Review of surface enhanced raman spectroscopy for malaria diagnosis and a new approach for the detection of single parasites in the ring stage

Malaria is a global disease that desires early diagnosis in the field, for which one way is to detect hemozoin (a unique biomarker of malaria infection) at low concentrations. Moreover, many anti-malarial drugs inhibit the formation of hemozoin and facilitate toxic free heme stacking to kill malaria parasites. Therefore, monitoring hemozoin within malaria parasites is important to malaria diagnosis and drug development. Here, we first review various surface enhanced Raman spectroscopy-based techniques for malaria diagnosis. Then, to enable hemozoin detection in single parasites in the ring stage for the first time, we report a method based on surface enhanced Raman spectroscopy for hemozoin detection in Plasmodium falciparum in the ring stage. In this method, silver nanoparticles are directly synthesized within parasites after the lysis of red blood cells and parasites are confirmed to be in the ring stage by Giemsa staining after a special procedure of sample postprocessing. The Raman spectra of hemozoin acquired from parasites with silver nanoparticles synthesized inside are compared with those from parasites mixed with nanoparticles synthesized separately. The results confirm the feasibility of detecting hemozoin crystals within single parasites in the ring stage. This method offers a promising strategy to investigate the mechanism of heme metabolism in malaria infection and a tool to evaluate the effectiveness of anti-malaria drugs.