Revealing the Friction Stress of Microalgae in Microfluidic Devices through Mechanofluorochromism

Polydiacetylenes are deeply investigated for their mechanofluorochromic behavior: the blue, non-emitting solid phase, obtained by photopolymerization of the diacetylene precursor, is converted to the red, emitting one by a mechanical stimulus. Inspired by the great potentiality of these compounds to act as microscale force probes, the mechanofluorochromism is implemented in microalgae biotechnology. Indeed, mechanical solicitations in a microfluidic chip can weaken the cellular envelope and facilitate the extraction of high-added value compounds produced by the microalgae. Herewith, a polydiacetylene-based mechanofluorochromic sensor is reported to be able to detect the stress applied to microalgae in microchannels. A triethoxysilane diacetylene precursor is designed that photopolymerizes in a purple, low-emissive phase, and is converted to the red, high-emissive phase upon mechanical stress. Hereafter, a protocol is set up to chemically graft in the microfluidic channels a polydiacetylene layer, and eventually proves that upon compression of Chlamydomonas reinhardtii microalgae in restricted areas, the friction stress is revealed by the mechanofluorochromic response of the polydiacetylene, leading to a marked fluorescence enhancement up to 83%. This prototype of microscale force probes lays the ground for microscale stress detection in microfluidics environments, which can be applied not only to microalgae but also to any mechano-responsive cellular sample.