Aptamer-Based Fluorescent Determination of Salmonella paratyphi A Using Phi29-DNA Polymerase-Assisted Cyclic Amplification

A rapid and ultrasensitive fluorescence aptasensor was developed for the detection of Salmonella paratyphi A based on aptamer and Phi29-DNA polymerase-assisted cyclic signal amplification. The method employed a designed arched probe, consisting of an aptamer and a primer, with a designed hairpin probe. The quenching groups and fluorescent groups were modified at the 3′ and 5′ ends of the hairpin probe, respectively. In the absence of the target, the primer was not released and the hairpin probe was not opened to produce fluorescence. The addition of target led to the release of the primer, which hybridized with the hairpin probe and triggered the chain-displacement polymerase reaction and produced a high fluorescence intensity. Under the optimized conditions, the linear range of this aptasensor was from 10² CFU·mL^?1 to 10⁸ CFU·mL^?1 with a detection limit of 10² CFU·mL^?1. Compared with other reported fluorescence detection methods, this approach has two advantages. First, this fluorescence aptasensor does not require nanomaterials as the quencher, which reduces the cost and saves time. Second, the chain-displacement polymerase reaction was used in this fluorescence aptasensor to amplify the signals, which further enhanced the sensitivity and lowered the detection limit. As this method was suitable for the detection of Salmonella paratyphi A in milk samples and potentially other bacteria, environmental monitoring and related food safety analysis should also be possible by this approach.