Because reactive oxygen species are involved in a range of pathologies, developing analytical tools for this group of molecules opens new vistas for biomedical diagnostics. Herein, we fabricate a porous silicon microcavity (pSiMC) functionalized with luminescent singlet oxygen (O-1(2)) probe EuA ((Eu(III)-2,2 ',2 ''-(10-(24(4-(24(4-(2-((anthracen-9-ylmethyl)amino)ethyl)-1H-1,2,3-triazol-1-71)amino)-2-oxoethyl)-2-oxo-1,2-dihydroquinolin-7-y0amino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triy1)triacetic acid) as proof of concept of an optical sensor for reactive oxygen species. We characterize each surface modification step of the pSiMC by means of FTIR and X-ray photoelectron spectroscopy as well as by determining the optical shifts of the resonance wavelength of the pSiMC. The luminescence signal upon detection of O-1(2) on the EuA-modified pSiMC is enhanced similar to 2-fold compared to that of a single layer and a detuned microcavity. The sensing performance of the EuA probe is improved significantly on the pSiMC compared to that in aqueous solution, giving a limit of O-1(2) detection of 3.7 x 10(-8) m.