June 2025

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Oceanography | Vol. 38, No. 2

66

DIY OCEANOGRAPHY

THE PIXIE

A LOW-COST, OPEN-SOURCE, MULTICHANNEL IN SITU

FLUOROMETER APPLIED TO DYE-TRACING IN HALIFAX HARBOR

By Kyle Park, Dariia Atamanchuk, Aaron MacNeill, and Vincent Sieben

INTRODUCTION

Submersible, or in situ, fluorometers are devices used in fresh­

water and marine environments to measure the presence of

compounds (fluorophores) that fluoresce when exposed to spe­

cific wavelengths of light. These measurements can be used,

for example, as indicators of water quality, contamination, and

flow dynamics. The earliest submersible fluorometers (Wheaton

et al., 1979) were designed with a single channel (i.e., measur­

ing fluorescence at a specific wavelength while rejecting the

rest of the spectrum). However, the presence of multiple fluo­

rescent species in natural waters makes it sometimes challeng­

ing to attribute the measured signal to a single compound with

certainty due to spectral overlap, so multichannel fluorometers

have been employed more recently.

Climate change and its associated impacts are increasing

the demand for high-resolution monitoring of the environ­

ment using optical sensors that enable fast detection and are

small enough to be integrated into mobile platforms. For exam­

ple, harmful algal blooms (HABs) can cause billions of dol­

lars in direct damages to fisheries (Davidson et al., 2020) and

fishery-​dependent communities (Weir et al., 2022), and reduce

the socioeconomic value of recreational areas (Mardones et al.,

2020). Preventative and mitigative actions can be taken if

warning signs, such as the concentrations of the fluorophores

chlorophyll a (Chl-a) and phycocyanin (PC) (Shen et al., 2012),

are monitored and detected early (Davidson et  al., 2020).

In another example, the assessment of marine carbon diox­

ide removal strategies, such as point-​source oceanic alkalinity

enhancement, requires a careful understanding of the near-field

dynamics that are studied using dye tracer experiments (Fennel

et  al., 2023). These experiments use fluorescent rhodamine

water tracer (RWT) dye to make spatio-​temporal measure­

ments of dye plume dispersion. In another example, petroleum-​

derived contaminants such as crude oil can be detected using

ultraviolet fluorometry. Overall, the scope and scale of human

activity put enormous pressure on the global ocean and water­

ways, thus warranting the development and improvement of

autonomous sensors, including fluorometers, for improved

monitoring and response.

Access to this technology as well as to the education required

to take advantage of it, both currently dominated by high-​

income countries, is a challenge recognized by the United

Nations Decade of Ocean Science for Sustainable Development

(2021–2030) (Harden-Davies et  al., 2022). The current price

of relevant industrial, single channel, in situ fluorometers is

$3,400–$7,800 USD (Park et al., 2023). Industrial multichannel

systems such the three-channel RBRtridente (RBR Ltd., Ottawa,

Canada), Turner C3 (Turner Designs, San Jose, CA), or ECO

Puck (Sea-bird Scientific, Bellevue, WA) have price and perfor­

mance characteristics comparable to the single channel devices

on a per-channel basis. To improve access and the use of sensor

technology, the documentation on some oceanographic devices,

their construction, use, and handling have been released to

the public as open source (Butler and Pagniello, 2021; see also

https://tos.org/diy-oceanography for additional open-source

instrument projects published in Oceanography).

ABSTRACT. 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 mea­

surement 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.

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