# Utilizing Constrained Bicyclic Peptides for In Vitro Diagnostics

## TL;DR

Researchers developed small peptide molecules that bind tightly to a SARS-CoV-2 protein and can be used in sensitive diagnostic tests.

## Contribution

Demonstrated the first use of constrained bicyclic peptides as diagnostic tools for detecting SARS-CoV-2 with high sensitivity.

## Key findings

- Bicycle molecules showed micromolar to low nanomolar binding affinity to SARS-CoV-2 nucleocapsid protein.
- Validated use in enzyme-linked and lateral flow immunoassays for detecting ultralow concentrations of the target protein.

## Abstract

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.