Evaluation of microparticle materials for enhancing the performance of fluorescence lifetime based optrodes

Fiber optic based sensors have many advantages over electrochemical sensors, and as a result have broad application for sensing in agriculture, basic biology, the environment, and medicine. An important component of a fiber optic sensor is the sensing element, usually a solid-state matrix containing the analyte specific fluorescent dye, immobilized on an optical fiber. The fluorescence output of the dye can be calibrated to analyte concentration based on intensity or lifetime. The membrane matrix immobilizes and entraps the fluorescent dye molecules by providing the mechanical support at the optrode tip. The present study used micro- and nanoparticles of TiO2 and microparticles of different materials (BaSO4, Cr, CuO, diamond, Au, PbO and ZnS) to investigate the phenomena underlying the role of accessory materials for optrode performance enhancement. We found that 2 μm particles amplified fluorescence intensity better than 10–150 nm particles. Materials with high refractive indexes performed better, provided that they have low absorbance across the visible region. Microparticles with either high refractive indices or high reflectance will amplify the fluorescence output, but microparticles with both properties enhance optrode performance at lower dye concentrations. The results of these experiments have allowed us to engineer membrane microparticle content to optimize a platinum-tetra-fluoro-phenyl-porphyrin (PtTFPP) O2 optrode.