Nanoparticle tracking analysis to characterise exosomes

NANOPARTICLE Tracking Analysis (NTA) is being used to characterise exosomes for use in delivering therapeutic moieties to specific tissues in vivo at the Science and Engineering Institutes (SCE) in Singapore.

In the Molecular Engineering Laboratory, established in 2009 by Nobel Laureate Sydney Brenner, post-doctoral fellows undertake a variety of research ranging from organic fluorophore development to characterisation of marine biomaterials, to genetic therapies.

Dr Seow Yiqi is working to use exosomes (nanoparticles secreted by cells around 100nm in size) to deliver therapeutic moieties to specific tissues in vivo. Describing his work, which sprand from his earlier studies at Oxford, he said: “I use targeted exosomes loaded with siRNA to effect knockdown in the brain after intravenous exosome injection.

“Using the NanoSight system has proved to be invaluable in providing size and concentration measurement for each exosome purification. This data allows me to check the quality and purity of the preparation as well as to look at the physical effects of my surface modifications and loading protocols on the physical characteristics of exosomes.”

Other than NTA, he had used dynamic light scattering (DLS) for bulk measurement, and transmission electron microscopy using negative staining with phosphotungstanic acid for sizing. He reports that DLS was useful if the purification was pure and the sample being measured was relatively homogenous, but in practice the population purified tended to be polydisperse with nanoparticles of varying sizes in the same preparation. That biased the DLS measurements and it was difficult to get reproducible results with the system.

In contrast, the TEM was accurate and precise, but the preparation was arduous and time-consuming and the results are a very small representation of the bulk, so it was not useful in working out concentration or size distribution.

Concluding, he says, “Using Nanoparticle Tracking Analysis overcame these issues perfectly for my work. Measurements were rapid and by counting particle by particle, the true polydisperse nature of the samples was reported.”

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