Monte carlo modeling for implantable fluorescent analyte sensors

Monte Carlo simulation of photon propagation through human skin and interac tion with a subcutaneous fluorescent sensing layer is presented. The algori thm will facilitate design of an optical probe for an implantable fluoresce nt sensor, which holds potential for monitoring many parameters of biomedic al interest. Results are analyzed with respect to output light intensity as a function of radial distance from source, angle of exit for escaping phot ons, and sensor fluorescence (SF) relative to tissue autofluorescence (AF), A sensitivity study was performed to elucidate the effects on the output d ue to changes in optical properties, thickness of tissue layers, thickness of the sensor layer, and both tissue and sensor quantum yields. The optical properties as well as the thickness of the stratum corneum, epidermis, (ti ssue layers through which photons must pass to reach the sensor) and the pa pillary dermis (tissue distal to sensor) are highly influential. The spatia l emission profile of the SF is broad compared that of the tissue fluoresce nce and the ratio of sensor to tissue fluorescence increases with distance from the source. The angular distribution of escaping photons is more conce ntrated around the normal for SF than for tissue AF, The information gained from these simulations will be helpful in designing appropriate optics for collection of the signal of interest.