Structure-switching locked hairpin triggered rolling circle amplification for ochratoxin A (OTA) detection by ICP-MS

Ochratoxin A (OTA) is usually found in the contaminated cereal food that its trace concentration would cause severe carcinogenicity and neurotoxicity. Herein, a recognition-triggered structure switching-based element spectrometric assay was proposed for ultrasensitive and highly specific detection of OTA. OTA aptamer was first adapted into a primer for the formation of a locked hairpin (LHP), and followed by attachment on the surface of magnetic beads (MBs). In the presence of OTA, the binding event between OTA molecule and its aptamer induced the liberation of the primer for that is otherwise unable to spontaneously structure-switching. For the rolling circle amplification (RCA), thereby a dumbbell structure was designed as the template (DT). The hybridization of the dumbbell template with free primer initiates the rolling circle amplification along with the production of repeated sequences. To obtain the signal output, the DNA-AuNP tag was prepared which contained the complementary sequences with RCA products. Thus, each tag can hybridize with the repeated sequences derived from the RCA, enabling the formation of detectable signal by the following ICP-MS measurement. Such design can translate a single recognition event into numerous AuNPs, enabling amplified detection of OTA. Taking advantage of this principle, the OTA in real sample (AFP, PSA) can be quantified at femtomolar concentration and it can be expanded into application in food safety inspection.