The Optofluidic Light Cage - On-Chip Integrated Spectroscopy Using an Antiresonance Hollow Core Waveguide.

Emerging applications in spectroscopy-related bioanalytics demand for integrated devices with small geometric footprints and fast response times. While hollow core waveguides principally provide such conditions, currently used approaches include limitations such as long diffusion times, limited light-matter interaction, substantial implementation efforts, and difficult waveguide interfacing. Here, we introduce the concept of the optofluidic light cage that allows for fast and reliable integrated spectroscopy using a novel on-chip hollow core waveguide platform. The structure, implemented by 3D nanoprinting, consists of millimeter-long high-aspect-ratio strands surrounding a hollow core and includes the unique feature of open space between the strands, allowing analytes to sidewise enter the core region. Reliable, robust, and long-term stable light transmission via antiresonance guidance was observed while the light cages were immersed in an aqueous environment. The performance of the light cage related to absorption spectroscopy, refractive index sensitivity, and dye diffusion was experimentally determined, matching simulations and thus demonstrating the relevance of this approach with respect to chemistry and bioanalytics. The presented work features the optofluidic light cage as a novel on-chip sensing platform with unique properties, opening new avenues for highly integrated sensing devices with real-time responses. Application of this concept is not only limited to absorption spectroscopy but also includes Raman, photoluminescence, or fluorescence spectroscopy. Furthermore, more sophisticated applications are also conceivable in, e.g., nanoparticle tracking analysis or ultrafast nonlinear frequency conversion.