A novel signal amplification biosensor for detection of Cd²⁺ based on asymmetric PCR

In this work, a novel signal amplification biosensor was utilized to detect Cd²⁺ based on asymmetric PCR. In the presence of Cd²⁺, it can bind with Cd²⁺-aptamer C1 which caused the complementary strand C2 to be released from double-stranded DNA C1-C2. Because the single-stranded C1 cannot be hydrolyzed by Exo III, it can be used as a template to take part in asymmetric PCR reaction. In the absence of Cd²⁺, the C1-C2 was digested by Exo III and no PCR template was left. During the experiment, an interesting phenomenon was found that the asymmetric PCR can obtain higher level of fluorescent signal than that of symmetric PCR. To the best of our knowledge, this is the first report of using asymmetric PCR to detect Cd²⁺. Through the asymmetric PCR amplification strategy, this biosensor had a low detection limit (19.93 nM) and a wide linear range (0-500 nM). Meanwhile, this biosensor showed a satisfactory selectivity and recovery rate.