Previously, we created antiresonant reflecting optical waveguides (ARROWs) with hollow cores that guide light through gas and liquid media. We have demonstrated that these ARROWs can be used in sensing applications with single particle sensitivity using fluorescence correlation spectroscopy. To increase sensitivity for single molecule sensing, we have improved our initial designs and fabrication methods to decrease ARROW background fluorescence and improve transitions between solid and hollow waveguides. Photoluminescence of ARROW layers creates background fluorescence that masks the desired fluorescence signals. To improve sensitivity, we have optimized the PECVD ARROW layers to minimize the photoluminescence of each layer. Sensing applications require that hollow waveguides interface with solid waveguides on the substrate to direct light into and out of test media. Our previous ARROW designs required light at these interfaces to pass through the anti-resonant layers. Although in theory, high transmission through ARROW layers can be achieved, in practice, passing through these layers has limited transmission efficiencies. A new design coats the top and sides of the hollow core with only silicon dioxide, allowing light at interfaces to pass directly from silicon dioxide into the hollow core. This new design exhibits good mode confinement in the hollow core.