Electrochemical Aptamer-Based Biosensor for Detecting Pap31, a Biomarker for Carrion’s Disease

Carrion's disease, caused by infection with the bacterium <i>Bartonella bacilliformis</i> (<i>B. bacilliformis</i>), is effectively treated with antibiotics, but reaches fatality rates of ~90% if untreated. Current diagnostic methods are limited, insufficiently sensitive, or require laboratory technology unavailable in endemic areas. Electrochemical aptamer-based (E-AB) biosensors provide a potential solution for this unmet need, as these biosensors are portable, sensitive, and can rapidly report the detection of small molecule targets. Here, we developed an E-AB biosensor to detect Pap31, a biomarker of Carrion's disease and an outer membrane protein in <i>B. bacilliformis</i>. We identified an aptamer with Pap31-specific binding affinity using a magnetic pull-down assay with magnetic bead-bound Pap31 and an aptamer library followed by electrophoretic mobility shift assays. We incorporated the Pap31-binding aptamer into a DNA oligonucleotide that changes conformation upon binding Pap31. The resultant Pap31 E-AB biosensor produced a rapid, significant, and target-specific electrical current readout in the buffer, demonstrating an apparent K_D of 0.95 nM with a limit of detection of 0.1 nM, and no significant signal change when challenged with off-target proteins. This proof-of-concept Pap31 biosensor design is a first step toward the development of more rapid, sensitive, and portable diagnostic tools for detecting Carrion's disease.