Chemical patterning on preformed porous silicon photonic crystals: towards multiplex detection of protease activity at precise positions† †Electronic supplementary information (ESI) available: SEM images, XPS result and more optical reflectivity data. See DOI: 10.1039/c4tb00281d Click here for additional data file. Ying Zhu, Alexander H. Soeriyadi, Stephen G. Parker, Peter J. Reece, J. Justin Gooding2014Figure S1. Scanning electron microscopy images of PSi rugate filter. (a) top view of the PSi with an average pore size 40 nm. (b) Cross section view of the PSi with a thickness 8 m; (insert) PSi cross section view with a higher magnification.