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 ∘C), "transition" patterns (from 44 to 50 ∘C), and "eye" patterns (from 58 to 63 ∘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 ∘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.

Feasibility of the use of a pixelated transmission chamber to measure scattered-radiation in projection radiography: I. Monte Carlo analysis of x-ray scatter propagation and detector modeling.

In this paper, we propose the use of a pixelated transmission chamber, placed between the patient and the imaging detector, to measure the scatter component of a radiation beam impinging on said imaging detector. Using Monte Carlo simulation, a three-parameter model for the propagation of the scatter component in the transmitted beam is first developed. The use of the transmission chamber to determine the model parameters is then modeled, again using Monte Carlo simulation, and the feasibility of this approach is determined. The amount of radiation backscattered from the imaging detector into the transmission chamber was also calculated, for several separation distances between the two. It is shown that at a separation of 10cm, the amount of backscatter radiation is independent of the imaged object and that therefore it can be determined as part of a calibration procedure for the transmission chamber.