PfHRP2 detection using plasmonic optical fibers: a step towards early malaria diagnosis

Biosensing using optical fibers allows the detection of low concentrations of analytes. To exploit this property, we study a cost-effective fiber-based solution to target the presence of Plasmodium falciparum histidine-rich protein 2 (PfHRP2), a biomarker for malaria diagnosis. In this work, unclad multimode optical fiber probes (400 mu m core diameter) are coated with a thin gold film to excite Surface Plasmon Resonance (SPR), yielding high sensitivity to surrounding medium and more precisely to target-bioreceptor interactions. They are connected to a portable white light source and a spectrometer for read-out. The covalent immobilization of anti-PfHRP2 antibodies on gold and its passivation allowed specific detection in different types of media. The use of secondary antibodies as amplifiers in a sandwich assay also allowed us to improve the sensitivity of the method. Different blocking agents (fish gelatin, bovine serum albumin and casein) were studied to optimize the surface selectivity. The detection of PfHRP2 was first calibrated using spiked proteins into phosphate buffer saline (PBS) and then tested in vitro using fresh cultures of Plasmodium falciparum. The shifts observed with our technique were also compared with results obtained from an ELISA (gold-standard technique for detection and quantification of targets), and commercial paper-based lateral-flow assays, usually used on field. As malaria affects many people worldwide, improvement and multiplexing of this technique can be a perspective to overcome the limitations of currently available point-of-care tests in the future.