Effects of substrate temperature on patterns produced by dried droplets of proteins

Rapid diagnosis provides better clinical management of patients, helps control possible outbreaks, and increases survival. The study of deposits produced by the evaporation of droplets is a useful tool in the diagnosis of some health problems. With the aim to improve diagnostic time in clinical practice where we use the evaporation of droplets, we explored the effects of substrate temperature on pattern formation of dried droplets in globular protein solutions. Three deposit groups were observed: functional patterns (from 25 to 37 circle C), transition patterns (from 44 to 50 circle C), and eye patterns (from 58 to 63 circle C). The dried droplets of the first two groups show a ring structure (coffee-ring) that confines a great diversity of aggregates such as needle-like structures, tiny blade-shape crystals, highly symmetrical crystallization patterns, and amorphous salt aggregates. In contrast, the eye patterns are deposits with a large inner aggregate surrounded by a coffee ring, and they can appear from the evaporation of droplets in protein binary mixtures and blood serum. Interestingly, the unfolding proteins correlates with the formation of eye patterns. We measured stain diameter, coffee-ring thickness, radial density profile, and entropy computed by GLCM-statistics to quantify the structural differences among deposit groups. We found that functional patterns are structurally indistinguishable among them, but they are clearly different from elements of the other deposit groups. An exponential decay function describes pattern formation time as a function of substrate temperature, which is independent from protein concentration. Patterns formation at 32 circle C takes place up to 63% less time and preserves the structural characteristics of dried droplets in proteins formed at room temperature. Therefore, we argue that droplet evaporation at this substrate temperature could be an excellent candidate to make a more efficient diagnosis based on droplet evaporation of biofluids.

Automated summary

Rapid diagnosis is crucial for patient management and outbreak control. Study of droplet evaporation deposits shows distinct patterns that can be used for health issue diagnosis. Different deposit groups exhibit unique features with eye patterns correlating with protein unfolding.