S17-440 Upconverting Nanoparticles as In Vivo and In Situ Optical Electric Field Sensors This nanoparticle platform for electric field detection is the first inorganic platform to use both intensity and spectro-ratiometric (relative color change) readout for the determination of local electric fields in vitro, in vivo, and in situ. Randy Mehlenbacher Alice Lay Rea Kolbl Miriam Goodman Jennifer Dionne