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During the intraerythrocytic stage of malaria, the parasite digests hemoglobin and aggregates the released heme as an insoluble crystalline material called hemozoin. This detoxification step is an excellent drug target for developing new antimalarials, which can bind to hemozoin surface to inhibit further growth. Although the bulk crystalline properties of hemozoin are well-known, the surface properties remain poorly defined. Here, we use a combination of spectroscopic and adsorption techniques to study the surface of synthetic hemozoin, hematin anhydride, produced by two different methods. We show that the two synthetic methods produce crystals with major differences, such as the amount of water adsorbed on the surface and surface carboxylate groups. These results imply that the methodology to produce hematin anhydride affects its surface reactivity; this information needs to be considered whenever hematin anhydride is used as a model to study host immune response or to design new antimalarials.

In this work, a new kind of peroxidase-mimicking DNAzyme (G-quadruplex-hemin DNAzyme, G4-hemin) was constructed by using hemin-modified G-rich DNA (hemin-G-DNA). Experimental results demonstrated that the G-rich DNA can form a G-quadruplex structure by the inducement of terminally modified hemin, rendering the assembly of hemin and G-quadruplex structure spontaneously and efficiently. As a result, G-hemin revealed higher peroxidase activity than traditional G-quadruplex/hemin DNAzyme (G4/hemin). Besides, different from G4/hemin, G4-hemin was constructed in one step without the participation of metal ions and adscititious hemin. Accordingly, the construction procedure was significantly simplified and the background signal from dissociative hemin was remarkably reduced. In a proof-of-concept trial, according to the colorimetric signals of G4-hemin, a novel biosensor for the detection of S1 nuclease activity was established, which provides a novel perspective for designing peroxidase-mimicking DNAzyme-based biosensors.