Designed Multifunctional Isopeptide for Enhanced Annexin A1 Biosensing Based on Peptide–Protein Interactions in Human Blood

Specific peptide–protein interactions play an important role in biosensing systems based on functional peptides; however, the non-specific interactions with unrelated biomolecules and poor proteolytic stability restrict the clinical application of natural peptides. Here, we leveraged a self-designed multifunctional isopeptide (MISP) to construct an electrochemical biosensing platform for annexin A1 (ANXA1) detection in human blood. The MISP was designed to contain two parts: an antifouling cyclotide cyclo-C(EK)4 and a d-amino acid-containing carbohydrate-mimetic recognizing peptide IF-7 (D-IF7) connected by the isopeptide bond. We have discussed the properties of the cyclotide and illustrated its unique advantage over the natural linear antifouling peptides by molecular dynamics simulations, and the results were further confirmed by dissipative quartz crystal microbalance (QCM-D). In addition, through electrochemical experiments and fluorescence imaging experiments, we demonstrated that the MISP-based biosensor possessed excellent antifouling ability and proteinase hydrolysis stability. Interestingly, the assaying results of the MISP-biosensor were consistent with those of the commercial ANXA1 kits in a variety of healthy and ANXA1-upregulated clinical blood samples, and, more importantly, for the analysis of blood samples with lower ANXA1 expressions, the sensing capability of the biosensor was greatly superior to that of the kits because of the lower detection limit of the MISP-biosensor. This biosensing platform based on the designed MISP offers enormous potential for achieving accurate biomarker detection with robust operation in complex biological samples.