Grafting of Oligo(ethylene glycol)-Functionalized Calix[4]arene-Tetradiazonium Salts for Antifouling Germanium and Gold Surfaces

Abstract

Biosensors that can determine protein concentration and structure are highly desired for biomedical applications. For the development of such biosensors, the use of Fourier transform infrared (FTIR) spectroscopy with the attenuated internal total reflection (ATR) configuration is particularly attractive, but it requires appropriate surface functionalization of the ATR optical element. Indeed, the surface has to specifically interact with a target protein in close contact with the optical element and must display antifouling properties to prevent nonspecific adsorption of other proteins. Here, we report robust monolayers of calix[4]arenes bearing oligo(ethylene glycol) (oEG) chains, which were grafted on germanium and gold surfaces via their tetradiazonium salts. The formation of monolayers of oEGylated calix[4]arenes was confirmed by AFM, IR, and contact angle measurements. The antifouling properties of these modified surfaces were studied by ATR-FTIR spectroscopy and fluorescence microscopy, and the nonspecific absorption of bovine serum albumin was found to be reduced by 85% compared to that of unmodified germanium. In other words, the organic coating by oEGylated calix[4]arenes provides remarkable antifouling properties, opening the way for the design of germanium- or gold-based biosensors.

Synthesis of a Calix[4]arene‐Monodiazonium Salt for Surface Modification

“…Besides, when R contains a functional group such as COOH, a post‐functionalization of the surface can be readily achieved under mild conditions. Calix[4]arene‐tetradiazonium salts were notably used for the modification and further post‐functionalization of gold, carbon and germanium surfaces,, but also polymers and nanomaterials such as gold nanoparticles . Furthermore, this method allows for controlling the composition of binary mixed monolayers, which is essential for sensing applications , .…”

“…Surface modification with calix[4]arene‐tetradiazonium salts X 4 N 4 a – c , . Inset: targeted calix[4]arene‐monodiazonium salt 1 .…”

Robust hydrophobic gold, glass and polypropylene surfaces obtained through a nanometric covalently bound organic layer

“…The development of surfaces with controlled wettability 1-3 is of great importance for applications such as anti-biofouling, 4,5 anti-frosting and anti-fogging, 6,7 self-cleaning, 8 anti-corrosion, 9,10 or water-proong. 11 Wettability is usually assessed by contact angle measurements, with regimes that span from superhydrophilic, characterized by contact angles smaller than 10 , to superhydrophobic, with contact angles greater than 150 and negligible adhesion forces.…”

“…Recently, calix [4]arene-tetradiazonium derivatives have been developed and used for (electro)chemical modications of a wide variety of surfaces ( Fig. 1).…”

“…1). 4,[40][41][42][43][44][45][46][47] Calix [4]arenes are macrocycles composed of four phenolic units that are parasubstituted and linked in the ortho position through methylene bridges. These methylene bridges prevent polymerization of the diazonium derivatives, and hence lead solely to formation of monolayers.…”