Nano-in-Micro Smart Hydrogel Composite for a Rapid Sensitive Immunoassay.

Immunoassays are an important tool in various bioanalytical settings, such as clinical diagnostics, biopharmaceutical analysis, environmental monitoring, and food testing. An enzyme-linked immunosorbent assay (ELISA) is usually used to amplify immunoassay signals; however, it requires labor-intensive and time-consuming procedures, which hinders its application to rapid cytokine detection. In this study, a nano-in-micro composite system, where immunosensing polystyrene beads (≈320 nm) are incorporated within a stimuli-responsive microgel matrix (≈40 µm) via microfluidics, is investigated. The intrinsic volume phase-transition change properties of the smart microgels allows an enzyme-free enhanced immunoassay, enabling instant enhancement in signal-to-noise ratios of ≈5-fold. This nano-in-micro hydrogel composite offers a simple yet highly effective method for sensitive and multiplexed cytokine analysis without complex enzyme-based signal amplification steps, greatly benefitting advanced immune medicine.