Folic Acid Dual-Mode Detection Platform Based on a Selected Aptamer and DNA Tetrahedron-Assisted Catalytic Hairpin Assembly

Synthetic folic acid (FA) is widely used in food fortification and nutritional supplementation, and is crucial for maintaining human one-carbon metabolism and physiological homeostasis. However, inaccurate labeling, adulteration, or degradation during food processing and storage may lead to abnormal FA levels, highlighting the need for sensitive and reliable detection methods. Here, a colorimetric-electrochemical dual-mode aptasensor for FA detection was developed using a Pd/CoOOH nanozyme combined with a DNA tetrahedron-assisted catalytic hairpin assembly (TDNs-CHA) amplification strategy. A high-affinity FA aptamer (S2), screened via Capture-SELEX, served as the specific recognition element, with strong affinity and specificity confirmed by ITC assay and SYBR Green I assay. The Pd/CoOOH nanocomposite exhibited enhanced peroxidase-like activity, acting as the signal reporter. By integrating aptamer recognition with TDNs-CHA amplification, the sensor enabled sensitive FA detection over 0.04-2000 ng/mL, with limits of 0.056 ng/mL (colorimetric) and 0.0024 ng/mL (electrochemical). It was successfully applied to fortified foods, achieving recoveries of 98.1-102.4% with RSDs below 5%, offering a promising platform for nanozyme-based dual-mode FA sensing in food analysis.