Ratiometric optical fiber sensor for dual sensing of copper ion and dissolved oxygen

This paper develops a new ratiometric optical dual sensor for Cu2+ ions and dissolved oxygen (DO) incorporating a sol-gel matrix doped with palladium tetrakis pentafluorophenyl porphine as the oxygen-sensitive material, CdSe quantum dots as the Cu2+ ion-sensing material, and 7-amino-4-trifluoromethyl coumarin as the Cu2+ /DO practically independent fluorescent dye. The feasibility of coating an optical fiber with the sensing film to fabricate a ratiometric optical fiber dual sensor is investigated. Using an LED with a central wavelength of 405 nm as an excitation source, it is shown that the emission wavelengths of the Cu2+ ion-sensitive, DO-sensitive dye and the reference dye have no spectral overlap and therefore permit Cu2+ ion and DO concentration to be measured using a ratiometric-based method. The ratiometric optical fiber dual sensor has been tested with regard to monitoring different Cu2+ ion (0-10 μM) and DO concentrations (0-38 mg/L). The results show that the luminescence properties of the Cu2+ ion sensor are independent of the presence of the oxygen sensor and have a uniquely good linear response in the 0-10 μM range. The proposed ratiometric sensing approach presented in this study has the advantage of suppressing spurious fluctuations in the intensity of the excitation source.