Matthias Franzreb

Zeta potential measurement as a diagnostic tool in enzyme immobilisation

The efficiency of binding during enzyme immobilisation does not only depend on the chemical properties of the enzyme and the matrix particle, but also on their surface potential. Zeta potential quantifies the electrostatic interactions between enzyme and matrix particles, and can therefore, be used as an indicator of the binding efficiency in the enzyme immobilisation studies. In order to establish a correlation between the zeta potential and the binding efficiency, we used CALA (Candida antarctica A-type lipase) as a model protein for immobilisation on non-porous magnetic microparticles with epoxy (M-PVA E02), carboxy (M-PVA C12) and amine (M-PVA N12) terminations. We observed maximal binding of CALA onto the M-PVA N12 beads, due to the electrostatic attraction between negatively charged protein and carrier particles with slightly positive zeta potential. The binding of CALA was lower when M-PVA E02 beads were used, followed by M-PVA C12 beads. The decreasing binding efficiency was obviously the result of increasing electrostatic repulsion between the interaction partners. This could be correlated to the increasing negative zeta potential of the magnetic particles. Moreover, the medium of suspension of the particles also makes a significant difference. We found highest specific activity of the lipase immobilised on M-PVA E02 beads in a medium concentrated buffer (0.3M). The results demonstrate a clear correlation between zeta potential and binding efficiency but no correlation between the bead related specific activity and the zeta potential. These findings are advocating the possibility of using the zeta potential as a diagnostic tool in enzyme immobilisation.

Filter Capacity Predictions for the Capture of Magnetic Microparticles by High-Gradient Magnetic Separation

We present experimental and theoretical methods to predict maximum and working filter capacities for the capture of superparamagnetic microparticles through high-gradient magnetic separation (HGMS). For this, we employed various combinations of nine different HGMS filter matrices and two types of superparamagnetic microparticles. By calculating the separated particle mass per filter mesh area, we clearly demonstrated the influences of wire diameter and wire mesh spacing on the particle build-up density. Here, we introduce a simple experimental method for estimating average build-up densities in HGMS. Together with known physical parameters of the filter matrix and the background field, such average build-up densities allow good predictions of the operational working filter capacities