On-chip optofluidic grating spectrograph for biomedical applications

This paper presents a liquid metal based on-chip optofluidic grating spectrograph integrated with polydimethylsiloxane (PDMS) microfluidics for biomedical applications such as handheld fluorescence-actuated cell sorting, fluorescence immunosensing and Raman spectroscopy. We designed a Czerny-Turner spectrograph with 1.4nm spectral resolution, 300nm FSR and a footprint of 1cm by 2cm. The spectrograph structure was fabricated in PDMS using conventional replica molding soft lithography, and then filled with room temperature liquid metal, Gallium-Indium-Tin Alloy. The material and fabrication method is fully compatible with PDMS microfluidics, which allowed us to integrate a sheath flow based microfluidic cell focusing system with the spectrograph on the same substrate. This integration represents an important step towards a handheld flow cytometer. In addition, as a new class of on-chip optofluidic components, liquid metallic optical elements such as mirrors, gratings and pinholes will likely find other applications for building miniaturized optofluidic systems.