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Quality reference

NTA vs MRPS Particle Counting

Reviewed by ExaVeyra Sciences editorial team · Updated 29 August 2026

Particle count is the number most often quoted about an exosome preparation and the one least often qualified. Two certificates for comparable material can differ by an order of magnitude without either being wrong, because the figure is not a property of the vial so much as a property of the instrument that produced it.

This page covers what the common methods physically measure, why that makes their numbers non-interchangeable, and what to ask so two quotes can be compared at all.

What each method physically measures

Nanoparticle tracking analysis watches particles scatter light and infers size from how they move under Brownian motion. Resistive pulse sensing pushes particles through a small aperture and measures the electrical blip each one makes as it displaces fluid.

One infers size from motion in an optical field, the other from displaced volume in an electrical one. Neither is a count of vesicles as such: both count events they can detect and attribute a size to.

The same method varies more than most buyers expect

Before comparing methods, it is worth knowing how much a single method varies. Published variation work on nanoparticle tracking analysis shows measured size and concentration shifting with instrument settings and operator choices rather than with the sample.

That is not a criticism of the technique. It means a bare number with no settings attached carries less information than it appears to, even when the method is named.

Orthogonal platforms on identical material still disagree

The most useful evidence here comes from running the same preparations across several single-particle platforms at once. Doing so shows systematic differences between instruments in both the concentration reported and the size distribution recovered.

The practical reading is not that one platform is correct. It is that a count is only meaningful alongside the method, and comparing two suppliers means comparing two methods first.

What to ask, so two quotes become comparable

  • Which method and instrument produced the count, named specifically.
  • The size range reported, since a total without a range hides the detection floor.
  • Whether the count is per millilitre or per vial, which are different claims about a different denominator.
  • Whether the figure is lot specific or a process typical value carried across lots.
  • What dilution was used, because dilution is where much of the within-method variation enters.

A supplier who answers all five has given you something comparable. A supplier who answers none has given you a number, which is not the same thing.

Read the count alongside the marker data

Concentration says how many detectable particles were present. It says nothing about what fraction of them are vesicles rather than other material of similar size, and nothing about the cargo they carry.

That is why particle count belongs beside the marker data rather than instead of it, and why neither figure indicates suitability for any patient or procedure.

How to get a comparable count

The five items above are things a supplier either records or does not, and asking for them at quotation is the moment they are cheapest to produce. Two suppliers answering all five give you numbers you can actually set against each other.

ExaVeyra states the method alongside the count on lot-specific certificates, released to practices once NPI verification is complete. The same step makes pricing and the formulary visible.

Sources

  1. 21 CFR Part 1271, human cells, tissues, and cellular and tissue-based products (accessed 29 August 2026)

Scientific literature

Each source carries the kind of study it was and, where the study enrolled people, how many. Study design decides what a result can establish, so it is stated rather than left to be inferred. Each line also says what that source is carrying on this page.

  1. Arab T, Mallick ER, Huang Y, et al. Characterization of extracellular vesicles and synthetic nanoparticles with four orthogonal single-particle analysis platforms. Journal of Extracellular Vesicles, 2021. doi:10.1002/jev2.12079 PMID:33850608In vitroSource 1 supports: The same preparations measured on four orthogonal single-particle platforms. This is the closest thing in the literature to the head-to-head this page was originally specified around, and it is why the page argues that a count is inseparable from its method.
  2. Vestad B, Llorente A, Neurauter A, et al. Size and concentration analyses of extracellular vesicles by nanoparticle tracking analysis: a variation study. Journal of Extracellular Vesicles, 2017. doi:10.1080/20013078.2017.1344087 PMID:28804597In vitroSource 2 supports: Variation within a single method, attributable to settings and operator choices rather than to the sample. Cited for the point that naming the method is necessary but not sufficient.
  3. Calado MRC, Lage TC, André DAM, et al. Nanofluidic resistive pulse sensing for characterization of extracellular vesicles. Lab on a Chip, 2024. doi:10.1039/d4lc00364k PMID:39051540In vitroSource 3 supports: The resistive pulse approach described on its own terms. Cited so the description of what that method physically measures rests on the method literature rather than on a summary of it.
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Common questions

Which method is more accurate?
The question does not resolve cleanly, because the methods measure different physical properties and each has a detection range where it performs best. Published work comparing single-particle platforms on identical material shows systematic differences rather than one instrument being correct and the others wrong.
Can we convert a count from one method to another?
Not reliably. The differences arise from what each instrument can detect and how it assigns size, not from a fixed offset, so there is no conversion factor that survives across preparations. Compare like with like, or compare methods explicitly.
Why does a supplier quote particles per millilitre rather than per vial?
Both are used and they are not interchangeable. Per millilitre is a concentration and depends on fill volume to become a total; per vial is a total and depends on the fill being accurate. Ask which is meant before comparing two figures.
Is a count with no method named worth anything?
Very little for comparison purposes. It establishes that a measurement was taken, which is better than nothing, but without the method, the size range and the dilution it cannot be set against another supplier’s figure.

Related reading

CD9, CD63, and CD81 marker panelsMISEV2023 and supplier documentationQualifying a supplier before the first orderHow to evaluate an exosome supplier COAExosome CMC requirements

These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease. There are no FDA-approved exosome products. Biomolecular signaling vesicle products distributed by ExaVeyra Sciences are supplied for topical aesthetic treatments in clinics and for medical, molecular biology, and biochemistry research applications, and are not tissue products as defined by FDA guidelines.

This guide summarizes publicly available federal regulation for licensed practitioner education. It is for informational purposes only, it is not legal advice, medical advice, or regulatory guidance, and it does not establish that any particular product or practice is compliant. Regulation changes, and state requirements frequently differ from the federal floor. Consult a healthcare attorney licensed in your jurisdiction and your own state boards before acting on anything here.