Analysis of mixed prostate specific antigen and Tween-20 sessile droplets for the reduction in interfacial PSA adsorption

Abstract

The effect of non-ionic surfactants (Tween-20) in droplet-based systems where a prostate-specific antigen (PSA) laden droplet is placed on an anti-PSA immobilized PDMS substrate was investigated. The role of surfactants in such (antibody-antigen system with surface reaction) droplet-based systems has not been studied before and there are no studies involving surfactant-protein-colloids in droplet-based systems with surface reaction, and this is the motivation of the present work. In this article, we investigated the interactions between protein-surfactant-colloid systems in evaporating sessile droplets with antibody-antigen surface reactions using dynamic surface tension (DST), micro-PIV and confocal microscopy. The presence of Tween-20 showed dampening of the velocities in systems with surface reaction even though the Marangoni number was observed to increased. The dynamic surface tension curves of the pure Tween-20 samples were higher than those of the mixed samples (Tween-20+PS+PSA), indicating the influence of Tween-20 and its contribution to interfacial tension reduction. With an increase in the bulk concentration of Tween-20, the surface tension relaxations also increase implying that more surfactant molecules are transported to the interface and get adsorbed there leading to more homogeneous distribution of the surfactant, PS and PSA. The deposition patterns were homogeneous at all Tween-20 concentrations which is desired in biosensors. The results from this study can be useful for designing biosensors with reduced non-specific binding and lesser interfacial adsorption by incorporating the optimum concentration of Tween-20 in the droplets.

Keywords

• Sessile droplets
• Non-ionic surfactant
• Antibody-antigen reactions
• Dynamic surface tension
• Micro-PIV
• Marangoni flow