Underway measurement of cyanobacterial microcystins using a surface plasmon resonance sensor on an autonomous underwater vehicle.

Freshwater cyanobacterial harmful algal blooms (CHABs) are a well-known global public health threat. Monitoring and early detection of CHAB toxins are currently accomplished using labor-intensive sampling techniques and subsequent shore-based analyses, with results typically reported 24-48 hours after sample collection. We have developed and implemented an uncrewed, autonomous mobile sampler-analytical system capable of conducting targeted in situ toxin measurements in less than 2 hours. A surface plasmon resonance (SPR) instrument was combined with the Environmental Sample Processor (ESP) to fully automate detection and quantification of particle-associated cyanobacterial microcystins (pMC). This sensor-sampler system was integrated with a Long-Range Autonomous Underwater Vehicle (LRAUV) and deployed in western Lake Erie for field trials in the summer of 2021. The LRAUV was remotely piloted to acquire samples at selected locations within and adjacent to a CHAB. Sixteen pMC measurements ranging from 0.09 to 0.55 μg/L lake water were obtained over a 14-day period without recovery of the LRAUV. The SPR/ESP/LRAUV system complements existing satellite, aerial, and manual sampling CHAB survey techniques, and could be used to enhance predictive models that underpin bloom and toxicity forecasts. This system is also extensible to detection of other algal toxins in freshwater and marine environments, with its near real-time assessment of bloom toxin levels potentially offering additional socioeconomic benefits and public health protection in a variety of settings.