Efficient amplification of self-gelling polypod-like structured DNA by rolling circle amplification and enzymatic digestion.

The application of DNA as a functional material such as DNA hydrogel has attracted much attention. Despite an increasing interest, the high cost of DNA synthesis is a limiting factor for its utilization. To reduce the cost, we report here a highly efficient amplification technique for polypod-like structured DNA (polypodna) with adhesive ends that spontaneously forms DNA hydrogel. Two types of polypodna with three (tripodna) and four (tetrapodna) pods were selected, and a template oligodeoxynucleotide, containing a tandem sequence of a looped tripodna or tetrapodna, respectively, along with restriction enzyme (TspRI) sites, was designed. The template was circularized using T4 DNA ligase, and amplified by rolling circle amplification (RCA). The RCA product was highly viscous and resistant to restriction digestion. Observation under an electron microscope revealed microflower-like structures. These structures were composed of long DNA and magnesium pyrophosphate, and their treatment with EDTA followed by restriction digestion with TspRI resulted in numerous copies of polypodna with adhesive ends, which formed a DNA hydrogel. Thus, we believe this technique provides a new approach to produce DNA nanostructures, and helps in expanding their practical applications.