Ultrasensitive, high temperature and ionic strength variation-tolerant Cu²⁺ fluorescent sensor based on reconstructed...

A previously reported Cu²⁺-dependent DNAzyme/substrate complex was reconstructed in this work, which makes possible the use of an intramolecular stem-loop structure and is, therefore, a good choice for the design of Cu²⁺ sensors. To demonstrate this, a fluorescent sensor was designed on the basis of the reconstructed complex. In this sensor, the fluorophore/quencher pair was caged tightly in an intramolecular double-helix structure; thus, the background signal was greatly suppressed. Cu²⁺-dependent cleavage of the complex could cause the release of the fluorophore, leading to restoration of the fluorescence signal. High quenching efficiency provides the sensor with three important characteristics: high sensitivity, high temperature variation tolerance and high ionic strength tolerance. The proposed sensor allows specific detection of aqueous Cu²⁺ down to a limit of 0.6 nM, and the performance is independent of temperature and ionic strength in the range of 4-40 °C and 0.8-3.0 M NaCl, respectively. This work identifies a good choice for sensor design on the basis of DNAzymes containing triple-helix structures.