Rapid yet ultrasensitive and accurate detection of tetracycline (TC) in aquatic environments subjected to composite pollution remains challenging. CRISPR-mediated biosensors have been extensively studied to achieve ultrasensitive detection. However, these biosensors have always been coupled with a time-consuming nucleic acid amplification process to improve the sensitivity, which may cause erratic signal due to the sophisticated biochemical reaction cascades, hence leading to inaccurate results. To address this issue, we proposed a novel amplification-free fluorescent aptasensor based on polyacrylamide-deoxyribonucleic acid hydrogel integrated with a dual-acting CRISPR/Cas12a system for ultrasensitive and rapid detection of TC in water. With this well-designed dual-acting CRISPR/Cas12a system, a single aptamer-target specific molecular binding event can synchronously initiate pairing between two distinct CRISPR RNA and their target nucleic acid modified on the hydrogel, enabling dual activation of Cas12a. The aptasensor instantly emitted quantifiable strong fluorescence due to the efficient cleavage of reporter probes by the twofold activated Cas12a, demonstrating a TC detection limit of 0.035 μg/L, with approximately 10.6-fold and 5.6-fold sensitivity improvement over the two corresponding single-crRNA systems. The entire detection process can be accomplished in one pot within 10 min. The one-step hydrogel aptasensor shows superior resistance to matrix interference over the conventional solution-phase system, achieving satisfactory recovery percentages (92 %-105 %) for TC in different water matrices. This study offers a new perspective on CRISPR/Cas12a biosensor design and advances the environmental antibiotic monitoring field.
