Self-assembly of the polymer brush-grafted silica colloidal array for recognition of proteins

Three-dimensional photonic crystal sensors are attractive platforms for autonomous chemical sensing and colorimetric bioassays. At present, the photonic crystal sensors with inverse opal structure were extensively studied, which swells or shrinks in response to the analytes. However, the fabrication of inverse opal sensors still remains a major challenge. Herein, we propose a simple and versatile approach to fabricate 3D opal photonic sensors. This photonic crystal is fabricated via assembly of monodispersed silica particles grafted with linear polymeric ligands (SiO2@LPs). Acrylic acid (negatively charged monomer) and N-tert-butylacrylamide (hydrophobic monomer) were incorporated with N-isopropylacrylamide to achieve strong affinity between the designed polymer ligands and proteins. The proposed photonic crystal displays a maximum redshift of 23 nm in response to 2 mg/mL lysozyme, accompanied by the structure color change from blue to green. Compared to the cross-linked polymers, the linear polymer with flexible structure allows the colloidal array to recognize lysozyme with higher sensitivity (as low as 5 μg/mL) and broader linearity (from 5 to 2000 μg/mL in aqueous media). In the future, this photonic crystal sensor can be used as universal tools for the detection of a broad range of analytes.