Self-Assembled Monolayers as Platform for Biosensors

Abstract

In chapter one, self-assembled monolayers (SAMs), the platform for biosensors, were discussed in detail regarding surface pKa, stability, and chemical reactions. Mixed self-assembled monolayers, especially when incorporated with poly(ethylene)glycol, has become an important platform for protein immobilization as well as a model system for studying protein-surface interactions. Following self-assembled monolayers, the core technology of immunological biosensors, antibody immobilization, were discussed with emphasis on antibody orientation immobilization schemes. Last, a brief review of microscopy and characterization techniques used for biosensor research was given. In chapter 2, random antibody immobilization on mixed SAMs of 16- mercaptohexadecanoic acid and 11-mercapto-1-undecanol formed at 60°C showed slightly higher surface antibody density than that formed at room temperature. Rabbit IgGs have been immobilized on uniform SAMs surface through Fc region attachment. Non-contact mode AFM has been successfully used to image the attached antibody surface. It is speculated that antibodies on the surface adopt a parallel orientation. Further in-situ AFM antibody-antigen binding experiments in liquid need to be carried out to confirm the findings. In chapter 3, rabbit anti-Salmonella IgGs were covalently immobilized on pure or mixed SAMs surfaces, and the antibody functionalized surfaces were capable of detecting Salmonella enterica Typhimurium in PBS solution. The surfaces of captured bacteria and bacteria coverage were examined by SEM. The random antibody immobilization approach provided highly uniform and partial surface bacteria coverage when exposed to high concentration of Salmonella enterica Typhimurium solution. Pure thioctic acid SAMs provided the best bacteria coverage of 7.83 × 10^6 cells/ cm2 amongst all the SAMs tested. A preliminary study of the efficacy of site-directed antibody immobilization on detection of Salmonella enterica Typhimurium was carried out, and a bacteria density of 1.64 × 10^6 cells / cm2 was achieved. Further optimization of the experimental conditions of site-directed method is needed in order to provide higher bacteria density on gold surfaces. The reported SAMs based protein immobilization provides a generic platform of bioreceptor immobilization in biosensor development which can be tailored for detection of Salmonella enterica Typhimurium and a variety of other foodborne pathogens.