Preblocking procedure to mitigate non-selective protein adsorption for carboxyl-SAMs used in biosensing

Across a wide range of biomarker detection schemes, carboxyl-terminated thiol self-assembled monolayers (COOH-SAMs) on Au are utilized to functionalize the sensing surface with a bioreceptor via amine coupling. However, commonly used COOH-SAM preparation methods result in large defect densities due to cooperative hydrogen bonding between carboxylic acid end groups, which in turn leads to large non-selective adsorption (NSA) of proteins to hydrophobic surfaces exposed by these defects. In this work, X-ray Photoelectron Spectroscopy is used to characterize the quality of COOH-SAMs by differentiating properly and improperly bound S groups. NSA of model small (Lysozyme), medium (Bovine Serum Albumin, BSA), and large (Fibrinogen) proteins on COOH-SAMs is presented. Due to large NSA to COOH-SAMs, blocking is necessary for sensor reliability. However, conventional blocking techniques occur after functionalization (postblocking) and fail to prevent receptor NSA to the sensor surface during functionalization, whic...