Nanoparticle tracking analysis as a process analytical tool for characterising magnetosome preparations

Research output: Contribution to journalArticlepeer-review


  • Stephan Joseph
  • Moritz Ebeler
  • Matthias Franzreb
  • Daniel Bracewell

Colleges, School and Institutes


Nanoparticle Tracking Analysis (NTA) has been employed to measure the particle concentration and size distribution of magnetosomes extracted and purified from Magnetospirillum gryphiswaldense MSR-1, and then exposed to probe ultrasonication for various times, or 1% (w/v) sodium dodecyl sulphate (SDS) for 1 h. Particle concentration increased 3.7-fold over the first 15 min of ultrasonication (from 2 × 108 to >7.3 × 108 particles mL-1), but fell steeply to ~3.6 × 108 particles mL-1 after 20 min. NTA of untreated magnetosome preparation confirmed a wide particle distribution dominated by larger species (D[1,0] = 312 nm; Dn50 = 261 nm; mode = 243 nm) with no particles in the size range of isolated single magnetosomes. After 5 min of ultrasonication the whole particle size distribution shifted to smaller size (D[1,0] = 133 nm; Dn50 = 99 nm; mode = 36 nm, corresponding to individual magnetosomes), but longer treatment times (15 and 20 min) reversed the previous transition; all characteristic numbers of the particle size distributions increased and very few small particles were detected. Side-by-side comparison of NTA and TEM sizing data revealed remarkable similarity at low ultrasonication times, with both showing single magnetosomes accounted for ~30% population after 5 min. Exposure of magnetosomes to SDS resulted in a ~3-fold increase in particle concentration to 5.8 × 108 particles mL-1, narrowing of the size distribution and gross elimination of particles below 60 nm. We conclude that NTA is a rapid cost-effective technique for measuring particle concentration, size distribution and aggregation state of magnetosomes in solution.

Bibliographic note

Funding Information: This work was supported by: the ERA-IB grant EIB.13.016 ProSeCa, funded by the UK Biotechnology & Biological Sciences Research Council (BBSRC); an Aston Institute of Materials Research (AIMR) Seed-corn grant; and the UK Engineering and Physical Sciences Research Council (EPSRC) Centre for Innovative Manufacturing in Emergent Macromolecular Therapies. The authors acknowledge the expert technical assistance of Theresa Morris and Paul Stanley of the University of Birmingham's Centre for Electron Microscopy.


Original languageEnglish
Pages (from-to)426-434
Number of pages9
JournalFood and Bioproducts Processing
Early online date26 Mar 2021
Publication statusPublished - May 2021


  • Biomanufacturing, Bioprocessing, Magnetic nanoparticles, Nanobiotechnology, Process analytical technology, Quality control