Controlled CRISPR/Cas12a activation via DNAzyme-mediated splitting of chimeric substrate for lead detection

Chronic lead exposure poses severe threats to human health, which demands a rapid detection strategy beyond conventional instrumentation-dependent approaches. While CRISPR/Cas12a systems offer promising alternatives through trans-cleavage activity, conventional Pb²⁺ biosensors relying on DNAzyme-generated intact activators suffer from high background signals due to interference from uncleaved substrates. To address this limitation, we developed a steric-hindrance-controlled activation strategy by employing a chimeric DNAzyme substrate (Sub) that prevents Cas12a binding until Pb²⁺-dependent cleavage occurs. This DNAzyme-mediated splitting releases two fragments (A1/A2) that rearrange into split activators, triggering the CRISPR/Cas12a trans-cleavage of a quenched reporter (6-FAM/BHQ1). Under the optimal condition, the sensor achieved a linear detection range of 2.5-25 μM (R² = 0.998) with 2.18 μM LOD and high selectivity against interferents. Validation in tap water matrices demonstrated 98.6%-102.6% recovery (RSD 3.0%-7.5%), which showed robustness in real samples. This split-activator design paradigm eliminates background from uncleaved substrates without additional pretreatment steps to provide a versatile template for converting metal ions into CRISPR-detectable signals.