The PIXIE: A Low-Cost, Open-Source, Multichannel In Situ Fluorometer Applied To Dye-Tracing in Halifax Harbor

Fluorometers are ubiquitous tools in the fields of oceanography, limnology, and water quality assessment. Fluorescent species in our waters range from in vivo chlorophyll, contaminants like crude oil, or intentionally added agents like rhodamine. Submersible in situ fluorometers can collect real-time data at scales that cannot be matched by discrete bottle samples with lab/​shore-side analysis. However, accessibility of sensors remains a problem recognized by the United Nations Sustainable Development Goals. Here, we introduce the PIXIE, an open-source, multichannel, in situ fluorometer that performs high-quality fluorometry at a low cost. The PIXIE is assembled by simple means from almost entirely off-the-shelf components. The few necessary custom parts are either easily outsourced or printed by consumer-grade 3D printers. The PIXIE draws an average of 225 mW during measurement and has been tested to depths of 45 m. It has been calibrated to demonstrate a limit of detection 0.01 ppb rhodamine WT (a fluorescent dye) in a range up to 60 ppb, and a limit of detection of 0.02 ppb chlorophyll a. The PIXIE has been deployed as part of a dye-tracer experiment in Halifax Harbor, Canada, demonstrating its performance in a quasi-simultaneous profiling of rhodamine WT dye and chlorophyll a.