Our group offers

5-6 months Master 2 internship on

Development and characterization of luminescent nanosensors for imaging in microalgae cells

From February 2023

Project Description:

Phosphorus, an essential element for Life, is presently engaged in a broken biogeochemical cycle:¹ inefficient agricultural practice steadily transfers limited phosphorus deposits (projected to last for only 100 years) to aquatic environments where it generates eutrophication. To secure humanity’s food on a long term requires to close the phosphorus cycle by optimally recovering phosphorus from wastewater and use it to replenish soils for agriculture.

Microalgae are endowed with highly favorable features for sustainably closing the broken phosphorus cycle. Extracting their energy from light and their matter from inorganic sources, they accumulate polyphosphates (polymers of the orthophosphate anion), which have been demonstrated to yield excellent soil fertilizers slowly releasing the phosphate nutrient upon hydrolysis.² Yet the dynamic accumulation and mobilization of PolyPs in the algal cell remains poorly characterized and understood, which slows down to turn these observations into biotechnological applications.

Aiming at much better analyzing and understanding these processes, we intend to develop and characterize a range of luminescent nanosensors for imaging accumulation of PolyPs in single microalgae cells, an approach which has only been seldom used to interrogate photosynthetic organisms.³ In particular, we intend to achieve remote and non-invasive sensing at various parts of the phosphate storage pathway. Hence, we wish to sense pH, divalent cations, and ATP. To produce and characterize such luminescent nanosensors for sensing in photosynthetic organisms is precisely the goal of the present internship.

The first step of the internship will be to participate to the production of a series of luminescent nanosensors either based on gold nanoclusters⁴ or polymeric nanoparticles. The resulting sensors will be then evaluated for their permeability through the cell membrane and toxicity towards microalgae, Chlamydomonas reinhardtii as well as higher plants. The sensors displaying both permeability and absence of toxicity will be subsequently characterized for the dependence of their photophysical properties on the concentration on the sensed analyte and time resolution for sensing. The last part of the internship will be dedicated to validating their functional relevance in living cells of Chlamydomonas reinhardtii.

2. Techniques ou méthodes utilisées / Specific techniques or methods

During her/his internship, the master student will be exposed to the production and characterization of nanosensors, photophysics (UV-Vis absorption, steady-state and time-resolved fluorescence emission), optical microscopy, and manipulation of biological samples (e.g. cultured algae). She/He will also acquire good knowledge about (nano)sensors, photosynthesis, and its interplay with the production of polyphosphates.

3. Références / References

1. Slocombe, S. P. et al. Fixing the Broken Phosphorus Cycle: Wastewater Remediation by Microalgal Polyphosphates. Frontiers in Plant Science (2020); 2. Sanz-Luque, E. et al. Polyphosphate: A Multifunctional Metabolite in Cyanobacteria and Algae. Frontiers in Plant Science (2020); Li, K. et al. Microalgae-based wastewater treatment for nutrients recovery: A review. Bioresource Technology (2019); 3. S.-Y. Kwak et al, Rev. Anal. Chem., 2017, 10, 113; 4. L.-Y. Chen et al, Fluorescent Gold Nanoclusters: Recent Advances in Sensing and Imaging, Anal. Chem., 2015, 87, 216-229.

To apply, please send a detailed resume and a brief motivation letter to the scientific coordinator of the project Prof. Ludovic Jullien (Ludovic.Jullien@ens.psl.eu).