Unique ssDNA-Induced Fluorescence Enhancement of a Conjugated Polymer Brush for Label-Free Sensing of S1 Nuclease and ATP

Nuclease plays a vital role in DNA replication, repair, and recombination. Taking advantage of the unique ssDNA-induced fluorescence enhancement of a cationic conjugated polymer brush (PPE-PLL), we constructed a new simple strategy for the detection of S1 nuclease and ATP simultaneously. It was found that the fluorescence of PPE-PLL can be enhanced by ssDNA significantly, which is quite different from traditional conjugated polymers. However, in the presence of S1 nuclease, the ssDNA was cleaved into small oligonucleotide and mononucleotide fragments. The fragments showed much weaker electrostatic interactions with PPE-PLL, resulting in a decreased fluorescence. Furthermore, when ATP was introduced as an inhibitor of S1 nuclease, a relatively high fluorescence signal was observed. Our strategy has high specificity and selectivity, and it works well in complicated system. The limit of detection for S1 nuclease and ATP can be estimated to be 0.15 U/mL and 0.068 mM, respectively. Additionally, the mechanism of the unusual ssDNA-induced enhancement of PPE-PLL was discussed by dynamic light scattering, fluorescence, and zeta potential measurements. Therefore, this simple, sensitive, label-free, and low-cost method may be extended to the sensing of other DNA-related biomolecules.