Fluorescence quenching by polystyrene microspheres in UV-visible and NIR tissue-simulating phantoms.

Tissue-simulating phantoms are widely used for controlled studies of photon transport in turbid media. Here, we describe how polystyrene microspheres, which are often used to simulate optical scattering in such phantoms, can reduce fluorophore quantum yield via collisional quenching. We report studies on UV-visible (fluorescein-based) and NIR (IR125-based) phantoms with differing fluorophore and scatterer concentrations, as well as differing microsphere sizes. Results consistent with the Stern-Volmer relation suggest that the fluorophore intrinsic excited-state lifetime decreased due to collisional quenching from polystyrene microspheres and that the quenching efficiency was dependent on the concentration ratio of fluorophores to microspheres. Lifetime decreases ranging from 10-35% (20%) were measured for fluorescein-based (IR 125-based) phantoms. Since polystyrene microspheres are commonly used in tissue-simulating phantoms for quantitative studies of fluorescence light propagation, their quenching effects on fluorescence intensities may be difficult to separate from intensity losses attributed to optical absorption and scattering in the phantom unless fluorescence lifetime measurements are performed simultaneously.