On-the-fly tunable liquid microlenses capable of both in situ integration within microfluidics and real-time tuning

We demonstrate an in situ fabricated tunable microlens through a relatively simple process by manipulating fluids in microchannel networks. The microlens is formed via a surface tension-bounded liquid droplet that is generated and pinned at the corners of a microchannel junction. Wide focal length tuning range from hundreds of micrometers to +infin is realized by changing the pneumatic pressure across the microlens. The in situ fabrication with fluids can produce instant, reconfigurable, tunable liquid microlenses without using sophisticated microfabrication techniques, different substrate materials, and time-consuming optical alignment. By varying its focal length, the microlens can scan through the fluorescence detection areas and enhance the fluorescent emission at the focused area by up to four times compared to without the microlens, and can optimize the fluorescence output for a shifted laminar stream containing fluorescein. This technique can find applications in on-chip optical detections of low- concentration biomolecular analytes, such as laser- induced fluorescence detection.