Immobilization of streptavidin onto biotin-functionalized Langmuir–Schaefer binary monolayers chemisorbed on gold

• Published in: Sensors and actuators. B, Chemical Chemical, 2004-09, Vol.102 (2), p.207-218
• Main Authors: Ihalainen, P., Peltonen, J.
• Format: Article
• Language: English
• Subjects: Langmuir–Schaefer monolayer; One-dimensional crystallization; Quartz crystal microbalance; Scanning probe microscopy; Streptavidin
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2004.04.023

Binary films of 1-palmitoyl-2-(16-( S-methyldithio)-hexadecanoyl)- sn-glycero-3-phosphocholine (DSDPPC) and 1,2-dipalmitoyl- sn-glycero-3-phosphoethanolamine- N-(Cap Biotinyl) (biotin-Cap-DPPE) with different molar ratios were formed at the air–water interface. The Langmuir–Schaefer deposition of the binary monolayers onto a gold substrate with good transfer ratio was demonstrated by quartz crystal microbalance (QCM) and scanning probe microscopy (SPM) studies. In these molecular assemblies, DSDPPC binds the monolayer covalently to the gold substrate, whereas the embedded receptor molecules (biotin-Cap-DPPE) make the created solid-supported lipid surface biofunctional. Low molar ratio of biotin-Cap-DPPE was found to be optimal for protein immobilization. Immobilization of streptavidin onto the biotinylated lipid surface was demonstrated by QCM and SPM. The SPM image data was transformed into accurate surface density values by applying a self-made image analysis subroutine. The algorithm of the subroutine effectively eliminates the tip-sample convolution allowing the counting of bound proteins. The results show that immobilized streptavidin molecules organized themselves in chain-like structures indicating 1D instead of 2D crystallization. The amount of immobilized proteins measured as the frequency shift by QCM in liquid phase was systematically 2.4±0.1 times higher than the topographical surface coverage measured by SPM for dry samples.