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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. [ABSTRACT FROM AUTHOR]

Low limit of detection (LOD), high sensitivity and selectivity are essential performance criteria of a sensor. As the naturally occurring uranyl ion (U6+) is toxic, a sensor with suitable performance parameters for measuring U6+ in drinking water is of interest. In this work, four aspects of the detection of U6+ are presented. First, a composite synthesized from aniline, N-phenylglycine and graphene oxide (GO) was used for the first time to detect the uranyl ion. Second, the ligand 2-(5-bromo-2-pyridylazo)-5-(diethylamino) phenol (BromoPADAP) was used as a ligand, attached at the composite surface, functionalized with diamine (Design I) and also as a complexing agent in the electrolyte (Design II), and a comparative study for both the cases was conducted. The parameters for comparison were the sensitivity, LOD and interference from several test ions. It was found that for Design I, the LOD was 50 ppt, while for Design II the LOD was 8 ppb. Next, the interference phenomena were explained by the conventional peak reduction (PR) technique and the barrier width (BW) technique. The BW technique was used for the first time to scale the interference of test ions toward the target analyte Cd2+, as in our previous works. PR technique requires a higher number of tests, while the BW technique employs a couple of tests, thus minimizing the effort. In this work, the BW technique supported the PR technique results in predicting the interference behavior. Finally, the BW technique was used to explain the difference in Design I and II results. [ABSTRACT FROM AUTHOR]

The investigation of antigen-laden droplet deposition patterns on antibody-immobilized substrates has potential for disease detection. Stationary droplets that contain antigens on surfaces immobilized with antibodies can function as microreactors. Temperature modulation enhances reaction efficiency and reduces detection time in droplet-based systems. Thus, the aim of this study is to explore the impact of substrate heating on the structures of protein deposits and the influence of substrate temperature on thermo-solutal Marangoni convection within the droplets. Previous research has explored deposition patterns as diagnostic tools, but limited investigations have focused on the effects of substrate heating on protein deposit structures and the influence of substrate temperature on thermo-solutal Marangoni convection within droplets, creating a knowledge gap. In this study, we conducted experiments to explore how heating the substrate affects the deposition patterns of droplets containing prostate-specific antigen (PSA) on a substrate immobilized with anti-PSA IgG. Additionally, we investigated the thermo-solutal Marangoni convection within these droplets. Our findings reveal distinct deposition patterns classified into dendritic structures (heterogeneous), transitional patterns, and needle-like (homogeneous) structures. The presence of prominent coffee rings and the variation in crystal size across different groups highlight the interplay between thermal and solutal Marangoni advection. Entropy analysis provides insights into structural differences within and between patterns. This work optimizes substrate temperatures for reduced evaporation and detection times while preserving protein integrity, advancing diagnostic tool development, and improving understanding of droplet-based systems. [ABSTRACT FROM AUTHOR]