Biomolecules have been incorporated as designed planar defect layers in colloidal photonic crystals using self- assembly techniques (see figure). Through shifts of the photonic intragap defect mode, for example, DNA conformational changes and the enantioselective intercalation of a chiral anticancer drug can be optically monitored. This newfound capability for optically monitoring biochemistry bodes well for the development of a new generation of simple on-the-spot color readout biosensors.