Infected Blood Cells' Electrical Properties Indicate Early Malaria

A new prototype device recognizes electrical properties of Plasmodium falciparum-infected cells as signatures of disease.

Scientists examined whether it was possible to use electrical impedance as a diagnostic signal for malaria. Several types of infection, including malaria, alter a cell’s impedance, a measure of electrical resistance across the cell membrane. Previous studies had demonstrated electrical changes in later-stage infected cells, but it was not clear that cells that had reached only the ring stage of infection would exhibit electrical changes.

A microfluidic device was constructed that takes a drop of blood and streams it across an electrode that measures a signal differentiating infected cells from uninfected cells. The work, which recognizes ring-stage Plasmodium falciparum infected blood cells, was published August 8, 2003, in the journal Lab On A Chip, could be the first step toward a field-ready, low-cost, portable malaria-detection device.

The microfluidic device built by the scientists was capable of measuring the magnitude and phase of the electrical impedance of individual cells. The device is essentially a cell-counting device, similar in approach to other low-cost, portable devices being developed to diagnose illnesses such as HIV.

“Ultimately the goal would be to create a postage stamp-sized device with integrated electronics that can detect if a person has malaria and at what stage,” said Anantha Chandrakasan, the Joseph F. and Nancy P. Keithley professor of electrical engineering and a principal investigator at Massachusetts Institute of Technology's (MIT; Cambridge, MA, USA) Microsystems Technology Laboratories (MTL) who specializes in developing low-power electronic devices. Similar diagnostics may be applicable to other infections and diseases.

In tests of cells of four cell types—uninfected cells and infected cells at the ring stage, trophozoite, and schizont stages—the device detected small differences in measures of magnitude and seemingly random differences in phase, but not quite enough to definitively differentiate among stages.

However, by mathematically combining the measures into an index called delta, the differences between uninfected cells and all three stages became clear. “It’s much more significant,” said corresponding author Ming Dao, a principal research scientist in the Nanomechanics Laboratory. “It’s a more holistic approach. By using all of the information we can measure, we can detect the differentiating signals much more clearly.”

Malaria is a curable disease, but diagnosis remains a challenge. This ability to discern the circulating parasite’s stage from a drop of blood opens the possibility of building a device that could be used to rapidly diagnose malarial infection in places where laboratories and skilled medical personnel are scarce.

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