Carbodiimide/NHS Derivatization of COOH-Terminated SAMs: Activation or Byproduct Formation?

• Published in: Langmuir Vol. 30; no. 16; pp. 4545 - 4550
• Main Authors: Palazon, Francisco, Montenegro Benavides, Cindy, Léonard, Didier, Souteyrand, Éliane, Chevolot, Yann, Cloarec, Jean-Pierre
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 29.04.2014
• Subjects: Analytical chemistry; Biosensing Techniques; Carbodiimides - chemistry; Carboxylic Acids - chemistry; Chemical Sciences; Solvents - chemistry; Spectrometry, Mass, Secondary Ion; Surface Properties; THIN-FILMS; GOLD; FT-IR SPECTROSCOPY; SELF-ASSEMBLED MONOLAYERS; SURFACE FUNCTIONAL-GROUPS; ANTIBODY; ACID-BASE REACTIONS; ADSORPTION; ELABORATION; IMMOBILIZATION
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la5004269

COOH-terminated self-assembled monolayers (SAMs) are widely used in biosensor technology to bind different amine-containing biomolecules. A covalent amide bond, however, can be achieved only if the carboxylic acids are activated. This activation process usually consists of forming an N-hydroxysuccinimidyl ester (NHS-ester) by consecutively reacting carboxylic acids with a carbodiimide and NHS. Though many papers report using this method, − the experimental conditions vary greatly between them and chemical characterization at this stage is often omitted. Evidence of an efficient activation is therefore rarely shown. Furthermore, recent publications − have highlighted the complexity of this process, with the possible formation of different byproducts. In this paper, we have conducted a study on NHS activation under different conditions with chemical characterization by polarization-modulation infrared reflection–absorption spectroscopy (PM-IRRAS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Our results indicate that the nature of the solvent and carbodiimide and the reactant concentrations play crucial roles in activation kinetics and efficiency.