Silver quartz crystal microbalance for differential diagnosis of Plasmodium falciparum and Plasmodium vivax in single and mixed infection.

The most severe form of malaria is cerebral malaria caused by Plasmodium falciparum. Standard malaria diagnosis is Giemsa stained peripheral blood smear but false negative findings are always reported. Moreover, mixed infections are underestimated by routine microscopy. Many methods have been developed to overcome these disadvantages and the most specific and sensitive is molecular diagnosis. Specific malaria genes are amplified by polymerase chain reaction (PCR) and many post-PCR methods have been created. We developed a gold fabricated quartz crystal microbalance (QCM) as a post-PCR method of malaria diagnosis. In this work a cheaper silver fabricated QCM was developed to identify both single and mixed infection of P. falciparum and Plasmodium vivax. The biotinylated malaria probe was immobilized on silver surface via specific avidin-biotin interaction. The target DNA fragment of 18s rRNA gene was amplified and hybridized with a QCM immobilized probe. Mass changes due to DNA hybridization were indicated by changes of quartz resonance frequencies. Validation showed that malaria silver QCM had high diagnostic potency. Evaluation of suspected 67 febrile blood samples from malaria endemic area demonstrated that the malaria silver QCM could identify both false negative and misdiagnosis cases of routine microscopy. The analysis cost of malaria silver QCM was $1/sample and analysis time was 30 min after blood collection. The malaria silver QCM is stable at tropical temperature for up to 6 months. Thus, it can be transported to be used in a remote endemic area. Thus, the malaria silver QCM is accurate, precise, rapid, cheap, and field applicable.