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Core streptavidin & superparamagnetic beads: Maximising high-affinity binding for immunodiagnostic applications

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  • The biotin-streptavidin bond: The strongest noncovalent biological interaction
  • Core streptavidin: A fully truncated molecule maximising biotin binding affinity
  • Superparamagnetic nanoparticles: a super support for core streptavidin
  • Our native core streptavidin options: homogeneous, reproducible and cost-effective



Streptavidin-biotin systems are the most widely used tools in biochemistry consequently, finding strong success across a wide range of biotechnological applications. Despite this, sourcing cost-effective core streptavidin is critical with factors such as heterogeneity compromising lot performance, alongside the increased demand for automation-compatibility.

So, what are the characteristics of high-quality streptavidin – and which emerging solid phase support is at the fore of the next generation of immunodiagnostic applications?


The biotin-streptavidin bond: The strongest noncovalent biological interaction

The widespread adoption of the biotin-streptavidin conjugation system is primarily attributed to its high-affinity interaction (Kd in the order of 10-14 M), alongside their relatively small size which enables extensive binding to biological molecules without compromising their biological activity.

Although streptavidin-biotin systems are the most widely used tools in biochemistry, the risk of biotin interference has becoming a growing concern. However, awareness of the risk should be balanced by evidence demonstrating that the risk of a clinically relevant impact on assay results is low and effective strategies to mitigate interference are being increasingly used.


Core streptavidin: A fully truncated molecule maximising biotin binding affinity  

The manufacture of streptavidin from its natural source presents a significant challenge resulting from proteolytic processing of its N- and C- termini during preparation. Although complete proteolytic processing produces a “core” streptavidin which improves its binding to biotin conjugates and minimises binding interference, the resulting preparations are heterogenous. Poorly reproducible binding properties result, threatening the consistency of lot-to-lot performance.

 Purity, therefore, is an essential property to consider when selecting core streptavidin. However, products can vary in the degree of truncation, and so when selecting your choice of streptavidin, homogeneous preparations of single isoform core streptavidin are key.

 Alongside homogeneity, we know there are additional challenges. These include non-specific binding, protease-mediated digestion of target proteins, and the nucleolytic degradation of DNA and RNA. With these additional considerations, what characteristics should you identify when sourcing your streptavidin?

 Selecting streptavidin preparations with a neutral isoelectric point can minimise non-specific interactions – with the additional benefit of immobilisation-suitable applications. Damage from protease and nuclease presence can also be prevented by selecting preparations free from these degradative enzymes.

 After selecting an appropriate core streptavidin, a solid support is critical for the immunodiagnostic design process – and functional nanostructures have emerged as potentially revolutionary materials in the field of immunodiagnostics.


Superparamagnetic nanoparticles: a super support for core streptavidin

Among functional nanostructures encompassing nanorods, quantum dots, and nanoshells, superparamagnetic nanoparticles are well-established and increasingly popular support particles for sensitive immunodiagnostic applications, particularly in the automated setting.

 Superparamagnetic beads are surface-modified, optimised and validated for automated immunoassays. With automation the cornerstone of rapid and scalable immunodiagnostics, efficiency and cost-effectiveness are fundamental features that may ultimately determine the success of the platform – features that superparamagnetic beads can offer. What is more, these beads are highly suitable for incorporation into rapid diagnostic test (RDT) kits – potentially increasing device sensitivity with the capacity to detect very low concentrations of biological molecules from crude samples.


Click here to find out more about Smartbond Streptavidin, our Ultra-high purity native core streptavidin.


Our native core streptavidin options: homogeneous, reproducible and cost-effective

When developing future-focused immunodiagnostic approaches, you need a core streptavidin preparation capable of high specific activity and a magnetic support particle that offers a cost-effective solution for developing a wide range of automated assays.

SEKISUI Diagnostics has developed Smartbond Streptavidin, a specialised streptavidin for the enhancement of signal generation, and offers Smartbond Streptavidin Magnetic Beads, which feature our core Smartbond Streptavidin covalently coupled to superparamagnetic beads via proprietary linkers. These are surface-modified, optimised and validated for use with high-throughput random access magnetic platform analysers in the application of immunodiagnostics.

 Smartbond Streptavidin is produced using an enhanced manufacturing process optimised for core homogeneity, which results in a molecule with the highest binding affinity towards biotin. With a high specific activity (≥ 16 U/mg), and near-neutral isoelectric point associated with lower non-specific binding, it offers greater binding capacity and is suitable for use in immobilisation reactions. In addition, minimal protease and nuclease contamination preserves protein and nucleic acid integrity and enables more effective conjugation reactions and molecular biology applications.

Smartbond Streptavidin 1μm Magnetic Beads enhance the characteristics of our Smartbond Streptavidin. The beads are coated using a proprietary coupling chemistry, offering a binding capacity >200 μg biotinylated IgG/mg beads, outperforming competitors on free-biotin binding capacity and a non-specific binding ~2-fold lower than the leading “Gold Standard”. The 1μm size is best suited for automation applications due to its small size, low sedimentation rate, and high magnetic mobility.

This highest binding feature enables R&D scientists to use the minimum possible beads per application, requiring one-tenth of the competitors‘ concentration to perform similar assays – a cost-effective solution for automated assay development. Our uniform beads demonstrate excellent inter-lot reproducibility with highly defined and consistent product characteristics.

SEKISUI Diagnostics addresses the challenge of sourcing core streptavidin that possesses single-isoform homogeneity for maximum affinity binding to biotin for sensitive immunoassay development. Available as a single preparation or conjugated to superparamagnetic beads via proprietary linkers, we help R&D scientists working on the next generation of both immuno- and in vitro diagnostic applications.