3D-printed fiber-bundle fluorescence microscope for quantifying single-cell responses to high-power radiofrequency sources.

Modern telecommunications systems rely on the ubiquitous use of radiofrequency (RF) fields. To ensure the safety of living systems under RF exposure, standards have been developed which rely on observed thresholds that produce an adverse response. Unfortunately, real-time imaging of single-cell responses to high-peak power RF exposures is experimentally difficult, as high-power RF may damage sensitive electronics such as cameras or photodetectors, and any metal in the exposure zone (such as a microscope objective or translation stage) interacts with the RF by reflecting the RF field, acting as an antenna, or altering the dose delivered to the sample. In this work, we present a custom fluorescence microcopy system compatible with high-power RF environments. Our device uses a custom, 3D-printed objective consisting entirely of plastic and glass components as well as a coherent fiber bundle to relay light between the exposure zone and the fluorescence detection scheme. Our device was validated against a high-end commercial confocal microscope by comparing cellular responses to a well-characterized nanosecond pulsed electric field (nsPEF) stimulus delivered via an electrode pair. Our system performed well under extreme RF exposure, demonstrating continuous fluorescence imaging and maintenance of the focal plane despite >40°C temperature variation at the sample caused by high peak power free-field RF exposure at a frequency of 2.8 GHz. This system is intended to aid researchers in investigating real-time biological responses to radiofrequency and microwave sources.