A microfluidic paper analytical device using capture aptamers for the detection of PfLDH in blood matrices

Background: The prevalence and death rate arising from malaria infection, and emergence of other diseases showing similar symptoms to malaria require the development of malaria-specific and sensitive devices for its diagnosis. To address this, the design and fabrication of low-cost, rapid, paper-based analytical devices (mu PAD) using surface-immobilized aptamers to detect the presence of a recombinant malarial biomarker-Plasmodium falciparum lactate dehydrogenase (rPfLDH)-is reported in this study. Methods: Test zones on paper surfaces were created by covalently immobilizing streptavidin to the paper, subsequently attaching biotinylated aptamers to streptavidin. Aptamers selectively bound rPfLDH. The measurement of captured rPfLDH enzyme activity served as the means of detecting this biomarker. Enzyme activity across three replicate sensors was digitally quantified using the colorimetric Malstat assay. Results: Screening of several different aptamers reported in the literature showed that aptamers rLDH7 and 2008s immobilized in this manner specifically recognised and captured PfLDH. Using rLDH7, the sensitivity of the mu PAD sensor was evaluated and the mu PAD sensor was applied for preferential detection of rPfLDH, both in buffered solutions of the protein and in spiked serum and red blood cell lysate samples. In buffered solutions, the test zone of the mu PAD sensor exhibited a K-D of 24 +/- 11 nM and an empirical limit of detection of 17 nM, respectively, a limit similar to commercial antibody-based sensors exposed to rPfLDH. The specific recognition of 133 nM rPfLDH in undiluted serum and blood samples was demonstrated by the mu PAD. Conclusion: The reported mu PAD demonstrates the potential of integrating aptamers into paper-based malarial rapid diagnostic tests.

Automated summary

This study reports the design and fabrication of low-cost, rapid, paper-based analytical devices (mu PAD) for the detection of a specific biomarker-rPfLDH for malaria. The mu PAD demonstrated high sensitivity and specificity in detecting rPfLDH in buffered solutions and spiked serum and blood samples, indicating its potential as a diagnostic tool for malaria.