Low-cost colorimeter development for the field-based detection of harmful algal blooms

The real-time detection of harmful algal bloom (HAB)-causing organisms is crucial to preventing human illness and death, animal mortalities, and significant economic losses for coastal and fishing communities. However, most identification schemes are time-consuming and costly, which limit their use for rapid risk assessment. To address this problem, a simple colorimetric test for the HAB-causing Alexandrium fundyense/tamarense/catanella dinoflagellate species complex is presented. This work integrates an indicator dye-based bioassay for detecting toxigenic Alexandrium RNA with a custom-built two-color detector. A peptide nucleic acid (PNA) probe is used to capture target RNA, and the formation of the PNA-RNA duplex is visible as a solution color change from blue to purple with the addition of the cyanine dye 3,3´-diethyldithiacarbocyanine iodide (DiSC₂(5)). PNA-RNA hybridization and discrimination against mismatched sequences is achieved within minutes at 25°C. Hybridization signals obtained from the colorimeter are comparable to those from a benchtop spectrophotometer. The advantages of this method represent a step towards field-compatible, easy-to-use and inexpensive detection schemes that require minimal training for successful use.