Biomarker-Mediated Disruption of Coffee-Ring Formation as a Low Resource Diagnostic Indicator

Abstract

The ring pattern resulting from the unique microfluidics in an evaporating coffee drop is a well-studied mass transport phenomenon generating interest in the research community mostly from a mechanistic perspective. In this report, we describe how biomarker-induced particle-particle assemblies, magnetic separation, and evaporation-driven ring formation can be combined for simple pathogen detection. In this assay design, the presence of biomarkers causes self-assembly of a magnetic nanoparticle and a fluorescently labeled micrometer-sized particle. A small spherical magnet under the center of the drop prevents these assemblies from migrating to the drop's edge while a nonreactive control particle flows to the edge forming a ring pattern. Thus the presence or absence of biomarker results in distinctly different distributions of particles in the dried drop. Proof-of-principle studies using poly-L-histidine, a peptide mimic of the malaria biomarker pfHRPII, show that the predicted particle distributions occur with a limit of detection of approximately 200-300 nM.

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].…”

Evaporation-Driven Bioassays in Suspended Droplets

“…The higher rate of evaporation along the contact line produces these flow patterns (or capillary flow), also known as primary radial flow 17 . The coffee-ring effect has been exploited to perform immunoassays and to separate particles by size 12,[18][19][20] .…”

50 & 100 Years Ago

“…This process is shaped by the physics of drying, for which better control than is currently possible is desired 2 . Additionally, proteins dried on a surface leave a pattern distinctive of that protein, opening up the possibility of simple, low-cost detection of protein or other disease markers in blood or saliva 4,14 . More than 300 years ago, the Dutch microscopist Antonie van Leeuwenhoek discovered a world of microorganisms when he peered through a microscope into a tiny liquid droplet.…”

“…Pollinators use a combination of olfactory and visual cues to find flowers 4,5 . For bees, the colours and shapes of flowers are probably the dominant discriminatory factors.…”