CRISPR/Cas12a-Based Dynamic Light Scattering Assay for Nucleic Acid Amplification-Free and Ultrasensitive Detection of <i>Listeria monocytogenes</i>

Ultrasensitive signal transduction systems are essential for developing rapid, robust, and sensitive nucleic acid tests using the amplification-free CRISPR-Cas12a system. In this study, we introduce a novel platform termed CRISPR-DART (dynamic light scattering Assisted Rapid Test), which combines CRISPR-Cas12a with a dynamic light scattering (DLS) signal readout. We systematically evaluated the effects of nanoparticle size (20, 60, and 100 nm) and morphology (spherical, cubic, and flower-like) on DLS sensing performance. Results demonstrate that larger and more structurally complex nanoparticles significantly enhance scattering intensity, allowing stable DLS signals at lower concentrations and improving sensitivity for detecting low-abundance nucleic acid targets. By utilizing the high specificity and trans-cleavage activity of CRISPR-Cas12a, target-triggered cleavage of single-stranded DNA linkers modulates nanoparticle aggregation, enabling quantitative nucleic acid detection. Notably, CRISPR-DART based on 100 nm gold nanoflowers with large size and complex morphology achieves a detection limit (LOD) of 32 aM, an improvement of 5 orders of magnitude over conventional CRISPR-Cas12a assays using fluorophore-quencher as signal output. Furthermore, the amplification-free CRISPR-DART platform also achieves a LOD of 92 CFU/mL for Listeria monocytogenes in food samples, and after a brief preincubation step, successfully detects 1 CFU in 25 g of food sample. In summary, the CRISPR-DART platform provides a straightforward, highly sensitive, and specific tool for rapid on-site diagnostics and food safety monitoring.