Engineering Micrometer-Sized DNA Tracks for High-Speed DNA Synthesis and Biosensing

phi 29 DNA polymerase (Pol phi 29) is capable of synthesizing long-chain single-stranded (ss) DNA molecules by copying the sequence of a small ss circular DNA template (ssCDT) in a process known as rolling circle amplification (RCA). The use of a ssCDT in RCA, however, comes with a key drawback: the rate of DNA synthesis is significantly reduced. We hypothesize that this issue can be overcome using a very long linear ssDNA template with a repeating sequence. To test this idea, we engineered a DNA assembly, which we denote micrometer-sized DNA track (mu DT). This mu DT, with an average length of approximate to 13.5 mu m, is made of a long chain DNA with a primer-binding domain at its 3 ' end and approximate to 1000 repeating sequence units at its 5 ' end, each carrying a DNA anchor. We find that Pol phi 29 copies mu DT at a speed approximate to 5-time faster than it does a related ssCDT. We use this to design a simple all-in-one printed paper device for rapid and sensitive detection of microRNA let-7. This paper sensor is capable of detecting 1 pM let-7a in 10 minutes.