The goal of this project is to develop massively parallel "imaginary" magnetic tweezers for quantifying intermolecular binding forces. In contrast to conventional magnetic tweezers, which employ large external magnets to apply field gradients and force on the colloidal particles, the proposed imaginary tweezer system is unique in that the force is produced by the particle's near-field interaction with its own image appearing in a planar substrate. The image repulsion is achieved by immersing the colloidal particle inside a solution of magnetic nanoparticles, known as ferrofluid. The primary goal of this proposal is to demonstrate the "proof of principle" of imaginary magnetic tweezing, by rupturing a Streptavidin-Biotin bond, a process which will be observed by tracking the motion of the colloidal particles on the substrate in a range of uniformly applied magnetic field.
The *broader impact* of this work lies in the development of self-assembly "inspired" instrumentation for probing biomolecular interactions. The proposed magnetic tweezers enable investigation of force loading rates spanning a wide range of time scales from milliseconds to hours, a spectrum which is mostly inaccessible to the widely employed atomic force microscopy technique for stretching molecules. The parallel nature of this technique will be adapted to perform competitive binding assays, in which tweezing of multiple particles is performed simultaneously on an array of different chemical patches, thereby enabling a statistical distribution of unbinding forces to be measured in a single experiment. The PI and co-PI have a track record of encouraging participation of undergraduate and graduate students in research and education, particularly the hearing impaired and African-American minority students, who will spend two summer months in the in the PI's laboratory performing molecular stretching experiments.
