NEW YORK (360Dx) – Researchers at the University of Southern California, Los Angeles, and Johns Hopkins University are developing a portable magneto-optic detection system that they hope will eventually be available at the point of care in low-resource settings for early detection of malaria.
In the journal ACS Sensors this month, the researchers described the design, construction, and validation of a system based on differential optical spectroscopy that monitors changes in optical power before and after a magnet is applied. In so doing, they determined the concentration in rabbit whole blood of β-hematin, a mimic of the human malaria pigment hemozoin.
Malaria is treatable but sometimes overlooked because it can be asymptomatic, and clinicians are lacking in methods to detect it early. The researchers believe that, if successful, their new system could become a valuable detection and epidemiological tool in the fight against the deadly disease.
For operation and detection, the system relies on the properties of hemozoin, an insoluble nanocrystal manufactured in the blood by the malaria parasite, Andrea Armani, a study coauthor and professor of engineering at USC Viterbi School of Engineering, said in an interview. Unlike other naturally occurring materials in the blood, hemozoin exhibits strong magnetic behavior, and when it's detected in a patient’s blood, it is indicative of malarial infection, said Armani, one of the developers of the malaria early detection system.
The primary source of nutrients for the mosquito parasite that infects human hosts is hemoglobin. When mosquitoes infect human hosts, a parasite digests hemoglobin and creates heme, a byproduct that's highly toxic to the parasite and host. To protect it against toxicity, the parasite converts heme into hemozoin.
Researchers have created a hemozoin mimic, β-hematin, enabling them to study hemozoin without the need to handle malaria-infected samples.
To detect the presence of β-hematin, a mimic for all strains of human malaria, the new detection system shines a red laser light similar to a presentation pointer through the blood sample. The platform takes two measurements, with and without the magnet near the sample. When the magnet is near the sample it pulls all the magnetic nanoparticles out of the beam path. The system calculates the concentration of hemozoin in the blood by analyzing the difference between the two signals before and after the application of the magnet.
The portable optical diagnostic instrument as described in the paper "could become useful in malaria endemic communities … given its ease of use, with minimal basic skills needed and its battery powered utility and portability," Mary Galinski, a professor of medicine, infectious diseases, and global health at Emory University School of Medicine, said in an interview.
Galinski said that she and her colleagues plan to conduct pre-clinical trials at the Yerkes National Primate Research Center of Emory to assess the portable magneto-optic diagnostic instrument. They will analyze "different malaria parasite species, with different biological features, to determine its effectiveness for each," she said.
Her group is planning studies to quantitatively assess the presence of hemozoin in the blood from the time an infection begins through its progress in a patient and after treatment. They will first test hemozoin from cultured parasites grown in laboratory flasks. Initially, they will use several nonhuman primate model systems that mimic malaria in humans, Galinski said. "Human studies can follow, potentially within a few years, but it is early to plan these," she added.
Armani also noted that a commercial diagnostic system available for use in low-resource settings at the point of care is at least a few years away, and its progress will depend on proving its clinical utility for effective detection in human blood samples.
However, diagnostics that enable early treatment of the infected population are needed to eradicate malaria. According to the US Centers for Disease Control and Prevention, illness and death from malaria can usually be prevented, and treatment is nearly 100 percent effective when properly prescribed and administered based on the infection being detected early.
Although malaria is found in nearly every country, the burden of the disease rests primarily in the developing world, and seventy percent of deaths occur in children under five years. According to the World Health Organization, more than 216 million people were infected with malaria in 2016, and 445,000 people died from the disease.
The gold standard for malaria diagnosis is use of a microscope to analyze and count red blood cells in a sample. It is the most reliable among current methods of identifying infections from all malaria parasites, but it is low-throughput, labor-intensive, and expensive, Armani said, adding that the reliability of the method depends on a technician's training and experience.
Researchers have also designed rapid diagnostic tests based on the presence of different proteins and biomarkers, such as histidine-rich protein 2, which is specific to Plasmodium falciparum, the deadliest species that causes malaria in humans. The approach involves rapidly diagnosing malaria, within about 15 minutes, but it requires reagents that need refrigeration, which is often unavailable in low-resource settings.
Other methods to consistently detect clinically relevant concentrations of hemozoin are laser desorption mass spectrometry, Raman spectroscopy, flow cytometry, and polarization microscopy, the researchers said. However, they noted that these methods are also time consuming and require extensive training and equipment to achieve accurate results.
Because malaria primarily impacts people in low-resource settings where supply chain management is difficult and access to power can be unreliable, an effective malaria diagnostic must address both issues, Armani noted.
In the design of their system, the researchers placed a strong emphasis on engineering for operation in low-resource settings with a goal of detecting clinically relevant concentrations in whole blood, Armani said. They emphasized reducing cost, weight, and the requirements for energy, as well as on eliminating reagents and using disposable materials that one could easily replace by 3D printing, Armani said.
In operation, light from the system's 635 nm laser diode passes through a poly(methyl methacrylate) microcuvette containing 500 μL of whole blood sample to a photodetector. The detection strategy reduces the effect of sample-to-sample variation, which is inherent in human specimens, the researchers said. Their current prototype weighs fewer than 10 pounds and is powered by a netbook computer battery for eight hours per charge. Because it operates on whole blood, the system requires minimal sample processing and handling, and it currently analyzes five to seven drops, up to 500 μL, of blood in up to 15 minutes.
The researchers are working on the next generation of the device to improve its ruggedness and reduce the sample volume to less than 200 μL, or one to two drops of blood. They are working to eliminate the use of a netbook as a power source in favor of an external battery pack that could operate for more than 30 hours, and bring the price point for manufacturing the system to within $300.
Galinski said she is hopeful that the portable optical diagnostics system "will become a valuable new tool for the diagnosis of malaria," but she noted that the work needed for this to happen includes "some optimization, and both pre-clinical and clinical testing."
Galinski said that the instrument will not serve to determine which species of the parasite is causing the disease. However, it could help to expedite detection and treatment, especially when the parasite is present in asymptomatic patients that are not seeking treatment, she noted, and become an important epidemiological tool that prevents its transmission.