Half antibody fragments improve biosensor sensitivity without loss of selectivity.

We show for the first time that half antibody fragments obtained by reduction via tris(2-carboxyethyl)phosphine (TCEP) gave a larger response with shear-mode resonating mass sensors than physisorbed whole antibody or antibody immobilized via Protein G. The reduced antibody is shown to preserve the antigen-binding region and was determined via the antigen binding response. Reduction exposed the native thiol group in the antibody that readily chemisorbed onto the gold-coated sensor surfaces with the right orientation for antigen binding. Comparing responses obtained on a quartz crystal microbalance for the detection of pathogenic Escherichia coli O157:H7 using TCEP-reduced antibody with native antibody showed that the proposed method enhances device sensitivity. Examining the half antibody fragments for detection of the pathogen in the presence of the nonpathogenic wild strain showed that the antibody fragments retained their specific antigen binding capability without loss of selectivity.