Investigating the Effect of Antibody–Antigen Reactions on the Internal Convection in a Sessile Droplet via Microparticle Image Velocimetry and DLVO Analysis

Abstract

The evaporation of antigen-laden sessile droplets on antibody-immobilized PDMS substrates could be used in place of microwells for detection purposes owing to the lesser requirements of analytes and a reduced reaction time. To develop such techniques, the effects of different parameters on the reaction efficiency and on the resulting deposition patterns of antigens on the surface after evaporation need to be well understood. While the resultant deposition patterns from the evaporation of droplets of biological fluids on surfaces are being studied for various biomedical applications, systems where the analyte of interest in the droplet binds to the surface have not been investigated until now. While the effect of temperature on the internal convection within sessile droplets has been studied, the effect of the analyte (antigen in this work) concentration and the analyte–surface (antigen–antibody in this work) binding on the internal convection has not been studied until now. Therefore, to gain insight, the evaporation dynamics of sessile droplets with different concentrations of antigens along with polystyrene microspheres (used as tracers) in phosphate-buffered saline (PBS) on antibody-immobilized PDMS substrates were experimentally studied using microparticle image velocimetry (PIV). It was found that Marangoni flow due to concentration gradients and surface reactions was responsible for the observed velocity field. The antibody–antigen reaction (as compared to the control case of no surface reaction) and higher concentrations of prostate specific antigen (PSA) resulted in increased strength of Marangoni convection. To obtain further insight into the different deposition patterns obtained, the contributions of different particle–particle and particle–substrate forces were determined, and it was observed that the Marangoni forces along with surface tension and DLVO forces create a uniform deposition of the particles present within the droplet. This learning could be used to design biosensors.

Transition from Dendritic to Cell-like Crystalline Structures in Drying Droplets of Fetal Bovine Serum under the Influence of Temperature

“…To do this, we considered the spherical-like geometry of the protein macromolecules in fetal bovine serum. 41 − 43 The approach for the calculation of hydrodynamic and intermolecular forces is similar to that employed in other studies ( 32 , 44 , and 45 ), treating proteins as spherical macromolecules. The equations used for the estimation of electrostatic and van der Waals forces on macromolecules may also be found in other works ( 46 and 47 ).…”

“…In an attempt to understand the phenomena governing the pattern formation, we have performed an approximate analysis of the hydrodynamic (capillary, drag) and intermolecular forces acting in the droplets at the onset of drying (see the Supporting Information). To do this, we considered the spherical-like geometry of the protein macromolecules in fetal bovine serum. − The approach for the calculation of hydrodynamic and intermolecular forces is similar to that employed in other studies , , and , treating proteins as spherical macromolecules. The equations used for the estimation of electrostatic and van der Waals forces on macromolecules may also be found in other works and .…”

Monte Carlo simulation of particle size separation in evaporating bi-dispersed colloidal droplets on hydrophilic substrates

“…In some applications, solutions containing mixtures of particles of different sizes are of interest. As an example, we will mention only some applications: evaporative lithography [1][2][3][4] , diagnostics in medicine 5 , development of biosensors 6 , formation of supraparticles [7][8][9][10] and nanocomposites 11 , creation of photonic crystals 7,12,13 , production of color filters for displays 14 , nanosphere lithography [15][16][17][18] and inkjet printing 19 . Mixtures of particles are also used in other technologies for the formation of structures that are not associated with evaporation, for example, the Langmuir-Blodgett method 20,21 , spin-coating 22 , transfer of a particle monolayer from the liquid-air interface onto an inclined substrate in the process of liquid discharge from a glass container with a tap 23 , etc.…”