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Antibodies have become a well-established tool in the fields of diagnostics and treatments, especially within oncology, immunology, and infectious diseases. Despite their effectiveness, antibodies are limited by their size, high production costs, and immunogenicity, which in the long run can lead to significant challenges in the medical field. Some well-researched options to antibodies are non-antibody proteins and peptide scaffolds. In this report, focus lies on providing an overview of designed ankyrin repeat proteins (DARPins), Ankyrons, Affibodies, Anticalins, Adnectins and bicyclic peptides, all different formats of non-antibody proteins and peptide scaffolds. Ranging from 1-20 kDa, these non-antibodies feature stable structural elements and modifiable regions for highly specific bonds with high affinity. While originating from natural sources, non-antibodies can be produced synthetically at a low cost, while also decreasing immunogenicity. This report presents the structures of the chosen six formats, and also their function in various applications, as well as their potential to overcome the hurdles of regular antibodies. With the increasing risks of emerging diseases and other health-related issues, non-antibody proteins and peptide scaffolds show great potential for replacing or assisting conventional antibodies in healthcare and biomedical research.

A series of bicyclic peptides have been designed and synthesized to provide ammonium ion complexation sites via hydrogen bonding in a tetrahedral geometry. Molecular modeling dynamics and electrostatics studies indicate that target compounds 1d-6d may provide better selectivity for ammonium ions over potassium ions than the ammonium ionophore currently used for blood analysis applications, nonactin. Attempts to synthesize 1d, cyclo(L-Glu1�D-Val2�L-Ala3�D-Lys4�D-Val5�L-Val6)-cyclo-(1ã-4å), were unsuccessful due to poor solubility of the synthetic intermediates. This led to the design of 2d-6d in which specific amino acid residues were chosen to provide higher solubility. Compound 2d, cyclo(L-Glu1�D-Ala2�D-Ala3�L-Lys4�D-Ala5�L-Ala6)-cyclo-(1ã-4å), was successfully synthesized, but was also too insoluble for characterization or testing in an ion selective electrode (ISE) sensor format. Compound 6d, cyclo(L-Glu1�D-Leu2�Aib3�L-Lys4�D-Leu5�D-Ala6)-cyclo-(1ã-4å), was successfully synthesized and characterized. When 6d was incorporated into an ISE sensor and tested as an ammonium ionophore, results indicated that the bicyclic peptide lacked solubility in the ISE membrane. A 13C-NMR study has been initiated in order to evaluate selectivity of 6d for ammonium over potassium and sodium cations in solution. Preliminary results with the potassium ionophore valinomycin as a control have been completed.

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