Ultrasensitive Homogeneous Electrochemiluminescence Biosensor for <i>N</i>-Nitrosodimethylamine Detection Based on Vertically-Ordered Mesoporous Silica Film-Modified Electrode and CRISPR/Cas12a-Driven HRCA with Triple Signal Amplification

Herein, we present an innovative electrochemiluminescence (ECL) biosensor for the ultrasensitive detection of <i>N</i>-nitrosodimethylamine (NDMA). The biosensor utilizes a triple signal amplification strategy, combining rolling circle amplification (RCA), CRISPR/Cas12a-driven hyperbranched rolling circle amplification (HRCA), and electrostatic repulsion with size exclusion effects from vertically ordered mesoporous silica film (VMSF)/indium tin oxide (ITO) on double-stranded DNA (dsDNA)-Ru(phen)₃²⁺ complexes. In this system, aptamers and circular DNA undergo RCA reactions, followed by the CRISPR/Cas12a-mediated HRCA process, producing abundant dsDNA. The electropositive ECL indicator, namely Ru(phen)₃²⁺, was subsequently adsorbed onto the electronegative dsDNA, forming dsDNA-Ru(phen)₃²⁺ complexes. These complexes are subjected to electrostatic repulsion and size exclusion by the VMSF-modified ITO electrode, resulting in a lower ECL intensity. Upon introducing NDMA, the aptamer preferentially binds to NDMA, thereby preventing the formation of long dsDNA. This process releases free Ru(phen)₃²⁺, which diffuses to the electrode surface through narrow mesoporous channels via electrostatic adsorption. Consequently, an enhanced and strong ECL signal is observed. The integration of VMSF enhances selectivity and sensitivity by excluding larger impurities and promoting the electrostatic repulsion of dsDNA-Ru(phen)₃²⁺ complexes near the electrode surface. Additionally, the CRISPR/Cas12a system eliminates the formation of primer dimers and reduces false positives through its unique <i>cis</i>- and <i>trans</i>-cleavage activities. The biosensor demonstrated excellent performance with a linear correlation between the ECL signal and NDMA concentration in the range spanning from 10 pg/mL to 10 μg/mL, achieving a low limit of detection of 5.33 pg/mL. This platform offers a reliable and robust solution for detecting NDMA in complex matrices, making it a promising tool for environmental monitoring, public health, and safety applications.