Au-doped photonic crystal allows naked-eye determination of small organic molecules

An Au nanoparticle-(Au NP)-doped molecularly imprinted photonic crystal (Au-MIPC) is successfully prepared for naked-eye analysis. The resultant crystal displays a periodically ordered inverse opal structure. The proposed photonic crystal (PC) overtly reveals a 69 nm red shift accompanied by a naked-eye distinguishable structural color change from blue to green when detecting bisphenol A from 1 ng ml−1 to 1 mg ml−1. By comparing the detection results of the MIPC without Au NPs with those of non-molecularly imprinted PCs (NIPCs) with and without Au NPs, we note that the introduction of Au NPs can effectively amplify the response signal but it does not interfere with the response signals of NIPCs. The naked-eye distinguishable color change and amplification effect are also observed in monocrotophos- and ractopamine-imprinted Au-MIPCs. All of these Au-MIPCs possess high selectivity for target molecules. Thus, Au-MIPCs can potentially be applied to the equipment-free detection of various molecules in-field to facilitate significant naked-eye detection as pH paper. We expect to form new functional photonic materials or sensors for molecular analysis.