Some literarture which may be of help with the immobilization of the ligand.
Lahiri, J., L. Isaacs, J. Tien, et al. A Strategy for the Generation of Surfaces Presenting Ligands for Studies of Binding Based on an Active Ester as a Common Reactive Intermediate: A Surface Plasmon Resonance Study. Analytical Chemistry 71: 777-790; (1999). Goto reference
This paper describes the immobilization of ten proteins and two low-molecular-weight ligands on mixed selfassembled monolayers (SAMs) of alkanethiolates on gold. The immobilization was achieved by a two-step procedure: generation of reactive N-hydroxysuccinimidyl esters from the carboxylic acid groups of 2 in the SAM and coupling of these groups with amines on the protein or ligand. Because this method involves a common reactive intermediate that is easily prepared, it provides a convenient method for attaching ligands to SAMs for studies using surface plasmon resonance spectroscopy. These SAMs were resistant to nonspecific adsorption of proteins having a wide range of molecular weights and isoelectric points. The pH of the coupling buffer, the concentration of protein, the ionic strength of the solution of protein, and the molecular weight of the protein all influenced the amount of the protein that was immobilized.
Bergström, G. and C. F. Mandenius Orientation and capturing of antibody affinity ligands: Applications to surface plasmon resonance biochips. Sensors and Actuators B: Chemical 158: 265-270; (2011). Goto reference
A surface plasmon resonance (SPR) sensor chip with immobilized protein G was used for simultaneously capturing, purifying and orienting antibody ligands. The ligands were further stabilized by chemical cross-linking. This procedure of designing the sensor chip improved efficient use of the ligands and could prolong the analytical use. The procedure was evaluated on standard dextran-coated sensor chips onto which commercial semi-purified antibodies towards human serum albumin and human troponin where captured and used for analysing their antigens. The procedure demonstrates a general design approach for presenting the biorecognition element on a biosensor surface which enhances sensitivity, stability and selectivity at the same time as an impure ligand is purified
Makaraviciute, A. and A. Ramanaviciene Site-directed antibody immobilization techniques for immunosensors. Biosensors and Bioelectronics 50: 460-471; (2013). Goto reference
Immunosensor sensitivity, regenerability, and stability directly depend on the type of antibodies used for the immunosensor design, quantity of immobilized molecules, remaining activity upon immobilization, and proper orientation on the sensing interface. Although sensor surfaces prepared with antibodies immobilized in a random manner yield satisfactory results, site-directed immobilization of the sensing molecules significantly improves the immunosensor sensitivity, especially when planar supports are employed. This review focuses on the three most conventional site-directed antibody immobilization techniques used in immunosensor design. One strategy of immobilizing antibodies on the sensor surface is via affinity interactions with a pre-formed layer of the Fc binding proteins, e.g., protein A, protein G, Fc region specific antibodies or various recombinant proteins. Another immobilization strategy is based on the use of chemically or genetically engineered antibody fragments that can be attached to the sensor surface covered in gold or self-assembled monolayer via the sulfhydryl groups present in the hinge region. The third most common strategy is antibody immobilization via an oxidized oligosaccharide moiety present in the Fc region of the antibody. The principles, advantages, applications, and arising problems of these most often applied immobilization techniques are reviewed