Real-time and label-free biosensing using moir?e pattern generated by bioresponsive hydrogel

Bioresponsive hydrogels are smart materials that respond to various external stimuli and exhibit great potential as biosensors owing to their capability of real-time and label-free detection. Here, we propose a sensing platform based on bioresponsive hydrogels, employing the concept of moire ' patterns. Two sets of line patterns with different pitch sizes are prepared; a hydrogel grating whose pitch size changes according to external stimuli and a reference grating with constant pitch size. The volume changes of the hydrogel caused by external stimuli changes the pitch size of the hydrogel grating, and subsequently, the pitch sizes of the moire ' patterns (moire ' signal), whose values can be obtained in a real-time and label-free manner through customized moire ' microscopy and signal processing. After confirming that the pH-induced swelling of hydrogel could be monitored using moire ' patterns, we performed moire ' pattern-based detection of specific proteins using protein-responsive hydrogel that underwent shrinking via interaction with target proteins. Brain-derived neurotrophic factor and platelet-derived growth factor were selected as the model proteins, and our proposed system successfully detected both proteins at nanomolar levels. In both cases, the pitch size change of hydrogel grating was monitored much more sensi-tively using moire ' patterns than through direct measurements. The changes in the moire ' signals caused by target proteins were detected in ex-vivo environments using a custom-made intraocular lens incorporating the hydrogel grating, demonstrating the capability of the proposed system to detect various markers in intraocular aqueous humor, when implanted in the eye.

Automated summary

This study proposes a sensing platform based on bioresponsive hydrogels, using moire patterns for real-time and label-free protein detection. The system demonstrates sensitive monitoring of pH-induced swelling and protein-induced shrinkage of the hydrogel, successfully detecting model proteins.