Magnetic sensor particles: an optimized magnetic separator with an optical window

Magnetically separable optical sensor particles represent a good alternative for conventional electrochemical and fibre-optical oxygen and pH sensors. Further improving the suitability of magnetically separable optical sensor particles, we reconstructed the separation adapters. Computer simulations of magnetic fields indicated that an assembly of radially magnetized rings is preferred. We investigated different materials and dimensions of adapters and improved commercially available, axially magnetized rings using a magnetically soft iron cone together with the rings. Adapters simulating a radially magnetized ring were constructed out of several block magnets arranged like a star around an optical fibre. These adapters collected the sensor particles exactly in the field of view ensuring high efficiency and, on top of that, showed a higher resistance of the resulting sensor spot against shear forces in stirred liquid. All adapters were characterized in a stirred flask recording signal intensity versus stirrer speed plots.