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

Abstract

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.

Texture analysis of protein deposits produced by droplet evaporation

“…The majority of investigators with interest in the structural characterization of deposits use empirical observations to identify shapes. For example, to the detection of different proteins, glycans, hepatotoxins and a malaria biomarker; the droplet evaporation method aim is to recognize the coffee ring on the deposits 65 – 68 . If such structure is identified, the presence of the molecule or the diagnostic of the pathology is positive; in contrast, the diagnostic is negative if the deposit shows a uniform coating.…”

Droplet Drying Patterns on Solid Substrates: From Hydrophilic to Superhydrophobic Contact to Levitating Drops

“…The coffee-ring effect has been used as low-resource diagnostics for detection of the malarial biomarker Plasmodium falciparum [270] and also as a biomarker elsewhere [138,[271][272][273]. Blood drop patterns are used extensively for diagnostic purposes [20].…”

Nondestructive Characterization of Drying Processes of Colloidal Droplets and Latex Coats Using Optical Coherence Tomography

“…Additionally, environmental conditions such as temperature and humidity and the substrate properties also affect the drying process and final deposition [13,14]. Insights gained from these studies of evaporating droplets may ultimately translate to practical applications in polymer science, biomedicine, and nanotechnology [14], such as inkjet printing [15], DNA chip [16], biosensor [17,18] and disease diagnosis based on deposition pattern of biological fluid [19][20][21][22], food quality analysis [23], particle separation [24], and production of nanoparticles for drug delivery [25,26]. All above-mentioned applications are related to mass transportation during drying of a liquid suspension and the resultant film property.…”