Abstract
A pH dependent reversible sponge like behavior of a bovine serum albumin (BSA) nanolayer adsorbed at the gold-saline interface is revealed by quartz crystal microbalance with dissipation (QCM-D), atomic force microscope (AFM) and contact angle measurements. During the saline rinsing cycles, the BSA layer adsorbs water molecules at pH 7.0 and releases them at pH 4.5. The phenomenon remains constant and reproducible upon multiple rinsing cycles. The BSA layer thickness also increases upon rinsing with saline at pH 7.0 and reverses back to its original thickness at pH 4.5. Varying ionic strength with water further desorbs more water molecules from the BSA layer, which decreases its mass and thickness. However, upon both pH and ionic strength changes, all the BSA molecules remain adsorbed irreversibly at the gold interface and only the sorption of water molecules occurs. The study aims at engineering high efficiency pH-responsive biodiagnostics and drug delivery systems.
Highlights
Serum albumins are proteins commonly used in bio-diagnostics and as model in bio-interface research (Rosi and Mirkin, 2005; Singh et al, 2005; Arcot et al, 2015)
A reversible pH responsive water sorption phenomenon of bovine serum albumin (BSA) molecules adsorbed at the solid-liquid interface is studied by quartz crystal microbalance with dissipation (QCM-D) with rinsing cycles of saline solution at pH 7.0 and 4.5
Multiple articles have previously reported the adsorption of BSA and similar proteins near the isoelectric point to be driven by hydrophobic interactions which outweigh the electrostatic interactions (Uyen et al, 1990; Tilton et al, 1991; Figueira and Jones, 2008; Norde, 2008; Jeyachandran et al, 2009; Rabe et al, 2011; Huang et al, 2017; Xu et al, 2018; Attwood et al, 2019)
Summary
Serum albumins are proteins commonly used in bio-diagnostics and as model in bio-interface research (Rosi and Mirkin, 2005; Singh et al, 2005; Arcot et al, 2015). Bovine serum albumin (BSA) is the cheapest and a protein widely used as blocking agent in ELISA tests (Maingonnat et al, 1999). BSA (Huang et al, 2018) selectively increases paper hydrophobicity to improve bio-fluids and elution flow by decreasing liquid absorption. BSA protects and increases the lifetime of functional biomolecules dried on paper. The functionality and longevity of immunoglobin G and immunoglobin M dried on BSA treated surfaces can increase by an order of magnitude (van Remoortere et al, 2001). BSA prevents unspecific adsorption of analytes proteins for quantitative analysis
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