Grafting of Diazonium Salts on Surfaces: Application to Biosensors

This review is divided into two parts; the first one summarizes the main features of surface modification by diazonium salts with a focus on most recent advances, while the second part deals with diazonium-based biosensors including small molecules of biological interest, proteins, and nucleic acids.

Reversible Trapping of Functional Molecules at Interfaces Using Diazonium Salts Chemistry

Developing thin polymeric films for trapping, releasing, delivering, and sensing molecules is important for many applications in chemistry, biotechnology, and environment. Hence, a facile and scalable technique for loading specific molecules on surfaces would rapidly translate into applications. This work presents a novel method for the trapping of functional molecules at interfaces by exploiting diazonium salt chemistry. We demonstrate the efficiency of this approach by trapping two different molecules, 4-nitrobenzophenone and paracetamol, within polycarboxyphenyl layers grafted on gold and glassy carbon (GC) and by releasing them in acidic medium. The former molecule was chosen as a proof of concept for its electrochemical and spectroscopic properties, and the latter one was selected as an example of a pharmaceutical molecule. Advantages of the present approach rely on the simplicity, rapidity, and efficiency of the procedure for the reversible, on demand, trapping and release of functional molecules.

Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing

The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol⁻¹) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films.

Self-assembled monolayers (SAMs) have shown tremendous number of applications but can suffer from low stability. Here, the authors report air and bench stable carbene precursors allowing facile SAM formation, and furthermore demonstrate an application in biosensing

Highly sensitive and selective detection of the pyrophosphate anion biomarker under physiological conditions

Self-assembled monolayers on gold of a multidentate adsorbate bearing a bis(carbazolyl)urea unit are prepared and used as a surface resonance plasmon sensor for the detection of hydrogen pyrophosphate anions under physiological conditions.

Electrochemical functionalization of gold and silicon surfaces by a maleimide group as a biosensor for immunological application

In the present study we investigated the preparation of biofunctionalized surfaces using the direct electrochemical grafting of maleimidophenyl molecules with subsequent covalent immobilization of specific peptide to detect target antibody, thereby extending the application of the biosensing systems towards immunodiagnostics. Para-maleimidophenyl (p-MP) functional groups were electrochemically grafted on gold and silicon surfaces from solutions of the corresponding diazonium salt. A specially synthesized peptide modified with cysteine (Cys-peptide) was then immobilized on the p-MP grafted substrates by cross-linking between the maleimide groups and the sulfhydryl group of the cysteine residues. Accordingly, the Cys-peptide worked as an antigen that was able to bind specifically the target antibody (anti-GST antibody), while it was non-sensitive to a negative contrast antibody (i.e. anti-Flag β). The immobilization of both specific and non-specific antibodies on the Cys-peptide-modified surfaces was monitored by infrared spectroscopic ellipsometry, a quartz crystal microbalance integrated in flow injection analysis system and potentiometric response. The results obtained clearly demonstrated that the direct modification of a surface with maleimidophenyl provides a very simple and reliable way of preparing biofunctionalized surfaces suitable for the construction of immunological biosensors.

Versatile and nondestructive photochemical process for biomolecule immobilization

Covalent immobilization of unmodified biological materials as proteins has been performed through a one-step and soft method. This process is based on a polyazidophenylene layer derived from the electroreduction of the parent salt 4-azidobenzenediazonium tetrafluoborate on gold substrates. The wavelength used (365 nm) for the photochemical grafting of a large variety of molecules as biomolecules is a key point to this nondestructive immobilization method. This simple process is also versatile and could be used for covalently binding a wide range of molecules such as polyethylene glycol moieties, for example. To validate this approach for biochip or microarray fabrication, a surface plasmon resonance imaging (SPRi) platform for immobilization of various antibody families was created by grafting G-protein through this process. This SPRi antibodies platform was tested with several consecutive cycles of antigen injections/regeneration steps without loss of activity.