Catapult-like DNA actuator for highly stable and ultrasensitive detection of urinary miRNA

Urinary miRNA detection is a non-invasive, simple, and user-friendly diagnostic tool, enabling frequent testing in early bladder cancer diagnosis. Field-effect transistor (FET)-based biosensors hold great promise for miRNA detection due to their exceptional sensitivity, capable of detecting single or few molecules through electrical signals. However, their practical application in urine faces significant challenges, including non-specific adsorption by abundant biomolecules and short sensing distance imposed by the Debye length in high-ionic-strength fluids like urine. Here we introduce a catapult-like actuating DNA nanostructured probe into a FET biosensor to address both non-specific adsorption and Debye length limitation issues. Notably, the designed probe effectively protects the sensor surface through steric hindrance, and when the target approaches, it activates to extend upward from the surface in a catapult-like manner. This actuation induces surface potential changes within Debye length, enabling reliable and sensitive detection of miRNA in urine. The developed biosensor achieved the detection limit of 10 fM in undiluted urine and was applied to detecting miRNA from 20 patient urine samples, including those with hematuria. It successfully discriminated bladder cancer patients from healthy donors within 20 min without RNA extraction or nucleic acid amplification.