Escherichia coli surface-displayed by Sup35NM nanofibrils and Z-domains fusion protein for signal enhancement in a biolayer interferometry-based immunoassay

Generally, immunoaffinity BLI biosensors detect target analytes via selective adsorption through antigen-antibody interactions. For increased sensitivity, various particles have been introduced into pre-bound analytes on BLI biosensors. With the growing interest in using proteins to assemble functional materials, Sup35NM amyloid fibrils with customized functions attract attention since they are ideal scaffolds for designable materials. In this work, we described a simple strategy through the genetic fusion of Z-domain with the protein Sup35NM for antibody binding and employed amyloid fibrils functionalized E. coli as signal enhancers. The target analytes attached to the BLI biosensor were loaded with antibody-coupled E. coli cells and the optical thickness of the layer greatly changed, thereby inducing a significant wavelength interference. Additionally, the IgG-trapping ability of the bacteria was characterized using ELISA and the BLI method. The signal was amplified in a sandwich assay format utilizing two model antigens, NS1 and PIC. The detection limit of NS1 decreased from 93.98 ng/mL to 0.82 ng/mL under optimized conditions and the signal of PIC is also improved by 8.4-fold. The whole detection takes 30 min. The findings demonstrate that functionalized E. coli may be utilized to amplify the signal of biosensors, in a rapid and sensitive manner.