Coffee rings as low-resource diagnostics: detection of the malaria biomarker Plasmodium falciparum histidine-rich protein-II using a surface-coupled ring of Ni(II)NTA gold-plated polystyrene particles.
We report a novel, low-resource malaria diagnostic platform inspired by the coffee ring phenomenon, selective for Plasmodium falciparum histidine-rich protein-II (PfHRP-II), a biomarker indicative of the P. falciparum parasite strain. In this diagnostic design, a recombinant HRP-II (rcHRP-II) biomarker is sandwiched between 1 μm Ni(II)nitrilotriacetic acid (NTA) gold-plated polystyrene microspheres (AuPS) and Ni(II)NTA-functionalized glass. After rcHRP-II malaria biomarkers had reacted with Ni(II)NTA-functionalized particles, a 1 μL volume of the particle-protein conjugate solution is deposited onto a functionalized glass slide. Drop evaporation produces the radial flow characteristic of coffee ring formation, and particle-protein conjugates are transported toward the drop edge, where, in the presence of rcHRP-II, particles bind to the Ni(II)NTA-functionalized glass surface. After evaporation, a wash with deionized water removes nonspecifically bound materials while maintaining the integrity of the surface-coupled ring produced by the presence of the protein biomarker. The dynamic range of this design was found to span 3 orders of magnitude, and rings are visible with the naked eye at protein concentrations as low as 10 pM, 1 order of magnitude below the 100 pM PfHRP-II threshold recommended by the World Health Organization. Key enabling features of this design are the inert and robust gold nanoshell to reduce nonspecific interactions on the particle surface, inclusion of a water wash step after drop evaporation to reduce nonspecific binding to the glass, a large diameter particle to project a large two-dimensional viewable area after ring formation, and a low particle density to favor radial flow toward the drop edge and reduce vertical settling to the glass surface in the center of the drop. This robust, antibody-free assay offers a simple user interface and clinically relevant limits of biomarker detection, two critical features required for low-resource malaria detection.
Department of Chemistry, Vanderbilt University , Station B 351822, Nashville, Tennessee 37235-1822, United States.
Christopher P
CP
Gulka
Joshua D
JD
Swartz
Joshua R
JR
Trantum
Keersten M
KM
Davis
Corey M
CM
Peak
Alexander J
AJ
Denton
Frederick R
FR
Haselton
David W
DW
Wright
D000818:Animals; D000953:Antigens, Protozoan / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism*; D006046:Gold / Q000737:chemistry*; D016778:Malaria, Falciparum / Q000469:parasitology*; D046529:Microscopy, Electron, Transmission; D010963:Plasmodium falciparum / Q000378:metabolism*; D011137:Polystyrenes / Q000737:chemistry*; D015800:Protozoan Proteins / Q000378:metabolism*; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
D000953:Antigens, Protozoan; D015415:Biomarkers; C514457:HRP-2 antigen, Plasmodium falciparum; D011137:Polystyrenes; D015800:Protozoan Proteins; D006046:Gold; D014025:Titanium