Decoupling DNA Twist and Stretch: Development and Application of a Magneto-Optical Tweezers Fluorescence Microscope

DNA is a complex biopolymer, support for the genetic information of most living organisms on Earth. Beyond this passive role of information carrier, its physical properties such as its topology or elasticity are now known to be critical to the function of living systems. The development of highly precise quantitative methods to probe these properties one molecule at a time can offer an invaluable insight into the complex multidimensional response of DNA to various physicochemical stimuli, shedding light on their causes and consequences. This works presents the development of a unique device to carry out those measurement, unique in the combination of robust techniques proven to be highly relevant during the last three decades of experimental single-molecule biophysics. We show an ability to observe DNA molecules by detecting fluorescent molecules bound to it, directly detecting structures such as DNA braids for the first time for long periods of up to a minute. The ability to decouple DNA torque and tension in this configuration is also achieved, showing that the fusion of those three technologies (magnetic tweezing, optical trapping and fluorescence imaging) can be achieved without significant drawbacks.