Antibody-Gold Nanoparticle Bioconjugates for Biosensors: Synthesis, Characterization and Selected Applications

Antibody-Gold nanoparticle (Ab-AuNP) bioconjugates are widely used in the field of biosensing. This prompted researchers to set up various strategies to conjugate antibodies to gold nanoparticles. Optimal conjugation is of critical importance, as the Ab-AuNP bioconjugates should be stable while maintaining the ability of the antibody to recognize and bind its corresponding antigen. All the same, a high coverage of antibodies on AuNPs is a key-step to build up a sensitive biosensor, but an ideal coverage requires to be perfectly balanced with the orientation and accessibility of the conjugated antibodies. In this review, we intend to provide the reader with the key elements allowing for mastering the conjugation of Ab to AuNP and rationalizing, at the molecular level, the mechanisms involved together with the expected antibody coverages and orientations. We will focus on IgG-type antibodies conjugated to spherical AuNPs as these bioconjugates are the most commonly used ones for biosensors. First, we report an exhaustive survey of the methods of conjugation, via strategies of physisorption and chemisorption. Then we provide a critical restitution of the relevant strategies allowing the quantification of antibodies coverage on gold nanoparticles either through direct analysis of the bioconjugates or indirect analysis of the supernatant. In the last part, we review and discuss selected applications of these Ab-AuNP bioconjugates in optical biosensing.