Measuring and controlling local chemical concentrations in tissue is key for understanding fundamental biological processes as well as for detecting and monitoring diseases. Optical methods to modulate and monitor local chemical signaling are attractive because light can be delivered at a distance, easily controlled, and focused. Optical approaches are consequently used in many applications including optogenetics, photodynamic therapy, and infection detection. However, delivering light to specific sites though thick tissue is challenging because optical absorption and scattering attenuate the signal and cause it to spread out over a large region. One method to address these limitations is to use nanophosphors as an X-ray excited local light source within the tissue. X-ray radiation penetrates through deep tissue, has a much smaller scattering cross-section than visible light, allowing ballistic propagation through tissue. Using Monte Carlos simulations of X-ray and optical photon propagation through tissue, we discuss the tradeoffs between X-ray dose, phosphor concentration, spatial resolution, and signal intensity for sensing and actuation applications. We also show applications for monitoring local drug release and detecting local pH changes during implant-associated infection.

Radioluminescent phosphors as local light sources within tissue: Opportunities and challenges for chemical sensing and control

256th National Meeting (2018)

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