With the application the rotating magnetic-field scheme, we assembled the first – laboratory-grade – version of our malaria diagnostic tool. As light source an ordinary laser diode (1) is applied. The polarized light (2) is transmitted through the sample (5), which is placed in the bore of a magnetic Halbach ring (3). This magnet is rotated at adjustable speed by a dc electric motor.
The hemozoin crystals – present in malaria-infected blood samples – follow the rotation of the field, thus modulating the polarization and intensity of the transmitted light owing to their dichroic behaviour. This modulation is detected with the application of a Rochon prism (7) separating the light path into two orthogonally polarized beams, whose differential intensity is measured by a balanced photodiode bridge. The frequency selective and phase sensitive detection is carried out via lock-in detection with the external reference signal acquired from an optical sensor (6) measuring the frequency of the rotation.
This setup provides an unprecedented sensitivity for spotting hemozoin in blood, which projects the development of an ultra-sensitive, quantitative and cost-effective device for the use of clinical in-vivo malaria diagnosis.