A Monte Carlo simulation of photon propagation in fluorescent poly(ethylene glycol) hydrogel microsensors

A Monte Carlo simulation of photon propagation through fluorophore-containing poly(ethylene glycol) hydrogel networks is described. Poly(ethylene glycol) (PEG) hydrogel microspheres are being studied for fluorescent biosensing of small molecular weight analytes such as glucose and paraoxon. A computational approach to assess the fluorescent output from these sensors was developed, in particular investigating the impact of sphere characteristics such as size, scattering, and fluorophore concentrations on sensor response. Monte Carlo simulations of both individual spheres and packed sphere beds were developed to model photon propagation through homogeneous, water-swollen PEG hydrogel microspheres with encapsulated fluorescein isothiocyanate (FITC) and tetramethylrhodamine isothiocyanate (TRITC) dyes. Experimental studies using an integrating sphere were conducted to determine the hydrogel optical properties used in the simulation and spectrofluorimetry studies performed to verify assumptions made in the model regarding quantum yield. Changes in fluorescence quantum yield, hydrogel scattering and absorption coefficients (μs and μa), hydrogel scattering anisotropy (g), and depth of the sphere bed were used to predict optimum sphere size, gel chemistry, and collection geometry.