Toehold-mediated strand displacement in CRISPR/Cas12a reactions: Advances in programmable and universal biosensing...

CRISPR/Cas12a-based biosensors have emerged as powerful tools for nucleic acid detection due to their programmability, high sensitivity, and versatility. However, challenges such as PAM dependence, limited mismatch discrimination, and difficulty in detecting non-nucleic acid analytes constrain their universality. Toehold-mediated strand displacement (TMSD) offers a programmable mechanism to overcome these limitations by dynamically regulating hybridization kinetics and molecular interactions. This review systematically summarizes recent advances integrating TMSD into CRISPR/Cas12a systems, including crRNA release, crRNA-DNA activation, activator generation, and reporter signal modulation. By coupling TMSD's precise strand exchange capabilities with Cas12a's trans-cleavage activity, these hybrid biosensors achieve improved specificity, tunable kinetics, and multi-analyte adaptability. The review further discusses design principles, thermodynamic foundations, and application examples across biomedical, environmental, and food diagnostics. Collectively, TMSD-assisted CRISPR/Cas12a biosensing provides a universal, programmable framework for next-generation molecular diagnostics with enhanced control, sensitivity, and functional diversity.