Utilizing Constrained Bicyclic Peptides for In Vitro Diagnostics.

Constrained bicyclic peptides (Bicycle molecules) with high affinity for biological targets have emerged as potentially powerful therapeutic agents, particularly for the in vivo targeting of cancer receptors. However, their antibody-mimetic properties have yet to be explored for use in diagnostic immunoassays. These synthetically derived compounds serve as biorecognition scaffolds that allow for facile site-selective modification and large-scale production. A phage display screen against various constructs of the SARS-CoV-2 nucleocapsid (N) protein identified several Bicycle molecules with binding affinities ranging from the micromolar to the low nanomolar range. These Bicycle molecules were validated in the development of enzyme- and nanozyme-linked immunosorbent assays, as well as enzymatic and colorimetric nanoparticle-based lateral flow immunoassays (LFIA) for the detection of ultralow concentrations of the SARS-CoV-2 N protein. We envision that these moieties enable robust, cost-effective, and large-scale development of ultrasensitive biosensors for a diverse range of biomarkers by leveraging their high binding affinity, minimalistic scaffold, and synthetic accessibility.