Asymmetric volume-mediated buffer control overcomes sensitivity limits in one-pot RAA-CRISPR/Cas12a visual detection.

Rapid, low-cost, and visual nucleic acid detection methods are highly attractive for curbing colistin resistance spread through the food chain. CRISPR/Cas12a combined with recombinase-aided amplification (RAA) offers a one-pot, aerosol-free approach for visual detection. However, traditional one-pot systems often run Cas12a trans-cleavage in a buffer suitable for RAA, thus limiting Cas12a cleavage efficiency. This study proposes an asymmetric volume-optimized RAA-CRISPR/Cas12a assay for ultrasensitive visual detection of mobile colistin resistance gene mcr-1. Unlike conventional one-pot systems constrained by buffer incompatibility, our design spatially segregates a minimal-volume RAA-MIX (lid) from a CRISPR-dominant buffer microenvironment (tube bottom). This architecture leverages RAA's exponential amplification power to ensure sufficient product yield from minimal reaction volumes, while enabling subsequent enhancement of Cas12a trans-cleavage through automatic buffer assimilation upon mixing. The results were able to be visually observed under UV light, achieving 63.1% cost reduction compared to standard one-pot methods. The sensitivity of the proposed method for the mcr-1 gene was 2.5 copies/reaction, with anti-interference against other plasmids or bacteria. This method was applied to the detection of mcr-1 in animal-derived foods, showing satisfactory practical performance. By fundamentally reengineering buffer microenvironments through volume asymmetry, this work provides a general strategy for one-pot molecular diagnostics, achieving dual optimization of amplification and cleavage without trade-offs.