A comparative study of the drying evolution and dried morphology of two globular proteins in de-ionized water solutions.

Anusuya Pal,Amalesh Gope,Germano S Iannacchione,Ari S Athair

doi:10.1039/d0ra01748e

Anusuya Pal, Amalesh Gope + Show 2 more

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https://doi.org/10.1039/d0ra01748e

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Abstract

Pattern formation in drying protein droplets continues to attract considerable research attention because it can be linked to specific protein–protein interactions. An extensive study of the drying evolution and the final crack patterns is presented, highlighting the concentration dependence (from 1 to 13 wt%) of two globular proteins, lysozyme (Lys) and bovine serum albumin (BSA), in de-ionized water. The drying evolution starts with a constant contact radius mode and shifts to a mixed mode where both fluid front and contact angle changes. The contact angle monotonically decreases, whereas, the fluid front exhibits two regimes: an initial linear regime and a later non-linear regime. Unlike the linear regime, the non-linear regime is faster for Lys droplets. This results in the formation of a “mound”-like structure in the central region. A new feature, a “dimple” is observed in this mound which is found to be dependent on the initial concentration. The different crack morphology of BSA and Lys depends strongly on the initial state of the solution and can be interpreted using a simple mechanical model. In fact, when dried under uniform conditions (surface, humidity, temperature, droplet diameter, etc.), the evolution and the final pattern displays as a fingerprint of the initial state.

Highlights

A colloidal droplet deposited on a surface either spreads over the surface or remains as it is depending on the wettability of the surface
The consistent reduction of the contact angle during the drying process helps in identifying the different modes of evaporation
The relatively higher initial protein concentration used in this study facilitated the identi cation of a “dimple” on the moundstructure in the dried Lys droplets

Summary

Introduction

A colloidal droplet deposited on a surface either spreads over the surface or remains as it is depending on the wettability of the surface. The droplet endures a whole range of interfacial phenomena (wetting dynamics, adsorption, and adhesion), internal ow (diffusion and convection), and particle–substrate interactions during the solvent evaporation (drying).[1,2] The pattern formation of a bio-colloidal droplet, even on an ideal surface, is exposed to additional complexity during the drying process. Some bio-colloidal droplets such as blood and plasma serum are ubiquitous, and, most notably, are used in medical diagnostics and forensics analysis.[3,4,5,6] Studies on drying droplets reveal that the evolution and the emerging patterns depend on multiple factors including the nature of the solute particles (size, chemical composition initial concentration), different type of substrates (hydrophilic, hydrophobic), geometry, substrate wetting, and various drying conditions (temperature, pH, relative humidity).[7,8,9,10,11] it turns out to be

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