Coffee Ring Diagnostics
In developing countries where tropical diseases are prevalent, early diagnosis is essential to control spread, eliminate drug resistance, and identify asymptomatic carriers of the disease. Independent of antibodies and thermally sensitive materials, we are developing a novel, low-resource malaria diagnostic platform selective for pfHRP-II, a biomarker indicative of the Plasmodium falciparumparasite strain. The assay is driven by a robust gold nanoparticle platform, where initially, a red to purple colorimetric change is induced upon crosslinking reactions with recombinant HRP-II (Scheme 1). The AuNP-protein aggregates are then deposited onto a surface and captured by selectively sandwiching the protein biomarker in between Ni(II)NTA AuNPs and a Ni(II)NTA-functionalized glass slide, mimicking an ELISA assay. Evaporation of the solution on the slide elicits the microfluidic coffee ring phenomenon, where a dark ring is generated by the accumulation of AuNP aggregates at the drop contact line. Rings are visible to the naked eye in the presence of 48 nM protein concentration, but image processing yields a limit of detection of 14 nM (Figure 1). Our innovative diagnostic proof-of-concept provides a simple user interface performed in timeframes comparable to current rapid diagnostic tests (RDTs).