An ultrasensitive electrochemical immunosensor for Cry1Ab based on phage displayed peptides

The rapid and widespread adoption of Bacillus thuringiensis (Bt) proteins in genetically modified (GM) crops has raised concerns about the impact of GM crops on environment and food safety. A sensitive and specific method for detecting Bt proteins in GM crops is of great significance for environment and food risk assessment. In this study, using Cry1Ab as a model Bt protein, an ultrasensitive electrochemical immunosensor for Cry1Ab protein has been developed based on phage displayed peptide. Phage displayed peptides against Cry1Ab protein were obtained from a phage displayed peptide library without animal immunization process through biopanning-elution strategy. After modification of electrode with gold nanoparticles, selected phage displayed peptide was applied to electrochemical immunosensor for Cry1Ab. Under the optimized conditions, the peptide-based immunosensor showed a dynamic range of 0.01–100   ng/mL and a limit detection of 7   pg/mL. Specific measurement of this established method was conducted by testing cross-reactivity of Cry1Ac (88% amino acid sequence homology to Cry1Ab protein), and the result showed that peptide-based immunosensor has negligible cross-reactivity with analogue. In addition, the accuracy and reproducibility of this established immunosensor was evaluated by testing the recovery of spiked samples and assay coefficients of variation, respectively. The results showed that the average recovery of corn and wheat sample was 90–120% and 86.7–120%, respectively; the intra-assay coefficient of variation was 7.4% (n = 6), and the inter-assay coefficient of variation was 6.9% (n = 6) at 1   ng/mL Cry1Ab solution. Furthermore, the novel concept of peptide-based immunosensor may provide a potential application in general method for the ultrasensitive detection of various Bt proteins.