Concave Magnetic-Responsive Hydrogel Discs for Enhanced Bioassays

Abstract

Receptor-based biosensors often suffer from slow analyte diffusion, leading to extended assay times. Moreover, existing methods to enhance diffusion can be complex and costly. In response to this challenge, we presented a rapid and cost-effective technique for fabricating concave magnetic-responsive hydrogel discs (CMDs) by straightforward pipetting directly onto microscope glass slides. This approach enables immediate preparation and customization of hydrogel properties such as porosity, magnetic responsiveness, and embedded particles and is adaptable for use with microarray printers. The concave design increased the surface area by 43% compared to conventional hemispherical hydrogels, enhancing diffusion rates and accelerating reactions. By incorporating superparamagnetic particles, the hydrogels become magnetically responsive, allowing for stirring within reagent droplets using magnets to improve mixing. Our experimental results showed that CMDs dissolved approximately 2.5 times faster than hemispherical ones. Numerical simulations demonstrated up to a 46% improvement in diffusion speed within the hydrogel. Particles with lower diffusion coefficients, like human antibodies, benefited most from the concave design, resulting in faster biosensor responses. The increased surface area and ease of fabrication make our CMDs efficient and adaptable for various biological and biomedical applications, particularly in point-of-care diagnostics where rapid and accurate biomarker detection is critical.

Keywords: bioassays; concave hydrogel discs; magnetic-responsive hydrogels.

Figure 1

Schematic of the magnetic-responsive hydrogel disc preparation: (a) concave hydrogel discs; (b) hemispherical hydrogel discs.

Figure 2

Hydrogel disc geometries and revolved models in the numerical simulation: (a) 2D axisymmetric geometry of the hemispherical hydrogel disc; (b) 2D axisymmetric geometry of the concave hydrogel disc; (c) 3D visualization of the hemispherical disc obtained by revolving the 2D geometry; (d) 3D visualization of the concave hydrogel disc obtained by revolving the 2D geometry.

Figure 3

Images of the magnetic-responsive hydrogel disc: (a) side-view images; (b) time-lapse comparison of drying behaviour in concave and hemispherical magnetic-responsive hydrogel discs. Monochrome images were taken every 10 min.

Figure 4

Mesh refinement on the computational model: (a) meshed computational domain of the developed model for different numbers of elements; (b) concentration of lysozyme in the centre of concave discs’ base (red point) for different numbers of elements.

Figure 5

Concentration of different bioparticles in concave (dashed line) and hemispherical hydrogel discs (solid line) at different times in numerical models.

Figure 6

Relative concentration changes of particles in concave versus hemispherical hydrogel discs in numerical models.

Figure 7

Concentration of lysozyme in concave (a) and hemispherical (b) hydrogel discs and droplets at t = 10 s, 100 s, 1000 s, and 2000 s in numerical model.

Figure 8

Comparison of the dissolution of concave and hemispherical magnetic-responsive hydrogel discs in an EDTA solution over time. The gel–bead regions are circled.