Quantum dot molecular beacons achieve sub-10 pM CRISPR-Cas detection in field-ready assays

CRISPR-Cas systems have revolutionized molecular diagnostics through their specificity and programmability, yet their broad adoption is hindered by the reliance on expensive and complex instrumentation. Here, we present an optimized quantum dot (QD) molecular beacon (QD-MB) platform that integrates Förster resonance energy transfer (FRET)-based detection with CRISPR-Cas functionality, achieving sub-picomolar sensitivity without the need for target amplification. By systematically tuning components, including His-tag modifications for improved QD conjugation, nucleic acid hairpin structures for enhanced enzyme interaction, and QD surface passivation strategies, we demonstrate a two-order-of-magnitude improvement in detection sensitivity. Using LwaCas13a and RNA targets, the limit of detection (LOD) decreased to under 1 pM with plate-reader-based fluorescence measurements and below 10 pM with a lamp-and-smartphone setup, establishing the feasibility of portable, field-ready applications. This work highlights the transformative potential of QD-MBs in biosensing and sets a foundation for further advances in CRISPR-based diagnostics and nanotechnology-enabled sensing platforms.