The ability to measure pH on a cellular scale has a wide range of potential use in biology and medicine. In this paper, we describe our work on creating a nanoscale pH sensor via the conjugation of upconverting nanoparticles (UCNPs) with a fluorescent dye. We will the explain the origin of the optical pH sensitivity, the conjugation procedure, as well as the various measurement techniques used to confirm the sensitivity. These nanoparticles allow simple optical sensing of pH without complicated intensity calibration process and could thus be widely applicable to many complex biological systems.
Law enforcement officers and public safety personnel are a critical component of the Global Nuclear Detection Architecture, and would benefit from additional opportunities to train for this mission in realistic threat scenarios. Physical Sciences Inc. (PSI) is developing a Virtual Source Training Toolkit (VSTT) system capable of reproducing the response of handheld radiation detectors to a virtual source in a complex occlusion and shielding environment. The toolkit will allow additional low-cost training opportunities for these officers inside operationally relevant public areas in order to reduce the time required to detect and localize a realistic radiological threat. The main components of the VSTT are a user position estimation system and a radiation propagation algorithm. Both algorithms operate at 10 Hz update rate on a handheld Android smart device that simulates the user interface of a radiation detector. The user position and orientation are determined through a Bayesian fusion process between the smart phone IMU measurements and range estimates to Bluetooth beacons. The radiation propagation algorithm simulates both attenuation and scattering of radiation between the programmed virtual source position and the user’s estimated position. The VSTT has been demonstrated to provide an average localization error < 1.2 m while traversing a complex interior space including walls and magnetic perturbations. The simulated radiation spectra achieve Spectral Angle Mapping values < 0.93 between simulated and measured source configurations through multiple shielding materials and thicknesses. In a series of experiments, an operator is able to rapidly localize a virtual source using a prototype VSTT.