In-channel integration of designable microoptical devices using flat scaffold-supported femtosecond-laser microfabrication for coupling-free optofluidic cell counting

The high-precision integration of three-dimensional (3D) microoptical components into microfluidics in a customizable manner is crucial for optical sensing, fluorescence analysis, and cell detection in optofluidic applications; however, it remains challenging for current microfabrication technologies. This paper reports the in-channel integration of flexible two-dimensional (2D) and 3D polymer microoptical devices into glass microfluidics by developing a novel technique: flat scaffold-supported hybrid femtosecond laser microfabrication (FSS-HFLM). The scaffold with an optimal thickness of 1-5 mu m is fabricated on the lower internal surface of a microfluidic channel to improve the integration of high-precision microoptical devices on the scaffold by eliminating any undulated internal channel surface caused by wet etching. As a proof of demonstration, two types of typical microoptical devices, namely, 2D Fresnel zone plates (FZPs) and 3D refractive microlens arrays (MLAs), are integrated. These devices exhibit multicolor focal spots, elongated (>three times) focal length and imaging of the characters 'RIKEN' in a liquid channel. The resulting optofluidic chips are further used for coupling-free white-light cell counting with a success rate as high as 93%. An optofluidic system with two MLAs and a W-filter is also designed and fabricated for more advanced cell filtering/counting applications.