An analytical device including an optically opaque cladding, a sequencing layer including a substrate disposed below the cladding, and a waveguide assembly for receiving optical illumination and introducing illumination into the device. The illumination may be received from a top, a side edge, and a bottom of the device. The waveguide assembly may include a nanoscale aperture disposed in the substrate and extending through the cladding. The aperture defines a reaction cell for receiving a set of reactants. In various aspects, the device includes a sensor element and the illumination pathway is through the sensor element. Waveguides and illumination devices, such as plasmonic illumination devices, are also disclosed. Methods for forming and operating the devices are also disclosed.