Oxygen sensor nanoparticles for monitoring bacterial growth and characterization of dose–response functions in microfluidic screenings
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We are presenting a microfluidic droplet-based system for non-invasive, simultaneous optical monitoring of oxygen during bacterial cultivation in nL-sized droplets using ~350 nm nanobeads made from polystyrene and doped with the NIR-emitting oxygen probe platinum (II) 5, 10, 15, 20-meso-tetraphenyltetrabenzoporphyrin (PtTPTBP). Data were readout by a two-channel micro flow-through fluorimeter and a two-channel micro flow-through photometer. The time-resolved miniaturized optical multi endpoint detection was applied to simultaneously sense dissolved oxygen, cellular autofluorescence, and cell density in nL-sized segments. Two bacterial strains were studied that are resistant to heavy metal ions, viz. Streptomyces acidiscabies E13 and Psychrobacillus psychrodurans UrPLO1. The study has two main features in that it demonstrates (a) the possibility to monitor the changes in oxygen partial pressure during metabolic activity of different bacterial cultures inside droplets, and (b) the efficiency of droplet-based microfluidic techniques along with multi-parameter optical sensing for highly resolved microtoxicological screenings in aquatic systems.
KeywordsDroplet-based microfluidics Oxygen sensor Optical probe-doped micro and nanoparticles Micro cultivation Highly-resolved dose/response function
J. Cao is funded by German Federal Environmental Foundation under contract No. 20009/009. S. Nagl is funded by and thanks the German Research Foundation (DFG, NA 947/1-2). The authors gratefully acknowledge the funding from German Federal Ministry of Education and Research in the frame of the project BactoCat (Kz: 031A161A). We thank S. Schneider, F. Weise and F. Möller for excellent experimental and technical assistance, Prof. N. Sträter and Dr. C. Roth (Institute of Bioanalytical Chemistry, University of Leipzig) for dynamic light scattering and Dr. A. Funfak (Laboratoire d'Hydrodynamique, Ecole Polytechnique, Palaiseau, France) for helpful discussions.
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