Low-Fouling Characteristics of Ultrathin Zwitterionic Cysteine SAMs

Abstract

Surface fouling remains an exigent issue for many biological implants. Unwanted solutes adsorb to reduce device efficiency and hasten degradation while increasing the risks of microbial colonization and adverse inflammatory response. To address unwanted fouling in modern implants in vivo, surface modification with antifouling polymers has become indispensable. Recently, zwitterionic self-assembled monolayers, which contain two or more charged functional groups but are electrostatically neutral and form highly hydrated surfaces, have been the focus of many antifouling coatings. Reports using various compositions of zwitterionic polymer brushes have demonstrated ultralow fouling in the ng/cm range. These coatings, however, are thick and can hinder the target application of biological devices. Here, we report an ultrathin (8.52 Å) antifouling self-assembled monolayer composed of cysteine that is amenable to facile fabrication. The antifouling characteristics of the zwitterionic surfaces were evaluated against bovine serum albumin, fibrinogen, and human blood in real time using quartz crystal microbalance and surface plasmon resonance imaging. Compared to untreated gold surfaces, the ultrathin cysteine coating reduced the adsorption of bovine serum albumin by 95% (43 ng/cm adsorbed) after 3 h and 90% reduction after 24 h. Similarly, the cysteine self-assembled monolayer reduced the adsorption of fibrinogen as well as human blood by >90%. The surfaces were further characterized using scanning electron microscopy: protein-enhanced adsorption and cellular adsorption in human blood was found on untreated surfaces but not on the cysteine SAM-protected surfaces. These findings suggest that surfaces can be functionalized with an ultrathin layer of cysteine to resist the adsorption of key proteins, with performance comparable to zwitterionic polymer brushes. As such, cysteine surface coatings are a promising methodology to improve the long-term utility of biological devices.

Grafted Polymer Coatings Enhance Fouling Inhibition by an Antimicrobial Peptide on Reverse Osmosis Membranes

“…The initial adhesion of biofouling material on a surface is a complex process where the surface charge, hydrophilicity, and chemical composition play roles. , Hydrophilically charged polymer compositions, in particular, zwitterionic polymers, are known to inhibit the binding of proteins and other substances that lead to biofouling . The very strong hydration layer caused by the zwitterionic surface prevents the adherence of proteins and other solutes. − PEG-based materials have also been demonstrated to have antifouling properties. − Such surface modifications with various compositions and properties can be conveniently prepared using various types of radical polymerization reactions. For example, a “grafting-from” surface reaction using redox initiators and acrylate monomers results in covalently bound polymers on surfaces with high thermal and solvent stability.…”

Antifouling Coatings Generated from Unsymmetrical Partially Fluorinated Spiroalkanedithiols

“…Together with ellipsometry, a common and easily accessible method, we chose to explore the use of other, more sensitive biophysical techniques, such as SPR − and QCM, − to examine the protein resistance of thin films derived from the adsorbates, as shown in Figure . The biophysical methods are needed not only to evaluate the validity of the ellipsometry data but also to gain broader insight into the antifouling performance of the unique “conflicted” interfaces prepared herein.…”

Ultrasensitive SERS Substrate for Label-Free Therapeutic-Drug Monitoring of Paclitaxel and Cyclophosphamide in Blood Serum

“…Also, increasing the stability of the zwitterion through the unavailability of the thiols is the rationale for l -cysteine oxidation . It has already been reported that l -cysteine functionalization on gold surfaces decreases the fouling of BSA by 98.5% compared with that on bare gold surfaces. , l -Cysteine serves as an ideal zwitterionic molecule for SAuNP modification because of its low surface thickness and ability to retain the analytes close to the SAuNP surfaces, which is excellent for SERS detection with a minimum distance of 1.24 nm . Also, the nanometer size of l -cysteine maintains the spacing between SAuNPs of ∼2.28 nm, which promotes the generation of hotspots for SERS analysis .…”