Sickle cell hemoglobin detection in drying drops: from protein/nanoparticle interaction to low resource diagnostic tools

The coffee-ring effect denotes the accumulation of particles at the edge of an evaporating drop pinned on a substrate, as one can observe in the black ring of a coffee stain. Because it can be detected by simple visual... [ view full abstract ]

The coffee-ring effect denotes the accumulation of particles at the edge of an evaporating drop pinned on a substrate, as one can observe in the black ring of a coffee stain. Because it can be detected by simple visual inspection, this ubiquitous phenomenon has been recently combined with specific particle formulations to develop robust and cost-effective diagnostic tools. Here we analysed the deposit morphology of drying drops containing polystyrene nanoparticles of different surface properties with human native and mutant hemoglobin. We show that deposit patterns reveal information on both the adsorption of proteins on the particles and their reorganization following adsorption. We then established the conditions that enable to distinguish between native and sickle cell hemoglobin by simple pattern analysis. The suppression of the coffee ring effect and the formation of a disk-shaped pattern is primarily associated to particle neutralization by protein adsorption. However, our findings also suggest that protein reorganization following adsorption can dramatically invert this tendency. Exposure of hydrophobic residues can lead to disk deposit morphologies independently of the global particle charge due to accumulation of particles at the liquid/gas interface during evaporation. This general behaviour opens the possibility to probe protein adsorption and reorganization on particles by the analysis of the deposit patterns, the formation of a disk being the robust signature of particles rendered hydrophobic by protein adsorption. This method is sensitive enough to detect a single point mutation in a protein, as demonstrated by the distinct patterns formed by human native hemoglobin HbA and its mutant form HbS responsible for sickle cell anemia (1). The coffee-ring effect can translate various types of molecular interactions between nanoparticles and proteins into easily distinguishable macroscopic patterns, thus providing valuable insights for the development of future cost-effective diagnostic tools.

Reference
(1) Devineau S, Anyfantakis M, Marichal L, Kiger L, Morel M, Rudiuk S, Baigl D. Protein adsorption and reorganization on nanoparticles probed by the coffee-ring effect: application to single point mutation detection. JACS (2016) 138, 11623-11632