Graphene oxide-decorated hyrogel inverse opal photonic crystal improving colorimetric and fluorescent responses for rapid detection of lipocalin-1

In this paper, the colorimetric and fluorescent biosensors prepared from polyethylene glycol diacrylate (PEGDA)-based inverse opal photonic crystal (IOPC) decorated with graphene oxide (GO) (termed as GO-modified PEGDA-based IOPC) have been explored for simple and rapid semi-quantitative and quantitative detections of biomarker lipocaline-1 (LCN1) in tear at low level, respectively. We found that only after the concentration of GO (C_GO) was sufficiently high to create a thin GO layer due to intermolecular interactions between neighboring GO molecules on the PEGDA surface, the red-shift of the reflection peak position (λ_stb) became effective. This widening of the shift in λ_stb became significant when GO-modified PEGDA-based IOPC was selectively attached with LCN1 via the immunoassay, because the attachment with LCN1 caused a reverse shift in λ_stb. Correspondingly, the visualizable photonic color could vary in wider range depending on the concentration of LCN1 (C_LCN1), from orange color of blank solution to light blue color of solution containing LCN1 at C_LCN1 of 0.06 mg/mL using C_GO = 2.5 mg/mL. For quantification, C_GO and enrichment time of LCN1 were optimized for getting the maximum fluorescence microscopy intensity. The diagram for the relationship between fluorescence intensity and C_LCN1 showed various advantages of GO-modified PEGDA-based IOPC over non-GO-modified PEGDA-based IOPC. Those were higher fluorescence intensity, wider linear range and higher detection sensitivity. Thus, our results revealed potential applications of GO-modified PEGDA-based IOPC in screening patients with diabetic retinopathy (DR) in early stage.