A Tunable Optofluidic Microlaser in a Photostable Conjugated Polymer

Abstract

The optofluidic laser has become an important platform for biological sensing and medical diagnosis. To date, fluorescent dyes and proteins have been widely utilized as gain materials for biological analysis due to their good biocompatibility, but the limited photostability restricts their reliability and sensitivity. Here, an optofluidic microlaser with an ultralow threshold down to 7.8 µJ cm−2 in the ultrahigh‐Q whispering‐gallery microcavity, which is filled with a biocompatible conjugated polymer, is demonstrated. This conjugated polymer exhibits a significant enhancement in the lasing stability compared with a typical laser dye (Nile red). In the experiment, after 20 min of illumination with the excitation intensity of 23.2 MW cm−2, the lasing intensity of the conjugated polymer experiences a decrease of less than 10%, while the lasing feature of Nile red completely disappears. Additionally, by mechanically stretching the resonator, the lasing frequency can be fine‐tuned with the range of about 2 nm, exceeding the free spectral range of the resonator.

Advances in Conjugated Polymer Lasers

“…There exist some ways to improve the stability of conjugated polymer laser materials, for example, Tang et al investigated the photostability of conjugated polymer microlasers. Compared with traditional dye laser materials, the conjugated polymer substituted with electrophilic cyano is much more photostable [24].…”

“…The latest works on conjugated polymer lasers come from 2018. In 2018, Xiao et al demonstrated an optofluidic microlaser using a biocompatible conjugated polymer (poly[2-methoxy-5-(2- ethylhexyloxy)-1,4-(1-cyanovi-nylene-1,4-phenylene)]) (CN-PPV) as gain materials, due to the electrophilic CN-group substituent, the photostability and lasing stability of the whole conjugated polymer were improved greatly compared with a typical dye laser [24].…”

Whispering-Gallery Sensors

“…There is still significant progress to be made in the development of WGM microresonator structures, such as deformed microresonators, 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 endoscopic sensing probes, 145 , 146 and WGM sensors in chip-based microfluidics channels. 147 Not only will these lead to further improvement in device sensitivity but they will also allow for the detection of analytes that are beyond the reach of current techniques.…”

Review of biosensing with whispering-gallery mode lasers

“…One of the possible ways to address this problem is the replacement of dyes with polymers 84 . For example, an optofluidic microlaser with an ultralow threshold down to 7.8 µJ cm −2 in an ultrahigh‐Q WGM microcavity filled with a biocompatible conjugated polymer has been demonstrated 85 . This conjugated polymer exhibits a significant enhancement in lasing stability compared with Nile red.…”