Rapid and sensitive detection of Karlodinium veneficum using RAA and CRISPR-Cas12a technologies

The harmful algal species Karlodinium veneficum (K. veneficum) poses a significant threat to aquatic ecosystems, economic stability, and human health due to its toxin production and widespread occurrence. Rapid climatic changes and eutrophication have intensified harmful algal blooms (HABs), making the timely detection of K. veneficum critical. To address this need, we developed a rapid and accurate detection method of K. veneficum by combining Recombinase Aided Amplification (RAA) with CRISPR/LbCas12a. This method targets the internal transcribed spacer (ITS) sequence of K. veneficum and utilizes the "collateral activity" of CRISPR/LbCas12a for visualization. Our method can detect plasmid DNA as low as 5.9 × 10² copies/µL and genomic DNA as low as 3.6 × 10^-2 ng/µL, achieving a detection limit of 10 cells of K. veneficum through a simplified DNA extraction process. The entire detection process, from DNA crude extract to result visualization, can be completed in as fast as 90 min, making it suitable for field applications requiring a rapid response. In addition, our method was validated against a wide range of non-target microalgae species, confirming its specificity to K. veneficum and eliminating the risk of cross-reactivity. Overall, the RAA-CRISPR/LbCas12a system is simple, accurate, and sensitive, showing great potential for field applications in monitoring K. veneficum.