Micro-optical characterization of biomolecules and chemical interactions using half-coated fluorescent particle

We introduce new experimental technologies and theories for the measurements of very weak intermolecular forces and of the torsional spring modulus of a ds-DNA by using half-coated fluorescent nanoparticle. Compared to current measurement techniques these new methodologies provide a number of advantages.; For the measurement of intermolecular forces, our method is able to characterize very weak noncovalent intermolecular forces in the femto-newton range, which has been considered very difficult even with existing state-of-art techniques such as AFM (atomic force microscopy) or optical tweezers. Also the molecular systems under investigation with our technique do not experience any deformation of their structures thus maintain their physical properties. This is due to that our technique uses only Brownian force resulting from thermal agitation of the fluidic environments as the only power source. This is very important because it is well known that applying external forces stronger than the forces to measure while the molecular systems are being investigated could disturb the systems themselves. Therefore the interaction forces could have been already affected during the measurement, which does not allow us to acquire their pure intrinsic properties.; For the measurement of torsional spring modulus of ds-DNA molecule, we propose a method to measure the torsional modulus value isolated from other undesirable side effects resulting from bending or buckling of the DNA chain. Up to now torsional elastic properties of DNA have been investigated by applying an external torque around the axis of a vertically stretched DNA. A DNA under stretch, while torque is applied, can avoid the formation of plectoneme caused by molecular buckling. However, an applied stretching force may cause overestimate of the intrinsic DNA torsional modulus via elastic coupling between twisting, bending and stretching. Therefore, the reported results from the existing methods may deviate from the actual DNA property under physiological condition. Since we can measure the intrinsic torsional modulus of a ds-DNA under Brownian motion induced torque, absent of any externally applied stretching force, the data presented in this thesis can show the pure torsional elastic modulus of a ds-DNA, isolated from stretching, bending, or buckling of DNA chains.