Highly efficient fluorescence detection in picoliter volume liquid-core waveguides

We report loss improvement and fluorescence detection in integrated antiresonant reflecting optical waveguides with liquid cores. The minimum waveguide loss is reduced to $0.33∕cm$ by compensating for thickness variations in the fabrication process. We demonstrate fluorescence detection from as few as $490molecules$ in a $57pl$ core using these optimized waveguides. We measure angular fluorescence collection factors as high as 15% per facet in good agreement with theory. This demonstrates the potential of integrated hollow-core waveguides as optical sensors for single-molecule spectroscopy.