Sensitive fluorescence sensing of T4 polynucleotide kinase activity and inhibition based on DNA/polydopamine nanospheres platform

5'-Polynucleotide kinase (PNK) is a crucial enzyme that catalyzes the phosphorylation of nucleic acid with 5'-OH termini and this phosphorylation reaction has been involved in many important cellular activities. The evaluation of PNK activity has received an increasing attention due to the significance of PNK. Here, the poly dopamine nanospheres (PDANS) could adsorb single-stranded DNA (ssDNA) through pi-pi stacking or hydrogen bonding between nucleobases and aromatic groups of PDANS, while the interaction between double-stranded DNA (dsDNA) with PDANS was weakened due to the changed conformation. Hence, a novel DNA/PDANS platform was constructed for the sensitive and selective determination of T4 PNK activity based on the preferential binding properties of PDANS for ssDNA over dsDNA and the excellent fluorescence quenching property of PDANS. The dye-labeled dsDNA was phosphorylated by T4 PNK and then digested by lambda exonuclease, yielding dye-labeled ssDNA, which would be adsorbed on the surface of the PDANS and the fluorescence was greatly quenched by PDANS. Because of the preferential binding properties of PDANS for ssDNA over dsDNA and the high quenching property of PDANS, the developed DNA/PDANS platform exhibited good analytical performance for T4 PNK sensing in complex biological matrix and applied to screening inhibitors. The proposed DNA/PDANS based platform is promising in developing high-throughput assays for drug screening and clinical diagnostics.