pH Controlled Impedimetric Sensing of Copper(II) Ion Using Oxytocin as Recognition Element

Recent advances in the peptide-based biosensor designs

Biosensors have rapidly emerged as a high-sensitivity and convenient detection method. Among various types of biosensors, optical and electrochemical are the most commonly used. Conventionally, antibodies have been employed to ensure specific interaction between the transmission material and analytes. However, there has been increasing recognition of peptides as a promising recognition element for biosensor development in recent years. The use of peptides as recognition elements provides high level of specificity, sensitivity, and stability for the detection process. The combination of peptide designs and optical or electrochemical detection methods has significantly improved biosensor efficacy. These advancements present opportunities for developing biosensors with diverse functions that can be used to lay a strong scientific foundation for the development of personalized medicine and various other fields. This paper reviews the recent advancements in the development and application of peptide-based optical and electrochemical biosensors, as well as their prospects as a sensor type.

A zinc selective oxytocin based biosensor

Oxytocin is a peptide hormone with high affinity to both Zn²⁺ and Cu²⁺ ions compared to other metal ions. This affinity makes oxytocin an attractive recognition layer for monitoring the levels of these essential ions in biofluids. Native oxytocin cannot differentiate between Cu²⁺ and Zn²⁺ ions and hence it is not useful for sensing Zn²⁺ in the presence of Cu²⁺. We elucidated the effect of the terminal amine group of oxytocin on the affinity toward Cu²⁺ using theoretical calculations. We designed a new Zn²⁺ selective oxytocin-based biosensor that utilizes the terminal amine for surface anchoring, also preventing the response to Cu²⁺. The biosensor shows exceptional selectivity and very high sensitivity to Zn²⁺ in impedimetric biosensing. This study shows for the first time an oxytocin derived sensor that can be used directly for sensing Zn²⁺ in the presence of Cu²⁺.

Direct Assembly and Metal-Ion Binding Properties of Oxytocin Monolayer on Gold Surfaces

Peptides are very common recognition entities that are usually attached to surfaces using multistep processes. These processes require modification of the native peptides and of the substrates. Using functional groups in native peptides for their assembly on surfaces without affecting their biological activity can facilitate the preparation of biosensors. Herein, we present a simple single-step formation of native oxytocin monolayer on gold surface. These surfaces were characterized by atomic force spectroscopy, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. We took advantage of the native disulfide bridge of the oxytocin for anchoring the peptide to the Au surface, while preserving the metal-ion binding properties. Self-assembled oxytocin monolayer was used by electrochemical impedance spectroscopy for metal-ion sensing leading to subnanomolar sensitivities for zinc or copper ions.