Binding kinetics of bisintercalator Triostin a with optical tweezers force mechanics.

The binding kinetics of the intercalative binding of Triostin A to lambda-DNA was investigated by measuring the force extension response of the DNA-ligand complexes with an optical tweezers system. These force response curves, containing the information about different binding properties, were analyzed based on a recent method (put forth by another research group) for monointercalators that was extended to bisintercalators. Our binding analysis reveals an exponential dependence of the association constant on the applied external force as well as a decreasing binding site size. In general, our results are in agreement with those for the monointercalator ethidium. However, to explain the high-force binding site size, a new model for bisintercalation of Triostin A at high forces is proposed.

Single beam optical tweezers setup with backscattered light detection for three-dimensional measurements on DNA and nanopores.

We introduce a versatile and high precision three-dimensional optical tweezers setup with minimal optical interference to measure small forces and manipulate single molecules in the vicinity of a weak reflective surface. Our tweezers system integrates an inverted optical microscope with a single IR-laser beam that is spatially filtered in an appropriate way to allow force measurements in three dimensions with remarkably high precision when operated in backscattered light detection mode. The setup was tested by overstretching a lambda-DNA in x and z directions (perpendicular and along the optical axis), and by manipulating individual lambda-DNA molecules in the vicinity of a nanopore that allowed quantitative single molecule threading experiments with minimal optical interference.