pH effects on capture efficiency and deposition patterns in sessile droplet immunoassays: An XDLVO analysis

Immunosensors are crucial for various applications, with capture efficiency and detection time as key performance parameters. Sessile droplets on functionalized substrates have demonstrated potential as micro-reactors for antibody-antigen binding, reducing detection time and analyte volume due to the presence of convective currents. Tuning the surface charges by adjusting buffer pH can modulate antigen capture efficiency. While the impact of pH has been studied on antibody-antigen binding in flow and non-flow systems, the use of sessile droplets and the specific impact of buffer pH on the capture efficiency of surface-functionalized antibodies remains understudied. Understanding how pH affects capture and deposition patterns is vital for optimizing immunosensor design. Additionally, the mechanisms governing internal flow within the droplet and dominant driving forces require further investigation. We investigated the effect of varying buffer pH on prostate-specific antigen (PSA) capture by anti-PSA functionalized polydimethylsiloxane substrates. Capture efficiency was measured using the Brown-Anson model applied to cyclic voltammetry, validated with electrochemical impedance spectroscopy. pH significantly influenced PSA capture by surface-immobilized anti-PSA IgG. The extended Derjaguin-Landau-Verwey-Overbeek theory explained the interplay between pH and internal flow. Micro-particle image velocimetry (PIV) confirmed internal flow, primarily driven by Marangoni flow from solute concentration gradients. Controlling buffer pH in biosensors offers higher capture efficiency and desired deposition patterns. These insights advance immunosensor design and hold potential for biomedical and diagnostic applications.