Scope: This includes fresh whole blood and fractions and dilutions thereof. Eventually it may include other biofluids for diagnostic information.
Purpose: Interpreting structure morphology from deposit to diagnostic
A study of the drying of blood-droplets on prepared substrates with an initial objective of generating a simple, cheap field-diagnostic for anaemia and other disorders, by mapping a haematocrit phase diagram. The wider objective is to quantify the mechanisms underlying the development of structure within the droplet. Observations of evaporating sessile droplets of colloidal suspensions have been made using a high-resolution video apparatus, including blood from research donors (NHSBT), blood-substitute (Securacell) and analogues (6 µm rigid polystyrene spheres, 240 nm PMMA nanoparticles) on a range of substrates of varying contact-angle, generating a concentration vs contact-angle phase-diagram.
A new method and apparatus based on image-intensity has allowed tracking of time-evolution deposition profiles via advection of particulates to be studied. Morphologies include; ‘coffee-ring’, ‘dimple’ and unusual blood ‘column’ profiles, often terminating in cracking. The presence of a ‘halting’ compaction front reported in the literature was confirmed. A characteristic time-evolution of advection-profiles has been identified for what is believed to be the first time, showing a distinct initial peak near the droplet rim collapsing back progressively towards the centre, generating a spectrum of the colloquially-known ‘coffee-ring’ residue-profiles.
The positional variation of the ‘temporal maximum’ in intensity may provide confirmation of the ‘de-wetting’ status of the compacted structure, and warrants further investigation along with the halting front, and an interesting mode of darkening, which may be related to the porosity of the bed, and refraction at the surface menisci exposed on the droplet.