Exploiting the potential of spherical PAM antenna for enhanced CRISPR-Cas12a: a paradigm shift toward a universal amplification-free nucleic acid test platform

The CRISPR-Cas12a system has shown tremendous potential for developing efficient biosensors. Albeit important, current CRISPR-Cas system-based diagnostic technologies (CRISPR-DX) highly rely on an additional preamplification procedure to obtain high sensitivity, inevitably leading to issues such as complicated assay workflow, cross-contamination, etc. Herein, a spherical protospacer-adjacent motif (PAM)-antenna-enhanced CRISPR-Cas12a system is fabricated for universal amplification-free nucleic acid detection with a detection limit of subfemtomolar. Meanwhile, the clinical detection capability of this sensor was further verified using gold-standard real-time quantitative polymerase chain reaction through Mycobacterium tuberculosis measurement, which demonstrated its good reliability for practical applications. Importantly, its excellent sensitivity is mainly ascribed to high efficiency of target search induced by a localized PAM-enriched microenvironment and improved catalytic activity of Cas12a (up to 4 folds). Our strategy provides some new insights for rapid and sensitive detection of nucleic acids in an amplification-free fashion.