Malaria
is a serious disease that threatens the public health,
especially in developing countries. Various methods have been developed
to separate malaria-infected red blood cells (i-RBCs) from blood samples
for clinical diagnosis and biological and epidemiological research.
In this study, we propose a simple and label-free method for separating
not only late-stage but also early-stage i-RBCs on the basis of their
paramagnetic characteristics due to the malaria byproduct, hemozoin,
by using a magnetic field gradient. A polydimethylsiloxane (PDMS)
microfluidic channel was fabricated and integrated with a ferromagnetic
wire fixed on a glass slide. To evaluate the performance of the microfluidic
device containing the ferromagnetic wire, lateral displacement of
NaNO2-treated RBCs, which also have paramagnetic characteristics,
was observed at various flow rates. The results showed excellent agreement
with theoretically predicted values. The same device was applied to
separate i-RBCs. Late-stage i-RBCs (trophozoites and schizonts), which
contain optically visible black dots, were separated with a recovery
rate of approximately 98.3%. In addition, using an optimal flow rate,
early-stage (ring-stage) i-RBCs, which had been difficult to separate
because of their low paramagnetic characteristics, were successfully
separated with a recovery rate of 73%. The present technique, using
permanent magnets and ferromagnetic wire in a microchannel, can effectively
separate i-RBCs in various developmental stages so that it could provide
a potential tool for studying the invasion mechanism of the malarial
parasite, as well as performing antimalarial drug assays.