Bio-nanocapsule-based scaffold improves the sensitivity and ligand-binding capacity of mammalian receptors on the sensor chip

Bio-nanocapsules for oriented immobilization of DNA aptamers on aptasensors

The oriented immobilization of sensing molecules (e.g., IgGs, receptors, lectins, and DNA aptamers) on sensor chips is particularly important for maximizing the potential of the sensing molecules, thereby enhancing the sensitivity and target-binding capacity of biosensors. We previously developed ∼30 nm bio-nanocapsules (ZZ-BNCs) consisting of the hepatitis B virus envelope L protein fused with the tandem form of protein A-derived IgG Fc-binding Z domain (ZZ-L protein). ZZ-BNC acts successfully as a scaffold, enhancing both the sensitivity and binding capacity of IgG, a Fc-fused receptor, and Fc-fused lectin to antigens, cytokines, and sugar chains through an oriented immobilization on a biosensor surface. To expand the versatility of ZZ-BNC, we modified ZZ-BNC by replacing the ZZ domain with a DNA-binding single-chain lambda Cro (scCro) domain, thereby developing scCro-BNC. The scCro-BNC was synthesized in yeast cells and homogeneously purified as ∼30 nm sized nanoparticles. In a quartz crystal microbalance, an scCro-BNC-coated sensor chip immobilized with thrombin-binding DNA aptamers showed an ∼5.5-fold higher thrombin-binding capacity and ∼6000-fold higher detection sensitivity than a sensor chip directly coated with DNA aptamers. In addition, the number of bound thrombin molecules per molecule of DNA aptamer increased by ∼7.8-fold with an scCro-BNC coating, consistent with the theoretical thrombin-binding capacity. Collectively, scCro-BNC was shown to perform as an ideal scaffold for maximizing the potential of the DNA aptamer by immobilizing it in an oriented manner. Facilitating a highly sensitive detection of various target molecules, these BNC-based scaffolds are expected to improve a wide range of biosensors while minimizing the number of sensing molecules required.

Enhanced sugar chain detection by oriented immobilization of Fc-fused lectins

We report a novel scaffold for clustering and oriented immobilization of human IgG1 Fc-fused lectins on biosensors without chemical modifications. This approach uses a bio-nanocapsule (BNC) displaying a tandem form of IgG Fc-binding Z domains derived from Staphylococcus aureus protein A (ZZ-BNC). Incorporating ZZ-BNC effectively increased both the sensitivity and sugar chain-binding capacity compared with the condition without ZZ-BNC.

Two-dimensional membrane scaffold for the oriented immobilization of biosensing molecules

The orientation and density of biosensing molecules on sensor chip should be precisely controlled to improve sensitivity and ligand-binding capacity. We previously developed a ~30-nm bio-nanocapsule (ZZ-BNC), consisting of the hepatitis B virus envelope L protein fused with the tandem form of protein A-derived IgG Fc-binding Z domain (ZZ-L protein). This is used as a robust nanoparticle scaffold to enhance the sensitivity and ligand-binding capacity of IgGs and Fc-fused sensing molecules (Fc-fused receptors). However, due to their rigid particle structure, the surface density of ZZ-L proteins could not be optimized for biosensor functions, and useless ZZ-L proteins become stuck between ZZ-BNC and the sensor chip. Here, we have developed a planar lipid membrane embedded with ZZ-L micelles (ZZ-L membrane), which could modify the surface of any biosensor chip with a controlled density of ZZ-L proteins. Compared with ZZ-BNC, the sensitivity and ligand-binding capacity of IgGs were enhanced about 10-fold with the ZZ-L membrane. Furthermore, the immobilized IgGs could capture their respective antigens almost stoichiometrically, indicating that ZZ-L membrane is the most ideal scaffold for Fc-fused sensing molecules in terms of both clustering and oriented immobilization.

Editorial: Translating the advances of biosensors from bench to bedside

Biosensors have been found with numerous applications in many areas including genetic analysis, detection of infectious diseases, environmental monitoring and forensic analysis. We have witnessed rapid advances in this field, especially with the emergence of nanotechnology in the past decade.