Immunoassay, Mini Mass Spec Combined for Malaria Detection

Currently, several different technologies are available for diagnosing malaria, but each has drawbacks. PCR, for instance, is highly sensitive and specific, but it requires upfront sample processing and specialized equipment. While point-of-care and home PCR testing has come to market in recent years, these assays are quite expensive.

There are also rapid antigen tests for malaria, but these tests can be expensive. Microscopy is the traditional gold standard for diagnosing malaria, but it is labor intensive and subjective as well as technically challenging. A protein detection workflow that combines paper-based immunoassays with miniaturized mass spectrometry to enable diagnostic testing in resource-constrained areas has been developed.

Biochemists at Ohio State University (Columbus, OH, USA) used ionic probe technology for malaria detection and suggested it could be applied for large-scale surveillance and screening for the disease. The probes provide a more stable alternative to reagents used in conventional immunoassays, making them potentially useful for work in areas where cold storage is not widely available. The probes remain stable for several weeks under ambient conditions and are designed to release, upon treatment with ammonium hydroxide, mass tags that can be detected using paper spray ionization mass spectrometry.

The investigators synthesized pH-sensitive ionic probes and coupled them with monoclonal antibodies specific to the Plasmodium falciparum histidine-rich protein 2 (PfHRP2) malaria antigen. They then used the antibody-ionic probe conjugates in a paper-based immunoassay to capture PfHRP2 antigen from untreated whole blood. After the immunoassay, the bound ionic probes were cleaved, and the released mass tags were analyzed through an on-chip paper spray mass spectrometry strategy.

The test was able to detect the malaria antigen PfHRP2 in untreated human serum at levels down to 0.216 nmol/L, below the 0.227 nmol/L sensitivity threshold recommended by the World Health Organization for evaluating symptomatic patients. In terms of cost, the test is currently more expensive than the low end of the rapid antigen market, but it is expected costs will come down once the test is fully developed and being manufactured at scale. The team used a Continuity miniature mass spectrometer (BaySpec, Jose, CA, USA).

Abraham Badu-Tawiah, PhD, a Professor of Chemistry and senior author of the study, said, “Bigger mass spectrometers need to run continuously to maintain performance. Not so with portable instruments. The portable mass spectrometer is robust and can be turned it off when not in use, and turn it on when needed. It takes only 10 minutes to get it ready for analysis.”

The authors concluded that the stability and sensitivity of the developed paper-based immunoassay platform will allow miniature mass spectrometers to be used for point-of-care malaria detection as well as in large-scale surveillance screening to aid eradication programs. The study was published on October 4 2022 in the journal Analytical Chemistry.

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