New insights into ROS dynamics: a multi-layered microfluidic chip for ecotoxicological studies on aquatic microorganisms

Abstract

Reactive oxygen species (ROS) play an important role in the life of every cell, including cellular defense and signaling mechanisms. Continuous and quantitative ROS sensing can provide valuable information about the cell state, but it remains a challenge to measure. Here, we introduce a multi-layered microfluidic chip with an integrated optical sensor for the continuous sensitive detection of extracellular hydrogen peroxide (H₂O₂), one of the most stable ROS. This platform includes hydraulically controlled microvalves and microsieves, which enable the precise control of toxicants and complex exposure sequences. In particular, we use this platform to study the dynamics of toxicity-induced ROS generation in the green microalga Chlamydomonas reinhardtii during short-term exposures, recovery periods, and subsequent re-exposures. Two cadmium-based toxicants with distinct internalization mechanisms are used as stress inducers: CdSe/ZnS quantum dots (Qdots) and ionic cadmium (Cd²⁺). Our results show the quantitative dynamics of ROS generation by the model microalga, the recovery of cell homeostasis after stress events and the cumulative nature of two consecutive exposures. The dissolution of quantum dots and its possible influence on toxicity and H₂O₂ depletion is discussed. The obtained insights are relevant from ecotoxicological and physiological perspectives.

Keywords:

• Cadmium
• complex exposure sequences
• microalgae
• post-oxidative stress
• quantum dots

Acknowledgements

The authors are very grateful to Prof. Sebastian Maerkl for the utilization of the microarray robot, to Prof. Christof Holliger for the access to the algae incubator and to Mr. Sylvain Coudret for assistance with ICP-MS.

Declaration of interest

The authors are responsible for writing of the article and report no conflicts of financial, consulting, and personal interests.

This work was supported by the Swiss National Research Program NRP 64 project no. 406440-131280/1 of the Swiss National Science Foundation.

Supplementary material available online

Supplementary Tables S1–S6 and Figures S1–S7