Tying Knots in DNA with Holographic Optical Tweezers

It has been demonstrated that holographic optical tweezers can be used to tie a trefoil knot in double-stranded DNA [1]. We have developed an advanced holographic optical tweezers system with several types of intuitive control interfaces [2-5]. It has been used in a range of research projects including the characterization and assembly of structures [6-8]. Here the process of tying increasingly complex knots with holographic tweezers will be described. The DNA is of the order of 50 $\mu$ m in length and is fluorescently labeled, in order that it can be visualized in the optical microscope of the tweezers system. With a knot was tied, the effect of increasing the persistence length of the DNA by partial methylation of the DNA molecule was investigated. 1. Xiaoyan R \textit{et al. PRL} \textbf{91} (2003) 265506 2. G Gibson \textit{et al.} \textit{Rev Sci Instr} \textbf{83} (2012) 113107 3. G Whyte \textit{et al.}, \textit{Optics Exp} \textbf{14} (206) 12497-12502 4. JA Grieve \textit{et al.} \textit{Optics Exp} \textbf{17} (2009) 3595-3602 5. C Muhiddin \textit{et al., J Optics} \textbf{15} (2013) 075302 6. DB Phillips \textit{et al.} \textit{Nature Photonics} \textbf{8} (2014) 400-405 7. OEC Gould \textit{et al. Nature Comms} \textbf{6} (2015) 10009 8. H Qiu \textit{ et al., Science} \textbf{352} (2016) 697-701