Label-Free Fluorescence Sensing Strategy Based on Functional Nucleic Acids via Energy Transfer between DNA-Templated...

A simple and low-cost fluorescence signal-on sensing strategy has been developed based on functional nucleic acids (FNAs) via energy transfer between DNA-templated silver nanoclusters (DNA-AgNCs) and gold nanorods (GNRs). FNAs were used as highly selective recognition probes, in which an aptamer was used to detect small molecules represented by tetracycline, and DNAzyme was used to detect heavy metal ions represented by Pb²⁺. The fluorescent DNA-AgNCs were synthesized by the designed oligonucleotide sequences, which consisted of three parts: AgNCs synthesis template C₆G₅C₆, spacer T₅, and complementary sequences of the aptamer or enzyme strand. The difference in electrostatic interactions between ss/dsDNA and positively charged GNRs leads to energy transfer with different efficiencies. The analytes represented by tetracycline and Pb²⁺ can destroy the dsDNA structure and reduce the energy-transfer efficiency between DNA-AgNCs and GNRs, thus achieving fluorescence recovery and a signal-on analytical strategy. This strategy has excellent specificity and sensitivity with limit of detections of 4.411 nM for tetracycline and 1.416 nM for Pb²⁺ and has been successfully applied to detect tetracycline in milk and Pb²⁺ in river water. Using DNA-AgNCs formed in situ as signal probes, this strategy does not require labels or modifications and can be completed without complex analytical instruments. Moreover, this strategy can be extended to detect other targets by replacing FNA sequences. Therefore, it has promising prospects in the sensitive, simple, and rapid detection of contaminants in food and environment samples.