters: intermolecular distance, spectrum compatibility, and Donor's quantum yield. In this work, the inter-molecular distances of Donor-Acceptor pairs of a lifetime based optical dissolved ammonia sensor were characterized by varying the ratio of both molecules' concentration. The efficiency of the de-excitation then will be calculated by using phase fluorometry method. The optimization of the dyes' concentration has improved the efficiency of the FRET de-excitation at 82%. This work demonstrates that the need of characterization of the inter-molecular distances of Donor-Acceptor pairs in any FRET system in order to achieve the optimum de-excitation efficiency.