Measure biotin-streptavidin bond forces with a single magnetic nanoparticle

Master's project Loes van Zijp

Our aim is to measure biological bondforces using individual magnetic beads. We use beads with a size of 1 micrometer or smaller. As a model system we use the biotin-streptavidin couple. First the surface of the chip is activated with biotin and the surface of the bead with streptavidin. One of the methods is to couple biotin to the chip using self-assembled monolayers (SAMs). Streptavidin is a relatively large protein and has four binding sites for the smaller biotin molecule. Once the binding of a single bead is established, one can pull the bead away from the surface by applying a magnetic field. From the release of the bead one can study the strength and the character of the bond. The figure shows a sketch of a bead connected to the surface with the aid of a mixed SAM (self-assembled monolayer).

Loes: "This project is on the interface between physics and biochemistry. The first challenge is to get a grip on the surface chemistry. To establish the binding, a protocol with different reaction steps is needed and many variables are involved. And when the bead is finally attached, it is a challenge to determine what type of binding it is, e.g. if it is a specific or a non-specific binding. I work in the chemical as well as the physical labs. The methods and results should be compared with the most recent theories on surface activation and detection with magnetic particles. Fields of study are for example biochemistry, surface analytical methods, electromagnetism and signal processing".